网湖沉积物正构烷烃分布特征及其记录的环境变化
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摘要
通过对网湖沉积岩芯中正构烷烃含量和组成特征的分析,探讨了网湖近百年来的湖泊环境变化.结果表明,网湖沉积岩芯中正构烷烃的碳数范围在n-C14~n-C33之间,其中以高碳数组分为主,并具有明显的奇偶优势,反映了沉积物有机质以大型水生植物和陆生植物贡献为主,较低的2n-C31/(n-C27+n-C29)比值指示陆源输入中以木本植物输入为主.根据正构烷烃参数指示的沉积物有机质来源变化特征,近百年来网湖水体环境变化具有如下3个阶段:20世纪50年代以前,网湖与长江水体交换频繁,湖泊水体处于低营养环境状态,沉积物正构烷烃高/低分子量正构烷烃比值(H/L)和陆/水生类脂物比值(TAR)较高,沉积物有机质主要来源于陆生植物和大型水生植物,湖泊浮游藻类贡献少;20世纪50~80年代,H/L和TAR值明显下降,中、短链正构烷烃的比例略有升高,表明陆源植被对沉积物有机质的贡献降低,水生植物和浮游藻类贡献的有机质增加,但较低的2n-C17/(n-C23+n-C25)值表明浮游藻类有机质较低,此时湖泊水体较为稳定,湖泊受长江水位影响减小,湖泊营养水平有所升高;1980s以来,总体上湖泊受流域人类活动影响明显,湖泊水体营养水平升高,沉积物正构烷烃表现为H/L和TAR值升高后下降,正构烷烃总量和2n-C17/(n-C23+n-C25)比值显著升高,2000年后尤其明显,表明湖泊沉积物有机质输入增加,其中湖泊浮游藻类贡献明显增加.
Concentrations and distribution of n-alkanes( n-C14 to n-C33) in Lake Wanghu sediment core were analyzed to investigate the environmental changes in the lake during the past ~ 100 years. Relatively higher concentrations of mid-and long-chain n-alkanes with a strong odd-over-even carbon number predominance indicated organic matter contributions dominated by aquatic macrophytes and terrestrial plants. The lower values of 2n-C31/( n-C27+ n-C29) highlighted a type of landscape dominated by woody plants. The environmental changes that have been happening over the past 100 years in Lake Wanghu can be divided into three stages,based on the organic matter sources inferred from the changes in n-alkane parameters in the sediments. Before the 1950 s,higher values of terrigenous/aquatic ratio( TAR) and high-/low-molecular weight n-alkanes( H/L) indicated vascular,plant-derived sediments deposited during a low-nutrient,clear-water phase with frequent water exchange between the lake and the Yangtze River. Between the1950 s and 1980 s,decrease in values of H/L and TAR,and increase in the proportion of mid-and short-chain n-alkanes indicated a shift towards mid-and shorter-chain components likely associated with the increasing contribution of macrophytes and algae. Lower 2nC17/( n-C23+ n-C25) values indicated a relatively low algal abundance. In that stage,the lake trophic state increased slightly with the decreasing influence of the Yangtze River flow. After the 1980 s,H/L and TAR values increased and then decreased,total n-alkane concentrations and 2n-C17/( n-C23+ n-C25) increased significantly,especially after 2000 s,suggesting the main contributor to high organic matter input most likely shifted to algae because of the eutrophication caused by anthropogenic activities.
Concentrations and distribution of n-alkanes( n-C14 to n-C33) in Lake Wanghu sediment core were analyzed to investigate the environmental changes in the lake during the past ~ 100 years. Relatively higher concentrations of mid-and long-chain n-alkanes with a strong odd-over-even carbon number predominance indicated organic matter contributions dominated by aquatic macrophytes and terrestrial plants. The lower values of 2n-C31/( n-C27+ n-C29) highlighted a type of landscape dominated by woody plants. The environmental changes that have been happening over the past 100 years in Lake Wanghu can be divided into three stages,based on the organic matter sources inferred from the changes in n-alkane parameters in the sediments. Before the 1950 s,higher values of terrigenous/aquatic ratio( TAR) and high-/low-molecular weight n-alkanes( H/L) indicated vascular,plant-derived sediments deposited during a low-nutrient,clear-water phase with frequent water exchange between the lake and the Yangtze River. Between the1950 s and 1980 s,decrease in values of H/L and TAR,and increase in the proportion of mid-and short-chain n-alkanes indicated a shift towards mid-and shorter-chain components likely associated with the increasing contribution of macrophytes and algae. Lower 2nC17/( n-C23+ n-C25) values indicated a relatively low algal abundance. In that stage,the lake trophic state increased slightly with the decreasing influence of the Yangtze River flow. After the 1980 s,H/L and TAR values increased and then decreased,total n-alkane concentrations and 2n-C17/( n-C23+ n-C25) increased significantly,especially after 2000 s,suggesting the main contributor to high organic matter input most likely shifted to algae because of the eutrophication caused by anthropogenic activities.
