Transport of mercury from a cultivated field during snowmelt

Total mercury (THg) was determined in snow, overland snowmelt runoff, and soil from a small cultivated catchment. Total mercury concentrations in snow were low [mean concentration = 1.04 ng/L (liquid basis); n = 9; CV = 23% ], while THg concentrations in snowmelt runoff were much higher, ranging from 16 to 22 ng/L. The THg concentration of suspended particulates in the runoff (52 μg/kg) was much higher than observed surface soil THg concentrations (mean concentration = 26 μg/kg; n = 6; CV = 16%). Particle size analysis showed the clay content of the runoff sediment was approximately twice that of the bulk surficial soil. These results suggest that snowmelt runoff preferentially mobilizes very fine soil particles (clays) that have a THg concentration that is greater than that of the bulk surficial soil. The total mass of THg in the snowpack prior to snowmelt was 1.26 mg, and that delivered from the catchment during the snowmelt event was 0.36 mg. This suggests there was a net accumulation of THg in the catchment soil over the winter. Soil erosion and transport are the primary mechanisms that control THg delivery from this catchment during snowmelt events.