Bacterial and archaeal assemblages in sediments of a large shallow freshwater lake, Lake Taihu, as revealed by denaturing gradient gel electrophoresis

Aims:  To explore the association of microbial community structure with the development of eutrophication in a large shallow freshwater lake, Lake Taihu.
Methods and Results:  The bacterial and archaeal assemblages in sediments of different lake areas were analysed using denaturing gradient gel electrophoresis (DGGE) of amplified 16S rDNA fragments. The bacterial DGGE profiles showed that eutrophied sites, grass-bottom areas and relatively clean sites with a eutrophic (albeit dredged) site are three respective clusters. Fifty-one dominant bacterial DGGE bands were detected and 92 corresponding clones were sequenced, most of which were affiliated with bacterial phylotypes commonly found in freshwater ecosystems. Actinobacteria were detected in the centre of the lake and not at eutrophied sites whereas the opposite was found with respect to Verrucomicrobiales . Twenty-five dominant archaeal DGGE bands were detected and 31 corresponding clones were sequenced, most of which were affiliated with freshwater archaeal phylotypes.
Conclusions:  The bacterial community structures in the sediments of different areas with similar water quality and situation tend to be similar in Taihu Lake.
Significance and Impact of the Study:  This study may expand our knowledge on the relationship between the overall microbial assemblages and the development of eutrophication in the shallow freshwater lake.     

Current status and future tendency of lake eutrophication in China

Current trophic status and trend of Chinese freshwater lakes were investigated in this study. The results showed that all lakes studied were commonly undergoing the eutrophication process, water quality decreased and lake's ecosystem is being declined. Most of the urban lakes are facing serious eutrophication. Many medium-sized lakes are in metrophic or eutrophic status, some local water are even approaching the hypertrophic level. The famous five freshwater lakes in China have entered into eutrophication in the condition of higher nutrient load. Lake Taihu, Hongze and Caohu are already in eutrophic state. Eutrophic lakes are mainly distributed in the middle and lower reaches of Yangtze River and Yungui plateau. Lake eutrophication developed rapidly. Among the 34 lakes studied in 1970's, most of lakes were in the mesotrophic status,mesotrophic water area accounted for 91.8%. With the nine year of 1978-1987 the area percentage of oligotrophic lakes decreased from 3.2% to 0.53%, and that of eutrophic lakes increased from 5.0% to 55.01%. Recent data showed 57.5% lakes were in eutrophic and hypertrophic status of the 40 surveyed lakes.Eutrophic trend of Lake Taihu, Chaohu and Xuanwu in the region of the middle and lower reaches of Yangtze River was predicated using the ecological stress model. The results showed that in 2008 Lake Taihu, Chaohu and Xuanwu might be of eutrophication, eutrophication and hypertrophication, respectively if no control measurement is taken. Provided the pollution water treatment rate is 60% in 2030, approximately 30 billion ton pollution water would still be discharged directly in the lakes. Therefore, in 2030 the urban lakes in China might be eutrophication or hypertrophication, and most of the medium-sized lakes at the urban-rural fringe might be in eutrophication or hypertrophication. The famous five biggest freshwater lakes in China might be eutrophication if control countermeasures are taken as now.Lake eutrophication has become a serious environmental problem in China. Based on the domestic and foreign experiences of the eutrophic control technologies, both nutrient pollution control and lake ecological restoration should be carried out and this may be the guidance for the eutrophic control of lakes in China.     

