Analysis of the Distribution and Exchange Fluxes of Inorganic Nitrogen at the Sediment-water Interface of Poyang Lake in Different Hydrological Periods

The objective of this study is to reveal the exchange process of inorganic nitrogen at the sediment-water interface and the characteristics of "source/sink" dynamics in Poyang Lake. Consequently, the investigation centered on the sediment and overlying water under varying hydrological conditions within the lake. Through meticulous analysis of the spatial and temporal distribution and exchange flux of inorganic nitrogen, we have successfully identified the "source/sink" roles of these nitrogen forms. The findings demonstrate that the fluctuations in the concentrations of total nitrogen (TN), ammonium (NH₃-N), nitrate (NO₃^--N), and nitrite (NO₂^--N) in the overlying water followed the sequence of: low water period > high water period. The concentrations of TN, NO₃^--N, and NO₂^--N were higher in the northern and inlet areas of the lake, while NH₃-N concentrations were elevated in the central region. According to laboratory simulation experiments, during the wet season, the exchange fluxes of TN, NH₃-N, NO₃^--N, and NO₂^--N ranged from 0.30 to 8.41, 0.63 to 3.81, -3.32 to -0.13, and 0.03 to 0.12 mg·m^-2·h^-1, respectively. During the dry season, the exchange fluxes ranged from 0.59 to 5.41, 0.34 to 2.32, 0.31 to 1.87, and 0.02 to 0.06 mg·m^-2·h^-1, respectively. The sediment was found to be a "source" for TN, NH₃-N, and NO₂^--N. During the dry season, the sediment functioned as a nitrate source, whereas in the wet season, it served as a sink for nitrate. Correlation analyses reveal a strong correlation between nitrogen exchange fluxes and chlorophyll a (Chl-a) and total phosphorus (TP). In order to prevent excessive growth of algae and reduce the risk of eutrophication in Poyang Lake, it is imperative to regulate the release of endogenous nitrogen from sediments. The phosphorus ratio and Chl-a have substantial impacts on nitrogen exchange flux; It is suggested that TP concentration and chlorophyll concentration may be important factors affecting the change of nitrogen exchange flux in Poyang Lake.