Long-term alterations of nutrient dynamics and phytoplankton communities in Daya Bay, South China Sea

Dynamics of phytoplankton in coastal waters is a function of nutrient influx and the present study investigated the trend in nutrient dynamics and phytoplankton abundance of Daya Bay (DB), South China Sea, from 1986 to 2020. Dissolved inorganic nitrogen (DIN), Dissolved inorganic phosphate (DIP) and Silicates were measured. DIN concentration exhibited an increasing trend over the last decades, and it was above the threshold for the phytoplankton growth. DIP level showed a significant decreasing trend throughout the studied period, falling below the threshold for phytoplankton growth in the last decade, where harmful algal blooms were dominated by the dinoflagellates. Long-term anthropogenic influences severely change influx of DIN, DIP, and silicates which in turn shape the architecture of phytoplankton communities. Thus, the understanding of the complex interaction between nutrient influx, anthropogenic activities and dynamics of both water quality and biological elements are particularly important to decide criteria to manage coastal ecosystems.