| With development of modern technology, as a famous great river worldwide, Changjiang River has been evolving as main artery of Chinese economy. In the catchment along the Changjiang River as the most developed area, especially Changjiang River Delta, a lot of heavy metals are discharged into the river, soil system when the economy is developing, which make ecosystem go bad to worse. In great river basin, besides weathering of geological minerals, the influence of big cities and developed area on the river also increases gradually. So it is significantly important to keep industrial and agricultural sustainable development in Changjiang River basin by enhancing monitoring heavy metals pollution and research on the geochemical behavior of heavy metals.On the basis of comparing differences of heavy metals in suspended solids and sediment of Changjiang River temporally and spatially, this research emphasizes heavy metals concentrations and geochemical behaviors in sediment of Changjiang River and tributary rivers and cropland soil in Changjiang River Delta throughout Jiangsu, Zhejiang and Shanghai districts, and pollution area distribution. Likewise, comparison with geochemaical characteristics of heavy metals in sediment of the whole Changjiang River basin, the potential sources and influence factors of heavy metals in sediment of lower reach of Changjiang River were analyzed. And ecological effects of heavy metals were analyzed preliminarily to provide the reference data for remediation of acidifying soil polluted by heavy metals.In this study, Suspended solids and sediment in Changjiang River, sediment of lower reach of Changjiang River, river sediment of Changjiang River Delta, soil and rice plant of Changjiang River Delta were selected for analysis in order to (1) understand spatial changes and characteristics of geochemical behavior of heavy metals through PCA analysis; (2) expatiate on the spatial distribution of heavy metals in tributary rivers of Changjiang River Delta, build and compare spectral models for metals in sediments, and analyze spatial changes, speciation and mobilization and differences under different pH condition of heavy metals in paddy rice soil of Changjiang River Delta; (3) understand geochemical behaviors characteristics during the transfer of heavy metals in soil-rice system, and transfer of heavy metals under different soil pH and effects of nutrient elements. The main results of this study are listed:1. From the whole Changjiang River basin, As and Cd had the highest index of geoaccumulation (Igeo),reaching moderate pollution level. The mining areas of Northeast Yunnan, Nanling in Hunan Province and Tongling in Anhui Province had significant influence on the concentrations of heavy metals in suspended solids and sediment of Changjiang River. Two pairs of metals, As, Cd and Pb, Zn were influenced by mining area mainly. And Pb and Zn in sediment and suspended solids of dry season had significant linear correlation because of influence of mining areas. But besides mining area, the peak values of Co, Cr, Cu and Ni concentrations appeared in the suspended solids and sediment of river sections around the big cities and developed areas along the river. Heavy metals in sediment of lower reach of Changjiang River may come from the mining area in Tongling.2. According to the PCA/MLR analysis, particle size effect influenced more than 50%of geochemical behaviours of Co, Cr, Cu, Ni and Zn which mainly existed in particles with size<16?m. Abnormality of Cd, Pb and Magnetic susceptibility (MS) were related to fly ash. Fly ash explained geochemical characteristics of 69.0%of Cd and 51,8%of Pb, likewise fly ash also contribut geochemical behaviour of other metals except Hg; Geochemical behaviour of Hg was related to black Carbon (BC), which both of them came from precipitation of coal combustion exhaust. Comparison of distribution of power plants along the lower reach of Changjiang River, it can be concluded that power plants are the main sources of heavy metals in sediments.3. Cadmium, copper and zinc in sediment of tributary rivers of Changjiang River Delta had the highest Coefficient of Variation (CV>100%), which suggested that some samples had higher levels for Cd, Cu and Zn; Through PCA analysis and spatial distribution of heavy metals, it could be found that the polluted rivers distribute in Taizhou and Nantong in Jiangsu Province, Ningbo and Jiaxing in Zhejiang Province. According to test analysis, the levels of Hg, Cr, Cu, Pb and Zn in sediment of Zhejiang Province were significantly higher than those in Jiangsu Province. Arsenic, cadmium and lead levels in sediment of tributary rivers were lower than those in sediemnt of Changjiang River.4. Differences between reflectance spectra of samples and orders of heavy metals in cluster groups were big, which resulted in the bad predictive models of spectra for metals, with RPD<1.1 for each model. Because of homogeneous spectrally-active composition in sediment, the spectra PLS models for heavy metals in sediment of whole Changjiang River basin and lower reach of Changjiang River had better predictive ability with RPD>1.1 for all models. Meanwhile, for sediment of Changjiang River the MIR spectra PLS model had better predictive ability than NIR spectra.5. Spatial variation of heavy metals in rhizosphere and non-rhizosphere soil in rice fields of Changjiang River Delta was significant, and CV values of Cu, Cd, Zn and Hg exceeded 50%. The results of sequential extraction showed that the order of mobilization of metals was Cd>Pb>As>Cr, Hg, and proportion of labile fraction of Cd, Pb and As were higher which suggested that these three metals had strong bioavailability. Spatial distribution showed that metals levels in soil samples in Zhejiang Province were higher than those in Jiangsu Province, especially peak values of heavy metals concentrations appeared in Hangzhou, Shaoxing and Ningbo of Zhejiang Province. Spatial variation of metals was significant with pollution of Cd, Cu and Zn for Zhejiang, and As for Jiangsu because of usage of fertilizers and pesticides.6. Proportion of labile Cd and Pb in rhizosphere soil of Changjiang River Delta were high, reaching-50%and-10%respectively; Total and labile As in soil of Jiangsu were higher than Zhejiang, but total and labile Cd, Pb, Hg, Cu and Zn of Zhejiang were higher than Jiangsu. In rice shoot and grain samples, As, Pb, Hg and Zn levels in Zhejiang were higher than Jiangsu, but Cu levels were lower. And the peak values of other elements appeared around the Taihu Lake mainly. From spatial distribution, the rice plants in Zhejiang were polluted more strongly than those in Jiangsu.7. The order of transfer factors from soil to rice shoot (TFShoot/soii) of heavy metals were:Cd>Cu>As, Hg, Zn>Pb>Cr; The order of transfer factors from rice shoot to rice grain (TFgrain/Shoot) of heavy metals were:Zn>Cd, Hg, Cu, Cr>As>Pb, and transfer factor of Cd, Hg, Cu and Zn exceeded 0.2 which indicated that these metals can enter into rice relatively easily. TFgrain/shoot of metals in Jiangsu were little higher than Zhejiang, which suggested that transfer of heavy metals could increase with stronger growth activity because of lower pollution in rice. In samples with low soil pH, the transfer factors of As, Cd and Zn were significantly higher than those in samples with high soil pH. The TFgrain/Shoot of metals decreased with shoot metals levels and/or TFshoot/soii exponentially.8. Because of the same influence of Ca and K on the geochemical behaviour of heavy metals, metals could enter into rice grain through the Ca and K channel. In rice shoot competative assimilation between Ca2+and K+, As, Hg, Pb, Cr and Zn could enter into shoot through Ca channel, but Cd, Cu and Zn transfer through K channel. Soil CaO inhibited accumulation of heavy metals in rice shoot and grain more strongly than K2O, suggesting that liming not only could supply the nutrient element but also neutralize acidified soil to inhibit accumulation and transfer of heavy metals in soil-rice system. |
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