Characteristics of Nitrogen Release at the Sediment-Water Interface in the Typical Tributaries of the Three Gorges Reservoir During the Sensitive Period in Spring

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Overlying water and sediment interstitial water samples were acquired to study the nitrogen release between sediments and water interfaces in Xiangxi Bay in April 2016 during the Sensitive Period in spring. The spatial distribution of different forms of nitrogen in the sediment was analyzed, the diffusion fluxes of different forms of nitrogen in the sediments and water systems were also measured, and a correlation analysis with environmental factors was conducted. The results show that overlying water and sediment interstitial water ρ(TN) ranges from 1.10 to 6.90 mg·L-1 and 6.19 to 32.57 mg·L-1 respectively; indicating the nitrogen concentrations in the overlying and interstitial water of sediments have a certain variation along the process and vertically. The interstitial water nitrogen concentrations in the upstream area are higher than those in the downstream area. The interstitial water ρ(NH4+-N) in the sediment is significantly larger than that in the overlying water, but the interstitial water ρ(NO3--N) in the sediment is slightly smaller than that in the overlying water. Xiangxi Bay sediment acts as a source of NH4+-N; however, for NO3--N it is a sink. The diffusive fluxes of NH4+-N range from 2.70 to 4.72 mg·(m2·d)-1; and the diffusive fluxes of NO3--N range from -1.61 to -0.62 mg·(m2·d)-1. Nitrogen is mainly present in the form of ammonium nitrogen in the sediment of Xiangxi Bay. The ρ(NH4+-N) in the sediment ranges from 69.97-1185.97 mg·kg-1, ρ(NO3--N) ranges from 2.78-38.17 mg·kg-1, and the ρ(NH4+-N) in sediments in the surface at 0-8 cm changes with the same trend.