Model of Sulphate Concentration in a Small Stream in the Harp Lake Catchment, Ontario

Abstract

A model previously used for Norwegian catchments was modified to predict discharge and S concentration in a stream draining a small catchment in Ontario. The annual input of S roughly balances the output, the average S flux being about 1.6 g S .cntdot. m-2 .cntdot. yr-1. The average dry deposition was estimated to be about 0.4 g S .cntdot. m-2 .cntdot. yr-1. For good agreement between calculated and observed S concentrations, it was necessary to introduce a reduction (or adsorption) process for SO42- in deeper soil layers during summer and fall. During dry periods, SO42- is produced by oxidation in the upper soil layer. The SO42- concentrations in streamwater during snowmelt are remarkably constant. According to model results this could be explained by the existence of a reservoir of easily soluble S in the soil considerably larger than the annual S flux. The basic structure of the models applied to the Ontario stream and to 2 streams in Norway was the same. It seems likely, therefore, that the model may, with moderate modifications, be applicable to many catchments.