The Fremont State Lake System (FLS) is made up of 20 sandpit lakes adjacent to the Platte River near Fremont, Nebraska and is used by 800,000 visitors annually. These lakes were created as early as the 1940s and many are now experiencing water quality problems related to eutrophication. High nutrient concentrations in the water column are driven primarily by internal loading from nutrient-rich sediments accumulated through deposition of leaves fallen from trees, shoreline vegetation, fish excrement, and decaying remains of fish and aquatic vegetation. Eight of the lakes in the Fremont State Lakes are on Nebraska's 2012 section 303(d) list of impaired waters with 30 different impairments. In the fall of 2012, 16 lakes were chemically treated (with aluminum sulfate, alum) to reduce nutrients available for phytoplankton growth. In addition, four lakes were also treated with rotenone for a fishery renovation, which subsequently included removing bottom-feeding species and restocking with a more desirable assemblage.
Given the alterations to the chemical and biological structure of the lakes, the goal of this study is to understand how physical drivers (e.g., lake-basin structure) and biological drivers (e.g., fish community composition) interact to affect the longevity and effectiveness of alum additions for improving water quality. This will be addressed through three major tasks:
GoalsThe goal of this study is to understand how physical drivers (e.g., lake-basin structure and groundwater flow) and biological drivers (e.g., fish community composition) interact to affect the longevity and effectiveness of alum additions for improving water quality. This will be addressed through three major tasks:
1. Monitoring physical and chemical water quality
2. Analyzing the internal and external phosphorous (P) budgets
3. Discerning how altered fish communities indirectly affect water-quality dynamics.
Alum additions improved water quality by decreasing TP and chlorophyll a. Combining alum and biomanipulation (fish renovation) together had the added benefit of decreasing phytoplankton and cyanobacteria densities. Restoration treatments, however, were ineffective for shifting the phytoplankton community away from cyanobacteria dominance. Furthermore, microcystin toxin, produced by cyanobacteria and a key target of many water quality restoration efforts, varied more year-to-year than by restoration technique. We conclude that if water quality restoration goals are focused on biological improvements, as opposed to solely chemical improvement, then adding biomanipulation in a dual treatment may enhance restoration success. The information collected during this project will be useful in designing future lake renovation projects and developing long-term management plans for renovated lakes.
Principal Investigator(s)-Amy Burgin, University of Nebraska-Lincoln
-Steve Thomas, University of Nebraska-Lincoln
-Mark Pegg, University of Nebraska-Lincoln
-Kevin Pope, NE CFWRU
Graduate Student(s)-Meg Trowbridge M.S.
-Christa Webber M.S.(2014)
Project DurationApril 2012- September 2015
Funding-Nebraska Department of Environmental Quality
-Nebraska Game and Parks Commission