Stillwater Sciences. Stillwater Sciences. Marin Municipal Water District 220 Nellen Ave. Corte Madera, CA 94925

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1 FINAL STUDY PLAN SEPTEMBER 2015 Soulajule Reservoir & Arroyo Sausal Methylmercury Control Study PREPARED FOR Marin Municipal Water District 220 Nellen Ave. Corte Madera, CA PREPARED BY 2855 Telegraph Avenue, Suite 400 Berkeley, CA Brown and Caldwell 201 North Civic Drive, Suite 115 Walnut Creek, CA 94596

2 Additional report preparers: Dr. Alex Horne, University of California, Berkeley, and Dr. Marc Buetel, Washington State University, Pullman, Washington. Suggested citation: Soulajule Reservoir and Arroyo Sausal Methylmercury Control Study Final Study Plan. Prepared by, Berkeley, and Brown and Caldwell, Walnut Creek, California for the Marin Municipal Water District, Corte Madera, California. Cover photos: Soulajule Reservoir and Arroyo Sausal, and Marin Municipal Water District. i

3 Table of Contents 1 INTRODUCTION Project Goals BACKGROUND Watershed Context Regulatory Context Reservoir Conditions Methylmercury in Reservoirs Overview of factors controlling methylmercury production and bioaccumulation in lakes and reservoirs Relevant case studies Climate Change POTENTIAL MANAGEMENT METHODS Initial Screening of Methods Methods Applicable to Soulajule Reservoir Reduce sediment mercury loads Manage water chemistry to reduce methylation Decrease levels of blue-green algae Manage fisheries to reduce methylmercury in fish tissue Summary of Conceptual-level Cost Estimates for Management Methods Applicable to Soulajule Reservoir WATER LEVEL FLUCTUATION RANKING OF POTENTIAL MANAGEMENT METHODS AND RECOMMENDED PILOT STUDIES Ranking Approach Ranking Results Biomanipulation sport fish stocking Hypolimnetic oxygenation system Erosion control for uplands soils in the Eastern Arm VEM in the Eastern Arm Biomanipulation prey fish stocking Dredging of reservoir sediments in the Eastern Arm Capping of reservoir sediments in the Eastern Arm Water Level Fluctuation Prioritization of Pilot Studies PILOT STUDIES TO FILL DATA GAPS Pilot Study 1 Additional Characterization of Methylmercury in Water and Biota Objectives ii

4 Hypotheses Sampling design Data analysis and reporting approach Implementation schedule Estimated cost Pilot Study 2 Assessment of Littoral Zone Extent and Productivity as Related to Increased Water Level Fluctuation Objectives Hypotheses Approach Data analysis and reporting approach Implementation schedule Estimated cost Pilot Study 3 Assessment of Reservoir Fish Community Composition Objectives Hypotheses Sampling design Data analysis and reporting approach Implementation schedule Estimated cost Pilot Study 4 Assessment of Reservoir Food Web Structure Objectives Hypotheses Approach Data analysis and reporting approach Implementation schedule Estimated cost Pilot Study 5 Evaluation of Reservoir Seasonal Oxygen Demand and Sediment Response to Hypolimnetic Oxygenation Objectives Approach Data analysis and reporting Implementation schedule Estimated cost Pilot Study 6 Evaluation of Potential for Mercury Loading from Upland Soils in the Eastern Arm Objectives Hypotheses Sampling design Data analysis and reporting approach Implementation schedule Estimated cost Summary of Pilot Study Schedule and Estimated Costs iii

5 7 REFERENCES Tables Table 1. Minimum flow release requirements for Soulajule Reservoir Table 2. Soulajule Reservoir and relevant case studies for primary productivity, water level, and mercury control issues Table potential methods for in-lake and watershed water quality management Table 4. Applicability of selected in-lake and watershed management methods for methylmercury control in Soulajule Reservoir Table 5. Conceptual-level cost estimates for in-lake and watershed management methods applicable to Soulajule Reservoir Table 6. Rating criteria and weighting factors for Soulajule Reservoir in-lake and watershed potential methylmercury control actions Table 7. Ranking summary and key assumptions for Soulajule Reservoir in-lake and watershed methylmercury control actions Table 8. Priority pilot studies for Soulajule Reservoir mercury control actions Table 9. Sampling sites Table 10. Number of water, algae, zooplankton, and fish methylmercury samples Table 11. Estimated cost of Pilot Study 1 Additional Characterization of Methylmercury in Water and Biota Table 12. Estimated Cost of Pilot Study 2 Assessment of Littoral Zone Extent and Productivity as Related to Increased Water Level Fluctuation Table 13. Fish sampling methods and reaches Table 14. Estimated cost of Pilot Study 3 Assessment of Reservoir Fish Community Composition Table 15. Estimated cost of Pilot Study 4 Assessment of Reservoir Food Web Structure Table 16. Estimated Cost of Pilot Study 5 Evaluation of Reservoir Seasonal Oxygen Demand and Sediment Response to Hypolimnetic Oxygenation Table 17. Upland soil mercury characterization soil sampling locations Table 18. Estimated Cost of Pilot Study 6 Evaluation of Potential for Mercury Loading from Upland Soils in the Eastern Arm Table 19. Approximate schedule for pilot studies Table 20. Estimated costs for pilot studies iv

6 Figures Figure 1. Location of Soulajule Reservoir and Arroyo Sausal, Marin County, California Figure 2. Original dam and construction of larger dam at Soulajule Reservoir Figure 3. Hypsographic curve for Soulajule Reservoir Figure 4. Soulajule Reservoir high water mark along the main portion of the reservoir east of the dam during November Figure 5. Western Arm of Soulajule Reservoir exhibiting low water levels, November Figure 6. August 29 30, 2012 Soulajule Reservoir in situ water quality profiles measured near the dam Figure 7. Water column methylmercury concentrations in the hypolimnion in Soulajule Reservoir during April, August, and December Figure 8. Total mercury in sediments in Soulajule Reservoir, August 29 30, Figure 9. Reservoir outlet concentrations of DO from Stevens Creek Reservoir during test oxygenation in 2013 and Figure 10. Hypolimnion concentrations of methylmercury in Calero Reservoir compared to volume of reservoir with DO concentration less than 1.0 mg/l Figure 11. Excessive algal productivity in Lake Hodges Figure 12. Cyanobacteria bloom in Lake Hodges on July 17, 2013, as detected by post-processed satellite imagery Figure 13. Installation of a Speece cone in Camanche Reservoir, California, to oxygenate hypolimnetic waters and eliminate seasonal H2S production Figure 14. Indian Creek Reservoir showing location of Speece Cone and equipment building used as part of the hypolimnetic oxygenation system Figure 15. Daily mean dissolved oxygen concentration measured at three locations in Indian Creek Reservoir Figure 16. Total phosphorus concentrations measured at Indian Creek Reservoir Figure 17. Chlorophyll-a measured at Indian Creek Reservoir Figure 18. Secchi depth measured at Indian Creek Reservoir Figure 19. Trailer mounted temporary LOX storage system at Twin Lakes, WA Figure 20. Relation between oxygen addition and mercury in zooplankton Figure 21. (A) Relationship between mercury concentrations in young-of-the-year yellow perch and maximum water levels relative to the previous year, for San Point Lake, Minnesota, from 1991 to (B) Relationship between Secchi depths and maximum water levels. (C) Mercury concentrations in yellow perch Figure 22. Area of Soulajule Reservoir considered for capping or dredging due to elevated total mercury concentrations in sediments Figure 23. Cell counts and identified algal groups by site in surface water samples in Soulajule Reservoir, at the reservoir discharge and Arroyo Sausal during August v

7 Figure 24. Conceptual placement of VEM system in the shallow Eastern Arm of Soulajule Reservoir Figure 25. District reservoir fisheries composition at individual lakes Figure 26. Soulajule Reservoir sampling sites for additional characterization of methylmercury in water and biota Figure 27. Approximate fish sampling reaches in Soulajule Reservoir Figure 28. Conceptual gill net array in the deepest area of the reservoir and along the shoreline of Soulajule Reservoir Appendices Appendix A. General Applicability of 17 In-lake and 5 Watershed Management Methods to Soulajule Reservoir and Arroyo Sausal Methylmercury Control Appendix B. Ranking Detail for Potential Management Methods vi

8 1 INTRODUCTION Soulajule Reservoir is a small surface water impoundment located in the western portion of Marin County, California. Water from Soulajule Reservoir is released downstream to Arroyo Sausal, which then flows to the confluence of Salmon Creek and Walker Creek, then to Tomales Bay, and eventually to the Pacific Ocean (Figure 1). To address legacy mercury (Hg) mining issues in the surrounding watershed of Soulajule Reservoir, the San Francisco Bay Regional Water Quality Control Board (Regional Board) issued a letter on May 18, 2010, which requested a monitoring plan and time schedule for assessing methylmercury (MeHg) production and bioaccumulation in Soulajule Reservoir and its downstream waterbody Arroyo Sausal. Marin Municipal Water District (District) subsequently undertook the development and implementation of the Soulajule Reservoir Mercury Occurrence and Bioaccumulation Study (Brown and Caldwell and 2013). In their May 7, 2014 letter to the District, the Regional Board requested a series of next actions aimed at reducing methylation and bioaccumulation of mercury in Soulajule Reservoir. Next Action A was an addendum to the 2013 Study Report, which provided clarifications and additional data analysis requested by the Regional Board with respect to sampling locations, monthly reservoir storage patterns, and methylmercury mass accumulation estimates ( 2014). Next Action B involves the development and implementation of a Study Plan to identify and pilot test management methods for controlling methylmercury production in Soulajule Reservoir. Accordingly, this Study Plan includes the following: Section 1 this introduction and statement of project goals. Section 2 background information relevant to methylmercury control in Soulajule Reservoir, including an overview of factors controlling methylmercury production and bioaccumulation in lakes and reservoirs and a summary of relevant case studies. Section 3 overview of 17 potential in-lake and 5 watershed management methods and discussion of those most applicable to Soulajule Reservoir with respect to overall reservoir management objectives as well as methylmercury control. Section 4 discussion of the potential for more frequent use of Soulajule Reservoir for drinking water supply, and the potential effects of increased water level fluctuations on mercury methylation and bioaccumulation. Section 5 ranking of potential management methods and recommended pilot studies to fill existing data gaps. Section 6 pilot studies to fill data gaps identified for each of the potential management methods, including study objectives, hypotheses, sampling design, data analysis and reporting, anticipated implementation schedule, and estimated costs. 1

9 Figure 1. Location of Soulajule Reservoir and Arroyo Sausal, Marin County, California. 2

10 1.1 Project Goals The primary goal of Study Plan development is to identify a set of effective and fiscally responsible management methods for controlling methylmercury in Soulajule Reservoir that would be included and implemented in a long-term reservoir management plan. The selected management methods must be consistent with water supply management objectives for Soulajule Reservoir, which currently include the following: 1. Provide storage and supply for municipal drinking water; 2. Achieve flows in downstream Walker Creek (see Table 1); 3. Support appropriate water quality objectives within Soulajule Reservoir and in downstream Arroyo Sausal. Table 1. Minimum flow release requirements for Soulajule Reservoir. Season Normal Water Year Dry Water Year Critical Water Year Winter 20 cfs 10 cfs 0.5 cfs Summer 5 cfs 2 cfs 0.5 cfs Under Next Action B, the Regional Board identified four mercury management objectives for Soulajule Reservoir and the downstream Arroyo Sausal. These objectives have been considered during development of this Study Plan: 1. Reduce loads of mercury from historical mining waste and mercury-laden sediment; 2. Manage water chemistry, especially redox conditions, to reduce methylation; 3. Decrease levels of harmful blue-green algae and increase fish-edible green algae; and, 4. Manage fisheries to decrease methylmercury tissue concentrations. Combined, the aforementioned water supply management objectives and mercury management objectives have been used to evaluate potential approaches to addressing elevated methylmercury in fish tissue in Soulajule Reservoir. Consistent with Next Action B, pilot studies of priority management methods will be undertaken by the District during to inform development of the long-term reservoir management plan. 3

11 2 BACKGROUND 2.1 Watershed Context The Soulajule Reservoir watershed extends approximately 2 mi 2 with grassland/ rangeland and open space as the predominant land uses. Historical land uses were similar, with the exception of mercury mining in the Walker Creek watershed during the 1960s and early 1970s. The Gambonini Mine, the largest mercury mine in the watershed, was active from 1964 to By 1972, all mining had ceased in the watershed, with remediation and clean-up of the Gambonini Mine site beginning in 1999 (SFBRWQCB 2008a). Soulajule Reservoir is situated within the Northern California Coastal region. The region has a Mediterranean climate, characterized by rainfall in the winter and cool, dry summers with coastal fog. 2.2 Regulatory Context The Regional Board required the District to perform a mercury study (see also letter referenced in Section 1), based on findings and implementation actions established in the Total Maximum Daily Load (TMDL) for Mercury in the Walker Creek Watershed (SFBRWQCB 2008a). Actively eroding mining waste on the site of the Gambonini mercury mine, located outside of the reservoir watershed, was the initial concern that led first to a cleanup action on the mine site beginning in 1999 (see above), and later to the development and adoption of the mercury TMDL (SFBRWQCB 2008a). The TMDL established that Soulajule Reservoir was impaired because some fish in the reservoir exceeded mercury levels for human consumption, and the narrative bioaccumulation water quality objective was not being met. Although there were anecdotal references to submerged mine works, a report by the District located the historic mines along the eastern arm of Soulajule Reservoir (MMWD 2010), well above the water line. This finding suggested the possibility of direct contamination of Soulajule Reservoir sediments as a result of runoff from the upland mine sites, resulting in a plan to investigate the potential presence of legacy mercury contamination in sediments related to historic mining (Brown and Caldwell and 2012). The Soulajule Reservoir Mercury Occurrence and Bioaccumulation Study was completed in 2013 (Brown and Caldwell and Stillwater Sciences 2013). Subsequently, the Regional Board requested a series of next actions aimed at reducing methylation and bioaccumulation of mercury in Soulajule Reservoir, including an addendum to the 2013 Study Report ( Next Action A ), which is now complete ( 2014) and the development and implementation of a Study Plan to identify and pilot test management methods for controlling 4

12 methylmercury production in the reservoir ( Next Action B ), which is the focus of this project. The Walker Creek Mercury TMDL establishes the following numeric targets for the Walker Creek watershed, including Soulajule Reservoir: To protect wildlife and rare and endangered species, the average methylmercury concentration in fish consumed by piscivorous birds shall not exceed 0.05 mg/kg fish (wet weight), measured in whole fish 5 15 cm in length, nor shall it exceed 0.1 mg/kg (wet weight), measured in whole fish cm in length. To protect aquatic organisms, water column mercury concentrations shall not exceed the water quality objective of 2.4 ug/l (one-hour average), measured as total mercury. To protect humans who consume Soulajule Reservoir and Walker Creek fish (assuming future conditions allow for the consumption of Walker Creek fish), water column mercury concentrations shall not exceed the California Toxics Rule (CTR) criterion of ug/l (averaged over a 30-day period). The Regional Board translated the above Walker Creek Mercury TMDL numeric targets into the following load allocations for Soulajule Reservoir and the Arroyo Sausal Watershed (SFBRWQCB 2008a): 0.04 ng/l dissolved methylmercury (annual average) 0.5 mg/kg total mercury in suspended sediment (riverine portions of the watershed) The water column load allocation (0.04 ng/l) is based on the USEPA draft national average bioaccumulation factor (BAF) of 1,300,000 for dissolved methylmercury in lakes and methylmercury in trophic level (TL) 1 3 fish (USEPA 2001). Dividing the Soulajule Reservoir target tissue concentration for fish 5 15 cm in length by the average BAF (0.05 mg/kg divided by 1,300,000) and multiplying by 10 6 (to convert from milligrams to nanograms) yields 0.04 ng/l dissolved methylmercury. The suspended sediment load allocation (0.5 mg/kg) is based on the assumption of a one-to-one relationship between fish tissue mercury and water column particulate mercury concentrations, combined with daily TSS measurements in Walker Creek for the period 10/01/03 to 5/31/04 (SFBRWQCB 2008a). Based on this assumption, the load allocation represents a calculated reduction needed from pre-remediation particulate mercury levels in the watershed to meet safe mercury levels for wildlife, expressed in terms of particulate mercury concentration. The Regional Board anticipates revising the methylmercury 1 The common designation of trophic levels (TL) in aquatic food webs is TL1 for primary production or algae, TL2 for primary consumers such as invertebrates, TL3 for secondary consumers such as prey fish, and TL4 for piscivorous fish. 5

13 allocations to reflect site-specific conditions in Soulajule Reservoir as additional data are collected (SFBRWQCB 2008a). 2.3 Reservoir Conditions Soulajule Reservoir was initially constructed as an earthen dam in 1969 on privately owned lands to serve a recreational second-home development, Soulajule Ranch. In 1979, after the District acquired the reservoir area, a larger impoundment was created by the construction of a larger dam (Figure 2). Original, small earthen dam constructed in 1969 Larger dam constructed in 1979, downstream of original dam Figure 2. Original dam and construction of larger dam at Soulajule Reservoir. Source: MMWD. Currently, Soulajule Reservoir has a (maximum) surface area of 310 ac, a storage capacity of 10,560 ac-ft, and a maximum depth of approximately 80 ft. The reservoir serves as an infrequent water supply, providing approximately 13 percent of the District s total storage capacity. Regulated flow releases in the summer and winter (Table 1) result in typical seasonal volume fluctuations between approximately 8,000 and 10,500 ac-ft (roughly 25%), and water level fluctuations of approximately 9 ft (elevation between 332 ft and 323 ft) (Figure 3). The District is currently considering more frequent use of Soulajule Reservoir for drinking water supply, which could alter the future magnitude, frequency, and duration of volume and water level fluctuations (Section 4). 6

14 0 10 Capacity (ac-ft) 0 2,000 4,000 6,000 8,000 10,000 12,000 Typical seasonal volume fluctuations (~9 ft) 20 Depth from top (ft) Spillway Elevation = 332.0' Figure 3. Hypsographic curve for Soulajule Reservoir. Data source: MMWD (2013). Under normal operating conditions, the theoretical hydraulic residence time (storage/flow) for Soulajule Reservoir is approximately two years; however, the significant additional flow that occurs over the spillway during most wintertime rain events results in a substantially reduced actual hydraulic residence time. For example, during December 2012, when the reservoir was spilling, the estimated hydraulic residence time was approximately 2 months (MMWD unpub. data). Soulajule Reservoir shorelines tend to be steep and not well vegetated (Figure 4). The eastern and western arms are shallow and exhibit relatively broad shorelines; however, these shorelines tend not to be vegetated other than seasonal grasses which are grazed by cattle when reservoir levels are low (Figure 5). 7

15 Figure 4. Soulajule Reservoir high water mark along the main portion of the reservoir east of the dam during November Figure 5. Western Arm of Soulajule Reservoir exhibiting low water levels, November Soulajule Reservoir is monomictic, typically exhibiting complete water column mixing throughout the winter months. Although thermal stratification tends to develop during 8

