【作者】 阮小燕；

【导师】 殷鸿福； 谢树成；

【作者基本信息】 中国地质大学 ， 第四纪地质学， 2010， 博士

【摘要】 湖泊是陆地水圈的重要组成部分,是大气圈、生物圈和岩石圈各圈层相互作用的连接点。湖泊因沉积速度快,经历时间长,沉积连续,保存信息丰富,而成为全球气候、环境变化研究的重要载体。长时间尺度的湖泊沉积物记录了气候、环境演化的自然过程和机制,为研究青藏高原的隆升、季风气候的分异等提供了丰富的证据。短时间尺度的湖泊沉积物记录了人类活动对湖泊流域的影响,为重建湖泊水体的自然和人为富营养化过程、流域—湖泊污染的历史提供了重要依据。长江中游湖泊是长江流域生态环境最脆弱的地区之一当前面临的最突出的环境问题是湖泊富营养化和底泥复合污染。重建湖泊的准自然营养本底以及富营养化的发展历程、研究湖泊底泥中污染物类型和蓄积历史是当前湖泊沉积研究的两大任务。湖泊沉积物中的类脂物来源于湖泊水生生物、湖泊周围陆地生物、湖泊内或湖泊流域土壤中的细菌和微生物。由于其结构精细,种类丰富,是特定的生物分类单元的生物标志物,能示踪湖泊生态组分的发展演化及其相关的环境演变。湖泊类脂物能弥补菌藻类生物遗存或生物化石不易保存的不足,在分子水平上指示湖泊菌藻生态系统的发展变化,是重建湖泊富营养化过程、指示人类活动及湖泊流域—环境污染历史的重要指标。本论文选取长江中游两个不同富营养化程度的湖泊—武汉东湖和梁子湖的三孔沉积物作为研究对象,系统分析了147个沉积物样品中类脂物的组成及分布规律；在高精度的210Pb年代框架下综合前人对沉积物中水生高等植物、介形虫、腹足类、变形虫等生物遗存以及色素、有机碳同位素等研究成果,揭示了湖泊富营养化的过程及其生态响应,重建了两湖生态系统特别是菌藻生态系统的演变历史；提取了人类活动影响及其污染的信息,为湖泊富营养化和环境治理提供依据。通过地质历史时期的地球生物学事件与现代地球生物学事件的类比,揭示人类活动对新的生物绝灭事件的影响。研究表明：1、两湖中类脂物种类极为丰富,一些具有特定生物来源的类脂物被检出。东湖及梁子湖沉积物中均检出正构烷烃、高分支异戊二烯烃、脂肪酸、醇、酮、蜡酯化合物、甾类和萜类化合物。其中以各种醇类化合物(脂肪醇、甾醇、藿醇)含量最高。蜡酯化合物不仅含量高,而且以低碳数系列化合物种类丰富为特征。一些类脂物指示特定的生物种群,如：丰富的低碳数异构及反异构的脂肪酸、脂肪醇及蜡酯,指示来源于格兰氏阳性菌；高碳数的、具有强烈奇偶优势的正构烷烃、正构烷醇和正构烷酮,指示来源于高等植物；高分支异戊二烯烃HBI C25化合物和C28：2△5，22甾醇指示来源于硅藻；2-甲基藿醇指示兰细菌的来源,4,23,24-三甲基胆甾醇类化合物指示着甲藻的来源,C27：1△5甾醇指示着动物或浮游生物来源,而含量极高、种类极为丰富的藿醇、藿烯、藿烷指示着湖泊生态系统中细菌及微生物的贡献。2、类脂物分子在两湖三个不同的剖面中的分布存在着差异,在同一剖面的不同历史阶段差异更为显著。在空间分布上,东湖两孔类脂物总量高,低碳数组分高,沉积物中菌藻来源的类脂物分子如低碳数的正构烷烃、脂肪酸、脂肪醇、蜡酯及藿类化合物等含量高,种类丰富；而梁子湖的类脂物总量低,菌藻来源的组分少、含量低,以水生植物或高等植物来源的类脂物如高碳数的正构烷烃、脂肪酸、脂肪醇相对量高。在时间分布上,三孔沉积物在20世纪60年代以前,类脂物的总量很低,其中菌藻来源的组分如低碳数的异构及反异构脂肪酸、脂肪醇及藿类化合物含量低,缺失蜡酯化合物及高支链异戊二烯HBI C25化合物；水生植物或高等植物来源的组分如中、高碳数的正构烷烃、脂肪酸、脂肪醇、甲藻甾醇含量相对较高,正构烷烃、正构烷醇和正构烷酮的平均碳链长度(ACL)较长,水生／陆源(Paq)、低碳数组分／高碳数组分都较低。60年代以后,各类类脂物组分及类脂物的总量快速上升,特别是菌藻来源的类脂组分呈急剧上升趋势。高支链类异戊二烯化合物HBI C25、蜡酯等大量出现,正构烷烃、脂肪酸、脂肪醇等的低碳数组分增高,异构及反异构的脂肪酸、脂肪醇增加,正构烷烃、正构烷醇和正构烷酮的平均碳链长度(ACL)降低,水生／陆源(Paq)增高；藿类化合物含量急增,来自兰细菌的标志物2-甲基藿醇增加数倍至数十倍；甾醇类化合物增加迅速,含量高,且各组分增加幅度不同,与C29甾醇相比较,甲藻甾醇、C27甾醇、C28甾醇增加的幅度更大,显示甲藻、浮游动物、硅藻等浮游生物量的快速增加。3、类脂物在时间序列上分布的差异性指示了湖泊生态组分及生态环境的历史演变。三孔下部沉积物类脂物以C21-C33正构烷烃,C22-C32正构烷醇及C25-C33正构烷酮为主,有一定的浮游动物组分(C27甾醇)及甲藻甾醇组分(4,23,24-三甲基胆甾醇),藿类化合物及支链的、低碳数的脂肪酸和脂肪醇化合物含量低,指示草型湖泊、以水生植物及陆地高等植物为主、有一定浮游藻类及浮游动物、细菌组分低的生态组分的特点。此外,该段沉积物中类脂物总量及TN、TP含量低,无蜡酯及不饱和的高支链异戊二烯烃,姥植比相对较高,指示水体富氧、厌氧细菌少、蜡酯水解、不饱和烃组分降解、水质良好的水生环境。三孔上部沉积柱TN、TP、TOC高,类脂物总量高、硅藻(C28：2△5,22甾醇及HBI C25)、甲藻(4,23,24-三甲基胆甾醇)、蓝藻(2-甲基藿醇)及细菌类脂物(藿类化合物及低碳数烷、酸、醇、酯组分及异构反异构组分)含量高,高等植物及水生生物的类脂组分(高碳数正构烷烃、烷醇、烷酮等)相对较低,指示藻型湖泊的生态组分特征。同时,低的姥植比指示水体及沉积物表层含氧量下降,蜡酯等组分未被水解,厌氧细菌增加,水质恶化的水生环境。相关调查资料及水生动植物遗存研究表明,20世纪60年代以前,两湖均是水质清澈、水草丰美的草型湖泊,挺水植物、浮叶植物及沉水植物发育齐全,底栖动植物属种丰富,浮游生物以甲藻及硅藻为主,细菌和病毒含量低。20世纪60年代以后,大量藻类繁盛,细菌滋生,水生植被遭受破坏,底栖生物剧减,许多藻类、水生动物出现小型化现象,生物分异度急剧降低。类脂物记录的湖泊生态组分的变化与前人在两湖取得的生物学、古生物学及沉积学的研究成果具有一致性。4、类脂物组分记录了东湖的富营养化过程及水华事件。2-甲基藿醇及里白烯、C32ββ藿醇等藿类化合物、iC15、iC17脂肪酸等作为蓝藻及细菌的特定生物标志物,在50年代后快速增加,1973-1984年间形成第一个高峰。20世纪80年代至90年代降低,20世纪90年代后形成第二个高峰,至表层形成最高峰。这与东湖富营养化、水华爆发的历史记录相符。自20世纪60年代以来随着东湖湖区周边人口快速增长,大量工业和生活废水被排入东湖,水体及沉积物中,使得藻类大量繁盛,藻类在湖泊水体和沉积物中富集,刺激了细菌的生长。