Elemental Geochemical Characteristics And Environmental Quality Assessment In Xiangshang,Ningxia

The local farmers put the river gravel?uncategorized?on the surface of soil during the selenium-sand-watermelon planting in the alluvial fan of Xiangshan,Ningxia since the gravel will enter the soil through the time passing and repeated farming.The area belongs to the semi-arid desert landscape area,and the surface effect is mainly physical weathering and mechanical transportation,so the content of soil can be characterized by the elemental content of water sediments.Therefore,we collected 2,827 samples of sediments here and analyzed113,080 pieces of data,then evaluated the safety of sand and gravel in the study area according to relatd specification.We drew the nutrient grade maps of oxides and elements e.g.B,Co,Cu,Mn,Mo,P,V,Zn,Fe₂O₃,MgO,CaO,K,ect.,and explored the distribute regulation according to the"specification for Geochemical Evaluation of Land Quality".The result shows that:1.Co,Cu,Mo,V,Zn,Fe₂O₃,MgO,K enrichment ereas distribute large proportion,2.B,CaO,Mn enrichment and depleted erea distribute normal proportion,3.P enrichment erea lacks relatively,4.Heavy metal elements have lower potential risks.Thus fertilization need the supplement of P in the process of selenium-sand-watermelon planting.Cd,Hg,As,Pb,Cr,Cu,Ni,Zn were evaluated according to the“Control Standards for Soil Environmental Quality Pollution in Agricultural Land”.Hg,Pb,Cr,Ni,and Zn are normally distributed.There are individual points in Cd and Cu that exceed the risk screening value.There are large areas of As exceeding the risk screening value and a small number of areas exceeding the risk control value.The area whose comprehensive grade of environmental assessment is less than the risk screening value is 9032 km²,accounting for 82.1%of the total area and the risk of soil pollution is low here.So there's no heavy metal pollution since the gravel used in the main planting areas of selenium-sand-watermelon comes from this area abovementioned.The area whose comprehensive grade of environmental assessment is bigger than the screening value and equal to or less than the control value is 1836 km²,accounting for 16.7%of the total area of the study area.There may be risks such as the production of edible agricultural products that do not meet safety standards,and the gravel mining in the area should be restricted.The area larger than the control value is 132 km²,which accounts for 1.2%of the total area.The risk of soil pollution is high and gravel mining should be forbidden in this area.The main over-standard elements in the study area are arsenic elements related to coal mineralization and mining.The over-standard area is mainly located in the tupo area of the middle and low mountainous areas.There is no agricultural planting activity,and it does little harm to human beings.