[Denitrification in water of Daliao River estuary in summer and the effect of environmental factors].

Ratios of nitrogen loss and N2O production by denitrification were observed in Daliao River and the estuary in summer 2013. The results showed that the concentrations of N and P in the main stream of Daliao River were significant higher than those in the estuary (P < 0.05). Decrease of nutrients concentration in the estuary might be integrally caused by water diluting and biogeochemical processes. The net increase of dissolved N2 (ΔN2) ranged between -11.01 and 71.37 μmol x L(-1), in which the negative values were mostly determined in the main stream of the river, indicating the consumption amount of N2 was higher than the production in the fresh water. The mean ratio of N2O production during the process of denitrification was about 0.007%, and the N2O flux across water-air interface was about 0.04% of the total fluxes (N2O + N2). In this study, ΔN2 was not related with DO, while exhibited a significant positive correlation with water temperature and salinity, and a negative correlation with NO3-. This suggests that denitrification was not totally regulated by DO level in the estuary, and coupled nitrification-denitrification was the main denitrification process. Finally, we estimated that 26% of the TN, 37% of the DIN, and 43% of the NO3- were removed by denitrification in the Daliao River estuary based on the ratio of ΔN2 to N concentrations.