Ground Water-Surface Water Seepage at Select TIME Sites

The bi-directional exchange of groundwater with coastal surface waters may influence not only coastal-water and geochemical budgets, but may also impact and direct coastal ecosystem change (D'Elia, et al., 1981; Valiela, et al., 1990; Burnett et al., 2003). For example, the widespread discharge of nutrient-enriched submarine groundwater into an estuary or lagoon may contribute directly to the onset and duration of eutrophication (Bokuniewicz, 1980; Giblin and Gaines, 1990), as well as the development of harmful algal/bacterial blooms (Laroche et al., 1997). Most often, this submarine groundwater discharge (SGD) (defined here as a composite of meteoric, connate and sea water) occurs as hard-to-constrain diffuse seepage, rather than as focused discharge either through vent or collapse features (Swarzenski et al., 2001). As a result, quantifying SGD rates has remained difficult for both oceanographers and hydrologists alike.

This project uses an adaptation of an old tool, the Lee-type manual seepage meter (Lee, 1977), with a state-of-the-art electromagnetic flow meter that enables rapid, autonomous, bi-directional measurements of fluid exchange rates across the sediment/water interface (Rosenberry and Morin, 2004). When such measurements are coupled and interpreted with surface and groundwater pressure, salinity and temperature data, as well as other complementary measurements such as excess watercolumn 222Rn activities, then realistic groundwater/surface-water exchange rates can be obtained in dynamic coastal environments (Swarzenski et al., 2004).