What factors control the amount of methylmercury in streambed sediment and pore water?
Both the activity of microbes that methylate mercury and the availability of inorganic mercury to those microbes control the formation of methylmercury in streambed sediment. Microbial activity was typically higher in organic-rich sediment. In reducing (anoxic) sediment, inorganic mercury was less available to microbes than in more oxygenated sediment. Methylmercury concentrations in sediment pore water tended to be higher in streams with higher pore-water dissolved organic carbon concentrations. Similar to the stream-water findings, streams with abundant wetlands in the watershed had high dissolved organic carbon concentrations in sediment pore water. Urban streams had more total mercury in sediment than nonurban streams. However, in nonurban streams, a higher proportion of total mercury was in the methylmercury form than in urban streams.
