SPATIAL AND TEMPORAL PATTERNS OF GROUNDWATER ELEVATION AND SALINITY ON ASSATEAGUE ISLAND

Assateague Island is a 37-mile long barrier island located along the eastern shore of the Delmarva Peninsula spanning two states – Maryland to the north and Virginia to the south. Assateague Island National Seashore is a popular tourist destination due to its wild horse population and the diversity of coastal environments. Three miles are developed, with campgrounds and nature trails; the rest of the barrier island is a mosaic of ocean, dune, forest, and marsh ecosystems. Assateague Island provides habitat for several protected species including the Piping Plover and Seabeach Amaranth.

Unlike coastal environments with riverine or continental groundwater input, there is no external source of freshwater other than precipitation; the plants and animals on the barrier island, especially those in the interior forest ecosystem, rely on the fresh groundwater and freshwater ponds. This freshwater is replenished by precipitation and is vulnerable to changes in salinity and volume. In the short term, it is susceptible to mixing with saltwater as a result of storm surges. In the longer term, climate change and sea level rise may change the volume of freshwater available through altering patterns in precipitation and reducing the land area on the island.

The National Park Service, in a joint project with the U.S. Geological Survey, is studying the Island's water resources with a series of 32 groundwater wells and six meteorological stations distributed throughout the Maryland district. This study is focused on understanding the distribution of fresh groundwater on Assateague Island, the seasonal patterns in groundwater changes, and assessing the vulnerability to climate change. Preliminary results show a dynamic water table responsive to daily evapotranspiration and tides, seasonal precipitation, and storm surges, with spatial heterogeneity in changes in water table responsiveness and salinity within shallow wells. These changes in freshwater availability are important to quantify and model, as they may result in ecosystem shifts by increasing susceptibility to disease and infestation of vegetation due to stress from exposure to salt or limitation of gas exchange through roots in the unsaturated zone of the ground.