Distribution of selenium and its relationship to the eco-environment in Bohai Bay seawater

We determined the selenite (Se(IV)) and selenate (Se(VI)) concentrations in the surface and bottom waters of Bohai Bay to understand the behavior of selenium in this area. The average concentrations of selenite and selenate were 0.72 nM and 0.36 nM, respectively. The surface concentration of selenite and selenate decreased from the western bay to the bay mouth, with the highest value near the Haihe Estuary. The bottom concentration of selenite and selenate displayed a similar distribution as the surface concentration. The selenium distribution was mainly controlled by environmental factors, riverine discharges and biological activities. Based on the data in this study, a preliminary estimate of the selenium budget via riverine input has been established. According to our estimate, about 7.18 × 107 mmol/yr of selenium reaches the Bohai Bay via rivers. Selenium showed significant positive correlations with dissolved inorganic nitrogen (DIN), phosphate and silicates, reflecting its strong nutrient-type behavior. The selenium concentration also correlated well with the chlorophyll a concentration and phytoplankton biomass, possibly implying that selenium plays a key role in regulating the phytoplankton productivity and that phytoplankton dynamics also affect the selenium inventory in Bohai Bay. Furthermore, the selenium concentration in each site was lower than the “no-effect” value of selenium and seemed to be required for the normal growth and development of phytoplankton, but it may have adverse effects for higher trophic levels due to the bioaccumulation of selenium.