Submarine groundwater discharge and its implication for nutrient budgets in the western Bohai Bay, China

Submarine groundwater discharge (SGD) supplies substantial quantities of nutrients from land to oceans. However, SGD and associated nutrient fluxes have long been ignored in Bohai Bay, which is subjected to the serious environmental problem. Here, we investigated the concentrations of radon (²²²Rn) and nutrients in groundwater and surface water in the western Bohai Bay during May 2017. The flushing time in the bay was estimated to be 38.8–58.3 days based on tidal prism model. The SGD flux was estimated to be 7.3 ± 4.8 cm d⁻¹ based on ²²²Rn mass balance model. The SGD associated nutrient fluxes were estimated to be (6.3 ± 4.1) × 10⁷ mol d⁻¹ for dissolved inorganic nitrogen (DIN), (1.2 ± 0.8) × 10⁶ mol d⁻¹ for dissolved inorganic phosphorus (DIP) and (7.5 ± 4.9) × 10⁷ mol d⁻¹ for dissolved inorganic silicon (DSi). By establishing nutrient budgets, we found that SGD was a major source, contributing 80.8% of all source for DIN, 90.7% of all source for DIP and 78.4% of all source for DSi into the western Bohai Bay. This study shows that SGD associated nutrient fluxes may have significant impact on nutrient budgets in the western Bohai Bay.