藻类尸体的腐烂分解,消耗了水体中大量的氧气,使得下层水体和表层沉积物缺氧,为细菌有机质的保存创造了良好的条件。东湖在20世纪70年代中期至80年代中期每年夏天爆发微囊藻(Microcystis)、鱼腥藻(Anabaena)、束丝藻(Aphanizomenon)三个属组成的蓝藻水华。自1985年以后,通过鲢、鳙的放养,蓝藻水华消失。但近年局部水域又有严重的蓝藻水华爆发,此外,4,23,24-三甲基胆甾醇在20世纪90年代中后期出现峰值,指示东湖的甲藻繁盛,这与近年观察到的甲藻水华相符。5、类脂物记录了湖泊工业污染等人类活动的影响。沉积物中的碳屑及多环芳烃多与化石燃料的燃烧有关,东湖沉积物20世纪30年代中后期以来出现较多碳屑,与此相对应的是多环芳烃菲的不断增加。指示了湖区自30年代中后期开始人类活动开始增强,20世纪50年代后人口大量增加及周边大型钢铁企业的建立,从而大量使用化石燃料,致使沉积物中菲大量增加。此外,类脂物记录了1973年东湖的事故性排放含酚废水事件,表现为类脂各组分含量在该时段的突然降低,尤其是指示菌藻及水生组分的类脂物下降更为剧烈。6、类脂物记录的人类活动引发的地球生物学事件可以与地质历史时期的地球生物学事件相类比。人类活动对东湖生态系统的显著影响始于20世纪30年代中期,至20世纪60年代以后已根本地改变了东湖的水生环境,大量动、植物种群消失,生物多样性急剧下降,生物体小型化、灾难种占居绝对优势,各种菌藻类随之繁盛。这一过程与二叠-三叠之交的生物环境危机事件过程具有相似性。以古示今,人类应当保护地球,避免第六次生物大绝灭。总之,湖泊类脂物分子精细地记录了东湖及梁子湖在人类活动影响下的湖泊菌藻生态系统的变化以及富营养化发展的历史过程,揭示了两湖当前的生态环境状况,为长江中游湖泊富营养化和环境治理提供了历史本底和现实依据。更多还原

【Abstract】 As an important component of the hydrosphere on land, lakes link the atmosphere, biosphere and lithosphere. Due to their continuous and rapid deposition and long temporal range that contains biological and geological information, lake sediments are principal archives for global climate and environmental changes. Lake sediments spanning long time interval record dynamic processes of climate and environment and can act as proxies to trace the uplift of Tibetan Plateau and the shift of monsoon system in Asia. On the other hand, short sequences of lake sediments can be used to reflect the effect of human activities on lake system, such as natural and cultural eutrophication and environmental pollution. In the middle reach of the Yangtze River, fragile lake ecosystems encounter quite lots of environmental problems, such as eutrophication and pollution. Restoring these lakes to their natural conditions is a vital mission as one of the two major governmentally led research projects.In lake sediments, lipids may be derived from aquatic and land plants as well as microbes living in the lakes and the surrounded watershed. These compounds, possessing high diversity in both structures and classes, are taxonomic indicators of their precursors, and thus can be used to reflect the evolution history of the lake system. Algae and bacteria are rarely preserved as fossils in lake sediments; however, their lipids can compensate this shortcoming by leaving a molecular record through the evolution of lake ecosystems.In this dissertation, three cores were recovered from the East Lake system (ELI from the Guozheng Lake,64 cm; EL2 from the Tangling Lake,45cm) and the Liangzi Lake (LFM from East Liangzi Lake,38 cm), which developed quite a different degree of eutrophication. Totally 147 sediment samples were selected for lipid analysis. Combing with a high precise 210Pb chronology, lipid data and previously published results in the literature (on studies of pigments, organic