Hydrologic monitoring of a small semi-isolated depressional wetland on St. Simons Island Georgia

Abstract:

Small depressional wetlands are important landscape features in terms of ecological, hydrologic, and biogeochemical functions. In coastal environments, particularly barrier islands, depressional wetlands are highly understudied. This is the result of their small size and close proximity to highly charismatic salt marshes. Small freshwater wetlands on barrier islands can be driven by freshwater lens dynamics, precipitation – evaporation balance, or some combination. In some cases, these systems even show a tidal signal due hydraulic tidal influence on the freshwater lens. Our objectives were to 1) monitor water levels to determine likely hydraulic and hydrologic influences; 2) monitor solute balance in accordance with hydrologic balance to constrain possible water sources; and 3) delineate the wetland watershed to quantify land use / land cover and determine the potential source area.

The study site is a small semi-isolated freshwater wetland on a barrier island along the Georgia coast (USA). The wetland has known outflows but no discernable inflow channels. Connectivity to the freshwater lens and upland runoff are largely unquantified as is the response to direct precipitation in the wetland. Water levels and specific conductivity were recorded using a pressure transducer and conductivity probe with internal dataloggers in a stilling well. Several rain gauges have also been installed at the site. Our preliminary findings show that the wetland has a strong seasonal response to precipitation (draws down during summer and fills during winter/spring). Evidence of hydraulic connection to the freshwater lens was observed during preliminary analysis but require further investigation. The watershed delineation indicates substantial impervious cover (e.g parking lot and an primary school) and substantial forest cover. Further analysis will investigate variable source areas and potential solute response to rain events.