Stillwater Sciences. Stillwater Sciences. East Bay Municipal Water District th Street Oakland, CA 94607

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1 TECHNIC AL MEMORANDUM NOVEMBER 2016 Key Factors Influencing the Production of Taste & Odor Compounds and Soluble Manganese in PREPARED FOR East Bay Municipal Water District th Street Oakland, CA PREPARED BY Stillwater Sciences 2855 Telegraph Ave., Suite 400 Berkeley, CA Stillwater Sciences

2 Suggested citation: Key factors influencing the production of taste & odor compounds and soluble manganese in. Prepared by Stillwater Sciences, Berkeley, California, with assistance from Brown and Caldwell, Walnut Creek, California; Dr. Marc Buetel, University of California, Merced; and, Dr. William Taylor, Walnut Creek, California for East Bay Municipal Water District, Oakland, California. Cover photo:. Tony Iwane flickr.com, published under a Creative Commons License. i

3 Table of Contents 1 BACKGROUND WATERSHED CONTEXT RESERVOIR CONDITIONS Hydrology Seasonal Stratification Nutrient Cycling Water column Sediments Algae Planktonic Benthic Trophic Status and Nutrient Limitation Manganese and Taste and Odor Compounds Soluble manganese Geosmin and MIB SOBRANTE WATER TREATMENT PLANT Inorganic Water Quality Constituents Geosmin and MIB SUMMARY OF KEY FACTORS INFLUENCING THE PRODUCTION OF TASTE & ODOR COMPOUNDS AND SOLUBLE MANGANESE IN SAN PABLO RESERVOIR RECOMMENDATIONS/NEXT STEPS REFERENCES Tables Table 1. Seasonal wind speed and direction Table 2. Estimated relative contribution of water from the Sacramento River at Freeport Diversion to total inflow and storage during the 2014 and 2015 diversion periods Table 3. Carlson TSI associations with water quality Table 4. Carlson TSI for Table 5. Mass ratios of nitrogen to phosphorus in Table 6. Potential geosmin- and MIB-producing cyanobacteria genera in San Pablo Reservoir Figures Figure 1. location map Figure 2. inflows Figure 3. water surface and withdrawal-gate elevations Figure 4. Seasonal temperature isopleths with depth in Figure 5. Seasonal dissolved oxygen isopleths with depth in ii

4 Figure 6. In situ water quality profiles in in 2014 showing mixed water column conditions in the winter, the onset of stratification in the spring and full stratification in the summer, and fall Figure 7. Seasonal chlorophyll-a isopleths with depth in Figure 8. Nitrogen concentrations in water withdrawn from reservoir Figure 9. elevation 267 feet or 283 feet for the period Phosphorus concentrations in surface water or withdrawal from the reservoir at elevation 267 feet for the period Figure 10. Phytoplankton by group compiled across surface, elevation 267-feet and 283-feet sampling locations for the period Figure 11. Cyanobacteria abundance by date, compiled across surface, elevation 267-feet and 283-feet sampling locations for the period Figure 12. Total cyanobacteria counts and geosmin and MIB concentrations in San Pablo Reservoir at Sobrante Tower at gate elevations 267 and 283 feet for the period Figure 13. Total geosmin-producing cyanobacteria abundance and geosmin concentrations at Sobrante Tower at reservoir elevation 267 feet for the period Figure 14. Raw dissolved oxygen and total manganese concentrations at Sobrante WTP in Figure 15. Raw dissolved oxygen and total manganese concentrations at Sobrante WTP in Figure 16. Raw dissolved oxygen and total manganese concentrations at Sobrante WTP in Figure 17. Raw dissolved oxygen and total manganese concentrations at Sobrante WTP in Figure 18. Raw dissolved oxygen and total manganese concentrations at Sobrante WTP in Figure 19. Raw water iron, nitrate and manganese concentrations compared to raw water DO for the period Figure 20. Treated water iron, manganese, sulfate and nitrate compared to raw water DO concentrations for the period Figure 21. Raw water MIB and geosmin concentrations for the period 2009 September Figure 22. Reservoir cyanobacteria abundance and raw water geosmin and MIB concentrations Figure 23. Raw water temperature, geosmin and MIB concentrations Figure 24. Raw water MIB and geosmin concentrations for the period 2013 September Figure 25. Treated water MIB and geosmin concentrations for the period 2009 September Figure 26. Frequency of treated geosmin concentrations for the period Figure 27. Percent removal of geosmin for different influent concentration ranges at Sobrante WTP Figure 28. Raw water vs. treated water geosmin concentrations at the Sobrante WTP for different raw water concentration ranges Appendices Appendix A. Late Summer/Early Fall 2016 Algal Associations with Geosmin and MIB Production Appendix B. Sediment Flux Study iii

5 1 BACKGROUND Located in Contra Costa County, California, is a surface water impoundment of San Pablo Creek, north of the city of Orinda and south of the cities of El Sobrante and Richmond (Figure 1). East Bay Municipal Utility District (District) operates as the primary municipal and domestic water supply for the northern portion of the District s service area (e.g., Richmond, San Pablo, El Sobrante, Crockett) via the Sobrante and San Pablo Water Treatment Plants (WTPs). The reservoir also serves as emergency standby storage, regulation of the Mokelumne Aqueduct supply for the larger District water system, and storage of local runoff from Bear and San Pablo creeks. Other designated beneficial uses include sport fishing; cold freshwater habitat; warm freshwater habitat; fish spawning; noncontact recreation; and wildlife habitat (San Francisco Bay Basin Plan 2010). experiences thermal stratification on a seasonal basis and algae blooms in surface waters that deteriorate water quality in a variety of ways. In drinking water in particular, taste and odor (T&O) occurrences in the reservoir have been linked to the presence of the algalassociated metabolites geosmin [(4S,4aS,8aR)-4,8a-dimethyl-1,2,3,4,5,6,7,8- octahydronaphthalen-4a-ol] 1, causing an earthy flavor, and MIB (2-methylisoborneol), causing a musty flavor. Geosmin and MIB are two of the most common naturally occurring T&Ocausing contaminants in the world. Although they do not pose a health threat, these compounds create a displeasing T&O when present above sensory thresholds. Such T&O events can create a public relations problem for the water utility and can result in loss of consumer trust in the water s safety and healthfulness. In addition to T&O problems, water withdrawn from for drinking water purposes can contain high concentrations of soluble manganese during the late summer/early fall season, and in some years the early winter, coinciding with low dissolved oxygen in the reservoir bottom waters. Excessive manganese in treated water imparts a strong metallic taste to the water and causes black and brown staining of laundered clothing and fixtures. Removing soluble manganese from raw water through oxidation and sedimentation/filtration consumes chemical oxidants such as ozone, reducing capacity for treatment of T&O compounds. The magnitude and duration of T&O events have greatly increased in over the past three years, with reservoir geosmin concentration spiking to 460 ng/l in the summer of 2015, overwhelming Sobrante Water Treatment Plant (WTP) capacity for removal and resulting in a large number of customer complaints. The Sobrante WTP, the primary WTP accepting water from, currently uses intermediate ozonation with hydrogen peroxide to destroy T&O causing compounds, as well as to remove soluble manganese. The District is in the process of upgrading the ozone system at Sobrante WTP to address the relatively high T&O concentrations experienced in recent years. Minimizing the production of T&O compounds and soluble manganese often requires control of the affected waterbody. Since removal alternatives at the WTP can be very costly, the District has recently undertaken a project to develop a comprehensive water quality management program for, involving the following: 1 Other commonly applied nomenclature includes trans-1, 10-dimethyl-trans-9-decalol and 4, 8adimethyl-decahydronaphthalen-4a-ol. 1

6 1. Identify the sources of T&O and the factors that influence its formation; 2. Evaluate alternatives to reduce the T&O levels in the reservoir; and 3. Address the formation of soluble manganese in the reservoir. Prepared as part of work under Tasks 2 and 7 of the project, this technical memorandum summarizes the results of existing water quality data review and analysis and provides an assessment of the key factors and variables that influence formation of geosmin, MIB, and soluble manganese in. District staff and the Stillwater Team will use results of this analysis to develop solutions and recommendations to decrease T&O causing compounds and soluble manganese levels in the reservoir, under forthcoming tasks (Tasks 3 6) of the project. 2 WATERSHED CONTEXT The San Pablo Creek watershed is approximately 14,766-acre in size and consists mostly of District-owned land under District and City of Orinda jurisdictional authorities (EBMUD 2015a). The ratio of watershed to waterbody area for is approximately 18 (see Section 3.1 for reservoir surface area), which is not particularly high for a reservoir. San Pablo Creek is the largest source of runoff to, including runoff from the City of Orinda, portions of Highway 24, and water from Lauterwasser Creek, among others. The creek enters the reservoir in its southeastern arm (Figure 1). The creek exits the reservoir at the northwestern end and flows northwest into San Pablo Bay. is adjacent to Briones Reservoir, another District operated storage reservoir impounding the Bear Creek tributary. Bear Creek serves as the conduit for releases from Briones Reservoir and also enters at the southeastern arm of (Figure 1). Land use in the watershed is predominantly urban (31%) and open space, watershed protection, and parks (62%), with some grazing use. While there is no existing agricultural activity in the watershed, the District leases approximately 7,000 acres in the San Pablo Watershed for private grazing, including cattle and horses. The District also uses goat grazing from spring to early summer to manage herbaceous fuel loads (EBMUD 2015a). Within urban areas, most residential and commercial wastewater is collected and treated by the Central Contra Costa Sanitation District. However, there are still neighborhoods that are served by septic systems, including a small neighborhood along Lauterwasser Creek and the neighborhood of El Toyonal, located west of San Pablo Creek (EBMUD 2015a). Data from the Automated Weather Station indicate that air temperature, wind speed, and wind direction in the vicinity of the reservoir vary seasonally but are generally low, with average maximum hourly values typically less than 5 mph and average wind direction from the south-southeast, except in winter when it blows from the east-southeast (Table 1). However, anecdotal information from District staff most familiar with reservoir conditions indicates that it is often windy at the reservoir, and wind blows toward the southern end of the reservoir such that algae accumulates there and in small bays along the eastern shore. The automated weather station may be relatively sheltered from the wind and is thus not representative of broader conditions at the reservoir. Watershed geology is dominated by sandstone and shale, with some volcanic igneous bedrock west of. Surface soils are relatively uniform and are dominated by clay loam, 2

7 a soil type commonly associated with phosphorus. Most of the soils in the watershed have been identified as a moderate to high erosion risk (EBMUD 2015a). Season Table 1. Seasonal wind speed and direction ( ) 1. Average maximum hourly wind speed (mph) Average wind direction (degrees) Cardinal direction Average hourly mean air temperature ( o F) Winter (Dec Feb) E/SE 51 Spring (Mar May) S/SE 58 Summer (Jun Aug) S/SE 64 Fall (Sept Nov) S/SE 61 1 Data from Automated Weather Station, Source: EBMUD. 3