Current status and future tendency of lake eutrophication in China

Current trophic status and trend of Chinese freshwater lakes were investigated in this study. The results showed that all lakes studied were commonly undergoing the eutrophica-tion process, water quality decreased and lake's ecosystem is being declined. Most of the urban lakes are facing serious eutrophication. Many medium-sized lakes are in metrophic or eutrophic status, some local water are even approaching the hypertrophic level. The famous five freshwater lakes in China have entered into eutrophication in the condition of higher nutrient load. Lake Taihu, Hongze and Caohu are already in eutrophic state. Eutrophic lakes are mainly distributed in the middle and lower reaches of Yangtze River and Yungui plateau. Lake eutrophication developed rapidly. Among the 34 lakes studied in 1970's, most of lakes were in the mesotrophic status, mesotrophic water area accounted for 91.8%. With the nine year of 1978-1987 the area percentage of oligotrophic lakes decreased from 3.2% to 0.53%, and that of eutrophic lakes increased from 5.0% to 55.01%. Recent data showed 57.5% lakes were in eutrophic and hyper trophic status of the 40 surveyed lakes. Eutrophic trend of Lake Taihu, Chaohu and Xuanwu in the region of the middle and lower reaches of Yangtze River was predicated using the ecological stress model. The results showed that in 2008 Lake Taihu, Chaohu and Xuanwu might be of eutrophication, eutrophication and hypertrophication, respectively if no control measurement is taken. Provided the pollution water treatment rate is 60% in 2030, approximately 30 billion ton pollution water would still be discharged directly in the lakes. Therefore, in 2030 the urban lakes in China might be eutrophication or hypertrophication, and most of the medium-sized lakes at the urban-rural fringe might be in eutrophication or hypertrophication. The famous five biggest freshwater lakes in China might be eutrophication if control countermeasures are taken as now. Lake eutrophication has become a serious environmental problem in China. Based on the domestic and foreign experiences of the eutrophic control technologies, both nutrient pollution control and lake ecological restoration should be carried out and this may be the guidance for the eutrophic control of lakes in China.     

Ecological and economic analysis of lake eutrophication by nonpoint pollution

Abstract The hypothesis that economic damage due to nonpoint pollution exceeds costs of mitigation can be tested by ecologists, economists, and resource managers working at the spatial scale of watersheds for periods of years to decades. We present a framework for combining ecological and economic information to compare management scenarios for nonpoint pollution. Eutrophication of lakes caused by nonpoint phosphorus pollution, a common environmental problem, is the focus of our approach. Economic advantages of mitigating nonpoint pollution increase as the uncertainty of ecological predictions decreases. Uncertainty is measured by the prediction variance of nonpoint pollution models. A major source of variance in nonpoint pollution predictions is the effect of land use change on phosphorus transport. This variance is often large because calibration data sets do not have sufficiently wide ranges of land use variables. Ecological predictions and the resulting economic assessments could be improved by comparative studies of watersheds with contrasting land uses, and by viewing nonpoint pollution management as a large-scale experiment.     

Phosphorus eutrophication in the SW Frisian lake district 1. Monitoring and assessment of a dynamic mass balance model

In 1984 a frequent monitoring programme was started in the hypertrophic S.W. Frisian lake district, with emphasis on total phosphorus (TP) and chloride (Cl^–). The main objectives of the project were: to quantify the phosphorus flows, to gain insight in the process of eutrophication, and to simulate management scenarios. The seasonal variability in the lakes is due mainly to the man-made hydrology: reception of humic-rich polder water in wet periods (winter) and inlet of chloride-rich Usselmeer water in dry periods (summer). The yearly means of TP concentrations in the lakes (Tjeukemeer, Groote Brekken and Slotermeer) ranged from 0.23 to 0.29 mg l^–1. However, much higher concentrations (0.9 mg l^–1) were found in periods with high inflow of polder water.The simulations with a mass balance showed an acceptable similarity between measured and simulated concentrations of TP as well as of Cl^–. Chloride was modelled to verify the accuracy of a hydrodynamic model. A sensitivity analysis of the apparent settling rate in the P model showed that sensitivity was lowest in simulations of Groote Brekken and highest in simulations of Slotermeer, the difference being attributable to the influence of the water residence time. The model was found to be appropriate for simulating management scenarios.     

Species composition and distribution of free-living marine nematodes in Vostok Bay, Sea of Japan

The qualitative and quantitative composition of free-living marine nematodes have been studied in Vostok Bay (Peter the Great Bay, Sea of Japan). It is found that the population density of nematodes in the bottom sediments of Vostok Bay shows an uneven distribution. The mean population density equaled 56800 ± 23400 specimens/m². A correlation has been revealed between the population density of nematodes and the substrate type. Altogether, 85 species of nematodes have been found; they were dominated by Sabatieria palmaris, Rhabdodemania orientalis, Araeolaimus parvibulbosus, Oncholaimium paraolium, Doryolaimopsis peculiaris, and Metachromadora itoi. Six taxocenoses of nematodes were distinguished, taking into account the species dominating in the population density and using cluster analysis of the obtained data. The dominating trophic assemblage of nematodes was “scrapers.” In general, the species composition of nematodes in Vostok Bay is characterized by the relatively great similarity with that in other areas of Peter the Great Bay (Sea of Japan).     

