Large submarine groundwater discharge and benthic eutrophication in Bangdu Bay on volcanic Jeju Island, Korea

We estimated the submarine discharge of groundwater (SGD) and associated nutrients into the semienclosed Bangdu Bay on a volcanic island, Jeju, Korea, by analyzing Rn-222, Ra isotopes (Ra-224 and Ra-226), and nutrients in seawater, pore water, and coastal groundwater. The submarine inputs of groundwater into Bangdu Bay of 120-180 m(3) m(-2) yr(-1) (on the basis of Rn-222, Ra-224, Ra-226, and Si mass balances) were much higher than those reported from typical continental margins. The nutrient fluxes from SGD were about 90%, 20%, and 80% of the total input (except from open ocean waters) for dissolved inorganic nitrogen (DIN), dissolved inorganic phosphorus (DIP), and dissolved inorganic silicate (DSi), respectively. These excess nutrient inputs from SGD are the major sources of new nutrients in this bay. On the basis of photosynthetic pigments and benthic algal distributions, we suggest that the large fluxes of excess nutrients from SGD can cause benthic eutrophication in a semienclosed bay on this highly permeable volcanic island.