An approach at estimating present day base cation weathering rates: a case study for the Hermine watershed, Canada

A new methodological approach is described for estimating Ca, Mg and K fluxes from soil mineral weathering. This method combines Na flux in surface waters in the Hermine watershed with base cation (BC) concentrations to Na molar ratios from the soil weatherable pool obtained using sequential extraction method. Comparison of BC:Na molar ratios of the weatherable pool with those from other compartments of the watershed suggests possible accumulation of base cations in some areas of the watershed, while losses or minimal changes are observed in others. On average, present day Na weathering rates estimated using the watershed input-output budget method was 0.26 (range 0.16-0.36) kmol(c)ha(-1)yearr(-1), over the period of 1995-2006. For Ca, Mg and K, present day weathering rates estimated with the new methodological approach averaged 0.44 (range 0.27-0.60), 0.11 (range 0.07-0.15) and 0.02 (range 0.01-0.02) kmol(c)ha(-1)year(-1), respectively. These values are within the range of present day rates previously calculated for the same site and for forested soils from similar granitic environments using other methods. Candidate models for predicting BC weathering rates on individual annual observations were developed using Akaike's information criterion. The best model includes the number of frost days (inverse relationship) and explained 51% of the variation in total BC weathering rates. The newly developed method may be applicable to other watersheds, providing yearly estimates of nutrient BC at the watershed scale.