16 late spring/early summer (May to June), the onset of stratification has occurred as early as the end of February. The shallow side arms of the reservoir become fully mixed earlier in the season than the deeper portions of the reservoir, which remain fully stratified July through October (Figure 6). Full turnover usually occurs by mid-november (Brown & Caldwell and 2010). 0 Water Temperature ( C), Dissolved Oxygen (mg/l), & ph (s.u.) Depth (ft) Temp. ( C) DO (mg/l) ph Figure 6. August 29 30, 2012 Soulajule Reservoir in situ water quality profiles measured near the dam (Site S-WQ4). Soulajule Reservoir is also eutrophic, supporting large seasonal algal blooms that typically occur between March and May, but have also been observed in the fall during some years. Water clarity during bloom periods is low, with mean Secchi depth measured at 0.7 ft in April 2012 and 2.2 ft in August 2012 (Brown and Caldwell and 2013). The seasonal blooms provide readily degradable organic carbon from decomposing algal cells, which depress DO levels in the hypolimnion and can result in low oxygen to anoxic conditions near the dam during late summer/early fall. Conversely, reservoir surface waters can become supersaturated with DO during bloom periods, particularly in the shallow eastern arm (Brown and Caldwell and 2013). Seasonal ph profiles during stratification periods are consistent with high levels of photosynthesis in the surface waters and high levels of algal and bacterial respiration in the bottom waters (Brown and Caldwell and Stillwater Sciences 2013). Abundant phosphorus and limited nitrogen in Soulajule Reservoir create conditions where nitrogen fixing blue-green algae thrive. Despite the abundance of blue-green algae, levels of cyanotoxins measured in the reservoir have not historically 9

17 been of concern with respect to drinking water standards (Brown and Caldwell and 2013). The seasonally low DO and algal source of organic carbon in Soulajule Reservoir provide ideal conditions for methylating bacteria, including sulfate-reducing and iron-reducing bacteria associated with mercury methylation (see also Section 3.1). Results from the recent mercury occurrence and bioaccumulation study undertaken in Soulajule Reservoir (Brown and Caldwell and 2013) indicated that the highest methylmercury concentrations (2 3 ng/l) occurred in the hypolimnion, at the reservoir outlet, and in Arroyo Sausal during August, when the reservoir was stratified and bottom waters were anoxic (Figure 7). The opposite pattern was observed in the shallow eastern arm of the reservoir during spring and summer months, when surface water methylmercury concentrations were relatively higher ( ng/l) and were associated with supersaturated DO and high algal cell counts (Brown and Caldwell and 2013). Sediment sampling results indicated relatively higher concentrations of total mercury (390 5,940 ng/g dry weight) proximal to the historical Cycle and Franciscan mine sites on the eastern arm of the reservoir, with concentrations at or near the reported watershed background concentration of 200 ng/g (SFBRWQCB 2008a) moving towards the dam and in the western arm of the reservoir (Figure 8). Sediment results also indicated generally low methylation efficiency, as evidenced by MeHg:TotHg ratios of much less than 0.01, both in the shallow eastern arm near the mine sites and in deeper waters near the dam. The low methylation efficiency of the sediments may be due to a predominance of insoluble mercury sulfides, low organic carbon availability, low sulfate availability, and high ph, or a combination of these factors (Brown and Caldwell and 2013). All fish tissue methylmercury results from 2012 exceeded the Walker Creek TMDL numeric targets of 0.05 mg/kg (wet weight) for prey fish (5 15 cm FL) and 0.1 mg/kg (wet weight) for piscivorous fish cm FL. As compared with other mercury-mining impacted reservoirs in the San Francisco Bay Area, Soulajule Reservoir generally exhibits lower overall methylmercury bioaccumulation factors (e.g., L/kg for piscivorous fish) and lower fish tissue total mercury concentrations (e.g., 546-1,080 ng/g wet weight for piscivorous fish) (Brown and Caldwell and Stillwater Sciences 2013). 10

18 Figure 7. Water column methylmercury concentrations in the hypolimnion in Soulajule Reservoir during April, August, and December Note that the water column was not stratified in December, so the data for this month represent bottom water concentrations. 11

19 Figure 8. Total mercury (TotHg) in sediments in Soulajule Reservoir, August 29 30,

20 2.4 Methylmercury in Reservoirs Overview of factors controlling methylmercury production and bioaccumulation in lakes and reservoirs Hg biogeochemical cycling is complex, as mercury can exist in many forms in the environment, including elemental mercury (Hg 0 ), other inorganic mercury compounds, and organic mercury. Inorganic mercury compounds include a variety of relatively soluble mercury oxide, sulfate, and chloride complexes, as well as the less soluble mercuric sulfide, or cinnabar (HgS), the form of mercury that has been historically mined for use in gold recovery. Organic mercury compounds include mercury bound to carbon. The organic mercury compound (mono)methylmercury (MeHg), is of particular interest as it is bioavailable and toxic at elevated concentrations. The following is a brief overview of factors controlling methylmercury production and bioaccumulation in lakes and reservoirs Methylation and demethylation Many factors affect the formation and degradation of methylmercury in lakes and reservoirs, such as overall mercury concentrations, redox conditions (i.e., availability of oxygen, nitrate), labile or readily bioavailable organic carbon, sulfate (SO4 2- ), sulfide (S 2- ), temperature, solar radiation, and salinity (Ulrich et al. 2001). Mercury methylation is primarily mediated by heterotrophic sulfate-reducing bacteria, which are broadly present in lake and reservoir sediments and convert inorganic mercury to methylmercury during cellular respiration (Compeau and Bartha 1985, Gilmour et al. 1992, Fleming et al. 2006). Heterotrophic bacteria require an organic carbon source, such as dissolved organic carbon (DOC), to fuel respiration. Numerous other types of heterotrophic bacteria are commonly found in lake and reservoir sediments and the overlying water column, such as aerobic bacteria, denitrifiers, and iron-reducing bacteria; these microorganisms also require an organic carbon source for respiration, but they use oxygen (O2), nitrate (NO3 - ), or iron (Fe 3+ ), respectively, as electron acceptors during cellular respiration. Sulfate-reducing bacteria are generally suppressed by the presence of these other electron acceptors. Anaerobic (low oxygen) sediments of mercury-contaminated lakes have been found to be particularly active zones of methylmercury production and an important internal source of methylmercury, especially in lakes experiencing summer anoxia (Regnell et al. 1996). Methylmercury can also be produced directly in the hypolimnion of the water column if other electron acceptors such as oxygen and nitrate are in short supply (Eckley and Hintelman 2005, Watras et al. 1995). Although readily available sulfate and labile organic carbon can result in an increase in mercury methylation, sulfide produced during cellular respiration can, at high concentrations, form Hg-S complexes that are not bioavailable, and in the case of mercury sulfide (HgS) are insoluble (Benoit et al. 1999). Similarly, while DOC can stimulate sulfate-reducing bacteria, at high concentrations it 13

21 can also complex mercury such that it is not as readily available to methylating bacteria (Gorski et al. 2008). Demethylation is the degradation of methylmercury, which can occur under microbially mediated or abiotic conditions. The difference between the rate of mercury methylation and that of methylmercury degradation represents the rate of net methylmercury production. Photodemethylation is the abiotic degradation of methylmercury in the presence of solar radiation (Sellers et al. 1996, Gardfeldt et al. 2001). While the absolute rates of methylmercury photo-demethylation are uncertain, the process has been identified as a significant component of the mass balance of methylmercury in the Delta (Stephenson et al. 2008). Given sufficient water column clarity, photodemethylation may be an important loss pathway for methylmercury in lakes and reservoirs as well Bioaccumulation Methylmercury bioaccumulates, or biomagnifies, in the food web, which can result in biota concentrations that are orders of magnitude greater than ambient water concentrations (Weiner et al. 2003). Developing fetuses and young in humans and wildlife are primarily at risk from bioaccumulation, where the main route of exposure is consumption of mercury-contaminated fish (Fitzgerald et al. 1998). Many environmental factors affect mercury bioaccumulation in the food web of lakes and reservoirs, including physical-chemical properties of habitat that affect the formation of methylmercury, exposure time to methylmercury (via diet for higher tropic levels), potential for biodilution, and the growth rate of food web organisms. Phytoplankton (algae) is the primary entry point for methylmercury into the food web. Methylmercury concentrations in phytoplankton are typically 100-fold greater than concentrations in water (Mason et al. 1996; Pickhardt and Fisher 2007; Gorski et al. 2008), while methylmercury increases at each subsequent trophic level are typically only a factor of two to five (Wood et al. 2010; Stewart et al. 2008; Cabana et al. 1994; Peterson et al. 2007). As methylmercury exposure and subsequent bioaccumulation is directly related to food consumption, habitat and feeding niches for aquatic organisms at various lifestages are likely to be important determinants of ultimate methylmercury tissue concentrations at the higher trophic levels. Because phytoplankton serve such an important role in concentrating methylmercury in the aquatic food web, the degree of primary productivity or trophic status of a lake or reservoir may affect the degree of methylmercury bioaccumulation in higher trophic levels. Algal bloom dilution is a biological mechanism whereby a constant mass of methylmercury is distributed throughout a relatively large biomass of algae, resulting in a generally low concentration of methylmercury per cell and accordingly, low exposure for consumers. As more productive waterbodies tend to be dominated by larger-sized algal species, such as diatoms and green algae, the phenomenon of algal bloom dilution may be amplified by the tendency of more productive water bodies to contain larger bodied phytoplankton with a lower methylmercury bioaccumulation potential (Foe and 14

22 Louie 2014). Overall, the mechanism of bloom dilution suggests that methylmercury bioaccumulation in eutrophic lakes and reservoirs would be relatively low. While there is some evidence to support this hypothesis in California lakes and reservoirs (Foe and Louie 2014), the applicability of the biodilution hypothesis in eutrophic waterbodies such as Soulajule Reservoir, which have elevated fish tissue concentrations of methylmercury, is not well understood. Another form of biodilution, called somatic growth dilution, occurs when the growth rate of an organism is higher than the rate at which methylmercury is incorporated into tissue. At basal metabolism, the amount of food taken in by the organism balances metabolic requirements and no tissue growth occurs. Any methylmercury assimilated in food would gradually increase in concentration over time given the constant tissue mass. Alternatively, as food resources increase above basal metabolic needs, tissue growth occurs. In this case, any methylmercury assimilated in food would gradually decrease in concentration over time given the comparatively rapid increase in tissue mass. Somatic growth dilution has been observed in several lakes in Canada, where fish growth rates were significantly correlated to mercury concentrations and faster-growing fish exhibited lower mercury concentrations than slower-growing fish at a given length (Verta 1990, Gothberg 1983, Simoneau et al. 2005). Relevant case studies Case studies pertinent to Soulajule Reservoir, and for which there are existing available data, include the following (see also Table 2): regionally proximal reservoirs with mercury contamination issues and high algal productivity (Almaden, Calero, and Guadalupe Reservoirs, Lake Almaden, Lake Hodges); productive reservoirs in California being managed for algal impacts, but not necessarily mercury (Camanche Reservoir, Indian Creek Reservoir); lakes in other regions where methylmercury control studies are currently underway (Onondaga Lake, New York); and lakes in other regions undergoing management actions (i.e., oxygen addition, water level fluctuation) that may affect methylmercury production and bioaccumulation (Twin Lakes, Washington; various northern hemisphere lakes). 15

23 Table 2. Soulajule Reservoir and relevant case studies for primary productivity, water level, and mercury control issues. Waterbody Name Soulajule Reservoir Almaden, Calero, Guadalupe Reservoirs, Lake Almaden Lake Hodges Camanche Reservoir Region and/or State Northern California Coast Northern California Coast Southern California Coast Northern California, Sierra Nevada Watershed Area (WA), Surface Area (SA), Volume (V), Max Depth 1, Mean Water Level Fluctuation (WL) WA = 2 mi 2 SA = 125 ha V =10,560 ac-ft Max depth = 80 ft WL= 9 ft Almaden Reservoir WA = 12.5 mi 2 SA = 25 ha V = 1,780 ac-ft Calero Reservoir WA = 7.1 mi 2 SA = 136 ha V = 10,050 ac-ft Max depth = approx. 100 ft Guadalupe Reservoir WA = 6 mi 2 SA = 30 ha V = 3,723 ac-ft Lake Almaden SA = 12.9 ha Max depth = 42 ft WA = 303 mi 2 SA = 1,234 ac V = 30,251 ac-ft Max depth = 117 ft WA = 619 mi 2 SA = 3,100 ha V = 423,000 ac-ft Max depth = 100 ft Mixing State Seasonal Primary Productivity/Trop hic Status Mercury Control Strategy? Monomictic High/Eutrophic To be determined Monomictic Monomictic Monomictic High/Eutrophic High/Eutrophic Low/Oligotrophic Water column mixing (solar bees) (2007) Hypolimnetic oxygenation system (HOS) line diffuser (2013 current) Hypolimnetic oxygenation system (HOS) Speece cone Hypolimnetic oxygenation system (HOS) Speece cone 16

24 Waterbody Name Indian Creek Reservoir Twin Lakes Onondaga Lake Finnish Reservoirs (40 reservoirs) Eastern South Dakota Lakes (18 natural lakes) Region and/or State Northern California, Sierra Nevada Northern Washington New York Finland South Dakota Watershed Area (WA), Surface Area (SA), Volume (V), Max Depth 1, Mean Water Level Fluctuation (WL) WA = 122 mi 2 SA = 55 ha V = 3,160 ac-ft Max depth = 37 ft North Twin Lake WA = 28.2 mi 2 SA = 370 ha V = 29,600 ac-ft Max depth = 49.9 ft South Twin Lake WA = 5.4 mi 2 SA = 413 ha V = 34,200 ac-ft Max depth = 57.1 ft WA = 285 mi 2 SA = 1,191 ha V = 106,200 ac-ft Max depth = 63 ft SA = ,700 ha V = 3,080 1,672,500 ac-ft Max depth = ft WL= ft SA = 157 7,331 ha WL= 0 3,580 ha 2 Mixing State Seasonal Primary Productivity/Trop hic Status Mercury Control Strategy? Dimictic High/Eutrophic Not applicable Dimictic Dimictic Low/Oligotrophic Moderate/ Mesotrophic Not required, although hypolimnetic oxygenation system (HOS) line diffuser is being used to control seasonal anoxia Nitrate addition Polymictic Eutrophic hypereutrophic 17

25 Waterbody Name Voyageurs National Park Lakes (6 reservoirs and 8 lakes) Sand Point Lake Region and/or State Northeastern Minnesota Northeastern Minnesota Watershed Area (WA), Surface Area (SA), Volume (V), Max Depth 1, Mean Water Level Fluctuation (WL) Reservoirs: SA= ,00 ha Depth =25 45 ft WL= ft Lakes: SA=670 11,600 ha Depth = 7 20 ft WL= ft SA = 3,580 ha Max depth = 184 ft WL= 1.9 ft 1 Values provided where data are readily available. 2 Water level fluctuations were presented in change of surface area (Selch et. al 2007) indicates no information available Mixing State Seasonal Primary Productivity/Trop hic Status Mercury Control Strategy? Oligotrophic 18

26 Almaden, Calero, and Guadalupe reservoirs and Lake Almaden The Santa Clara Valley Water District (SCVWD), located in the South San Francisco Bay Area, California, manages a number of reservoirs within the historical New Almaden Mining District for flood control and water capture/groundwater recharge. Some of the reservoirs have been impacted by past mercury mining activities and currently exhibit high levels of methylmercury accumulation (sometimes > 30 ng/l) in anoxic bottom waters during the summer stratification period. Lake Almaden, and Guadalupe, Almaden and Calero reservoirs are part of the Guadalupe River Watershed Mercury TMDL includes the following specific mercury criteria for a range of ecosystem compartments (SFBRWQCB 2008b): Total mercury (TotHg) in creek waters 0.2 mg Hg per kg dry suspended sediment, annual median; Methylmercury in reservoir bottom waters 1.5 ng/l seasonal maximum; and Methylmercury in fish tissue < 50 ug/kg wet weight for 5-15 cm fork length and < 100 ug/kg wet weight for cm fork length. During , SCVWD installed SolarBee solar-powered vertical mixing devices in Lake Almaden and in Almaden and Guadalupe reservoirs. While some benefit in water quality was achieved in Lake Almaden, including an apparent improvement in the oxidation-reduction potential (ORP) in lake bottom waters, there was little actual increase in DO levels or substantial drops in water column methylmercury concentrations. SCVWD then embarked on an ambitious program to design, construct, and install a hypolimnetic oxygenation system (HOS) at four reservoirs including Stevens Creek (outside of the Guadalupe River Watershed and not impacted by mining), Calero (in the Guadalupe River Watershed but not impacted by mining), Almaden, and Guadalupe reservoirs. The HOS line-diffuser systems each deliver less than 1 ton/day of oxygen to the sediment-water interface of the two reservoirs. Preliminary data from 2013 and 2014 indicate that oxygen addition is increasing DO levels in bottom waters of both reservoirs (D. Drury, SCVWD, pers. comm.). Results of test oxygenation in Stevens Creek Reservoir indicated a rapid decline in DO in early spring during both 2013 and 2014, at a rate typical of productive reservoirs (approximately 0.1 mg/l/d) (Figure 9). During test oxygenation periods, DO levels in Stevens Creek Reservoir outlet waters increased, ranging 4 6 mg/l. In Calero Reservoir, test oxygenation decreased peak hypolimnetic methylmercury levels from 2 4 ng/l to < 0.7 ng/l (Figure 10) (D. Drury, SCVWD, pers. comm.). Future testing of the systems in the SCVWD reservoirs will likely involve oxygenation prior to the onset of low DO (i.e., < 5 mg/l) each spring, as preliminary data from 2013 and 2014 indicate that it is considerably more difficult to increase DO concentrations in bottom waters once anoxia has become established. Small fish ( mm fork length, multiple species) sampled in fall 2014 at Calero Reservoir were not lower in methylmercury than in the three years prior to pilot HOS operation. Monitoring of water and small fish continues as additional HOS installations become operational. 19

27 Figure 9. Reservoir outlet concentrations of DO from Stevens Creek Reservoir during test oxygenation in 2013 and HOS was cycled on and off in May June 2013 and June August Preliminary data provided by David Drury (SCVWD) and Stephen McCord (McCord Environmental). Figure 10. Hypolimnion concentrations of methylmercury in Calero Reservoir (right axis) compared to volume of reservoir with DO concentration less than 1.0 mg/l (left axis). The reservoir was oxygenated in Seasonal maximum criterion for methylmercury in the hypolimnion (1.5 ng/l) is shown in red. Preliminary data provided by David Drury (SCVWD). 20

28 Lake Hodges The City of San Diego (City) Public Utilities Department owns and operates Lake Hodges Reservoir, located about 30 miles north of San Diego, California. The reservoir has a maximum capacity of 30,251 ac-ft, maximum depth of 117 ft, and encompasses an area of 499 ha, with 303 mi 2 of upstream catchment area (see also Table 2). It is an important part of the San Diego County Water Authority (SDCWA) Emergency Storage Projects and is needed to increase the ability to deliver water within San Diego County during significant water supply shortage (Brown and Caldwell 2014). The Regional Water Quality Control Board, San Diego Region (RWQCB) 2008 Clean Water Act Sections 305(b) and 303(d) Integrated Report states that Lake Hodges Reservoir currently does not meet water quality objectives for the following five parameters: ph, manganese, turbidity, nitrogen and phosphorous. This assessment means that current Lake Hodges conditions no longer fully support one or more of its beneficial uses. In addition, in the Statewide 2010 Integrated Report (Clean Water Act Section 303(d) List), the State Water Resources Control Board (SWRCB) included mercury on the list of pollutants causing impairment in Lake Hodges. The mercury listing is based on findings in the 2009 Surface Water Ambient Monitoring Program report entitled Contaminants in Fish from the California Lakes and Reservoirs. Excessive algal productivity in Lake Hodges impairs the reservoir s usability as a drinking water source because of taste and odor events, high levels of disinfection by-product precursors, filter clogging, high turbidity, and contribution to anoxic conditions in the reservoir s deeper water. Senescent algae settle out of the water column, providing labile organic carbon that fuels sulfate reduction in deeper, anoxic waters and supports methylmercury production (see also Section ). Thus, managing odor and taste producing algae is key to restoring and sustaining Lake Hodges dominant and overarching beneficial use as a source of drinking water supply. It also concurrently reduces the potential for methylmercury formation since it removes a large source of organic carbon to bottom sediments. Excessive loading of nutrients (nitrogen and phosphorous) and organic carbon, both from both external catchment sources and internal nutrient cycling, currently fuel the lake s high algae productivity (Figure 11 and Figure 12). 21

