Soil Production and Chemical Weathering Rates from Intrusive Bedrock in the East River in Colorado
Authors
José M. Marmolejo-Cossío* (jmarmolejo@umass.edu), Isaac J. Larsen, John R. Slosson
Institutions
University of Massachusetts–Amherst, MA
Abstract
The productivity of aquatic and terrestrial ecosystems relies on the release of essential elements from bedrock. The rate at which elements become accessible to biota depends on the rate soil is produced from bedrock by both physical and chemical weathering. Steep mountain catchments are global hot spots for erosion and weathering and hence strongly influence global biogeochemical cycles. However, there are still outstanding questions regarding the mechanisms of soil production and solute generation in mountain landscapes. Here, the project investigates the role vegetation plays in influencing soil production and chemical weathering within the East River watershed in Colorado. The team collected soils from forest (n=5) and alpine (n=4) ecosystems on intrusive igneous rocks and used cosmogenic nuclides and geochemical mass balance to determine soil production and chemical weathering rates. The mean chemical depletion fractions for forest and alpine soils were 0.27 and 0.15 respectively, indicating chemical weathering is a much higher proportion of soil production in forest versus alpine sites. Beryllium-10 concentration measurements are pending for additional samples, but preliminary results from forest (n=1) and alpine (n=3) indicate soil production rates are approximately 0.05 millimeter per year and 0.03 mm yr-1, respectively, suggesting bedrock is more rapidly converted to soil in the forest. Soil chemical weathering rates are 0.013 mm yr-1 and 0.006 mm yr-1 in the forest versus alpine sites, indicating that solute production in forests is higher than alpine sites. These findings suggest that migration of forests to higher elevation as climate changes will be accompanied by increases in solute generation and fundamental changes to alpine soils.