Lake restoration can be a dirty job.

Transcription

1 What Works Carter Lake: Restoring the Crown Jewel John Holz, Ph.D.; Sara Mechtenberg, PE; Mark Porath; and Chris Larson Introduction Lake restoration can be a dirty job. The restoration of Carter Lake was no different, both literally and figuratively, from navigating through toxic algae blooms to disposing of dead fish, coordinating the goals of two states and piecing together project funding. In many ways, the Carter Lake restoration provides a road map for unique and complex lake rehabilitation projects. Strong grass-root support, community-based planning, and innovative technical leadership formed the backbone of solutions that met competing lake user goals and addressed multiple pollutant sources. As a high-profile lake in the Omaha metropolitan area, Carter Lake had generated a lot of interest due to poor water quality and recreational use restrictions. The lake s struggle with water quality had compromised its local title as the Crown Jewel of the region. Years of effort from the community and intensive involvement from state and local government agencies have resulted in the following success story: The Rehabilitation of Carter Lake. Legend Lake Depths Based on WSE at ft Coves (22.0 acres) 0-2 ft (23.8 acres) 2-4 ft (18.8 acres) 4-6 ft (21.0 acres) 6-8 ft (67.4 acres) 8-10 ft (162.8 acres) ft (21.7 acres) ft (0.7 acres) > 14 ft (3.8 acres) Background Carter Lake is 315-acre oxbow lake that was formed when a side channel of the Missouri River became isolated from the main channel during an 1877 flood. The lake is located on the Nebraska/Iowa border and is surrounded by the cities of Omaha, NE and Carter Lake, IA (80% of the lake lies in Nebraska and 20% is in Iowa). This urban lake is relatively shallow with a mean depth of 7.2 feet and a storage volume of 2,320 acre-feet (Figure 1). Carter Lake has a watershed of 1,435 acres of mixed urban land uses and receives inputs from storm sewers and overland runoff. The lake has a recent history of poor water quality and is classified as hypereutrophic. Average total phosphorus (TP) concentrations at Carter Lake prior to restoration were very high (177 µg/l) during the summer and average water transparency was low (13 inches), due to high levels of algal and suspended sediment turbidity. Average chlorophyll a concentrations were very high (124 µg/l) due to frequent and intense algal blooms. The lake has a history of blooms of a toxin-producing species of cyanobacteria (genus = Cylindrospermopsis spp.) that closed the lake to primary contact recreation for 24 weeks during Figure 1. Bathymetric map of Carter Lake. 46 Spring 2015 / NALMS LAKELINE