8 Figure 1. location map. 4

9 3 RESERVOIR CONDITIONS 3.1 Hydrology has a storage capacity of approximately 38,600 acre-feet, with a total surface area of 834 acres. The reservoir is approximately 2.8 miles long, 0.5 miles wide at the widest point, and has a maximum depth of 200 feet near the dam. Reservoir storage varies seasonally, ranging 16,960 to 38,600 acre-feet over the period Runoff varies seasonally with precipitation, with over 90% of regional annual precipitation occurring in the winter and spring (November April). Accordingly, the relative contribution of precipitation and runoff to inflows is highest in winter and spring, with these sources typically comprising 50 90% of inflows from January to April each year. From August 2014 to March 2015, precipitation and runoff contributed 100% of inflows to the reservoir, as drought conditions restricted water transfers from other sources (Figure 2). Under normal operating conditions, the reservoir receives inflow from the Mokelumne Aqueduct, which is primarily sourced from the Mokelumne River via Pardee Reservoir in the Sierra foothills. During summer and fall, the aqueduct can be the primary source of water to San Pablo Reservoir (Figure 2). However, in drought years, the District supplements aqueduct inflows with water from the Sacramento River at Freeport Diversion (FRWP). From April 2014 through July 2014, Sacramento River water constituted 62 91% of total inflows to, and from April 2015 through October 2015, this source constituted 77 92% of total inflows (Figure 2). During these periods, estimated FRWP inflow as a percent of reservoir storage ranged 2% to 30% (Table 2). Just prior to the FRWP inflow period in 2015, the District drew down San Pablo Reservoir somewhat to maximize the amount of water that could be transferred into the reservoir (Figure 3). inflows also include small amounts of adjacent Briones Reservoir discharge and wash water from the nearby Orinda WTP. All imported waters enter the reservoir via San Pablo Creek, where the water travels from the diversion works approximately 1.5 miles along the creek and into the reservoir. Figure 2. inflows

10 Table 2. Estimated relative contribution of water from the Sacramento River at Freeport Diversion (FRWP) to total inflow and storage during the 2014 and 2015 diversion periods. Monthyear End of month storage (AF) a Change from previous month storage (AF) a Total inflow (AF) a FRWP inflow (AF) b % of total inflow from FRWP Estimated FRWP inflow as % of storage (max dilution) Estimated FRWP inflow as % of storage (min dilution) Apr-14 32,910 7,080 7,758 6,551 84% 16% 25% May-14 35,650 2,740 5,683 5,151 91% 13% 16% Jun-14 34,370-1,280 2,434 1,877 77% 6% 5% Jul-14 34, ,538 2,180 62% 6% 6% Apr-15 22, ,114 2,409 77% 11% 11% May-15 22, ,038 2,795 92% 13% 13% Jun-15 22, ,004 2,738 91% 12% 12% Jul-15 20,710-1,620 1,448 1,335 92% 7% 6% Aug-15 17,950-2, % 2% 2% Sep-15 20,840 2,890 5,827 5,344 92% 23% 30% Oct-15 23,600 2,760 5,362 4,128 77% 16% 20% Nov-15 25,370 1,770 3,663 2,535 69% 9% 11% Dec-15 25, , % 1% 1% a EBMUD 2014, 2015b b FRWP 2014 transfers (EBMUD 2015a); FRWP 2015 transfers (EBMUD 2016) With a spill elevation of 313 feet, water surface elevation (WSE) varies depending on season and year (Figure 3). In 2010 and 2011, WSEs varied by 5 10 feet across the year. In 2012, at the start of the drought, WSEs varied by approximately 15 feet across the year, with the lowest levels occurring in October. In 2013, WSEs variation was from approximately 305 feet in March down to almost 280 feet in October, or approximately 25 feet during this period and 2015 variation in WSEs was generally less at feet across the year. has no regulatory requirement for discharge downstream into San Pablo Creek; releases from the reservoir only occur to avoid uncontrolled spillway releases to San Pablo Creek (EBMUD 2015a). Withdrawals (drafts) from the reservoir occur primarily via the Sobrante Tower, located in the dam s left abutment, which provides raw water to the Sobrante WTP. The tower has four withdrawal gates with 60-inch butterfly valves to control flow, located at 219, 267, 283, and 295 feet. The lowest gate (219 feet) is connected to the outlet tunnel and has been used in the past to drain the reservoir, but otherwise would be used only in emergency or drought conditions when the water surface elevation was atypically low. The District used the 267-ft withdrawal gate as the only gate used to supply Sobrante WTP between 2010 and September 8, 2016: then the District switched to the 283-ft gate because the reservoir water surface elevation was higher than normal. The District does not use the 295-ft gate because it is often too close to the water surface (Figure 3). During normal conditions, the Sobrante WTP operates from March to November to supply higher summer demand. In recent years ( ), the Sobrante WTP has been operated year-round as part of the District drought operations to treat supplemental water supplies stored in the reservoir. Withdrawals from the reservoir infrequently occur through the intake tower for San Pablo WTP, located at the west side of the reservoir. Six valves located at elevations between 294 feet and 221 6

11 feet (Figure 3) allow water to flow into the San Pablo Tower. However, since the District operates the San Pablo WTP intermittently, either for outage of major District facilities or for drought operation, withdrawals from the reservoir do not typically occur at this tower. In September and November 2006, withdrawals were made from gates at elevations 282, 280, and 252 feet. In September 2016, the District began operating San Pablo WTP to prepare for major construction work and an Orinda WTP outage starting in. Since September 2016, withdrawals from the San Pablo tower have occurred from the gate at 266 feet. Figure 3. water surface and withdrawal-gate elevations Seasonal Stratification is a warm monomictic (mixing once per year) waterbody. Reservoir mixing typically occurs in the late fall and is maintained throughout the winter (Figure 4). Thermal stratification begins in the spring, with a distinct thermocline developing by May. Stratification is maintained throughout the summer and early fall (Figure 4). Thermal stratification is particularly strong in, with temperature differences between the epi- and hypolimnion of up to 7 10 o C in the summer and fall. Because historically the most frequently used withdrawal gate elevation is 267-feet (Section 3.1), raw water is generally withdrawn from the upper hypolimnion, except during peak stratification in periods with low total reservoir storage, when withdrawals may be taken from the epi- or metalimnion (Figure 4). From June 2014 to October 2014, when Sacramento River water constituted 62 91% of total inflows to, water temperatures in the epilimnion were slightly higher than in 2010, 2011, and 2012 (Figure 4), although the difference is not statistically significant. Sacramento River water constituted 77 92% of total inflows during April 2015 through October 2015; however, relative annual differences in water temperatures are not discernable from the shorter 2015 in situ data record. Distinct dissolved oxygen (DO) profiles accompany the strong thermal stratification in San Pablo Reservoir, with 7 12 mg/l DO in the epilimnion and anoxic conditions in the hypolimnion (Figure 5, Figure 6). Anoxia is common at depths less than forty feet (40 feet) below the reservoir s water surface during peak stratification. Although temperatures were consistent throughout the water column in January/February 2015 (Figure 4), DO remained at or near zero in the bottom waters during the same period (Figure 5), suggesting that the reservoir water 7

12 column did not fully mix in the winter following the first inflows of Sacramento River water (i.e., April 2014 through July 2014). Similarly, DO concentrations remained low (2 3 mg/l) in the bottom waters during February 2015 (Figure 5), following inflows of Sacramento River water from April 2015 through December 2015, suggesting that the reservoir did not fully mix for the second year in a row. The data show elevated epilimnion ph ( s.u.) during stratification (Figure 6), likely resulting from higher photosynthetic uptake of CO 2 in the photic zone during periods of high primary productivity. 8

13 Elevation (ft) Apr 2010 Jul 2010 Oct 2010 Jan 2011 Apr 2011 Jul 2011 Oct 2011 Jan 2012 Apr 2012 Jul 2012 Oct 2012 Jan 2013 Apr 2013 Jul 2013 Oct 2013 Jan 2014 Apr 2014 Jul 2014 Oct 2014 Jan 2015 Apr 2015 Jul 2015 Oct 2015 Jan 2016 Apr 2016 Jul Temp (C) Figure 4. Seasonal temperature isopleths with depth in ,3. Elevation (ft) Apr 2010 Jul 2010 Oct 2010 Jan 2011 Apr 2011 Jul 2011 Oct 2011 Jan 2012 Apr 2012 Jul 2012 Oct 2012 Jan 2013 Apr 2013 Jul 2013 Oct 2013 Jan 2014 Apr 2014 Jul 2014 Oct 2014 Jan 2015 Apr 2015 Jul 2015 Oct 2015 Jan 2016 Apr 2016 Jul DO (mg/l) Figure 5. Seasonal dissolved oxygen isopleths with depth in ,3. Arrows indicate periods where the water column did not fully mix. 2 The horizontal dashed line represents the primary Sobrante Tower withdrawal gate. 3 Vertical dashed lines show high point density from in situ sampling on October 7,

14 SOTW 1/7/2014 SOTW 3/27/ WQ metric (see legend for units) WQ metric (see legend for units) Depth (ft) DO (mg/l) ph Temp (C) Depth (ft) DO (mg/l) ph Temp (C) Water Temperature (C) Water Temperature (C) SOTW 7/15/2014 SOTW 10/7/ WQ metric (see legend for units) WQ metric (see legend for units) Depth (ft) DO (mg/l) ph Temp (C) Depth (ft) DO (mg/l) ph Temp (C) Water Temperature (C) Water Temperature (C) Figure 6. In situ water quality profiles (temperature, ph, and dissolved oxygen [DO]) in San Pablo Reservoir in 2014 showing mixed water column conditions in the winter (a), the onset of stratification in the spring (b) and full stratification in the summer, (c) and fall (d). Figure 7 shows the seasonal and annual variability in the vertical distribution of chlorophyll-a. Prior to April 2014, in situ profiles may have over-estimated chlorophyll-a concentrations due to turbidity interference. The District switched to a YSI EXO instrument in April 2014, and subsequent chlorophyll-a data are more consistent with high algal abundance in the surface waters where light is available. 10

