Enhanced Chemical Weathering from Geomorphic Features in the East River Watershed, Colorado

Authors

John R. Slosson¹* ([email protected]), Isaac J. Larsen¹, Matthew Winnick¹, José Marmolejo¹, Kenneth Williams²

Institutions

¹University of Massachusetts–Amherst, MA; ²Lawrence Berkeley National Laboratory, Berkeley, CA

Abstract

Physical and chemical weathering in Earth’s high-elevation regions provides sediment to downstream fluvial systems, controls river chemistry, and regulates long-term climate. Mountain landscapes contain a diverse set of landforms generated by geomorphic processes, including landslides, moraines, and rock glaciers. These landforms generate unique flowpaths and water-rock interactions for precipitation as it moves through the critical zone before becoming streamflow.

Prior work has identified landslide deposits as “hotspots” that increase dissolved solute concentrations in tectonically active mountains, but there is still considerable uncertainty as to the magnitude of which geomorphic processes influence solute chemistry across different tectonic and climatic regimes. The team measured cation and anion concentrations in 79 surface water samples collected from areas that drain a variety of geomorphic features in the East River watershed in Colorado. The results show that landslides produce higher solute loads than streams draining soil-mantled hillslopes long after landslide occurrence. Watersheds with evidence of active bedrock incision also generate high solute concentrations, whereas solute concentrations in surface waters draining glacial moraines and rock glaciers are comparable to values from watersheds draining soil-mantled hillslopes. The results have implications for understanding the sources of solute generation in alpine watersheds, including hotspots for chemical weathering and temporal variability in weathering rates.