Slope-Aspect Control on Geochemical Weathering within the Boulder Creek Critical Zone Observatory
Abstract
Geochemical weathering in the Critical Zone (CZ) results in regolith formation and solute generation, which are essential parts of landscape evolution and nutrient cycling. A process-based understanding of geochemical weathering is integral to prediction and evaluation of how Earth surface processes will respond to natural and anthropogenic perturbations, such as global climate change and land use. In part due to the difficulty of collecting deep samples, previous CZ investigations focused primarily on shallow (<3 m) weathering. This study evaluates chemical and mineralogical changes from the surface to depths of up to 15 m as function of hillslope aspect in the Gordon Gulch watershed of the Boulder Creek Critical Zone Observatory (BcCZO). In the shallow subsurface, weathering intensity is higher for south-facing hillslopes than for north-facing slopes. However, the thickness of weathered material is deeper on north-facing hillslopes based on exchangeable cation concentration and clay fraction trends. Variability of these depths and intensities are possibly linked to unconstrained structures and mineralogy in the underlying bedrock. Pervasive geologic heterogeneity throughout the BcCZO complicates identification of parent material for the weathering profile, and as a result, commonly used methods for calculating weathering rates (e.g., mass-balance models) do not accurately characterize the complex variability of protolith composition and mineral reactions. Ultimately, this study finds that additional data, such as depth-dependent quantitative mineralogy, are needed in order to comprehensively evaluate weathering processes in areas with highly heterogeneous bedrock, such as the BcCZO.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2016
- Bibcode:
- 2016AGUFMEP43C0978E
- Keywords:
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- 0439 Ecosystems;
- structure and dynamics;
- BIOGEOSCIENCESDE: 1039 Alteration and weathering processes;
- GEOCHEMISTRYDE: 1813 Eco-hydrology;
- HYDROLOGYDE: 1824 Geomorphology: general;
- HYDROLOGY