15 Elevation (ft) Apr 2010 Jul 2010 Oct 2010 Jan 2011 Apr 2011 Jul 2011 Oct 2011 Jan 2012 Apr 2012 Jul 2012 Oct 2012 Jan 2013 Apr 2013 Jul 2013 Oct 2013 Jan 2014 Apr 2014 Jul 2014 Oct 2014 Jan 2015 Apr 2015 Jul 2015 Oct 2015 Jan 2016 Apr 2016 Jul Chl-A (µg/l) Figure 7. Seasonal chlorophyll-a isopleths with depth in , Nutrient Cycling Water column Water column nutrient concentrations in depend on external nutrient sources as well as internal nutrient cycling processes. Concentrations vary in space and time within the reservoir, depending on seasonal variations in physical and biological processes. Nitrogen and phosphorus, the two most critical nutrients for biological productivity, exist in the water column in multiple forms, including dissolved forms, suspended particulate forms, and forms assimilated in live biomass. While the majority of water column nitrogen and phosphorus is typically bound up in organic matter, the abundance of dissolved inorganic forms tends to control biological productivity, as these forms are more readily available for biological uptake and assimilation Nitrogen Potential sources of nitrogen to the water column include inorganic and organic nitrogen in watershed runoff and water transfers, nitrate (NO 3- ) deposition from rainfall, and nitrogen (N 2) fixation in sediments and the water column. Potential nitrogen sinks occur through microbially-mediated denitrification, outflow from the reservoir, and deposition and permanent burial of nitrogen-containing compounds in reservoir sediments. While rainfall is likely to contribute only a small amount of nitrogen to the water column, runoff from the surrounding watershed, including the City of Orinda, may be a significant source of nitrogen to the system, particularly during wet winter periods. Septic systems and occasional sewage spills are likely contributors to nitrogen in the reservoir; there were four 4 raw sewage spills ( gallons each) that occurred in the watershed during the period that 11

16 were discharged to San Pablo Creek (or another local creek) and then traveled into the reservoir (EBMUD 2015a). Additional data are necessary to assess the relative impact of nitrogen loading from local runoff to the reservoir. The District collected nitrogen data in the water column for the period Limited nutrient data from withdrawals to the Sobrante WTP (i.e., raw water withdrawn from Sobrante Tower gates at 267 and 283 feet) indicate that ammonium (NH 4+ ) (n=6) ranged from 0.01 to mg/l (July August 2013). Nitrate was variable, but tended to be higher in winter months, ranging from to 0.33 mg/l during periods when the reservoir was mixed (n=13), and from to 0.18 mg/l during stratified periods (n=45; ). Nitrite (NO 2- ) ranged from to 0.02 mg/l during mixed periods (n=13) and from to mg/l during stratified periods (n=45) ( ) (Figure 8). Generally, eutrophic lakes (see Section 3.5 for trophic indices) have higher ammonium concentrations in the hypolimnion than the epilimnion because of sediment release to bottom waters and uptake from autotrophic organisms in the epilimnion. The opposite pattern is frequently observed with nitrate, depending on loading rates and the ratio of nitrate to ammonium. Additional data are necessary to determine the vertical distribution of various nitrogen compounds in. Some genera of nitrogen fixing cyanobacteria, including Anabaena and Aphanizomenon, appear to be abundant in San Pablo Reservoir (Section 3.4), indicating that nitrogen fixation may be an important system nitrogen source, particularly during algal bloom periods. Figure 8. Nitrogen (as ammonium, nitrite, and nitrate) concentrations in water withdrawn from reservoir elevation 267 feet or 283 feet (Sobrante WTP raw water) for the period

17 Phosphorus Potential phosphorus sources to include runoff of organic and inorganic material from the surrounding watershed, turbulence-induced upwelling from reservoir sediments, and reservoir water transfers. Potential sinks occur through deposition and permanent burial of phosphorus in reservoir sediments and reservoir outflow or withdrawal. Soils in the San Pablo watershed are dominated by clay loam (see Section 2). Fine-textured soils such as clay loam are associated with relatively higher levels of phosphorus than coarser soil types, because aluminum and iron oxides in clays tend to sorb phosphorus. Most soils in the San Pablo watershed have been identified as a moderate to high erosion risk (EBMUD 2015a), suggesting that local runoff is a major source of total phosphorus to. Additional data are necessary to assess the relative impact of phosphorus loading from local runoff to the reservoir. A limited number of surface grab samples in 2010 indicate that orthophosphate (PO 4 3- ) concentrations can be higher in the winter ( mg/l; mean=0.046) when the reservoir is mixing, decreasing to lower levels (< mg/l; mean=0.001 mg/l) during summer and early fall when algal biomass is highest in surface waters and the reservoir is stratified. In the upper hypolimnion, grab samples taken at Sobrante Tower gate elevation 267 feet indicate that phosphorus concentrations vary seasonally and annually, with peaks most frequently occurring in the winter months when the water column is mixing (Figure 9). Lower phosphorus concentrations during late summer and fall are consistent with depletion due to algal uptake. Orthophosphate ranged from to mg/l at elevation 267 feet ( ) and to mg/l at the surface (January September 2010). Total phosphorus (elevation 267 feet; ) ranged from to 0.11 mg/l. On average, orthophosphate comprised 38% of total phosphorus for the period , suggesting that more than a third of water column total phosphorus is bioavailable. While there are significant gaps in the existing data (e.g., winter 2013, 2014), overall, phosphorus appears to be plentiful in. 13

18 Phosphate-P SOTW SURF Phosphate-P SOTW 267 Total P SOTW Jul-2009 Jan-2010 Jul-2010 Jan-2011 Jul-2011 Jan-2012 Phosphorus (mg/l) Jul-2012 Jan-2013 Jul-2013 Jan-2014 Jul-2014 Jan-2015 Jul-2015 Figure 9. Phosphorus (as orthophosphate or total P) concentrations in surface water or withdrawal from the reservoir at elevation 267 feet (Sobrante WTP raw water) for the period Sediments Bottom sediments are an important contributor to reservoir-wide nutrient cycling. Numerous types of bacteria are commonly found in reservoir sediments, including aerobic bacteria, denitrifiers, iron-, manganese-, and sulfate-reducing bacteria, all of which require an organic carbon source for cellular respiration and use oxygen (O 2), nitrate (NO 3- ), iron (Fe 3+ ), manganese (Mn ), or sulfate (SO 4 ), respectively, as electron acceptors. In productive reservoirs, algae provide a readily available source of organic carbon to fuel microbial activity, as algal biomass from surface waters settles to bottom sediments following senescence. Given an abundant organic carbon source, high levels of microbial activity can deplete DO in sediment pore waters and the overlying water column during periods of reservoir stratification, when bottom waters are effectively disconnected from re-supply of oxygen at the air-water interface (see also Section 3.2). Microbial activity mediates the conversion of nitrate in sediment pore waters to ammonium (NH 4+ ), also a highly bioavailable form of nitrogen, along with oxidized forms of iron (Fe 3+ ) and manganese (Mn 4+ ), which are converted to more soluble forms (Fe 2+, Mn 2+ ); each of the reduced compounds can subsequently diffuse upwards through the sediment profile to be released into reservoir bottom waters. Although not directly mediated by microorganisms, transformation of relatively non-bioavailable total phosphorus to the bioavailable form of orthophosphate also occurs under low oxygen conditions in sediments, allowing a pulse of orthophosphate from reservoir sediments. Once mixed into surface waters, these reduced forms of nutrients can stimulate spring and summer algal or aquatic macrophyte growth. 14

19 In order to assess the potential for redox-mediated cycling of manganese and other redox sensitive compounds (i.e., ammonia, nitrate, orthophosphate, iron, sulfate), the District and the Stillwater team collected intact sediment cores to allow experimental verification of DO conditions at the sediment-water interface. Results of the chamber experiments are summarized below and presented in detail in Appendix B Nitrogen Results of the chamber experiments suggest that maintenance of a well-oxygenated sedimentwater interface in will result in decreased internal loading of nitrogen to the reservoir water column. Under oxygenated (oxic) conditions, ammonium (NH 4+ ) present in the chamber overlying water column was converted to nitrate (NO 3- ), and much of this nitrate was lost from the system due to microbial denitrification and conversion to nitrogen gas (N 2) (Appendix B). Under anoxic conditions, ammonium was released from sediments, with ammonium fluxes from sediments collected proximal to the Sobrante Tower approximately twice as high (10 35 mg-n/m 2 d) as those collected proximal to the San Pablo Tower (5 15 mg- N/m 2 d). Sediments near the deeper Sobrante Tower likely remain anoxic much of the year, such that any organic matter depositing in these areas is not oxidized by heterotrophic bacteria that would otherwise flourish under oxic conditions and decrease levels of nitrogen in bottom sediments. The Sobrante Tower site may also accumulate more organic matter than the San Pablo Tower site because of its greater depth (i.e., 127 feet versus 74 feet at the time of sampling). Overall, anoxic release rates for both locations in were similar to rates measured in other local reservoirs, including Upper San Leandro Reservoir (5 15 mg-n/m 2 d) and Lafayette Reservoir (15 25 mg-n/m 2 d) (Beutel 2006). Anoxic release rates of ammonium from San Pablo Tower sediments were typical of eutrophic lakes (10 20 mg-n/m 2 d), while rates from Sobrante Tower SB were typical of hypereutrophic lakes (20 40 mg-n/m 2 d) (Beutel 2006), suggesting that internal loading is an important component of nitrogen cycling in San Pablo Reservoir under current conditions (Appendix B). However, development of an annual nutrient budget for the reservoir would help to confirm the relative importance of both internal and external nitrogen loading and implications for algal growth Phosphorus Results of the chamber experiments suggest that oxygenated conditions at the sediment water interface in would also promote the formation of iron hydroxides that bind with phosphate and repress its release from sediments (Appendix B). Under oxic conditions, sediment chambers exhibited negligible (San Pablo Tower site) to low ( mg-p/m 2 d; Sobrante Tower site) release rates. Under anoxic conditions, orthophosphate was released from the sediments in all chambers, increasing to approximately mg-p/m 2 d (San Pablo Tower site) and 8 13 mg-p/m 2 d (Sobrante Tower site). The sediment release rates were slightly greater than rates reported in prior studies at nearby reservoirs, including 5 mg- P/m 2 d at Upper San Leandro Reservoir and 8 9 mg-p/m 2 d at Lafayette Reservoir (Beutel 2000). Sediment release rates were typical of eutrophic lakes (5 20 mg-p/m 2 d) (Nurnberg 1994), suggesting that internal loading is an important component of phosphorus cycling in San Pablo Reservoir under current conditions (Appendix B). As with nitrogen, development of an annual nutrient budget for the reservoir would help to confirm the relative importance of both internal and external phosphorus loading and implications for algal growth. Further, determination of iron and phosphorus content of reservoir sediments would provide additional information regarding the long-term phosphorus-binding capacity of reservoir sediments. An iron to phosphorus mass ratio ranging from 5:1 to 15:1 is typically recommended to ensure that sediment has enough 15