29 Figure 11. Excessive algal productivity in Lake Hodges 22

30 Figure 12. Cyanobacteria bloom in Lake Hodges on July 17, 2013, as detected by postprocessed satellite imagery. Currently, multiple in-lake management methods to manage and control excessive algal productivity and address the 303(d) listings of water quality impairments have been identified for Lake Hodges. The alternatives have been combined into an overall plan with several key components, presented in order of implementation priority: 23

31 Speece Cone HOS is proposed to add DO to the reservoir s bottom water, to prevent anaerobic conditions from occurring. Mid-lake vigorous epilimnetic mixing (VEM) is proposed at the middle section of the reservoir to mix shallow areas to discourage the growth of potentially toxic blue green algae. Upper wetland filtering through constructed wetlands is proposed at the upper section of the reservoir, which would skim and pump floating algae from the lake and remove it through the wetland system. Biomanipulation is being considered to focus on harvesting carp that stir up the bottom sediments and hence recycle nutrients, as well as netting out small fish that feed on zooplankton (good organisms that feed on algae). Algaecides/molluscicides are being considered if Quagga mussels (or other deleterious organisms) establish themselves in Lake Hodges. In addition, a comprehensive sediment testing effort and mercury monitoring program are underway at Lake Hodges. The sediment testing effort will assess sediment oxygen demand (SOD) and sediment release rates of redox sensitive compounds (i.e., ammonia, phosphate, iron, manganese, and methylmercury) under oxic versus anoxic conditions using laboratory bench-scale chambers. Results will help to determine the design oxygen delivery rate for an HOS and confirm that maintenance of an oxygenated sediment-water interface will improve water quality by suppressing the sediment release of redox sensitive compounds. The mercury monitoring program also will evaluate monthly total mercury and methylmercury at several locations within the reservoir s water column at multiple sites. Collection of profile data, rather than discreet surface, middle and bottom samples, will support the development of a more precise mercury mass balance for the reservoir. Lastly, the monitoring program will evaluate monthly total mercury and methylmercury levels in zooplankton, a key link between water column mercury and fish tissue concentrations Camanche Reservoir Camanche Reservoir is a large East Bay Municipal Water District (EBMUD) reservoir (423,000 ac-ft, max depth approx. 100 ft) located on the east side of the California Central Valley, approximately 15 mi northeast of Lodi. It is fed by the Mokelumne River, which originates in the Sierra Mountains. Camanche Reservoir was constructed in 1964, primarily as an agricultural water supply. It is situated just downstream of Pardee Reservoir, which supplies drinking water to 1.3 million EBMUD customers. The combination of the two reservoirs allows EBMUD to better manage water supply. As the construction of Camanche Dam blocked access to upstream spawning habitat for Chinook salmon and steelhead, the Mokelumne River Fish Facility was constructed just below the dam and supplied with cool water from the hypolimnion of Camanche Reservoir. In the mid-1980s, two large fish kills occurred in the hatchery and were 24

32 ascribed to hydrogen sulfide (H2S) production in the anoxic hypolimnion waters and sediments of the reservoir. In 1992, an HOS consisting of a Speece Cone pure oxygen, bubble-free plume system was installed near Camanche dam to add oxygen directly to the bottom waters and sediments and eliminate H2S production (Figure 13). Because it was determined that one of the fish kill incidents was induced by reservoir draw-down in the summer to meet downstream flow requirements, thereby exacerbating fish exposure to H2S, the HOS implementation was combined with minimum hypolimnion pool volume and maximum temperature requirements. During the last 20 years, there have been no reported fish kills due to poor water quality at the Mokelumne River Fish Facility. Further, in 2014, during a record drought in California, small hatchery fish from other state facilities were relocated to the Mokelumne River Fish Facility because of its preferred water quality. Other reservoir water quality parameters, such as chlorophyll-a and water clarity, improved following Speece Cone implementation, and seasonal blue-green algae nuisance blooms were eliminated because nutrients fueling the blooms were no longer recycled from anoxic reservoir sediments. Although H2S was the prime cause of fish kills, concentrations of ammonia, trace metals (e.g., copper), and turbidity were high enough in reservoir bottom waters to cause concern for hatchery and river fish, especially at the egg stages. These contaminants were also reduced by HOS, including copper, which can be elevated in the reservoir due to an upstream abandoned copper mine. Hydropower operations at Camanche Dam, which had been reduced due to the need to first remove H2S through a spray release valve, were restored following HOS implementation. In addition, the temperature-oxygen squeeze that previously limited reservoir habitat for trout has expanded to encompass much of the hypolimnion, to the benefit of local anglers and EBMUD licensees. The added flexibility provided by a minimum oxygenated and cool hypolimnion allowed reservoir operation at lower water elevations during drought periods, such that emergency water did not have to be purchased at relatively high prices. Downstream water quality in the Mokelumne River has also improved and, over the last 20 years, numbers of spawning wild Chinook salmon have increased almost three fold and spawning Steelhead have increased from zero to 278/yr. Although some of the fisheries benefits were due to in-river improvements such as additional spawning gravel, better hatchery operation, and targeted Delta releases, none would have been possible without the improved water supply downstream of Camanche Dam provided by HOS. Unlike other case studies presented herein, no known mercury contamination exists at Camanche Reservoir; however, this case study is included because it presents an example of an engineered system designed to reduce hypolimnion anoxia. 25

33 Figure 13. Installation of a Speece cone in Camanche Reservoir, California, to oxygenate hypolimnetic waters and eliminate seasonal H2S production. Photo Source: East Bay Municipal Utility District Indian Creek Reservoir Owned and operated by South Tahoe Public Utility District (STPUD), Indian Creek Reservoir (ICR) is a small, relatively shallow high-elevation reservoir located in Alpine County, California, about 26 miles southeast of Lake Tahoe. The reservoir comprises approximately 55 ha, with a total volume of approximately 3,160 ac-ft, a mean depth of ft and typical maximum depth of about 37 ft. At times the maximum depth has increased to about 45 ft (see also Table 2). It was originally constructed in 1967 to hold tertiary treated, high-nutrient wastewater from the STPUD wastewater treatment plant prior to re-use for irrigation purposes in Alpine County. No longer used for this purpose, STPUD continues to operate the reservoir as a recreational facility, primarily for trout fishing. Located in a dry valley on the eastern slopes of the Sierra Nevada Mountains, the reservoir has almost no natural inflows and would have dried up in a few years, but since 1989 it has been solely supplied with water diverted through several miles of channels from Indian Creek or the Carson River. Despite inflow water quality improvement, ICR is included on the Clean Water Act Section 303(d) list for eutrophication. Since the 1970s, it has exhibited symptoms of eutrophication including impairment of aquatic life and recreational uses and violation of narrative and numerical water quality objectives. Extensive sampling has identified 26

34 phosphorus as the primary nutrient contributing to eutrophication, with internal loading of phosphorus from bottom sediments as the main source. Unlike most other case studies presented herein, no known mercury contamination exists at ICR; however this case study is also included because it presents an example of an engineered system designed to meet TMDL requirements, especially hypolimnion anoxia. In July 2002, the Lahontan Regional Water Quality Control Board (LRWQCB) established numeric targets for five (5) indicator parameters for ICR: total phosphorus, DO Secchi Depth, chlorophyll-a, and Carlson Trophic State Index (TSI). STPUD studied a variety of alternatives and determined that HOS was the optimal method to address the beneficial use impairment by reversing eutrophication in the reservoir and meeting TMDL objectives (Kennedy Jenks Consultants 2004). Specifically, investigations identified a submerged down-flow contact oxygenation system (SDCO or Speece Cone) as the best device for use at ICR (A. Horne Associates 2005). In December 2006, the District was awarded a Clean Water Act Section 319 (h) Nonpoint Source Implementation Grant for the purpose of reducing internal loading of phosphorus to ICR and optimizing reservoir management for protection and enhancement of aquatic life and recreational uses. The recommended ICR HOS consisted of a Speece Cone located in the deepest portion of the reservoir, an on-site oxygen generation system, and underground and submerged utilities connecting the oxygen generator to the Speece Cone (Figure 14) (Brown and Caldwell 2007). The ICR HOS became operational in STPUD now operates the HOS during the late spring and summer to deliver oxygen to ICR for water quality and aquatic habitat improvement. 27

35 Figure 14. Indian Creek Reservoir showing location of Speece Cone and equipment building used as part of the hypolimnetic oxygenation system. (STPUD 2014) The ICR TMDL tracking plan requires collection and evaluation of indicator parameters to ascertain progress toward achieving ICR numeric targets. The following figures from the 2013 TMDL Progress Report (STPUD 2014) show the marked improvement in water quality. With an exception in 2011, daily mean dissolved oxygen concentrations have remained above the 4.0 mg/l interim target (Figure 15). This change has led to lower total phosphorus in the reservoir (Figure 16), lower algae concentrations (as measured by chlorophyll-a) (Figure 17), and greater Secchi depths (Figure 18). Operating the HOS routinely has allowed STPUD to comply fully with interim ICR TMDL limits. 28

36 Figure 15. Daily mean dissolved oxygen concentration (averaged in water column) measured at three locations in Indian Creek Reservoir. ICR HOS began operating in (STPUD 2014) Figure 16. Total phosphorus concentrations measured at Indian Creek Reservoir. ICR HOS began operating in (STPUD 2014) 29

37 Figure 17. Chlorophyll-a measured at Indian Creek Reservoir. ICR HOS began operating in (STPUD 2014) Figure 18. Secchi depth measured at Indian Creek Reservoir. ICR HOS began operating in (STPUD 2014) 30

38 Onondaga Lake Onondaga Lake is a large, temperate urban lake located north of Syracuse, New York. The lake has a surface area of 1,191 ha, a volume of 106,200 ac-ft, and a maximum depth of 63 ft (see also Table 2). Its surrounding watershed extends 285 mi 2 with predominant land use activities including agriculture, forestry, and urbanization. Onondaga Lake is dimictic, mixing once from top to bottom in the spring following ice melt, and again at fall turnover. The lake flushes approximately 4 times per year and as a result responds relatively rapidly to changes in external loading (Doerr et al. 1994). The lake is currently mesotrophic, with summer mean chlorophyll-a concentrations less than 10 ug/l and no major summer algal blooms observed since 2007 (Onondaga County 2011, Suryadevara 2014). Despite this, anoxic conditions in the hypolimnion typically prevail from July through October, during the summertime stratification period (Matthews et al. 2008). Due to the abundance of gypsum (CaSO4) in the surrounding watershed, sulfate water column concentrations are relatively high (approximately 96 mg/l) and can account for a high percentage of total annual organic matter mineralization in the lake (Matthews et al. 2008). Over the past century, development of the watershed surrounding Onondaga Lake resulted in contamination from both domestic and industrial sources. The lake s bottom sediments and numerous subsites around the lake and its tributaries were added to the USEPA Superfund National Priorities List in 1994 due to industrial inputs of mercury, aromatic volatiles, chlorinated benzenes, polycyclic aromatic hydrocarbons, and polychlorinated biphenyls (Parsons and UFI 2011). An estimated 75,000 kg of mercury were discharged to the lake during historical shoreline manufacturing operations, resulting in subsequent contamination of lake water column, sediments, and biota (Matthews et al. 2013). Effluent from the Metropolitan Syracuse Wastewater Treatment Plant has accounted for a significant fraction of annual Onondaga Lake inflow over time (currently at 20% [Matthews et al. 2013]), adding high levels of phosphorus and nitrogen to the lake. During the mid-2000s, elevated total phosphorus concentrations in treated wastewater effluent resulted in routine violations of receiving water quality standards (Effler et al. 2010). Further, internal loading of methylmercury from bottom sediments has resulted in hypolimnetic concentrations >15 ng/l during periods of summer anoxia (Bloom and Effler 1990; PTI Environmental Services 1994; Sharpe 2004). In recent decades, major rehabilitation programs have been underway to address the impacts of both domestic and legacy industrial wastes in Lake Onondaga, including source control, dredging, in situ sediment capping, habitat restoration, and monitored natural recovery (Parsons and UFI 2011). In 2004, year-round nitrification of wastewater was initiated at the Metropolitan Syracuse Wastewater Treatment Plant, resulting in decreased ammonia levels and a doubling of water column nitrate concentrations in the lake at spring turnover (Effler et al. 2010). Subsequent treatment upgrades in 2005 caused major decreases in phosphorus concentrations and transformed the lake from eutrophic to mesotrophic (Effler et al. 2008). High nitrate concentrations (approximately 31

39 2 mg N/L) and elevated N:P ratios were maintained to discourage blooms of nuisance N- fixing cyanobacteria in the epilimnion. As a consequence, the duration of nitrate presence in the hypolimnion was increased by nearly two months, and the onset of sulfate reduction shifted to later in the summer or was completely eliminated. The enhanced supply of nitrate alleviated anaerobic conditions and exerted strong regulation on methylmercury concentrations, resulting in > 50% decreases in hypolimnetic accumulations of methylmercury (Todorova et al. 2009). These findings prompted investigations into the feasibility of adding nitrate to the hypolimnion to further reduce transport of methylmercury from profundal sediments. During , a pilot study was conducted in Onondaga Lake to evaluate the effectiveness of nitrate application in controlling hypolimnetic methylmercury concentrations during summer anoxia. A neutrally-buoyant plume of liquid calcium nitrate solution was added to the hypolimnion during summer stratification from a motorized barge at three locations. Each location received 18,000 L of the solution approximately once per week, such that nitrate concentrations were maintained at greater than 1 mg N/L at the sediment-water interface (Matthews et al. 2013). During the first year of the pilot study, maximum hypolimnetic concentrations of methylmercury were reduced by 94% and maximum concentrations of soluble reactive phosphorus were decreased by 95%. Hypolimnetic concentrations of both methylmercury and phosphorus were maintained at background levels during the final two years of the nitrate addition pilot study. The results were attributed to increased redox potentials and enhanced sorption to iron and manganese oxyhydroxides in surficial sediment layers. Methylmercury concentrations in the upper waters during fall turnover were also substantially reduced, resulting in decreased exposure of aquatic organisms to methylmercury (Matthews et al. 2013). Recent reductions in fish mercury levels have been measured in Onondaga Lake; however, in general the majority of fish tissue samples still exceed levels safe for human consumption (Honeywell International, Inc. 2013). Based on the pilot study, the New York State Department of Environmental Conservation (NYSDEC) and USEPA are modifying the proposed remedy for clean-up of the Onondaga Lake Superfund Site to require full-scale implementation of nitrate addition in lieu of the original plan to evaluate the effectiveness of oxygenation (NYSDEC and USEPA 2014). This decision was based upon an assessment of relatively low recreational and environmental impacts of nitrate addition, as well as low costs. Dredging activities included in the clean-up plan were completed in November 2014, removing approximately 2.2 million cubic yards of sediment from Onondaga Lake (Honeywell International, Inc. 2015). In situ capping of an additional 450 ac of lake bottom sediments and 50 ac of wetland restoration are scheduled for completion in 2016 (Honeywell International, Inc. 2015). 32

40 Twin Lakes North Twin (SA = 370 ha); maximum depth = 49.9 ft) and South Twin (SA = 413 ha); maximum depth = 57.1 ft) (see also Table 2) lakes are mesotrophic, dimictic lakes located on the Confederated Tribes of the Colville Indian Reservation, a 1.4 million-ac reservation in eastern Washington State that is rich in timber, wildlife, fish, and water resources. While the lakes have fairly similar bathymetry, North Twin Lake has a larger watershed (28.2 mi 2 versus 5.4 mi 2 ) and a shorter mean hydraulic residence time (2.7 yr versus 9.4 yr) relative to South Twin Lake. The lakes are especially prized for warm- and cold-water recreational fishing opportunities. Typical Secchi depths in the lakes are ft. Both North Twin and South Twin lakes exhibit symptoms of summertime hypolimnetic anoxia including bottom water buildup of redox-sensitive compounds such as manganese, iron, and sulfide. To improve summertime cold-water habitat for trout, hypolimnetic oxygen addition to North Twin Lake was initiated in The oxygenation system consisted of a 6,000 gallon trailer-based on-shore liquid oxygen storage tank and evaporator connected to a 2,461 ft fine-bubble line diffuser located near the lake bottom (Figure 19). The system was typically operated between May and October and delivered cfm of pure oxygen gas to the lake, of which an estimated 80 percent dissolved into bottom waters. Figure 19. Trailer mounted temporary LOX storage system at Twin Lakes, WA. Black pipe on bottom left delivers oxygen gas to lake through a line diffuser near the bottom of the lake. 33

41 Hg in the water column, zooplankton and fish, and related water quality parameters were assessed in Twin Lakes from 2009 to Since methylmercury buildup in bottom waters is commonly associated with hypolimnetic anoxia (Section 2.4.1), hypolimnetic oxygenation was hypothesized to reduce mercury in bottom waters and biota in North Twin Lake relative to South Twin Lake. Part of this hypothesis was confirmed, but unexpectedly another was refuted. Oxygen addition led to significantly higher DO (mean hypolimnetic DO: 2 8 mg/l versus < 1 mg/l) and lower methylmercury (peak mean hypolimnetic MeHg: ng/l versus ng/l) in North Twin Lake compared to South Twin Lake. But mercury levels were significantly higher in zooplankton (TotHg range: versus ug/kg dry weight) and trout (spring 2010 stocking cohort of eastern brook trout mean total Hg: 74.9 versus 49.9 ug/kg wet weight) in North Twin Lake when compared to South Twin Lake, where the latter appeared to be a naturally low mercury bioaccumulating system. Very high chlorophyll levels (20-80 ug/l) were observed in the bottom water of South Twin Lake, so methylmercury in bottom waters may have been incorporated into a large pool of algae, thereby resulting in low methylmercury uptake per unit of algae consumed by zooplankton, a phenomenon known as algal bloom dilution (Section 2.4.1). In addition, in South Twin Lake the bottom waters were so anoxic (DO < 0.1 mg/l and sulfide odor in very deep waters) that zooplankton did not migrate into methylmercury-rich bottom waters. The vertical disconnect between the location of zooplankton and methylmercury in the water column could have accounted for low mercury in South Twin Lake zooplankton. Finally, bottom waters in South Twin Lake were high in sulfide approximately 0.2 mg/l), which has a high binding affinity with methylmercury (Section 2.4.1). This may have repressed the bioavailability of methylmercury for uptake into algae at the base of the food web. These results do not necessarily indicate that lake oxygenation enhances methylmercury bioaccumulation. In North Twin Lake, high DO in 2009 and 2011 co-occurred with lower levels of methylmercury in bottom waters and less total mercury in zooplankton, confirming a positive linkage between oxygen addition and lower bioaccumulation (Figure 20). Another critical facet of this study was the measurement of iron and manganese in North Twin Lake bottom waters even during oxygenation. Typically, oxygen addition suppresses iron and manganese accumulation in bottom waters by locking these metals into sediments in the form of particulate metal oxides. The presence of iron and manganese in bottom water indicated that the line diffuser oxygenation system, while maintaining elevated DO in the upper hypolimnion and improving cold-water trout habitat, was not oxygenating the sediments. If the oxygenation system had been successful in oxygenating sediments, it is possible that methylmercury levels would have been lower in North Twin Lake bottom water and zooplankton than were observed in the study. 34

