【作者】 徐亚岩；

【导师】 宋金明； 孙培艳；

【作者基本信息】 中国科学院研究生院（海洋研究所） ， 海洋化学， 2010， 博士

【摘要】 本文聚焦于2008年所取的渤海湾沉积物,集中研究了沉积物中常量元素、微量元素以及海水中重金属的生物地球化学特征,通过剖析元素形态并结合对渤海湾生态环境信息的综合分析,系统探讨了渤海湾沉积物元素的分布特征、潜在生态风险、影响控制因素以及演变趋势,获得了以下一系列新的结果和认识:1.根据渤海湾沉积物稀土元素的配分模式,明显的Eu负异常和Y/Ho比值特征揭示了陆源自然输入而非人为输入是渤海湾沉积物的主要来源,另外稀土元素的埋藏通量可以指示洪水等的异常输入。稀土元素在渤海湾沉积物中的含量水平差异较小,不同形态稀土元素从大到小的含量顺序为:残渣态(R5)、铁锰氧化物结合态(L3)、碳酸盐结合态(L2)、有机结合态(L4)、可交换态(L1),可浸取态稀土元素容易富集在细颗粒物含量较高的站位。渤海湾沉积物的稀土配分模式具有明显的Eu负异常,没有明显的轻重稀土分异,由渤海湾沉积物的Y/Ho比值及其配分模式可以推断出渤海湾沉积物主要是海河和黄河等陆源自然输入而非人为输入。20世纪30年代末对应的海河口附近柱子的沉积层,稀土元素埋藏通量发生了异常改变,对应1939年海河北系的大洪水,洪水带来的物质“稀释”了稀土元素的浓度,导致其埋藏通量的降低。2.渤海湾海水和沉积物中重金属的地球化学分布特征揭示了重金属有不同的来源。从总含量角度分析,渤海湾沉积物总体状况良好。基于形态分析的污染评价显示,Zn、Co、Cu、Ni和Pb都有不同程度的污染,Pb是所有重金属中污染最严重的。表明评价海洋沉积物的重金属污染状况必须结合各形态和生物可利用性有关的浓度,而不能简单地采用重金属的总浓度来评价。渤海湾海水中重金属主要在海河口附近富集,海水中As、Cd、Cr、Cu、Zn和Hg主要来自径流输入,Pb的来源有径流输入和大气沉降两部分组成。表层沉积物中重金属在渤海湾中央的泥质区富集。海河口附近沉积柱重金属的含量有几次突变,分别对应:1939年海河北系的洪水,导致20-22 cm段重金属达极小值;1963年海河南系洪水,导致10-12 cm重金属达极小值;1963年至今重金属含量有逐渐增加的趋势。另外,不同形态重金属的百分含量从大到小的顺序为:R5 >L3 >L2 >L4 >L1。重金属元素在海河口附近站位都表现出较高的可浸取态百分含量。总量重金属富集因子顺序为:Pb>Cd>Zn>Cr>V>Co>Cu>Ni,其中Pb、Cd和Zn的富集因子均大于1,说明其受到了污染。但渤海湾沉积物总体质量良好,潜在生态风险较低。从重金属的形态角度评价,V和Cr基本无污染;Zn大部分无污染或有轻微污染,Co大部分轻度污染,Cu的污染水平由中度污染变到基本无污染,Ni则是由重度污染到轻度污染,Pb是所有重金属污染最严重的。综合两种评价方法,得出Pb是渤海湾污染最严重的重金属,Cu和Zn有潜在污染的可能性,V、Cr和Co基本是清洁的。3.渤海湾沉积物中碱金属和碱土金属的生物地球化学特征可用来表征径流输入和环境变化对渤海湾的影响,研究显示Li/Ba和Rb/Sr是反映环境气候变化信息的良好指标。陆源输入是影响碱金属和碱土金属含量的主要因素,外界环境条件也会对其含量造成一定程度的影响。残渣态Rb、Cs和Ba对其总量起决定性的作用,而Sr的可浸取态百分含量较高,其碳酸盐结合态的百分含量已经超过残渣态的百分含量,说明Sr是这些元素中最易受环境条件影响的元素。Sr和Ca的高度富集说明碳酸盐对渤海湾的沉积过程有重要影响,Sr/Ba的垂向变化特征显示,虽然百年来渤海湾沉积物一直是陆源淡水沉积,但海相沉积作用却有所增强。根据Rb/Sr和Li/Ba出现的极小值可推断出,对应年代Sr和Ba淋溶量的增加是海河流域1939年和1963年两次大洪水导致的。Rb/Sr和Li/Ba近年来均有降低的趋势,而A6沉积柱对应Rb/Sr和Li/Ba的减小程度均大于A2沉积柱,说明Sr和Ba向渤海湾的迁移逐渐增加,且向渤海湾中央海区方向发生了较大程度的迁移。4.渤海湾沉积物可浸取态Nb、Ta、Zr和Hf的研究表明,它们的特定比值也可用来指示异常洪水及泥沙的输入等外来因素的影响。地球化学环境条件的改变可使Nb和Ta的形态发生较大的分馏,但对Zr和Hf的影响相对较小。Nb、Ta、Zr和Hf都在渤海湾中央的细颗粒沉积海域出现高值区,各形态含量的大小顺序为Nb:R5>> L4> L3> L1> L2;Ta:R5>> L1> L2> L3> L4;Zr:R5>> L4> L3 > L1> L2;Hf:R5>> L4> L3> L2> L1。残渣态在各形态中占据绝对优势,但各浸取态元素及特征比值的变化能指示地质环境的变化情况。Nb较容易与水合氧化物、有机质等有机配体结合,Ta更易以可交换态和碳酸盐结合态等无机态形式存在,可浸取态Zr和Hf与各个配体的结合情况差异不大,都是较易以有机配体等形式存在。根据Ti/Nb垂直变化的异常点推断,可能影响A2柱的主要环境事件有1938年黄河改道向南、1939年海河北系的大洪水和1963年海河南系的大洪水。可能影响A6柱的主要环境事件有1947年后黄河改道向北和1984-1990年期间的高含沙洪水。不同形态Nb、Ta、Zr和Hf近百年来的含量变化特征表明,近期渤海湾沉积环境条件的变化,使得可浸取态Nb和Ta的分馏越来越大,尤其是有机结合态Nb和Ta的分馏最为显著,但并没有造成可浸取态Zr和Hf分馏的明显增强。更多还原

【Abstract】 The Bohai Bay is a semi-enclosed epicontinental sea in the southwestern Bohai Sea. With experienced rapid industrial developments, marine environmental quality of the Bohai Bay has seen a major decline due to the increase of populations and pollutants. Sediment samples were collected at 27 stations and two cores of Bohai Bay, North China in 2008. Sequential extractions have been carried out. Combining with heavy metals in sea water and ecological environmental information, a series of results and viewpoints with regard to biogeochemical characteristics of major and trace elements were presented, going with ecological risk and controlling factors:1. Geochemical characteristics and NASC patterns of REE in sediment were discussed in detail to reveal the source and their main regulating