Thermal and nutrient fluctuations are known to determine ecological structure in shallow lakes. However, their forcing on algal assembly in large and deep lakes remains largely unclear in subtropical regions. Here, a monthly survey was conducted in 2015 to examine the mechanisms for epilimnetic diatom assembly across 16 sites of Fuxian Lake in subtropical China. In this deep system (maximum depth 158.9 m), there existed a clear seasonality in the dominant diatoms, shifting from colonial Fragilaria crotonensis (January-February) to heavily silicified Aulacoseira granulata (March-April), before small-sized Pantocsekiella ocellata predominated (> 50 %) from May to December when thermal stability was strong. While species turnover over time was notable (2.07 +/- 0.18 SD, n = 16) and driven by nutrient and thermal factors (55.0 % variance), spatial species turnover was lower (1.10 +/- 0.22 SD, n = 12), and nutrient and thermal factors explained much less variance (14.3 %). Specifically, temperature and nutrients independently explained 24.1 % and 17.6 % of the temporal variation, respectively, with a strong interaction (13.3 %). Structural equation modeling (SEM) further suggested that strong thermal stability, enhanced by rising temperature and reduced wind speed, may have significantly shaped diatom assembly. Additionally, rising stability was associated with decreased epilimnetic nutrient concentrations, possibly due to a weaker exchange with bottom-water, which can inhibit diatoms with high nutrient demands. Overall, our in situ observational evidence indicates that thermal stability governs seasonal succession of diatom communities and also interacts with fluctuating nutrients, suggesting that continued warming may seasonally enhance lake-water thermal stability and intensify species turnover in deep subtropical lakes.

Arsenic contamination has become an important environmental issue of some water bodies in China under the background of economic development and basin exploitation. However, limited attention has been paid to the effects of arsenic pollution prevention and ecological restoration. Phytoplankton is the key primary producer in lake ecosystems. Arsenic can directly affect the phytoplankton growth, species succession and primary productivity, and has become a sensitive indicator of arsenic pollution and its ecological effects. Lake Yangzong has a long history of arsenic pollution and subsequent remediation efforts. We conducted a seasonal survey on phytoplankton and environmental factors of Lake Yangzong covering the south, central and north parts of the lake from 2015 to 2019. The survey data were used to identify the spatio-temporal pattern and driving factors of phytoplankton biomass, and to evaluate the mechanism of phytoplankton biomass changes and effect of eco-restoration under arsenic pollution and treatment. The results showed that the phytoplankton was mainly composed of Cyanophyta. The phytoplankton biomass was in a range of 0.7-30.4 mg/L, with the lowest value in 2016 ((3.0±1.8) mg/L) and the highest value in 2017 ((10.5±8.9) mg/L). The phytoplankton biomass showed significant seasonal variations, but did not show significant spatial difference. The correlation analysis showed that the phytoplankton biomass had a significantly negative correlation with arsenic concentration and transparency, but had a significantly positive correlation with water temperature and pH. The multivariable linear regression model further showed that temperature and arsenic were the key environmental factors in driving the change of phytoplankton biomass. Thus, the arsenic residues in water body still inhibit phytoplankton growth after remediation in heavy metal polluted lakes, indicating that heavy metal pollutants may have long-term effects due to sediment release and enduring ecotoxicological impacts.