42 Figure 20. Relation between oxygen addition (x-axis) and mercury in zooplankton (y-axis). Years with high oxygen addition (2009 and 2011) had lower mercury levels in zooplankton Northern hemisphere lakes with fluctuating water levels Fluctuating water levels have been correlated with increased fish tissue mercury concentrations in several reservoirs and natural lakes in the northern hemisphere (Selch et al. 2007, Sorensen et al. 2005, Evers et al. 2007, Verta et al. 1986). For example, Verta et al. (1986) indicated that water-level fluctuations were a key explanatory variable related to elevated mercury fish tissue concentrations in a study of 20 dimictic hydroelectric and flood control reservoirs in Finland. The authors suggested that fluctuations can increase shoreline erosion, delivering organic carbon and mercury into the reservoir; this process was particularly important for reservoirs that experienced ice cover during reservoir drawdown, which appeared to increase erosive forces in steepsided reservoirs. Increased mercury concentrations in fish tissue were observed in 18 natural lakes in eastern South Dakota following an extended wet period that significantly increased lake surface areas. Mercury concentrations in walleye were positively correlated with the magnitude of surface area expansion, and higher growth rates of walleye were positively correlated with mercury concentrations in fish tissue (Selch et. al. 2007). 35

43 In a three-year study of 14 northeastern Minnesota lakes, there was a strong positive correlation between mercury concentrations in yellow perch young-of-the-year (YOY) and changing water levels (Sorensen et al. 2005). For all 14 lakes, the authors observed significant positive correlations between mercury in fish and multiple measures of water level, with the strongest apparent correlation for mean water levels occurring during summer/early fall. Water color, TOC, and conductivity also correlated positively with mercury fish tissue concentrations in these lakes. In one lake in particular (San Point Lake), where 12 years of additional data are available, YOY yellow perch mercury levels increased as average Secchi depth decreased (r 2 = 0.62), and Secchi depth decreased as maximum water increased (r 2 = 0.77) (Figure 21), suggesting a positive link between reservoir level, algal productivity, and fish tissue mercury concentrations in this lake (Sorensen et al. 2005). Figure 21. (A) Relationship between mercury concentrations in young-of-the-year yellow perch and maximum water levels (March July) relative to the previous year, for San Point Lake, Minnesota, from 1991 to (B) Relationship between Secchi depths and maximum water levels. (C) Mercury concentrations in yellow perch. Bars represent standard error ranges. Source: Sorensen et al. (2005). 36

44 Mechanistic explanations for the observed effects of water level fluctuations on fish tissue mercury concentrations vary depending on study conditions. In general, microbial and chemical processes supporting methylation appear to be relatively greater in organic-rich littoral zones as compared with pelagic (open water) zones, and bioaccumulation from detrital/ bacterial matter consumed by littoral zooplankton is greater than bioaccumulation from algae consumed by pelagic zooplankton (Tremblay et al. 1998). Alternating drying and flooding of soils within the littoral zone may further enhance littoral zone methylation and bioaccumulation, whereby flooding increases rates of mercury methylation due to decomposition of organic matter and subsequent stimulation of sulfate reducing bacteria (Munthe et al. 2007). Accordingly, the ratio of littoral zone area to total reservoir volume may inform the potential for methylmercury bioaccumulation in lakes/reservoirs experiencing a high degree of water level fluctuation. Steep-sided reservoirs with organic-poor substrates may exhibit less efficient methylmercury production, lower ambient methylmercury concentrations, and less bioaccumulation compared to reservoirs possessing relatively large, shallow littoral zones with organic rich soils (Evers et al. 2007). Further, less frequent water level fluctuations within the littoral zone may reduce average mercury concentrations in fish tissue. 2.5 Climate Change Climate change could indirectly affect methylmercury cycling in Soulajule Reservoir and Arroyo Sausal through associated changes to physical, chemical, and biological processes in the reservoir and creek. Future projections of climate change under the Fourth Assessment of the International Panel on Climate Change indicate that by late in this century (2080s) average annual surface temperatures in northern coastal California will rise from current levels by 2 8 o F (1 4.5 o C) assuming a range of potential greenhouse gas emissions scenarios. The long-term effects of global climate change on the North Coast region are uncertain. However, the following effects are likely, based on the current state of scientific knowledge and associated climate change projections: Increased average air temperatures. These increases may be somewhat mitigated by potential increases in coastal fog formation. Increased water temperatures. Again, these may be somewhat mitigated by potential increases in coastal fog formation. Increased intensity and frequency of storm events, shifts in inter-annual timing and magnitude of peak floods, and associated increases in erosion and sedimentation. Increased intensity and frequency of droughts and, potentially, wildfires. 37

45 Increased frequency and magnitude of coastal storm surges/flooding events due to sea level rise. Increases in air and water temperatures may result in earlier seasonal stratification and a longer overall period of stratification for Soulajule Reservoir. This could extend the growth season for algae in reservoir surface waters and the period of methylmercury production in anaerobic/anoxic bottom waters, affecting concentrations that are released to Arroyo Sausal. Increased intensity and frequency of storm events and associated increases in erosion could affect the rate of sedimentation in Soulajule Reservoir from eroding upland soils. If the latter are a source of total mercury to the reservoir, this could affect overall mercury loading rates. Increased intensity and frequency of droughts could change the way in which Soulajule Reservoir is managed for water supply. The District is currently considering more frequent use of Soulajule Reservoir for drinking water supply. Although speculative at this time, this Study Plan includes consideration of the potential effects of climate change on mercury methylation in Soulajule Reservoir as part of developing successful long-term strategies for methylmercury control and overall reservoir management. 38

46 3 POTENTIAL MANAGEMENT METHODS 3.1 Initial Screening of Methods While the Regional Board had already identified a number of potential management approaches in their May 7, 2014 letter (e.g., erosion control plan for targeted areas in the Eastern Arm, capping of reservoir sediments in the Eastern Arm, hypolimnetic oxygenation/aeration, fisheries management), development of the Study Plan commenced with a screening workshop to evaluate 17 potential in-lake management methods, as well as 5 broader watershed management methods (Table 3), for their applicability in addressing overall reservoir management objectives as well as methylmercury control. Initial consideration of a broader list of potential management methods, including those suggested by the Regional Board, was undertaken to ensure that the project did not inadvertently overlook possible viable approaches. Workshop participants included District staff involved in managing and monitoring Soulajule Reservoir and Arroyo Sausal, the San Francisco Bay Regional Water Quality Control Board, as well as project team members with expertise in water quality, fisheries, watershed management, methylmercury biogeochemical cycling, and engineering. Table potential methods for in-lake and watershed water quality management. In-lake/Reservoir Method 1 Dredging 2 Water level fluctuation 3 Mixing and/or destratification 4 Macrophyte harvesting 5 Wetland filters (fringe) 6 Algae harvesting 7 Selective withdrawal of hypolimnion 8 Dilution/flushing 9 Sediment sealing/capping (fabrics) 10 Algaecides/herbicides or molluscicides 11 Oxygenation/aeration/nitrate addition 12 Shading/dyes 13 Sediment sealing (chemical, alum, etc.) 14 Pathogens/diseases of algae 15 Grazers (on algae or macrophytes) 16 Nutrient harvesting from fish/weeds 17 Biomanipulation Watershed Method 1 Land re-sculpture & stream re-routing 2 Standard erosion control measures (BMPs) Unit process natural treatment (UPNT) 3 wetlands 4 Volatilization in dry cultivated wetlands 5 Volatilization in crops 39

47 Assignment of general applicability and the associated rationale for each of the 17 potential in-lake and 5 watershed management methods discussed at the workshop is presented in Appendix A. Of the 22 total management methods considered, 7 were judged to have general applicability or potential applicability for methylmercury control in Soulajule Reservoir, given its broader water quality challenges, physical characteristics, and consideration of the four mercury management objectives identified by the Regional Board (Table 4). Table 4. Applicability of selected in-lake and watershed management methods for methylmercury control in Soulajule Reservoir. Method Applicability Mercury management objective 1: Reduce sediment mercury loads Erosion control Potentially applicable Sediment sealing/capping (fabrics) Potentially applicable Dredging Potentially applicable Mercury management objective 2: Manage water chemistry to reduce methylation Oxygenation/aeration (not including nitrate addition) Applicable Mercury management objective 3: Decrease levels of blue-green algae Mixing and/or destratification vigorous epilimnetic mixing Applicable Mercury management objective 4: Manage fisheries to reduce methylmercury in fish tissue Biomanipulation stocking of predator fish un-impacted by mercury Potentially applicable Biomanipulation stocking prey fish un-impacted by mercury Potentially applicable Water level fluctuation, while occasionally used to control fisheries, aquatic vegetation, and algal growth, is not currently understood to be a method for controlling mercury methylation and bioaccumulation in lakes and reservoirs. The District is considering more frequent use of Soulajule Reservoir for drinking water supply, which could alter the future magnitude, frequency, and duration of volume and water level fluctuations. Accordingly, workshop participants recommended that the potential effects of increased water level fluctuation on methylmercury production and bioaccumulation be considered as part of the Study Plan. Because it represents a potential change in reservoir conditions that may affect mercury methylation and bioaccumulation, rather than a true mercury management approach, water level fluctuation is addressed separately in Section 4. Each of the seven applicable (or potentially applicable) management methods is discussed further below, organized by mercury management objective (i.e., reduce sediment mercury loads, manage water chemistry, decrease levels of blue-green algae, manage fisheries). 3.2 Methods Applicable to Soulajule Reservoir The intent of the below methods is to reduce mercury loads from external (watershed) and internal (in-lake) sources into Soulajule Reservoir. 40

48 Reduce sediment mercury loads Erosion control for upland soils in the Eastern Arm Eroding sediments from upland soils may significantly contribute to total mercury loading to Soulajule Reservoir, particularly in the Eastern Arm, near the historical Franciscan and Cycle Mines (Figure 8). If erosion of soils containing elevated mercury is occurring, a soil erosion control plan could be developed to reduce sediment loads to the reservoir. Specific recommendations arising from an erosion control plan would be based on data gathered as part of a site reconnaissance and soil testing to assess the erosion contribution of mercury from anthropogenic (mining/mine tailings) and natural background sources under current conditions (see Pilot Study 6, Section 6.6). Implementation of the upland source evaluation could be initiated in 3 to 6 months. Development of a soil erosion control plan, should it be required, could be accomplished within 6 to 12 months, with the caveat that implementation of erosion control BMPs would require landowner agreements; the District does not own the upland areas surrounding Soulajule Reservoir. Reduction of mercury concentrations in the reservoir water column and/or fish tissue may not be easily observable in the short term, but the decreased mercury loading would be effective in the long term. Goals and capabilities The goal of sediment erosion control is to reduce mercury source loading from upland soils and sediments adjacent to Soulajule Reservoir. At the nearby Gambonini Mine, slope stabilization and native-plant revegetation were successfully employed as part of a 1999 Superfund (CERCLA) cleanup to control surface erosion from a 12-ac mercury mining waste pile, avoiding the following: offsite disposal, importing of clean soils, and placement of an impervious cap. Intensive stormwater discharge monitoring conducted in 2005 and 2010 indicated that site cleanup had reduced mercury loads by an estimated 92 93% (Kirchner 2011). Example applications The focus of BMPs is to prevent sediment containing elevated levels of mercury from contact with streams, ponds or the reservoirs, where methylmercury can be formed. For example at the New Almaden Mine in Santa Clara County (the 5 th largest mercury mine in the world), soil erosion control BMPs have been used to stabilize slopes and protect waterbodies within the Guadalupe River watershed and reduce TMDLs of mercury that contribute to mercury levels in San Francisco Bay (Stantec 2010). Phase I of the TMDL corrective action focused on erosion control at former mine sites, methylmercury controls at reservoirs, and an assessment of Alamitos Creek (URS 2011). The Phase I work included reducing erosion from upland sources of fresh and spent ore, kiln dust and any soil exceeding 0.2 mg/kg mercury in sediments (URS 2011). Phase I of this effort also included mapping mercury concentration in sediments, identifying seeps, mapping slopes, vegetative cover, gullies and other erodible areas. Upland soil erosion control 41

49 focused on stabilizing mercury impacted sediments within 100 feet of a stream, river or surface water body. The Phase II long term remedy to stabilizing these areas within the riparian corridor began with recommended earthwork needed to remove high concentration sources of mercury (tailings), reducing slope length, enhancing natural terraces, catchments or other topographic features to reduce stormwater runoff velocity, gully and rill erosion (URS 2011). Relevant existing information The highest concentrations of total mercury in Soulajule Reservoir sediments are adjacent to the Cycle Mine, in the Eastern Arm of the reservoir (Figure 8). In addition, the Environmental Impact Report (EIR) for construction of Soulajule Reservoir suggests that cinnabar mine tailings were present in upland portions of the reservoir watershed (Madrone Associates 1976). The EIR concluded that the potential environmental impact on water quality from the mines was insignificant, because they were small, operated only for a year or two each, and because cinnabar is sparingly soluble unless exposed to concentrated acidity (less than ph 4). Despite the perceived lack of significance, the EIR suggested placing any associated tailings into the mines prior to construction of the reservoir. Inundation or flooding of the mines was not considered as a potential environmental impact; however, the EIR suggested that mine tailings be placed above the high water level of Soulajule Reservoir. Although the formation of methylmercury was generally understood in the 1970s, conditions that could contribute to methylation of mercury (e.g., mine tailings eroding into the reservoir, stratification of the water column, elevated organic carbon and anoxia in the upper sediment layer) were not specifically analyzed in the EIR (Madrone Associates 1976). Lastly, the Franciscan and Cycle Mines are small mercury mines with a short (1 2 year) history of operation and no documented use of processing equipment. The Franciscan Mine is located several hundred feet upland of Soulajule Reservoir, whereas the Cycle Mine is closer to the reservoir water level and thus may be a potential source of soil erosion to the reservoir. Additional information needs The following additional information is needed to assess the need for an erosion control plan in the Eastern Arm of Soulajule Reservoir compared with other applicable reservoir management approaches: Evidence of erodible, unvegetated, or disturbed soils with elevated total mercury concentrations in the vicinity of the Cycle and Franciscan mine sites. Surface soil analytical data for total mercury and grain size at and downslope of the Cycle and Franciscan mine sites and at undisturbed background sites. Analyzing grain size along with the mercury content of soil samples will provide information to support the appropriate selection of sediment control measures. For 42

50 example, if mercury is associated with a larger grain size such as gravel, sediment transport and soil erosion control BMPs will likely be an effective means of reducing mercury transport from upland sediments. Conversely, if mercury is primarily associated with smaller grain sizes (e.g., silts, clayey soils), sediment transport BMPs (e.g., fiber rolls, silt fences) will be less effective and the mercury-laden soils may need to be capped and stabilized with clean soils and /or vegetation to reduce mercury transport. Compatibility with reservoir management objectives and downstream beneficial uses Development (and eventual implementation) of an erosion control plan in the Eastern Arm of Soulajule Reservoir would not affect reservoir storage, downstream flows, water temperatures, or dissolved oxygen in the reservoir or Arroyo Sausal and thus would be compatible with all current water supply objectives. Permit requirements No permits would be required for surface soil sample collection at the upland mine site or the eventual implementation of BMPs. Landowner permission is needed to allow for reconnaissance and soil sampling at the mine sites and eventually for BMP installation. Conceptual engineering, infrastructure, and cost considerations There are no engineering and/or infrastructure requirements identified for site reconnaissance, surface soil sampling, or development of a soil erosion control plan. Requirements specific to BMP implementation will be determined as part of plan development. The cost of this effort would include an initial evaluation of potential upland mercury sources (see Pilot Study 6, Section 6.6) and subsequent development of a soil erosion control plan, if needed, based on the upland investigation. The anticipated cost for this effort is $32,000 for the initial evaluation. Development of a soil erosion control plan may cost an additional $50, ,000, depending on the area included in the plan and the complexity of the likely erosion control measures. The cost of developing an erosion control plan (if necessary) does not include implementation of the erosion control measures recommended in the plan Cap reservoir sediments in the Eastern Arm In-situ capping of mercury impacted sediments involves the placement of an impermeable liner between the sediments and the overlying water column of a lake or reservoir. With respect to mercury, this management approach has the potential to reduce the solubility, transport, methylation and bioaccumulation of mercury in the aquatic food web of Soulajule Reservoir. Capping is typically accomplished in 6 12 months. While reduction of mercury concentrations in the water column may not be easily observable in the short term, overall reduced mercury loading to the waterbody would be effective in the long term. Goals and capabilities 43

51 The goal of sediment capping is to reduce the methylation of mercury and reduce the transport of both total mercury and methylmercury into the water column. Limitations of this technology are tied to accurately delineating the extent of mercury impacted sediments. Other technical and logistical constraints include installing the cap without disturbing mercury impacted sediments, maintaining a durable, impermeable cap, avoiding or managing obstructions (e.g., stumps, etc.) and ability to limit disturbance by human activity (e.g., boating) or by natural processes (e.g. current, sedimentation) especially if the reservoir level fluctuates. Example applications In-situ sediment capping is a remediation technique that has been implemented effectively at approximately 15 EPA Superfund (CERCLA) sites throughout the United States to control the release of contaminants to the aquatic food web. Successful sediment capping also has been used, for example, in Emerald Bay and other areas around Lake Tahoe, California for aquatic weed and invasive species control (about 10 acres total). Relevant existing information Current data suggests that the highest concentrations of total mercury in Soulajule Reservoir sediments are adjacent to the Cycle Mine, and to a lesser degree, the Franciscan Mine (Figure 5). The rough extent of elevated concentrations is approximately 8 ac. These sediments appear to be largely non-mobile (Brown and Caldwell and 2013). The reservoir bathymetry in the Eastern Arm is generally low gradient, with typical water depths ranging ft depending on distance from the dam. Reservoir water levels typically fluctuate by approximately 9 ft on an annual basis (Figure 3), indicating that sediments containing elevated concentrations of mercury in the Eastern Arm remain submerged under normal reservoir conditions. Presumably, reservoir storage would need to drop to roughly 50% capacity or less before these sediments would be exposed (Figure 3). 44

52 Figure 22. Area of Soulajule Reservoir considered for capping or dredging due to elevated total mercury concentrations in sediments. Based on existing data, the current extent of sediments exhibiting 600 to >1,000 ng/g total mercury (orange polygon) is approximately 8 ac and ng/g total mercury (red polygon) is 27 ac, for a total of approximately 35 ac. Additional information needs Given the potentially high cost of capping, and the relatively large area of elevated sediments (Figure 22), additional characterization of the surficial extent of elevated mercury in the sediments of the Eastern Arm is needed. Mercury speciation/reactivity may provide additional useful information for better understanding the efficacy of capping, but total mercury is likely to be the most important factor. Supplemental sediment sampling is a key component of this management approach to more precisely define the extent of any proposed cap. Detailed bathymetry of the Eastern Arm also would be needed for sediment capping, including information regarding potential obstructions from stumps, abandoned mining equipment, or other underwater conditions that would affect capping. Based on the aforementioned information, appropriate capping materials and costs would be determined. Lastly, additional information regarding the potential for continuing upland erosion to deliver elevated mercury to Soulajule Reservoir is needed (see Study 6 Section 6.6). As a method to address internal loading of mercury to the reservoir, sediment capping would be largely ineffective if the historical mines and/or other sources are a continuing source (i.e., external loading source) of elevated mercury to the Eastern Arm. 45