carbon stable isotopes and remains from aquatic plant, ostracods, gastropods and amoebae), the evolutionary history of these two lakes has been reconstructed. The aim of this study was to examine the ecological response of lake systems to eutrophication, and to investigate how human activities affect lake systems with the attempt to use the well documented history as a reliable reference for environmental remediation. Through comparison with other geobiological events in the deep earth history, we can also better understand how human activities may cause biotic extinction.The major findings in this study include:1.Lipids are very abundant in the sediments of these two lakes, particularly with some taxonomic specific biomarkers (e.g. highly branched isoprenes (HBI) and 2-methyl hopanol). These compounds are comprised of n-alkanes, HBI, fatty acids, fatty alcohols, n-alkan-2-ones, wax esters, steroids, and hopanoids. Alcohol compounds (fatty alcohols, sterols, and hopanols) dominate the recovered sediment samples. Wax esters are characterized by their high abundance and low-molecular-weight homologues. Among these lipids, some compounds are specific biomarkers for their biological precursors. For example, low-molecular-weight iso-and anteiso-fatty acids, alcohols and wax esters are derived from Gram positive bacteria; long-chain and strong odd-over-even predominance n-alkanes, fatty alcohols, and n-alkan-2-ones are biomarkers of higher plants. C25 HBI and C28:2△5,22 sterol originated from diatoms living within lakes; 2-Methyl hopanol and 4,23,24-trimethylsterol can indicate cyanobacteria and dinoflagellate, respectively. In addition, C27:1△5 sterol can indicate zooplanktons or phytoplanktons. Hopanoids (hopanols, hopenes and hopanes) may originate from bacteria living in the watershed.2.Lipids show highly temporal and spacial variations among these three sedimentary cores. The total concentration of lipids in ELI and EL2 cores are higher than that in the Liangzi Lake core. In addition, the two cores in the East Lake System possess more bacteria and algae derived lipids, such as short-chain n-alkanes, fatty acids, fatty alcohols, wax esters and hopanoids. The Liangzi Lake core is dominated by lipids from aquatic and land higher plants. All three cores show low abundance in lipids before 1960 AD, with low quantity of low-molecular-weight branched fatty acids, fatty alcohols and hopanoids and absence of wax esters, and C25 HBI. On the contrary, medium and long-chain n-alkanes, fatty acids, fatty alcohols and dinosterol show predominance in the lower sections of these sedimentary cores. After 1960AD, the total concentration of lipids increases sharply, especially those from bacteria and algae:C25 HBI and wax esters emerge with high abundance. In addition, short-chain