A Scope for the Subsurface: How Geophysics Can Inform Hydro-biogeochemical Studies in Managed and Unmanaged Systems

Abstract:

One of the greatest challenges in studies of hydrological and biogeochemical processes is determining the distribution of sub-meter scale subsurface structural features and characteristics. Bedrock fractures, preferential flow paths, and soil texture are first-order controls on the fates of water, carbon (C), and nutrients (e.g., nitrogen, sulfur, and phosphorus) in terrestrial systems, yet they are also highly variable and difficult to determine across scales of interest (e.g., from point to hillslope to catchment). Geophysical techniques provide a “scope” that can help to characterize these subsurface properties; providing guidance for the design of observational/experimental studies if made in advance, or an independent dataset to test the results of these studies if made following. In this talk, I will provide examples from research in both managed (i.e., agricultural) and unmanaged (i.e., high elevation, mountainous catchments) where geophysical surveys have helped us to test our understanding of hydrological flow paths and residence times of C and nutrients. I will show how in combination, hydrobiogeochemical observations, geophysical surveys, and modeling techniques have provided us with relevant information and compelling visuals to inform farmers’ decision-making in managed systems, and greater understanding of critical zone structure and function in unmanaged systems. Finally, I will suggest how geophysics may be helpful in some of our ongoing research projects in the Critical Zone Observatory (CZO) Network, the Long-term Ecological Research (LTER) Network, and in agricultural systems in Colorado and California.