Reversal of eutrophication in Lake Geneva: evidence from the oligochaete communities

1. In Lake Geneva (Switzerland), total phosphorus concentrations have decreased from 90 mg m^?3 in 1979 to 55 mg m^?3 in 1990. 2. To assess the effects of this improvement, tubificid and lumbriculid communities were sampled in 1982 and in 1991 in the same areas, at a depth of 40 m. 3. Abundance of mesotrophic species (mostly Potamothrix vejdovskyi) and of eutrophic species (mostly Potamothrix hammoniensis) was lower in 1991 than in 1982; in contrast, oligotrophic species (mostly Peloscolex velutinus) were more abundant in 1991 than in 1982. 4. The changes recorded in 1991 were the same as those associated with a decrease of organic sedimentation. 5. Mean relative abundance of oligotrophic species increased from 17% in 1982 to 41% in 1991. According to these values, Lake Geneva was mesoeutrophic in 1982, but mesotrophic in 1991.     

Contrasting responses of oligochaete communities to the abatement of eutrophication in Lake Geneva

Tubificid and lumbriculid worms were used to monitor, at depths of 150 m, the recovery of Lake Geneva (Switzerland) from eutrophication. As predicted from the decrease of phosphorus concentrations, relative abundance of oligotrophic species was higher from 1988 to 1993 than in 1983, i.e. before the abatement of eutrophication. However, this trend towards oligotrophication can be reversed, as indicated by a decrease of oligotrophic species, recorded in 1993. But this change corresponded to the effects of an increase of water temperature on the abundance of the mesotrophic species Potamothrix vejdovskyi rather than to a deterioration of the profundal. In addition to this short-term setback, oligochaete communities located at a depth of 150 m responded more slowly and less clearly to the decrease of phosphorus concentrations than those located at a depth of 40 m. However, the zoobenthos indicated more clearly the recovery of Lake Geneva than the phytoplankton.     

Unimodal patterns of microbial communities with eutrophication in Mediterranean shallow lakes

The role of the microbial communities in the classical planktonic food web and its response to eutrophication in shallow lakes is still contradictory. Mediterranean shallow lakes with different eutrophication levels were sampled to study the influence of eutrophication on the microbial food web (MFW) and their contribution to the planktonic food web. Percentage of ciliate biomass in the metazooplankton (MZP) showed a U-shaped trend with eutrophication, with maximum at both ends of the chlorophyll-a (Chla) gradient. The MZP to phytoplankton ratio demonstrated a unimodal pattern with minimum values at the two ends of the Chla gradient and maximum values in the Chla range 5-10 μg l^?1. In contrast, the MFW to phytoplankton ratio reached its minimum in the central part of the Chla gradient and maximum values at the extremes of the gradient. These patterns support the hypothesis that the relative importance of bacteria and ciliates is lowest in mesotrophic shallow lakes, and highest in oligotrophic and hypereutrophic systems. These results stress the importance of protozoan in the trophic web, and indicate it is essential to include this group, especially ciliates, when quantifying zooplankton in warm shallow lakes.     

Classifying aquatic macrophytes as indicators of eutrophication in European lakes

Aquatic macrophytes are one of the biological quality elements in the Water Framework Directive (WFD) for which status assessments must be defined. We tested two methods to classify macrophyte species and their response to eutrophication pressure: one based on percentiles of occurrence along a phosphorous gradient and another based on trophic ranking of species using Canonical Correspondence Analyses in the ranking procedure. The methods were tested at Europe-wide, regional and national scale as well as by alkalinity category, using 1,147 lakes from 12 European states. The grouping of species as sensitive, tolerant or indifferent to eutrophication was evaluated for some taxa, such as the sensitive Chara spp. and the large isoetids, by analysing the (non-linear) response curve along a phosphorous gradient. These thresholds revealed in these response curves can be used to set boundaries among different ecological status classes. In total 48 taxa out of 114 taxa were classified identically regardless of dataset or classification method. These taxa can be considered the most consistent and reliable indicators of sensitivity or tolerance to eutrophication at European scale. Although the general response of well known indicator species seems to hold, there are many species that were evaluated differently according to the database selection and classification methods. This hampers a Europe-wide comparison of classified species lists as used for the status assessment within the WFD implementation process.     

