AbstractsBiology & Animal Science

Hydrologic connections from the groundwater to the lower atmosphere are well established in natural systems, but much less is known about groundwater-surface water interactions in watersheds with significant human development. Groundwater can provide an important buffer to surface variability through baseflow and groundwater-supported evapotranspiration. However, it is unclear how widespread groundwater pumping and irrigation have altered these exchanges both spatially and temporally. Understanding the dynamics of developed hydrologic systems, and how they vary from natural systems, is an important step to better predicting and managing for future change. This dissertation addresses this gap using integrated numeral modeling to systematically analyze groundwater-surface water interactions in developed watersheds. Novel statistical tools are developed to evaluate the spatio-temporal impacts of moisture-dependent groundwater pumping and irrigation within fully integrated systems. Results demonstrate groundwater development effects that extend beyond typical water balance considerations. For example, feedbacks between irrigation demand and groundwater pumping are observed when water table depths are within a critical range (roughly 2-10m). Furthermore, groundwater pumping and surface water irrigation are shown to alter the temporal memory of both groundwater storage and land energy fluxes. These results indicate that regional management operations can alter the variability and sensitivity of integrated systems. Regional analysis of groundwater behavior is also extended to the continental scale using the first high-resolution fully integrated groundwater surface water model of the contiguous US. Analysis of a predevelopment simulation establishes baseline behavior and demonstrates the utility of integrated modeling for evaluating systems that are too large to characterize with sparse observation networks. Finally, extensions of the pre-development model to managed systems are outlined in a framework to evaluate the impacts of 20th century groundwater depletions on streamflow behavior across the US. Advisors/Committee Members: Maxwell, Reed M. (advisor), Singha, Kamini (committee member), Hering, Amanda S. (committee member), Lund, Jay (committee member).