n-alkanes, fatty acids, fatty alcohols, and n-alkan-2-ones relatively increase. The concentration of cyanobacterial derived 2-methyl hopanols increases by an order of magnitude. Among sterols, dinosterol, C27 and C28 sterols increase more than C29 sterols, indicating the elevation of plankton biomass (dinoflagellate, plankton animal and diatom) during this interval.3.The temporal variations of lipids in the three drill cores infer an evolutionary history for the lake ecosystems. Before 1966 AD, the three cores are dominated by C21-C33 n-alkanes, C22-C32 n-fatty alcohols and C25-C33 n-alkan-2-ones, together with traces of C27 sterols, dinosterol, hopanoids and branched fatty acids and alcohols. All these lipid features indicate that the East Lake System and the Liangzi Lake belong to grass-type lakes, which are dominated by aquatic plants. The total amount of lipids, TN and TP are rather low, while wax esters and C25 HBI are totally absent. The values of Pr/Ph ratio are relatively higher in this interval, revealing that the water column is full of oxygen with good water quality. After 1966 AD, the lipid profiles changed. The total concentration of lipids, TN, TP, and TOC increase sharply. Diatom (C25 HBI and C28:2△5,22),dinoflagellate (4,23,24-trimethylsterol), cyanobacteria (2-Methyl hopanol) and common bacteria (hopanoids and short-chain alkanes, fatty acids, fatty alcohols and wax esters, and branched fatty acids and fatty alcohols) are abundant, whilst lipids from aquatic and land plants are relatively low. During this interval, the East Lake System and the Liangzi Lake have changed to algae-type lakes, with low oxygen content in the water column and the water quality decrease sharply. My interpretations based upon lipid distributions are consistent with previous reports in the literature. In the 1960s, human activities brought great effects to these two lakes: more nutrition was introduced into these lakes, causing serious eutrophication and pollution that destroyed native aquatic plant ecosystems.4. The temporal and spacial variations of lipid compounds in these three cores can be used to indicate different degrees of eutrophication conditions in these two lakes. In the East Lake System, sedimentary samples contain much higher total lipid concentrations. In addition, bacteria and algae derived lipids take predominance during recent 30 years, revealing that severe eutrophication occurred in the East Lake System. On the other hand, bacteria and algae derived lipids are composed of a small proportion in Liangzi Lake samples, corresponding to the middle degree of eutrophication in the Liangzi Lake. In addition, lipids in East Lake samples can record algae bloom events. The cyanobacteria and bacteria lipids (2-methyl hopanol, diploptene, hopanoids, iC15 