Nitrogen distribution and diffusive fluxes in sediment interstitial water of Poyang Lake

The concentration and distribution characteristics of nitrogen in the sediment interstitial water from the Poyang Lake were determined. Diffusive fluxes of nitrogen between interstitial water and overlying water were estimated. The results showed that the average concentration of total nitrogen and nitrate nitrogen in surface sediment interstitial water of Poyang Lake were 1.29 and 0.76 mg/L. Total nitrogen existed mainly in the form of nitrate nitrogen, which amounted to 45.38–73.54 % of the total nitrogen. The spatial distribution characteristics of total nitrogen and nitrate nitrogen concentration in surface sediment interstitial water are similar, and the contents of total nitrogen and nitrate nitrogen do not show significant spatial variation at all sampling sites. The profiles of nitrogen were characterized by sharp gradients near the sediment–water interface. The contents of nitrogen increased with degree of depth at first and then decreased with degree of depth. The concentrations of nitrogen in surface sediment interstitial water were much higher than that in the overlying water at most sites, indicating that nitrogen tended to release from sediment to water. The average diffusive fluxes of total nitrogen and nitrate nitrogen at the sediment–water interface were 0.87 and 0.86 mg/m² day, respectively.