Responses of distribution of water quality in the Sansha bay on the land discharge and aquaculture

Based on nutrients and hydrological data of one fixed station and twelve navigation stations in 2018 flood season in the Sansha bay, Fujian province, this paper found: (1) The average concentrations of SiO₃-Si、NO₃-N、NH₄-N、PO₄-P and SSC in ebb (includes drainage of the Ningde city) are about 1.2, 3.6, 6, 2.5 and 2 times higher than that in the flood (seawater) in Dajinxi estuary, respectively. (2)The concentrations of NO₃-N and SiO₃-Si decrease by 31% and 50% with the increased of salinity, the result indicated SiO₃-Si and NO₃-N variation were controlled by river discharge. However, with increase of salinity, the concentrations of NH₄-N and PO₄-P showed a slight decrease trend, and NO₂-N even showed an increase trend, the result implicated that change of NH₄-N、PO₄-P and NO₂-N were mainly controlled by aquaculture in the bay. (3) The average concentrations of inorganic nitrogen (DIN) on twelve navigation stations was 57.33>21.41 μmol/L, PO₄-P (DIP) was 2.28>1.45 μmol/L, and DIN/DIP was between 8～30, such level of above parameters indicated that the water quality in the Sansha bay had exceeded the grade IV water quality standard and reached the state of eutrophication.