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 sulphur concentration in a stream draining a small catchment in Ontario. The annual input of sulphur roughly balances the output, the average sulphur flux being about 1.6 g S∙m−2∙yr−1. The average dry deposition was estimated to be about 0.4 g S∙m−2∙yr−1. For good agreement between calculated and observed sulphur concentrations, it was necessary to introduce a reduction (or adsorption) process for sulphate in deeper soil layers during summer and fall. During dry periods, however, sulphate is produced by oxidation in the upper soil layer. The sulphate 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 sulphur in the soil considerably larger than the annual sulphur flux. The basic structure of the models applied to the Ontario stream and to two streams in Norway was the same. It seems likely, therefore, that the model may, with moderate modifications, be applicable to many catchments.