A model for sulphate in streamwater at storgama, Southern Norway

Abstract

The sulphate budget and a model for sulphate concentrations in streamwater have been established for a small (0.60 km 2), gauged catchment in Telemark country, southern Norway. The annual input roughly balances the output; the average annual flux through the catchment for four years is about 3500 mg SO 4m −2. Dry deposition is estimated to be 10% of the total sulphur input. The budget shows a marked seasonal pattern with net accumulation in the summer, net washout in the autumn, particularly in years with heavy autumn rains following dry summers, a second net accumulation due to the snowpack, and a pronounced net output during spring snowmelt. The concentrations in streamwater show minimum values (≈ 2 mg SO 4l −1) at the end of melting, and maximum values (6–8 mg SO 4l −1) at the start of melting and in the first runoff following dry summer periods. The model simulates main trends in the observed sulphate concentrations and is based on a simple reservoir hydrologic model. In the model, water-soluble sulphate accumulates in the reservoir representing the surface soils during dry periods because of dry deposition, evapotranspiration of summer rainfalls and mineralization. During wet summer periods, water-soluble sulphate is removed due to reduction or adsorption. The concentration pattern during snowmelt is largely dependent upon the fractionation of sulphate held by the snowpack. The model is particularly useful as a data interpretation tool.