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Observation of tidal influence on porewater nutrients in a submarine groundwater discharge zone
Abstract

Observation of tidal influence on porewater nutrients in a submarine groundwater discharge zone

Nathaniel Winn and Matthew C. Schwartz
American Geophysical Union, Fall Meeting 2020, Vol.2020
American Geophysical Union 2020 fall meeting (Virtual, 12/12/2020–12/17/2020)
12/2020

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Abstract

Submarine groundwater discharge (SGD) is the process by which fresh or brackish groundwater moves through porous sediments to the surface water. SGD is a method of transportation for different nutrients, metals, pollutants, and freshwater to enter our coastal waters. Tidal pumping and sub-surface hydraulic pressure are the key driving forces that move groundwater through the land-sea interface. At high tide, porewater in the subterranean estuary (STE) is predicted to have a low concentration of nutrients due to seawater recirculation. During the ebb tide, SGD through the STE will cause nutrient concentrations to increase. The objective of this study is to observe how porewater nutrient concentrations are impacted by tides at an SGD positive zone. The area of study is located at the Gulf Islands Nation Seashore: Naval Live Oaks Preservation Area in Santa Rosa County, Florida. The area of interest ranges from the shoreline to about 30 meters offshore in Santa Rosa Sound. Previous research has indicated this site as an SGD positive through radon isotope analysis. Piezometers are inserted into the sediment on the seafloor at different depths to extract groundwater. The transects of porewater extent to three different distances away from shore to show the movement of groundwater. Elevated nutrient levels are present in the subterranean estuary. The nutrient concentrations appear to have spatial variability but are showing changes as the tidal cycle progresses. Collecting evidence of nutrients moving through a subterranean estuary and interacting with the SGD interface can provide a better understanding of tidal pumping and the impacts that it can have on an aquatic ecosystem.

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