and iC17 fatty acids) increase greatly in the late 1950s, then reached a spike during 1973-1984. A second spike occurs in the 1990s, followed by the third spike in the surficial horizon. The above shift of cyanobacteria and bacteria lipids is consistent with the historical records of eutrophication and algae blooms in the East Lake System. Since the 1960s, population around the East Lake grows rapidly. More and more industrial and municipal waste water was drained into the East Lake System, causing server eutrophication. During the middle 1970s and the 1980s, cyanobacteria bloom (Microcystis, Anabaena and Aphanizomenon) happened every summer. Since 1985,large number of silver carp and bighead carp has been introduced into the East Lake. Then cyanobacteria blooms disappeared. Recently, server cyanobacteria blooms reoccur in some part of the East Lake. Furthermore, the content of dinosterol (4,23,24-trimethylsterol) reaches its peak value during the mid-and-the late 1990s, which is consistent with the dinoflagellate bloom event recorded in recent years.5.Lipids also record industrial pollution around the East Lake. From the late 1930s, charcoal and polycyclic aromatic hydrocarbons (PAHs) increased in large quantity. Both charcoal and PAHs correlate with the combustion of fossil fuels. The enrichment of charcoal and PAHs probably results from the increasing human activities around the lake from the late 1930s. From the 1950s, population increases greatly and several large-scale iron and steel enterprises built in these areas surrounding the East Lake. Accordingly, more phenanthrene was deposited in lake sediments.6. In principle, the lipid recorded geobiological events caused by human activities can also be compared to those during the Earth history. The anthropogenic influence began from the mid 1930s and increases from the 1960s. The native aquatic ecosystem was destroyed completely. A number of higher plants and animals disappeared and the biodiversity decreased sharply. Consequently, minimized and disaster species became predominance and algae blooms occurred frequently. These processes are similar to biotic events such as Tr/P crisis in principle. If the history is a mirror to the present, then humanbeings have to take great effects to protect our Earth from the sixth mass extinction.In summary, lipids in the three recovered sedimentary cores from the East Lake and the Liangzi Lake record the evolutionary history, especially the eutrophication process in these lakes. These molecular results demonstrated chronologically how human may affect lake ecosystems, and revealed the current natural conditions of these lake systems. The data provide an important foundation for environmental remediation of these lake systems in the lower Yangtze River reach.更多还原