What is the role of in-channel processes versus watershed processes in controlling methylmercury concentrations in stream water?
Two key lines of evidence point to watershed processes as more important than in-channel processes. First, stream-reach-integrated measures of total mercury and methylmercury concentrations in sediment, and methylmercury production in sediment, were not correlated to methylmercury concentrations in the stream water. This study was one of the first to assess methylmercury production in streambed sediment. Second, in streams where methylmercury was frequently detected in stream water, it usually correlated positively with streamflow, dissolved organic carbon, and suspended sediment, pointing to runoff from the watershed as the dominant source of methylmercury to the stream.