引文
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[25]史小丽,秦伯强.长江中游网湖近代沉积环境演变及其对人类活动的响应[J].地理研究,2013,32(5):808-816.Shi X L,Qin B Q.Environmental evolution of Wanghu Lake in the middle Yangtze River and its responses to human activities[J].Geographical Research,2013,32(5):808-816.
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[34]房吉敦,吴丰昌,熊永强,等.滇池湖泊沉积物中游离类脂物的有机地球化学特征[J].地球化学,2009,38(1):96-104.Fang J D,Wu F C,Xiong Y Q,et al.Organic geochemical characteristics of free lipids in Lake Dianchi sediments[J].Geochimica,2009,38(1):96-104.
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[2]傅家谟,盛国英.分子有机地球化学与古气候、古环境研究[J].第四纪研究,1992,12(4):306-320.Fu J M,Sheng G Y.Molecular organic geochemistry and its application to the study of paleoclimate and paleoenvironments[J].Quaternary Sciences,1992,12(4):306-320.
[3]SchefuE,Ratmeyer V,Stuut J B W,et al.Carbon isotope analyses of n-alkanes in dust from the lower atmosphere over the central eastern Atlantic[J].Geochimica et Cosmochimica Acta,2003,67(10):1757-1767.
[4]Cranwell P A,Eglinton G,Robinson N.Lipids of aquatic organisms as potential contributors to lacustrine sediments—II[J].Organic Geochemistry,1987,11(6):513-527.
[5]Ficken K J,Li B,Swain D L,et al.An n-alkane proxy for the sedimentary input of submerged/floating freshwater aquatic macrophytes[J].Organic Geochemistry,2000,31(7-8):745-749.
[6]Meyers P A,Ishiwatari R.Lacustrine organic geochemistry—an overview of indicators of organic matter sources and diagenesis in lake sediments[J].Organic Geochemistry,1993,20(7):867-900.
[7]Meyers P A.Applications of organic geochemistry to paleolimnological reconstructions:a summary of examples from the Laurentian Great Lakes[J].Organic Geochemistry,2003,34(2):261-289.
[8]Schwark L,Zink K,Lechterbeck J.Reconstruction of postglacial to early Holocene vegetation history in terrestrial Central Europe via cuticular lipid biomarkers and pollen records from lake sediments[J].Geology,2002,30:463-466.
[9]林晓,朱立平,王君波,等.西藏纳木错表层沉积物中正构烷烃的来源与空间分布特征[J].湖泊科学,2009,21(5):654-662.Lin X,Zhu L P,Wang J B,et al.Sources and spatial distribution character of n-alkanes in surface sediments of Nam Co on the Tibetan Plateau[J].Journal of Lake Sciences,2009,21(5):654-662.
[10]饶志国,吴翼,朱照宇,等.长链正构烷烃主峰碳数作为判别草本和木本植物指标的讨论:来自表土和现代植物的证据[J].科学通报,2011,56(10):774-780.Rao Z G,Wu Y,Zhu Z Y,et al.Is the maximum carbon number of long-chain n-alkanes an indicator of grassland or forest?Evidence from surface soils and modern plants[J].Chinese Science Bulletin,2011,56(16):1714-1720.
[11]Hanisch S,Ariztegui D,Püttmann W.The biomarker record of Lake Albano,central Italy—implications for Holocene aquatic system response to environmental change[J].Organic Geochemistry,2003,34(9):1223-1235.
[12]He Y X,Sun D Y,Wu J L,et al.Factors controlling the past~150-year ecological dynamics of Lake Wuliangsu in the upper reaches of the Yellow River,China[J].The Holocene,2015,25(9):1394-1401.
[13]Zhang Y D,Su Y L,Liu Z W,et al.A sediment record of environmental change in and around Lake Lugu,SW China,during the past two centuries[J].Journal of Paleolimnology,2016,55(3):259-271.
[14]欧杰,王延华,杨浩,等.正构烷烃及单体碳同位素记录的石臼湖生态环境演变研究[J].环境科学,2013,34(2):484-493.Ou J,Wang Y H,Yang H,et al.Eco-environmental evolution inferred from n-alkanes andδ13C records in the sediments of Shijiu Lake[J].Environmental Science,2013,34(2):484-493.
[15]王自翔,王永莉,吴保祥,等.泸沽湖沉积物正构烷烃分布特征及其古植被意义[J].海洋地质与第四纪地质,2015,35(2):169-177.Wang Z X,Wang Y L,Wu B X,et al.Distribution of n-alkanes in the Luguhu Lake sediments and their paleovegetation significance[J].Marine Geology&Quaternary Geology,2015,35(2):169-177.
