The synergistic influence of multiple environmental stressors on lake ecosystems has typically been evaluated paleolimnologically, through examination of a single biological indicator. Aquatic organisms, however, may display heterogeneous responses because of differences in their ecological sensitivity, and/or because of ecological consequences caused by strong interactions among multiple stressors. We applied paleolimnological methods to compare patterns of algal and invertebrate response to multiple stressors in a large, shallow lake in southwest China over the last two centuries. Our multi-proxy records show a clear trajectory of lake eutrophication (greater total nitrogen) and increasing lake productivity (greater sediment Chlorophyll- a concentration) during the last century. Nutrient enrichment and lake productivity played significant, but different roles, in structuring diatom and cladoceran assemblages, accounting for 31.4 and 77.3% of the total variance in the communities, respectively. Furthermore, there was a pronounced influx of the endemic diatom species Cyclotella rhomboideo - elliptica Skuja, which was strongly associated with the second axis of a diatom PCA (Principal Component Analysis). This occurred synchronously with a documented reversal of hydrological connectivity with a downstream, nutrient-poor lake during the early twentieth century, suggesting a role for species dispersal in modulating community reorganization. There are also strong differences between the two organism groups in their sensitivity to hydrological fluctuations, as hydrodynamics, indicated by sand content, was a significant driver for cladocerans (>25%), but showed only minor influence on diatom assemblages in our selection of minimum adequate models. The proportion of the total variance explained by our measured variables (<30%) was much lower for diatom assemblages than for both cladoceran assemblage and accumulation data (~77%), reflecting differences in community reorganization between the two biological indicators. The sediment-based evaluation of community responses revealed the differential impact of eutrophication and hydrological fluctuations on the biota of this large, shallow lake. Therefore, multiple biological indicators should be evaluated in limnological surveys to assess the full scope of ecological changes in highly stressed lake systems targeted for conservation or restoration.

The increased intensity and frequency of extreme droughts due to global warming have led to the dedine of water levels and significant shortage of water resources in many lakes and reservoirs, which could severely threaten the socio-economic development and ecological security. To date the ecological evaluation of extreme droughts have been mainly focused on terrestrial ecosystems in China. This study aim to assess the impact of extreme droughts on diatom assemblages and diversity patterns through multi-proxy sediment analyses in Yuxian Lake, which has experienced sig-nificant water level change during the period of 2009 to 2013. The grain size records showed an increase in sediment particles starting from about 2011, which corresponded to the occurrence of the most recent drought event. The isoto-pic and elementary records indicated that the trophic state remained oligotrophic over the past century. Diatom as-semblages were dominated by benthic and limnetic diatoms (i.e.Fragilaria construens/pinnata), but these taxa were there after replaced by fluvial and riverine taxa (i.e.Nitzschia and Navicula) with the most recent decline of lake levels. Our results demonstrated that the diatom PCA axis was strongly associated with extreme climate, which accounted for 55.8% of the total variance for diatom assemblages. Our study provided sediment evidence for the role of extreme droughts in regulating freshwater environment and biota and highlighted the urgency of climate mitigation actions in maintaining water security and ecosystem functioning for this climate-sensitive region.

To investigate the distribution pattern and significance of grain size and provide accurate analogues for grain size records from lake cores, we analyzed surface sediments from 15 lakes of Yunnan Province, China for grain size.Meanwhile, the grain size components of the surface sediments of the 15 lakes were partitioned using the log-normal distribution function method.The results showed that frequency curves of samples indicated polymodal and consisted of two to five grain-size components with the modal size varying within ranges of 0.6~423.0 μm.These components are specified from fine to coarse modes as clay (C1), fine silt (C2), silt (C3), fine to medium sand (C4) and coarse sand (C5).The grain size analysis reveals that the C1 components were the long-term superfine dust and aerosol in the atmosphere which entered the lake water body through the process of gravity and precipitation, and may have represented the background level of atmospheric dust and aerosols in southwest China;C2 and C3 were the main components of surface sediments, the modal size of which reflected the precipitation intensity of the watershed;C4 and C5 components only appeared in minority surface sediments of lakes with the contents were extremely low, and were significantly related to the lake hydrodynamic force.For the large lakes, such as Dianchi and Fuxian Lakes, it requires two processes for the sand components to reach the central part of lakes: process of from drain basin to lakes and from lakeshore to the middle of lakes, and the second one plays a main role, affected by lake current, water depth, gradient of lake basin and so on.Under the background of the drought in southwest China, some small lakes in Yunnan shrinked and even disappeared.However, because of the decrease of precipitation and weakening of general circulation, surface runoff and hydrodynamics of lakes recede, thus the material which transmit to the center of the lakes were primarily fine grain.Small lakes located in the mountainous region, with the limited catchment area and conspicuous terrain slope, can be affected by the surface runoff directly and strongly.Therefore, the increase of coarse grain in the sediments of this kind of lakes reflected the enhancement of precipitation or the precipitation intensity.