factors, and a large flood event can be reflected by the burial fluxes of REEThe total REE fluctuate slightly in Bohai Bay sediment. Four labile phases were leached in Exchangeable (L1), Bound to carbonates (L2), Bound to Fe-Mn oxides (L3), Bound to organic matter (L4), and the remainder was Residual (R5). Percentages of fractions followed the order: R5> L3> L2> L4> L1. Sediments in Bohai Bay were mainly composed of clay and silt. Leached REE would rather enrich in the fine-grained particles. Normalized to North American Shale Composite (NASC), REE generally indicated significantly negtive Eu anomaly, showing no significant fractionations of REE. According to REE patterns and Y/Ho ratios of samples, REE are not anthropogenic or oceanic sources but riverine input, whereas suitable environment varieties can slightly affect the patterns and fractionations of REE, espacially for L2.Based on the distributions and burial fluxes of REE, it reflected that there was a large flood event in 1939, followed by the decreasing discharge of sediments from then on.2. Geochemical characteristics of heavy metals in sea water and sediment were discussed to reveal their sources, main regulating factors and ecological risk. Based on total contents of heavy metals, the quality of Bohai Bay sediment was good, while there were different results from fraction view, that was, Zn, Co, Cu, Ni, Pb all were in potential ecological risk. It suggested that the quality of sediment should be estimated not only by total contents but also by concentrations in fraction. The contents of heavy metals (except Pb) was low in central area while high inshore especailly near Haihe estuary. Heavy metals mainly came from river input, while the source of Pb were composed of river input and atmospheric deposition. Heavy metals in sediments were mainly concentrated in the middle region with fine particle. According to sedimentary data and vertical distribution of heavy metal, there were several break which could be corresponding as follow: The lowest level occurred in 1939 resulting from the flood of Haihe basin; there was another flood in 1963 resulting in the decreasing of heavy metals by the dilution of flood; the contents of heavy metals kept increasing from 1963. Percentages of fractions followed the order: R5 >L3 >L2 >L4 >L1. Labile heavy metals were enriched near the estuary of Haihe River.The order of enrichment factors (EF) of heavy metals was Pb> Cd> Zn> Cr> V> Co> Cu> Ni. And the EF of Pb, Cd and Zn were above 1, suggesting that they could be polluted by exterior input. The ratios of labile and residual fraction showed that V and Cr were clean, Zn was mostly clean or in slightly polluted, Co was mostly slightly polluted, Cu and Ni were polluted in different levels at different stations, Pb was polluted heaviest in all heavy metals. In conclusion, the ecological risk of Bohai Bay was low and indicated that the sediment quality was relatively good in general. What have been studied on ecological risk of heavy metals in sediment suggested that the level of polluted sediment should be related to labile fractions of heavy