53 Compatibility with reservoir management objectives and downstream aquatic beneficial uses In-situ capping of sediments in the Eastern Arm of Soulajule Reservoir would not affect reservoir storage, downstream flows, water temperatures, or dissolved oxygen in the reservoir or Arroyo Sausal and thus would be compatible with all current water supply objectives. In-situ capping may impact the Eastern Arm of the Reservoir temporarily due to higher turbidity during capping activities. Permit requirements We anticipate that in-situ capping would require a California Department of Fish and Wildlife (CDFW) Lake or Streambed Alteration permit (Fish and Game Code Section 1602) and may also require consultation with the U.S. Army Corps of Engineers (USACE) under Clean Water Act (CWA) Section 404 and with the State Water Resources Control Board under CWA Section 401. USACE may consult with the U.S. Fish and Wildlife Service (USFWS) and National Marine Fisheries Service (NMFS) on permit applications depending on species that may be impacted; permits may include conditions to avoid, minimize and/or mitigate impacts to these species. The RWQCB and the Department of Toxic Substances Control may also require permits for dredging, as related to temporary water quality impacts and the dewatering and disposal components of the project. Conceptual engineering, infrastructure, and cost considerations Conceptual engineering of the sediment cap, extent required, and installation methods are required. This process would including better determining the areas requiring capping, investigating existing bottom conditions, and coordinating with diving contractors regarding access requirements and likely methods and cost. Based on initial conversations with an experienced installation contractor (Underwater Resources, San Francisco, CA), we estimate that the cost of materials and installation to be approximately $300,000 to $600,000 per acre required, not including contingency or engineering/permitting. This cost is based on recent work conducted by the contractor in Lake Tahoe. Assuming a 40% contingency allowance and 25% for engineering design and permitting, the total capital cost could be $0.55M 1.1M per acre, which would result in a total project cost of approximately $4.4M 8.8M for 8 acres of capping Dredge and dispose of sediments with elevated mercury from the Eastern Arm Dredging is the removal of accumulated lake sediments from lake bottoms with the goal of improving water quality, recreation, navigation or other uses (IEPA and NIPC 1998). With respect to Soulajule Reservoir, dredging would remove mercury impacted sediments from the Eastern Arm and transfer them to an above-ground processing facility for dewatering, testing, transport and off-site disposal. Implementation would require at least 12 months. Reduction of mercury concentrations in the reservoir would be easily observable in the short term and permanent as long as other mercury sources are eliminated. 46

54 Goals and capabilities Assuming that all other mercury source areas are controlled, the goal of sediment dredging and disposal is to eliminate mercury methylation by removing the primary source of mercury to the waterbody. In some cases, dredging can improve water quality by deepening a lake or other water body enough to create thermal stratification and limit nutrient movement from the deeper areas to the upper waters. The entire lake bottom can be dredged or dredging can be conducted in certain zones where it may be most beneficial (e.g., areas with the thickest layer of contaminated sediments). There are two primary methods used for lake dredging: mechanical dredging and hydraulic dredging. Hydraulic dredging is the preferred method for dredging lake sediments because it does not require drawing down lake levels, is faster than mechanical dredging, creates less turbidity and can effectively remove loose, watery sediments. Thus, dredging of sediments in the Eastern Arm of Soulajule Reservoir would most likely be accomplished by a hydraulic dredge. Hydraulic dredging also requires the design and construction of a settling basin to which the slurry (sediment/water mix) is piped and sediments settle out from the water column. In some cases the sediment slurry can be decanted prior to being transported to the settling basin, which significantly decreases the amount of land required for the basin (CDM 2011). After settling (and treatment, in some cases), the water is pumped back into the lake and the sediments are left in the basin to dry. Ultimately the sediments are utilized or disposed of in a variety of ways, including agricultural soil augmentation, fill for planned projects or, if contaminated, hauled to a landfill. Example applications Sediment removal and disposal by dredging is a common remediation technique that has been implemented effectively at more than 100 EPA Superfund (CERCLA) sites and other sites. For example, Caltrans removed, dewatered and disposed of sediments in support of constructing the eastern span of the Bay Bridge. Relevant existing information Current data suggests that the highest concentrations of total mercury in Soulajule Reservoir sediments are adjacent to the Cycle Mine, and to a lesser degree, the Franciscan Mine (Figure 8). The rough extent of elevated concentrations is approximately 8 acres (Figure 22). The reservoir bathymetry in the Eastern Arm is generally low gradient, with typical water depths ranging ft depending on distance from the dam. Reservoir water levels typically fluctuate by approximately 9 ft on an annual basis (Figure 3), indicating that sediments containing elevated concentrations of mercury in the Eastern Arm remain submerged under normal reservoir conditions. Presumably, reservoir storage would need to drop to roughly 50% capacity or less before these sediments would be exposed (Figure 3). Additionally, upland side slopes may be locally steep, which can be an additional challenge for dredging and for installing silt curtains required to control water column turbidity. 47

55 Additional information needs Similar to in situ capping, dredging design would rely heavily on characterization of total mercury in impacted sediments. However, while additional information needs for capping are limited to the horizontal extent of elevated mercury in sediment in the Eastern Arm, dredging also requires information regarding the vertical extent of mercury in sediment. Supplemental sediment sampling is a key component of this alternative to define precisely the extent of the proposed dredging and removal. Mercury speciation may have some benefit in defining the limits of excavation and removal, but total mercury is likely to be the most important factor. Ultimately, dredging would require more complete testing of the sediments (e.g., all metals, organic contaminants) to determine proper re-use or disposal options. Lastly, additional information regarding the potential for continuing upland erosion to deliver elevated mercury to Soulajule Reservoir is needed (see Study 6 Section 6.6). Dredging would be largely ineffective if the historical mines are a continuing source of elevated mercury to the Eastern Arm. Compatibility with reservoir management objectives and downstream aquatic beneficial uses Properly executed, dredging, transporting and removing mercury impacted sediments in the Eastern Arm of Soulajule Reservoir would not adversely affect reservoir storage, downstream flows, or water temperatures or dissolved oxygen in the reservoir or Arroyo Sausal and thus would be compatible with all current water supply objectives. Dredging may impact the Reservoir s Eastern Arm temporarily with higher turbidity during dredging activities. Depending on the depth of sediments to be removed from the Eastern Arm, reservoir storage may be slightly increased as a result of dredging. Permit requirements Typically, dredging requires a California Department of Fish and Wildlife (CDFW) Lake or Streambed Alteration permit (Fish and Game Code Section 1602) and may also require consultation with the U.S. Army Corps of Engineers (USACE) under Clean Water Act (CWA) Section 404 and with the State Water Resources Control Board under CWA Section 401. USACE may consult with the U.S. Fish and Wildlife Service (USFWS) and National Marine Fisheries Service (NMFS) on permit applications depending on species that may be impacted; permits may include conditions to avoid, minimize and/or mitigate impacts to these species. The RWQCB and the Department of Toxic Substances Control may also require permits for dredging, as related to temporary water quality impacts and the dewatering and disposal components of the project. Conceptual engineering, infrastructure, and cost considerations Dredging implementation requires a suite of complex technical and logistical considerations. The dredge must be safely transported to and deployed within the Eastern Arm. Turbidity and other required water quality protection measures must be implemented before, during and after dredging. After dredging the sediment slurry 48

56 must be transported from the dredge to the shore (a distance that may exceed 0.5 miles). A dewatering facility, most likely located near the dam, must be constructed to contain and separate water from sediments prior to transport. All water must be contained until tested. Sediments must be dewatered for transport and disposal. Water extracted during dewatering also likely would require special treatment before returning it to the reservoir. Impacted sediments must be loaded onto trucks and transported off-site at an approved landfill. Cost considerations include the following: Site selection for disposal facility or beneficial re-use Final design Permitting Sediment quality characterization (i.e., beyond total mercury) Dredging (including mobilization/demobilization, turbidity control) Operation and maintenance Monitoring at disposal facility or re-use site Based on existing information, we estimate that the cost of this work to be in the range of $375,000 per acre for dredging and disposal. Including a 40% contingency and 25% for design engineering and permitting, the total cost could be approximately $660,000 per acre, or roughly $5.3M assuming 8 acres of dredging required. Manage water chemistry to reduce methylation The intent of the below method is to manage water chemistry in Soulajule Reservoir to prevent anaerobic/anoxic conditions that lead to mercury methylation Hypolimnetic oxygenation/aeration A hypolimnetic oxygenation system (HOS) could be used to prevent the occurrence of anaerobic conditions in Soulajule Reservoir and make the environment unsuitable for sulfate reducing bacteria that also produce methylmercury. As observed for Lake Hodges (Section ) and Indian Creek Reservoir (Section ), chlorophyll-a, water clarity, and large seasonal blue-green algae blooms would be expected to improve following HOS implementation because nutrients fueling the blooms would no longer be recycled from anoxic reservoir sediments. Water enriched with dissolved oxygen using pure oxygen gas would be injected into the deepest area of the reservoir near the dam and Eastern Arm, and possibly the Western Arm. Design and construction of the HOS and supporting equipment could take approximately 1 2 years. Oxygen addition would take place yearly from late spring shortly after stratification until after overturn in late fall/early winter. 49

57 Goals and capabilities The main goal of a HOS is to oxygenate the hypolimnion and adjacent sediments during summer months to prevent anaerobic conditions that result in mercury methylation. The systems are designed and operated to maintain positive dissolved oxygen in the water column and at sediment/water interface, which will reduce methylation and is also a benefit to general water quality and fish populations. The HOS would be sized based on oxygen demands calculated from historical and new dissolved oxygen profiles and from sediment oxygen demands (SODs) measured through chamber incubation of reservoir sediment samples. Example applications Although we do not know of any HOS that has been implemented specifically for mercury methylation control, numerous successful applications of hypolimnetic oxygenation systems are available for preventing anoxia and improving bottom water quality (Section 2.4.1). Relevant existing information The District s ongoing water quality monitoring and sampling and field measurements carried out in 2012 demonstrated the occurrence of an anaerobic water column and sediments (Brown and Caldwell and 2013). For example, in August 2012, the hypolimnion was anaerobic and sulfide levels exceeded 0.3 mg/l. In combination with reservoir-capacity (hypsographic) curves, these data can be used to estimate the oxygen mass required for HOS design. Additional information needs Ultimately, a preliminary engineering design effort is required to better define the project and develop estimated capital and operating costs for an HOS. As a first step, Pilot Study 5 will inform certain aspects of HOS design, namely those that involve system size, extent, and in-reservoir location (Section 6.5). Compatibility with reservoir management objectives and downstream aquatic beneficial uses A properly designed HOS could minimize mercury methylation in sediments by maintaining a positive dissolved oxygen concentration in the hypolimnion. The installation of an HOS is not expected to significantly impact reservoir storage, although a minimum storage may be necessary during the summer to properly operate the system. The HOS would improve dissolved oxygen concentrations in the reservoir and Arroyo Sausal, but would not affect downstream flows or water temperatures. Permit requirements The installation of an HOS would likely require CEQA compliance and potential California Department of Water Resources Division of Safety of Dams clearance, depending upon final facilities configuration. 50

58 Conceptual engineering, infrastructure requirements An HOS is an engineered system, and numerous engineering investigations and cost estimates will be required as part of preliminary and final design. As a first step, Pilot Study 5 will inform certain aspects of HOS design, namely those that involve system size, extent, and in-reservoir location (Section 6.5). Decrease levels of blue-green algae Because algae provide organic carbon to fuel methylation and serve to concentrate methylmercury in the aquatic food web, the degree of primary productivity or trophic status of a lake or reservoir may affect the degree of methylmercury bioaccumulation in higher trophic levels. Blue-green algae, along with other bacteria (e.g., actinomycetes) and several types of green and brown algae, also produce intracellular by-products that are associated with earthy and musty tastes and odors, including geosmin (trans-1, 10- dimethyl-trans-9-decalol) and MIB (2-methylisoborneol). The presence of these compounds in drinking water is associated with taste and odor complaints at concentrations as low as 5 to 10 parts per trillion. During intense algae blooms, relatively high concentrations of these compounds are released into the water. Minimizing the production of taste and odor compounds often requires control of algae blooms in the affected waterbody since removal alternatives at the water treatment plant can be very costly. Further, some blue-green algae, such as Anabaena flos-aquae and Microcystis aeruginosa can produce toxins that are harmful to fish, mammals and humans. In contrast, diatoms and green algae are typically the more desirable species for lake and reservoir primary productivity because they are a preferred food source for zooplankton and fish. With respect to mercury control, the effects of reducing bluegreen algae (and, concomitantly, increasing diatoms and green algae) on bioaccumulation in the food web of lakes and reservoirs are currently untested, particularly with respect to algal bloom dilution (Section ) Vigorous epilimnetic mixing Vigorous epilimnetic mixing (VEM) is a physical management method that focuses on the surface waters (epilimnion) of a lake or reservoir. VEM is intended to reduce algal scums and it is typically situated in relatively shallow areas of the reservoir where the photic zone makes up a significant fraction of the water column and seasonal algal blooms tend to occur. VEM installation is typically a long-term strategy due to the capital investment required, but it can be coupled with other long-term management approaches to improve water quality, such as reduction in external nutrient loading, such that its use can be curtailed over time. Goals and capabilities The goal of VEM is to disrupt the successful growth of blue-green algae by physically mixing the upper layer of the water column, such that blue-greens cannot out-compete 51

59 diatoms or other algal species (e.g., cryptomonads, green algae) and form large seasonal surface scums. In general, blue-green algae are successful in warm stratified lakes and reservoirs because they can regulate their buoyancy, moving from high to optimum light levels during the day and migrating into deeper waters at night where nutrients are more abundant. Buoyancy regulation for blue-green algae, whose largest colonies are the size of a small pea, cannot be effective when the water is mixing vertically faster than they can rise or sink, at a rough maximum of 0.1 cm/s. In contrast, diatoms, which grow faster and are heavier than blue-green algae, thrive in waters that are mixing sufficiently to keep them suspended in the photic zone. During late spring/early summer, as the water column of most temperate lakes and reservoirs becomes thermally stratified, the heavier diatoms sink out and blue-green algae can prosper. Artificial mixing of surface waters using VEM shifts the balance away from blue-green algae dominance. VEM is accomplished by introducing a column of bubbles at depth via an air diffuser placed approximately 1 ft above the bottom sediments. The rising airbubbles cause water in the bottom waters to rise, pulling water upwards and toward the surface and creating a mixing cell around the bubble column. Although described as such, this type of mixing is only vigorous from the viewpoint of the algae; upward water column velocities of 0.1 cm/s are barely noticeable by a recreational lake user. While VEM is suitable to reduce nuisance scums of blue-green algae (e.g., Aphanizomenon, Anabaena) it may not reduce algae overall or even the percent of nonscumming (single filament) blue-greens (e.g., Cylindrospermopsis). Example applications Cherry Creek Reservoir is a 13,960 ac-ft flood-control reservoir near Denver, Colorado, that is owned and operated by the US Army Corps of Engineers. The reservoir has experienced seasonal nuisance algal blooms and was not meeting the chlorophyll-a water quality standard (15-ug/l) from 1996 through In 2008, a destratification system was installed in the deepest portion of the reservoir near the dam to strongly mix the water column and oxidize the deep bottom sediments to reduce the release of nutrients from the sediments into the water column (Ruzzo 2008). Although not referred to as VEM, a primary objective of the destratification system was to vertically mix algae in surface waters to reduce production of blue-green algae, which is consistent with the VEM approach. Since installation of the destratification system, Cherry Creek Reservoir has exhibited a shift in the algal species composition whereby blue-green algae have decreased from 41 76% of algal density ( ) to 1 8% of algal density ( ) (Leonard Rice Engineers, Inc. et al. 2012). Cryptomonads, diatoms, and green algae have become the numerically dominant algal types, accounting for the largest chlorophyll-a levels observed in the reservoir. However, as a consequence of the efficient mixing, the relatively constant supply of soluble nutrients to the algal community allows all types of 52

60 algae to maximize their productivity. As a result, the Cherry Creek Reservoir exhibited extremely high chlorophyll-a levels (19 30 ug/l) during June to September 2012 (Leonard Rice Engineers, Inc. et al. 2012). Relevant existing information Algae collected from Soulajule Reservoir surface waters during August 2013 included 32 species of algae in the following 7 groups: Bacillariophyta (diatoms) Chlorophyta (green algae) Cryptophyta Cyanobacteria (blue-green algae) Euglenophyta Haptophyta Pyrrhophyta (dinoflagellates) Several miscellaneous species of algae were also identified (Brown and Caldwell and 2013, Appendix C). The highest cell counts were observed in the Eastern Arm at site S-WQ1 and S-WQ2 (Figure 23) corresponding to dense blooms of algae at these locations. At all sites, bluegreen algae were the dominant algal group in the sample accounting for anywhere from approximately 75 to 99% of total cell numbers (Figure 23). At all reservoir sites the most abundant species was the filamentous blue-green algae Aphanizomenon flos-aquae, while at the reservoir discharge and in Arroyo Sausal, the most abundant species was the filamentous blue-green algae Pseudanabaena sp.. Additional information needs The following additional information is needed to rank and prioritize VEM implementation in Soulajule Reservoir compared with other applicable reservoir management approaches: Frequency of dense algal blooms in the shallow Eastern Arm of the reservoir as compared with other locations in the reservoir. Compatibility with reservoir management objectives and downstream beneficial uses Use of VEM to reduce blue-green algae dominance in the Eastern Arm of Soulajule Reservoir would not affect reservoir storage or downstream flows and thus would be compatible with current water supply objectives 1 and 2 (Section 1.1). Seasonal VEM application in the Eastern Arm would likely destratify the entire water column, mixing cooler bottom waters with warmer surface waters and eliminating any potential thermal refugia for fish in this location. However, existing data (2012) suggest that this potential refugia is likely to be a short-lived condition in the late spring/early summer, where the thermocline progressively descends all the way to the bottom sediments by mid-summer and the relatively shallow water column becomes fully mixed (Brown and 53

61 Caldwell and 2013). Further, the extent of this affect would be limited to the Eastern Arm and would not affect water temperatures or dissolved oxygen elsewhere in the reservoir or in downstream Arroyo Sausal. Therefore, VEM application would be compatible with current water supply objective 3 (Section 1.1). Figure 23. Cell counts and identified algal groups by site in surface water samples in Soulajule Reservoir (S-WQ1 through S-WQ4, and S-WQ6), at the reservoir discharge (S-WQ5) and Arroyo Sausal (AC-WQ1) during August Note the logarithmic scale on the y-axis. Percent of cell count as blue-green algae for each sample is shown in parentheses. Source: Brown and Caldwell and (2013). Permit requirements While agency permits would not be required to install VEM within the reservoir footprint, landowner agreements may be needed to allow periodic access to shorelines along the Eastern Arm for equipment installation, staging and long-term operation and maintenance of the VEM system. Conceptual engineering, infrastructure, and cost considerations Installation of a VEM system in the shallow Eastern Arm would require the following: Multiple 8-inch diameter diffusers placed along the channel thalweg, ranging approximately 1,000 2,500 linear feet (LF), at a total combined length of 8,500 ft (see Figure 24) 54

