GEOCHEMICAL STUDIES OF SOILS, STREAM SEDIMENTS, WATER, AND BIOTA IN A SMALL WATERSHED IMPACTED BY MERCURY AMALGAMATION AT AN ABANDONED GOLD MINE IN NORTHERN VIRGINIA
Mercury concentrations and d15N, d13C, and d34S values of muscle tissue from frogs (bull, green, and pickerel; n = 7) and fish (bluegill, sunfish, and white suckers, among others; n = 18) document relationships among trophic level, other behavioral characteristics, and the bioaccumulation of mercury. Stable isotope signatures of frogs (d15N = 3.6 to 6.3 ; d13C = -27.6 to -23.7 ; d34S = 2.4 to 4.1 ) indicate that they occupy the lowest trophic level sampled, which is consistent with their comparatively low mercury concentrations (14.6 to 87.5 ng/g). The highest concentrations (> 34.2 ng/g) were found near the Greenwood site. Stable isotope compositions of fish (d15N = 7.5 to 9.6 ; d13C = -31.7 to -25.9 ; d34S = 3.0 to 6.2 ) lack significant variation on the basis of species and reflect a higher trophic level than the frogs. Concentrations of mercury in muscle tissue of fish are highest at the mine site (743 to 1,130 ng/g) and decrease downstream (11 km: 89 to 178 ng/g) compared to background values (172 to 244 ng/g). Relative to other fish, mercury and isotopic compositions (19.2 ng/g Hg; d15N = 12.9 ; d13C = -22.7 ; d34S = 7.9 ) of a juvenile American eel are anomalous and reflect its anadromous behavior. Trophic level is important; however, proximity to the source of contamination and reliance on aquatic food sources have a greater effect on determining the bioaccumulation of mercury by fish and frogs in the watershed.