随着人类活动的增强与全球气候变暖的持续,近年来云南湖泊的生态系统功能持续退化,而目前对云南湖泊生态系统的研究还主要集中于单一环境压力的生态效应.以星云湖为研究对象,通过沉积物记录与现代监测资料,识别在湖泊富营养化、气候变化以及人类强烈干扰下硅藻群落结构响应的过程,并甄别驱动群落变化的主要环境压力及其强度.结果显示随着湖泊生产力水平(如沉积物叶绿素a浓度)的增加,硅藻物种组成发生了明显的变化,主成分分析表明了水体富营养化是驱动群落变化的主要环境因子(r=-0.63,P＜0.001).简约模型与方差分解的结果表明近200年来(钻孔长度38cm),湖泊营养水平和水动力是驱动星云湖硅藻群落变化的主要环境因子,分别解释了群落变化的18.8％和2.9％;而1951年以后,湖泊营养水平和温度分别解释了硅藻群落结构变化的31.4％和26.8％.研究结果表明了硅藻群落长期变化的主控因子是湖泊营养水平,而人类活动及气候变化等可以通过改变湖泊水动力及湖水温度来驱动硅藻群落的演替,同时抚仙湖-星云湖的连通性也对硅藻群落的演替产生了一定影响.

Fish introduction and nutrient enrichment are two major environmental stressors for many freshwater lakes. Thus far, their ecological impacts have largely been evaluated independently, despite that fish invasion and predation may interact with lake trophic status. We examined paleoecological records from four large lakes of Southwest China to quantify the strength and interaction of icefish invasion and eutrophication in affecting zooplankton over time. There was a significant and positive relationship (P < 0.01) between sediment Chl a concentration and bosminid flux in each lake with bosminid size structure being greater in more productive lakes, indicating a strong bottom-up control. Furthermore, a consistent decrease in bosminid body sizes after fish introduction was found in Fuxian where icefish grew most successfully among our lakes. The variance partitioning results showed a decrease in the relative importance of planktivorous predation in driving zooplankton production with increased trophic status across lakes, with their joint effect showing a unimodal model in strength. In all, there was regional heterogeneity in the population status and ecological impact of invasive icefish that varied with lake trophic status over time. Therefore, nutrient status needs to be considered in assessing long-term ecological status and consequences of fish invasion in stressed freshwaters.

通过对异龙湖短钻岩芯沉积物粒度、碳酸盐以及有机质含量等环境代用指标研究,结合文献资料和当地气象数据并参考实验室其他项目组137Cs-210pb方法建立的年代标尺,讨论了异龙湖流域1880年以来的环境变化和人类活动对湖泊沉积环境的影响.结果表明:岩芯35 ～ 25 cm段(1880-1936年)碳酸盐含量、中值粒径均值较高,表明这一时期为暖湿气候,TOC含量处于低值且平缓,证实人类活动对周围环境影响较小,湖泊环境变化的影响因素以自然因素为主;至25 ～ 15 cm段(1936-1996年)碳酸盐含量明显下降,有机质含量快速增加,指示湖泊沉积环境受人类活动影响强烈,碳酸根离子等其他化合物含量、反应条件、过程及碳酸盐沉淀保存条件发生改变,在此种情况下,指标已不能指示湖泊环境变化;岩芯15～0 cm段(1996-2013年)沉积物粘土含量升高,砂含量降低,应与异龙湖流域防护林工程有关,这一时期的指标特征表明人类活动强度较之前有所减弱,并且开始有意识地恢复流域生态.