62 Assuming horizontal extent of aeration plume is a maximum of 15 times the vertical water depth: - At water depths < 25 ft and reservoir channel width 350 ft, two parallel diffusers required - At water depths > 25 ft and reservoir channel width 450 ft, one diffuser required Onshore low-pressure air compressors with control valves for diffusers at different depths Power source Vehicle access for equipment installation, staging and long-term operation and maintenance Based on equipment and installation costs for a proposed VEM system of approximately the same size at Lake Hodges, San Diego, California, VEM implementation in the Eastern Arm of Soulajule Reservoir would range $500,000 to $1,500, ft water depth 350 ft wide channel ~1,500 LF ~2,200 LF ~1,300 LF ft water depth 350 ft wide channel ft water depth 450 ft wide channel Figure 24. Conceptual placement of VEM system in the shallow Eastern Arm of Soulajule Reservoir. Two diffuser lines are required in the channels < 25 ft deep, while one line is required in the channel > 25 ft deep. 55

63 Manage fisheries to reduce methylmercury in fish tissue Existing data describing sediment total mercury and fish tissue mercury in reservoirs throughout California illustrate the limited potential for improving conditions based on mercury source reduction alone and point to the need for in situ methylation and bioaccumulation controls (SWRCB 2013). Along these lines, the California Statewide Mercury Control Program for Reservoirs includes food web management/biomanipulation among the set of potential control options, with a focus on changing fish growth rates through increasing productivity, intensive fishing, and/or stocking (SWRCB 2013). As applicable to Soulajule Reservoir, the stocking approach is discussed further below with respect to both direct and indirect controls on bioaccumulation Stocking of sport fish un-impacted by mercury Stocking of sport fish is a biomanipulation technique that typically aims to increase the population of piscivorous fish in a waterbody in order to affect desired change in the food web. In the case of reservoir mercury management, the waterbody would be stocked with sport fish that do not contain elevated levels of mercury. As an isolated management approach, stocking activities would need to occur on a long-term, seasonal basis to maintain the desired effect, since methylmercury tissue concentrations in stocked fish presumably would increase over time as a result of consuming mercury in their prey. However, stocking can be coupled with other long-term management approaches to reduce methylmercury production and bioaccumulation in the food web, such that its use can be curtailed over time. Goals and capabilities With respect to reservoir mercury management, the goal of sport fish stocking is to dilute the average body burden of mercury in the broader sport fish population by adding mercury-free individuals. While mercury levels in individual sport fish that have consistently resided in Soulajule Reservoir would remain unchanged, this would be a direct effect on average mercury concentrations in the sport fish population, where the TMDL numeric target for average methylmercury concentration in fish consumed by piscivorous birds is 0.05 mg/kg fish (wet weight), measured in whole fish 5 15 cm in length, and 0.1 mg/kg (wet weight), measured in whole fish cm in length (Section 2.2). As a classic top-down biomanipulation activity, sport fish stocking for mercury control would also be expected to affect populations of organisms occupying lower trophic levels, according to the ecological phenomenon of trophic cascade. For example, the addition or removal of predators could result in reciprocal changes in abundance, biomass, or productivity of organisms across multiple links in the food web (Cooke et al. 2005). Assuming that predation is the primary population control mechanism, a simple model of trophic cascading effects in Soulajule Reservoir would indicate that increases in sport fish abundance would increase predation of smaller fishes and insects, reducing 56

64 their populations accordingly. The resulting decrease in planktivory from smaller fishes and insects would then increase zooplankton populations and increase grazing pressure on algal species, leading to an overall decrease in algal populations. While the aforementioned trophic level effects would not be directly related to mercury fish tissue concentrations, stocking of sport fish may indirectly affect mercury tissue concentrations, in both sport fish and prey fish. This is because the increase in zooplankton populations coupled with a decrease in competition for food resources among prey fish may allow for increased growth rates within the prey fish populations themselves. This could result in somatic growth dilution of mercury tissue concentrations in prey fishes, where the latter occurs due to biomass growth rates that are higher than the rate of methylmercury uptake (Section ). The degree to which somatic growth dilution would occur depends upon the magnitude of growth rate changes in prey fish, as a response to increases in the sport fish population, as well as the rate of methylmercury uptake. Further, the reduction in algal populations, resulting from piscivorous sport fish stocking, may indirectly reduce mercury methylation rates in Soulajule Reservoir. Heterotrophic sulfate-reducing bacteria responsible for hypolimnetic mercury methylation require an organic carbon source to fuel respiration (Section ). Algae that die and settle to the bottom of the reservoir provide a source of organic carbon, such that reduced algal populations may reduce mercury methylation during stratification periods. Ultimately, this potential effect depends on whether methylation in Soulajule Reservoir is carbon limited, and the path of mercury bioaccumulation from zooplankton to predator fish. Example applications Our general review of the literature regarding control of mercury methylation and bioaccumulation in lakes and reservoirs did not identify management case studies related specifically to sport fish stocking as a means to reduce fish tissue mercury concentrations. However, a number of field and laboratory studies support the occurrence of somatic growth dilution through measured decreases in mercury concentrations with increasing tissue growth (Foe and Louie 2014). Classic top-down biomanipulation has also been used in multiple temperate lakes to reduce algal populations through the addition of piscivorous fish (Cooke et al. 2005), and by inference, could reduce average fish tissue mercury concentrations in piscivorous fish through mass biodilution as well as in prey fish through somatic growth dilution. However, the food web effects on mercury concentrations in biota due to top-down biomanipulation are currently untested. Relevant existing information Algal species collected in Soulajule Reservoir in 2012 are described in Section Small prey fish (5 15 cm FL) collected during both August and December 2012 were exclusively juvenile largemouth bass. Larger prey fish (15 35 cm FL) included black 57

65 crappie and bluegill. Although fish surveys have not been conducted in Soulajule Reservoir, the species observed during the 2012 surveys are similar to those observed at several other District reservoirs (Figure 25). Figure 25. District reservoir fisheries composition at individual lakes. Data from

66 Additional information needs The following additional information is needed to rank and prioritize stocking of sport fish in Soulajule Reservoir compared with other applicable reservoir management approaches: community survey for relative abundance of sport fish required stocking rate (i.e., number of fish un-impacted by mercury) for meeting TMDL numeric targets (0.1 mg/kg wet weight) With respect to second bullet above, assuming a simple ratio between the existing Soulajule average fish tissue methylmercury concentration of 0.54 mg/kg (wet weight) for piscivorous fish (15 35 cm FL) and the Walker Creek TMDL numeric target of 0.1 mg/kg (wet weight), the sport fish population would need to be increased by roughly 5 times. An estimate of the current abundance of fish in Soulajule Reservoir would help to determine whether this represents an unreasonably large number of fish to be stocked. However, because determining the actual population size of fishes within a reservoir requires an intensive sampling effort, the recommended approach is the following: 1. identify the relative abundance of fishes within the reservoir via community survey 2. identify the target fish for stocking 3. adaptively manage stocking levels over time, based on mercury concentration in fish tissue during subsequent surveys Based on existing information, the target fish for stocking is likely to be largemouth bass; however, this assumption should be tested through additional investigation (see Section 6.3 Pilot Study 3). Further, the determination of potential and indirect cascading trophic effects of increased sport fish population on mercury cycling and methylation requires additional information: current composition and distribution of prey fish mercury bioaccumulation pathway from zooplankton to piscivorous fishes stomach content assessment of fishes captured during survey Compatibility with reservoir management objectives and downstream beneficial uses Stocking of sport fish to manage fish tissue mercury concentrations in Soulajule Reservoir would not affect reservoir storage or downstream flows and thus would be compatible with current water supply objectives 1 and 2 (Section 1.1). Designated downstream beneficial uses include cold freshwater habitat, preservation of rare and endangered species, fish spawning habitat, and wildlife habitat. While stocking would not affect water temperature or dissolved oxygen in the reservoir or in downstream Arroyo Sausal (water supply objective 3, Section 1.1), introduced sport fish species could be washed downstream and could impact habitat beneficial uses by competing with or preying upon native aquatic species, including central California coast Coho salmon (Oncorhynchus kisutch) and steelhead trout (Oncorhynchus mykiss). 59

67 Additionally, while potential stocking species such as largemouth bass can disturb bottom sediments during spring spawning periods, typically their activity is limited to shallow, littoral sediments. Given the relatively small area of disturbance, they are unlikely to significantly increase methylmercury release from reservoir sediments. Permit requirements The California Fish and Game Code authorizes CDFW to issue permits for the stocking of fish in private and public waters throughout the state. Under CDFW s regulations, a stocking permit must be issued once the department has determined that the proposed stocking would be consistent with the department s fisheries management plans and would avoid the introduction of diseased or parasitized fish into California waters. The permit must provide the following information: a list of species currently in the reservoir; species, number, and size of fish to be stocked; and, identification of the registered aquaculturist from whom the fish will be obtained. We assume that stocking practices would be consistent with CDFW stocking program guidelines, policies, and requirements (e.g., EIR/). Conceptual infrastructure and cost considerations Stocking of sport fish would require a local or regional source of fish un-impacted by mercury (e.g., hatchery) and sufficient vehicle access during early spring through late fall to allow for placement of fish directly into the reservoir from a stocking truck. Based on the price of $10 per fish for cm (10 12 in) fork length (FL) largemouth bass (Professional Aquaculture Services [PAS], the annual stocking cost for providing 2,000 2,500 sport fish would be approximately $20,000 $25,000 (not including transportation). The appropriate number of fish for stocking would be determined based on the results of a fish community composition study (see Pilot Study 3 Section 6.3) Stocking of prey fish un-impacted by mercury Stocking of prey fish is another common biomanipulation technique that aims to increase the population of planktivorous fish in a waterbody in order to affect desired change in the food web. In the case of reservoir mercury management, the waterbody would be stocked with prey fish that do not contain elevated levels of mercury. As an isolated management approach, stocking activities would need to occur on a long-term, seasonal basis to maintain the desired effect. However, as with the stocking of sport fish, this approach can be coupled with other long-term management approaches to reduce methylmercury production and bioaccumulation in the food web, such that its use can be curtailed over time. 60

68 Goals and capabilities As with the stocking of sport fish (Section ), the goal of this biomanipulation technique with respect to reservoir management is to dilute the average body burden of the total prey fish population by directly adding mercury-free individuals. While mercury levels in individual prey fish that have consistently resided in Soulajule Reservoir would remain unchanged, this would be a direct effect on average mercury concentrations in the prey fish population, where the TMDL numeric target for average methylmercury concentration in fish consumed by piscivorous birds is 0.05 mg/kg fish (wet weight), measured in whole fish 5 15 cm in length, and 0.1 mg/kg (wet weight), measured in whole fish cm in length (Section 2.2). For prey fish stocking, trophic cascade effects would be expected to occur somewhat differently than with sport fish stocking. Assuming that predation is the primary population control mechanism in the waterbody of interest, a simple model would presume that increases in prey fish would increase predation of zooplankton and thus decrease their populations accordingly. The resulting decrease in grazing pressure on algal species would lead to increased algal populations. While the aforementioned trophic level effects would not be directly related to mercury fish tissue concentrations, stocking of prey fish may indirectly affect mercury tissue concentrations, in both sport fish and prey fish. An increase is prey fish and algal populations may increase growth rates of both sport fish and zooplankton. Somatic growth dilution of methylmercury may occur within these populations if biomass is gained at a higher rate relative to methylmercury uptake (see also Section ). However, stocking of prey fish may have the opposite effect on overall rates of mercury methylation in Soulajule Reservoir, with increased algal populations increasing available carbon for mercury methylation. Again, this potential effect depends on whether methylation in Soulajule Reservoir is carbon limited. Example applications Prey fish stocking, as a way to reduce mercury levels in sport fish, was studied recently in College Lake, a small (62-ac), shallow (20 ft maximum depth) lake on the Colorado State University Campus (Lepak et al. 2012). Based on the dominant sport fish population of northern pike (1,000 fish), approximately 9,000 rainbow trout with low mercury concentrations were stocked in March 2009 (Lepak et al. 2012). Approximately 50 days later, the study found that northern pike total mercury concentrations were reduced by up to 50% (20% on average), and average individual biomass increased by about 15%. However, northern pike mercury concentrations and growth rates rebounded to pre-experiment levels 1 year after stocking ceased. Relevant existing information Relevant information for Soulajule Reservoir is discussed in Section

69 Additional information needs The following additional information is needed to rank and prioritize stocking of prey fish in Soulajule Reservoir compared with other applicable reservoir management approaches: community survey for relative abundance of prey fish required stocking rate (i.e., number of fish un-impacted by mercury) for meeting TMDL numeric targets (0.05 mg/kg wet weight) With respect to second bullet above, assuming a simple ratio between the existing Soulajule average fish tissue methylmercury concentration of 0.22 mg/kg (wet weight) for prey fish (5 15 cm FL) and the Walker Creek TMDL numeric target of 0.05 mg/kg (wet weight), the prey fish population would need to be increased by roughly 4 times. An estimate of the current abundance of fish in Soulajule Reservoir would help to determine whether this represents an unreasonably large number of fish to be stocked. However, because determining the actual population size of fishes within a reservoir requires an intensive sampling effort, the recommended approach is the following: 1. identify the relative abundance of fishes within the reservoir via community survey 2. identify the target fish for stocking 3. adaptively manage stocking levels over time, based on mercury concentration in fish tissue during subsequent surveys Further, the determination of potential and indirect cascading trophic effects of increased prey fish population on mercury cycling and methylation requires additional information relative abundance of sport fish mercury bioaccumulation pathway from zooplankton to piscivorous fishes stomach content assessment of fishes captured during survey Compatibility with reservoir management objectives and downstream beneficial uses As with sport fish stocking, the stocking of prey fish to manage fish tissue mercury concentrations would not affect reservoir storage or downstream flows and thus would be compatible with current water supply objectives 1 and 2 (Section 1.1). While prey fish stocking would not affect water temperature or dissolved oxygen in the reservoir or in downstream Arroyo Sausal (water supply objective 3, Section 1.1), introduced prey fish species could be washed downstream and could impact habitat beneficial uses by competing with or preying upon native aquatic species. Additionally, likely prey stocking species such as bluegill are planktivorous fish that reside in the littoral zone and are not likely to disturb bottom sediments, thereby increasing the potential for methylmercury release from reservoir sediments. 62

70 Permit requirements Permit requirements for prey fish stocking are the same as those for sport fish stocking. Conceptual infrastructure and cost considerations Infrastructure requirements for prey fish stocking are the same as those for sport fish stocking, but would also include distributing the smaller, less mobile fish throughout the reservoir via boat. Based on the price of $2.50 per fish for 5 10 cm (2 4 inches) FL largemouth bass (Professional Aquaculture Services [PAS], the annual stocking cost for providing 3,000 5,000 prey fish would be approximately $7,500 12,500 (not including transportation). An alternative option may be to stock with a less expensive prey fish species such as blue gill. Based on the price of $1.50 per fish for 5 10 cm (2 4 in) FL bluegill (Professional Aquaculture Services [PAS], the annual stocking cost for 3,000 5,000 prey fish would be approximately $4,500 7,500 (not including transportation). The appropriate number of fish for stocking would be determined based on the results of a fish community composition study (see Pilot Study 3 Section 6.3). 3.3 Summary of Conceptual-level Cost Estimates for Management Methods Applicable to Soulajule Reservoir Conceptual-level cost estimates for each of the seven applicable (or potentially applicable) management methods for Soulajule Reservoir are presented in Table 5. The cost estimates were used to help rank and prioritize the methods for further implementation, including identification of appropriate pilot studies (Section 5). 63

71 Table 5. Conceptual-level cost estimates for in-lake and watershed management methods applicable to Soulajule Reservoir. Management Method Conceptual-level Cost Estimate Reduce Sediment Mercury Loads Erosion control for upland soils in Eastern Arm $50 70K 1 Cap reservoir sediments in Eastern Arm $ M (8 ac) 2,3 Dredge and dispose of sediments from Eastern Arm $5.3M (8 ac) 3,4 Manage Water Chemistry Hypolimnetic oxygenation system (HOS) $1.5 3M Decrease Levels of Blue-Green Algae Vigorous epilimnetic mixing (VEM) $0.5M $1.5M Manage Fisheries Stocking of sport fish un-impacted by mercury $20 25K (annual) Stocking of prey fish un-impacted by mercury $ K (annual) 1 Cost is for an evaluation of the potential for mercury loading from upland soils in the Eastern Arm. Cost does not include development of erosion control plan (estimated additional $50-100K) or implementation of plan recommendations. 2 Cost of capping per acre is estimated to be $0.55M $1.1M. The 8-ac estimated cost applies to the area of sediments exhibiting 600 to > 1,000 ng/g total mercury. The estimated cost of capping 35 ac applies to the area of sediments exhibiting 300 to > 1,000 ng/g total mercury = $ M. 3 Due to the unknown extent of sediments requiring capping or dredging, this estimate assumes a cost range per acre, and includes a 40% contingency allowance and 25% allowance for engineering design and permitting. 4 Estimated cost of dredging 8 ac applies to the area of sediments exhibiting 600 to > 1,000 ng/g total mercury. Estimated cost of dredging 35 ac applies to the area of sediments exhibiting 300 to > 1,000 ng/g total mercury = $23.2M. 5 District evaluation of the feasibility of increased use of Soulajule Reservoir for drinking water supply is not evaluated as part of this Study Plan. 64

72 4 WATER LEVEL FLUCTUATION As a lake/reservoir management approach, water level fluctuation has been applied to control fisheries and aquatic vegetation (e.g., invasive macrophytes such as water milfoil), as well as algae. For example, fluctuating water surface elevations during the spring can disrupt bass spawning in the shallow (e.g., < 1.5 ft water depth) margins of a lake/reservoir, reducing overall bass populations. If timed properly, seasonally fluctuating water levels can also reduce recruitment and maintenance of vegetated areas along lake/reservoir margins, and could reduce the volume of water available for supporting large algal blooms. We are unaware of applications of water level fluctuation to manage mercury methylation and bioaccumulation in reservoirs. However, as the District is currently considering more frequent use of Soulajule Reservoir for drinking water supply, this Study Plan considers the potential for effects related to changing magnitude, frequency, and duration of reservoir volume and water level fluctuations on mercury methylation and bioaccumulation. Because it represents a potential change in reservoir conditions that may affect mercury methylation and bioaccumulation, rather than a targeted mercury management approach, water level fluctuation is addressed below, separate from the other management methods. Currently, Soulajule Reservoir storage fluctuates on a seasonal basis between approximately 8,000 and 10,500 ac-ft (roughly 25%) and 9 ft of depth (elevation between 332 ft and 323 ft) (Figure 4) due to regulated flow releases (Table 1) and evaporation loss. The District currently anticipates increasing volume withdrawals by 2,000 3,000 ac-ft on an annual basis, which would result in depth fluctuations ranging ft (elevation between 314 ft and 309 ft) Drawdown would typically begin May 1 and continue for approximately three months. Withdrawals earlier in the season (e.g., January) could occur, if downstream storage capacity is available. Water would be transferred from the area immediately downstream of the Soulajule Reservoir spillway, through an existing approximately 3-mi pipeline, and into an unnamed intermittent creek that flows roughly 1.3 mi before entering Nicasio Reservoir. Soulajule Reservoir water could also be transferred to other District locations, as needed. The anticipated increases in Soulajule Reservoir volume withdrawals may result in annual storage fluctuations on the order of 40 50%. Readily available literature sources suggest that increasing water level fluctuation in lakes/reservoirs would result in increased bioaccumulation of mercury (Section ). However, this effect may be related to the ratio of littoral zone area to total reservoir volume. Steep-sided reservoirs with organic-poor substrates may exhibit less efficient methylmercury production, lower ambient methylmercury concentrations, and less bioaccumulation compared to reservoirs possessing relatively large, shallow littoral zones with organic rich soils 65