Fish trophic divergence along a lake productivity gradient revealed by historic patterns of invasion and eutrophication

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Cladocera in space and time: Analysis of lake sediments

Shells of Bosminidae and Chydoridae are quantitatively preserved in lake sediments. The chronological deposition of these remains provides the means for longterm observation of these Cladocera, both in terms of species and communities. Chydorid analysis, as based on subfossil assemblages, is an analysis of community and provides direct observation of community dynamics over extended periods of time. It has proved to be a valuable method to obtain information on the influence of environmental factors and time on community characteristics. Morphological variation inBosmina (Eubosmina) has been followed for some thousand years. This is of special interest for the evaluation of taxonomic rank (species, forms) if closely related taxa have co-existed. Bosmina successions, as well as shifts in the chydorid fauna, are related to environmental change. Thus, cladoceran analysis of lake sediments provides information on the developmental history of lakes and allows observation of the effects of longterm environmental changes, such as climatic changes and eutrophication.     

Phosphorus eutrophication in the SW Frisian lake district 2. Phosphorus balances and simulation of reduction scenarios

The lakes and interconnecting canals in the S.W. Frisian lake district are highly eutrophic. In the mid-1980's a project on eutrophication and lake restoration research was started. This project was aimed at modelling water transport and phosphorus (P) dynamics and at simulating management scenarios. A simple dynamic P-balance model was used to calculate total phosphorus (TP) balances and to simulate three TP reduction scenarios in each of three lakes: Tjeukemeer, Groote Brekken and Slotermeer. The model covered three periods in 1985, 1986 and 1987. The external loads to Tjeukemeer were highest, moderate to Groote Brekken, and lowest to Slotermeer. The major P sources in the area were discharges from the surrounding polders, used mainly for agriculture, and from IJsselmeer.Despite a 75% TP-reduction in water from the surrounding polders the 0.07 mg l^–1 target level could be reached only occasionally in Tjeukemeer, while in the other two lakes this level was not even approached. The effect of a 75% reduction in water from IJsselmeer was greatest in Groote Brekken (but again approached the target only occasionally), moderate in Tjeukemeer and least in Slotermeer. The simulations showed that only a 75% reduction in both external loads (from polders and from IJsselmeer) will lead to achieving the target level in Tjeukemeer and Groote Brekken during the summer periods. In Slotermeer, a relatively isolated lake, other measures are necessary to reach the target level. The results are confirmed by an approximate theoretical analysis of the effects of load reduction.     

基于神经网络简单集成的湖库富营养化综合评价模型

根据中国水利部推荐的地表水富营养化控制标准,以叶绿素a、总磷、总氮、化学需氧量和透明度为评价指标,采用线性插值方法生成均匀分布的训练样本,建立了用于湖泊、水库富营养化综合评价的神经网络简单集成模型,其个体网络采用反向传播网络。通过递增法分别确定个体网络隐含层节点数为3,集成规模为40。所有个体网络均采用弹性反传训练算法和带动量的梯度下降学习算法。将该模型应用于巢湖富营养化综合评价,结果表明该模型有效消除了单个反向传播神经网络对初始网络权重的敏感性,泛化能力得到显著的提高。该模型的评价结果与综合营养状态指数法差异极显著,而与插值评分法差异不显著;但相关性较高,相关系数分别为0．9406和0．8891。通过对比分析,表明该模型较好地归纳了评价标准中的潜在评价规则,评价结果客观、可靠。     

The occurrence of oligochaetes in lake chains receiving pulp mill waste and their relation to eutrophication on the trophic scale

Earlier conceptions of oligochaetes as indicators of trophy were somewhat enlarged to include more littoral, meiofaunal and naidid species. The amplitudes of different species on the oligotrophy-eutrophy axis seem to be generally large. Certain species which probably originally occur mainly in very humic environments seem also to be able to endure very strong organic loading caused by pulp mills. Species of this kind seem to be Dero digitata, Specaria josinae, Slavina appendiculata and Aulodrilus pluriseta. Chaetogaster langi and Arcteonais lomondi are also species which live in areas receiving pulp mill wastes. A. lomondi and D. digitata seem to be species living in greater depths than the naidids generally. Tubifex tubifex densities as high as 600000 ind · m^-2 were found near a pulp mill when the meiofauna method was used. A third of the T. tubifex were found deeper than 5 cm from the sediment surface. S. josinae and S. appendiculata may be found down to depths between 5 and 10 cm.     

