Research On Distributed Migration Model Of Heavy Metals In Watershed

With the development of social economy and the continuous growth of population,all river basins in China are facing different water resources and environmental problems,which have certain impact on the local economic development of the basin.The drainage area is vast,and the amount of meteorological,hydrological and geological data is huge.It is the main research method to calculate and master the watershed environmental state and hydrological migration model by means of computer technology.In this study,the field sampling investigation of the Daxia River Basin was carried out.The chemical laboratory measurement method was used to determine the contents of heavy metals As,Cd,Cr,Cu and Pb.The geospatial information system and fractal theory were used to study the distribution characteristics of heavy metals in the basin,and the Daxia River Basin was referred to.The actual situation,distributed estimation of heavy metal migration capacity in the Daxia River Basin.The results of this paper are as follows:1.Descriptive statistical analysis was carried out on the contents of As,Cd,Cr,Cu and Pb in the soil around the Daxia River Basin.The results show that the measured average content of Cu and Pb is lower than the local background value of Gansu Province,and the measured average content of As,Cr and Cd is higher than that of Gansu Province.From the average of heavy metals,the order is:Cr>As>Cu>Pb>Cd.2.Using the ArcGIS software,the DEM data was processed by the grid method in the Daxia River Basin and the sub-basin.Its water system fractal dimension is 1.0163<1.6.According to the similar hydrological characteristics of the Daxia River,the linear relationship between fractal dimension and runoff is fitted,and the runoff data of the Daxiahe sub-basin is obtained according to the fitted curve.3.The improved output coefficient model is used to estimate the non-point source load of the Daxia River Basin.The order of non-point source load of different land use types is:grassland>forest land>dry land>residential land>wetland>water area.It can be seen that the heavy metal pollution load of the Daxia River has the largest contribution to grassland and the contribution rate of wetland and water area is small.The reason may be that the grassland and woodland in the Daxia River Basin have a relatively large land area and a relatively concentrated distribution.The annual average source loadings of As,Cd,Cr,Cu and Pb in the Daxia River are 1.0717t/a,0.3221t/a,9.3289t/a,2.4369t/a,and 2.6559t/a,respectively.4.The total migration of heavy metals As,Cd,Cr,Cu and Pb in the Daxia River Basin was calculated by the SCS-CN model to be 0.6269 t/a,0.1973 t/a,5.8051 t/a,1.5961 t/a,and 1.7140 t/a.The distributed heavy metal migration model was used to estimate the migration amount of 0.6709t/a,0.2098t/a,6.2816t/a,1.7465t/a,and 1.8378t/a.By comparing the two sets of data,the results are basically the same,indicating that the overall estimation ratio of the heavy metal distributed migration model in the basin is reasonable.