Geochemical Characteristics Of Heavy Metals And Acidification With Their Response To Carbonate Minerals In Agricultural Soils From The Southern Jiangsu Province

With the development of society, the problem of soil environment has gradually become a serious obstacle to the sustainable development of national economy. The heavy metal pollution of agricultural soil has been one of the centre issure for a long time. Since the middle of last century, scientiests have made a lot of research on soil problems, including heavy metal pollution and acidification, and their impact on crops. Varieties of suggestions have been put forward to the remediation of heavy metal contaminated soil. In spite of this, the knowledge of variation characteristics of soil heavy mental accumulation and pH value distribution is scant, so does the knowledge of carbonate mineral occurrence and leaching rules. The impact on the risk of heavy metal pollution of pH value variation and response to heavy metal geochemical characteristics of carbonate minerals are still in the exploratory stage.Based on the field investigation, experimental analysis and data processing, this study did an in-depth investigation of the geochemical characteristics of the soil heavy metal pollution and acidification, established in the southern part of Jiangsu Province, which has a long history of agriculture. Geochemistry and leaching characteristics of carbonate minerals in soil has been researched as the point of penetration. Its influence and enlightenment on soil acidification and heavy metal pollution has been discussed. Some main results and conclusion are as follow:(1) The spatial distribution of soil heavy metals in Southern Jiangsu area defference in the two sides of Taihu Lake. Heavy metal content was higher in the eastern part, including Suzhou and Wuxi than that in the western part, including Zhenjiang and Nanjing. The situation of heavy metal pollution has been slightly improved since 2008. The contaminated samples are mainly distributed in the surrounding areas of Zhenjiang, Wuxi, Jiangyin, Zhangjiagang and Suzhou Cities, partly similar to the Se element distribution pattern. Distinguished from natural background, the existence of human endmember of heavy metal and Se elements were proposed.(2) The spatial distribution pattern of soil pH in 2010s was significantly different from that in 1980, with lower soil pH values in the west part of the research areas than those in the east. Two phases of pH change have been observed before and after 2003, especially presented in Jurong Countries where soil acidification has occurred in the later 10 years after alkalization in previous 20 years, and Suzhou-Wuxi Countries where it displayed the opposite trend. Soil acidification occurred inthree typical regions, Suzhou, Taicang and Zhangjiagang during 2010 and 2015. Soil acidification was most prominent in the suburb of Suzhou (ΔpH=-1.0), and less in Taicang (ΔpH=-0.36). Zhangjiagang is not presented obvious change. The most point with Cd, Hg or Cu exceeded the standard has an acidification history. It showed that there was an inherent relationship between heavy metal enrichment and soil acidification.(3) In three regions, the average content of carbonate in 2010 was 3%, the average content of dolomite was 1.2%. And the average content of carbonate content was 2.1%, the average content of dolomite was 0.7% in 2015. In addition to the increase of carbonate content in some areas, the content of carbonate and dolomite in the surface soil was decreased in the five years. The distribution characteristics of carbonate content in soil profile showed that there were significantly different degrees of leaching characteristics of carbonate minerals in the three regions of Suzhou, Taicang and Zhangjiagang.(4) Carbonate minerals in soil are sufferring acidification and leaching, and receiving some new supply at the same time. The correspondence of carbonate minerals and soil pH showed that surface soil of suburban Suzhou in 2003 does not contain carbonate minerals, so the carbonate minerals appeared in the 2010 local soil indicates carbonate sources related with human activities such as urban construction.Soil carbonate minerals have important influence on soil acidification and heavy metal pollution. Relationship between the change of soil carbonate content and the changes of soil pH value is close. The increase or decrease of carbonate minerals drives the spatial temporal variation of pH values. And the variation of pH value of soil is one of the important factors in inducing heavy metals pollution. Some areas with higher level of heavy metals content in Southern Jiangsu Province are located in carbonate leaching regions. With carbonate minerals reduced and the acidification intensified, the soil would be classified as over polluted category. The risk of soil heavy metal pollution will be greatly enhanced by then.