Structural and functional measures of leaf-associated invertebrates and fungi as predictors of stream eutrophication

Eutrophication is a major threat to freshwater ecosystems worldwide that affects aquatic biota and compromises ecosystem functioning. In this study, we assessed the potential use of leaf decomposition and associated decomposer communities to predict stream eutrophication. Because leaf quality is expected to affect leaf decomposition, we used five leaf species, differing in their initial nitrogen concentration. Leaves of alder, chestnut, plane, oak and eucalyptus were placed in coarse-mesh bags and immersed in six streams along an eutrophication gradient to assess leaf decomposition and the structure of associated decomposer communities. A hump-shaped relationship was established between leaf decomposition and the eutrophication gradient for all leaf species, except for eucalyptus. Invertebrate biomass and density as well as fungal biomass and sporulation were lowest at the extremes of the gradient. Leaf-associated invertebrate and fungal assemblages were mainly structured by stream eutrophication. The percentage of shredders on leaves decreased, whereas the percentage of oligochaeta increased along the eutrophication gradient. The Iberian Biological Monitoring Working Party Index (IBMWP) applied to benthic invertebrates increased from oligotrophic to moderately eutrophic streams and then dropped sharply at highly and hypertrophic streams. Overall, leaf decomposition was a valuable tool to assess changes in stream water quality, and it allowed the discrimination of sites classified by the IBMWP within class I and class IV. Moreover, decomposition of most leaf species responded in a similar way to eutrophication when decomposition was normalized by the quality of leaves.     

北京四校园人工湖浮游藻类与富营养化特征分析

浮游藻类作为重要的生物指标已被广泛运用于各种水体的富营养化监测与评价中.论文对北京市4个校园人工湖的浮游藻类群落组成及季节变化展开调查,探讨了浮游藻类生物指标和富营养化的关系及其季节变化规律.调查期间,镜鉴得到39个属,隶属于蓝藻,绿藻和硅藻门.4个水体生物密度的季节平均值均高于500 cell·mL^-1,多样性指数普遍介于2～3之间.TN,TP和COD显示各水体都已处于富营养化状态.综合生物指标和水质指标进行聚类分析,结果显示:4个人工湖不同季节的水体可分为绿藻型,蓝,绿藻型和硅藻型三大类富营养化水体:荷花池,荷塘浮游藻类群落相似性最高,而荷塘、未名湖夏季富营养化程度最接近.     

云南程海湖泊系统响应富营养化与水文调控的长期模式

流域开发和气候变化背景下,逐渐增强的人类活动已经显著影响湖泊系统演替及功能。本研究以云南程海为研究对象,通过对程海湖泊沉积物记录与现代调查数据相结合,重建了程海近250年来的生态环境变化过程,探讨了程海湖泊系统在富营养化以及水文波动等多重环境压力影响下的长期响应模式。结果表明: 1970年之前程海营养水平整体偏低,1970—2000年间缓慢增长,2000年后快速增加,初级生产力呈长期上升趋势。1993—2000年期间,引水工程显著增加了湖泊水动力强度和物种扩散能力,促进了直链藻和菱形藻的增加。程海沉积物记录的碳循环变化主要受内源输入的长期影响。富营养化是硅藻群落长期演替的主要驱动因子,其次是湖泊水动力条件的波动。对程海的生态修复与流域管理不仅需要关注水体营养盐的富集与流域污染物的控制,同时还要考虑到湖泊水文调控和水位波动的影响。     

Living within dynamic social-ecological freshwater systems: System parameters and the role of ecological engineering

