Linking Physical Infiltration Processes to Changes in Water Quality and the Potential to Address Legacy Contaminants during Flood-Managed Aquifer Recharge

Abstract:

We are conducting linked column and field experiments to elucidate relations between infiltration dynamics and water quality during infiltration for flood-managed aquifer recharge (Flood-MAR). There is interest in California for applying Flood-MAR as a strategy to manage flood flows, and to address chronic declines in groundwater levels. To increase the effectiveness of this strategy, it is important to identify soils with appropriate properties to allow rapid infiltration while also considering potential impacts to water quality. Contaminants present in infiltrating water, legacy pools from past land use, and leaching from soils are issues of concern when implementing Flood-MAR across large areas. We wish to understand which soils provide appropriate infiltration rates, how soil properties may change during Flood-MAR, and how different soil types and infiltration rates may affect nitrogen cycling. We are also evaluating if soil carbon amendments could help to enhance rates of denitrification during infiltration. We collected soil cores from a working vineyard adjacent to the Cosumnes River (Central Valley, California), where a Flood-MAR project is intended to operate. Six 1-m-long, intact soil cores were collected from two locations at the site, then transported back to the laboratory used to run flow through experiments. Soil samples co-located with sediment cores will be analyzed for texture and total carbon/nitrogen (C/N). Conditions in unaltered cores will be compared to cores amended with a carbon source (wood chips and almond shells). A solution containing elevated nitrate concentrations will be continuously pumped through the cores to maintain saturated conditions. Each test will run for 20 days, with infiltration rates of 0.1 to 0.5 m/day. Daily fluid samples will be collected from each column and analyzed for nutrient concentrations and dissolved organic carbon. Upon completion of the flow through experiments, soil samples will be collected from the cores for analysis of total C/N and microbiological analyses. We have also measured water levels and infiltration rates at the field site during natural flood events, and completed soil textural analyses from field samples. We plan to use these results to estimate infiltration rates during Flood-MAR and anticipate potential impacts on water quality.