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胶州湾沉积物重金属生物地球化学特征及对人类活动导致的环境演变潜在讯息解析
梁宪萌1,2
学位类型硕士
导师宋金明
2016-05-20
学位授予单位中国科学院大学
学位授予地点北京
学位专业环境科学
关键词重金属 形态 粒径分级 沉积物 环境演变 生物地球化学 胶州湾
摘要对胶州湾这一典型人为影响性海湾生态环境变化的研究,对于促进近海环境可持续利用意义重大。本文对2015年采集的胶州湾表层及柱状沉积物进行了系统分析,重点研究了沉积物中重金属(Cr、Cu、Ni、Zn、Cd、Sb、Sn、Pb等)的生物地球化学特征,诠释了表层沉积物中重金属的形态特征、来源及潜在生态风险,探寻了简洁且能够有效提取活性组分、表征人为影响的元素形态浸提方法,甄别了柱状沉积物不同粒径组分对人为活动和自然变化的指示意义。获得主要结论如下:
1、  胶州湾表层沉积物中重金属总量的空间分布主要受控于沉积物粒径、有机质含量及生物过程相关物质的稀释作用等因素;重金属的形态分布模式是人为活动影响、元素自身特征、沉积物理化环境综合作用的结果,重金属残渣态主要为自然来源,而活性形态(非残渣态)与人为影响的来源密切相关,沉积物中重金属的形态特征更能表征人为活动对海湾沉积物环境的影响。化学形态和富集因子综合表明胶州湾表层沉积物中Cd潜在生态风险较高。
沉积物中重金属含量的高值区位于Ca、Sr、Ba含量的低值区,重金属与Ca、Sr、Ba含量呈显著负相关,较高的內源生物沉降对沉积物中重金属的丰度产生稀释作用,从而掩盖重金属受人为影响程度。此外,表层沉积物中重金属的总量与沉积物粒径及有机质含量呈显著正相关,有机质含量较高的细粒径沉积物更易于富集重金属。
不同重金属的形态分布主要受控于人为活动影响、元素自身特征和沉积物理化环境。人为活动主要影响重金属活性形态在总量中所占的比例,受人为活动影响较大的沉积物中重金属的活性形态含量在总量中所占比例较高;相关性分析和主成分分析综合表明胶州湾沉积物中活性形态(酸可提取态、可还原态、可氧化态)主要来源于人类工农业生产的排放,而残渣态主要为自然来源。重金属在沉积物中的结合方式受元素自身特征的控制,不同重金属与有机质及铁锰氧化物的结合能力不同。此外,受沉积物pH、氧化还原条件变化的影响,重金属不同形态之间存在相互转化。
沉积物中重金属的富集因子(EF)及潜在生态风险评价(PAC)的结果综合表明,沉积物Cd污染较严重,其潜在生态风险相对较高;Pb、Sn和Sb的富集因子虽较高,但生态风险程度较低;Cu、Ni和Zn人为污染程度较低,但生态风险处于中等风险等级。因此需要严格控制胶州湾Cd、Cu、Ni和Zn的人为污染输入。
2、  实验筛选比较了0.1 mol/L HCl(方法1)、1 mol/L HCl(方法2)和1 mol/L HCl+1.75 mol/L HNO3(方法3)三种沉积物单级提取方法对于甄别重金属人为污染的有效性。结果表明方法1对沉积物中CuPbZn的人为污染具有较高的辨识度,其浸提结果与BCR三步提取方法具有较高相关性;对胶州湾而言,方法1浸提的重金属活性组分的空间分布特征与其实际污染状况相吻合,明显反馈了胶州湾沉积物重金属人为污染的讯息。因此,方法1作为一种简洁的形态分析方法更适合于进行大范围沉积物重金属人为污染评价。
三种单级浸取法对陆源碎屑元素(Al、Sc、Ti、Th、Fe)提取率由大到小依次为:方法3>方法2>方法1,反映了方法1对较大颗粒物的破坏程度最小。  三种单级提取法对稀有元素的提取率表明方法2、方法3与BCR方法具有显著差异,不适用于作为BCR分级提取的替代性方法。
人为信号指数(ASI)的评价结果表明方法2和方法3提取结果的重金属ASI值较低,容易释放出沉积物较大颗粒内层中的“惰性”重金属;0.1 mol/L HCl提取结果的重金属ASI值较高,表明浓度较低的盐酸对重金属活性组分的提取效率更高,尤其对于Cu、Pb和Zn,0.1 mol/L HCl提取结果的ASI值与BCR浸取方法接近。Al归一化后,胶州湾表层沉积物中0.1 mol/L HCl提取的重金属含量的高值区出现在李村河口和海泊河口,与以往研究结果和实际污染状况相吻合,表明0.1 mol/L的HCl浸提的重金属活性组分含量能够解析胶州湾沉积物人为污染讯息。
3、  柱状沉积物不同粒径组分对自然变化和人为活动的响应讯息不同。沉积物细粒径和中粒径组分中的重金属更显著地记录了人为活动影响的讯息和程度。而粗粒径沉积物中重金属的垂直变化更多地反映了区域历史气候的自然变化。
