Effects of climate on chemical weathering in watersheds

Climatic effects on chemical weathering are evaluated by correlating variations in solute concentrations and fluxes with temperature, precipitation, runoff, and evapotranspiration (ET) for a world-wide distribution of 68 watersheds underlain by granitoid-type rocks. Chemical fluxes for SiO2 and Na exhibit statistical increases with precipitation, runoff, and temperature. In contrast, K, Ca, and Mg fluxes exhibit no climatic correlation, implying variabilities dominated by processes such as nutrient cycling and soil ion exchange reactions. An optimization model defines the reinforcing effects of climate by exponentially increasing the slope of a linear precipitation function as temperature increases, and by linearly increasing the intercept of an exponential Arrenhius temperature function as precipitation increases. The respective SiO2 and Na activation energies calculated from this model are 62 and 70 kJ•mol-1. Such a climatic reenforcement model provides a simple analog for the use of watershed data for calibrating a weathering feedback in climate models.