Alpine lakes are often located remotely without the direct impacts of human activities, and usually characterized by small size, low nutrient level, and simple trophic structure, and thus being highly sensitive to climate change and nutrient inputs. Along the southeastern margin of Qinghai-Tibet Plateau, there exists a high flux in nitrogen deposition and a significant increase in temperature. Previous studies had shown that there might exist regional heterogeneity in lake responses in this area that can be linked with lake types and landscape features. In this study, three small-sized lakes (Gaigong Cuona, Wodi Co and Bigu Tianchi) with different water depths, all of which are slightly alkaline and located below the tree line, were selected for sediment surveys and comparative analyses. Multi-proxy analyses, including sample dating, physio-chemical and algal indicators (e.g., diatom assemblage and algal pigments), were carried out in combination with data collation on quantitative reconstruction of regional climate and nitrogen deposition, aiming to evaluate the degree of concordance in algal changes over the last three centuries and the mediating effect of lake depth among lakes. The results showed that there were significant differences in the dominant diatom species and composition of diatom community across lakes. The diatom community was dominated by plankton species (~ 82%) in Gaigong Cuona (maximum depth=39.4 m), including Pantocsekiella ocellata and P. comensis. In Wodi Co (maximum depth=20.7 m), planktonic and benthic taxa accounted for about 50% of the community, respectively, and the dominant species were Pantocsekiella ocellata and Staurosira construens. In contrast, benthic diatoms (~ 99%) was highly dominant in the shallowest lake of Bigu Tianchi (maximum depth=1.7 m), including Achnanthidium minutissimum and Encyonopsis microcephala. In both deep-water lakes (Gaigong Cuona and Wodi Co), the diatom composition showed no significant shift but the primary production (i.e., pigments) displayed a continous increase over the past 300 years. Meanwhile, the diatom community in the shallow lake (Bigu Tianchi) showed obvious changes while the pigment concentration showed a general trend of declining. Specifically, the relative abundance of Achnanthidium minutissimum increased and became the dominant species since ~1968. It was further shown that environmental factors may differ strongly in driving diatom assemblages across lakes. The diatom community was mainly affected by hydrological fluctuations in Gaigong Cuona, but was mainly related to total nitrogen (TN) in both Wodi Co and Bigu Tianchi. Along the depth gradient, TN had a stronger effect on diatom community in shallower lakes. Regarding the driving factors of lake primary production, the hydrological and temperature changes were significant in Gaigong Cuona, TN and temperature factors were obvious in Wodi Co, and the hydrological and TN fluctuations were important in Bigu Tianchi. In conclusion, the algae succession in alpine lakes was found to be significantly linked with lake typology such as water depth, and there may exist a higher degree of sensitivity in algal changes in shallow-water lakes in response to regional warming and atmospheric deposition in Southeast Tibet Plateau.

Algae are important primary producers in lake ecosystems, with high species diversity and sensitivity to changes in water environment. Algal productivity and community structure can serve as reliable indicators for tracking the lake environmental gradient and ecosystem features. The succession of dominant diatom species and the identification of environmental gradients are important in evaluating lake ecological health and environmental quality. In order to quantify the spatio-temporal variations in lake-water chlorophyll- a(Chl. a) and diatom communities, a seasonal survey of diatom composition and limnological characteristics was carried out at 20 sampling sites of Lake Yilong for assessing the driving factors of algal distribution and the degree of similarity between both indicators. From December 2020 to September 2021, the water environment displayed strongly seasonal fluctuations, and the trophic state index ( TSI) varied with a mean of 74.76, suggesting the persistence of a eutrophic level across seasons. A total of 68 diatoms species belonging to 21 genera were identified in 80 water samples, mainly comprising planktonic species (relative abundance, mean±SD: 79.33%±20.69%). Specifically, Aulacoseira ambigua (61.62%±20.26%) was found to be the dominant species across seasons. Principal components analysis (PCA) showed that there were significant spatial heterogeneity and seasonal variations in diatom communities. The results of redundancy analysis and variance partitioning showed that nutrient variables (e.g., TN, TP and N: P) were the important factors causing spatial variation of lake-water chlorophyll- a concentration (an explained variance of 19.08%±11.4%), while the gradients of water temperature and depth played a secondary and moderate role (9.63%±11.31%). Similarly, nutrition variables (e.g., TN, TP, N: P and SiO32-) were identified as key factors in structuring diatom communities, accounting for 27.55%±15.83% of the community variances. While water temperature and depth were insignificant in influencing the spatial variation of diatom community structure (2.53%±3.78%), however, their interaction with nutrient level played a much stronger role (15.95%±11.45%). The results of multiple regression analysis further showed that water temperature had predominant impacts on the seasonal variation in both algae biomass and diatom community distribution (56.4% and 20.1%), while the role of nutrient factors (TN, TP, N: P and SiO32- etc.) was relatively small (6.5% and 19.2%). In conclusion, the nutrient served as a key factor in causing spatial heterogeneity of algal distribution, while water temperature was an important driver of seasonal changes in phytoplankton in Lake Yilong. Meanwhile, there existed significant differences in the driving processes for seasonal and spatial distribution of lake-water algae as indicated by diatom community structure and primary productivity. This study provides empirical evidence on the strongly seasonal fluctuation and spatial heterogeneity in the limnological property and ecological processes in subtropical shallow lakes, and implies that it is imperative to combine multiple indicators of algae for an integrated assessment of lake environment quality and ecological health.

