| The Yanghe watershed, located in the Farming-pastoral ecotone of Northern China, is not only a major drinking water source of Beijing, but also a main sink for industrial and agricultural pollutants from many counties along the Yanghe river. Serious pollution with heavy metals happened and caused the Guanting reservoir, an important drinking water source, ceasing water supply for Beijing since China’s reform and opening up. However, current research about heavy metals pollution were mainly focused on water and ignored the soil environment quality caused by metals in the whole watershed which is a complex system. In this present study, the spatial variation of land use change in 1990,2000 and 2013 of Yanghe watershed was analyzed, based on which soil sampling was conducted. Soil the physical and chemical propensities, and concentrations of heavy metals including Cd, Cr, Ni, Zn, As, Pb and Cu were analyzed. Meanwhile, closest distance from sampling to river stream, road, enterprise, and other land use were calculated. Using geographic information system (ArcGIS), SPSS, Excel and Minitab software, the kriging interpolation methods, the characteristics of soil heavy metals pollution and their spatial distribution and integrated pollution level within the Yanghe watershed were revealed. Correlation analysis and the principal component analysis (PCA) were combine to explore the main sources of soil heavy metals accumulation in the Yanghe watershed. Conclusion are listed below:Farmland increased from 1990-2000 and then dereased, however, woodland decreased from 1990-2000 and then increased. Grassland declined, while urban and rural land and industrial and mining land kept increasing. The direction of land use change were similar both period of time. The spatial transformation of urban and rural land and industrial and mining land, agricultural land, forest land and grass land use type took place frequently at border of xinghe county, Tianzhen county and Yanggao county in Yanghe watershed upstream, and border of Wanquan county, Xuanhua county, zhangjiakou county and huailai county in Yanghe watershed middle and lower reaches during two period.Relatively high concentrations of metals were mainly distributed at border of Xinghe, Tianzhen and Yanggao counties in upstream of Yanghe watershed, and border of Wanquan, Xuanhua, Zhangjiakou and Huailai counties in middle and downstream of the watershed. The spatial distribution of Cd continuity is stronger, presents the southeast in Xuanhua county as the center to the periphery gradually decreasing trend, has obvious characteristics of northwest - southeast direction. Cr and Ni mainly concentrated at border of Xinghe county, Tianzhen county and Yanggao county, and day parts of Shangyi county and Wanquan county, but have slight pollution overall. Zinc were mainly distributed in the southeast region of study area and most parts of Xinghe county, Yanggao county and Tianzhen county. As has a relatively high value area (8.6-15 mg/kg) mainly distribution in southern area, at the border of Xinghe county and north of Shangyi county, pollution was more serious at upstream of river watershed. High concentration of Pb (59.2 436.5 mg/kg) were mainly distributed in the west area of Huaian county and east of Xuanhua county. Cu content of the high value area (31.5 56.6 mg/kg) mainly appear the border of Xinghe county, Yanggao county and Tianzhen county.Farmland soil heavy metal elements have strong spatial variability, heavy metal pollution degree of order from high to low was Cd>Cr>Ni>Pb>As>Cu>Zinc. Cd and near distance index has significant correlation, the main pollution sources may be sewage irrigation and atmospheric precipitation, meanwhile, there may be exist greatly influenced by human activities. Cr and Ni content were mainly controlled by the process of soil materials. Content of Pb was not overweight, but local pollution phenomenon exists.There have weak spatial variability of woodland soil heavy metals, the overall pollution trend to a lesser degree. The highest overrate were Cd, Cr and Ni, As and Cu are slightly polluted, the rest of the elements have a larger degree of local pollution, there may be a local human activities influence. Grassland soil heavy metal pollution from large to small can sort for Cd>As>Pb>Cu>Cr, there was no pollution of Zinc and Ni.Urban and rural land use in the soil heavy metal pollution level from high to low was Cd>Cu>As>Pb>Ni>Cr>zinc. Due to industrial and mining enterprises around the soil heavy metal accumulation near the drainage outlet, lead to the accumulation of a large number of Cd and Pb, which order from high to low was Cd>Cu>Pb>As>Cr>Ni>Zinc. Integrated different ways of land use soil heavy metal pollution can be found:the farmland pollution with metals is most serious, followed by the industrial and mining land use and urban and rural land, woodland and grassland pollution was the lowest.Land use for a long time (> 20 years) is more easy to cause the accumulation of heavy metal Cd, belongs to the moderate pollution, followed by heavy metal Cr and Ni slight pollution.20 years (1990-2013) and 10 years (2000-2013) from other classes into for farmland soil heavy metal Cd, Cr, Ni, As and Pb whole belongs to the slightly polluted, the rest of the pollution-free.Soil:long-term use of forest land soil Cd, Cr, Ni, zinc, As, Pb and Cu basic pollution-free.But 20 years from other classes into for woodland soil Cr, Ni, zinc, Pb and Cu content is higher than the 10 years into for forest soil.Soil in the urban and rural land use:7 kind of heavy metal pollution levels from high to low, respectively is:use for a long time to>10 years to 20 years.Industrial and mining land use, the longer the soil Cd, Cr, zinc, the As and Pb pollution is heavier, while Ni and Cu instead. |
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