20 binding capacity to retain phosphate under oxic conditions. Should sediment be low in iron relative to phosphorus, enhancement strategies could be considered (e.g., alum addition) to enhance the capacity for long-term phosphorus inactivation Manganese and Iron Manganese and iron fluxes followed expected patterns in the sediment chambers, with concentrations in the overlying water column decreasing under oxic conditions and increasing under anoxic conditions (Appendix B). Under oxic conditions, manganese and iron concentrations decreased in the overlying chamber water due to biotic and abiotic oxidation of dissolved forms to the particulate metal oxides, which then settled on the surface of the sediments. At the end of the 12-day oxic phase, metal concentrations in chamber water from both sampling sites were less than 0.06 mg/l for manganese and 0.2 mg/l for iron, where the secondary maximum contaminant limit (SMCL) for manganese is 0.05 mg/l dissolved and iron is 0.3 mg/l dissolved. Under anoxic conditions, manganese concentrations peaked at mg/l (Sobrante Tower site) and mg/l (San Pablo Tower site), with corresponding sediment release rates of (Sobrante Tower site) and 5 40 mg/m 2 d (San Pablo Tower site). Iron concentrations peaked at mg/l (both sites), with release rates of 5 20 mg/m 2 d (Sobrante Tower site) and 5 10 mg/m 2 d (San Pablo Tower site). As described for nutrients, the deeper sediments near the Sobrante Tower likely accumulate more organic carbon due to more sustained anoxic conditions, making theses sediments relatively more conducive to releasing metals than those at San Pablo Tower. In chambers from both sites, manganese was released from sediment immediately upon the onset of anoxic conditions with release rates decreasing over time, whereas iron release lagged but then exhibited continuing release. This is consistent with typical redox and mineral oxide dissolution patterns for these two metals. iron release rates were slightly lower than those measured from sediments in nearby Lafayette Reservoir (20 40 mg/m 2 d) (Beutel 2000) and on the lower end of those measured in sediment from the eutrophic Lake Hodges Reservoir (San Diego, CA) mg/m 2 d (Beutel 2015). Overall, the sediment release rates measured for were typical of those reported for eutrophic lakes (10 50 mg/m 2 d for manganese and iron) (Beutel 2000). 3.4 Algae Planktonic Planktonic algae (i.e., phytoplankton) are algae that float in the water column. The District has collected phytoplankton samples at multiple sites in on an approximately monthly basis since 2010, with large temporal data gaps in 2012 and Sample collection has occurred at the reservoir surface and at depth, following American Public Health Association (APHA) Standard Method (SM) Plankton, with algal identification to genus. Based on available data, the phytoplankton community composition varies annually and seasonally (Figure 10) and is dominated by diatoms (Bacillariophyceae) and cyanobacteria (Cyanophyceae). Diatoms typically comprise 38% of total phytoplankton abundance, compiled across sampling sites for the period , while cyanobacteria account for 26% of total abundance. Diatoms are present in low to moderate levels year-round, with one bloom (where bloom is defined as > 1x10 6 cells/100ml) observed in the summer of Green algae (Chlorophyceae), which comprise 18% of total abundance on average, bloomed in the summer of Euglenids (Euglenophyceae), which typically comprise a low proportion of total abundance, bloomed in February

21 Figure 10. Phytoplankton by group compiled across surface, elevation 267-feet and 283-feet sampling locations for the period Cyanobacteria abundance varies annually and seasonally, with blooms commonly occurring in May July following reservoir stratification onset (Figure 11). In general, cyanobacteria blooms occur after stratification, when relatively high nutrient concentrations (resulting from runoff during wet periods and benthic upwelling following reservoir mixing) coincide with warm water temperatures in the photic zone. However, additional data are necessary to assess the association between cyanobacteria blooms and seasonal variations in nutrient concentrations in San Pablo Reservoir. 17

22 2.5E E+07 Cell count (#/100mL) 1.5E E E E+00 1/19/2010 4/20/2010 5/25/2010 6/15/2010 7/7/2010 7/27/2010 8/17/2010 9/7/2010 9/30/ /2/2010 4/26/2011 7/12/ /11/2011 1/22/2013 1/7/2014 3/12/2014 4/24/2014 6/3/2014 7/15/ /7/2014 2/17/2015 5/22/2015 8/18/ /20/2015 1/20/2016 4/19/2016 7/19/2016 Figure 11. Cyanobacteria (Cyanophyceae) abundance by date, compiled across surface, elevation 267-feet and 283-feet sampling locations for the period Benthic Benthic algae are attached species associated with sediments and other bottom substrates (e.g., rocks, rooted aquatic macrophytes) within the photic zone of a waterbody, such as shallow areas near the shoreline. Benthic algae can be an important component of overall primary productivity in lakes and reservoirs. Although there are no available benthic algae data for San Pablo Reservoir, they may be an important part of the algal community with respect to overall nutrient cycling and/or production of T&O compounds (see Section 3.6.2). 3.5 Trophic Status and Nutrient Limitation The Trophic State Index (TSI) developed by Carlson (1977) is one available tool for assessing s relative productivity. The trophic state of a lake or reservoir is based on overall system productivity and is a function of both physical features (e.g., latitude and elevation; ratio of watershed to waterbody areas; reservoir depth; hydraulic residence time), chemical features (e.g., nutrients, oxygen) and biological responses (e.g., primary productivity, zooplankton and fish assemblage food webs and biomass). The trophic status of San Pablo Reservoir was examined using the Carlson TSI for temperate lakes to validate assumptions about the relationships between measured physical and chemical parameters. TSI is a quantitative lake index ranging from 0 to 100 (Table 3). 18

23 TSI Table 3. Carlson TSI associations with water quality. Trophic status and water quality conditions < 30 oligotrophic; clear water; high DO throughout the year in the entire hypolimnion oligotrophic to mesotrophic; clear water; possible periods of limited hypolimnetic anoxia mesotrophic; moderately clear water; increasing chance of hypolimnetic anoxia in summer; fully supportive of all swimmable/aesthetic uses mildly eutrophic; decreased transparency; anoxic hypolimnion; macrophyte problems; warm-water fisheries only; supportive of all swimmable/aesthetic uses but threatened eutrophic; cyanobacteria dominance; scums possible; extensive macrophyte problems hyper-eutrophic; heavy algal blooms possible throughout summer; dense macrophyte beds > 80 algal scums; summer fish kills; few macrophytes due to algal shading TSI values are based on the relationship between nutrients (as measured by total phosphorus), algal biomass (chlorophyll-a), and water clarity (Secchi disk depths). Three relationships are used to estimate the TSI: TSI SD = ln (Secchi depth in m) Equation 1 TSI Chl-a = ln (chlorophyll-a in µg/l) Equation 2 TSI TP = ln (TP in µg/l) Equation 3 Although these values may be averaged, differences between them can indicate other important water quality conditions. For example, the reservoir may be light- or nitrogen-limited instead of phosphorus-limited, and Secchi depth may be affected by transport of silt or clays rather than by algae. With the exception of relatively low chlorophyll-a data in the fall, TSI values based on TP (TSI = 56 to 69) and chlorophyll-a (TSI = 43 to 62) for indicate the reservoir is mildly eutrophic to eutrophic (Table 4). Secchi depth data are relatively limited for the period and are therefore not included in the TSI calculations. Table 4. Carlson TSI for. Parameter Winter (Dec Feb) Spring (Mar May) Summer (Jun Aug) Fall (Sept Nov) Mean TP a (ug/l) Mean Chl-a (ug/l) b Trophic Status Index (TSI) TSI (TP) a TSI (Chl-a) a Water column samples collected at Sobrante Tower 267' elevation. Available data Oct 2010 Jun b In situ measurements in surface waters. 19

24 To examine potential phosphorus and nitrogen limitations in, the mass ratio of N:P was estimated from the sum of total nitrogen (nitrate + nitrite + ammonium + organic nitrogen) divided by total phosphorus, for available data. Results were compared to empiricallyderived ratios for freshwater algae, where a mass N:P ratio greater than 17 suggests phosphorus limitation, a ratio less than 10 suggests nitrogen limitation, and values between 10 and 17 suggest that either nutrient may be limiting (Forsberg and Ryding 1980, Hellström 1996). Mass ratios of total inorganic nitrogen (TIN = nitrate + nitrite + ammonium) and soluble reactive phosphorus (SRP) (SRP = orthophosphate) also were calculated as an indication of the relative amounts of the more bioavailable fractions of nitrogen and phosphorus. Limited data collected from elevation 267-feet (i.e., n = 6 in March, July, and August 2013) suggest co-limitation of nitrogen and phosphorus is more likely than limitation by either nitrogen or phosphorus in (Table 5). However, given that data are so limited, and they are predominantly from the hypolimnion during summer stratification, it is difficult to draw overarching conclusions regarding nutrient limitation of algae in the reservoir. 3.6 Manganese and Taste and Odor Compounds Soluble manganese Manganese data were not collected in the water column during the period ; rather, manganese concentrations are routinely quantified in the WTP raw water. Accordingly, manganese data and associated trends are discussed in Section Geosmin and MIB Planktonic Cyanobacteria (Cyanophyceae) are commonly implicated as the source of geosmin and MIB in reservoirs. However, only some genera of cyanobacteria can produce geosmin and MIB, and within those genera, actual production is strain- and condition-dependent. Analysis of planktonic cyanobacteria cell counts and geosmin and MIB concentrations over time shows that total cyanobacteria abundance is not correlated with geosmin concentration in (Figure 12). Further analysis of abundance and geosmin concentration using ln-transformed data to account for data distributions that are skewed by a small number of very high values, also indicates a lack of correlation between these two variables (R 2 =0.01, p=0.4). These findings suggest that: (a) reservoir production of geosmin by cyanobacteria varies with unidentified parameters; (b) geosmin production is not distributed equally across planktonic cyanobacteria taxa; (c) other phytoplankton taxa contribute significantly to geosmin production; and/or (d) other sources, such as benthic algae, contribute significantly to geosmin production. A number of phytoplankton taxa other than Cyanophyceae found in are known to produce geosmin and/or MIB (Table 6). On average, genera capable of producing geosmin comprise only six percent (6%) of total algal abundance. Existing data indicate that total abundance of potentially geosmin-producing taxa does not predict water column geosmin or MIB concentrations (Figure 13). Additional data are necessary to identify the primary sources of geosmin and MIB in, as well as the conditions under which high levels of these compounds are produced. 20

25 Table 5. Mass ratios of nitrogen to phosphorus in. Collect date Ammonium as N (mg/l) Nitrate as N (mg/l) Nitrite as N (mg/l) TKN as N (mg/l) Org-N (mg/l) Orthophosphate as P (mg/l) Total phosphorus as P (mg/l) TN:TP Suggested nutrient limitation TIN:SRP Suggested nutrient limitation 3/1/ N, P 7/25/ N, P 13 N, P 8/1/ P 9 N, P 8/8/ N, P 7 N, P 8/15/ N, P 2 N 8/22/ P 18 P 8/29/ P 4 N Ammonium MDL = 0.01 mg/l; nitrate MDL = mg/l; nitrite MDL = mg/l; TKN MDL = XX mg/l; orthophosphate MDL = mg/l; total phosphate MDL = XX mg/l. 21

