Variation in groundwater salinity in a tidal salt marsh basin, North Inlet Estuary, South Carolina

Event Location: 
BCCMWS Room 100
Event Date: 
Thursday, November 13, 2014 - 3:00pm
Event Type: 
SCMSS Seminar Series

Presenter: Matthew Kestner

Salt marshes are very important to coastal ecosystems. Not only are they very effective storm buffers and nursery grounds, they are also highly productive. This productivity is influenced heavily by groundwater providing a geochemical exchange of nutrients. Carter et al, 2008 look at the brackish/fresh groundwater interchange to see how this interface changes over the course of a year. They focus in on how precipitation and evapotranspiration (ET) affect Crabhaul Creek, a tidal salt marsh basin at the boundary of terrestrial and marine environments in North Inlet. The installment of Piezometers where installed  in transects to measure salinity while monthly Electrical Resistivity data was collected at spring tides to monitor the fresh/brackish groundwater interface. The study then constructed hydrogeologic models using SUTRA Suite from the USGS to determine whether variations in freshwater infiltration could cause movement in the fresh/brackish groundwater interface. The resistivity showed a zone of freshwater to the west every month and would periodically migrate into the eastern part of the survey.

Resistivity models suggest two hydrologic flow systems within the marsh basin: a shallow, upper flow system in the top 1 m of the marsh mud, and a deeper flow system controlling the position of the freshwater-brackish interface (Carter et al, 2008). This upper layer is found to be ubiquitous dominated by tidal inundation.  At lower depths however, it appears that tides are not the dominant driving force. The models suggest that the sand layer is a preferred conduit for freshwater from the uplands to flow into the marsh. Rainfall events and ET where explored as driving forces but no pattern was developed. Electrical Resistivity was effective in defining the freshwater-brackish interface, but additional studies will be required to fully understand how ET and freshwater movement affect the deeper flows.