Risk Assessment And Landscape Impact Of Heavy Metal Pollution In Cultivated Soil In Typical Agricultural Watershed

Heavy metal pollution of soil is widespread all over the world.Soil heavy metal pollution is closely related to the health of ecological environment and the quality and safety of agricultural products,thus affecting human health.Heavy metal pollution in cultivated soil is serious in China,and heavy metal pollution can accumulate in the human body through the food chain,causing a serious impact on human health,according to the national soil pollution bulletin.The Three Gorges Reservoir area is an important water resources reservoir in our country,and monitoring agricultural soil pollution in the basin is very necessary,and small watershed is the basic component unit of basin.Basin control is usually taken as the typical model.At present,heavy metal pollution in cultivated land is usually concentrated in the plain area and large grain production area.There is less heavy metal pollution in soil cultivated land with small agricultural watershed in hilly area as the research unit,so it is of certain practical significance to systematically explore heavy metal pollution in agricultural watershed in hilly area,understand the pollution situation and spatial distribution characteristics of soil heavy metal pollution in the research area,and discuss the driving mechanism of heavy metal pollution in agricultural watershed soil.To our country farmland protection has the important guiding function.As one of the four municipalities directly under the Central Government,Chongqing’s environmental monitoring data are not optimistic in recent years due to its original industrial base background.Jiangjin District of Chongqing,as one of the important areas of agricultural modernization,has great agricultural potential.Jiangxiaobai demonstration base of grain and wine industry is established in Jiangjin,so it is very necessary to carry out systematic research of soil environment assessment in this region.Therefore,this study took Huangdun River Basin,Jiangjin District,Chongqing as the research object to understand the basic situation of soil heavy metal pollution in the study area.Single factor index method,Nemerow comprehensive pollution index method and ground accumulation index method were used to evaluate the soil environmental quality in the study area.Combined with the land use mode and landscape index in the study area,The relationship between soil heavy metals,land use pattern and landscape index was discussed.The main research results are as follows:(1)The average pH value and the median value of surface tillage soil in Huangdunxi Basin of Jiangjin District of Chongqing were 5.62 and 5.61.Most soils in the study area were acidic,and organic matter content was 22.50 g/kg-1,which was lower than the national average level.In general,soil nutrients in Huangdunxi Basin were low.(2)The statistical analysis of heavy metals in the surface soil of Huangdunxi Watershed in Jiangjin District of Chongqing showed that Cd in Huangdunxi watershed exceeded the soil risk screening value and soil risk control value,and the soil environment was at a high risk of Cd pollution.(3)The single factor index method,the soil accumulation index and the Nemero pollution index were used to evaluate the heavy metal pollution of the cultivated land in the Huangdun River Basin.The main pollution factor of soil heavy metal in the basin was Cd,and the soil accumulation index showed that the Cd pollution in most areas of the basin was between light pollution and moderate pollution.Nemerow comprehensive pollution index in the basin,the overall Cd pollution is severe,and some sampling points have light Pb pollution.The Cd pollution in the basin should be paid attention to.The potential ecological risk method evaluates the potential ecological pollution in the basin.Only Cd has a high potential ecological risk in the basin,while the whole basin has a medium potential ecological risk.The medium potential ecological risk of Cd to the whole basin is more than 90%.(4)Pearson correlation analysis and RDA analysis of multi-scale landscape indexes and soil heavy metals were carried out after subdivision of Huangdunxi watershed.Pearson correlation results showed that heavy metal concentration in soil was correlated with some topographic indexes,but had little correlation with landscape indexes.The results of RDA analysis showed that there was an internal interaction between soil heavy metal concentration and landscape indexes,and the concentration of Cd was significantly correlated with the proportion of building land,water area and river course in the sub-watershed.For Cd pollution control mainly existing in the basin,targeted control can be carried out from the proportion of suitable construction land including roads in the overall land use,and further investigation of heavy metal pollution in Huangdun Stream runoff.