Program

To investigate geochemical impacts of submarine groundwater discharge (SGD) on subtropical Sansha Bay, southeastern China, we estimated seasonal fluxes of submarine groundwater discharge in the bay based on the mass-balance of ²²⁴Ra and ²²⁸Ra. The flux of SGD was 2.54±0.80×10⁷ - 1.98±0.90×10⁸ m³ d^-1 in the winter and 1.67±0.50×10⁸ - 3.08±2.98×10⁹ m³ d^-1 in the summer, of the same order of magnitude as the concomitant total river discharge into the bay. Great seasonality was similarly present for the net flux of dissolved inorganic nitrogen (DIN) and phosphorus (DIP) via SGD, which was 3.1×10⁷ mol d^-1 for DIN and 4.6×10⁵ mol d^-1 for DIP in the winter and about 40 and 90 times, respectively as high in the summer. The SGD-associated net flux of dissolved organic carbon (DOC) and dissolved silicate (DSi) showed less seasonality, 0.3-3.4×10⁷ mol d^-1 in the winter and 0.9-21.5×10⁷ mol d^-1 in the summer for DOC and 1.5-10.5×10⁷ mol d^-1 in the winter and 3.8-66.1×10⁷ mol d^-1 in the summer for DSi. The material fluxes via SGD were overall a few times higher than that from the river discharge in Sansha Bay, indicating that SGD is the main source of carbon and nutrients.