Sulphate dynamics in a northern wetland catchment during snowmelt

Abstract

Fluxes and stores of SO42− were measured in a small Canadian Shield basin during the 1989 snowmelt. Sulphate flux from the unsaturated zone (14.1 ± 7.3 kg ha−1) was four times the amount supplied in meltwater and precipitation (3.5 ± 0.4 kg ha−1). This reflects flushing of soluble S04- from organic and upper mineral soil horizons during melt, 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 overlying soils and conversion of the capillary fringe to phreatic water due to rising water table levels. Streamflow conveyed 70% of the total SO42−1 export of 10.1 ± 2.3 kg ha−1, and was largely supplied by groundwater discharge from a wotland in the lower portion of the basin. The remaining 30% of total export was via shallow subsurface flow. Results highlight the importance of unsaturated and saturated zone processes for SO42− dynamics and export during snowmelt.