Sediment Deposition Process And Nitrogen Storage Characteristics Of The Xiangxi Bay Of The Three Gorges Reservoir

Suspended particulate matter is the existence form or important carrier of various pollutants or nutrients in water.Three GorgesAfter the reservoir,different periods of operation will force the hydrodynamic and water environment conditions in the reservoir area to change drastically,changing the characteristics of hydrodynamic and water environment.The characteristics,content,composition,migration and sedimentation characteristics of suspended particles in water bodies during different periods of operation also appear to be very different from those of natural rivers and lakes.In this paper,the Zhongxiangxi Reservoir Bay of the reservoir area is taken as the research object.The routine monitoring is carried out during the pre-flood,flood and storage periods in 2019,and suspended matter traps are placed at different points and different depths to collect suspended matter.Based on the monitoring results,analyze the hydrodynamic and spatial-temporal characteristics of Xiangxi River Reservoir Bay;the suspended sediment trap experiment was used to analyze the suspended sediment deposition characteristics of Xiangxi River Reservoir Bay at different water levels during operation to determine the thickness of new sediments at various points in Xiangxi River And its nitrogen storage form;combined with the special water layering characteristics of Xiangxi River Reservoir Bay,the effect of environmental conditions on the nitrogen storage on the surface of suspended matter was studied.The main conclusions are as follows:(1)The main bodies of the main stream in the pre-flood,flood and storage periods are submerged into the Xiangxi River Bay by means of the gravity flow of the bottom,middle and upper layers,and middle and lower layers respectively;The absolute value of the velocity in the pre-flood decline period is 0.16 m/s;the absolute value of the velocity in the flood season is 0.3 m/s,and the absolute value of the velocity in the storage period is 0.09 m/s.During the operation period of different water levels,the water environment conditions have obvious stratification characteristics.(2)There is a large gap between suspended matter in the water body of the reservoir bay during different water level operation periods.The suspended matter in the preflood and storage periods is less,and the suspended matter in the flood season is the most.At the same time,due to the influence of hydrodynamic conditions,the settlement flux The point gradually decreases from the estuary to the upstream,and increases with increasing depth.(3)The particle size of suspended matter is also different in each operation period.From the whole,silt has the largest proportion,followed by clay,and finally sand.The sand content showed an increasing trend along the Xiangxi River estuary to the upstream.The organic matter content in the flood season is greater than the impoundment period and greater than the pre-flood decline period,and the organic matter content is higher in the upstream than downstream.(4)The total nitrogen content of suspended matter decreases with increasing depth,the ammonia nitrogen content of suspended matter increases with increasing depth,and the nitrate nitrogen content of suspended matter decreases with depth.(5)Changes in the water environment of the Xiangxi River in different operation periods have a promoting effect on the reduction of total nitrogen and nitrate nitrogen in the flood season.Changes in the environmental conditions of the Xiangxi River have no obvious effect on the increase of ammonia nitrogen.The reduction of nitrate nitrogen is directly related to the reduction of dissolved oxygen.