26 Cyanophyceae TW SO 267 Cyanophyceae TW SO 283 TW SO 283 MIB TW SO 267 MIB TW SO 283 Total Geosmin TW SO 267 Total Geosmin 1.E+07 10,000 1.E+06 1.E+05 1,000 Cyanophyceae (#/100ml) 1.E+04 1.E+03 1.E+02 1.E E+00 1.E-01 0 Jan-2010 Apr-2010 Jul-2010 Oct-2010 Jan-2011 Apr-2011 Jul-2011 Oct-2011 Jan-2012 Apr-2012 Jul-2012 Sep-2012 Dec-2012 Apr-2013 Jul-2013 Sep-2013 Dec-2013 Apr-2014 Jul-2014 Sep-2014 Dec-2014 Apr-2015 Jul-2015 Sep-2015 Dec-2015 Mar-2016 Jun-2016 Sep-2016 Dec-2016 Geosmin and MIB (ng/l) Figure 12. Total cyanobacteria (Cyanophyceae) counts and geosmin and MIB concentrations in at Sobrante Tower (TW SO) at gate elevations 267 and 283 feet for the period The horizontal black line represents the geosmin and MIB concentration (5 ng/l) at which taste and odor complaints typically occur for San Pablo Reservoir. Table 6. Potential geosmin- and MIB-producing cyanobacteria genera in. Group Cyanobacteria (Cyanophyceae) Genus Potentially geosminproducinproducing Potentially MIB- Anabaena X Aphanizomenon X Oscillatoria X X Pseudanabaena X X 22

27 3.00E E Count (#/100ml) 2.00E E E Geosmin Concentration (ng/l) 5.00E E+00 0 ANABAENA LARGE CELL ANABAENA MEDIUM CELL ANABAENA SML CELL COILED ANABAENA SML CELL STRAIGHT APHANIZOMENON OSCILLATORIA PSEUDANABAENA TW SO 267 Total Geosmin Figure 13. Total geosmin-producing cyanobacteria abundance and geosmin concentrations at Sobrante Tower at reservoir elevation 267 feet for the period Benthic Often overlooked by water utilities suffering from T&O events is the potential for production by benthic (attached) cyanobacteria, especially if planktonic species also are present. If treatment is proposed for a T&O event, then it is imperative to identify the specific source of the production correctly since treatment methods differ for planktonic and benthic algae. Planktonic problems often are readily observed in the surface water and sample collection is easy. Benthic production is not always visible and sampling is more of a challenge, requiring modified sampling techniques or SCUBA. It is more difficult to determine the cause of a benthic T&O problem than a planktonic one, and this difference is due in large part to the relative scarcity of literature data characterizing benthic T&O problems. The Metropolitan Water District of Southern California (MWD) has decades of experience dealing with both types of T&O production. Early in MWD's program in the late 1980s, Lake Mathews, a large surface water reservoir in Riverside County, California, was treated at excessive rates with copper sulfate for what was thought to be a planktonic issue for several years because the importance of benthic production was not understood. Divers finally found the T&O source in an unexpected location between 30 and 80 feet deep, previously thought to be a light-limiting zone. The MIB-producing Phormidium sp. was low-light adapted and able to form carpet-like mats across hundreds of acres of the reservoir bottom sediments. With this knowledge, treatment strategies were modified to target the Phormidium mats with great success and with significant reductions in copper sulfate and application effort. Since then, MWD isolated and cultured dozens of cyanobacteria producing 23

28 MIB and geosmin, where many of the species were benthic. Attached algal species can thrive in water with low nutrient concentrations. In flowing water, such as transfer and supply canals, nutrients are continually delivered to the algae, while on lake and reservoir bottoms the algae have ready access to sediment-associated nutrients. During T&O events where planktonic conditions do not fully explain T&O production, extending the search for benthic production sites is advisable. Generally, benthic T&O producers take longer to create unacceptable conditions compared to planktonic blooms, where the latter can create extreme conditions within one or two weeks. Finally, it is not uncommon to have multiple producing species active at the same time. This subject is more thoroughly reviewed in AWWARF (2006). As previously noted, the District has no available benthic algae data for. Additionally, given the relatively low phytoplankton biomass observed during or just after the most recent T&O event in (mid- to late September 2016) and the lack of any discernable relationship between geosmin or MIB water concentrations and cyanobacteria (Cyanophyceae) abundance for species capable of producing these compounds during the September 29 synoptic survey (see Appendix A), a benthic algae may be a component to T&O events in. Accordingly, the forthcoming Task 5 Water Quality Monitoring Plan under this project will consider a benthic algae monitoring component and the potential for supporting rapid District mobilization for bloom-related sampling to connect T&O events more definitively to particular algal species and habitats. 4 SOBRANTE WATER TREATMENT PLANT Sobrante WTP is a 60-million-gallon/day (MGD) conventional treatment plant located in El Sobrante, just northwest of. The WTP consists of aeration, coagulation, flocculation, sedimentation, ozonation, filtration, and disinfection (EBMUD 2015a). Raw and treated water quality at the Sobrante WTP were evaluated for the period in order to: Assess potential trends in raw water total manganese and other inorganic constituents as an indication of San Pablo reservoir water quality over time, as well as the capability and capacity of the Sobrante WTP to maintain manganese concentrations below the secondary maximum contaminant limit (SMCL) (manganese = 0.05 mg/l dissolved; iron = 0.3 mg/l dissolved). Further inform the evaluation of water quality and biological activity in San Pablo Reservoir related to earthy/musty taste and odor (E/M T&O) events. 4.1 Inorganic Water Quality Constituents The entire period was analyzed where data were available; in a few cases (e.g., DO), only more recent data were available. Based on the District s existing data, raw water manganese concentrations tended to increase during the late summer/early fall months, coincident with reductions in DO in the reservoir s water column. Figure 14 through 20 present measured DO and total manganese for the period These results are decoupled through most of the year since for all data shown, the reservoir withdrawals occurred at elevation 267 feet which was primarily from the upper hypolimnion but occasionally originated from within the epilimnion or metalimnion (Figure 4). In 2012, withdrawal at the 267-ft gate would have extracted water primarily from the upper hypolimnion. There are not enough 2013 in situ data to confirm the link 24

29 between withdrawal gate elevation and lake layers during this year, but based on the steep reservoir drawdown from April 2013 to November 2013, it is likely that the 267-ft gate started out in the hypolimnion in April and moved into the epilimnion by August. Such a change would explain the increasing DO and decreasing total manganese concentrations (Figure 15). The 267-ft gate was located within the upper hypolimnion in April, and likely moved into the bottom of the epilimnion by mid-june. Interestingly, low DO appears to have extended up into the epilimnion in June (Figure 4 and Figure 16). While the 267-ft withdrawal appears to have been located within the bottom of the epilimnion in early to mid-summer 2015, insufficient profile data are available to confirm that this change corresponded with the dip in raw water DO exhibited in mid-july (Figure 17). In 2016, it appears that the 267-ft gate was extracting water from the bottom of the epilimnion and again low DO extended up into the epilimnion (Figure 18). Overall, raw water DO concentrations were consistently greater than 0 mg/l, with a minimum value of approximately 2 mg/l. Total manganese concentrations were frequently low, indicating that for the most part WTP raw water did not include water rich in soluble manganese originating from the deeper portion of the hypolimnion (i.e., where manganese solubilization from anoxic sediments can occur). However, the periodic and seasonal elevated manganese concentrations in WTP raw water indicates that the hypolimnion experienced some degree of vertical mixing during periods of stratification, transporting soluble manganese from just above the sedimentwater interface upward to the top of the hypolimnion. For example, the raw water total manganese concentration increased dramatically (e.g., July/August 2012, late 2013, and late 2015) when water was withdrawn from the epilimnion, coincident with lower water surface elevations or from a water column mixed nearly uniformly top to bottom. In the latter case, manganese solubilized in anoxic sediments during reservoir stratification and residing in the hypolimnion, would have suddenly mixed throughout the water column. Figure 14. Raw dissolved oxygen (DO) and total manganese (Mn) concentrations at Sobrante WTP in

30 Figure 15. Raw dissolved oxygen and total manganese concentrations at Sobrante WTP in Figure 16. Raw dissolved oxygen and total manganese concentrations at Sobrante WTP in

31 Figure 17. Raw dissolved oxygen and total manganese concentrations at Sobrante WTP in Figure 18. Raw dissolved oxygen and total manganese concentrations at Sobrante WTP in Other raw water inorganic constituents, including iron, nitrate, and sulfate (SO 4- ), exhibited patterns relative to DO and total manganese for the period Figure 19 provides a comparison between raw water DO and total manganese, iron, nitrate, and sulfate concentrations for the period The raw water data show that DO decreased as the seasons progressed from spring through fall, followed by increases with late fall/winter vertical mixing in the reservoir. This pattern could require WTP oxidation for iron and manganese removal. For example, elevated raw water iron and manganese concentrations would tax the WTP s oxidation systems and consume ozone that would serve the District better if it remained available to oxidize 27

32 organic matter. Treated water iron and manganese concentrations never exceeded their SMCLs (Figure 20). Figure 19. Raw water iron, nitrate and manganese concentrations compared to raw water DO for the period Figure 20. Treated water iron, manganese, sulfate and nitrate compared to raw water DO concentrations for the period

33 4.2 Geosmin and MIB The Sobrante WTP has experienced periodic E/M T&O events in the spring and the summer for several years, consistent with water quality indicators in. The primary E/M T&O source is algae in, upstream of the WTP. Odor threshold concentration (OTC) studies report OTCs ranging from 1 to 15 ng/l at room temperature for both geosmin and for MIB. When geosmin and MIB are both present, their effects are additive. The presence of chlorine or chloramine can mask geosmin and MIB odors (Oestman et al. 2004). The water industry considers a range of 5 to 10 ng/l to be the general public s OTC (Mackey et al. 2013). EBMUD uses the lower end of the OTC, 5 ng/l, as a treatment goal to minimize consumer detection of musty/earthy T&O. These values are based upon the geosmin or MIB geometric mean where 50 percent of the population can detect them. The OTC has a corresponding Flavor Profile Analysis (FPA) value of 1, correlating to a slight odor intensity for the average consumer. A review of the recent trends for geosmin and MIB concentrations in the Sobrante WTP raw water indicates that the WTP experiences E/M T&O events in the spring and summer months, typically peaking in May and June; such events also occurred in July and August during the period These events typically last about two weeks (Figure 21). Figure 21. Raw water MIB and geosmin concentrations for the period 2009 September Consistent with reservoir data (Figure 12), E/M T&O in raw water at Sobrante WTP does tend to co-occur with an increase in cyanobacteria (Cyanophyceae) counts in the reservoir, as well as raw water temperature; however, neither show a clear correlation and are not predictive of an E/M T&O event (Figure 22 and Figure 23). 29

