SULFATE DYNAMICS IN A NORTHERN WETLAND CATCHMENT DURING SNOWMELT

Fluxes and scores of SO42- were measured in a small Canadian Shield ba sin during the 1989 snowmelt. Sulphate flux from the unsaturated zone (14.1 +/- 7.3 kg ha(-1)) was four times the amount supplied in meltwat er and precipitation (3.5 +/- 0.4 kg ha(-1)). This reflects flushing o f soluble SO42- from organic and upper mineral soil horizons during me lt, which counteracted potential dilution of groundwater SO42- levels by large water inputs to the basin. 35.6 +/- 12.4 kg SO42- entered the saturated zone during melt, supplied equally by leaching from overlyi ng soils and conversion of the capillary fringe to phreatic water due to rising water table levels. Streamflow conveyed 70% of the total SO4 2- export of 10.1 +/- 2.3 kg ha(-1), and was largely supplied by groun dwater discharge from a wetland in the lower portion of the basin. The remaining 30% of total export was via shallow subsurface flow. Result s highlight the importance of unsaturated and saturated zone processes for SO42- dynamics and export during snowmelt.