三沙湾亚硝酸氮、氨氮、磷酸盐的异常、机制及影响

Sansha Bay in East Fujian is the most typical closed bay where many rivers flows into. It is the largest cage breeding base for Pseudosciaena crocea in the world and one of most important fishery breeding bases in China. However, several surveys have found that the algae production in this bay is far low compared to other bays, which presents the unique ecological characteristics of "more nutrients and less algae", but the mechanism has not been discussed in-depth. Using fixed-stations and large-scale navigation methods, in this study it investigated the tidal movement and spatial distribution of five nutrients (active silicate (SiO₃-Si), nitrate nitrogen (NO₃-N), nitrite nitrogen (NO₂-N), ammonia nitrogen (NH₄-N) and active phosphate (PO₄-P)) in 2018-2020. The results show follows. (1)The upstream input causes the ebb concentration of SiO₃-Si and NO₃-N to be greater than the rise concentration, and they decrease linearly from the shore to the bay with salinity. (2) The aquaculture in the bay and the output of the natural ecosystem cause the rise concentrations of NO₂-N, NH₄-N, and PO₄-P to be greater than the ebb concentrations, and the concentration in flood season is greater than that in the dry season. NO₂-N increases nonlinearity with salinity from the shore to the bay instead of it is an abnormal phenomenon that NH₄-N and PO₄-P are evenly distributed along with the increase of salinity. However, the fall concentrations of NH₄-N and PO₄-P near the coastal sewage outlet are greater than the rise concentration. (3) The high concentrations of NH₄-N and PO₄-P imported from sewage discharge in the bay and coastal areas are the main cause of serious water pollution. Eutrophication in the Sansha Bay is the main factor of the unique ecological characteristics of "more nutrients and less algae".