From pore-scale to watershed: parameterizing heterogeneous rock properties across scales to inform predictive environmental models

Abstract

Mountainous watersheds throughout the United States are going to change in the future due to continued shifts in land use and climate patterns, and it is imperative that scientists understand how current systems operate in order to better predict how these regions are going to change in the future so that we can better allocate our critical resources. The East River Valley (ERV) watershed, a mountainous watershed located near Crested Butte, Colorado within the Upper Colorado River Basin is an intensely studied hydrologic and biogeochemical system, where localized igneous intrusions have contact metamorphosed Mancos Shale bedrock, imparting heterogeneity to an otherwise fairly homogeneous marine shale. This study focuses on a) characterizing and parameterizing intrinsic rock properties of the variably metamorphosed Mancos Shale bedrock in the ERV in order to reduce watershed scale heterogeneity and assist in predictive modeling of hydrobiogeochemical dynamics, b) addressing possible contributions to scale-dependent weathering rates by reporting a detailed experimental investigation of the microscale network of fluid pathways which drive weathering processes at a watershed scale, and c) analyzing whole rock and carbonate isotopic concentrations of the ERV bedrock in order to trace carbon and nitrogen movement during contact metamorphism, providing insight into the watershed-scale carbon and nitrogen sourcing from bedrock weathering. This study shows that by characterizing intrinsic rock properties, we can parameterize heterogeneous rock properties across scales to inform predictive environmental models.