Chlorophyll a (Chla) and diatom community structure are two indicators of lake water quality. In this study, we investigated the environmental parameters, chlorophyll a, and diatom community of four small urban lakes in Kunming (Beitan, Beihu, Nanhu and Longtan lakes in the campus of Yunnan Normal University) between March 2017 and December 2019. The results showed that the concentrations of total nitrogen (TN), total phosphorus (TP), and Chla in the four lakes showed significant seasonal fluctuation. The Chla concentration in Nanhu Lake, which had the highest nutrient level among the four lakes, was significantly higher than that in the other three lakes and largely affected by TN. In comparison, water temperature significantly contributed to the increases in Chla concentration in the other three lakes. Water temperature and TN were significantly correlated with Chla across the four lakes. Diatom assemblages in Beitan, Nanhu, and Longtan lakes were dominated by planktonic diatoms, and benthic diatoms were dominant in the shallowest lake Beihu, suggesting that water depth significantly affected the proportion of planktonic diatoms and dominant taxa. Water depth, TN, TP, transparency, and water temperature affected the spatio-temporal changes of diatom community structure, with water temperature as the major factor in causing the seasonal variation in diatom community, and TN and TP as the major drivers for community variation among lakes within the same season.

Under the background of regional climate warming, frequent fluctuation of water level caused by drought events and pollutant influx due to catchment development can directly threaten the ecological safety of reservoirs. Through the analysis of physical (particle size, loss on ignition), chemical (carbon, nitrogen), biological (diatom community) and other substitute indicators of sediment, combined with monitoring data and investigation data, we reconstructed the environmental changes in Taiping Reservoir in Yunnan Province from 1937 to 2018, and analyzed the succession characteristics of diatom community and its environmental impact factors. The grain size records indicated that the hydrodynamic condition of Taiping Reservoir was increased during the impounding period (1956-1984) and was steadily reduced thereafter, corresponding well with the documented history of reservoir construction and hydrologic regulation. Changes of total nitrogen, total carbon and organic matter contents indicated the decline of water nutrient level during the construction of the reservoir and the rising process of primary productivity and endogenous organic matter after the completion of the reservoir. The dominant taxa of diatom community shifted from planktonic species to benthic species and then to planktonic ones. The main factors driving the succession of diatom community in Taiping Reservoir were climate change, hydrodynamic condition, and nutrient level. Under the background of long-term climate warming, strict controlling exogenous nutrition input, and reasonable hydrological regulation would be the important premise to maintain ecological health and environmental safety of reservoir water.

浮游生物是湖泊食物网的重要组成,其碳、氮稳定同位素能够反映元素地球化学循环和食物来源的波动,是了解水域生态系统结构变化的重要手段之一.本文选取云南4个不同类型湖泊,开展浮游生物碳、氮稳定同位素组成(δ 13 C、δ 15 N)的季节变化与湖泊对比研究.大型深水湖泊（抚仙湖和阳宗海）中,浮游植物δ 13 C值在夏、秋季（-20.34‰±1.98‰）显著高于冬、春季（-28.00‰±2.51‰）,反映夏秋季藻类生长速率较高、HCO 3 - 无机碳源利用增多等的影响.而小型浅水湖泊（长桥海和大屯海）中浮游植物δ 13 C值在夏季最高（-21.24‰±0.88‰）,可能与雨季流域输入增强、陆源有机质占比增加有关.4个湖泊浮游生物δ 15 N值具有一致的变化特征,春季显著高于其他季节.分析表明,云南地区雨季以面源污染为主向旱季以点源污染为主的转变,导致氮素营养盐季节性来源差异,并通过生物吸收作用影响了浮游生物δ 15 N值的季节变化.在浮游动物与浮游植物的稳定同位素差值（即富集度）方面,营养水平高的小型浅水湖泊中δ 13 C富集度为1.61‰±0.90‰、δ 15 N富集度为2.71‰±1.22‰,显著小于营养水平低的大型深水湖泊（分别为2.60‰±0.98‰和4.19‰±1.25‰）,表明随着湖泊营养水平的增加,浮游动物更多地以浮游植物为食,导致有机碳在不同营养级之间的传输过程中具有更强的耦合作用,且相邻营养级之间具有更低的δ 15 N富集度特征.