Changes in aquatic macrophyte communities in Loch Leven: evidence of recovery from eutrophication?

This article assesses changes in the macrophyte community of Loch Leven over a period of 100 years. Evidence is presented that shows that these changes are associated with eutrophication and with subsequent recovery from eutrophication when anthropogenic nutrient inputs to the loch were reduced. This study uses macrophyte survey data from 1905, 1966, 1972, 1975, 1986, 1993, 1999 and 2008. In each of the four most modern surveys, the loch was divided into 19 sectors, each with at least one transect ranging from the shallowest to the deepest occurrence of macrophytes. From these data, a range of indicators of recovery were derived at the whole lake scale: the relative abundance of taxa, taxon richness and evenness. All of these metrics showed an improvement since 1972. Species richness, measured at the scales of survey sector and individual samples, also appeared to have increased in recent years. All of these measures, coupled with ordination of the presence/absence composition data from all survey years, indicate that the macrophyte community in the loch is recovering towards the state that was recorded in 1905.     

湖泊细菌群落构建机制及其对富营养化的响应

细菌是湖泊生态系统的重要组成部分,在驱动湖泊生态系统元素物质循环和调控湖泊水质方面发挥关键性作用。揭示湖泊细菌群落多样性的形成和维持机制,即群落构建机制,是湖泊微生物生态学研究中的核心目标。近年来,微生物组学技术的发展,极大推动了湖泊细菌群落构建机制的研究。富营养化是当前我国湖泊生态系统面临的最大环境挑战之一,也是决定湖泊细菌群落组成和多样性的重要因素。研究综述了湖泊细菌群落构建机制的理论基础和发展脉络。概述了湖泊细菌群落构建机制的主要分析方法。总结了富营养化对湖泊细菌群落构建机制的影响的最新研究进展。针对富营养化影响下湖泊细菌群落构建机制研究所面临的问题,提出了未来的研究展望。     

Production of some oligochaete species in large Estonian lakes

The production of Potamothrix hammoniensis, Lamprodrilus isoporus, and Uncinais uncinata was estimated in the eutrophic lakes Peipsi-Pihkva and Vôrtsjärv. Growth characteristics of these species are briefly described. Calculated production values were 6–32 (P. hammoniensis), 19–79 (L. isoporus), and 1–4 kJ m² (U. uncinata), respectively. The annual P/B ratios for the same species were, 0.8–1.7, 2.5–4.8, and 4.4–5.4, respectively.     

Engineering and biological approaches to the restoration from eutrophication of shallow lakes in which aquatic plant communities are important components

Engineering approaches (nutrient removal, sediment pumping, hypolimnion oxygenation, alum treatments) may be most appropriate to deep lakes where the aim of restoration from eutrophication is simply to reduce the production and crop of one component, the phytoplankton. They do not always give the desired results because the nutrient loading may only be reduced to a limited extent. There are additional problems in shallow lakes where change of state between community dominance (aquatic plants versus plankton) is wanted. Each community has powerful buffering mechanisms and biomanipulation may be essential to switch one state to another even with considerable nutrient reduction. For the phytoplankton-dominated community the buffers include the advantages of early growth, lower diffusion pathways for CO₂, overhead shading, and an absence of large cladoceran grazers. This later is because open-water shallow environments provide no refuges against predation for the large Cladocera which are both the most efficient grazers and the most favoured prey for fish. Restoration of aquatic plants may then require provision of refuges for the grazers. Different sorts of refuge are discussed using case studies of Hoveton Great Broad and Cockshoot Broad in the Norfolk Broadland.     