2 2007 due to elevated microcystin concentrations. In 2002, Carter Lake was placed on Nebraska s Section 303(d) List of Impaired Waters for algal toxins, total phosphorus, total nitrogen, chlorophyll a, and ph. Carter Lake was also on the 303(d) in 2004 for bacteria, but was removed for this parameter in 2005 (NDEQ 2006; CLEAR WC 2008). The fish community prior to restoration was comprised of mostly common carp, gizzard shad, big- and small-mouth buffalo, black and yellow bullhead, yellow bass, and freshwater drum; fish species with low recreational fishing value and habitat denigrating life cycles. Located within the metropolitan Omaha area, Carter Lake remains a popular destination for fishing, swimming, jet skiing, waterskiing, power boating, wildlife viewing, and the Creighton University Rowing Team. Given that the lake is located in a high-use urban park and in close proximity to the largest population base in Nebraska and Iowa, the lake has a significant economic value to both Nebraska and Iowa. Despite the poor water quality, the estimated prerehabilitation economic value of Carter Lake was large (> $13 million annually) (Herriges 2009). Project Development and Initial Planning Although local interest in improving Carter Lake dates back to the 1980s, the awareness peaked after the 303(d) listing. In 2005 a local citizens group called the Carter Lake Preservation Society (CLPS) was formed. Since the lake is split between two states, this was the first group to unite those from different communities, cities, counties and states as a shared voice of advocacy. Their general mission is to improve the water quality and fish and wildlife habitat of the lake through cooperation with city, county, state and federal agencies as well as educational institution, foundations and other private resources. In early 2006, the Cities of Carter Lake and Omaha requested assistance from several resource agencies to address water quality issues and in July 2006 the Nebraska Department of Environmental Quality (NDEQ) initiated a communitybased planning process that was funded by the U.S. Environmental Protection Agency (EPA) Region 7 Section 319 Program. The planning process ultimately resulted in the Carter Lake Water Quality Management Plan (WQMP) in 2008 (CLEAR WC 2008). Two important groups were formed to guide the process: Carter Lake Environmental Assessment and Rehabilitation Water Council (CLEAR WC) a group of 15 interested citizens selected to represent the community. Technical Advisory Team (TAT) staff members from local, city, state, and federal agencies capable of providing technical input. The agencies involved included the City of Omaha, City of Carter Lake, NDEQ, Iowa Department of Natural Resources (IDNR), Nebraska Game and Parks Commission (NGPC), Papio-Missouri River Natural Resources District (P-MRNRD), West Pottawattamie Soil and Water Conservation District, U.S. EPA, University of Nebraska Extension, Carter Lake Preservation Society, Iowa Division of Soil Conservation, Natural Resources Conservation Service, and Metropolitan Area Planning Agency. Over a period of two years, these groups met 11 times to develop water quality goals for the lake and implementation strategies to meet those goals. Three public meetings were held to develop public awareness, gain input, develop project goals, and present final recommendations. Also in 2006, NDEQ initiated a Total Maximum Daily Load (TMDL) study on Carter Lake. The TMDL was later submitted jointly by Nebraska and Iowa and was approved by U.S. EPA Region 7 in 2007 (NDEQ 2007). The TMDL established a target TP concentration of 96 µg/l to achieve water quality that would fully support the lake s designated uses. In order to achieve the target concentration, the total annual phosphorus loading Table 1. Carter Lake Phosphorus Summary Existing* TMDL Goal WQMP Goal Phosphorus Concentration (µg/l) Phosphorus Load (lbs/yr) 3,166 1, Phosphorus Load Reduction (lbs/yr) --- 1,703 2,192 *as listed in the TMDL (NDEQ 2007) would need to be reduced from 3,166 lbs to 1,462 lbs, which is a 1,704-lb or percent reduction (CLEAR WC 2008). Phosphorus loading reductions remained the focus throughout the entire water quality improvement process. Table 1 summarizes the target phosphorus concentration and phosphorus load reduction goals set forth by the TMDL and the WQMP. Note that the communitybased plan set a more aggressive goal in order to achieve IDNR s Lake Restoration Program goal of 4.5 feet of water clarity. Estimating phosphorus sources and loads was the next step of the planning process. The watershed was modeled using the U.S. EPA-approved Spreadsheet Tool for Estimating Pollutant Load (STEPL) to calculate the watershed load on a subbasin level. The internal phosphorus load was estimated using the difference between the total existing load reported in the TMDL and the modeled watershed load. Watershed and internal load estimates were later refined and calibrated in subsequent phases of the project. A comprehensive set of watershed best management practices (BMPs) was incorporated into the STEPL model to estimate potential load reductions that could be achieved in the watershed. Phosphorus reductions were also estimated for in-lake alternatives outside the STEPL model based on technical understanding and typical efficiencies of the management practice. The following management practices were recommended in a conceptual design to achieve a 2,155 lb annual load reduction. Watershed Treatment o Bioswales/Bioretention o Detention Basins o Septic Tank Inspections and Upgrades o Water Quality Inlets Spring 2015 / NALMS LAKELINE 47

