Phosphorus Assimilation Below a Point Source in Big Creek

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Pollock, Jeff B.
Meyer, Judy L.
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Big Creek is a tributary of the Chattahoochee River that has received effluent from a poultry processing plant since 1987. Using the elevated concentrations of phosphorus and chloride in the effluent, we determined the stream's ability to remove phosphorus from the water by measuring the uptake length for soluble reactive phosphorus (SRP) on five dates from November 1999 through August 2000. Uptake length is the average distance traveled downstream by a molecule of phosphorus before it is removed from the water column. Shorter uptake lengths imply higher chemical and biological assimilation of added P. We collected water samples above the point of effluent discharge, immediately downstream of the discharge, and at seven sites downstream (ca. 40 km). Samples were analyzed for SRP and chloride, which we used as a conservative tracer to factor out concentration changes resulting from dilution. SRP concentrations in the effluent ranged from 21.2 to 27.5 mg P/L and decreased to 0.2 - 0.5 mg P/L before reaching the Chattahoochee River. Uptake lengths ranging from 15 to 138 km were not related to discharge, but were positively related to effluent SRP concentration. This suggests that Big Creek has a very limited capacity to assimilate SRP, and that SRP added to the stream by this point source is being transported long distances and contributing to excess nutrients downstream. Contemporary total phosphorus concentrations in Big Creek are an order of magnitude higher than was observed in the late 1970's when this point source of phosphorus was not present.
Sponsored and Organized by: U.S. Geological Survey, Georgia Department of Natural Resources, Natural Resources Conservation Service, The University of Georgia, Georgia State University, Georgia Institute of Technology
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