73 (Section ). With the exception of the eastern and western arms, Soulajule Reservoir shorelines tend to be steep and not well vegetated (Figure 4 and Figure 5). Further consideration of a potential relationship between water level and mercury methylation and bioaccumulation in Soulajule Reservoir would benefit from the following additional information: Area of littoral zone; Presence/absence of benthic algae, macrophyte stands, or other significant biomass in littoral zones of shallower arms; Soil grain size and nutrient content in the littoral zone; Understanding of the relative importance of littoral zones as a source of methylmercury in the food web; Effect of anticipated future changes in volume and water level fluctuations on seasonal stratification patterns, potentially changing: - the volume of epilimnion available for seasonal algal growth; and, - the volume of hypolimnion available for maintaining sufficient dissolved oxygen concentrations and minimizing methylmercury production throughout the stratification period. Accordingly, Pilot Study 2 (Section 6.2) explores the potential for increased mercury methylation and bioaccumulation in Soulajule Reservoir given the possibility of more frequent water level fluctuation in future years. This study includes a preliminary investigation of likely changes in epilimnion and hypolimnion volumes based upon existing data (i.e., not a detailed modeling effort) and in relation to effects on algal growth and mercury methylation. While confirmation of the link between water level fluctuation, stratification patterns, and fish tissue mercury in Soulajule Reservoir requires a long-term monitoring effort involving actual hydrology changes, Pilot Study 2 involves short-term monitoring to establish baseline conditions with respect to littoral zone extent and productivity and to develop an understanding of the likelihood and directionality of change with respect to current mercury methylation and bioaccumulation rates. 66

74 5 RANKING OF POTENTIAL MANAGEMENT METHODS AND RECOMMENDED PILOT STUDIES 5.1 Ranking Approach The in-lake and watershed management methods judged to have applicability or potential applicability for controlling methylmercury production and bioaccumulation in Soulajule Reservoir (Section 3) were subsequently ranked by the project team using 15 criteria weighted as either 1 (least important), 2 (moderately important) or 3 (most important) (Table 6). Ratings by criterion used a scale of 1 to 5 (negative 1 2, neutral 3, positive 4 5) and the weighted ratings were then summed and normalized to a scale of (Appendix B). Because water level fluctuation is being considered as a potential change in operating conditions for Soulajule Reservoir, rather than a methylmercury-specific control action, it was not ranked alongside the other potential management methods and is discussed separately (Section 5.3). 5.2 Ranking Results Results of the ranking exercise (Table 7) suggested three general rating ranges for potential methylmercury control actions: no negative ratings, most ratings positive most ratings neutral or positive <69 several negative ratings Results are discussed further in Sections

75 Table 6. Rating criteria and weighting factors for Soulajule Reservoir in-lake and watershed potential methylmercury control actions. Criteria Compatibility with water supply objectives Effectiveness (MeHg water) Effectiveness (MeHg fish) Weighting Factor Rating Descriptions Negative Neutral Positive Not compatible or limited Enhances ability to meet Compatible compatibility objectives Likely or potentially likely to Somewhat effective or extremely No effect on water result in an increase in water effective at decreasing water column MeHg column MeHg column MeHg Likely or potentially likely to result in an increase in fish tissue MeHg No effect on fish tissue MeHg Somewhat effective or extremely effective at decreasing fish tissue MeHg Weighted Rating = 3x rating = 3x rating = 3x rating Risk of failure 3 High or moderately high Moderate Limited or none = 3x rating Cost 3 Multiple benefits 2 Landowner acceptability 2 Longevity of treatment 2 Engineering requirements Operation and maintenance (O&M) requirements High (>$5M) to moderately high (>$3M to $5M) Would or may interfere with other benefits Surrounding landowners would not or may not support Short-term treatment (0 to 1 yr) Moderate (>$1M to $3M) No additional benefits No effect on surrounding landowners Moderately long treatment (> 1 to 5 yrs) Moderately low ($500K to $1M) to low (<$500K) Potential for or certainty of multiple benefits Surrounding landowners would potentially or definitely support Long-term treatment (> 5 yrs) = 3x rating = 2x rating = 2x rating = 2x rating 2 Intensive Moderate Limited or none = 2x rating 2 Intensive Moderate Limited or none = 2x rating Permitting 2 Intensive Moderate Limited or none = 2x rating Implementation time 1 Long (> 3yrs to 5 yrs) or very long (> 5 yrs) Moderate (2-3 yrs) Short (1-2 yrs) or very short (<1 yr) = 1x rating 68

76 Criteria Weighting Factor Time to effectiveness 1 Recreation effects 1 Need for pilot studies 1 Total Score (sum of all weighted ratings) Overall Rating (scale of 100) Rating Descriptions Negative Neutral Positive Long (> 3yrs to 5 yrs) or very Short (1-2 yrs) or very short (<1 Moderate (2-3 yrs) long (> 5 yrs) yr) Would have or may have a May have or would have a No effect negative effect positive effect Expensive and/or timeintensive studies Moderately expensive and/or time-intensive studies Limited cost and/or timeintensive studies or none Weighted Rating = 1x rating = 1x rating = 1x rating Sum Normalized sum 69

77 Biomanipulation sport fish stocking Sport fish stocking was the only potential management method that received no negative ratings (Table 7). This is largely because adding sport fish un-impacted by methylmercury is the most direct way to reduce average sport fish tissue methylmercury concentrations, it carries a relatively low risk of failure with respect to disturbance of the existing food web, it is relatively inexpensive, and it requires little to no engineering or operation/maintenance requirements.. Sport fish stocking also has the potential to reduce algal biomass in the reservoir via top-down cascading trophic interactions (Section ). While stocked sport fish could be washed downstream and interfere with habitat beneficial uses in Arroyo Sausal by competing with or preying upon native aquatic species, this would represent an incremental effect only, since largemouth bass are already in the reservoir. A key assumption related to this method is that it occurs in conjunction with another inlake approach (or approaches) focused on controlling methylmercury production and water column concentrations. We also assume that sport fish stocking would be implemented using an adaptive management approach with respect to annual stocking rates, with the goal of demonstrating near-term improvements in average sport fish tissue concentrations and reducing stocking over the long-term as other in-lake approaches successfully reduce methylation in the reservoir. Results of Pilot Studies 3 and 4 would inform the selection of appropriate annual stocking rates, which fish species would be the best choice, and which age-size classes should be stocked. Results of Pilot Study 1 would indicate whether methylmercury bioaccumulation is spatially distributed in Soulajule Reservoir and whether a stocking strategy should account for such a pattern. Hypolimnetic oxygenation system Installation of an hypolimnetic oxygenation system (HOS) was the only potential management method that received the highest rating for compatibility with water supply objectives because it would reduce blue-green algae dominance and associated taste and odor compounds, as well as nutrient release (ortho-p, NH4 +, Mn 2+, Fe 2+ ) from anoxic sediments during periods of stratification, and thus would enhance overall water quality in the reservoir (Table 7). By increasing dissolved oxygen in deeper waters, HOS also would increase the availability of daytime refugia habitat for zooplankton, which could increase grazing pressure on algae and further improve water quality. Fish habitat would extend into deeper waters, potentially enhancing sport fish recreational opportunities. In addition, HOS may provide a meaningful offset of the potential effects of changing reservoir stratification patterns (e.g., earlier seasonal stratification, longer period of stratification) associated with climate change projections for the northern coastal California region (Section 2.5). 70

78 With respect to mercury control, HOS directly and effectively would decrease water column methylmercury production, assuming that a Speece cone would be placed near the dam. This type of HOS application carries a low risk of failure, as it is a proven approach to oxygenating bottom waters and sediments in seasonally stratified lakes and reservoirs (Section 2.4.2). HOS scored lower with respect to costs, engineering requirements, and ongoing operation and maintenance requirements as, compared with other methylmercury control options considered, it is a relatively expensive and more technically intensive approach. Results of Pilot Study 5 would inform those aspects of HOS design that involve system size, extent, and in-reservoir location. Results of Pilot Study 1 would indicate whether an oxygen plume extending into the eastern and western arm is needed to reduce methylmercury bioaccumulation outside of the reservoir area nearest the dam. Erosion control for uplands soils in the Eastern Arm Overall, erosion control for soils in the vicinity of the mine sites was rated relatively high, driven primarily by low implementation costs and presumed effectiveness with respect to methylmercury in water and fish tissue (Table 7). However, our evaluation assumes that results of Pilot Study 6 would indicate that upland erosion is a significant external source of mercury to Soulajule Reservoir. We also assume that landowners of the mine sites would be amenable to recommended erosion control measures and that cattle grazing near mine sites would not interfere with erosion control measures, both of which must be confirmed as part of Pilot Study 6. Lastly, because reduction of mercury concentrations in the reservoir water column and/or fish tissue due to control of an upland source may not be easily observable in the short-term, we assume that upland erosion control measures (if needed) would occur in conjunction with another in-lake approach (or approaches) to more rapidly address methylmercury production and bioaccumulation. VEM in the Eastern Arm Vigorous epilimnetic mixing (VEM) in the Eastern Arm of the reservoir received a high rating for compatibility with water supply objectives because it would reduce blue-green algae dominance and associated taste and odor compounds and thus enhance overall water quality in the reservoir. Reducing turbidity associated with large blue-green algal blooms may also support photo-demethylation of mercury through increased water clarity, which would decrease methylmercury concentrations in water. However, while VEM has been applied successfully to control algal species in other studies, it is currently untested for methylmercury control. Results of Pilot Study 1 would indicate whether reductions in blue green algae in the Eastern Arm are likely to result in concomitant reductions in methylmercury in zooplankton and small fish in the Eastern Arm and, potentially, elsewhere in the reservoir. Like HOS, VEM may provide a meaningful offset of the potential effects of changing reservoir stratification patterns (e.g., earlier seasonal stratification, longer period of stratification) and a longer growth season for 71

79 blue-green algae, associated with climate change projections for the northern coastal California region (Section 2.5). Biomanipulation prey fish stocking Prey fish stocking, while similar to sport fish stocking in terms of relatively low costs and ease of implementation (e.g., no engineering or operation and maintenance requirements), was not rated as high as sport fish stocking due to potential food web impacts (Table 7). Assuming that predation is the primary population control mechanism in the waterbody of interest, an increase in prey fish would lead to an increase in algal biomass (Section ), which would reduce water quality. As with sport fish stocking, we assume that this method would occur in conjunction with another in-lake approach (or approaches) that is focused on controlling methylmercury production and water column concentrations. Stocking would be implemented using an adaptive management approach and would be reduced over the long-term. As with sport fish stocking, results of Pilot Studies 5 and 6 would inform the selection of appropriate annual stocking rates, which fish species would be the best choice, and which age-size classes should be stocked. Dredging of reservoir sediments in the Eastern Arm Dredging of Eastern Arm sediments exhibiting elevated total mercury was ranked relatively low (Table 7). Assuming that sediments in the Eastern Arm are an important pathway for bioaccumulation in Soulajule Reservoir, this method would decrease methylmercury in water and fish tissue by removing the mercury source. However, assuming that sediments in the Eastern Arm are not likely to be exposed given typical reservoir conditions, nor are they likely to be exposed if annual reservoir fluctuations increase by the anticipated 2,000-3,000 ac-ft (Section 4), dredging costs for the potentially broad extent of elevated sediments in the Eastern Arm are anticipated to be extremely high. Further, permits for this type of work are often difficult to obtain. Additionally, engineering requirements and implementation time for dredging projects are high. Accordingly, dredging is not considered further for mercury control in Soulajule Reservoir. Capping of reservoir sediments in the Eastern Arm Capping of Eastern Arm sediments exhibiting elevated total mercury was ranked the lowest of the potentially applicable management methods (Table 7). Assuming that sediments in the Eastern Arm are an important pathway for bioaccumulation in Soulajule Reservoir, this method would reduce methylmercury in water and fish tissue by isolating the source of mercury. However, cost, implementation time, and requirements for engineering, ongoing operation and maintenance, and permitting of reservoir sediment projects are typically high. As for dredging, we assume that sediments in the Eastern Arm are not likely to be exposed given typical reservoir conditions, nor are they likely to be exposed for easier access if annual reservoir 72

80 fluctuations increase by the anticipated 2,000-3,000 ac-ft (Section 4). Additionally, the risk of failure for capping is moderately high, based on potential issues with increasing reservoir water level fluctuation, low-water grazing impacts, and production of methane or other gases in reservoir sediments. Accordingly, this method is not considered further for mercury control in Soulajule Reservoir. 73

81 Table 7. Ranking summary and key assumptions for Soulajule Reservoir in-lake and watershed methylmercury control actions. Methylmercury (MeHg) Control Action Biomanipulation sport fish stocking Hypolimnetic oxygenation system (HOS) Upland erosion control in Eastern Arm Vigorous epilimnetic mixing (VEM) in Eastern Arm Weighted Rating (Scale 1-100) Key Assumptions Results of Pilot Studies 5 and 6 would inform selection of appropriate annual stocking rates, species, and age-size class Results of Pilot Study 1 would indicate whether methylmercury bioaccumulation is spatially distributed and whether any stocking strategy should account for a pattern Adaptive management approach on annual stocking rates, to demonstrate improvements in average sport fish tissue concentrations and reduced stocking over time Would occur in conjunction with other in-lake approaches to address methylmercury production Results of Pilot Study 5 would inform those aspects of HOS design that involve system size, extent, and in-reservoir location Results of Pilot Study 1 would indicate whether algae, zooplankton, and small fish near the dam exhibit highest levels of methylmercury bioaccumulation and accordingly where to focus HOS Liquid oxygen (LOX) could be trucked, delivered and stored adjacent to the existing pump station on District property. If LOX delivery is not feasible due to space/transportation constraints, onsite oxygen generation is also feasible, though more expensive and involves more equipment. A Speece cone and supporting equipment would be located near the dam, with extensions into reservoir arms if results of Pilot Study 1 indicate that methylation and bioaccumulation in the arms is important Results of Pilot Study 6 would indicate whether upland erosion is a significant external source of mercury Landowners at mine sites would be amenable to recommended erosion control measures Cattle grazing near mine sites would not interfere with erosion control measures Occurs in conjunction with other in-lake approaches to address methylmercury production and bioaccumulation Results of Pilot Study 1 would indicate whether algae, zooplankton, and small fish in the Eastern Arm exhibit relatively high levels of methylmercury bioaccumulation Note VEM works in theory but is yet untested for methylmercury control 74

82 Methylmercury (MeHg) Control Action Biomanipulation prey fish stocking Dredging of reservoir sediments in Eastern Arm Capping of reservoir sediments in Eastern Arm Weighted Rating (Scale 1-100) Key Assumptions Results of Pilot Studies 5 and 6 would inform selection of appropriate annual stocking rates, species, and age-size class Results of Pilot Study 1 would indicate whether methylmercury bioaccumulation is spatially distributed and whether any stocking strategy should account for a pattern Adaptive management approach on annual stocking rates, to demonstrate improvements in average prey fish tissue concentrations and reduced stocking over time Would occur in conjunction with other in-lake approaches to address methylmercury production Results of Pilot Study 6 would indicate whether upland erosion is a significant and continuing external source of mercury Results of an additional study (not proposed in this Study Plan) would indicate volume of sediments with elevated mercury Results of Pilot Study 1 would indicate whether algae, zooplankton, and small fish in the Eastern Arm exhibit relatively high levels of methylmercury bioaccumulation Results of Pilot Study 6 would indicate whether upland erosion is a significant and continuing external source of mercury Results of an additional study (not proposed in this Study Plan) would indicate areal extent of sediments with elevated mercury Results of Pilot Study 1 would indicate whether algae, zooplankton, and small fish in the Eastern Arm exhibit relatively high levels of methylmercury bioaccumulation Eastern Arm sediments are non-mobile 75

83 5.3 Water Level Fluctuation Currently, Soulajule Reservoir storage fluctuates on a seasonal basis between approximately 8,000 and 10,500 ac-ft (roughly 25%) and 9 ft of depth (elevation between 332 ft and 323 ft) (Section 4,). The District is currently considering more frequent use of Soulajule Reservoir for drinking water supply, which could alter the future magnitude, frequency, and duration of volume and water level fluctuations. For example, increasing volume withdrawals by 2,000 3,000 ac-ft on an annual basis would result in total storage fluctuations on the order of 40 50%. Readily available literature sources suggest that increasing water level fluctuation in lakes/reservoirs would result in increased bioaccumulation of mercury (Section 4,). However, this effect may be related to the ratio of littoral zone area to total reservoir volume. Steep-sided reservoirs with organic-poor substrates may exhibit less efficient methylmercury production, lower ambient methylmercury concentrations, and less bioaccumulation compared to reservoirs possessing relatively large, shallow littoral zones with organic rich soils (Section 4). With the exception of the eastern and western arms, Soulajule Reservoir shorelines tend to be steep and not well vegetated (Figure 4 and Figure 5). Pilot Study 2 explores the potential for increased mercury methylation and bioaccumulation in Soulajule Reservoir given the possibility of more frequent water level fluctuation in future years. While confirmation of the link between water level fluctuation and fish tissue mercury in Soulajule Reservoir requires a long-term monitoring effort involving actual hydrology changes, the pilot study involves short-term monitoring to establish baseline conditions and to develop an understanding of the likelihood and directionality of change with respect to current mercury methylation and bioaccumulation rates. 5.4 Prioritization of Pilot Studies Based on results of the management method ranking effort, six pilot studies are priority studies (Table 8). These are listed in the same general rank order as the management methods, with the first two studies (pilot studies 1 and 2) providing information relevant to all management method. Potential pilot studies associated with capping and dredging activities in the Eastern Arm are no longer considered as these two management methods were ranked relatively low. 76

84 Table 8. Priority pilot studies for Soulajule Reservoir mercury control actions. Pilot Study Study 1 Additional Characterization of Methylmercury in Water and Biota Study 2 Water level fluctuation Study 3 Soulajule Reservoir Fish Community Composition Study 4 Soulajule Reservoir Food Web Structure Study 5 Evaluation of Reservoir Seasonal Oxygen Demand and Sediment Response to Hypolimnetic Oxygenation Study 6 Upland Mercury Source Loading Characterization Rationale Would provide information relevant to all management methods considered, and in particular the two highest ranked actions (i.e., biomanipulation sport fish stocking, HOS) Would inform the likelihood and directionality of change for methylation and bioaccumulation rates given increased water level fluctuation and for all management methods considered Would inform implementation of biomanipulation sport fish stocking Would inform implementation of biomanipulation sport fish stocking Would inform conceptual design and detailed costing for HOS Would indicate whether erosion control of uplands in vicinity of the Cycle and Franciscan mines is needed 77