运用地累积指数(Igeo)和富集因子(EF)对沉积物不同粒径组分重金属富集程度进行评价,结果表明沉积柱细粒径和中粒径组分对人为源重金属富集程度较高。根据细粒径和中粒径组分中重金属人为影响因子(AF),将人为活动影响下胶州湾的环境演化分为三个阶段:1940s之前,青岛工农业发展缓慢,胶州湾受人为活动影响较小,细粒径和中粒径沉积物重金属人为影响因子较低;1940s-2000s期间,青岛工业农业逐步发展,胶州湾受人为活动影响程度增大,细粒径和中粒径沉积物重金属人为影响因子随之逐渐增加;2000s至今,随着人们对生态环境的日益关注,市政府加大监管力度,胶州湾的污染来源减少,细粒径和粗粒径沉积物中重金属人为影响因子逐渐降低。粗粒径沉积物中重金属含量自下而上表现为逐渐降低的变化趋势,受百年来青岛地区气温逐渐升高的影响,陆源碎屑颗粒的风化作用增强。
其他摘要The studies on the eco-environmental changes of the Jiaozhou Bay, which is a typical bay under the influence of human activities, have practical significance for the sustainable utilization of offshore environment. In this study, the biogeochemical characteristics, eco-environmnental risks, sources of heavy metals (Cr, Cu, Ni, Zn, Cd, Sb, Sn, Pb) in the surface sediments of the Jiaozhou Bay were systematically analyzed; The simple and effective methods to extract the labile fractions of elements were established;The indicator significance of heavy metals in different size fractions in core sediments was identified. The major results were as follows:
1.        The distribution pattern of heavy metals in surface sediments were attributed to the dilution by biological deposition, the contents of TOC and clay; The speciation pattern of heavy metals was affected synthetically by the sources, element geochemistries and sediment characteristics. The residual fractions mainly came from the natural input, whereas the non-residual fractions were attributed to the anthropogenic activities, suggesting that he speciation of heavy metals in sediments plays a more important role to reflect the human activities. The risk assessment codes and enrichment factorsEFsuggested that the potential ecological risk of Cd was high.
The high values of heavy metals appeared at the north area, the central bay and the bay mouth, where the content of Ca, Sr and Ba were low. The heavy metals had significant correlation with Ca, Sr and Ba, indicating that the content of heavy metals in surface sediments may be diluted by biological deposition. The quantities of heavy metals added by human activities cannot be reflected by the total concentrations. Besides, the content of heavy metals had significant correlation with the clay and TOC content, indicating that the metals were enriched in fine-sized particles.
