Evaluation of dissolved inorganic nitrogen eliminating capability of the sediment in the tidal wetland of the Yangtze Estuary

Estuarine wetlands serve as a natural barrier to remove the land-generated pollutants and attenuate the pollutant load from the land to the sea. As one of the most important estuarine wetlands, the Yangtze estuarine wetlands have attracted particular interests in the biogeochemical studies of nutrients. The objectives of this study were to characterize the seasonal and spatial distribution of dissolved inorganic nitrogen (DIN) fluxes across the sediment-water interface; to calculate the total DIN fluxes in a year and different seasons; and to evaluate the DIN removing capability of the sediment in the tidal wetlands of the Yangtze Estuary. The spatial distribution of DIN fluxes shows complicated seasonal variations and spatial differences. The annual DIN fluxes range from -22.22 mmol N m^-2 h^-1 to 19.54 mmol N m^-2 h^-1, with an average of -1.48±1.34 mmol N m^-2 h^-1. The tidal wetlands in the Yangtze Estuary behave as a source of water DIN in spring when DIN is released from sediment into overlying water, and the released amount of DIN is 1.33×10⁴ tons of nitrogen (T N). In summer, autumn and winter, the sediment absorbs the DIN from the overlying water, and the absorbed amounts of DIN are 4.36×10⁴ T N, 6.81×10⁴ T N and 2.24×10⁴ T N, respectively. The average amount of DIN in overlying water of the Yangtze Estuary is 52.6×10⁴ T N yr^-1, and the perennial average amount of DIN absorbed from the overlying water by the sediment is 12.1×10⁴ T N yr^-1. The annual DIN elimination rate of the tidal wetlands was 23.0%.