Transport of mercury from a cultivated field during snowmelt

Total mercury (THg) was determined in snow, overland snowmelt runoff, and s oil 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 runo ff (52 mu g/kg) was much higher than observed surface soil THg concentratio ns (mean concentration = 26 mu g/kg; n = 6; CV = 16%). Particle size analys is showed the clay content of the runoff sediment was approximately twice t hat of the bulk surficial soil. These results suggest that snowmelt runoff preferentially mobilizes very fine soil particles (clays) that have a Tug c oncentration that is greater than that of the bulk surficial soil. The tota l mass of THg in the snowpack prior to snowmelt was 1.26 mg, and that deliv ered from the catchment during the snowmelt event was 0.36 mg. This suggest s 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 de livery from this catchment during snowmelt events.