Dr. Audrey Sawyer
The Geological Sciences Colloquium Series presents Dr. Audrey Sawyer discussing “Surface water-groundwater exchange and nitrogen fate in tidal rivers” on Friday, April 12, at 2 p.m. in Clippinger 205.
Sawyer is Assistant Professor in the School of Earth Sciences at Ohio State University.
Abstract: Tides in coastal rivers can propagate tens to hundreds of kilometers inland and drive pulses in water and nutrient exchange between rivers and their surrounding aquifers. Our group is using observations and models to understand enhanced surface water-groundwater exchange and nitrogen transport in tidal rivers. At our field site in White Clay Creek (Delaware, USA), we observe that tidal water table fluctuations aerate shallow groundwater in the banks, which allows high nitrate concentrations to develop. Continuous depth-resolved measurements of redox potential suggest that the zone of elevated nitrate is relatively stable over tidal timescales but moves up or down in response to storms. Much of the nitrate is removed by denitrification along oscillating flow paths towards the channel. However, denitrification is limited near the sediment-water interface by the mixing of groundwater with oxygen-rich river water. Our models predict that the beds of tidal rivers play an important role in removing new nitrate inputs from discharging groundwater but may be less effective at removing nitrate from river water. Nitrate removal and production rates are expected to vary significantly along tidal rivers as permeability, organic matter content, tidal range vary. It is imperative that we understand nitrogen dynamics along tidal rivers and their role in nitrogen export to the coast.
Upcoming Colloquia
Chris Atchison of University of Cincinnati on “Moving beyond tradition: Rethinking field-based teaching and learning in the geosciences” on April 19 at 2 p.m. in Clippinger 205.
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