In the context of global warming, extreme drought events have occurred more frequently and this is projected to continue in the future in many parts of the world. However, their ecological consequences on shallow lakes are not well studied. Here we compare the succession of diatom assemblages of two medium-sized shallow lakes in southwest China during the past similar to 70 years, comprising an extreme drought event between similar to 2009 and similar to 2013. The diatom community of Lake Chahei showed a clear response to eutrophication from similar to 1980. The pioneer species Achnanthes minutissima increased strongly with elevated sedimentary total nitrogen content and at the expense of Epithemia sorex. In contrast, the diatom community of Lake Yuxian was stable and constantly dominated by the Fragilaria construens/pinnata complex. For both lakes, the most striking change occurred with the extreme drought event when environmental conditions and diatom compositions were homogenised. With strongly shrinking lake areas, peaks in the proportion of silt were observed in the sediments, suggesting increased particle burial rates and decreased light availability. These conditions selected for motile and presumably heterotrophic species mainly of the genera Navicula and Nitzschia which exhibited abrupt increases in their relative abundances at both lakes. Meanwhile, the degree of community homogeneity (inferred by Jaccard's similarity index) of the formerly distinct diatom assemblages increased strongly between both lakes. Hence, the extreme drought event has overridden and homogenised previous abiotic conditions and led to a decrease in beta diversity between the two study sites. Navicula and Nitzschia species may be reliable (paleo) indicators for extreme drought events in comparable shallow lake systems.

Lake nutrient budgets and hydrology are being altered by human activities and climate change, yet little is known of how fertilization and hydrologic mechanisms interact to structure assemblages of primary producers. Here, we present sediment records from a large shallow lake in Southwest China to separate the relative importance of nutrients and hydrological fluctuation in regulating the abundance and composition of primary producers during the twentieth century, with a focus on their differential effects on diatoms and cyanobacteria. Shifts in sedimentary particle-size distribution were consistent with the documented events of hydrological regulation during ~ 1953–1971 and subsequent changes in water level associated with severe droughts. Nutrient enrichment since ~ 1965 resulted in a significant increase in the abundance of total phototrophs (pheophytin a, β-carotene) as inferred from pigment analyses, with stronger responses of cyanobacteria (echinenone, zeaxanthin) over siliceous algae (diatoxanthin). Fossil diatom assemblages revealed a pronounced replacement of benthic taxa by eutrophic and planktonic species (e.g., Fragilaria crotonensis) since ~ 1973, but we observed a significant increase of small benthic Fragilaria sensu lato taxa following ~ 2005, which generally corresponded with a moderate increase in fossil pigments. Although eutrophication was the paramount predictor of changes in phototrophs during the last century, variation in lake hydrology due to climate and water management also modulated phototroph abundances and, more recently, diatom assemblages. Specifically, our sediment evidence suggests that hydrological fluctuation has overridden fertilization by nutrients in structuring diatom composition, leading to a heterogeneous response of cyanobacteria and diatoms to external forcing of this shallow lake.

浮游植物和浮游细菌在水生态系统的物质循环和能量流动中起重要作用,其分布规律及其驱动机制的识别和比较是评价水生生态系统健康的重要基础.阳宗海2008年经历了大规模的砷污染,且砷浓度目前仍处于超标水平,有必要识别砷污染水体中不同浮游生物群落分布的基本特征及其异同.通过显微镜检和聚合酶链式反应-变性梯度凝胶电泳(PCR-DGGE)方法,探究阳宗海浮游植物和浮游细菌的组成及其空间分布因子.结果 表明,蓝藻门在浮游植物中占绝对优势(全湖平均比例为91％),其次是甲藻门、绿藻门、金藻门、硅藻门、隐藻门和裸藻门.对DGGE条带中的DNA片段进行blast比对显示,阳宗海水体中的浮游细菌(异养细菌)主要包含放线菌纲、β-变形菌纲、α-变形菌纲和拟杆菌.PCA分析显示,浮游植物和浮游细菌群落空间分布存在差异,ANOSIM结果表明,南部和中北部的浮游植物群落存在显著差异(P＜0.05,R=0.48).多变量统计分析结果显示,空间变量和水温分别单独解释了阳宗海浮游植物群落变化的5.69％和16.51％,砷主要通过与水温和空间距离的相互作用对浮游植物的空间分布产生影响,水环境指标和空间距离与浮游细菌的空间分布没有显著关系(P＞0.05).与浮游细菌相比,浮游植物群落相似性存在显著的距离衰减关系(R2 =0.61,P＜0.001),可能与浮游植物扩散能力小于细菌有关.

