Long-term base cation weathering rates in forested catchments of the Canadian Shield

A number of methods exist for estimating mineral weathering rates. Yet, quantifying this crucial biogeochemical reaction in the field has always been a challenge because mineral weathering takes place in open systems whose initial state conditions are not well known and where material inputs and outputs vary in time and space. Here, using the soil profile mass balance method, we estimated long-term weathering rates of base cations (BCs) for a set of 21 watersheds, and we investigated the links between environmental variables and soil properties and the spatial variation in BC weathering rates in the study area. The watersheds are located in southern Quebec and vary with respect to hydro-climatic conditions, soil properties and forest cover. Average long-term estimates of annual BC weathering rates for the study area were 0.16, 0.10, 0.09 and 0.06 kmolc ha− 1 year− 1 for Ca, Mg, Na and K, respectively. Overall, redundancy analysis (RDA) indicated that soil surface area, percent deciduous canopy cover, elevation, as well as soil albite content were the most significant variables explaining together 56% of the total variation in BC weathering rates. Consistent with previous findings, our results showed that, beside soil properties, climate-related environmental variables played key roles in determining the variability of BC weathering rates in the study area. In the context of global climate change, more insights are needed for a better understanding of the effects of discrete climatic variables on BC weathering rates.