Study On Nitrogen Forms And Adsorption-Desorption Characteristics Of Nitrate Nitrogen In Sediments Of Xiangjiang River From Hengyang Section

Xiangjiang River is the largest river flowing through the territory of Hunan Province,its water environment quality and people's production and life are closely related.Nitrogen plays an important role in the water,and directly affect the quality of water.Therefore,study on the adsorption and desorption characteristics of nitrate nitrogen in sediments,will have an important significance to understand the effect of sediment on the carrying capacity of nitrate nitrogen,and the role of nitrate nitrogen on nitrogen cycling.The sediments of Hengyang section of Xiangjiang River were used as the research object,it attempts to present a study on the content and distribution characteristics of nitrogen in sediments by continuous grading method.and it also aims to explore the influencing factors,dynamics and thermodynamics of sediment absorption or desorptionof nitrate nitrogen by indoor simulated adsorption experiments.and to reveal its adsorption mechanism by means of SEM,FTIR and XRD.The results showed that the content of total nitrogen and organic matter in the Huangchaling section was the highest,and the pollution was the most serious.and the pollution level of Xintangbu section was the lowest,which could represent the most original water source condition in Hengyang section of Xiangjiang River.The contribution of nitrogen to total nitrogen content was about the same as the absolute content distribution,it is SOEF-N>IEF-N>WAEF-N>SAEF-N,SOEF-N and IEF-N are dominant in each sampling point.Changes in the environment or physical and chemical factors of sediments will have some effect on the adsorption and desorption of nitrate nitrogen.The increase of temperature will decrease the retention rate of nitrate nitrogen.The increase of the disturbance rate will be beneficial to the release of nitrate in the sediments.The removal of organic matter in the sediment will reduce the amount of nitrate nitrogen adsorbed while releasing a small amount of nitrate.The process of adsorption of nitrate nitrogen in sediments gradually stabilized after 60 min,and the process of equilibrium was more slowly.The process of adsorption and desorption of nitrate nitrogen in sediments is consistent with quasi-second-order kinetic model,which is mainly chemical reaction.The thermodynamic study shows that the reaction is in accordance with the Langmuir isothermal adsorption equation and it is a spontaneous exothermic monolayer adsorption process.The SEM shows that the surface layer of sediment is rough and porous.and it is lamellar structure with many adsorption sites,which is favorable to the adsorption of nitrate nitrogen.The FTIR shows that the sediments contained hydroxyl groups,acyl groups and other groups,and the mechanism of reaction with nitrate nitrogen was mainly manifested as replacement and adsorption.The XRD shows that the main components of the sediments are Si O₂.