Evaluation of three methods for estimating the weathering rates of base cations in forested catchments

This paper investigates three techniques that are commonly used to generate estimates of base cation (BC) weathering rates, i.e. the profile mass balance (PEDON), the watershed input-output budget (WATERSHED) and the PROFILE model (MODEL). These methods were compared for their relative performance in estimating BC weathering rates for 21 watersheds located in southern Quebec that vary with respect to hydro-climatic conditions, soil properties and forest cover. Average total BC weathering rates for the 21 watersheds were 0.41 ± 0.09 (± SE), 1.20 ± 0.17 and 1.71 ± 0.22 kmolc ha− 1 yr− 1 for PEDON, WATERSHED and MODEL, respectively. Passing and Bablok regression analysis demonstrated good agreement between WATERSHED and MODEL {regression formula: WATERSHED = − 0.08 + 0.74 MODEL, with 95% CI for intercept [− 1.13; 0.25] and for slope [0.40; 1.43]}, while poorer agreements were observed between these two methods and PEDON. Contrary to the WATERSHED and the MODEL methods, BC weathering rates obtained with PEDON were not significantly associated with the spatial variation of the soil calcite content and of the size of the soil exchangeable BC pools. We hypothesized that in the calcite-containing watersheds, the performance of PEDON was negatively impacted by environmental conditions that favored the partial dissolution and leaching of the calcite contained in the initial parent material, including in the material situated at the base of the profile (C horizon).