Fuxian Lake is an important deep lake in China with trophic status generally categorized as class I. However, there exists a trend of degradation in its ecological and environmental health under the increasing impacts derived from catchment development and recent global warming. Therefore, it is important to evaluate the community composition, distribution patterns, and driving factors of lake biota. In order to uncover the spatio-temporal variations in water quality and diatom communities, a monthly survey of diatom community composition and limnological characteristics was carried out in the surface waters of three sampling sites from the south, middle, and north of the lake basin in Fuxian in 2015. A total of 166 diatom species belonging to 31 genera were identified, which was dominated by planktonic diatoms with the extirpation of Cyclotella rhomboideo-elliptica, an endemic species for Yunnan. Diatom community structure showed significant seasonal succession across the three sites, which were dominated by Fragilaria crotonensis in January and February, by Aulacoseira granulata in March, by Cyclotella ocellata and F. crotonensis in April, and by C. ocellata for other months (i.e., relative abundance of ~80%). Over the spatial scale, the distribution of the dominant diatoms displayed a high degree of similarity. Principal component analysis further showed that there existed significant difference in the diatom community structure and lake environment over the temporal scale, but no significant deviance was found across the three sites. The results of redundancy analysis and variation partitioning revealed that the key driver included meteorological and physical factors (i.e., water temperature, wind velocity, and Secchi depth), which accounted for 27.6% of the total variance in diatom community changes. In combination with the thermocline analysis, the change in lake hydrodynamics may have influenced the thickness and duration of the thermal stratification of lake water, resulting in the reorganization of the diatom community. At the same time, the lake-water nutrients and ions also exerted an important influence on community structuring, which explained the 21.2% and 9.4% of the diatom variation, respectively. Therefore, regional warming and catchment development have significantly structured the biological community and ecosystem health of Fuxian Lake. In all, measures should be taken not only to control the watershed input of pollutants but also to actively mitigate the long-term impact of climate change for the protection and ecological remediation of Fuxian Lake.

Functional group classification based on the morphological, physiological and ecological characteristics of diatoms is advanced in describing the tolerance and sensibility of diatoms to environmental stressors. In this study, we examined the spatial distribution of diatom functional groups in surface sediments of Haixi Lake and explored the relationships between diatom distributions and environmental variables using multivariate analyses. Principal components analysis (PCA) and redundancy analysis (RDA) results showed that water depth and total nitrogen (TN) were the key drivers for the heterogeneous distribution of diatom functional groups. Water depth of ca. 8 m was the threshold depth in influencing diatom functional group structures linking with thermal stratification. These results provided a basis for fossil record interpretation of the short core. Diatom functional groups fluctuated over the last century, in keeping with mean annual temperature, sediment TN, and median grain size. Climate warming, accelerated nutrient enrichment and intensified hydrological changes led to the dominance of functional group D, MP and P. Additionally, climate warming and nutrient enrichment led to increased diatom functional group diversity, while increased water depth (led by damming and reservoir reinforcement) contributed to diversity loss around 1957 and 1990 AD, respectively.

云南高山湖泊对区域气候变化和流域人类活动十分敏感,部分水体同时面临着污染物增加、生物群落快速演替、生态系统功能降低等问题.位于滇西北高山地区的茈碧湖历史资料表明,该湖近现代以来经历了明显的水文波动与人类活动影响.本研究通过对茈碧湖沉积物进行年代序列测定、元素和粒度等多指标分析,重建了近300年来(对应于钻孔顶部18 cm深度样品)茈碧湖环境变化历史,并结合对硅藻的分析,识别了气候变化和人类活动对生物群落变化的驱动影响.结果表明,沉积物粒度记录了茈碧湖水文变化的长期波动,水库修建与水文调控的增强使得湖泊水位波动明显,与文献记录的水文事件基本一致.硅藻群落结构以浮游种为主,1860年前硅藻组合以对水体扰动力有较强耐受性的Cyclostephanos dubius为主要优势种;1860年以来小型硅藻Cyclotella ocellata占据主要优势,同时Cyclotella comta成为次优势种;1990年开始,底栖硅藻Fragilaria spp.属相对丰度增加并出现明显波动,喜营养盐的Fragilaria crotonensis出现.多变量数理分析显示,气候变暖以及湖泊营养水平变化的共同作用是驱动茈碧湖硅藻组合长期演替的重要因素,分别独立解释了群落变化的27.5％和21.3％;其中湖库改造工程导致的外源物质输入增多,使得营养水平总体上升,是导致20世纪90年代以来硅藻组合出现明显变化的诱因.因此,在气候变暖的背景下,对云南高山湖泊的保护需要进行流域开发和水文调控的综合评价.

