【作者】 段丽琴；

【导师】 宋金明；

【作者基本信息】 中国科学院研究生院（海洋研究所） ， 海洋化学， 2011， 博士

【摘要】 探讨水体和沉积物中稀有元素的生物地球化学行为对评价海洋生态环境和揭示海洋环境演变机制有着重要的科学意义。本学位论文选择我国典型海湾渤海湾及典型河口长江口水体和沉积物中的稀有元素作为主要研究对象,结合对生态环境对应关系的剖析,系统研究了水体和沉积物中稀有元素的地球化学分布特征、迁移机制、影响控制因素、潜在生态风险、来源、沉积环境演变趋势及与环境的关系,获得了一系列新的结果和认识:1.渤海湾海水中的溶解态稀有元素的生物地球化学特征和行为表明稀有元素具有明显的“拟营养盐”作用,溶解态稀有元素主要来源于河流输入与大气沉降。渤海湾海水中的硒主要以四价和六价两种形式存在,且以四价硒为主,约占总硒的66.7%;锑主要以三价和五价两种形式存在,且以五价锑为主,约占总锑的89%;碲主要以四价和六价碲两种形式存在,且以六价碲为主,约占总碲的71.4%。表层水中的硒、锑、砷和碲浓度均呈现出由湾近岸向湾中央降低的趋势,最高浓度出现在海河河口附近,这种分布模式主要与河流输入、环境条件和生物活动有关;在浮游植物生物量较高的区域,表层水中六价硒、五价锑和六价碲的浓度大于底层水,这与表层水中四价硒、三价锑和四价碲的生物氧化有关,说明生物过程是这些区域海水中硒、锑和碲的主控因素;河流输入对渤海湾硒、锑、砷和碲有重要的贡献,每年通过河流输入的硒、锑、砷和碲通量约为5.67、45.2、33.4和4.89吨/年。而表层水中的锡浓度呈现出由湾近岸向湾中央升高的趋势,其在海河河口附近的浓度也较高,这种分布模式主要与河流输入和大气输入有关;每年通过河流输入和大气沉降的锡通量分别为2和0.85吨/年。渤海湾海水中硒、锑、砷、碲和锡的浓度总体处于痕量水平,对水体生物系统没有明显的危害。硒、锑、砷、碲和锡均参与了生物循环,其与营养盐、叶绿素a浓度和浮游植物生物量有很好的相关性。其中,硒有利于浮游植物的生长;锑和砷通过磷的吸收途径被浮游植物摄取;碲和锡抑制浮游植物的生长,因此这些元素在一定程度上控制浮游植物初级生产的规模。2.渤海湾与长江口表层沉积物中稀有元素的分布模式受控于“沉积物类型-迁移过程-来源途径”;基于稀有元素的化学形态、富集因子和地质累积指数的结果显示,渤海湾和长江口表层沉积物中稀有元素的生态风险和污染程度各不相同,这两区域在总体水平上均呈轻度污染。渤海湾表层沉积物中稀有元素的含量随沉积物粒径的减小和粘土含量的增加而增加,且与铝、铁、锰氧化物含量呈显著正相关,表明稀有元素的分布受控于沉积类型和沉积模式及其形成的驱动力–物理迁移。稀有元素的化学形态含量随沉积环境条件(酸度、盐度、氧化还原状态)的改变而发生改变,表明化学迁移也是其分布的主控因素。稀有元素的含量随总有机碳含量和叶绿素a浓度的增加而增加,表明生物迁移是其分布的又一控制因素。富集因子显示,Sb、Te和Bi的富集因子>1.5,反映了这些元素的人为输入,而其它稀有元素的富集因子均小于1,说明其以自然输入为主。从稀有元素的化学形态角度评价,Sn、Ga和Tl为无风险;Ge、Sb、In、W和V为低风险;Te、Bi、Mo和U为中度风险;Cd为高风险。基于地质累积指数分析显示,Ga、W、U、Ge、Mo、In、Tl和V为未污染;Cd和Sn为轻度污染;Sb为中度-强度污染;Bi为强度污染;Te为极强度污染。渤海湾表层沉积物中所有稀有元素的平均Igeo值为0.46,说明该区域整体上处于轻度污染水平。长江口及邻近海域表层沉积物中的稀有元素含量均呈现出由近岸向外海降低的趋势,最高浓度出现在长江口和杭州湾口附近,这种分布模式主要与沉积物类型、河流输入、大气沉降和环境条件有关。稀有元素的含量高值区出现在高粘土区,说明其含量随着粘土含量的增加而增加。河流输入和大气输入对长江口及邻近海域的稀有元素有重要的贡献,每年通过河流输入的As、Hg、Bi、Se、Sb、Te、Sn和Ge的通量约为4426、37、194、92、383、19、1614、599吨/年;每年通过大气输入的As、Se、Sb、Sn和Ge的通量约为45.0、31.1、10.0、3.5、1.8吨/年。从稀有元素的化学形态角度评价,As、Hg、Sb、Sn和Ge为低风险;Bi和Se为中度风险;Te为高度风险。基于地质累积指数显示,Hg、Sn和Ge呈未污染状态;Se为轻度污染;As、Sb和Te为中度污染;Bi为中度-强度污染。长江口及邻近海域表层沉积物中八个稀有元素的平均Igeo值为0.78,说明该区域为轻度污染。3.渤海湾与长江口柱状沉积物中稀有元素不同化学形态之间存在相互转化,稀有元素的含量、富集因子和埋藏通量结果显示,近百年来渤海湾与长江口的沉积环境在时间序列上主要经历了三个明显的不同阶段。渤海湾和长江口柱状沉积物中稀有元素的分布模式主要与沉积物类型、来源和成岩作用有关,其含量随粘土和总有机碳含量的增加而增加。稀有元素的不同化学形态之间有很好的负相关性,说明不同化学形态之间发生了相互转化。根据稀有元素的含量、富集因子和埋藏通量的变化趋势,渤海湾和长江口的沉积环境在近百年来主要经历了三个明显的不同阶段。由于自然事件和人文活动发生的时间不同,渤海湾与长江口的环境演变历史也稍有不同。渤海湾近百年来的环境演变包括:(1)20世纪初到20世纪70年代较为波动,整体处于较高水平。该段时期入海径流量较高,沉积速率较高,埋藏通量也相应较高,沉积物中稀有元素主要为自然来源;(2)20世纪70年代到90年代呈上升趋势。该一阶段是渤海经济圈迅猛发展的阶段,加上各项治污措施和保护措施不当,这段时期渤海湾的环境恶化,是人类活动影响最为明显的一个阶段;(3)从20世纪90年代到21世纪初呈下降趋势。这一阶段是渤海湾环境质量不断改善的一个阶段。长江口近百年来环境演变包括:(1)20世纪初到20世纪60年代较为波动,埋藏通量大致在一个比较低的水平,说明在这期间几乎没有大的环境改变且沉积物中的稀有元素主要为自然来源;(2)20世纪60年代到90年代呈上升趋势。该一阶段是东海沿岸工农业迅猛发展的阶段,加上各项治污措施和保护措施不当,这段时期长江口及邻近海域的环境恶化,是人类活动影响最为明显的一个阶段,这种影响在80年代和90年代期间表现得尤为严重;(3)从20世纪90年代到21世纪初呈下降趋势。第三阶段是东海沿岸环境质量不断改善的一个阶段。更多还原

【Abstract】 The studies on the biogeochemical behaviors of trace rare elements in marine environments are of important scientific and practical significance in evaluating marine eco-environment and studying marine environmental evolution. In this study, the trace rare elements in seawaters and sediments from Bohai Bay and Changjiang Estuary, typical bay and estuary, were analyzed. The systemic study on the geochemical distributions, transport processes, controlling factors, potential ecological risks, sources and sedimentary environmental evolution of trace rare elements and the coupling relationships between trace rare elements and environmental