Introduction
Degradation of water quality in sandpit lakes is a concern in Nebraska. Currently, over 800 publicly and privately owned sandpit lakes exist in the State (NDEE, 2009). These lakes are typically created from sand and gravel mining operations and are used extensively for recreation by a large, diverse group of people with various interests (i.e. swimming, fishing, SCUBA-diving, hunting). Most sandpits lakes have very small drainage areas and water supplies are via groundwater inputs. A majority of the nutrients found in the water column of a sandpit lake are generated from groundwater and organic matter at the lake bottom. Nutrient loading, particularly phosphorus, has led to accelerated eutrophication of many sandpits throughout the State and has greatly reduced their recreational usage.
Fremont Lake #20 consists of 50 surface acres and is part of a chain of sandpit lakes collectively known as the Fremont State Lakes located near Fremont in Dodge County, Nebraska (Figures 1 and 2). The lake has a maximum depth of 16 foot, average depth of 11 feet, and impounds approximately 552 acre-feet of water (Figure 3). The Nebraska Game and Parks Commission (NGPC) estimates annual usage of the Fremont State Lake Complex to be around 800,000 people.
Lake monitoring conducted in 2005 by the Nebraska Department of Environment and Energy (NDEE) indicated high concentrations of the microcystin toxin. From 2005 to 2007, approximately 32 percent of the samples exhibited toxin concentrations greater than beach posting target, resulting in a significant loss of water contact recreation opportunities for lake users. Further monitoring conducted from 2005 through 2007 documented high concentrations of phosphorus and nitrogen as being the cause of blue green algae blooms.
The documentation of water quality problems at Fremont Lake #20 resulted in several independent studies being conducted. These studies included an assessment of pre- and post lake treatment nutrient and biological conditions, an evaluation of microcystin toxin accumulation in fish tissue, and an evaluation of microcystin toxin migration out of the lake to groundwater. A significant amount of physical, chemical, and biological data was collected through these studies. This report will summarize the results and conclusions of water quality monitoring efforts at Fremont Lake #20. |