USING WATER LEVELS AND SALINITY TO CHARACTERIZE THE FLOW REGIME IN A TIDALLY-RESTRICTED MID-ATLANTIC SALT MARSH IN GREENBACKVILLE, VA

Three observation wells were installed in summer 2014 across an anthropogenically modified salt marsh in Greenbackville, VA, as part of hydrologic network monitoring the effects of sea level rise. Tidal flow and saltwater influence in the marsh are restricted because ocean water input is limited to a drainage ditch connecting the northwestern part to a marina. Well locations were selected to determine groundwater flow direction and to characterize the hydrologic regime in different parts of the marsh. Water levels were recorded and salinity values were derived from Solinst LevelLogger™ data at each of the three sites. Over a study period of April to July 2015, the mean salinities were 13‰ in the northeast corner closest to bordering roads, 26‰ near the marina, and 23‰ in the southwestern part of the marsh at the edge of a stand of Phragmites. These values are lower than (13 and 23‰) or on the low end (26‰) of Chincoteague Bay salinities reported during April to July (2001 to 2015). Variations in water level profiles in each of the wells reflect each site’s hydrogeological response to precipitation events, surface salt water intrusion caused by wind transport, and tidal cycles. In the northern part of the marsh, water levels, but not salinities, seem to respond to both tidal influence and precipitation events to varying degrees. In the southwestern part of the marsh, water levels were constant and salinities declined steadily. Decreased salt marsh salinity may favor the advancement of invasive Phragmites and reduce biodiversity in Greenbackville marsh. Continuing analysis and classification of satellite imagery will track changes in marsh flora, such as trends in marsh community composition.