| The Chengdu Plain is known as "Land of Abundance", it is the main production base of the agriculture in our country. And the heavy metal in the soil can directly influence the human health and the agriculture sustainable development of the whole province. But as a typical of the gray alluvial paddy soils in Sichuan province, there are less reports on the study of Cd morphological characteristics on various diameters and the influencing factors. In this paper, the soil was divided into sand, silt, and clay by International system. This thesis has a deep research on the Spacial mutation characteristics of Cd (in gray alluvial paddy soils) on various diameters and in different forms and the influencing factors by using the Geostatistics components and ArcGIS software. The main conclusions are as follows:(1) In the gray alluvial paddy soils along Qingbaijiang River in Xin Du District, the contents of sand, silt, and clay account for52.56%,33.30%and14.14%, respectively. The average value of Cd in original soils is0.360mg/kg, the average values of Cd in sand, silt, and clay were0.210mg/kg,0.411mg/kg and0.478mg/kg. For Cd of different forms, the distribution of Cd in original soils, sand and silt is:the residual Cd was the highest, while the exchangeable cadmium was the lowest. In clay, the content of Fe-Mn oxide cadmium was slightly higher than residual cadmium, is the highest. The reason may be that the activity of Fe-Mn oxides is higher or the moreFe-Mn oxides will have in clay when under submerged condition. On various diameters, the average value of exchangeable cadmium is relatively high, it is0.035mg/kg,0.075mg/kg higher than the Cd content in silt and sand. The carbonate cadmium in clay were0.010mg/kg,0.027mg/kg higher than the Cd content in silt and sand. The content of Fe-Mn oxide cadmium in clay were0.055mg/kg,0.090mg/kg higher than the Cd content in silt and sand, while the average value of organic combination of cadmium and residual cadmium in silt was the highest.(2) The content of active Cd in the original soils is0.220mg/kg, it accounts for61.11%of total Cd. And the Cd contents in sand, silt, and clay were0.119mg/kg,0.272mg/kg and0.368mg/kg, respectively, they account for56.67%,66.18%and76.99%of total Cd. The content of active Cd on various diameters was:clay> silt> original soils> sand. A lot of active Cd could be absorbed as clay has strong specific surface area and mineral gel. So in the area that was slightly polluted by Cd, we can enhance the absorption energy of Cd by adjusting the soil texture, thereby efficiently reducing the harm to the environment when Cd releases directly.(3) The physical and chemical properties like pH, organic matter, free iron oxide, CEC, effective Ca and the contents of various diameters may have have different effects on the content of Cd in the soil.In original soils, the main factors that affect Cd are pH, organic matter, CEC, effective Ca and the contents of various diameters. pH and organic matter are the main factors that affect Cd in sand. In silt, the main factors were pH, organic matter and CEC, while in clay, pH is the main factor. Because the organic matter and mineral gel in sand soil were relatively small, so it has have weak adsorption on Cd. So in the soil of high sand content, it is easy to cause heavy metal pollution. We can reduce pollution by adjusting pH or adding organic matter. In silt, apart from adjusting pH and adding organic matter, we can alleviate the harm of heavy metal by improving the content of CEC. In clay, we can reduce Secondary contamination that Cd to the environment by adjusting pH or adding quicklime.(4) The Kriging Interpolation in different forms of Cd on various diameters in the study area has shown that:the big differences in regional soil texture and particle composition can lead to the changes of distribution characteristics of Cd in different forms and Cd on various diameters. So in the productive practice, we can reduce available Cd by regulating soil particle composition, Cd may be fixed in clay in low activity form and the harm of Cd can also be reduced.(5)In general, when Cd in sand, silt, and clay, the sand and silt has weak adsorption capacity of it, and it has high latent harm for living things. But clay has strong adsorption capacity of Cd, it can not be released easily. So in polluted areas, we can reduce Cd pollution by adjusting soil particle composition, pH, organic matter and effective Ca, providing some suggestions for the the safety production of food. |
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