3 In-Lake Treatment o Dredging o Fish Renovation o Sediment Forebays o Shoreline Stabilization o Watercraft Management o Wetland Creation o Whole Lake Alum Application Information and Education Program The predicted load reduction was slightly short of the WQMP goal. However load reductions associated with an information and education (I & E) program to reduce inputs from lawn fertilizer and pet wastes were not estimated and it was assumed these activities would provide sufficient reductions to reach or even exceed the goal. A full-time project coordinator position was funded by the U.S. EPA Region 7 Section 319 Program, to execute the I & E portion of the plan. Thus far, the project coordinator successfully organized the following activities: Developed and updates website with lake monitoring and outreach information Conducted workshops on rain barrels, rain gardens, vegetation management, lawn maintenance, and pet waste management Soil sampling and fertilizer recommendations Convinced local retailers to sell nophosphorus lawn fertilizer Convinced the golf course adjacent to the lake to use no-phosphors fertilizer Brochures for the public Contact for news stories Public speaking to community groups Lake level and water quality monitoring Field investigations of the topography and drainage patterns to Carter Lake were conducted to more accurately delineate the watershed boundary. Shoreline conditions were investigated and bank segments categorized to represent the severity of erosion. Soil phosphorus concentrations were determined at multiple shoreline locations as well. Not only was this useful in identifying locations that needed bank stabilization, but the information was used to more accurately estimate annual phosphorus loading rates specific to bank erosion. Stormwater was collected and discharge measured at eight stormwater outfalls during six rainfall events in 2009 to determine the average stormwater total phosphorus concentrations at these outfalls and to determine the relative contribution of each outfall to the total discharge. These data were used to calibrate the external phosphorus loading component of the watershed model. Six representative sediment core samples were collected from the lake bottom. The cores were sectioned and analyzed for various phosphorus fractions. This information was used to help estimate and allocated the internal load and to calibrate the internal load portion of the phosphorus loading model. A geophysical site characterization consisted of a land and water borne resistivity survey. The investigation characterized of the local hydrogeologic framework that affects the water quality of Carter Lake. Lithologic units with high hydraulic conductivities (sands and gravels) aquitards (silts and clays) peripheral and within Carter Lake were identified. Differentiation and delineation of site lithology, with respect to, electrical resistivity data provides information for understanding potential water seepage and how dredging may impact seepage. These efforts provided the level of detail needed to partition the load into watershed external and internal sources and refine the management practices identified earlier in the planning process. The STEPL model completed for the WQMP was modified with additional data and used to partition the watershed load into subwatersheds. This component of the model was calibrated with the data collected from the stormwater monitoring study. The subwatershed phosphorus loads are summarized in Figure 2. Refining the Plan A detailed analysis of the conceptual alternatives was performed to move toward the final design and implementation of the project. This effort included additional data collection, water quality modeling, and model calibration to more accurately estimate external and internal phosphorus loads. Specifically: Total Watershed Load = 941 lbs LEGEND Effective Drainage Area Flood Event Additional Drainage Area Storm Sewered Basin Figure 2. Carter Lake subwatersheds and associated phosphorus loads. 48 Spring 2015 / NALMS LAKELINE

4 The internal load is the pollutant load that is introduced to the water column from sources within the lake. There are three main sources of internal phosphorus loading at Carter Lake: shoreline erosion, natural release and lakebed resuspension (Figure 3). The internal load was allocated among the sources by applying the sampling data collected for the project (Table 2). The modeled external phosphorus loads and results from the internal loading studies and allocations were used to define the total annual phosphorus load to Carter Lake. Roughly 70% of the annual load originates from sources within the lake, while 30% enters from the watershed (Figure 4). The list of potential management practices (and their predicted phosphorus loading reductions) was applied to the refined information about the loads and sources. A comparison of the costto-benefit ratios for the internal and watershed alternatives was made to guide the final management recommendations and achieve a total phosphorus load of 2,192 lbs. The most cost effective alternatives were maximized to the greatest extent possible, but additional considerations such as secondary benefits, public acceptance, maintenance requirements, and permitting constraints were also considered. The final recommended management alternatives anticipated phosphorus load reductions and estimated construction costs are Table 2. Internal Phosphorus Load Breakdown by Source Source Pollutant % of Internal Breakdown Load (lbs/yr) Load Cause (lbs) Shoreline Erosion 119 5% Wind 48 Boat Induced 72 Release (Anoxia) % Anoxia 1249 Lake Bed Resuspension % Wind 76 Boat Induced 598 Fish/Biotic 168 Total % show in Table 3 and Figure 5 and were presented to the TAT and CLEAR WC in 2009 (Tetra Tech 2010). This project ultimately succeeded due to the unparalleled leadership and cooperation of the project partners and funding entities. A total of six funding partners from two states were able to recognize the restrictions on other partner s programs and creatively piece the funding puzzle together. The result of their innovative approach is shown in the funding matrix in Table 4. Project Implementation While the structural BMPs were undergoing final design, implementation of non-structural plan components kicked off in May 2010 with an alum application. Over the course of a week, 156,640 gallons of aluminum sulfate and 78,320 gallons of sodium aluminate were applied to the lake to reduce internal loading by inactivating the phosphorus in the bottom sediments and to reduce phosphorus in the water column (total dose = 25.3 mg AL/L). In June 2010 buoys were placed in the east arm of the lake to designate a 100-acre zone of no-wake boating to reduce phosphorus loading from sediment resuspension. The fish renovation followed in September 2010 when 2,520 gallons of rotenone was applied to eliminate the fish community. Over the course of four days, approximately 20 staff members from the IDNR and NGPC picked up fish carcasses and transferred them to the local landfill (>95% of the fish were common carp and buffalo) (Figure 6). It was estimated that approximately 176,000 lbs of fish (559 lbs of fish per acre) containing 4,013 lbs of phosphorus Figure 3. Carter Lake internal loading sources. Spring 2015 / NALMS LAKELINE 49

