Experimental Study On The Adsorption,desorption,migration And Transformation Of Ammonia Nitrogen In The Hyporheic Zone Sediments Of The Middle Reach Of Shaying River

Ammonia nitrogen,as the main nitrogen form at the sedimentary scale of the hyporheic zone,is essential for the prevention and control of surface water and groundwater nitrogen pollution.The Shaying River,as the largest tributary of Huai River,is also the most polluted river.Under the conditions of gradual improvement in water quality and frequent changes in river water level,nitrogen changes drastically in the hyporheic zone.Understanding the adsorption,migration and transformation laws of ammonia nitrogen in hyporheic zone sediments can make it easier to understand the ultimate fate of nitrogen in sediments,which is important for ensuring the safety of drinking water sources and treating surface water nitrogen pollution.Through field sampling and analysis,this thesis preliminarily explored the occurrence of nitrogen in the hyporheic zone sediments and overlying water bodies in the study area.At the same time,by using the sediment samples,the static adsorption-desorption batch experiment and the experiment that simulates the two-dimensional migration of ammonia nitrogen in the hyporheic zone sediments were carried out to explore and analyze the ammonia nitrogen adsorption and nitrification in the hyporheic zone sediments.The main conclusions of this thesis are as follows:（1）During the dry period,the background concentrations of nitrate nitrogen of the sediments in Zhoukou（ZK）and Shenqiu（SQ）were 1.667 mg/kg and 7.683 mg/kg,and the background concentrations of ammonia nitrogen were 10.905 mg/kg and 21.505 mg/kg.（2）Through the low-concentration ammonia nitrogen adsorption experiment,the sediment ENC₀（Equilibrium adsorption and desorption capacity）of ZK and SQ were 2.409 mg/l and1.781 mg/l,which corresponded to the overlying river water concentration of 0.19 mg/l and0.24mg/l.It was found that the hyporheic zone sediment was a source of nitrogen,and it was a risk of ammonia nitrogen being released to the overlying river water.（3）Through different depth adsorption and desorption thermodynamic and kinetic experiments,and through the isotherm adsorption equation to simulate the curve,quantitative comparison and analysis,it showed that the adsorption process was more suitable for first-order kinetic description.The adsorption rate of SQ was greater than ZK,and the maximum adsorption capacity of SQ was greater than ZK,which were 615-924 mg/kg and 285-788 mg/kg.The maximum adsorption capacity and the adsorption performance of ZK and SQ increased with the increase of depth.Adsorption was prone to occur in both places.The adsorption and adsorption performance of SQ is greater than that of ZK,mainly because SQ sediments have finer sediments.Particle size and higher organic content;ZK’s surface layer 0-5cm depth desorption capacity is much greater than other depths,ZK and SQ are more prone to desorption.The adsorption performance of SQ was greater than ZK,which was mainly due to the SQ sediments had finer sediment particle size and higher organic content;the desorption capacity of sediments at a depth of 0-5cm of ZK was much greater than that of other depths.Desorption was prone to occur in both places.（4）Through indoor sand tank experiments,a fixed-head infiltration of high-concentration ammonia nitrogen river water was set up,which showed that the migration speed of ammonia nitrogen in the sediments was slower than that of water,and it was obviously intercepted.In the sediments near the river（label 2）and far from the river（label 4）,the conductivity reached stable separately,and the time interval was 150 hours.The experiment ran for 747 hours and only polluted half the area of the sand tank.Nitrification occurred in the water level repeatedly falling and the continuous low-head infiltration,and the nitrate nitrogen was enriched in the sediments near the river 10～30 cm,and the river water level repeatedly falling had a stronger ability to produce nitrate.