Using Particle Tracking to Link Floodplain Hydrological Processes to Biogeochemical Function

David Rogers, Stanford University

Photo of David Rogers

Mountainous watersheds are often referred to as the world’s water towers, providing more than half of Earth’s freshwater. The interleaving processes that control water quantity and water quality starting from the head of a watershed to its outlet downstream are broadly termed the watershed “function”. It is well understood that floodplains, a fundamental component of watersheds, store large quantities of groundwater and promote significant biogeochemical activity. However, we still lack a quantitative understanding of the role floodplains play in overall watershed function and how different floodplain attributes (e.g., soil thickness, valley width, stream gradient) affect their contribution. The goal of this research is to develop a framework to quantitatively evaluate floodplain hydrologic and biogeochemical function across a parameter space representative of floodplains in mountainous watersheds. Biogeochemical function is related to net nutrient turnover or flux between components (e.g., between floodplain and stream), though this is difficult to quantify. It is easier to understand hydrologic regimes of floodplains by measuring, for example, groundwater levels and stream discharge. Therefore, in addition to exploring floodplain function, this research also aims to provide a link between hydrologic processes and biogeochemical function, primarily using groundwater residence time distributions. To quantify residence time distributions for the study floodplain, I will develop hydrologic simulations using an integrated hydrologic model coupled with a particle tracking tool. I will then use Monte Carlo methods and distance-based global sensitivity analysis to understand the effects of varying floodplain attributes on residence time distributions. Next, I will layer in a coupled geochemical model to quantify nutrient fluxes and turnover, accompanied by a global sensitivity analysis. The outcome of this research will include identification of a few salient floodplain features that drive residence time and nutrient fluxes within floodplains, allowing for a more robust and scalable understanding of how floodplains impact watershed function.

Abstract Author(s): D. Brian Rogers, Kate Maher, Department of Earth System Science, Stanford University