GSA Annual Meeting in Denver, Colorado, USA - 2016

Paper No. 189-3
Presentation Time: 8:40 AM


MICHAEL, Holly A., Department of Geological Sciences, University of Delaware, 255 Academy Street, Newark, DE 19716, HEISS, James W., Geological Sciences, University of Delaware, Newark, DE 19711, KIM, Kyra H., Geological Sciences, University of Delaware, 700 Pilottown Road, Rm 113-F, Lewes, DE 19958, ULLMAN, William, School of Marine Science and Policy, University of Delaware, Lewes, DE 19958, RUSSONIELLO, Christopher J., Geological Sciences, University of Delaware, Newark, DE 19716, DUQUE, Carlos, Department of Geological Sciences, University of Delaware, Newark, DE 19711 and BROOKS, Thomas W., Woods Hole Coastal and Marine Science Center, U.S. Geological Survey, 384 Woods Hole Road, Woods Hole, MA 02543-1598,

Accurate estimation of nutrient fluxes to estuaries and the ocean is essential for designing appropriate management strategies to protect coastal ecosystems. It is complicated, however, by challenges not only in quantifying groundwater fluxes, but also in assessing the impacts of both the origin of discharging water and biogeochemical reactions along subsurface flowpaths. Recent advances in integrating physical and biogeochemical processes is improving understanding of the various pathways for nutrient delivery and mechanisms for attenuation prior to discharge. In Indian River Bay, Delaware, a nitrogen-limited eutrophic estuary, watershed geometry is an important factor affecting fresh groundwater flux, while flowpaths determined by geologic heterogeneity regulate attenuation of nitrate prior to discharge. Ammonium is contributed by recirculating seawater, with fluxes dependent on exchange rate, residence time, and sediment type. In intertidal zones of Delaware beaches, mixing between infiltrating seawater and discharging groundwater promotes reactivity, resulting in denitrification in freshwater-saltwater mixing zones. Measurements and modeling illustrate the impacts of these processes on nutrient fluxes in these and other coastal systems. Consideration of both geological and hydrological influences on biogeochemical reactions in groundwater prior to discharge to coastal waters is critical for estimating and managing groundwater-borne nutrient loads to nearshore marine ecosystems.