ACCUMULATION OF PHOSPHORUS AND POTENTIALLY TOXIC ELEMENTS IN STREAM WATER, BOTTOM SEDIMENTS, AND SUSPENDED SEDIMENTS IN TRIBUTARIES OF LAKE ANNA, VIRGINIA

Anthropogenic release of potentially toxic elements (PTEs) (As, Cd, Cr, Cu, Ni, Pb, and Zn) and phosphorus (P) may originate from former mine sites or agricultural lands respectively, which occur in watersheds contributing to Lake Anna, Virginia. The purpose of this study is to quantify the amounts of P from agriculture and PTEs in stream waters, bottom sediments, and suspended sediments to understand potential impacts to aquatic life. Water collection and sediment core sampling occurred at 20 locations within 10 distinct watersheds surrounding Lake Anna, Virginia, including the lake’s outflowing river, seasonally beginning in March 2024. Elemental concentrations of water and sediments were extracted via strong acid digestion using hydrochloric acid (HCl) and reverse aqua regia (9:1 HNO3 to HCl) respectively. Results for stream water pH show that the majority of sample sites meet the EPA pH criteria for freshwater on average. One site was found to have a minimum average pH of 2.95 ± 0.04 compared to the regional minimum average of 6.75 ± 0.07. The streams that did not meet the EPA pH criteria had elevated levels of almost all PTEs, though As met guidelines. Seasonal variation of stream water pH and element concentration shows a decrease of pH and increase of potentially toxic element content from Spring to Summer. Results for bottom sediment pH show that most sample sites do not meet the EPA pH criteria for plant growth. Elemental analysis of bottom sediments shows consistently elevated concentrations of all PTEs at two sample sites. One site was found to have an average Cu concentration of 309 ± 272 ppm, exceeding the Virginia Department of Environmental Quality’s freshwater sediment screening value of 149 ppm. Sites that were found to have elevated concentrations of PTEs in stream water also had high concentrations of PTEs in bottom sediments. Elevated concentrations of P (maximum average of 1257 ± 73 ppm) were found in bottom sediments of several sites which also hosted elevated Ca amounts. From our findings, we conclude agricultural land use is associated with excessive amounts of P, and therefore a greater risk of eutrophication. The presence of former mines not properly reclaimed is associated with high amounts of PTEs that likely negatively impact aquatic life in the watersheds of Lake Anna, Virginia.