34 Figure 22. Reservoir cyanobacteria (Cyanophyceae) abundance and raw water geosmin and MIB concentrations. Figure 23. Raw water temperature, geosmin and MIB concentrations. In 2013, the District drew the reservoir down significantly in the summer and geosmin concentrations peaked at significantly higher levels than in prior recent years. In 2014 and 2015, the geosmin peaks were even higher than in 2013 (Figure 24), potentially due to increasing drought effects on reservoir water quality, such as inflows of Sacramento River water from April 2014 through July 2014 and April 2015 through October 2015, rather than Mokelumne Aqueduct 30

35 water sourced from Pardee Reservoir (Section 3.1). Geosmin and MIB were both present in the incoming Sacramento River water, peaking at ng/l and 2 20 ng/l, respectively, between August and October Nutrients present in the Sacramento River (which may have contributed to the high geosmin and MIB levels in the influent river water) may have supported a larger cyanobacteria bloom, and the resulting higher MIB and geosmin concentrations, in those years. Geosmin was by far the largest contributor to E/M flavors for the period MIB concentrations remained well below the 5 10 ng/l OTC most of the time, even when geosmin was well above those values. Geosmin and/or MIB concentrations above ng/l typically result in a very significant increase in consumer complaints. Figure 24. Raw water MIB and geosmin concentrations for the period 2013 September The red dashed line represents the lower end of the OTC (5 ng/l) as a treatment goal to minimize consumer detection of musty/earthy T&O. Sobrante WTP uses ozonation treatment and recently has upgraded this system to provide enhanced oxidation power, to address geosmin, MIB and other target organic contaminants. Even during intense E/M T&O events, the WTP can, in most instances, maintain geosmin concentrations at or near the OTC; furthermore, the treated water MIB has remained well below the OTC for all instances analyzed (Figure 25). A frequency analysis indicates that the E/M T&O of the treated water was below the upper end of the OTC 92% of the time, and the upper end of the OTC 98% of the time (Figure 26). Unless a relatively extreme T&O event occurs, as was seen in 2014 and 2015, the WTP (before the ozonation system improvements) had capacity and capability to remove most of the geosmin. 31

36 Figure 25. Treated water MIB and geosmin concentrations for the period 2009 September The red dashed line represents the lower end of the OTC (5 ng/l) as a treatment goal to minimize consumer detection of musty/earthy T&O. Figure 26. Frequency of treated geosmin concentrations for the period The red dashed line indicates the lower end of the OTC (5 ng/l) as a treatment goal to minimize consumer detection of musty/earthy T&O. 32

37 This analysis suggests that the current Sobrante WTP treatment train should handle most geosmin events successfully if the peak geosmin levels can be reduced to less than ng/l, depending upon the goal. An analysis of geosmin removal across the WTP, both in terms of percent removal (Figure 27) and raw influent versus effluent numbers (Figure 28), indicates that at influent concentrations below 50 ng/l, the effluent geosmin concentration was below the lower end of the OTC (5 ng/l) except for one instance on April 28, As the concentration rose to ng/l, treated water exceeded the lower OTC 32% of the time, with the concentration never exceeding about 10 ng/l, the upper end of the OTC. At that level, most consumers would have perceived a slight to moderate odor. In the ng/l range, the concentration also stayed below the lower OTC about two thirds of the time, and exceeded 10 ng/l in only two instances (on 5/24/2010 and 5/25/2010), when a strong odor would have been expected to be reported. The data indicate only eleven raw water quality measurements above 200 ng/l, peaking at 530 ng/l. In all cases, 95% removal or greater was achieved. As one would expect, with very high levels of geosmin, excursions above the lower OTC occurred more frequently and were more intense. However, the measured effluent geosmin concentration was below the OTC about one third of the time. Figure 27. Percent removal of geosmin for different influent concentration ranges at Sobrante WTP. 33

38 Figure 28. Raw water vs. treated water geosmin concentrations at the Sobrante WTP for different raw water concentration ranges. The red dashed line represents the lower end of the OTC (5 ng/l) as a treatment goal to minimize consumer detection of musty/earthy T&O. The aforementioned analysis indicates that the Sobrante WTP is capable of treating modest geosmin T&O events and can control many events with geosmin concentrations in the vicinity of 100 ng/l. However, ozonation is expensive and in-reservoir mitigation measures may reduce geosmin peak concentrations in raw water in the spring and summer, therefore reducing WTP maximum ozone doses. 5 SUMMARY OF KEY FACTORS INFLUENCING THE PRODUCTION OF TASTE & ODOR COMPOUNDS AND SOLUBLE MANGANESE IN SAN PABLO RESERVOIR The following are identified as key factors and variables that influence formation of geosmin, MIB, and soluble manganese in : Nitrate and phosphorus from local sources support relatively high productivity of planktonic algae, including cyanobacteria, in surface waters. Cyanobacteria can produce elevated concentrations of geosmin and MIB during intense blooms, although planktonic cyanobacteria abundance is not well correlated with geosmin and MIB levels in the reservoir, suggesting a planktonic source that is present at low abundance and/or a potential benthic source. High planktonic algal productivity provides an ongoing source of organic carbon to fuel the microbial community in the reservoir sediments and the water column, which in turn deplete dissolved oxygen from the hypolimnion and reservoir sediments during periods of stratification. Highly stable thermal stratification throughout the reservoir limits resupply of dissolved oxygen to bottom waters and reservoir sediments for 6 8 months each year. Low to no 34

39 oxygen for extended periods facilitates reduction of soluble manganese and release from reservoir sediments, along with other redox-sensitive compounds such as ammonium, orthophosphate, iron, sulfate, and potentially methylmercury. Ammonium and orthophosphate released from anoxic reservoir sediments contribute to overall internal nutrient loading that can further stimulate algal productivity in subsequent seasons. 6 RECOMMENDATIONS/NEXT STEPS Forthcoming tasks for the Water Quality Improvement Project include the evaluation of alternatives for improving reservoir water quality (Tasks 3 and 4) and development of a water quality monitoring plan associated with the preferred alternative (Task 5). The latter will include recommendations for additional monitoring to confirm levels of nitrogen and phosphorus entering the reservoir from local sources and Mokelumne Aqueduct inflows (i.e., Pardee Reservoir and Sacramento River sources), as well as targeted monitoring to identify planktonic and/or benthic algal species responsible for producing geosmin and MIB in the reservoir. 35

40 7 REFERENCES Beutel, M. W Inhibition of ammonia release from anoxic profundal sediments in lakes using hypolimnetic oxygenation. Ecological Engineering 28: Carlson, R. E A trophic state index for lakes. Limnology and Oceanography 22: EBMUD (East Bay Municipal Water District) Water Supply Engineering Statistical Report. Fiscal Year Ending June 30, p. EBMUD. 2015a. East Bay Watershed Sanitary Survey 2015 Update. December p. EBMUD. 2015b. Water Supply Engineering Statistical Report. Fiscal Year Ending June 30, p. EBMUD Freeport Regional Water Project 2015 Operations After-Action Report. EBMUD Water Operations Department. June p. Forsberg C., and S. O. Ryding Eutrophication parameters and trophic state indices in 30 Swedish waste-receiving lakes. Arch Hydrobiol 89: Hellström T An empirical study of nitrogen dynamics in lakes. Water Environ Research 68: Mackey, E. D, I. H. Suffet, and S. D. J. Booth A decision tool for earthy/musty taste and odor control. Water Research Foundation, Denver, Colorado. Nurnberg, G. K Phosphorus release from anoxic sediments: What we know and how we can deal with it. Limnetica 10: 1 4. Oestman, E., Schweitxer, L., Tomboulian, P., Suffet, M Effects of chlorine and chloramines on earthy and musty odors in drinking water. Water Science & Technology 49:

41 Appendices

42 Appendix A Late Summer/Early Fall 2016 Algal Associations with Geosmin and MIB Production

43 The District conducted additional algae and water quality sampling in on September 29, 2016, within days to a week of T&O complaints from customers receiving drinking water from the San Pablo WTP (Sobrante WTP was taken off line in early September 2016 in preparation for an upcoming Orinda WTP outage). The objective of the additional monitoring was to conduct a synoptic survey of water samples from in order to characterize the spatial distribution and abundance of planktonic algae, as well as geosmin and MIB concentrations, during a late summer bloom, with cyanobacteria identified to species. Sampling involved collection of in situ vertical profiles and grab samples at four sites in San Pablo Reservoir, including two sites along the main body of the reservoir, one site in the north eastern arm, and one site in the shallow portion of the reservoir near the mouth of San Pablo Creek (Table A-1, Figure A-1). In situ water quality parameters (water temperature, DO, ph, turbidity) were measured at each site to establish the relative depths of the epilimnion and metalimnion, such that samples could be collected 3 6 feet below the transition between the epilimnion and metalimnion (Table A-2, Figure A-2). Table A-1. Sampling sites. Site ID Description Latitude Longitude SOTW At San Pablo Tower, in vicinity of dam 37 56'29.88"N '37.03"W SPEA In shallow eastern arm of reservoir Along longitudinal center line of reservoir, approximately midway along the main reservoir body At Inlet, near mouth of San Pablo Creek 37 56'35.01"N '38.49"W SPMID 37 55'38.77"N '44.58"W SPRI 37 55'0.75"N '51.65"W A-1

44 Figure A-1. water quality sampling sites for additional characterization of cyanobacteria, geosmin, and MIB. Table A-2. Sample location within the water column, type, and parameters. Sample location Sample type Parameters Entire water column Vertical profile Water temperature, DO, ph, turbidity Epilimnion Grab Geosmin, MIB, algal cell count, algal ID to genus, cyanobacteria ID to species Metalimnion, 1 2 m below the epilimnion transition Grab Geosmin, MIB, algal cell count, algal ID to genus, cyanobacteria ID to species A-2

45 SOTW 9/29/2016 SPEA 9/29/2016 Depth (ft) WQ metric (see legend for units) DO (mg/l) ph Temp (C) Depth (ft) WQ metric (see legend for units) DO (mg/l) ph Temp (C) Water Temperature (C) Water Temperature (C) SPMID 9/29/2016 SPRI 9/29/2016 Depth (ft) WQ metric (see legend for units) DO (mg/l) ph Temp (C) Depth (ft) WQ metric (see legend for units) DO (mg/l) ph Temp (C) Water Temperature (C) Water Temperature (C) Figure A-2. In situ water quality profiles (temperature, ph, and dissolved oxygen [DO]) in San Pablo Reservoir during the September 29, 2016 synoptic survey. Results indicate that overall phytoplankton abundance was extremely low across all sampling locations and there were no dominant species in the samples. This is suggestive that there was not an ongoing phytoplankton bloom in at the time of sampling. None of the phytoplankton species identified during the September 29, 2016 event (Table A-3) appear in the District s algal database for , as identified to genus level. However, APHA SM Plankton, with algal identification to genus, is not likely detect very small filamentous species, such as Romeria leopoliensis, which has just a few cells in each filament. Jaaginema sp. is also a very fine filamentous cyanobacteria that was previously classified as Oscillatoria, and Dolichospermum smithii was previously classified under Anabaena. Overall, the species assemblage identified in the September 29, 2016 event is typical for the region, and the lack of overlap between the September 29, 2016 event and the District s algal database for is likely due to the difference in identification methods. A-3

