COMPARISON OF METHYLMERCURY ECOLOGY IN ADJACENT COASTAL PLAIN RIVERS IN SOUTH CAROLINA
Concentrations of total mercury were statistically higher in sediments from the Congaree River compared with those in sediments from the Edisto River. No statistically significant differences were observed in concentrations of methylmercury or in the range of net methylation potentials in sediments collected from various Edisto and Congaree hydrologic settings. In both systems, net methylation potentials were an order of magnitude or more lower in stream-channel sediments than in wetland sediments. These results are not consistent with the hypothesis that differences in fish-tissue mercury between the Edisto and Congaree basins reflect fundamental differences in the potential for each system to methylate mercury.
The marked differences in net methylation potential observed between the wetland and in-stream settings suggested an alternative hypothesis: differences in the efficiency of methylmercury transport from zones of production (wetlands) to points of entry into the food chain (channels) contribute to the observed differences in fish-tissue mercury concentrations between the two river systems. An assessment of the flood hydrodynamics of these two rivers is consistent with the alternative hypothesis.