Nutrient Contributions of a Coastal Plain Stream to Lake Blackshear
Cofer, Harland E., Jr.
Tietjen, William L.
Wysochansky, William J.
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Lake Blackshear is a hydro-electric impoundment located on the Flint River and is owned by the Crisp County Power Commission. The lake was created in 1930. It has a surface area of 34.5 km^2 and a mean depth of 5.4 m. It is located mainly between Crisp and Sumter Counties, also bordering on Dooley, Lee and Worth. The lake has had for many years a heavy growth of the filamentous blue-green algae Lyngbya (probably L. wollei, Larry Dyck, pers. comm.). This growth occurs in several of the lake tributaries. Other nuisance algae and related problems have caused concern for lake users. The lake was described as eutrophic based on a 1973 study (USEPA, 1975). In 1983, Proctor and Gamble Corp., owners of a bleached pulp plant upstream from Blackshear sponsored an intensive evaluation of the river and lake. This study was under the direction of the Academy of Natural Sciences of Philadelphia (ANSP, 1984). Study sampling was done in April, August, and October. Results demonstrated that nutrient loading was sufficient in the spring and summer to classify the lake as eutrophic. A nutrient budget study (Foth and Van Dyke, 1985) applying the model of Vollenweider (1978) to the nutrient data of the 1973 study (USEPA, 1974) was done at the request of the Crisp County Power Commission. The study stressed the importance of lake tributaries and local sources such as septic tanks as nutrient sources for this lake. The Gum Creek embayment was considered to be very important to this lake enrichment process. The Foth and Van Dyke study recommended the establishment of a Watershed Association and also recommended a detailed study of the Gum Creek system. The study reported here is an outcome of that recommendation and was conducted under the sponsorship of the newly formed Lake Blackshear Watershed Association. This study was designed to evaluate the relative non-point and point source nutrient contributions from different land usages and to develop recommendations for decreasing lake enrichment. We believe that this study more clearly delineates the nutrient sources of Gum Creek and once again demonstrates the role of stream habitats, including riparian woodlands, in reducing down-stream transport of nutrients. Management policy development derived from information of this study may be applied to other tributaries of Lake Blackshear, as well as to other stream systems in the State. As an outgrowth of this study, an extensive multi-agency project, sponsored by the State Soil and Water Conservation Commission, has been undertaken to evaluate agricultural impact and to demonstrate non-point source reduction activities in the Gum Creek watershed. This project has broad state and national significance.