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 (PO) and silicate (SiO) were generally stable, with a slight decrease of DIN and PO, and a slight increase of SiO, 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.