Study On The Spatial Variability Of Heavy Metals In Soil And Its Influencing Factors In Xijiang River Draining Of Guangxi

With the socio-economic development and climate change,slight disasters within the drainage basin,serious environmental pollution,the cumulative effect of heavy metals became more and more serious.The Xijiang River basin as the main grain producing area and mining activity area,has a long history of heavy metal pollution.In order to explore the spatial distribution of heavy metal pollution and the main influencing factors,the distribution of heavy metals in soils of Xijiang river basin,pollution degree,spatial variability and influencing factors were studied by using traditional statistics,geo-statistics and GIS in-depth,based on large scale soil heavy metal content in investigation.the main repeat are as follows:Descriptive statistical analysis shows that the contents of As,Cd,Pb,Cu,Ni,Zn,Cr and Sb in the Xijiang River Basin were as follows:0.01~171000?0.001~990.3?0.61~135800?2.14~2287?2.84~2287?2.84~385.01?2.01~15234?7~4063?0.02~3494mg/kg,the mean values were as follows: 382.9?5.260?376.5?38.88?36.06?375.0?97.28?38.54mg/kg,and the geometric mean values were as follows: 23.82?0.685?88.77?27.82?26.91?124.4?77.23mg/kg.Degree of variation: As> Pb> Cd> Sb> Zn> Cu> Cr> Ni,moderate strong variability.According to the natural,mining,paddy soil and dry-land soil classification,except Cr in the above four kinds of soil types were no significant difference,the mining area of heavy metal content were significantly higher than farmland and natural soil;According to the upstream(a)area(Diaojiang,Huanjiang River),upstream(b)area(Red River,Liujiang River),middle and downstream classification,except Cr in the lower reaches of the distribution was significantly lower than the upstream,the other heavy metals in the upstream(B)zone,middle and lower reaches.To sum up,the upstream area showed As,Cd,Pb,Zn,Sb compound pollution,no significant pollution in the middle and lower reaches.Spatial clustering and hot and cold analysis showed that the hot spots of soil heavy metal were main distributed in the Nadan Chehe and Dachang and the middle reaching of the Dahuan River,and its content is affected by the double effect of mining activities And river action.The cold spot was mainly distributed in large deposits and 500 Rice and above the mountain,and Qianjiang Xunjiang dry tributaries along the farmland soil,The middle and lower reaches of the basin are conducive to agricultural production activities.The semi-variation function analysis showed that the soil heavy metals in the Xijiang River Basin have significant spatial autocorrelation and structural variation,which is affected by natural conditions such as vegetation,topography,climate and soil parent material.In the upstream(a)region,except that Cu is best fitted with spherical model,the optimal fitting model of As,Cd,Pb,Ni,Zn and Cr is exponential model;Cd and Cr are best fitted by exponential model,and others are best fitted by spherical model in the upstream(b)region;In the Midstream area,As,Ni and Cr are best fitted by exponential model,and others are best fitted by spherical model;In downstream area,Pb,Ni and Cr are best fitted by Gaussian model,As,Cd and Zn are best fitted by exponential model,and Cu is best fitted by spherical model.Kriging interpolation method is feasible.From the spatial distribution map and the spatial interpolation map,the contents of As,Cd,Pb,Cu,Ni,Zn,Cr and Sb in the soil samples were <30,> 1,<250,<200,<100,<250,10 ~ 90 mg /kg based.The high content areas of As,Cd,Pb,Zn and Cu in the upper reaches of the basin are distributed in Diaojiang River Basin and Dahejiang River Basin,among which Cadmium high value is the most widely distributed,and the upper reaches are the most prominent,the high-density sample was distributed Nandan County Dachang Chehe area.Ni,Cr were distributed by a wide range and prominent in the Red River and Diaojiang upstream area of the high value.The Sb high-value area reaches the Duanjiang section of Diaojiang River and the Xinzhou section of the Hongshui River basin,and the watershed characteristics are obvious.The pollution of heavy metals in the Xijiang River Basin was evaluated by using the Nemero index method,the cumulative index method and AHP-based weighted pollution index method.The comprehensive pollution index of the Nemero is as follows: upstream(a)area(severe pollution)> upstream(b)area(severe pollution)> middle reaches(heavy pollution)> downstream(mild pollution);The comprehensive pollution index based on AHP is significantly lower than the Nemero index,and the pollution level in the upper reaches(b)and Midstream were down to moderate pollution.The results show that the pollution of Pb,Cd,Sb and Zn in the watershed is more extensive,especially in Jinchengjiang,Nandan and Yizhou.The compound ecological risk of heavy metals in the Xijiang River Basin is as follows: the upper reaches of the basin(a)area(higher ecological risk)> upstream(b)(moderate ecological risk)> middle reaches(moderate ecological risk)> downstream(low ecological risk).Cd is the dominant factor in the potential ecological risk of watersheds.Correlation analysis,principal component analysis and cluster analysis showed that As-Pb-Zn-Cu in the upstream(a)area moderate correlation.Pb and Zn,Sb,As and Sb,Ni and Cu,Cr moderate correlation in the upstream(b)area.The middle reaches of As-Sb and Ni were positively correlated with Cu and Cr,and the downstream Cd-Zn-Ni was moderately correlated;The distribution of heavy metals in the drainage basin was affected by the combination of industrial and mining sources,sewage irrigation and transportation sources,fertilization factors and soil forming factors.The content of Ni and Cr was mainly affected by natural factors,As,Cd,Pb,Zn,Cu,Sb were more prominent by human factors;The main factors affecting the distribution of heavy metals in the Xijiang River Basin Based on spatial analysis.The results show that the geological background significantly influence the content distribution of Cd in natural soil,mining activities have some influence on the distribution of heavy metal content in soil,the influence range of Cd most widely,Road traffic is not the main factor affecting the soil heavy metal content.Compared with other regions,the soil pollution problems of mine should be put on the agenda,the flood season should increase the intensity of mining safety investigation;The targeted treatment of soil along the Diaojiang River and Dahejiang River is imminent;Environmental pollution caused by historical mine mining in the upper reaches of the basin will continue,and local pollution problems will require long-term concern from the government and residents;In order to make the research results more convincing,it is suggested to carry out the research on the background value of soil heavy metals in the Xijiang River Basin and make it more credible through legislation.