B057-04
Using high spatiotemporal nitrate measurements to assess nutrient transport and transformations at the terrestrial-marine interface of a tidal watershed
Thursday, 10 December 2020: 19:12
Virtual
Emilio Grande, University of California Santa Cruz, Santa Cruz, CA, United States, Margaret A Zimmer, Duke University, Durham, NC, United States, Erin Cedar Seybold, Kansas Geological Survey, Lawrence, KS, United States, Anna Elizabeth Braswell, Duke University, Nicholas School of the Environment, Durham, NC, United States, Corianne Tatariw, University of Maine, Orono, ME, United States, Andria Greene, University of California Santa Cruz, Earth and Planetary Sciences, Santa Cruz, United States, Maya Montalvo, University of California Santa Cruz, Earth and Planetary Sciences, Santa Cruz, CA, United States, Francois Birgand, North Carolina State University, Biological and Agricultural Engineering, Raleigh, NC, United States and Ate Visser, Lawrence Livermore National Laboratory, Nuclear and Chemical Sciences Division, Livermore, CA, United States
Abstract:
Salt marshes have the potential to intercept and transform terrestrially sourced pollutants en route to sensitive marine environments. While the importance of riverine nutrient export to coastal systems has been widely described, the contributions and fate of nutrients, particularly nitrate, from diffuse groundwater sources remain poorly constrained. Here, we present results from our field-based study that characterizes nitrate contributions from groundwater and surface water to salt marshes as well as the internal biogeochemical processing rates within marshes at the Elkhorn Slough National Estuarine Research Reserve in Monterey Bay, CA. We instrumented a salt marsh transect with a network of shallow groundwater wells, connected to a multisource pump manifold. Combining this infrastructure with a field-based spectrophotometer, we
monitor porewater nitrate concentrations at sub-daily time scales at multiple positions across a marsh transect.
We used the spatiotemporal variation in nitrate concentrations at sub-hourly timescales to understand how nutrient flushing and loading to the salt marsh fluctuates across tidal cycles. To estimate denitrification rates across the study transect, we combined nitrate measurements with high-frequency in situ redox measurements and surveys of nitrogen-argon (N2:Ar) ratio in porewater. The high-frequency nitrate measurements coupled with analyses of porewater dissolved gases provides detailed information on subsurface transport of terrestrially-derived nitrate into marsh ecosystems and its potential removal mechanisms along shallow flowpaths. Specifically, these results highlight the complex nature of diffuse groundwater nutrient loads in coastal settings.
