Spatial Distribution Characteristics And Pollution Evaluation Of Heavy Metals In Soil Of Okeechobee Lake In USA

Soil is an important part of the environment, It is a ecosystem circulation medium among water, air, rocks and water.With the rapid development of economic and the improvement of industrial and agricultural modernization level, much soil have been polluted by heavy metal. It is very important for soil environmental protection and management to research the spatial distribution and pollution condition of soil heavy metals.The paper combine statistical method with GIS to research the spatial distribution and pollution condition of heavy metals in lake Okeechobee basin, and get the following conclusion:1.In the research area,characteristics of soil heavy metal data analysis results show that there is great variability of Cu、Zn、Pb in surface and Cu、Zn、Pb、Fe in the subsurface soil, with moderate variability of Fe、Cd、Co、Gr、Mn、 Ni in surface soil and Cd、Co、Cr、Mn、Ni in the subsurface soil;Cu, Zn, Pb, Cd, Co in Surface and Cu、Zn、Pb、Fe、Cd、Co、Cr in the subsurface soil all do not accord with normal distribution, Fe, Cr, Mn, Ni in the surface and Mn,Ni in the subsurface soil are accord with normal distribution.2.According to semi-variance analysis of soil heave metals,in the isotropic,Cu in surface and subsurface soils respectively agree with spherical model and exponential model,Zn in surface and subsurface soils all agree with exponential model,Pb in surface and subsurface soils respectively agree with exponential model and spherical model,Fe in surface and subsurface soils all agree with spherical model,Mn in surface and subsurface soils respectively agree with exponential model and gaussian model,Cd in surface and subsurface soils all agree with linear modeI,Co in surface and subsurface soils respectively agree with linear model and gaussian model,Cr in surface and subsurface soils all agree with gaussian model,Fe in surface and subsurface soils all agree with spherical model,Ni in surface and subsurface soils all agreed with gaussian model.3.In the anisotropic,variation of all metals in the defferent direction is obviously.In addition to the Co, Fe in the surface soil and Co, Fe,Mn in the subsurface soil showed evident characteristics of isotropy,the others all showed obvious directivity characteristics;Cd,Cr in surface and subsurface soil in all directions variation are larger.Cu in surface soil change gradually widened outside 2 km,Cu in subsurface has a great change outside 8 km.Mn in surface soil has a great change in north-south and northwest-southeast direction.The variation of Ni in surface and subsurface soil are bigger in all directions.Pb in surface soil has a great change outside 7km,Pb in subsurface soil change gradually widened outside 8km; Although Zn in surface soil change in all directions,but the trend is relatively moderate,Zn in subsurface soil has a great change outside 10km,specially in the northwest-southeast direction.4. According to the result of cross validation,the optimal interpolation method for Cu in surface and subsurface soil respectively are ordinary kriging and universal kriging respectively.Cu in surface and subsurface soil, the distribution characteristics are similar,they are all island combined with ribbon.For surface and subsurface Zn, the optimal interpolation method are ordinary kriging and Simple Kriging respectively,and the distribution both are island.Pb in surface and subsurface soil, the distribution characteristics are similar,both island,the optimal interpolation method for Pb in surface and subsurface soil are ordinary kriging and simple kriging respectively.Cd in surface and subsurface soil, the distribution characteristics are similar,both island,the optimal interpolation method for Cd are ordinary kriging and Simple Kriging respectively.Co in surface and subsurface soil, the optimal interpolation method is ordinary kriging and universal kriging respectively.they are distributed in island combined shape.Mn in surface and subsurface soil, the distribution characteristics are similar,both island,the optimal interpolation method for Mn both are simple kriging.The optimal interpolation method for Cr in surface and subsurface soil respectively are disjunctive kriging and simple kriging respectively. the distribution characteristics are similar,both island combined with ribbon.Fe in surface and subsurface soil, the optimal interpolation method is ordinary kriging and simple kriging respectively,they are distributed in island combined shape.For surface and subsurface Ni, the optimal interpolation method both are simple kriging,and the distribution both are island.5.According to the result of indexes of geo-accumulation method,in the surface of research area,Cd pollution is most serious,about 70% of the study area have been polluted by Cd,mainly in the northwest and south of lake Okeechobee region, especially in the south.Nearly half of the sample point, Cu pollution is serious, mainly in the northwest and southeast.According to the result of potential ecological indexes method,Cd pollution is most serious,the risk assessment index are in the order of Cd>Cu>Pb>Ni>Zn>Mn>Cr,while the potential ecological index RI is 166.55,it indicate that the surface soil has medium ecological harm.