Discharge of groundwater from the seafloor is known at least since the days of the Romans. Already Sonrel (1868) reported the discharge of freshwater from submarine springs and speculated on their use and risks for sailors.

Since then several studies have considered the importance of fluid discharge from sediments for nutrient budgets of coastal environments, formation of offshore plankton blooms, hydrological cycles, or the release of trace elements and gases such as radon from the seafloor (Johannes, 1980; Valiela et al., 1990; Moore, 1996; Cable et al., 1997; Laroche et al., 1997).

Seepage may occur over large areas and deliver significant amounts of fresh water, dissolved constituents, and trace gases to the world ocean.

New results from different regions around the World revealed that groundwater seepage is important to the coastal environment from a hydrological as well as environmental point of view.

Reports concerning fluid discharge in coastal areas, e.g., off Italy, Greece, Crete, Japan, Israel, Lebanon, Florida, and the Baltic proper, underlined the worldwide occurrence of this transport pathway from land to the ocean (Kohout, 1966; Zektser, 1996; Schlüter, 2002; 2004; Taniguchi et al., 2002). Considering the different regional settings, different modes of fluid flow from sediments can be distinguished: (1) focused flow along fractures in karst and rocky areas, (2) dispersed flow through soft sediments, and (3) recirculation of seawater through sediments. The compositions of fluids range from nearly pure freshwater, as is the case in karst areas, to the seepage of saline water, as reported for regions off Florida (Cable et al., 1997).