Model for Streamwater Chemistry of a Tributary to Harp Lake, Ontario

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Abstract
The model is an extended version of the "Birkenes" model and consists of a hydrological submodel with a snow reservoir and two soil reservoirs, a sulphate submodel, and a submodel including H+, Ca2+ + Mg2+, Al, Na+, HCO3- and organic anions. Major processes incorporated are different hydrologic flow patterns during highflow and lowflow, SO42- adsorption/desorption, ion exchange, weathering, gibbsite solubility, and equilibria with CO2 in soil and stream water. The model reproduces important daily and seasonal trends in the observed streamwater chemistry. Tentative model runs have been carried out to simulate the effects of both a doubling and a 50% reduction in the present sulphur deposition. At present the pH of the stream is generally above 5.7, with values approaching pH 5.3 during snowmelt highflow. According to the simulations, lowflow pH is not sensitive to changes in deposition. At snowmelt highflow, however, a 50% reduction in the deposition could cause a pH increase of 0.2-0.5 unit whereas a doubling could result in pH depressions of 0.5-0.9 unit.