Spatial Distribution Characteristics And Ecological Risk Assessment Of Soil Heavy Metals In The Middle Area Of "One River And Two Tributaries" Basin In Tibet

Soil,as an indispensable material basis for human existence,has a direct impact on the health status of human and ecological environment.With the rapid development of industrialization in China and the unreasonable use of various fertilizers and pesticides,the status of soil environmental system is not optimistic.Studies have shown that the Qinghai-Tibet Plateau soil heavy metal content in recent decades a significant upward trend,while“One River and Two Tributaries" basin in Tibet as an important part of the Qinghai-Tibet Plateau of the population settlements in central China and major economic development and agriculture is developed,the soil heavy metal pollution seriously affects the health of the people of the region and the development of economy.Therefore,the study on the soil heavy metal level and its ecological risk in this region can effectively and intuitively understand the soil pollution level,provide reference for the treatment and control of soil heavy metal pollution in the middle of the "One River and Two Tributaries",and provide environmental theoretical basis for the development of local economy.Based on the contents of heavy metals in four soil layers at different depths of 41 samples in the study area,this paper studies the spatial distribution,structural characteristics and possible sources of heavy metals through multivariate statistical and geostatistical analysis.Based on the local geoaccumulation index,enrichment factor and potential ecological risk index,the deterministic ecological risk assessment and the SS-TFN coupling model were used to study the ecological risk of heavy metals in the study area.The main conclusions are as follows:(1)the heavy metal content in the soil in the central area of "One River and Two Tributaries" is generally low,and the overall soil quality is good.The contents of heavy metal Cd are relatively high in the surface soil,and the degree of disturbance is relatively obvious.Besides,the contents of Cd,Pb and Ni in S1 soil layer are slightly higher than the national soil environmental quality level I standard,the contents of heavy metal in other studies are in line with the standard.(2)the space research shows that the concentration of heavy metal enrichment accumulated large area more concentrated in Lhasa,Rikaze and Shannan areas surrounding the cities,and the uneven distribution of heavy metal content in the space,on the spatial structure has obvious spatial heterogeneity,including heavy metals such as Cd,Cu,Pb,the correlation is low,indirectly show that the several kinds of metal affected by man-made factors.(3)analysis of the sources of heavy metals in each soil layer shows that many pairs of heavy metals in each soil layer have homology,but their pollution sources are not completely consistent;In the topsoil layer,Cd,Cr,Cu,Zn,Ni and other metals are basically controlled by natural sources with low pollution level,while Pb,Cd,Cu and other metals controlled by human factors have strong pollution level.Mn has little correlation with other heavy metals and is mainly controlled by soil parent material.(4)the study on ecological risk assessment based on the combination model of SS-TFN and definite ecological risk assessment shows that the soil in the study area has the highest ecological risk level of Cd,which is the moderate ecological risk level.Cu and Pb also have relatively obvious slight ecological risk,while the other heavy metals are of slight risk level or pollution-free.The overall ecological risk level in the study area is relatively low,and Cd should be taken as the priority ecological risk control factor to strengthen its prevention and control.Based on the above studies,the overall content of heavy metals in the soil in the study area is relatively low,the soil meets the national environmental protection standards,and the overall ecological risk is relatively low.The soil is in good condition.