46 Table A-3. Cyanobacteria species identified during September 29, 2016 sampling. Species Anabaenopsis circinalis Anabaenopsis elenkinii Chrysosporum ovalisporum Dolichospermum smithii Jaaginema sp.? Planktolyngbya limnetica Pseudanabaena limnetica Romeria leopoliensis Sphaerospermopsis aphanizomenoides Potentially geosminproducing X X Potentially MIB-producing X X Geosmin concentrations in the reservoir ranged 6 21 ng/l (total) and 4 10 ng/l (dissolved). MIB concentrations ranged 1 2 ng/l (total and dissolved) at the time of sampling. Raw water geosmin and MIB concentrations ranged 4 14 ng/l and ng/l, respectively, 1 2 weeks prior to the synoptic sampling event. Reservoir concentrations ranged 4 54 ng/l (geosmin) and 1 2 ng/l (MIB) 1 2 weeks prior to the synoptic sampling event. Although two species were identified during the September 29, 2016 event that can produce geosmin and two species were identified that can produce MIB, consistent with analysis of prior existing data (Figure 13), the abundance of cyanobacteria (Cyanophyceae) capable of producing geosmin and MIB showed no discernable relationship with geosmin or MIB concentrations in the water column at the time of sampling (Figure A-3). However, given the low phytoplankton biomass, the September 29 samples probably do not explain the associated MIB and geosmin water column concentrations. MIB can remain in the water column for days to weeks after the producers are gone, while geosmin tends to break down quickly once production is halted. Overall, the data collected during the September 29, 2016 are suggestive of a benthic algae component to geosmin and/or MIB in. A-4

47 100, , Cyanophyceae Filament Count (#/100ml) 1, Geosmin Concentration (ng/l) SOTW-EPI SOTW-META SPEA-EPI SPMID-EPI SPMID-META SPRI-EPI 0 Geosmin-producing Cyanophyceae Total Geosmin (ng/l) Dissolved Geosmin (ng/l) 100, , Cyanophyceae Filament Count (#/100ml) 1, Concentration (ng/l) SOTW-EPI SOTW-META SPEA-EPI SPMID-EPI SPMID-META SPRI-EPI MIB-producing Cyanophyceae Total MIB (ng/l) Dissolved MIB (ng/l) 0 Figure A-3. Abundance of geosmin-producing cyanobacteria (Cyanophyceae) filaments with total and dissolved geosmin (top) and MIB-producing cyanobacteria (Cyanophyceae) filaments with total and dissolved MIB (bottom) at five sampling locations in San Pablo Reservoir on September 29, A-5

48 Appendix B Sediment Flux Study

49 SAN PABLO RESERVOIR SEDIMENT FLUX STUDY Dr. Marc Beutel November 13, 2016 SUMMARY With the assistance of East Bay Municipal Utility (EBMUD) field and laboratory staff, I implemented a field and laboratory effort to assess metal and nutrient flux dynamics from sediments under oxic and anoxic conditions. We monitored triplicate experimental sediment-water chambers containing deep-water sediment collected at the Sobrante intake tower and the San Pablo intake tower for a range of water quality parameters including manganese, iron, ammonia, nitrate and orthophosphate. Since the reservoir has a history of taste and odor events related to manganese, of particular interest was how sediment manganese release would respond to oxic versus anoxic conditions. An additional focus was the response of nutrient release from oxic versus anoxic sediments, since nutrients released from sediment can exacerbate phytoplankton growth in surface waters. Water quality cycling of manganese, iron, ammonia, nitrate and orthophosphate followed expected patterns under oxic and anoxic conditions. Oxic conditions resulted in a drop in water column manganese, iron and ammonia. Anoxic conditions resulted in sediment release of manganese, iron, ammonia and phosphate. The magnitude of anoxic fluxes of these compounds were typical of other eutrophic and hypereutrophic lakes and reservoirs (Beutel 2000, 2006, 2015). Anoxic release rates were higher at the Sobrante station compared to the San Pablo station, indicating that sediments at the deeper Sobrante Tower are richer in organic matter and have greater potential to recycle metals and nutrients under anoxic conditions. Experimental results confirm that redox processes control the cycling of manganese at the reservoir s sediment-water interface. An oxygenated sediment-water interface repressed the biotic reductive dissolution of manganese and iron oxides, thereby keeping the metals sequestered as solids in the sediment. The maintenance of a well-oxygenated sedimentwater interface should coincide with a decrease of manganese and iron in the water column of. Enhancing oxygen conditions in bottom waters, coupled with selective withdrawal of waters below where algae are active, should yield raw water that is low in manganese, iron, and algal-related taste and odor compounds. Experimental results also suggest that maintenance of a well-oxygenated sediment-water interface will coincide with decreases in the internal loading of nitrogen and phosphorus. In the chambers, oxygenated conditions promoted the conversion of ammonia to nitrate, and much of this nitrate was lost from the system via microbial denitrification as dinitrogen gas. Oxygenated conditions also promoted the formation of iron hydroxides that bind with phosphate and repress phosphate release from sediment. But without a clear understanding of a temporal pattern of both external and internal nutrient loading to the reservoir, it is difficult to predict how a decrease in internal nutrient loading would affect nutrient concentrations and algae growth. Thus, I recommend the development of B-1

50 an annual nutrient budget for the reservoir. I also recommend that sediments be analyzed for iron and phosphorus content. An iron to phosphorus mass ratio ranging from 5:1 to 15:1 is needed to ensure that sediment has enough binding capacity to retain phosphate under oxic conditions. In the case that sediment is low in iron relative to phosphorus, sediment treatment strategies could be considered to enhance the sediment s capability to bind phosphorus, an important limiting nutrient in freshwaters. METHODS On September 13, 2016, I collected sediment-water interface samples at two deep-water stations at the reservoir, the Sobrante intake tower (Station SB) and the San Pablo intake tower (Station SP) (Fig. 1 3). Station SB was 127 feet deep and Station SP was 74 feet deep at the time of sampling. At each station, I collected three sediment-water samples into specialized flux chambers using an Ekman dredge. I transported the chambers to the laboratory for testing in an incubator in the dark at 11 C, the approximate temperature of bottom water in the reservoir (Fig. 4). Testing consisted of two phases. For the first oxic phase (Fig. 5), chambers were incubated under oxygenated conditions by bubbling with air for 12 days. Water samples were collected at day 0 (September 15, 2016), day 3, day 6, day 9 and day 12. For the second anoxic phase (Fig. 6), chambers were topped up with lake bottom water and incubated under anaerobic conditions by bubbling with nitrogen gas for an additional 12 days. For the anoxic phase, water samples were collected at day 0 (September 27, 2016), day 3, day 6, day 9 and day 12. Water samples were collected into three sample bottles supplied by EBMUD: (i) total manganese and iron, which was preserved with 0.15% trace metals grade nitric acid; (ii) ammonia, which was filtered through pre-washed 0.45 micron filters and frozen; and (iii) nitrate and orthophosphate, which was filtered through pre-washed 0.45 micron filters and frozen. Due to the limited volume of the chambers, minimal water volumes were sampled. QA/QC samples included a set of bottle blanks and a set of samples with excess sample volume. Samples were shipped overnight to EBMUD for water quality analyses in two batches; after day 12 oxic and after day 12 anoxic. The EBMUD lab analyzed water samples (approximate method detection limits in parentheses) for several compounds of interest including: total manganese (0.1 ug/l), total iron (0.5 ug/l), total ammonia (0.01 mg-n/l), nitrate (0.001 mg-n/l) and orthophosphate (0.001 mg-p/l). Estimating mass flux (mass per time and area, mg/m 2 d) is a practical way of assessing the effects of redox status on metal and nutrient cycling in sediment-water chamber experiments. Rates of flux of all compounds of interest were calculated for each set of samples collected 3 days apart (e.g, day 0-3, day 3-6, day 6-9, etc.). Thus, fluxes are reported for oxic phases 1-4 (blue bars in data figures) and anoxic phases 1-4 (brown bars in data figures). Fluxes in this study were calculated as the concentration at the end of the phase minus the concentration at the start of the phase, divided by the three day duration of the phase, divided by the area of the chamber (72 cm 2 ). A positive flux indicates that sediment released the compound of interest into overlying water. A negative flux indicates that the compound of interest was lost from the water column, either via a transformation where it was sequestered in the sediment (e.g., oxidation of dissolved B-2

51 reduced manganese into particulate oxidized manganese and subsequent gravitational settling onto sediment) or disappeared from the water altogether (loss of ammonia under oxic conditions by nitrifying bacteria that convert it to nitrate). Water quality data is tabulated in the data appendix at the end of this report. RESULTS AND DISCUSSION Manganese and Iron Flux Manganese and iron fluxes followed expected patterns under oxic versus anoxic conditions (Fig. 7), with metal concentrations in water overlying sediment decreasing under oxic conditions and increasing under anoxic conditions. These results confirm that redox processes control the cycling of manganese at the reservoir s sediment-water interface, and that maintenance of a well-oxygenated sediment-water interface should coincide with a decrease of manganese and iron in the water column of San Pablo Reservoir. Enhancing oxygen conditions in bottom waters, coupled with selective withdrawal of waters below where algae are active, should yield raw water that is low in manganese, iron and algal-related taste and odor compounds. Oxic Phase. Under oxic conditions metal fluxes were negative as metal concentrations dropped in chamber water due to the biotic and abiotic oxidation of reduced/dissolved metals to oxidized/particulate metal oxides, which then settled out of chamber water. Typical metal concentrations at the start of the oxic phase were around 1,000 µg/l for manganese and 750 µg/l for iron in the SB chambers, and around 600 µg/l for both manganese and iron in SP chambers (Fig 8). At the end of the 12-day oxic phase, metal concentrations in chamber water from both sites were < 60 µg/l for manganese and < 200 µg/l for iron. Anoxic Phase. Under anoxic conditions, fluxes were positive for both metals in all chambers. Typical metal concentrations at the end of the 12-day anoxic phase were 2,000-2,700 µg/l for manganese in SB chambers, 1,100-1,500 µg/l for manganese in SP chambers, and 600-1,000 µg/l for iron in both chambers (Fig. 8). Manganese was released from sediment immediately upon the onset of anoxic conditions as indicated by high fluxes during anoxic phases 1 and 2 (peak fluxes of mg/m 2 d). Manganese fluxes then tailed off in magnitude during anoxic phases 3 and 4. This is expected for manganese, which is very susceptible to reductive dissolution by manganese-reducing bacteria under mildly reducing conditions. In contrast to manganese, iron flux tended to start a bit later (anoxic phase 2 or 3), continued throughout the anoxic incubation, and tended to peak in anoxic phase 4 (peak fluxes of 5-20 mg/m 2 d). These patterns are typical for iron oxides, which tend to undergo bacterial reductive dissolution at lower redox potential than manganese. In other words, iron release tends to occur after manganese release as redox potential continues to drop at the sediment-water interface. In addition, unlike manganese which readily dissolves under anoxic conditions, iron oxides have multiple forms, some that readily dissolve and others that are more resistant to reductive dissolution. As a result, iron release from sediment tends to be more sustained as redox continues to decline at the sediment-water interface. B-3

