Monitoring And Spatial Estimation Of Contents Of Soil Heavy Metals

Heavy metal pollution of soils is a hot issue of soil ecology and environment Protection. With urban industrialization and intensive agricultural development, the impact of heavy metal pollution in suburban areas is more significant than the outer suburbs. The peri-urban area of Daxing District, Beijing is selected as a research object. In the context of landscape heterogeneity, the spatial distribution of heavy metals, the relationship between heavy metal accumulation and landscape features, visualization and expression of tracing heavy metal pollution sources and theory model of spatial estimating of heavy metal contents are observed. Our works are presented as follows:(1) Spatial distribution of soil heavy metals contents.Based on monitoring data of surface soil heavy metals mainly collected in Daxing district, it shows that the average contents of heavy metals of As, Cu, Pb, Hg, Cd,and Cr, are respectively6.5mg-kg-1,25.9mg.kg-1,20.6mg.kg-1,0.078mg.kg-1,0.15mg.kg-4,59.3mg.kg-1. Due to impact of human activities, accumulation of heavy metals occurs in a certain degree. For the elements of Cu, Cd and Cr, their averages of cumulative pollution index are greater than1, while ones of As, Pb, Hg less than1, and percentage of samplers ranged from12.8%to32.5%, whose accumulation pollution index is greater than1. According to a single factor pollution index, the evaluation results show that the As, Cu, Pb and Cd in six kinds of heavy metals, exceed the national secondary standard in a polluted state. There are12.87%of samples with Pb contents in the polluted state, and As, Cu, or Cd concentrations over the national secondary standard pollution are respectively0.20%,0.04%, and0.38%㏑elationships between soil metal accumulation and potential pollution sources.Soil metals in Beijing region were considered as a study case. A method is proposed to quantify the relationship between heavy metal accumulation and potential pollution sources (land use, road network, buildings). The results show that the probability confidence which Cu and Hg accumulate more than ones of As, Pb and Cu under there land use types of grain, vegetable, and orchard. The influence of road networks and buildings on the accumulation of soil heavy metals depends on the distances of monitoring samples to the road network and built-up areas, within the1,500meters, roads and construction areas in Daxing District, have no contributions to As, Pb, Cu and Cr accumulation of small, and but affect the contents of Cd and Hg.(3) Visualization and expression of tracing multi-point Pollution sources of heavy metals.A novel study method is established to visualize potential contamination sources of soil heavy metals. This method assumes that the pollution source is only one and the contents of soil heavy metals decrease with increasing distance to the source. Based on that, the monitoring samples of heavy metals will be mapped to a direct graph G=(V, E), that is:each sample is characterized by a node, indicating a possible potential sources of heavy metals, and the direct edge between two adjacent nodes stands for the diffusion process of pollutants from one node to neighboring nodes. Whether a node has a connected edge to its neighboring nodes is under control of two parameters of the radius R of pollutants spread and difference coefficient8of pollutants contents in the two adjacent nodes. Compared with traditional methods, the main advantages of this method includes1) dynamic visualization of heavy metal spread;2) easy to search out potential sources of pollution;3) For the occurrence of multiple heavy metal pollution areas, effectively to give the direction of the spread of heavy metal pollutants.(4) Theory model for spatial estimation of Heavy Metal ContentsThe theory model gives an assumption:since exogenous factors affecting soil heavy metal contents, such as vegetation type, topography, meteorology, hydrology and human disturbance have spatial heterogeneity in the global space and spatial homogeneity in the local space, the distributions of heavy metal contents are similar like that of the exogenous factors. The core ideas of the model include: classification of exogenous factors that affect the contents of heavy metals in the global space, and then achieve different soil unit classes; Construction of spatial estimation method, which adaptively restricts the interpolation of an unknown location within a spatial homogeneous soil unit.