Subtropical plateau lakes in Southeast Yunnan are known to have experienced multiple environmental stressors (lake pollution, eutrophication, land reclamation and droughts) during the past decades. Here, we applied multi-proxy analyses (i.e., diatom, grain size, C and N isotopic and chronology) of lake sediments, aiming to track the history of lake environment change and the characteristics of diatom community responses in Datun Lake for the past century. The results proved that the sedimentary diatom community records showed significant changes with the replacement of Fragilaria construens by Achnanthes minutissima. Combining with multiple-proxy records (i.e., isotopic data) and modern monitoring records, the ordination analyses and variation partitioning further suggested that industrial pollution and eutrophication were the major driving factors that led to the long-term shift of diatom community. In addition, the grain size results and meteorological data revealed that the reductions in hydrodynamic and water exchange intensity associated with damming and the occurrence of extreme droughts, thus led to the corresponding diatom community change.

以星云湖为代表的云南大中型湖泊近年来受到多个环境压力的胁迫,出现水质持续恶化、环境功能降低、生态系统退化等问题。目前针对这些湖泊生态环境的研究主要集中于以富营养化为代表的单一环境胁迫,且以短期监测为主,因此有效的湖泊治理与生态修复急需评价多重环境压力的长期驱动过程与特征。本文围绕星云湖枝角类群落沉积物记录,开展了多指标（如色素、粒度等）的综合分析,并结合湖泊调查、历史资料和多变量统计方法对主要环境压力与长期生态响应模式进行了识别。结果表明:沉积物分析中共鉴定出枝角类10属16种,其中盘肠溞属与象鼻溞属占绝对优势;在1890年之前湖泊沉积物色素浓度稳定在较低水平,随后湖泊生产力缓慢上升且沉积物颗粒（＞63μm）增加;1980年初开始沉积物色素含量快速上升,耐污种C.sphaericus明显增加并成为绝对优势种;随着湖泊生产力水平的上升,枝角类生物量持续增加（R2=0.753,P＜0.001,n=33）,且枝角类群落出现显著变化（R2=0.953,P＜0.001,n=33）;同时,随着外来鱼类的引入和鱼类捕食压力的变化,象鼻溞生物量总体下降但个体大小变化不明显;营养水平的持续增加与水生植物的逐渐消亡,可能导致了枝角类物种趋于单一,底栖枝角类生物量总体下降。总之,星云湖枝角类群落结构与生物量在过去100年来出现了显著变化,湖泊富营养化与生产力的变化是主要驱动因子,同时外来鱼类的引入、水文条件及水生植物的变化也对枝角类群落产生了重要的影响。

近几十年来,以大型湖泊为代表的云南部分湖泊受人类活动的持续影响出现了生态环境的明显变化.洱海作为云南面积第2大淡水湖泊,经历了多重环境压力(富营养化、外来鱼类引入、水生植被退化等)的影响.在湖泊现代监测数据面临时段较短、缺乏连续记录的背景下,湖泊沉积物的连续记录可以提供湖泊生态环境变化的长期历史并可用于生态响应模式的识别.以目前处于富营养水平的洱海为研究对象,应用湖泊沉积物记录进行多指标分析,探讨多重环境压力影响下洱海枝角类群落的长期变化特征以及影响因素,并与已有研究成果和现代监测数据进行对比,探讨了枝角类群落对环境压力响应的空间差异性.通过分析沉积物枝角类记录,重建了近百年来洱海枝角类群落的变化历史,结果表明过去100年来,枝角类的生物量总体呈增加趋势,尤其从1990年左右开始,象鼻溞生物量显著增加,物种相对组成出现明显变化(如Bosmina longispina被B.longirostris取代).同时象鼻溞的生物量、壳长与触角长度在1990s初期有明显降低的趋势,与同期外来鱼类(如银鱼)引种成功的时间一致.限制性聚类分析结果表明,枝角类群落结构的变化有3个主要阶段:1990s以前,底栖枝角类为群落的主要组成;1990-2000年左右,浮游枝角类(以象鼻溞为主)在枝角类群落结构中的比例迅速增加;从2000年以后,枝角类群落组成以浮游枝角类为主.同时,枝角类数据的主成分(PCA)分析显示,仅有PCA主轴1呈现显著的变化且解释了群落结构变化的61.64％,进一步分析表明水生植被变化可能是驱动枝角类变化的主要环境梯度,如底栖枝角类生物量减少响应了湖泊水生植被的退化.与已有研究对比表明,浅水湖区沉积物记录的枝角类生物量在1970s急剧增加与1980s急剧降低等现象并没有被深水区的沉积物记录所反映,指示了洱海生态系统的变化模式存在空间差异性.同时象鼻溞个体大小的变化模式反映了外来鱼类引入导致的鱼类捕食压力的变化.总之,本文揭示了枝角类群落结构与生物量的长期变化,反映了洱海富营养化过程、水生植被的退化与外来鱼类引入的长期驱动影响,因此对洱海的生态管理与修复工作应考虑多个环境压力的影响并加强对湖泊生态系统的评价.

