Evaluating control of slope-aspect on geochemical weathering within the Boulder Creek Critical Zone Observatory

Geochemical weathering in the Critical Zone is an important source of mobile regolith and solutes that drive landscape evolution and nutrient cycling. An in-depth understanding of geochemical processes is integral to prediction and evaluation of Earth surface response to natural and anthropogenic perturbations such as global climate change and land use. This study evaluates chemical and mineralogical changes from the surface to depths >15 m in the Gordon Gulch watershed of the Boulder Creek Critical Zone Observatory and investigates hillslope aspect control of weathering processes. These data exhibit trends consistent with higher weathering intensity at shallow depths on the south-facing compared to north-facing hillslopes, but deeper overall weathering on north-facing hillslopes. Geologic heterogeneity complicates interpretations of parent material for the weathering profile, and greater constraints are needed to quantitatively evaluate weathering processes in highly heterogeneous bedrock.