Soil Environmental Quality Monitoring In The Yangtze River Delta

In this study, heavy metal elements, such as arsenic(As), cadmium(Cd), mercury(Hg), chromium(Cr), copper(Cu), lead(Pb), zinc(Zn), nickel(Ni) in soils of Yangtze River Delta were focused, while their concentrations and spatial distribution in top soil, atmospheric wet and dry deposition, irrigation water, fertilizer and crops were analyzed. Based on the datas of heavy metal contents of soil between 2007 and 2014, the variation and accumulation rate of contents of heavy metals in top soil were studied. Combined with the input and output flux model, the biogeochemical cycle of harmful elements in the study area were analyzed, which provided a basis for the regional ecological risk assessment.It was resulted that Zn, Cu, Ni, Cd, Hg, Cr and Pb have been enriched in the top soil of farmland in Yangtze River Delta by 2014, comparing with national background value. It was inferred that the biggest ecological risks could be caused by Cd, Hg, Zn and Cu, and surrounding areas of Taihu, Shanghai, Jiaxing and other developed areas in the eastern part of the study area were the most polluted areas. Organic carbon content, cation exchange capacity and clay mineral are the main factors that affect the total amount of elements in top soil of the study area.Compared with the data of Multi-purpose Regional Geochemical Survey by 2007, the results of basic farmland monitoring sampling site have changed significantly, the concentrations of As, Cd, Cr, Pb have reduced, and Cu, Pb, Zn have increased.It was showed that the atmospheric dry and wet deposition fluxes of Yixing, Wuxi, Shanghai and Changzhou were higher, and Zn occupied the highest portions in the atmospheric dry and wet deposition-flux.The irrigation input fluxes of Nantong, Suzhou and Shanghai were higher, and Zn, Cu shared the highest portions in the irrigation input fluxes. The fertilizer input fluxes of Cr and Zn were higher, but the fertilizer input fluxes of Cd and Hg were smaller. According to the comprehensive study which presented atmospheric wet and dry deposition flux, irrigation input flux and fertilizer input flux in Yangtze River Delta, the proportions of fertilizer input of various elements is the smallest. Pb, Zn and Cr contributed the highest portion of atmospheric wet and dry deposition, but As, Hg, Cu and Cd has the highest irrigation input proportion.Wheat seeds were more easily enriched with Cd, Cu and Zn, while As, Pb, Cr were more difficult to be absorbed. Contents level of elements in soil, p H value and synergistic or antagonistic interactions between elements in the enrichment process were the main factors affecting accumulation of heavy metals in wheat seeds in this study.In the meantime, the output fluxes of Cu and Zn throμgh crop harvesting were relatively higher and the annual net increment of all heavy metal elements in soils were positive. The highest net input flux is Zn and followed by Pb, Cu and Cr.