85 6 PILOT STUDIES TO FILL DATA GAPS Pilot studies to further inform future management methods for Soulajule Reservoir involve multiple scales, depending on information needs, as follows. Bench-scale laboratory tests, such as experimental sediment core chambers, which can be subjected to varying physical and chemical conditions such as water velocities or water column dissolved oxygen concentrations. Experimental in-lake enclosures or mesocosms, where variations in nutrient availability to algae and zooplankton grazers can be tested against methylmercury uptake. Reduced-scale in-lake or out-of-lake assemblies deployed in a portion of the total treatment area to test effectiveness. Monitoring of water quality, sediment, and/or biota to determine patterns and trends under in situ conditions. Field reconnaissance surveys to determine current conditions, as required for further consideration of potential management approaches. The following sections describe pilot studies to fill data gaps identified for each of the potential mercury control methods discussed in Section Pilot Study 1 Additional Characterization of Methylmercury in Water and Biota Objectives The objective of Pilot Study 1 is to build on existing data describing methylmercury concentrations in water, zooplankton, and small fish in Soulajule Reservoir to better understand the role of conditions in the Eastern Arm and patterns of mercury bioaccumulation throughout the reservoir. The monitoring focus is on small prey fish as indicators of methylmercury exposure and bioaccumulation on a seasonal timescale (e.g., weeks to months) and at a localized spatial scale (e.g., reservoir arm or near the dam). Larger fish typically move throughout the reservoir and live for multiple years, and as such, they are broader spatial and temporal integrators of mercury bioaccumulation factors and would be unlikely to demonstrate patterns of mercury bioaccumulation at the scale of particular locations in the reservoir. Hypotheses The pilot study will test the following hypotheses: Seasonal algal blooms are concentrated in the Eastern Arm of Soulajule Reservoir and are dominated by blue green algae. 78

86 During algal blooms and periods of stratification, DO in the shallow Eastern Arm varies with water depth and time of day such that anaerobic conditions occur at or near the sediment water interface. Algal, zooplankton, and small (5 15 cm FL, TL3) prey fish methylmercury concentrations and bioaccumulation factors (BAFs) are higher in the mining impacted shallow, Eastern Arm of Soulajule Reservoir than the main body of the reservoir or the Western Arm. Algal, zooplankton, and small (5 15 cm FL, TL3) prey fish methylmercury concentrations and BAFs are higher in the fall than in the spring, independent of location in the reservoir. Measured BAFs are less than the 1,300,000 (L/kg) value assumed in the Walker Creek TMDL for development of the water column allocation (0.04 ng/l annual average dissolved methylmercury) (SFBRWQCB 2008a), such that an allocation based upon measured BAFs would be greater than 0.04 ng/l. Sampling design Sampling sites and monitoring constituents Methylmercury concentrations will be monitored in surface water and in algae, zooplankton, and small (5 15 cm FL, TL3) prey fish at three sites in Soulajule Reservoir (Table 9, Figure 26). In situ water quality parameters (water temperature, DO, ph, conductivity, oxidation-reduction potential [ORP]) will be monitored at the same three locations over varying time scales, depending on location. Water temperature, dissolved oxygen, methylmercury, and dissolved sulfides in water will be monitored at the dam outlet to Arroyo Sausal. EA-1 WA-1 D-1 Table 9. Sampling sites. Site ID Description Latitude Longitude Eastern arm, in vicinity of historical mining locations Longitudinal center line of western arm, potentially unaffected by historical mining locations In vicinity of dam, ideally between the original and the current dam 38 8'45.53"N '19.34"W 38 8'43.37"N '11.26"W 38 9'5.62"N '58.69"W A-1 1 At dam outlet to Arroyo Sausal 38 9'15.43"N '1.56"W 1 Water sample only. 79

87 A-1 D-1 WA-1 EA-1 Figure 26. Soulajule Reservoir sampling sites for additional characterization of methylmercury in water and biota. This pilot study involves four spatially-replicated sampling events in Soulajule Reservoir, including one fully-mixed winter/early spring event (January/February 2016) when algal productivity is low; just after the onset of stratification and during the spring algal bloom (April/May 2016); during stratification and the late summer algal bloom (July/August 2016); and, just prior to fall turnover when hypolimnion methylmercury concentrations and anoxia peak (October/November 2016). The following activities will take place during each sampling event: Collect vertical water column profiles for in situ parameters Collect 48-hr continuous measurements for in situ parameters in bottom waters of Site EA-1 in the Eastern Arm Collect individual surface water grab samples for analysis of dissolved methylmercury Collect multi-individual algal grab samples for methylmercury analysis, cell count, species identification, and spatial extent (via satellite imagery) Collect multi-individual zooplankton composite samples for methylmercury analysis Collect individual small (5-15 cm FL, TL3) prey fish for methylmercury analysis 80

88 Beginning in January 2016, the District will also collect monthly grab samples at site A-1 for in situ measurements of water temperature, dissolved oxygen, and analysis of dissolved methylmercury and dissolved sulfides. Sampling frequency will increase to every two weeks surrounding reservoir destratification in the late fall and the onset of stratification in spring. The number of methylmercury samples within each site, across sites, and across surveys is presented in Table 10. Sample sizes have been selected to support determination of statistical significance (e.g., α=0.05, p 0.05) between sites. Table 10. Number of water, algae, zooplankton, and fish methylmercury samples. Water 1 Algae 2 Zooplankton 3 Fish 4 Within-site sample replication Number of sites Number of samples per survey Number of surveys Total number of samples Individual grab samples 2 Multi-individual composite samples filtered from 1 L of water 3 Multi-individual composite samples from 1-2 vertical tows 4 Individual prey fish (5 15 cm) Field collection methods Water quality A YSI 600 series or YSI 6920 water quality Sonde will be used for vertical water column profiles of in situ parameters. A (separate) YSI 6920 Sonde will be used for continuous measurements of in situ parameters. The probe will be deployed approximately 0.1 m (0.5 ft) above the sediment water interface. The Sondes will be calibrated at elevations consistent with the associated monitoring site. After the 48-hour monitoring period, continuous data will be downloaded onto a Toughbook for further analysis. Pilot Study 1 will also include an investigation of the potential for cost-effective collection of in situ chlorophyll-a concentrations and blue-green algae relative biomass along with the standard in situ parameters (water temperature, DO, ph, conductivity, oxidation-reduction potential [ORP]). This data would provide a continuous indicator of relative algal biomass during probe deployment and would the supplement cell count and algal species identification data that will be collected as seasonal grab samples (see below). In addition, collection of in situ chlorophyll-a concentrations and blue-green algae relative biomass may facilitate future use of probes without laboratory confirmation. However, the simultaneous use of three optical probes (including dissolved oxygen) would require a different water quality Sonde and may result in a non-trivial increase in monitoring costs for Pilot Study 1. Therefore, as an initial step, the cost of using in situ chlorophyll-a and blue-green algae 81

89 probes will be investigated and discussed with the District during fall Deployment of the probes in 2016 will be based on the outcome of this investigation and the budget will be adjusted, as needed. Water samples Surface water grab samples will be collected from a boat. Samples for analysis of dissolved methylmercury concentrations will be field-filtered using capsule filters and pre-cleaned tubing and placed in pre-cleaned bottles with preservative supplied by the analytical laboratory. All water samples will be kept on ice while in the field, and stored at less than 12 C until analysis. Trace metal clean sampling techniques as prescribed by US EPA Method 1669 will be used for collection, handling and analysis of all methylmercury samples. Algae samples Algae samples will be collected from a boat in the epilimnion using a depth-integrated sampler (5 8 cm diameter). Algae samples will not be collected near the bottom, since cyanobacteria growth does not occur outside of the photic zone. Algal samples will be stored in ice coolers and preserved within 4 hrs of collection using one part Lugol s solution for each 100 parts of sample for sample preservation. Algal samples will be analyzed for methylmercury, cell count, and species identification. The spatial extent of spring and summer algae blooms will be confirmed by satellite imagery for 1 2 days prior, during, and after the field sampling event. Zooplankton samples Zooplankton samples will be collected from a boat using a non-metallic zooplankton net and repeated vertical tows. The tow net (64 um mesh size, 90 cm long) will possess a 30-cm polycarbonate ring and a nonmetallic bridle. During periods of high algal biomass in the photic zone, zooplankton sampling will be conducted just beneath the photic zone to avoid sampling algae. After each zooplankton tow, the net will be rinsed by hosing with lake water from the outside of the net, so that material adhering to the inside of net collects in the sample bottle. The sample bottle will be removed from the net and poured into a 1 L laboratory sample bottle. If the sample is not highly concentrated, it will first be dewatered by pouring the contents into netting held by strainer. Dewatered material will then be removed using a Teflon spatula and/or nylon forceps to the laboratory sample bottle for mercury analysis. Prior to collection, all Teflon ware will be acid-washed in concentrated nitric acid, rinsed with nanopure water, and stored in acid-washed polypro bags, double bagged. Sample bottles will be individually labeled and placed on ice for transport to the laboratory. Fish samples Gill nets for small (5 15 cm FL, TL 3) prey fish will be placed at each sampling site in shallow areas (3 5 ft depth) and adjacent to submerged aquatic macrophytes or under overhanging woody vegetation. Gill nets will be oriented perpendicular to the shoreline. With respect to mercury, protocols for fish handling and processing will generally follow methods described in USEPA (2000). After fish are captured, total length (TL, mm), fork 82

90 length (FL, mm), and weight (g) will be recorded. In order to confirm that small prey fish individuals have accumulated methylmercury for no more than one year (i.e., one stratification period), up to 10 scale samples will be taken as part of the spring survey (April/May 2016) fish collection. If a size threshold is identified above which fish are older than one year, then the quantities of fish collected above the threshold size will be reduced in future data collection, and a subset of the data will be identified as biosentinels that can be used to measure future effectiveness of management methods. Fish will be identified by species, individually labeled, and placed in zip lock plastic bags on wet ice for transport from the field and transfer to a commercial freezer for storage. Following laboratory protocol, frozen fish will be shipped overnight on wet ice to the analytical laboratory. At the laboratory, fish specimens will be analyzed using whole-body individual homogenization Laboratory analysis Methylmercury water and tissue samples will be sent to a lab capable of achieving ultralow detection limits (e.g., Brooks Rand Laboratories). Samples will be analyzed using USEPA Tissues will be digested in a KOH/methanol solution. Samples will then be analyzed by ethylation, Tenax trap pre-concentration, gas chromatography separation, pyrolytic combustion and atomic fluorescence spectroscopy (CV-GC-AFS). Data analysis and reporting approach In situ profiles collected at each site will be used to evaluate seasonal and spatial stratification patterns during the study period. Water column aqueous methylmercury, as well as algal, zooplankton, and small (5 15 cm FL, TL 3) fish methylmercury concentrations and BAFs in the shallow, Eastern Arm of Soulajule Reservoir will be compared to those in the deeper portion of the reservoir near the dam and the Western Arm for all sampling events to identify spatial and seasonal trends. BAFs will be calculated using the average methylmercury tissue concentration for each trophic level and surface water methylmercury concentrations in the following equation: BAF = log10 (MeHgwater/MeHgtissue) Aqueous methylmercury in water and mercury in fish tissue will be compared to criteria given in the Walker Creek TMDL (SFRWQCB 2008a) and evaluated within the context of other in situ and analytical water quality data collected during the study. Results will be summarized in a technical memorandum and provided to the District. In addition, a data report will be prepared for use with permitting authorities that includes: date, time, and location of sampling activities; species and number of species collected; and a copy of field data sheets. 83

91 Implementation schedule Ideally, the first sampling event would occur in late summer to early fall 2015, corresponding with a secondary seasonal algal bloom. The second event would occur following reservoir destratification and mixing in winter 2015/early spring 2016, and the third sampling event would occur in late spring/early summer 2016 following the onset of stratification and the first algal bloom of the season. Overall, we anticipate that the study will take months to complete. Estimated cost We estimate the cost of this study to be $256,700, including four field surveys, analytical costs, and reporting (Table 11). Table 11. Estimated cost of Pilot Study 1 Additional Characterization of Methylmercury in Water and Biota. Task Estimated Costs Permitting $2,000 1 Field effort $95,300 2 Algal imagery $9,000 3 Laboratory analysis $84,000 4 Data analysis and reporting $66,400 5 Total $256,700 1 Assumes coordination with CDFW for letter of authorization for reservoir sampling activities. 2 Assumes 3-day field effort x 4 surveys during 2016 for water and biota sampling in the reservoir, plus 5-hr field effort x 12 events during 2016 for water sampling at the dam outlet. Equipment included (e.g., nets, water quality meters, sampling bottles/coolers, GPS, boat rental). 3 Based on quote from Blue Water Satellite Inc. for 6 images. 4 Assumes MeHg in water ($164/sample, including filtration for dissolved fraction); dissolved sulfide in water ($65/sample, including filtration); MeHg in algae ($196/composite sample); MeHg in zooplankton ($196/composite sample), MeHg in fish ($172/individual); algal enumeration and species identification ($225/composite sample); zooplankton enumeration and species identification ($200/composite sample). MeHg quote provided by Brooks Rand, April Assumes one review cycle on draft and final report. 6.2 Pilot Study 2 Assessment of Littoral Zone Extent and Productivity as Related to Increased Water Level Fluctuation Objectives The objective of the study is to explore the potential for increased mercury methylation and bioaccumulation in Soulajule Reservoir given the possibility of more frequent water 84

92 level fluctuation in future years. While confirmation of the link between water level fluctuation and fish tissue mercury in Soulajule Reservoir requires a long-term monitoring effort involving actual hydrology changes, this study will involve short-term monitoring to establish baseline conditions and to develop an understanding of the likelihood and directionality of change with respect to current mercury methylation and bioaccumulation rates. Hypotheses The study will test the following hypothesis: The littoral zone in Soulajule Reservoir is relatively small and steep and supports low levels of benthic algal production and macrophytes. This study will also provide data to inform the following hypotheses, although they can only be fully tested through a long-term study: Increasing magnitude and frequency of water level fluctuations will result in increased mercury concentrations in fish tissue. Increased water level fluctuations will reduce spawning habitat for sport fishes, thereby reducing the sport fish population and subsequently increasing the prey and algae populations and increasing available carbon for mercury methylation (see also, Section ). Approach The areal extent of the littoral zone in Soulajule Reservoir will be assessed initially as a desktop GIS analysis, using aerial imagery, reservoir bathymetry, and existing data characterizing storage and water elevation and storage in Soulajule Reservoir. Groundtruthing will be completed during a late summer benthic algae and macrophyte survey, when water level is low and primary productivity is high. The approximate location and area of the littoral zone will be estimated by boating and/or walking the reservoir perimeter and shallow areas, where accessible. In addition, baseline information on sediment grain size and nutrient content will be assessed at up to six transects in the littoral zone, including up to two transects in the Eastern Arm, two in the Western Arm, and two between the dam and the Eastern Arm in the deeper portion of the reservoir. It is anticipated that three sediment samples per transect will be collected (up to 18 samples). The effect of water level fluctuations on mercury concentrations in fish tissue will be difficult to definitively determine if other management methods are underway, particularly in the long-term. However, collection of baseline data will be invaluable if reservoir storage 85

93 management changes in the future. Tissue samples for small prey fish (5 15 cm FL, TL3) collected as part of Study 3 (Section 6.1) can be used as baseline data for water-level fluctuation current conditions in Soulajule Reservoir, with continued sampling in the future if the management of Soulajule Reservoir is changed. Note that the food web structure study (Study 4) also addresses the question of littoral vs. pelagic food webs in Soulajule Reservoir. If the littoral zone is identified as an important pathway for mercury bioaccumulation, then additional water level studies may be required. Lastly, a literature review of studies involving reservoir water level fluctuation to manage fish spawning will be conducted, in order to explore the potential indirect effect of water level management on sport fish populations and mercury bioaccumulation. Data analysis and reporting approach The ratio of littoral zone area to Soulajule Reservoir volume (see also Section ) will be calculated and, along with field verification of benthic algae and macrophyte presence/absence, will be used to determine if the littoral zone is likely to be an important pathway for mercury bioaccumulation in Soulajule Reservoir. Results will be summarized in a report, including the literature review of potential effects on fish spawning and any relevant adaptive management recommendations related to future water level management in the reservoir. Implementation schedule The littoral zone GIS analysis will be undertaken in late summer/ early fall Ground truthing and the survey for benthic algae and macrophyte survey will be conducted during spring Overall, we anticipate this study to require 9 months to complete. Estimated cost We anticipate this effort to take 1 2 months to complete at an estimated cost of $22,000 (Table 12), including a 1- to 2-day ground-truthing survey effort and 1 day of sediment collection in mid- to late summer

94 Table 12. Estimated Cost of Pilot Study 2 Assessment of Littoral Zone Extent and Productivity as Related to Increased Water Level Fluctuation. Task Estimated Cost GIS analysis $3,600 Ground truthing field survey $3,600 Sediment collection and analysis 1 $6,000 Report $8,800 Total $22,000 1 Includes collection and analysis of approximately 18 samples for grain size and nutrient content. Assumes approximately $230 per sample ($50 for nutrient content [C,N,P], $180 for grain size). 6.3 Pilot Study 3 Assessment of Reservoir Fish Community Composition Objectives The objective of the study is to determine the relative abundance, distribution, and agesize class distribution of fishes within Soulajule Reservoir as a means of informing potential mercury bioaccumulation management approaches involving biomanipulation. This study will involve monitoring. Hypotheses The fish community composition study objective is descriptive and thus there are no associated hypotheses. Sampling design Reservoir sampling will be conducted using a combination of beach seines, boat electrofishing, and gill nets; sampling will occur during the spring and fall (Table 13). Spring sampling targets the spawning population, whereas fall sampling includes the year-1 (i.e., young-of-year) fish. Details of these methods are provided below. To assess fish age composition, up to 20 scale samples of each fish species will be collected from a subsample within a reservoir reach. Spring sampling will identify fish populations that piscivorous birds (e.g., kingfishers, herons) are most likely to consume before and after their breeding season. Fall sampling will identify fish populations when reservoir levels are relatively low, resulting in the highest sampling efficiency. 87

95 Table 13. Fish sampling methods and reaches. Sample Method Fish Population Sampling Reach (see also Figure 26) Habitat Sample Period Beach seine Boat electrofishing Juvenile W1, M1, M2, E1, E2, E3, E4 Adult W1, M1, M2, Juvenile E1, E2, E3, E4 Shallow shoreline Shallow locations <10 ft (cove or shallow arms) Fall and Spring Fall and Spring Gill net Adult W1, M1, M2, Juvenile E1, E2, E3, E4 Near shore and deep water Fall and Spring Gill net vertical array Adult Juvenile Near dam Throughout water column Fall Soulajule Reservoir will be divided into seven reaches to assess fish populations and distribution (Figure 27). The Eastern Arm will be divided into four reaches: the reach downstream of the Franciscan Mine (E1), the reach between the two mines that also exhibits the highest total mercury in sediments (E2), the reach upstream and to the east of Cycle Mine (E3), and reach upstream and to the south of Cycle Mine (E4) (Figure 27). The Western Arm will be represented by one reach (W1). The main body of the reservoir will be divided into two reaches (M1 and M2), where M1 represents the deepest portion of the reservoir, near the dam. A vertical array will assess the fish population distribution throughout the water column near the deepest location in the reservoir (Figure 27). One sampling event by beach seine (where feasible), adult gill net, juvenile gill net, and electrofishing will be conducted within a reservoir reach to determine the spatial population distribution of adult and juvenile fish within the reservoir (Table 13). Within reach site selection will occur in the field. Figure 27. Approximate fish sampling reaches (rectangles) in Soulajule Reservoir. The red rectangle marks the area with high total mercury levels in sediments. The orange line represents the approximate location of the vertical gill net array. 88