METHYLMERCURY IN RUNOFF FROM THE SVARTBERGET CATCHMENT IN NORTHERN SWEDEN DURING A STORMFLOW EPISODE

The dynamics of MeHg during rain-driven runoff episodes are important in calculating the output of MeHg from forested catchments. These dynamics may also provide insight into the processes controlling MeHg output from soils to surface waters. The concentrations of MeHg Hg-tot, TOC and associated chemistry were observed during a rain-driven, July runoff episode on two forested tributaries of the Svartberget Catchment, as well as at the outlet of a mire in the headwaters of that catchment. TOC concentrations in runoff increased during the episode. Hg-tot concentrations also tended to increase (from 3 to between 4 and 7 ng L(-1)), though the timing of that increase varied. MeHg concentrations, on the other hand, tended to decrease. The decrease was slight in the two forested tributaries (ca. 0.1 ng L(-1)), but greater in the mire runoff (from 0.8 to ca 0.3 ng L(-1)). These data are set in relation to a hypothesis about the processes which control MeHg output.