Assessing the role of internal phosphorus recycling on eutrophication in four lakes in China and Malaysia

Internal phosphorus recycling (IPR) is an important nutrient source driving algal growth and eutrophication in lakes. The complexity of eutrophication behaviours caused by high IPR complicates lake management and undermines restoration efforts. Hence, knowledge about the possible types of bifurcation behaviours caused by high IPR is essential for effective and sustainable lake eutrophication management. For this purpose, numerical bifurcation analysis is performed on an algae‑phosphorus model to investigate how IPR drives complex and rich eutrophication behaviours in two tropical and two subtropical lakes. The two tropical lakes are Tasik Harapan and Sunway Lagoon in Malaysia, while the two subtropical lakes are Lake Fuxian and Lake Taihu in China. For each specified level of IPR, co-dimension one bifurcation analysis is performed by means of XPPAUT. Co-dimension two bifurcation analysis is then carried out by means of MatCont. At low IPR, Lake Fuxian exhibits reversible behaviour, accompanied by higher external phosphorus loading (EPL) thresholds. Lake Fuxian is also more conducive to stable equilibrium and its lake dynamics are easily predictable. At moderate IPR, Sunway Lagoon is likely to exhibit stable equilibrium, accompanied by possible shifting between two stable steady states (hysteresis behaviour) and oscillations. With higher IPR, Lake Taihu and Tasik Harapan are prone to irreversibility, accompanied by lower EPL thresholds. Because of increased complexity in lake dynamics in Lake Taihu and Tasik Harapan, small changes in EPL or in algal mortality rates could trigger various transitions in lake dynamics. Overall, high IPR can trigger unexpected sharp increases in algal concentration and can reduce the resilience of an oligotrophic lake. For shallow lakes, high IPR would cause unexpected sharp increases in algal concentrations, undermine resilience of lakes, complicate lake management, and delay lake recovery process.     

Composition of freshwater bacterial communities associated with cyanobacterial blooms in four Swedish lakes

The diversity of freshwater bacterioplankton communities has not been extensively studied despite their key role in foodwebs and the cycling of carbon and associated major elements. In order to explore and characterize the composition of bacterioplankton associated with cyanobacterial blooms, large 16S rRNA clone libraries from four lakes experiencing such blooms were analysed. The four libraries contained 1461 clones, of which 559 were prokaryotic sequences of non-cyanobacterial origin. These clones were classified into 158 operational taxonomic units affiliated mainly with bacterial divisions commonly found in freshwater systems, e.g. Proteobacteria, Bacteriodetes, Actinobacteria, Verrucomicrobia and Planctomycetes. Richness and evenness of non-cyanobacterial clones were similar to other clone libraries obtained for freshwater bacterioplankton, suggesting that bacterial communities accompanying cyanobacterial blooms are as diverse as non-bloom communities. Many of the identified operational taxonomic units grouped with known freshwater clusters but the libraries also contained novel clusters of bacterial sequences that may be characteristic for cyanobacterial blooms. About 25% of the operational taxonomic units were detected in more than one lake. Even so, 16S rRNA heterogeneity analysis demonstrated large differences in community composition between lakes regardless of their similar characteristics and close proximity. Hence even the similar environmental conditions created by different cyanobacterial blooms may foster very dissimilar bacterial communities, which could indicate that the genetic diversity in lake bacteria have been underestimated in the past.     

城市湖泊富营养化成因和特征*

城市湖泊的功能主要体现在旅游、如愿、洪涝调蓄排水、调节气候以及改善城市生态环境等方面。根据湖泊所处地理位置和湖泊水质退化现象,阐述了城市湖泊水体从贫营养到富营养转变的主要原因;从水质的理化指标、底质污染物含量和水生态系统等方面初步时论了城市型浅水湖泊富营养化的特征。同非城市湖泊相比:大部分城市湖泊的水体透明度下降,污染严重的湖泊还会出现水体发黑或出现水华;水质和底质的氮磷及其它污染物含量较高,水生态系统急剧退化,水生植物以浮游植物为主,藻类大量繁殖,高等水生植物不断消亡。根据综合营养度指数对我国主要城市湖泊进行分级评价的结果表明,我国城市湖泊均达到了富营养化或严重富营养化程度。     

The contribution of nitrogen deposition to the eutrophication signal in understorey plant communities of European forests

