Estimation of Nutrient Fluxes on the Interface Bottom Water–Sediments in Shallow Bights of the Peter the Great Bay, Sea of Japan

— Fluxes of nutrients (ammonium, total nitrogen, dissolved inorganic phosphorus, total phosphorus, silica, and dissolved organic carbon) across the interface between bottom water and sediments were studied in three shallow bights (Voevoda, Novgorodskaya, and Uglovoj) of the Peter the Great Bay in the course of survey in September–October, 2019. At two stations in each of the bights, nutrient concentrations were measured in seawater sampled at 10 cm above the seafloor and in the pore waters of the sediment cores; and organic carbon, fulvic acids, humic acids, and chlorophyll a were analyzed in the solid phase of the sediments. Bioturbation coefficients were estimated from variations in chlorophyll a concentration with depth in the sediment cores. The fluxes of nutrients (ammonium, total nitrogen, phosphorus, total phosphorus, and silicon) and dissolved organic carbon (DOC) were evaluated by model calculations. The estimated nutrients fluxes were, with regard to the bioturbation, about one order of magnitude higher than those estimated by the Fick law. The highest concentrations of organic carbon, 6.5 and 5.5% per dry weight of sediments, were found in the top layer of sediments retrieved at sites covered by Zostera marina L. in the Voevoda and Novgorodskaya bights, respectively. However, the highest fluxes across the water–sediment interface were obtained for a site devoid of seagrass in the Novgorodskaya bight, where the top sediment layer contained 2.8% organic carbon. The annual specific fluxes of nutrients estimated for the water–sediment interface were comparable to or even higher than the annual specific fluxes of nutrients brought per surface area unit of the Amur bay by the Razdolnaya River and domestic waste waters from the city of Vladivostok.