The Evaluation Of Land Quality In Zhangye-yongchang Region Gansu Province

In this study,we obtained 54 indexes of soil organic carbon,total carbon and various elements（oxides）,analyzed distribution characteristics of surface and deep soil chemical elements,and investigated the major factor that affected regional geochemical distribution and the laws of migration and evolution in important chemical components.Through those works,the mechanism about geochemical distribution of soil elements could be established.We also studied the expression of important chemical components in agricultural ecosystem under the condition of natural state and human activity,and investigated the quality of soil environment and hold on soil geochemistry and environmental quality assessment.The study area is located in the city of Zhangye and Jinchang,Gansu Province（100°-103°E,38°-39°39′N;altitude:1600-3200 m）,study area is 8600 km².The main results are as follows:1.Compared with the national soil abundance,Au,As,B,Cd,Cr,Cu,F,Mo,Ni,P,Sb,Sr,U,Se,SC,Cl,Br,s,MgO,CaO and other elements were enriched in the deep soil than that in the surface soil,that were mainly caused by human activities,except for plant beneficial elements.Hg,Ni,Ti,Zr,Ga,SiO₂ and other elements in the surface soil were also relatively depleted in the deep soil,suggested that those elements had similar enrichment and dilution trends.Compared background value with reference value,most of the elements such as Corg,TC,N,P,Cd and Hg in the deep soil were relatively enriched that were also enriched in the surface soil,and the elements I was depleted in the surface soil and deep soil.2.The distribution uniformity of elements in surface soil and deep soil was similar.Most elements evenly distributed showed that the consistency of their sources.Ag,Bi,Mo,Sr,Se,I,TC,Cao showed relatively different,while cog,Hg showed significant difference in surface and deep soil.The reason for heavy metal pollution elements showed strong differentiation in the surface soil were strong late action of these elements,which may be the result of epigenetic geochemistry and human activities.The enrichment of plant nutrient elements showed the activity of elements in the surface soil environment,and also showed the pollution effect of agricultural cultivation and human activities.3.The concentration of Cd,Hg,Ni and Se in the surface soil of Zhangye City was significantly higher than the average value of the whole area.The highest value of Se in the abnormal area was 1.35ug/g,and the average value is 0.31ug/g.The high value points mainly appeared in the industrial and mining enterprises and farmland area near the railway station of Zhangye City,that indicated there is selenium rich soil in this area is enriched selenium.4.In order to reflect the influence of heavy metals on soil quality from the total amount,the national standard eight elements were mapped by the Nemero index according to the upper limit of threshold.The first grade quality area was 160.91 km²,accounting for 1.87%of the total area;the second grade quality area was 7492.86 km²,accounting for 87.13%of the total area;the third grade quality area was 852.91 km²,accounting for 9.92%;the fourth grade quality area was 93.32 km²,accounting for 1.09%.5.There were significant differences in soil geochemical environment,nutrient elements and soil availability in different landscape areas of the study area.In the study area,the concentration of magnesium,calcium,sulfur,potassium were much more,molybdenum,organic matter,phosphorus were poor in a large range,and nitrogen was lack in some areas.Except for the lack of Mo and Zn,the rest of Cu,B,Fe and Mn were in normal or rich level.Above all,the soil quality of the study area was in the normal level,but soil was polluted in some areas,accounting for 11.01%,in which the content of contaminated elements had exceeded the critical value.Some element concentration had endangered the growth of animals,plants and human health.Therefore,adequate attention should be given to prevent further deterioration of the environment,endanger the survival of human environment.