EXPLORING GROUNDWATER DYNAMICS IN A COASTAL FOREDUNE ENVIRONMENT

Barrier islands are sandy, low-lying landforms that are vulnerable to climate-change-induced rising sea level and changing storm activity. The height of the seaward-most dune (the foredune) on a barrier island largely determines how a barrier island will respond to changing conditions. Dune vegetation, such as perennial grasses, is essential to the growth and stabilization of foredunes. However, little is known about the effect of groundwater fluctuations on the growth of dune vegetation. To better understand water table fluctuations in the vicinity of dune vegetation, we installed 5 wells in June 2015 along a cross-shore transect parallel to an existing dune vegetation experiment, located on Hog Island, within the Virginia Barrier Islands chain. The wells extend from the crest of the foredune to near the water line and were outfitted with Schlumberger CTD (conductivity, temperature and depth) Divers to measure salinity and water elevation (pressure). We gathered two months of data and retrieved precipitation and tide level data from stations near our site. Water level at each of the wells fluctuates with the spring-neap tidal cycle, but only the wells closest to the shore reflect daily tidal fluctuations. We also found that the fresh water lens does not mimic the smaller scale (~1m) topography associated with a protodune located in between the foredune and sea level, suggesting that there may be less fresh water available for plants growing on a developing protodune relative to those growing on a fully developed foredune. Our next steps will include comparisons of root depth to test this hypothesis. An assessment of plant growth rate as a function of water table elevation will yield additional insights into the effect of groundwater dynamics on dune formation and growth.