THE EFFECTIVENESS OF BMP'S AND SEDIMENT CONTROL STRUCTURES AND THEIR RELATIONSHIP TO IN-LAKE WATER QUALITY

Abstract

ABSTRACT Lake Herman is a nitrogen limited, hypereutrophic, shallow (mean depth 1.7m), warm water lake located in Lake County, S.D. The lake has experienced extensive blue-green algal blooms, fish winterkills, and receives a high sediment load. Algal and macrophyte growth has diminished the open water surface area. The predominant land use is agriculture with permanent homes, small businesses, and public recreation areas surrounding the lake's shoreline. On January 13, 1978, Lake Herman and its associated watershed were selected to participate in the U.S. Department of Agriculture and U.S. Environmental Protection Agency sponsored Model Implementation Program. The primary objective of the project was to improve the water quality of Lake Herman by reducing phosphorus, nitrogen, and sediment loads through voluntary application of Best Management Practices (BMP's) and construction of sediment control structures. Approximately 5 years of water quality data from the lake, the tributaries, the outlet, and above and below the BMP's, and the sediment control structures are available from this project. Although the results of t-test analyses indicated that the sediment control structures are reducing the sediment and nutrient load, a corresponding reduction has not been observed in the lake. Therefore, two phosphorus mass budget models were used to predict the phosphorus concentrations in the lake: neither predicted the high phosphorus concentrations observed in the lake. It is assumed that another nonpoint source of phosphorus affects the lake (internal loading from resuspended sediments or aquatic macrophytes). The next step in the Lake Herman restoration project is to dredge selected areas to deepen them and reduce the resuspension of sediments.