Hydrological Control of Particle Entrainment and Nitrogen Cycling in Beach Aquifer Mixing and Reaction Zones

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Sandy beaches are valuable recreational and economic resources in coastal regions, and also provide important but often underappreciated biogeochemical and ecological services. Beach aquifers are important hydrological interfaces between land and sea through which terrestrial contaminants dissolved in groundwater pass prior to reaching the ocean. Within these aquifers are reactive zones that can moderate chemical fluxes; understanding of the processes that control such reactivity is essential for predicting the conditions that promote biogeochemical and ecological benefits. The objectives of this work are to gain new understanding of the role that physical processes of fluid flow and organic particle transport have in maintaining the reactivity of beach aquifers and to assess the potential impact of anthropogenic and natural changes on contaminant loads to the ocean. This field, laboratory, and modeling study will (1) assess the driving mechanisms, patterns, and rates of fluid flow and associated organic particle incorporation into sandy beaches as a result of tide and wave action, (2) characterize the amount, nature, and reactivity of organic matter in beach sediments and porewater, and (3) determine spatial and temporal variations in the concentrations and fluxes of nutrients to and through the beach resulting from flow, mixing, and respiration of particulate and dissolved organic substrates. The proposed work will fill a gap in knowledge that will allow inference of potential reactivity from the physical characteristics of beach aquifer systems. The predictive capacity developed from the scientific results can be transferred to other systems and processes (such as oil spill remediation) and will enable prediction of potential effects of human influences and longer-term changes in sea level and climate on the ecological services of beach aquifer reactors. The research will aid beach managers in assessing the ecological value of sandy beaches and the need for management activities to maintain ecosystem services. The work may also help managers concerned with coastal eutrophication make more accurate estimates of the nutrient loads to estuarine and coastal waters based on easily assessed physical characteristics of shorelines. The research will have educational impacts, providing interdisciplinary training for graduate and undergraduate students interested in increasingly inter- and multi-disciplinary environmental issues. The field sites will be developed into hands-on training sites for hydrogeology courses at the University of Delaware (UD) and for the UD TIDE Camp for high school students.