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Smith Lecture: Surface Water-Groundwater Exchange and Nitrogen Fate in Tidal Rivers

Audrey Sawyer, Ohio State University
Friday, September 8, 2017
3:30-4:30 PM
1528 C.C. Little Building Map
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 field observations and numerical models to understand enhanced surface water-groundwater exchange and nitrogen transformations in the riparian zones of 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 within centimeters of the sediment-water interface by the mixing of groundwater with oxygen-rich river water. Our models predict that the benthic zones 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.
Building: C.C. Little Building
Event Type: Lecture / Discussion
Tags: Lecture
Source: Happening @ Michigan from Earth and Environmental Sciences