Nutrient inputs from submarine groundwater discharge (SGD) in Masan Bay, an embayment surrounded by heavily industrialized cities, Korea

In order to estimate the magnitude of submarine groundwater discharge (SGD) and the associated nutrient fluxes in Masan Bay on the southern coast of Korea, we measured the concentrations of ²²⁶Ra and nutrients in seawater, brackish groundwater, and stream water in May and August 2006. Gauging unidentified nutrient fluxes through SGD is very important in this bay since diatom red tides have been occurring from April to October every year since the 1980s. Based on a ²²⁶Ra mass balance model, the submarine inputs of coastal groundwater were estimated to be 4.8 × 10⁶ and 5.7 × 10⁶ m³ d^− 1 (61 and 71 L m^− 2 d^− 1) in May and August, respectively, which were approximately 840% and 540% of the surface water discharge into the bay. The fluxes of dissolved inorganic phosphorus (DIP) and silicate (DSi) through SGD were 2-3 fold higher than those via stream water, while the fluxes of dissolved inorganic nitrogen (DIN) were comparable to those from surface waters during both sampling periods. Nutrient fluxes through stream waters relative to those from SGD were more significant in the inner part of the bay, which appears to be due to the direct influence of heavily polluted stream waters. Our study shows that the large and continuous supply of inorganic nutrients through SGD may play an important role in eutrophication and the occurrence of red tides in this bay, which should be taken into consideration in the environmental management of the bay.