The degree to which subsurface plumbing – pores space and its connectivity—fluctuates and/or evolves is largely ignored in predictions of how Earth’s critical zone is and will respond to changing climate, atmospheric (e.g., CO2), and land use/cover drivers. We argue that the community needs to consider that changes in the subsurface structure throttles the partitioning of water. We will provide several examples from across different land cover types and lithologies where subsurface pore space can respond to changes in these drivers altering groundwater recharge and interflow. Specifically, we focus on: 1) how changing summer rainfall patterns can alter groundwater recharge patterns in hillslopes overlain by shrink-swell soils, 2) how the encroachment of woody vegetation may create a greater degree of heterogeneity in patterns of interflow, 3) how shift in local and regional groundwater bodies can drive the generation of porosity at depths, and 4) how changes in wet-dry cycles, root growth, and carbon turn over may influences soil structure in measurable ways that alter subsurface hydrologic partitioning. We demonstrate that infrequent but high intensity storms can enhance groundwater recharge in hillslopes mantled by soils with shrink-swell properties, woody encroachment may enhance macropore generation at depth, increased mean annual precipitation can decrease effective porosity, and deepening the penetration of oxygen into the subsurface can increase porosity. Our goal is to prompt the community to not only ask if these are fundamental processes we must understand to better quantify water storage and fluxes, but should we consider what these shifts potentially mean when it comes to carbon, nutrient, and weathering fluxes.
Sullivan, Pamela L, Sharon A Billings, Daniel Hirmas, Li Li, Alejandro N Flores, Matthew G Sena, Hang Wen, Morgan Okeson, Caroline Nash, Ligia Souza, Kyler Lang (2019): Do we need to account for dynamic changes in subsurface plumbing to project blue water stocks and fluxes?. American Geophysical Union Fall Meeting, San Francisco, CA, December 9-13, 2019.
This Paper/Book acknowledges NSF CZO grant support.