Effects of tidal variations on total nitrogen concentration, speciation, and exchange flux in the Shuidong Bay coastal water, South China Sea

Nitrogen (N) plays an important role in marine ecosystems as a biogenic element for phytoplankton. The tidal cycle had major influence on various biogeochemical parameters of the bay and changed nutrients input with ebb flow tide. In this study, we collected samples from Shuidong Bay (SDB) China, August 2021, to explore periodic variations coastal waters during spring neap tides. effects tides different speciation nitrogen SDB exchange fluxes between South China Sea (SCS) were investigated. results indicated that concentrations particulate (PN) N-NO 2 - significantly ( P < 0.05). total (TN) 258.12 ± 89.49 μmol/L 231.77 56.86 μmol/L. During tides, dissolved (TDN) accounted 54.1% 52.2% TN, respectively. addition, organic (DON) 81.4% 69.9% TDN Furthermore, net showed TN transported SCS tide, 37.7 t 8.8 t, flux tide was 4.3 times higher than significant negative correlation observed inorganic (DIN) salinity 0.001 ), DIN mainly influenced by terrestrial sources inputs. A positive 0.01 ) PN Chlorophyll- implied assimilation large number planktonic organisms promoted formation. present revealed variation played regulating N waters, which great implications biogeochemistry water quality improvement SDB.