Groundwater Flow At The Georgia Coast: Magnitude And Drivers Across A Back Barrier Island – Marsh Transect

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The movement of groundwater in the coastal marsh plays a vital role in nutrient loading to the coastal ocean and in the structuring of marsh vegetation. To quantify the magnitude, distribution and driving forces of groundwater flow, a series of CTD meters were installed in a transect of shallow piezometers behind Blackbeard Island, a back barrier island at the coast of GA. Hydraulic conductivity was determined through slug tests and confirmed a relatively homogenous permeable layer consistent with core logs. The contribution of density driven flow was estimated from an analysis of co-registered measurements of pore water salinity and pressure, and found to contribute less than 10% to the overall flow velocity. Tidal variations in pressure time-series were removed through low-pass filtering. Comparison between the signal with tide removed and precipitation data demonstrated that precipitation is a critical driver of groundwater flow in the upland, with spatial gradients in freshwater head lagging precipitation accumulated over 2 by approximately 5 days. Understanding the current drivers of groundwater flow will help constraining the impact of climate change such as sea level rise or land use change on groundwater flow patterns in coastal marshes.