Influence Of Sediment Transport On Sediment Distribution At The Eutuary Of Tiao Xi Basin In Taihu Lake

With the rapid development of social economy,Taihu Lake ecosystem has been seriously affected,lake water body has been in eutrophication state for a long time,resulting in the root cause of eutrophication in Taihu Lake is excessive input of exogenous nutrients.The exogenous nutrient salt is mainly transported by suspended particulate matter such as sediment,so it is of great significance to study the generation,migration,settlement and physicochemical properties of suspended matter(sediment)to relieve eutrophication in Taihu Lake.Taking Tiaoxi into the estuary as an example,this paper constructs a distributed hydrological model of SWAT in Tiaoxi Basin,simulates and analyzes the sediment production and production flow in the basin,and establishes the regression equation by using MODIS reflectivity data and the measured suspension concentration data,and inversion to obtain the concentration distribution of suspended matter into the Lake estuary,Then the distribution characteristics of suspended particulate matter in estuary are analyzed according to the data of watershed outlet sediment transport simulated by SWAT,and finally,the spatial changes of physical and chemical properties of estuary sediments are analyzed through in-situ observation experiments in estuaries,which provide scientific basis and effective opinions for eutrophication management in Taihu Lake.The main research results are as follows:(1)Based on DEM data,land use data,soil data and meteorological data of Tiaoxi Basin,the SWAT model of Tiaoxi Basin was successfully constructed,and the model was determined and verified by the runoff data and sediment data,which indicates that the runoff simulation and sediment simulation of SWAT model in Tiaoxi Basin have high feasibility and reliability.The results of SWAT sediment simulation show that the total sediment content of Tiaoxi Basin in 2011 is 9.24?10~6 t/a,among which the total sediment volume of the West Tiaoxi stream is 3.15?10~6 t/a,which accounts for 34.1%of the total sediment volume of the river basin,while the total sediment volume of the East Tiaoxi stream is 6.09?10~6 t/a,Accounting for 65.9%of the total sediment volume of the river basin,the sediment production in the East Tiaoxi system is large,which is the main source of sediment production in the Tiaoxi Basin.The moderate and strongly eroded areas of the Tiaoxi Basin are mainly distributed in the middle and upper reaches,while the downstream erosion is weaker.The erosion degree of the stream system in the East Tiaoxi is obviously greater than that of the West Tiaoxi stream system.Slope is an important influencing factor of sediment load in Tiaoxi Basin,and the slope of area with large sediment load is often larger.Red soil is the main soil type in the strong area of soil erosion in Tiaoxi Basin.(2)The regression equation is constructed by using the surface reflectivity data of MOD09GQ and the measured suspension concentration data,and the results show that the index model constructed by MODIS Band 1 reflectivity data and measured suspension concentration is the most accurate,and the formula is=3.210)..(3)The change trend of sediment transport volume in the estuary of Tiaoxi is almost in agreement with the change trend of runoff,and the peak period of sediment transport is basically distributed in june~october,the lowest value is often distributed in winter,and the change of sediment transport volume in the whole year shows a trend of first rising and then falling.There is a significant positive correlation between the sediment transport quantity and the distribution area of the turbid zone area,the larger the sediment transport,the larger the area of the estuary turbid zone,the smaller the sediment transport,the smaller the turbid belt.(4)The spatial variation of sediment thickness is related to the spatial variation of suspended matter concentration.The sediment depth of the bottom of the lake is decreasing gradually with the SS decreasing.(5)Sediment enter into the lake from the estuary,because the water sediment carrying capacity gradually reduced,the large sediment first go down,then the small sedimentation go down.The median particle size of the surface sediments in the left and right estuary decreases with the increase of the horizontal distance from the estuary,but there is no obvious law in the change of the median particle size of the middle estuary,which is because the area is a waterway,and the wave disturbance caused by the large vessel affects the distribution of the surface sediment.(6)The vertical change trend of total nitrogen increases with the increasing of depth,the total nitrogen of sediment decreases gradually in the horizontal direction,the vertical change trend of total phosphorus is more moderate,the horizontal distribution,The total phosphorus of sediment decreased gradually,but the decrease was lower.The content of total nitrogen and total phosphorus in about 2.25 g/kg and0.45 g/kg respectively,both of which are relatively high.It can be reflected that sediment is an important carrier for nutrient salt to enter taihu lake.The study on the generation,migration and settlement of sediment is of great significance for the eutrophication treatment of taihu lake.