The speciation pattern of heavy metals was controlled by the sources, element geochemistries and sediment characteristics. Anthropogenic activities effected the percentage of non-residual fractions; The correlation analysis and principal component analysis indicated that non-residual fractions (acid-soluble, reducible and oxidizable forms) of heavy metals mainly came from industrial and agricultural productions, whereas the residual fractions mainly came from crustal inputs. In addition, the main non-residual fraction were determined by element geochemical characteristics and sedimentary environment (pH, oxidation-reduction).
The risk assessment codes and enrichment factors(EF)suggested that EF (Cd)>1.5, and Cd was at moderate pollution level; EF ( Pb, Sn, Sb)>1.5, but at low pollution level; EF ( Cr, Pb, Sb) <1.5, but at moderate pollution level.
2.        To explore a concise and effective method to detect anthropogenic metal contamination, we compared the extraction efficacy of 0.1 mol/L HCl (method 1), 1 mol/L HCl (method 2) and 1 mol/L HCl+1.75 mol/L HNO (method 3). The results indicated that 0.1 mol/L HCl, which was similar to the BCR procedure, was superior in its ability to characterize the degree of anthropogenic contamination. The spatial distribution of labile fractions of Cu, Pb and Zn extracted by 0.1 mol/L HCl, which were consistent with the actual contamination pattern, showed significant anthropogenic signals obviously. All data indicated that the 0.1 mol/L HCl leach was a valuable, rapid, and cost-effective analytical tool in contamination assessment of heavy metals.
Average extraction ratios of the clastic elements (Al、Sc、Ti、Th、Fe) in sediments using three extraction methods showed an order of method3>method2>method1, indicating that method1 had minimum impact on the alumino-silicate matrix of solids. The average extraction ratio of trace rare elements extracted by method2 and method3 were significantly different from that of the BCR procedure, indicating these two methods were not appropriate to served as alternative methods to the BCR procedure.
The ASI of metals extracted by method2 and 3 were low, which may be due to that the non-labile fractions of heavy metals in the inner layer of large particles were leached out by the higher acidity, enhancing the pollution signals of heavy metals in sediments. The metals extracted by the method1 had the highest anthropogenic signal index (ASI), indicating that the method1 had the highest extraction efficiency for labile fractions of metals among the three methods. Furthermore, the higher values of Cu, Pb and Zn extracted by method1 appeared at the east coastal area, which was consistent with the actual contamination pattern, demonstrating that 0.1 mol/L HCl can be recommended as an optimal partial decomposition procedure for assessing non-residual fractions of heavy metals in sediments.
3.        The responses of different size fractions in core sediment were variant to the natural changes and human activities. Heavy metals in the fine-grained(32μm) and middle-sized fractions32-63μmapparently recorded the informations and degrees of human activities, while the vertical variations of heavy metals in the sand-sized fractions(63μm) reflected historical climate changes.
The geoaccumulation index (Igeo) and enrichment factor (EF) indicated that the fine-grained and middle-sized fractions of the core sediment had high degree of enrichment for anthropogenic heavy metals. According to the anthropogenic factor (AF) of heavy metals in fine-grained and middle-sized fractions, the environmental evolution of the Jiaozhou Bay was divided into three periods, before 1940s, from 1940s to 2000s and after 2000s. In the first period, human activities had low effects on the Bay with lower AF and slow development of industry and agriculture. During the second period, Qingdao had progressively developed and the AF gradually increased which declaring high influence of human activities on the bay. In the third period, the sediment environment had been improved due to growing concerns of environments and increasing supervision from the government. Whereas the content of heavy metals in the sand-sized fractions was gradually decreased from bottom to the top corresponding to upregulated temperature and enhanced weathering of terrigenous detrital particles during the last century.
学科领域环境学
语种中文
文献类型学位论文
条目标识符http://ir.qdio.ac.cn/handle/337002/112552
专题海洋生态与环境科学重点实验室
作者单位1.中国科学院大学
2.中国科学院海洋研究所海洋生态与环境科学重点实验室
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梁宪萌. 胶州湾沉积物重金属生物地球化学特征及对人类活动导致的环境演变潜在讯息解析[D]. 北京. 中国科学院大学,2016.
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