52 For both manganese and iron, anoxic flux rates were higher in SB chambers compared to SP chambers (30-60 versus 5-40 mg/m 2 d for manganese; 5-20 versus 5-10 mg/m 2 d for iron). The deeper sediments near the Sobrante Tower likely accumulate more organic carbon and inorganic particulates, making SB sediment especially conducive to releasing metals under anoxic conditions. Release rates measured in this study were typical of those reported in the literature for eutrophic lakes, which typically range from mg/m 2 d for manganese and iron (Beutel 2000). Anoxic iron flux measured in sediments from nearby Lafayette Reservoir were mg/m 2 d (Beutel 2000). Anoxic iron flux recently measured in sediment from Lake Hodges Reservoir, a eutrophic reservoir in San Diego, were mg/m 2 d (Beutel 2015). Nutrient Efflux Nutrient fluxes followed expected patterns under oxic versus anoxic conditions (Fig. 9), with chamber water decreasing in ammonia towards the end of the oxic phase and increasing in ammonia and phosphate under anoxic conditions. These results suggest that maintenance of a well-oxygenated sediment-water interface will coincide with a decreases in the internal loading of nitrogen and phosphorus in. But without a clear understanding of a temporal pattern of both external and internal nutrient loading to the reservoir, and the development of a nutrient budget for the reservoir, it is difficult to predict how a decrease in internal nutrient loading would affect nutrient concentrations and algae growth. But if the reservoir has a history of fall blooms that coincide with lake overturn, this is a good indication that internal nutrient loading drives algal productivity, at least in some parts of the year. This in turn would suggest that lowering internal nutrient loading by enhancing bottom water oxygen would lower algal productivity at some times of the year. With regards to phosphorus cycling, I recommend that sediments be analyzed for iron and phosphorus content. An iron to phosphorus mass ratio ranging from 5:1 to 15:1 is needed to ensure that sediment has enough binding capacity to retain phosphate under oxic conditions (Schauser et al. 2006, Welch and Cooke 1995, Jensen et al. 1992). If sediments are iron poor in, then maintenance of a well-oxygenated sediment-water interface may not be fully effective in repressing phosphate release from profundal sediment. A range of sediment amendments can be added to enhance phosphorus retention in profundal sediment (Cooke et al. 2013). Aluminum sulfate (alum) and sodium aluminate have been used extensively in Washington State, but the use of aluminum salts faces regulatory hurdles in California due to aquatic toxicity concerns. Iron salt addition has been used as well. Iron has the advantage of not being toxic to aquatic biota. But unlike aluminum oxides, iron oxides are redox sensitive and may not retain phosphate under anoxic conditions. Phoslock ( phoslock/) is a clay with a very high phosphorus sorption capacity. While relatively expensive, Phoslock has been used in Canada and Europe where regulatory agencies do not permit aluminum addition. Iron addition to sediment coupled with oxygen addition to bottom water could be advantageous from both an economic and regulatory perspective. B-4

53 Ammonia. Under oxic conditions, positive ammonia fluxes decreased in magnitude and turned negative at the end of the oxic phase (Fig. 9). Typical ammonia concentrations at the start and end of the oxic phase were around 1 mg/l and 2 mg/l in SB chambers (Fig. 8) and 0.5 mg-n/l and 0.1 mg-n/l in SP chambers. The source of ammonia flux was decay of organic matter in lake sediment. The continued presence of oxygen at the sediment-water interface promoted the growth of bacteria that oxidize ammonia to nitrate. Negative ammonia fluxes correspond with positive fluxes of nitrate. This pattern was especially apparent in chamber SP1, where an extreme negative ammonia peak (-27 mg-n/m 2 d) in oxic phase 3 corresponded with a high positive flux of nitrate (16.4 mg- N/m 2 d). SP chambers responded more rapidly to oxic conditions as indicated by negative ammonia fluxes occurring earlier in the oxic phase when compared to SB chambers. In addition, as with metal fluxes, anoxic ammonia fluxes were higher in SB chambers (10-35 mg-n/m 2 d) compared to SP chambers (5-15 mg-n/m 2 d). These observations support the contention that sediment at the deeper Sobrante Tower are richer in organic matter. Since sediment at this site remains anoxic much of the year, there is little chance that accumulated organic matter is oxidized by heterotrophic bacteria under oxic conditions. The SB site may also accumulate more organic matter than the SP site because of its greater depth (127 feet versus 74 feet at the time of sampling). Anoxic release rates from SP sediment were typical of eutrophic lakes (10-20 mg-n/m 2 d), while rates from SB were typical of hypereutrophic lakes (20-40 mg-n/m 2 d) (Beutel 2006). Previous studies at nearby reservoirs measured anoxic ammonia release rates of 5-15 mg-n/m 2 d at Upper San Leandro Reservoir and mg-n/m 2 d at Lafayette Reservoir (Beutel 2006). Under anoxic conditions chambers from both sites showed positive fluxes of ammonia. In all chambers, ammonia concentrations increased from < 0.5 mg-n/l at the start of the anoxic phase to 1-3 mg-n/l at the end of the anoxic phase (Fig. 8). As noted above, anoxic conditions promote ammonia accumulation through a combination of organic matter decay (an ammonia source) and repressed nitrification (an ammonia sink). Lower bacterial growth rates under anoxic conditions (i.e., lower rates of ammonia assimilation into bacteria biomass) may also partly account for ammonia accumulation under anoxic conditions. Phosphate. Under oxic conditions, SB chambers showed low phosphate fluxes ranging from mg-p/m 2 d (Fig. 9). SP chambers showed negligible oxic phosphate fluxes. Under anoxic conditions, phosphate concentrations in all chambers increased from around 0.05 mg-p/l at the start of the anoxic phase to around 0.8 mg-p/l at the end of the anoxic phase (Fig. 8). In SB chambers, phosphate release increased to 2-3 mg-p/m 2 d in anoxic phase 1 and then peaked in anoxic phase 2 (8-13 mg-p/m 2 d). In SP chambers, phosphate flux did not commence until anoxic phase 2 and peaked in anoxic phase 3 (10-14 mg-p/m 2 d). Phosphate fluxes are typical of levels reported for eutrophic lakes (5-20 mg-p/m 2 d) (Nurnberg 1994). Previous studies at nearby reservoirs measured anoxic phosphate release rates of around 5 mg-p/m 2 d at Upper San Leandro Reservoir and 8-9 mg-p/m 2 d at Lafayette Reservoir (Beutel 2000). Phosphate is typically found in sediment in organic matter and sorbed to solid iron oxides in surfacial sediment. This phosphate is released to overlying water through two B-5

54 mechanisms, decay of organic matter and release from iron oxides that undergo reductive dissolution at low redox potential. In oxic sediment with high phosphate sorption potential, typically quantified as high ratios of iron to total phosphorus in sediment, phosphate released via decay is sorbed to iron oxides. But in sediment with low phosphate sorption potential, phosphate released via decay diffuses into overlying water. In this way, oxic sediment may (e.g., SB sediment) or may not (SP sediment) be a source of phosphate to overlaying waters. Decay coupled with low rates of anaerobic bacterial growth and phosphorus uptake, and potentially release from the reductive dissolution of manganese oxides, accounted for low levels of phosphate flux in SB chambers during anoxic phase 1, and SP chambers during anoxic phase 2. Then as iron reduction commenced in the following phase in each set of chambers, phosphate flux peaked. Patterns of phosphate flux and iron flux under anoxic conditions were especially similar in SP chambers (linear regression, R 2 = 0.75, p < 0.001, n = 12). Based on the observed linkage between iron and phosphate, and presuming sediment has adequate phosphate retention capacity, repressing iron release from sediment should also repress sediment phosphate release in. B-6

55 REFERENCES Beutel, M.W., Final Lake Hodges Reservoir Sediment Flux Study. Report for City of San Diego to Brown & Caldwell Consultants, Walnut Creek, CA. August 14, Beutel, M.W., Inhibition of ammonia release from anoxic profundal sediments in lakes using hypolimnetic oxygenation. Ecological Engineering, 28(3), Beutel, M.W., Dynamics and control of nutrient, metal and oxygen fluxes at the profundal sediment-water interface of lakes and reservoirs. Doctoral dissertation, University of California, Berkeley. Cooke, G.D., Welch, E.B. and Peterson, S.A., Lake and Reservoir Restoration. Elsevier. Jensen, H.S., Kristensen, P., Jeppesen, E. and Skytthe, A., Iron: phosphorus ratio in surface sediment as an indicator of phosphate release from aerobic sediments in shallow lakes. Hydrobiologia, 235(1), Nurnberg, G.K., Phosphorus release from anoxic sediments: What we know and how we can deal with it. Limnetica, 10(1), 1 4. Schauser, I., Chorus, I., and Lewandowski, J., Effects of nitrate on phosphorus release: comparison of two Berlin lakes. Acta Hydrochim. Hydrobiol. 34(4), Welch, E.B. and Cooke, G.D., Internal phosphorus loading in shallow lakes: importance and control. Lake and Reservoir Management, 11(3), B-7

56 Figures B-8

57 Figure 1. with sampling Station SB near the Sobrante intake tower and Station SP near the San Pablo intake tower. Figure 2. Sediment-water chamber collection in on September 13, B-9

58 Figure 3. Sediment-water chamber collection in on September 13, 2016, traveling from the Sobrante intake tower (left in far ground) to the San Pablo intake tower. B-10

59 Figure 4. Sediment-water chambers in the laboratory incubator. B-11

60 Figure 5. Photos of chambers from stations SB (left) and SP (right) at the end of the oxic phase on September 27, Surface sediment is brown-red indicating the presence of iron and manganese oxides and a well-oxygenated sediment-water interface. Oxygen penetration into the sediment is ~1 mm. Note the lack of sediment macrobenthos (e.g. worm burrows), a result of the anoxic and sulfidic conditions of the sediments when they were sampled, conditions that are not conducive to aerobic life in the sediment. B-12

61 Figure 6. Photos of chambers SB (left) and SP (right) after the end of the anoxic phase on October 12, Surface sediment is blackish-gray due to the reductive dissolution of iron and manganese oxides. B-13