5 Table 3. Management Practices Load Reductions and Estimated Construction Costs Alternative Load Reduction (lb) Estimated Construction Cost Figure 4. Total phosphorus load summary. Whole lake alum 1,336 (+) $1,530,000 No-Wake Zone 140 $20,000 Wetland Creation/ Sediment Forebays 164 $2,020,000 Shoreline Stabilization 65 $899,000 Targeted Dredging 0 $293,000 Fish Renovation 168 $200,000 Wet Detention 230 $612,000 Golf Course Swale Improvements 46 $180,000 Vegetated Buffer 2 $3,000 Watershed Stewardship Load Reduction Total 2,192 $5,757,000 Reduced Annual Load 1,015 WQMP Annual Goal 974 LEGEND Existing Storm Sewer Proposed Storm Sewer Wetland Open/Deep Water Wetland Vegetated Buffer Bioswale No Wake Zone Buoys Dredge Locations Rock Structures Geotube Structures Rock/Geotub Combination Figure 5. Recommended management practices for the restoration of Carter Lake. 50 Spring 2015 / NALMS LAKELINE

6 Table 4. Management Practices Actual Costs and Funding Sources Funding Agency Contribution Water Quality City of Nebraska Improvements Actual Omaha/ NDEQ/ Environmental Project Component Costs P-MRNRD IDNR NGPC N319 Iowa/ 319 Trust Fund Fish Renovation $137, $68,750 $68, Alum $807, $359,822 $447, Watercraft Management $5,305 $5, Structural BMP Construction $3,226,796 $257,383 $1,100,454 $837,185 $223,730 $183,044 $625,000 Engineering Contracts $928,970 $237,104 $38,269 $439,504 $214, I&E Program & Misc. Items (on-going) $215, $5,721 $6,664 $1,829 $201, Vegetation Management $363, $182,464 $181, Total $5,685,507 $499,792 $1,755,480 $1,980,974 $439,652 $384,609 $625,000 Figure 6. NGPC and IDNR staff transporting fish carcasses to landfill. and 18,480 lbs of nitrogen were removed from the lake during the renovation. In mid-october 2010 the lake was stocked with a balanced proportion of largemouth bass, bluegill, and channel catfish. The construction of the structural BMPs, which included shoreline stabilization, breakwaters (Figure 7), forebays and wetlands, wet detention, and dredging, took place between October of 2011 and October of Results The water quality of Carter Lake has improved dramatically since the restoration activities began in In fact, the lake has continued to retain improved water quality parameters that reach or are very near to the goals set for Carter Lake (Table 5). The average summer total phosphorus concentration was reduced by 56% to 76 µg/l, chlorophyll a was reduced by 76% to 27 µg/l and water transparency was increased by 300% to 3.6 ft, compared to pre-project values (Table 5, Figure 8). Bacteria (E. coli) was reduced by 75% (Table 5), the algal toxin microcystin was reduced by 87% (Figure 9, Table 5) and Carter Lake has been able to fully support its recreational uses. The combined reductions of phosphorus loading from the alum application, rough fish removal, and establishing the no waking boating area increased water clarity and macrophyte biomass in the lake due to greater light penetration. As part of the Carter Lake s vegetation management plan, a vegetation harvester was used to remove macrophyte biomass as needed in the boating areas beginning in The fish renovation and subsequent stocking greatly improved the fishery. Prior to renovation, the rough fish dominated community was significantly contributing to sediment resuspension and internal loading through their bottom feeding activities. This undesirable fish community comprised of common carp, gizzard shad, big and small mouth buffalo, black and yellow bullhead, yellow bass and freshwater drum was replaced with a more habitat friendly and angler desirable game fish community (largemouth bass, bluegill, crappie, and channel catfish) (Figure 10). References Nebraska Department of Environmental Quality (NDEQ) Title 117 Nebraska Surface Water Standards, Spring 2015 / NALMS LAKELINE 51