近几十年来,持续的流域开发与气候变化等环境胁迫已经对云南部分中小型湖泊生态系统产生了重要影响,古湖沼学的研究方法能有效弥补湖泊现代监测数据的不足,且有助于识别湖泊生态系统的长期演变特征并开展生态响应模式的评价.本研究以滇西北地区的剑湖31 cm深度钻孔为例,结合210Pb和137Cs定年,通过沉积物记录的多指标(硅藻、烧失量、粒度、元素与稳定同位素)分析及流域历史资料重建了近200年来剑湖生态环境的演化过程,结果显示剑湖水动力条件持续减弱,营养水平持续上升,硅藻已从45种减少到26种,且底栖类型物种持续减少,表征了剑湖生物多样性出现了持续降低的趋势.并运用主成分分析(PCA)和冗余分析(RDA)等方法,识别出驱动硅藻群落长期变化的重要环境变量为水动力条件和营养水平,进一步的方差分解结果表明,近200年来水动力条件和营养水平分别解释了硅藻群落变化的6.3％和1.4％,两者相互作用时解释了13.1％;而1960年以来,水动力条件、营养水平及气温分别独立解释了硅藻群落变化的6.5％、1.4％和0.2％,三者相互作用时解释了10.6％,表明剑湖的水动力条件、营养水平及气候变化是造成剑湖生态环境变化的重要环境梯度.综合剑湖生态环境长期变化特征分析表明,该湖受人类活动和气候变化的持续影响,其生态系统结构已经出现了明显变化.因此,在气候变暖的长期背景下,控制流域污染物输入及合理的水文调控是维持高原浅水湖泊生态系统健康的重要前提.

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.

Limnological studies have long focused on the nine largest plateau lakes and ecological assessment of lake eutrophication in Yunnan. However, comprehensive surveys of small and me-dium-sized lakes and their response to multiple stressors are largely absent. Here, we combined multi-proxy sediment analyses and documentary data, aiming to identify the long-term pattern of diatom community changes under the influence of climate change and anthropogenic disturbances, and to quantify their driving strengths. The results showed that Xihu Lake was in a pre-impact state with little ecological variability before the 1950s. Thereafter, expansion of land use increased the nutrient input and altered the lake hydrology, resulting in a significant shift of dominant diatoms from Cocconeis placentula to Fragilaria spp. From 1997, accelerating nutrient enrichment and hydrological changes led to the replacement of benthic diatoms by planktonic ones, resulting in a consistent loss of macrophytes and a decrease of ecological stability. Therefore, the types and strength of catchment development should be fully evaluated for effective protection of small and medium-sized alpine lakes in the context of global warming.

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.

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.

在人类活动持续干扰的背景下,云南部分湖泊面临着污染物输入增加的环境压力,特别是营养盐富集和重金属污染.以云南地区遭受过严重工业污染的阳宗海为研究对象,通过沉积物硅藻群落、砷浓度、营养元素与稳定同位素、粒度等多指标分析,结合文献记录和湖泊调查结果,揭示了阳宗海硅藻群落对湖泊富营养化和砷污染的长期响应特征,并识别了不同时期的主要环境压力与其驱动强度.结果表明:长期的营养盐累积使得浮游硅藻逐渐占据优势地位,且耐污染的底栖硅藻种的快速增加与砷污染出现的时段一致.在阳宗海长期富营养化的背景下,当水体砷污染物浓度达到一定阈值水平后,硅藻群落结构的改变和多样性的降低都指示了湖泊生态系统发生了灾难性的转变.同时1965年开始的湖泊引水工程导致了贫营养种的突然增加.因此,水体富营养化、重金属污染与湖泊水文调控是导致阳宗海硅藻群落长期变化的主控因子,对阳宗海的生态修复与综合治理需要综合考虑不同胁迫因子的长期影响与驱动作用.

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.