UC Santa Cruz

Due to population growth, shifts in land use, and climate change, there is an increasing demand for fresh water worldwide. Groundwater is an increasingly critical resource used to meet demand but is facing both decreasing supply and quality. Many aquifers have the capacity to store more groundwater, and managed aquifer recharge (MAR), in which surface water in infiltrated into shallow aquifers for later use, is a strategy that can help to replenish groundwater supplies and potentially improve water quality. In order to ensure that MAR systems deliver maximum benefits, it is critical to quantify the hydrologic and biogeochemical processes that occur during infiltration. In this dissertation, I present three original studies that use field, laboratory, and analytical techniques to investigate the linkages between the hydrologic and biogeochemical cycles during infiltration for MAR and the potential implications for groundwater management. In Chapter One, plot-scale infiltration tests showed that a readily-available soil carbon amendment (wood chips) could enhance nitrate removal during rapid infiltration. In Chapter 2, linked field and laboratory studies demonstrated that another soil carbon amendment, almond shells, can promote more efficient nitrate removal than wood chips, but also can facilitate the release of geogenic trace metals. In Chapter Three, multi-criteria decision analysis (MCDA) was paired with a GIS in order to assess where recharge occurs, could occur, or could be developed through MAR projects in Santa Clara County, California. Collectively, these studies help to further our understanding of both hydrologic and biogeochemical processes and inform sustainable water resource management.