7 Figure 7. Offshore breakwater with wetlands and shoreline stabilization on landside (left). Table 5. Carter Lake Water Sampling Results Water Quality Parameter Pre-Implementation Avg. Post-Implementation Avg. Total Phosphorus (µg/l) Total kjeldahl Nitrogen (µg/l) 2,330 1,210 Total Suspended Solids (ppm) 38 7 Chlorophyll a (µg/l) Microcytin Toxin (µg/l) Secchi Depth (ft) Bacteria (E. coli)(#/100 ml) nsf/pages/117-toc Nebraska Department of Environmental Quality (NDEQ) and Iowa Department of Natural Resources (IDNR) Total Maximum Daily Load for Algae and Turbidity Carter Lake, Iowa and Nebraska. 42 pp. Carter Lake Environmental Assessment and Rehabilitation Water Council (CLEAR WC) Carter Lake Water Quality Management Plan. 157 pp. Herriges, Joseph A., C.L. Kling, D.M. Otto, S. Bhattacharjee, K.S. Evans and Y. Ji A Report to the Iowa Department of Natural Resources The Iowa Lakes Valuation Project 2009 Summary and Findings. 51 pp. Tetra Tech Carter Lake Final Alternatives Analysis Report. Omaha, NE. 58 pp. Figure 8. Annual average total phosphorus and water clarity before and after project implementation. John Holz, Ph.D., is a limnologist with FYRA Engineering and has over 20 years of experience in surface water quality/aquatic habitat management and research. Specific areas of expertise include lake restoration and management, watershed management, fisheries management, internal phosphorus loading, phytoplankton ecology, nutrient inactivation, water quality monitoring, and water quality modeling. John is a past recipient of the NALMS Technical Excellence Award in recognition 52 Spring 2015 / NALMS LAKELINE

8 improve water quality, the aquatic community and fishing. Mark is a Certified Fisheries Professional. Chris Larsen is a fisheries biologist with the Iowa Department of Natural Resources Fisheries Bureau and has been involved with lake restoration projects for most of his career. Chris was one of the main drafters of the Iowa DNR s Community Based Watershed Improvement Framework for Lakes, which utilizes a watershed s stakeholders as an important part of the decision making process. c Figure 9. Microcystin toxin levels in Carter Lake. for Outstanding Research in Lake Restoration, Protection and Management, and has served on the NALMS Board of Directors. Sara Mechtenberg is an environmental engineer with FYRA Engineering and has been involved in a wide variety of projects including dam design, reservoir design, lake restoration, fishery enhancement, community- based watershed management planning, conceptlevel alternatives analysis, and stream/wetland restoration and mitigation. Sara is a licensed Professional Engineer. Mark Porath is a fisheries biologist with the Nebraska Game and Parks Commission. As the Aquatic Habitat Program Manager his work centers on the rehabilitation of impaired waters to PRE-RESTORATION Game Fish Species: 36% Undesirable Fish Species: 64% POST-RESTORATION Game Fish Species: 98% Undesirable Fish Species: 2% Figure 10. Fish community before and after restoration. Spring 2015 / NALMS LAKELINE 53