[16]Lin X,Zhu L P,Wang Y,et al.Environmental changes reflected by n-alkanes of lake core in Nam Co on the Tibetan Plateau since 8.4 ka B.P.[J].Chinese Science Bulletin,2008,53(19):3051-3057.
[17]Wang Y L,Fang X M,Zhang T W,et al.Predominance of even carbon-numbered n-alkanes from lacustrine sediments in Linxia Basin,NE Tibetan Plateau:implications for climate change[J].Applied Geochemistry,2010,25(10):1478-1486.
[18]Zhang Z H,Zhao M X,Yang X D,et al.A hydrocarbon biomarker record for the last 40 kyr of plant input to Lake Heqing,southwestern China[J].Organic Geochemistry,2004,35(5):595-613.
[19]蒲阳,张虎才,王永莉,等.青藏高原冰蚀湖沉积物正构烷烃记录的气候和环境变化信息:以希门错为例[J].科学通报,2011,56(14):1132-1139.Pu Y,Zhang H C,Wang Y L,et al.Climatic and environmental implications from n-alkanes in glacially eroded lake sediments in Tibetan Plateau:an example from Ximen Co[J].Chinese Science Bulletin,2011,56(14):1503-1510.
[20]房吉敦,吴丰昌,熊永强,等.中国典型湖泊沉积物中脂肪烃的分布特征及来源[J].环境科学研究,2010,23(10):1243-1249.Fang J D,Wu F C,Xiong Y Q,et al.Distribution characteristics and origins of aliphatic hydrocarbons in sediments from typical lakes in China[J].Research of Environmental Sciences,2010,23(10):1243-1249.
[21]舒卫先.太湖流域人与自然相互作用的湖泊沉积记录——以持久性有机污染物、重金属元素和正构烷烃为例[D].南京:中国科学院南京地理与湖泊研究所,2008.
[22]杨明生,张虎才,邹长伟,等.鄱阳湖沉积物正构烷烃特征及其生物源[J].福建师范大学学报(自然科学版),2014,30(3):111-118.Yang M S,Zhang H C,Zou C W,et al.Characteristics of nalkanes in modern sediments of Poyang Lake and its biological origins[J].Journal of Fujian Normal University(Natural Science Edition),2014,30(3):111-118.
[23]Yi C L,Liu H F,Rose N L,et al.Sediment sources and the flood record from Wanghu lake,in the middle reaches of the Yangtze River[J].Journal of Hydrology,2006,329(3-4):568-576.
[24]史小丽,秦伯强.长江中游网湖沉积物营养元素变化特征及其影响因素[J].地理科学,2010,30(5):766-771.Shi X L,Qin B Q.Nutrients distribution character and their influential factors in core sediments from Wanghu lake in middle reaches of Changjiang River[J].Scientia Geographica Sinica,2010,30(5):766-771.
[25]史小丽,秦伯强.长江中游网湖近代沉积环境演变及其对人类活动的响应[J].地理研究,2013,32(5):808-816.Shi X L,Qin B Q.Environmental evolution of Wanghu Lake in the middle Yangtze River and its responses to human activities[J].Geographical Research,2013,32(5):808-816.
[26]于革,沈华东.长江中游网湖百年花粉序列及其沉积动力和环境特征[J].湖泊科学,2011,22(4):598-606.Yu G,Shen H D.100a pollen sequence and the sedimentary dynamics and environments in Lake Wanghu,middle reaches of the Yangtze River[J].Journal of Lake Sciences,2010,22(4):598-606.
[27]王苏民,窦鸿身.中国湖泊志[M].北京:科学出版社,1998.200-201.
[28]Appleby P G,Birks H H,Flower R J,et al.Radiometrically determined dates and sedimentation rates for recent sediments in nine North African wetland lakes(the CASSARINA Project)[J].Aquatic Ecology,2001,35(3-4):347-367.
[29]Garcia-Orellana J,Sanchez-Cabeza J A,MasquéP,et al.Atmospheric fluxes of210Pb to the western Mediterranean Sea and the Saharan dust influence[J].Journal of Geophysical Research:Atmospheres,2006,111(D15).
[30]Bourbonniere R A,Meyers P A.Sedimentary geolipid records of historical changes in the watersheds and productivities of Lakes Ontario and Erie[J].Limnology and Oceanography,1996,41(2):352-359.
[31]Colombo J C,Pelletier E,Brochu C,et al.Determination of hydrocarbon sources using n-alkane and polyaromatic hydrocarbon distribution indexes.Case study:Rio de la Plata Estuary,Argentina[J].Environmental Science&Technology,1989,23(7):888-894.
[32]Cranwell P A.Chain-length distribution of n-alkanes from lake sediments in relation to post-glacial environmental change[J].Freshwater Biology,1973,3(3):259-265.
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