University Honors

Managed aquifer recharge (MAR) is a suite of methods used to replenish groundwater supply. Aquifer replenishment uses a range of water sources such as surface water, treated wastewater, and stormwater. In the critically overdrafted basins of Pajaro Valley, farm owners are using a unique MAR method, DSC-MAR, which allows for on-farm infiltration of untreated stormwater. Small infiltration basins (~4 acre) are installed on the farmland and surrounding stormwater is funneled into the basin. However, untreated stormwater in agriculturally-dense regions like Pajaro Valley can have high concentrations of pollutants including nitrates. To perform in situ remediation of stormwater nitrate, carbon-rich media such as almond shells and wood mulch have been added to the aquifer basins to induce denitrification, a naturally occurring soil microbial process that reduces nitrate to nitrogen gas, which is impacted by carbon availability and quality. However, the impacts of wet-dry cycling during seasonal rainfall events on carbon-rich amendments in MAR basins is not well understood. In this project, we used batch reactors to compare organic carbon release and degradation from carbon-rich amendments subjected to oxic, anoxic, or oscillating oxic-anoxic conditions. By assessing the influence of oxic-anoxic conditions on carbon amendment breakdown, we can determine which conditions promote dissolved organic carbon release and enhanced carbon media degradation. This would then allow for better insight into carbon amendment management at DSC-MAR sites for longer term in situ treatment of nitrate contamination in infiltrating waters.