The objective of ecological engineering is to design sustainable ecosystems that integrate human communities and their natural environment for the benefit of both. In this paper, we illustrate how social-ecological modeling can be used as a tool to clarify this objective at a landscape scale for freshwater systems. Coupled social-ecological systems (SESs) are open, dynamic systems subject to both ecological and socioeconomic perturbations. Here we demonstrate the interactive effects of social and technological uncertainties on SES dynamics over time. Additionally, we integrate research on ecosystem stability, social-ecological modeling, and ecological engineering to offer guidance for research at the human-environment interface. Based on a case study of Lake Erie's Sandusky watershed, we use an integrated human-biophysical model to investigate the influence of two parameters on SES dynamics: (1) regional societal preferences that impact watershed management and (2) technological innovation that alters agricultural nutrient efficiency. Our results illustrate ways in which SES dynamics and optimum management strategies depend on societal preferences within the region, indicating a key area of uncertainty for future investigation. As guidance for SES restoration, our model results also illustrate the conditions under which technological change that increases nutrient efficiency on farms can and cannot create a win-win, or increase both human welfare and SES resistance to eutrophication simultaneously. Using these results, we elucidate the value of ecological engineering and offer guidance for assessments of ecological engineering projects using social-ecological modeling.     

白洋淀富营养化湖泊湿地厌氧氨氧化菌的分布及对氮循环的影响

随着生物反应器和海洋生态系统中厌氧氨氧化反应的发现,自然生态系统的氮循环过程被重新认识,但是目前厌氧氨氧化过程是否也存在于富营养化湖泊湿地并发挥着重要作用,还未见报道。结合15N同位素示踪与分子生物学技术研究了白洋淀湖泊湿地沉积物中厌氧氨氧化菌的分布、菌群结构特性、生物多样性及其活性。结果表明,在藻类影响导致的高氨氮沉积物中,厌氧氨氧化菌具有广泛存在性。通过构建16S rRNA克隆文库发现,沉积物中厌氧氨氧化菌的生物多样性相对较低,在2%差异度的条件下,30个克隆序列只分为5个操作分类单元(OTUs),代表序列与Genebank数据库中已探明的厌氧氨氧化菌Candidatus Brocadia fulgida和Candidatus Brocadia anammoxidans同源性最高,分别可达97%和96%。同位素示踪结果表明,白洋淀湖泊湿地沉积物中厌氧氨氧化活性为0.19—7.78 nmol N g-1h-1,空间差异较大,产生的氮气占此沉积物总氮气生成量的0.64%—20.65%,体现了湿地的异质性。通过得出的厌氧氨氧化反应速率推算每年由厌氧氨氧化反应损失的氮量为1.8—78gN m-2a-1,对白洋淀氮循环起到非常重要的作用。富营养化湖泊湿地沉积物中厌氧氨氧化反应的发现为研究厌氧氨氧化对氮循环的重要影响提供了新证据。     

Phytoplankton population density and volume as indicators of eutrophication in the eastern part of the Adriatic Sea

Population density and volume-biomass of microplankton, nanoplankton and total phytoplankton were analyzed at 14 stations along the eastern part of the Adriatic Sea. Based upon data frequency distribution, four categories of ecosystems were established in the investigated area. Criteria for ecosystem categorization and biological evaluation of eutrophication are proposed.     

Patterns of morphological changes and hybridization between sympatric whitefish morphs (Coregonus spp.) in a Swiss lake: a role for eutrophication?

Whitefish, genus Coregonus, show exceptional levels of phenotypic diversity with sympatric morphs occurring in numerous postglacial lakes in the northern hemisphere. Here, we studied the effects of human‐induced eutrophication on sympatric whitefish morphs in the Swiss lake, Lake Thun. In particular, we addressed the questions whether eutrophication (i) induced hybridization between two ecologically divergent summer‐spawning morphs through a loss of environmental heterogeneity, and (ii) induced rapid adaptive morphological changes through changes in the food web structure. Genetic analysis based on 11 microsatellite loci of 282 spawners revealed that the pelagic and the benthic morph represent highly distinct gene pools occurring at different relative proportions on all seven known spawning sites. Gill raker counts, a highly heritable trait, showed nearly discrete distributions for the two morphs. Multilocus genotypes characteristic of the pelagic morph had more gill rakers than genotypes characteristic of benthic morph. Using Bayesian methods, we found indications of recent but limited introgressive hybridization. Comparisons with historical gill raker data yielded median evolutionary rates of 0.24 haldanes and median selection intensities of 0.27 for this trait in both morphs for 1948–2004 suggesting rapid evolution through directional selection at this trait. However, phenotypic plasticity as an alternative explanation for this phenotypic change cannot be discarded. We hypothesize that both the temporal shifts in mean gill raker counts and the recent hybridization reflect responses to changes in the trophic state of the lake induced by pollution in the 1960s, which created novel selection pressures with respect to feeding niches and spawning site preferences.