Hydrological controls on chemical weathering rates at the soil-bedrock interface

Abstract

Chemical weathering of bedrock is critical to maintaining terrestrial life, and climate, typically as manifested by precipitation, is often identified as having a first-order control on rates of chemical weathering. The ability of precipitation to dissolve rock, however, is modulated by the properties of the overlying soil that influence the contact time between water and minerals. Flume experiments were conducted to investigate the hydrological controls on rates of chemical weathering. Solute concentrations of runoff flowing across synthetic bedrock overlain by nonreactive pseudosoils of differing hydraulic conductivities were measured to examine the role of seepage velocity in influencing weathering rates on steep slopes. The results suggest that, where weathering is not limited by the supply of fresh minerals, weathering rates should increase with decreasing hydraulic conductivity. In addition, a mathematical relationship between hydraulic conductivity and chemical weathering on hillslopes is introduced to explore the hydrological controls on feldspar and calcite dissolution rates. The mathematical model supports the results from the experiments.