SIMULATION OF STREAM WATER ALKALINITY CONCENTRATIONS USING COUPLED MODELS OF SOIL AIR CO2 AND STREAM WATER CHEMISTRY

Abstract

The ability to predict stream alkalinity values over timescales shorter than monthly or annually is needed to understand the response of stream chemistry to acidic inputs which occur across short time scales (days). We develop and apply a coupled series of physically-based models which are able to predict daily stream alkalinity values by first calculating soil air CO2 concentrations. We apply the model to a 9 year record of discharge and stream chemistry from a small catchment in the Shenandoah National park of Virginia. We find that we are able to accurately predict the minimum daily stream alkalinity values for all years and we are able to accurately predict the entire annual cycle for 6 of the 9 years (Nash–Sutcliffe criterion equals 0.26). For the 3 years which we overpredict summer stream alkalinity, summer precipitation was greater than normal and much greater than the period for which the model was calibrated.