Wetland influences on mercury transport and bioaccumulation in South Carolina

Abstract

There are three distinct geological provinces in South Carolina (SC), with the blue ridge/piedmont regions in the west/central portion of the state and the coastal plain region in the central/eastern region of the state. Samples were collected along this gradient to identify potential factors contributing to the concentrations of total Hg and total organic carbon (TOC) throughout the state. Overall, there is a gradient across the state, with water column concentrations of total Hg (9–53 pM) and TOC (80–2721 μM) increasing as one moves from the blue ridge/piedmont region to the coastal floodplain region. Total Hg at all sites in SC is significantly ( R 2 = 0.78; P < 0.001) correlated with TOC in the water samples. This correlation explains 78% of the variance in the data and suggests that mercury is associated with organic matter in water bodies throughout the state. A study of mercury speciation within the coastal plain Waccamaw River indicates that concentrations of total Hg range from 10–68 pM and methyl Hg concentrations range from 1–7 pM. Watershed transport efficiencies for coastal floodplain rivers sampled in this study range from 32–72% for total Hg and 78–477% for methyl Hg. The coastal plain sites are located in watersheds that contain a significantly ( P < 0.001) higher percentage of wetlands (16.3 ± 5%) than the blue ridge/piedmont region (1.14 ± 1.6%), suggesting that drainage through wetlands contributes to the increased concentrations of TOC and total Hg found in SC coastal plain rivers. There is a significant correlation between mean fish Hg concentrations in largemouth bass from each watershed and percent wetland area in each watershed ( R 2 = 0.66; P = 0.003). This correlation explains 66% of the variance in the data and suggests that increasing percentages of wetland area contribute to fish Hg concentrations in SC coastal plain rivers.