In recent years, lakes of Yunnan Plateau have increasingly experienced the pressure of multiple environmental stressors like eutrophication and fish invasion, as well as their synergic effects.To date, most studies have focused on the ecological impacts of a single stressor, in spite of the interaction of these multiple stressors.This paper selected Lake Dianchi and Lake Fuxian, which are currently hypo-eutrophic and oligo-mesotrophic respectively , and conducted multi-proxy analyses of lake sediments from both lakes.We aim to quantify the impacts of both eutrophication ( bottom-up control) and predation pressure ( top-down control) in driving the long-term changes of zooplankton production, and to compare the intensity of their single forcing and interaction between both lakes.Our results showed that both lakes experienced increased primary production ( i.e.the production of sedimentary pig-ments) since the mid-20th century, which was consistent with the eutrophication history revealed by lake monitoring data .Concur-rently, the production of zooplankton ( i.e.sedimentary bosminid production ) increases significantly with a general trend of the ol-igotrophic taxon of Bosmina longispina replaced by B.longirostris found in both lakes.However, the bosminid production and body size (i.e.carapace and antennule length), displayed a decrease during the 1960s and 1980s, when exotic fish were introduced and/or established stable populations.With the methods of multiple regression and variance partitioning , our further analyses sug-gested that top-down control ( as indicated by bosminid carapace length ) exerted stronger impact on zooplankton production at Lake Dianchi than at Lake Fuxian (15.46% and 10.39%, respectively), while Lake Fuxian displayed a much stronger control of bot-tom-up (represented by sedimentary pigment concentration) forcing than Dianchi (69.74%and 19.67%, respectively).In addi-tion, we found that the interaction between bottom-up and top-down is much more significant at Lake Dianchi than the Lake Fuxian (42.12 % and 3.46 %, respectively), despite that both forcing exerted a similar degree of control on zooplankton production at Lake Dianchi (77.25%) and Lake Fuxian (83.59%).These results indicate the significant control of lake eutrophication on zoo-plankton production at both lakes, while the introduction of exotic fish intensify the predation pressure on zooplankton , which also showed strong dependence on the rapid increase of trophic status at the hypo-eutrophic shallow lake of Lake Dianchi.In contrast, the strength of the interaction between bottom-up and top-down control was insignificant at the oligo-mesotrophic deep lake of Fux-ian.Over all, our results infered that eutrophication and fish predation have led to the significant changes of ecosystem structure and trophic interaction at both large plateau lakes.Therefore, trophic status, the history of eutrophication and lake typology should be taken into account for sustainable management and ecological restoration of the plateau lakes in Yunnan .

目前国内对生产力-生物多样性关系(productivity-diversity relationship,PDR)的研究主要集中于陆地生态系统和空间尺度,少量关于湖泊系统的研究也主要集中于现代调查,缺乏较长时间尺度上的模式探讨.本文应用沉积物色素记录重建了抚仙湖和滇池初级生产力变化历史,对硅藻群落的主成分分析(PCA)表明两个湖泊的初级生产力都是驱动硅藻群落变化的主要环境梯度.进一步分析硅藻群落α与β多样性响应湖泊生产力水平的模式,发现滇池硅藻群落表现为随着系统生产力的上升物种丰富度减少,β多样性降低,而抚仙湖呈现相反的变化模式.两个湖泊β多样性与生产力平均水平的关系均表现出与α多样性相似的特征,但在与生产力变化幅度的关系上,滇池表现出显著的负相关,而抚仙湖则没有显著的变化.滇池硅藻群落生产力随硅藻多样性的降低显著增加(R2=0.597,P＜ 0.01),而在抚仙湖无显著变化,表明了滇池群落多样性的维持对群落生产力的影响较弱,如与营养盐富集的促进作用相比.滇池明显的富营养化过程与强烈的人类扰动带来的环境异质性降低可能对群落多样性-生产力的关系产生了明显的控制作用.