parameters in seawaters and sediments of Bohai Bay and Changjiang Estuary were helpful to develop the researches on the marine biogeochemical processes of trace rare elements. A series of results and viewpoints were presented as follows:1. The biogeochemical characteristics and behaviors of dissolved trace rare elements in Bohai Bay seawaters indicated their strong“nutrient-type”behaviors. The main sources for dissolved trace rare elements were the riverine input and atmospheric deposition.Se in Bohai Bay seawaters mainly existed as selenite (Se(IV)) and selenate (Se(VI)) and the predominant speciation was Se(VI), accounting for 66.7% of total Se; Sb mainly existed as antimonite (Sb(III)) and antimonate (Sb(V)) and the predominant speciation was Sb(V), accounting for 89% of total Sb; Te mainly existed as tellurite (Te(IV)) and tellurate (Te(VI)) and the predominant speciation was Te(VI), accounting for 71.4% of total Te. The dissolved trace rare element concentrations in the surface seawaters showed decreasing gradients from the coastal waters to the central bay with the higher concentrations near the Haihe Estuary. This distribution pattern was closely related to the riverine inputs, environmental conditions and biological activities. The concentrations of Se(VI), Sb(V) and Te(VI) at the surface waters were higher than those at the bottom waters in the regions with high phytoplankton biomasses, which was attributed to the biological oxidation of Se(IV), Sb(III) and Te(IV) at the surface waters, suggesting that biological process was a key factor controlling the speciation and concentrations of Se, Sb and Te in these regions. Besides, the riverine input was a main contributor to the trace rare elements in Bohai Bay. According to our estimate, about 5.67, 45.2, 33.4 and 4.89 t/yr of Se, Sb, As and Te reached Bohai Bay via rivers. However, the dissolved Sn concentration at the surface waters showed an increasing gradient from the coastal waters to the central bay with the higher concentration near the Haihe Estuary. Besides the riverine inputs, environmental conditions and biological activities, this distribution pattern was closely related to atmospheric input. About 2 and 0.85 t/yr of Sn reached Bohai Bay via rivers and atmosphere.The concentrations of trace rare elements (Se, As, Sb, Te and Sn) in Bohai Bay seawaters were present at the level of trace concentrations, which had no obvious harm on marine organisms. All of the trace rare elements had the significant relationships with nutrients, chlorophyll a concentrations and phytoplankton biomass, suggesting that they seemed to be involved in the biological cycling. Among these elements, Se was required for the normal growth and development of phytoplankton; Sb and As were assimilated by phytoplankton via the phosphate uptake pathway; Te and Sn could inhibit the growth of phytoplankton. Thus, these elements played key roles in regulating the phytoplankton productivity.2. The horizontal distribution pattern of trace rare elements in the surface sediments of Bohai Bay and Changjiang Estuary was coincident with the sedimentation pattern and controlled by the mode of“sediment type-transport process-sources”. Results of the chemical speciation, enrichment factors and geoaccumulation indexes of trace rare elements suggested that the potential