Chemical Weathering Rates, Erosion Rates and Mobility of Major and Trace Elements in a Boreal Granitic Till

Chemical weathering rates and erosion rates of granitic till in northern Sweden have been estimated. The present-day chemical weathering rate is compared with the long-term average weathering rate since the last deglaciation approximately 8,700 years ago. Also, the present-day release rates of major and trace elements due to chemical weathering are compared with the mobility of these elements in a spodosol profile as shown by soil water samples from the vadoze zone. The estimation of the past weathering rate is based on elemental depletion trends in a soil profile (typic haplocryod), whereas the present weathering rate is based on elemental input/output budgets in a small catchment (9.4 km2). The long-term average chemical erosion rate, expressed as the sum of major element oxides (SiO2, Al2O3, CaO, Fe2O3, K2O, MgO, MnO, Na2O, P2O5, TiO2), was estimated to be 4.9 gm−2 yr−1. The long-term base cation (Ca2+, Mg2+, Na+, K+) depletion was 0.325 keq ha−1 yr−1. The current chemical erosion rate was estimated to be 2.4–3.0 g m−2 yr−1, which is at least an order of magnitude higher than the rate of physical erosion, and the base cation flux due to chemical weathering is 0.356–0.553 keq ha−1 yr−1. However, 0.074 keq ha−1 yr−1 of this flux may be related to cation exchange processes induced by atmospheric input of acid rain. There is no evidence for any recently increased weathering rate of silicates in this area. The inputs of Cd, Cu, Ni and Zn exceed the outputs, and hence, these elements are currently accumulating in the