| On account of the unique features in karst district, it become the hot topics that many domestic and international scholars want to research it.But the research of the environmental quality of heavy metal in soil is insufficient. The scope of existing research on soil heavy metal environment problem is quite limited,which is just in some typical regions, such as the mining area, urban construction, cultivated land and so on, these studies are difficult to fully reveal the karst area anomaly sources of heavy metal elements in soil and its causes. Basin as a unit of research to analysis the sources of Cd and the mechanism in soil in karst district which is of great scientific significance, and it has an important practical significance to protect the ecological environment and promote regional sustainable development.In this article, taking the soil in a small basin of karst district as the object. Collecting soil samples in the surface, deep soil samples, the rock samples in the surface, analyzing the content of Cd element in soils and rocks; studying the distributing characteristic of Cd element in soil and rocks in the basin; determining the minimum thresholds of Cd element in the soil and the anomaly extension.; through the spatial analysis, looking for the sources of Cd content in the soil; combined with anomaly sources of Cd element in the soil of karst area, then get the anomaly formation mechanism. The results of the study are as follows:1. The average content of Cd element in the soil of the basin is 3.54 mg?kg-1, compared to the content of Cd element in 3 standard that mentioned in the state soil environment quality standard(GB15618-1995), the sample over standard rate is 78.85%;2.The areas with high content of Cd element in the soil mainly appeared in the middle region where the town located; the land use pattern high content of Cd element in the soil mainly appeared in urban construction land and rural residential areas and shrub land and cultivated land in the basin, the content of Cd element in the soil is inversely proportional to the height;3.Compared with the results obtained by fractal method and robust estimation and traditional methods(x+2S) and 85% of the cumulative frequency methods, the minimum threshold of Cd element in soil determined by fractal method was effective and reasonable, the result is 1.07 mg?kg-1;4.Using the spatial analysis,the areas with the anomaly content of Cd element in the soil are mainly distributed areas in lower altitude and urban areas and rural areas and mining areas in karst district, and preliminary judging the anomaly sources of Cd element in the soil include the natural source, artificial fertilization, mining operations;To study the distribution and the sources recognition of Cd element in the soil of the basin what we can get the cause of Cd element in soil of karst area: the karst area has the backgrounds of the unique geological and geomorphic conditions firstly, the soil mineral with a high content of Cd element in it, the Cd element can get to the surface through the process of geological cycle and biological cycle, the Cd element in the surface is weak to migrate, secondly human activities can make it enrichment in the soil. The most of human activities is concentrated in the karst valley, such as transportation, construction, agricultural production. these activities can convey a certain amount of Cd element in soil.it can further increased the content of Cd element in soil, eventually lead to anomaly content of Cd element in soil of the karst area. |
PDF Full Text Request