ecological risks and polluted levels were different for each element and these two areas were from unpolluted to moderately polluted level.Trace rare element concentrations increased with the sediment particle size decreasing and the clay content increasing. Besides, trace rare element concentrations had the significant positive correlations with Fe, Mn and Al oxide contents, suggesting that the distributions of trace rare elements were controlled by the physical transport and hydrodynamic processes, the dominant driving power affecting the sediment transportation and distribution. The chemical speciation of trace rare element concentrations changed with the change of sedimentary environmental conditions (e.g., pH, salinity, redox condition), suggesting that the distributions of trace rare elements also were controlled by chemical transport process. Besides, trace rare element concentrations increased with the total organic carbon (TOC) content and chlorophyll a concentration increasing, suggesting that biological transport process also influenced the distributions of trace rare elements. The environment factors (EFs) of Sb, Te and Bi were higher than 1.5, suggesting anthropogenic inputs; however, the EFs of other elements were lower than 1.0, revealing the natural inputs. Result of sequential extraction analyses showed that Sn, Ge and Tl were of no risk, Ge, Sb, In, W and V were at low risk, Te, Bi, Mo and U were at medium risk, and Cd was at high risk. The geoaccumulation index (Igeo) suggested that Ga, W, U, Ge, Mo, In, Tl and V could be regarded as unpolluted, Cd and Sn as unpolluted to moderately polluted, Sb as a moderately to strongly contaminated level, Bi as a strongly contaminated level and Te as a extremely contaminated level. The average Igeo (0.46) of all trace rare elements contained in the surface sediments of Bohai Bay reflected that this area was from unpolluted to moderately polluted level.Trace rare element concentrations in the surface sediments of Changjiang Estuary presented a decreasing trend from the coastal waters to the central sea with the highest concentrations near the Changjiang River and Hangzhou Bay. This distribution pattern was attributed to the sediment type, riverine input, atmospheric deposition and environmental conditions. The high concentrations of trace rare elements appeared at the high clay region, suggested that trace rare element concentrations increased with the clay content increasing. The riverine and atmospheric inputs were main contributors to trace rare elements in Changjiang Estuary. According to our estimate, about 4426, 37, 194, 92, 383, 19, 1614 and 599 t/yr of As, Hg, Bi, Se, Sb, Te, Sn and Ge reached the Changjiang Estuary via rivers and about 45.0, 31.1, 10.0, 3.5 and 1.8 t/yr of As, Se, Sb, Sn and Ge reached Changjiang Estuary via atmosphere. Result of sequential extraction analyses showed that As, Hg, Sb, Sn and Ge were of no risk, Bi and Se were at medium risk and Te was at high risk. The geoaccumulation indexes suggested that Hg, Sn and Ge contained in the sediments of Changjiang Estuary could be regarded as unpolluted, Se as unpolluted to moderately polluted, As, Sb and Te as a moderately contaminated level and Bi as a moderately to strongly contaminated level. The average Igeo (0.78) of the eight trace rare elements contained in the