Abstract: Based on the measured hydrological and water quality data of Xincun lagoon in December 2020, the characteristics of tide in Xincun lagoon were studied, and the effects of tidal elevation changes on nutrients in Xincun lagoon were discussed. The results show that the tide of Xincun lagoon is irregular diurnal. The tidal current at the inlet of the lagoon is a reciprocating current, lasting 15 h for flood tide and 10 h for ebb tide. The concentration of dissolved inorganic nitrogen (DIN), phosphate (PO3-4) and silicate (SiO2-3) vary from 0.91 to 20.87 μmol/L, 0.11 to 5.92 μmol/L and 2.36 to 134.75 μmol/L respectively. The concentrations of DIN, PO3-4 and SiO2-3 at the observation sites in the lagoons changed with the flood and ebb of the tidal process. The flow velocity at the inlet of the lagoon has an important influence on the change of tidal elevation at the observation sites, and the tidal flux basically determines the change of tidal elevation at the observation sites. There is a significant negative correlation between the nutrient concentration at the inlet of the lagoon and at the mariculture area and the tidal elevation, and the tidal current velocity has an important effect on the nutrient concentration at the inlet of the lagoon and the mariculture area. The results will provide scientific basis for pollution control and ecological restoration of Xincun lagoon.

Key words: Xincun Lagoon, Hainan Island, tidal elevation change, nutrient, correlation analysis