QUANTITATIVE IMPACTS OF LAKE-LEVEL STABILIZATION ON MATERIAL TRANSFERBETWEEN WATER AND SEDIMENT IN NEWNANS LAKE, FLORIDA

Spillways at lake outlets reduce water-level fluctuations but may acce lerate sedimentation in the lake. In eutrophic Newnans Lake, Florida, a transect of sedimentary profiles, dared with (210)pb and Cs-137 by g amma-ray spectroscopy, showed threefold increases in accumulation rate s of organic matter, total Kjeldahl nitrogen (TKN), and total phosphor us (TP) 1200 m lakeward of a spillway since its construction in 1967. Concentrations of TKN and TP increased 3.5 and 2.4 times, respectively , in sediments deposited since 1967. These increases were progressivel y less at stations farther from the spillway. Postspillway accumulatio n of TP was focused toward the dam whereas recent TKN deposition was s imilar lakewide. Flocculent sediment (>90% water) accumulated at 1.4 c m/yr. Dams designed to reduce water-level fluctuations may provide sho rt-term benefits for lake access and navigation but in the long-term m ay accelerate deposition of nutrient-rich detritus, reduce lake volume , cloud the water, alter plant communities, and change lake productivi ty.