surface sediments of Changjiang Estuary reflected that this area was from unpolluted to moderately polluted level.3. Results of chemical speciation of trace rare elements in core sediments of Bohai Bay and Changjiang Estuary suggested the translation among the different fractions. The concentrations, enrichment factors and burial fluxes of trace rare element in core sediments of Bohai Bay and Changjiang Estuary varied significantly in recent one hundred years, so that the past century was divided into three periods.The distribution patterns of trace rare elements in core sediments of Bohai Bay and Changjiang Estuary were closely related to the sediment type, sources and diagenesis. The concentrations of trace rare elements increased with clay and TOC content increasing. There were significant native relationships among the different chemical speciation of trace rare elements, suggesting the translation among the different fractions. Based on the concentration, enrichment factor and burial flux changes of trace rare elements, the environmental evolution of Bohai Bay and Changjiang Estuary was divided into three periods. Due to the different occurring time of natural events and anthropogenic activities, the environmental evolution history between Bohai Bay and Changjiang Estuary was slightly different.Environmental evolution of Bohai Bay was divided into three periods, before 1970s, from 1970s to 1990s and after 1990s. These three periods for temporal changes of trace rare elements in Bohai Bay in recent one hundred years were attributed to the natural and anthropogenic activities. In the first period, the concentration, enrichment factor and burial flux changes of trace rare elements displayed an increasing trend with depth. This period was characteristic of relatively high runoff and sedimentation rate, the trace rare elements was mainly from natural sources. The second period was the time when the Bohai Rim Economic Circle developed quickly, as well as the pollution treatment and protection measures were inappropriate. During this time, Bohai Bay had been subjected to various pollutant sources and its environment became worsen. Thus, the influence of this period by anthropogenic activities was significant. The third period was the time when sediment environment had been improved.The environmental evolution of the Changjiang Estuary was divided into three periods, before 1960s, from 1960s to 1990s and after 1990s. These three periods for temporal changes of trace rare elements in Bohai Bay in recent one hundred years were attributed to the natural and anthropogenic activities. In the first period, the burial fluxes of trace rare elements had a slight fluctuation with a low level, suggesting that there was no obvious environmental change and the natural input was a main source in this period. The second period was the time when industries and agricultures along the coast of East China Sea developed quickly, as well as the pollution treatment and protection measures were inappropriate. During this time, the Changjiang Estuary and its adjacent areas had been subjected to various pollutant sources and its environment became worsen. Thus, the influence of this period by anthropogenic activities was most significant. The third period was the time when the sediment environment had been improved.更多还原