Spatiotemporal changes of biogenic elements in the Changjiang River Estuary and adjacent waters in summer over the last decade

The long-term spatiotemporal changes of surface biogenic elements in the Changjiang River Estuary and adjacent waters during the summer of 2008−2016 were analyzed in this study. The concentrations of dissolved inorganic nitrogen (DIN), soluble reactive phosphate (${{\rm {PO}}_4^{3-}} $) and silicate (${{\rm {SiO}}_3^{2-}} $) were generally stable, with a slight decrease of DIN and ${{\rm {PO}}_4^{3-}} $, and a slight increase of ${{\rm {SiO}}_3^{2-}} $, which mainly occurred in the estuarine waters. The grey correlation analysis was carried out between biogenic elements and chlorophyll a (Chl-a). Results showed that compared with the absolute values of biogenic elements, the correlations between the concentration ratio of nitrogen to phosphorus (N/P), ratio of silicon to nitrogen (Si/N) and Chl-a were closer, indicating the important influence on phytoplankton by the structure of biogenic elements. The study area was generally in a state of potential P limitation, and could have potential impact on the phytoplankton community, triggering the shift of red tide dominant species from diatoms to dinoflagellates.