SIMULATION OF STREAM-WATER CHEMISTRY WITH SOIL SOLUTION AND GROUNDWATER-FLOW CONTRIBUTIONS

The mass balance equation was used to assess the contribution of water flowing from the solum (the upper 80 cm of soil) and subsoil to a first-order stream in the southern Laurentians, Quebec, during spring snowmelt. Dissolved reactive silicon was used as a tracer and showed that during high flow the solum contributed 50-95% of the stream discharge. During low flow, the stream was mainly fed by ground water. Based on this hydrograph separation and soil solution chemistry, a simple model was developed to predict stream chemistry. The simulations obtained for calcium, sodium, sulphate, nitrate, chlorine, and electrical conductivity showed good agreement with the stream chemistry. The predicted values of hydrogen and total aluminium followed the same pattern as the measured values but overestimated concentrations in the stream during high flow due to their reactive, non-conservative behaviour.