Estimating base cation weathering rates in Canadian forest soils using a simple texture-based model

Mineral weathering is the primary source of long-term buffering capacity in soils and is important for forest nutrient sustainability. Regional assessments of weathering rates in Canada and the U.S. have employed an empirical clay-based Soil Texture Approximation (STA) owing to limited data availability, although the STA is rarely calibrated before application to a study area. Soil weathering rates estimated with the STA at 75 sites in Canadian forests (6–367 eq ha−1 year−1) were on average seven times lower than estimates obtained using the PROFILE model and when mineralogy was not available, the Analysis to Mineralogy model and parameter estimation (143–2,119 eq ha−1 year−1). Comparison with a catchment mass balance at a subset of sites in Ontario (n = 19) demonstrated the reliability of PROFILE weathering estimates. A revised (generalized) STA model for total base cation weathering was developed at the 75 study sites to incorporate soil silt content (%) and loss-on-ignition (LOI, %) (BCw = (1.73 + 0.03 · silt − 0.06 · LOI) · 1,000 · depth). The model performance (Radj2 = 73%) and relative bias (−1%) suggested that the revised STA may have broad application to forest soils in Canada but may not necessarily be suited to all soil texture classes.