【作者】 宋垠先；

【导师】 季峻峰； Ray L.Frost； Godwin A.Ayoko；

【作者基本信息】 南京大学 ， 地球化学， 2011， 博士

【摘要】 长江是世界著名大河,随着现代科技的发展,逐渐成为了中国经济的大动脉。长江沿江是中国近年来经济发展最快的区域,特别是作为龙头的长江三角洲地区,在经济高速发展的同时,大量重金属污染物被排放进入了河流、土壤等环境系统中,造成了生态环境的日益恶化。大河流域除了流域的地质矿产风化释放大量的重金属造成污染外,沿江的大城市和经济发达区域对流域生态的影响也日益加重。因此,加大对长江流域重金属元素污染的监控力度以及增加地球化学行为特征的研究对保持长江流域工农业可持续发展有着重要意义。在对长江江水悬浮物和沉积中重金属元素在时空变化的研究基础上,本文重点对长江三角洲区域内的长江干流河段以及分布于江苏、浙江和上海三个省市的主要面网河流以及农田土壤的重金属污染和地球化学特征情况进行测试分析以及污染区域分布的调查；对比长江全流域沉积物重金属地球化学特征,分析了长江下游干流三角洲区域内河段沉积物重金属的来源以及影响因素；对长江三角洲地区重金属元素的生态效应做了初步分析,为导致水稻重金属污染的日益酸化土壤的治理提供参考数据。本文选择长江干、支流悬浮物和沉积物、长江干流下游沉积物、长江三角洲面网河流沉积物、长江三角洲水稻田土壤和水稻植株样品为研究对象,(1)运用主成份分析(PCA)探讨长江沉积物和长江三角洲面网河流沉积物中重金属元素含量的空间变化和地球化学行为特征,建立和对比面网河流沉积物和长江沉积物的光谱预测模型；(2)阐述了长江三角洲水稻田土壤重金属元素空间变化特征、赋存状态和迁移活性以及在不同pH值下重金属含量分布的差异性；(3)初步了解重金属在从土壤到水稻的迁移过程中的地球化学行为特征、不同pH值下重金属迁移情况和营养元素对水稻体中重金属的影响,主要得到以下结论：1.从长江流域来看,As和Cd的地累积指数最高,达到中度污染。滇东北、湖南南岭和安徽铜陵三个矿区是悬浮物、沉积物中重金属的主要来源。As和Cd以及Pb和Zn这两对元素主要表现为受到采矿活动的影响。沉积物和枯水期悬浮物中Pb和Zn受矿区影响具有显著的线性关系。而Co、Cr、Cu和Ni除了矿区外,在沿江大城市附近也存在明显峰值。铜陵矿区可能对下游沉积物重金属有输入作用。1.根据多元统计方法(PCA/MLR)分析,粒径分布对Co、Cr、Cu、Ni和Zn的地球化学行为贡献超过50%,这几种金属主要分布在粒径<16 gm的颗粒中；Cd、Pb和MS的异常与粉煤灰有关,粉煤灰对Cd和Pb的贡献分别为69.0%和51.8%,另外粉煤灰对除Hg外的其它重金属都有贡献；Hg的地球化学行为与黑碳BC有关,均来自燃煤废气沉降。对照长江下游沿岸电厂分布,可以推断出,沿江电厂是三角洲地区当地的主要的重金属污染来源。2.长江三角洲面网河流沉积物中Cd、Cu和Zn变异系数大于100%,表明这几种金属有含量异常高的样品存在；通过PCA分析和空间分布发现,江苏省污染区域主要集中在泰州和南通地区,而浙江省主要集中在宁波和嘉兴地区,其中宁波地区污染最为严重,在该地区河流沉积物中Cd, Cu和Zn均出现较高浓度。通过检验分析发现,浙江地区河流沉积物的Hg, Cr, Cu, Pb和Zn含量显著高于江苏省。面网河流沉积物中As、Cd和Pb明显小于长江下游沉积物,面网河流受当地污染影响大。3.长三角面网河流沉积物光谱差异性大,层次聚类分组中重金属元素含量顺序不一致造成沉积物重金属光谱预测模型效果差,预测模型剩余预测偏差(RPD)均小于1.1。相比之下,由于沉积物成份以及重金属元素分布较为均一,长江干支流沉积物以及下游干流河段沉积物重金属光谱PLS回归模型预测能力优于面网河流沉积物,模型RPD基本均大于1.1。对于沉积物的光谱回归模型预测能力MIR波段要好于Vis/NIR波段。4.长江三角洲水稻田根际土和非根际土重金属空间变化差异大,Cu、Cd、Zn和Hg的变异系数CV超过了50%。形态分析结果表明,重金属迁移活性大小顺序为Cd>Pb>As>Cr, Hg,其中Cd、Pb和As在土壤中活性形态所占比例较高,生物可用性强。重金属空间分布显示浙江地区土壤重金属含量整体要高于江苏地区,其中以杭州、绍兴、宁波一带重金属元素峰值出现较多,金属浓度空间变化有明显差异性,浙江地区污染主要以Cd、Cu和Zn为主,而江苏地区由于农药、化肥的施用,主要以As污染为主。5.长江三角洲水稻田土壤中Cd和Pb的活性部分所占比例较高,分别达到了-50%和-10%；江苏地区农田土壤中As含量显著高于浙江,而浙江地区土壤中Cd,Pb、Hg、Cu、Zn以及活性成分均高于江苏地区。江水稻秸秆和籽实样品As、Pb, Hg和Zn含量要比江苏地区样品高,而江苏地区水稻样品中Cu含量要高于浙江。空间分布来看,浙江地区水稻样品中重金属元素污染程度要高于江苏。6.长江三角洲水稻田重金属元素从土壤到秸秆中迁移系数TFshoot/soil顺序为：Cd>Cu>As, Hg, Zn>Pb>Cr,秸秆到籽实迁移系数TFgrain/shoot的顺序为：Zn>Cd, Hg, Cu, Cr>As>Pb,Cd、Hg、Cu和Zn的迁移系数均大于0.2,这四种金属更容易进入水稻中。江苏样品中各金属的TFgrain/shoot略高于浙江,说明由于水稻样品污染程度低,金属迁移受到植株生长活性增强而提高。在低pH值样品中,As,Cd和Zn的迁移系数显著高于高pH样品。金属元素的TFgrain/shoot与秸秆中的重金属含量以及TFshoot/soil之间都存在着指数递减关系。7.金属营养元素Ca和K在籽实中对重金属元素有着相同的地球化学行为,重金属可以通过Ca和K通道进入籽实,而在秸秆中,由于Ca2+和K+的竞争吸收作用,As、Hg、Pb、Cr和Zn可能主要通过Ca通道进入秸秆,而Cd、Cu和Zn可能通过K通道迁移。土壤中CaO对秸秆和籽实中重金属元素的抑制作用高于K2O,因此在农田里施加石灰,既可以提高营养元素Ca含量也可以缓解土壤酸化,更重要的是抑制重金属元素在土壤—水稻体系中的积累和迁移。更多还原

【Abstract】 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<16μm. 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.更多还原