metals, not simply employing the total content of heavy metals.3. Distributions of alkali metals and alkaline earth metals in Bohai Bay sediment were initially elucidated to reflect the influence of riverine input and filtrate the main factor indicating environmental changes. Li/Ba and Rb/Sr are good indicators reflecting the environmental change.Based on Principal Component Analysis (PCA), it was terrestrial input that held the key factor controlling the distribution of alkali metals and alkaline earth metals, suitable environmental varieties and sedimentary conditions can slightly affect the distributions. In different fractions, the R5 percentage of Rb, Cs, Ba were much higher than the sum of other fractions; while the L2 percentage of Sr was higher than R5, suggesting Sr was relatively sensitive to the environmental conditions.The significant enrichment of Sr and Ca can be explained that carbonate played an important role in Bohai Bay, the Sr/Ba ratio showed that core A6 was much more influenced by the decomposition of biology than core A2. The vertical distributions of Rb/Sr and Li/Ba showed that there were two floods in 1939 and 1963, resulting in the increasing input of Sr and Ba. The decreasing ratios of Rb/Sr and Li/Ba suggested that Sr and Ba were transferring into Bohai Bay more and more, and the ratios of Rb/Sr and Li/Ba in A6 were lower than those in A2, indicating that Rb/Sr and Li/Ba were also transferring from coastal area to the middle of Bohai Bay.4. Labile fractions of Nb, Ta, Zr, Hf were discussed to reveal that he specific ratios of Nb, Ta, Zr, Hf could account for the environmental change in Bohai Bay, such as the floods and the sandiness input. The environmental change could promote the fractionation of Nb and Ta, but the effect was much less on Zr and Hf.Nb, Ta, Zr, Hf in Bohai Bay sediments were mainly concentrated in the middle region with fine particle. Percentages of fractions followed the order Nb: R5>> L4> L3> L1> L2; Ta:R5>> L1> L2> L3> L4; Zr: R5>> L4> L3 > L1> L2; Hf: R5>> L4> L3> L2> L1. In different fractions, the R5 percentage almost control the total contents of Nb, Ta, Zr, Hf, while labile fractions can be used to indicate the environmental change. Ta preferred to exist in inorganic fractions, such as L1 and L2, and Ta can be easily combined in organic fractions, such as L3 and L4. The combinative ability of Zr in labile fraction was similar with that of Hf.Based on the vertical distribution of Ti/Nb, the environmental evens that affect core A2 were as follow: Yellow River changing its route to the south in 1938, the flood of northern Haihe drainage basin in 1939 and the flood of southern Haihe drainage basin in 1963. The environmental evens that have impacted A6 were Yellow River changing its route to the north in 1947 and the flood in heavy sandiness from 1984 to 1990. Recently the environment of Bohai Bay changed relatively, which could lead to the fractionations of Nb and Ta in labile fraction were more and more, especially for L4. But the change of environment played less impact on the fractionation of Zr and Hf in labile fractions.更多还原