COMPARATIVE ANALYSIS OF WATERSHED EROSION, RESERVOIR SEDIMENTATION AND SEDIMENT TRACE METALS IN TWO VIRGINIA LAKES

Two contrasting reservoirs in Virginia were studied to compare their environmental evolution based on watershed soil erosion, reservoir sedimentation and sediments trace metals variations. Lake Moomaw, located in the Blue Ridge Mountains, is a relatively pristine reservoir with extreme slopes surrounded by undeveloped, protected land. Lake Pelham is located in Culpeper County, which is a more human developed area consisting of agriculture and a variety of industrial developments. The Revised Universal Soil Loss Equation (RUSLE) was used in soil erosion estimates in the two watersheds. Three sediment cores from each reservoir were used for ²¹⁰Pb sediment accumulation rates estimates, as well as trace metal analysis. Bathymetric and sedimentation surveys of the two lakes were also conducted using a multi-frequency echo sounder system.

The RUSLE/SDR erosion model estimates 2.149 Mg/ha/yr for Lake Pelham, which is a 410% increase from assumed pristine conditions. For Lake Moomaw, 2.717 Mg/ha/yr of erosion was estimated, a 13% increase from pristine conditions. The average ²¹⁰Pb-based sediment accumulation rates were 0.348 ±0.053 g/cm²/yr for Lake Pelham and 0.246±0.043 g/ cm²/yr for Lake Moomaw. The geophysical survey results estimates sediment average accumulation rates of 0.599 cm/yr and 1.514 cm/yr for Lakes Moomaw and Pelham respectively. The sediment trace metal results show that both reservoirs have moderate to high enrichment of Cu and little enrichment of Zn and Pb. Overall, Lake Moomaw has relatively low sediment accumulation and watershed erosion rates due to the pristine nature of the watershed, but is also more vulnerable due to the steep slopes that characterize the basin. Comparatively, Lake Pelham has higher erosion rates, sediment accumulation rates and high metal enrichment of Cu and Zn, which directly reflects the impact of human development on its environmental evolution.