We evaluated effects of atmospheric deposition of nitrogen on the composition of forest understorey vegetation both in space and time, using repeated data from the European wide monitoring program ICP‐Forests, which focuses on normally managed forest. Our aim was to assess whether both spatial and temporal effects of deposition can be detected by a multiple regression approach using data from managed forests over a relatively short time interval, in which changes in the tree layer are limited. To characterize the vegetation, we used indicators derived from cover percentages per species using multivariate statistics and indicators derived from the presence/absence, that is, species numbers and Ellenberg's indicator values. As explanatory variables, we used climate, altitude, tree species, stand age, and soil chemistry, besides deposition of nitrate, ammonia and sulfate. We analyzed the effects of abiotic conditions at a single point in time by canonical correspondence analysis and multiple regression. The relation between the change in vegetation and abiotic conditions was analyzed using redundancy analysis and multiple regression, for a subset of the plots that had both abiotic data and enough species to compute a mean Ellenberg N value per plot using a minimum of three species. Results showed that the spatial variation in the vegetation is mainly due to “traditional” factors such as soil type and climate, but a statistically significant part of the variation could be ascribed to atmospheric deposition of nitrate. The change in the vegetation over the past c. 10 years was also significantly correlated to nitrate deposition. Although the effect of deposition on the individual species could not be clearly defined, the effect on the vegetation as a whole was a shift toward nitrophytic species as witnessed by an increase in mean Ellenberg's indicator value.     

青藏高原三个盐碱湖的产甲烷菌群和产甲烷代谢途径分析

【目的】分析青藏高原不同类型盐碱湖中的优势产甲烷菌群和优势产甲烷代谢途径。【方法】以不同盐度和植被类型的公珠错、昆仲错和无植被的兹格塘错的沉积物为研究对象,通过高通量测序和q PCR定量古菌16S r RNA多样性分析优势古菌类群;模拟原位盐浓度及p H,比较不同产甲烷底物(甲醇、三甲胺、乙酸和H_2/CO_2)富集沉积物的产甲烷速率,分析其优势产甲烷菌代谢类型。通过添加产甲烷抑制剂(2-溴乙烷磺酸盐),检测沉积物中产甲烷底物积累,确定不同盐碱湖中主要的产甲烷途径。【结果】昆仲错的优势菌群包括甲基/乙酸型的甲烷八叠球菌科(Methanosarcinaceae,11%),乙酸型的甲烷鬃菌科(Methanosaetaceae,7.9%)和氢型甲烷菌甲烷杆菌目(Methanomicrobiales,7.4%);公珠错和兹格塘错的优势菌群为甲烷鬃菌科(Methanosaetaceae)分别占15%和15.3%,及甲烷杆菌属(Methanobacterium)和甲基型的甲烷叶菌属(Methanolobus)。公珠错和昆仲错分别以乙酸和甲醇产甲烷速率最高,而兹格塘错从不同底物产甲烷速率无差异。抑制甲烷产生后,公珠错主要积累乙酸,昆仲错主要积累甲醇;兹格塘错不仅甲烷排放低,也无产甲烷物质显著积累。【结论】昆仲错沉积物中的甲烷主要来自甲醇,公珠错中的甲烷主要来自乙酸,而兹格塘错产甲烷和底物积累不活跃。因而推测高原盐碱湖主要的产甲烷途径和菌群可能与周围植被类型的相关性更高,而与盐度的直接相关性较低。     

Rotifer communities from some Araucanian lakes of southern Chile

During the last decade much information has been produced about the zooplankton communities in southern Chile; however, most of this is related to the crustacean assemblages. The present communication examines the spatial and temporal distribution of rotifer assemblages and their relation to the environmental variables during one-year period in four Araucanian lakes. A total of 19 species was found in these oligotrophic lakes. Keratella cochlearis, Synchaeta stylata, Trichocerca porcellus, Conochilus unicornis and Collotheca pelagica were widespread, and seven species exhibited a more restricted distribution among the lakes. Species richness varied from 6 to 12; similarly, one or two dominant species usually accounted for more than 80% of the total annual abundance. Similar dominant species occurred in two lakes, but their maximum peaks of abundance differed in time; in the remaining lakes the most important species were different. Calculated rotifer diversity showed a fluctuating pattern, with low values during the year in three lakes, and high ones in Lake Llanquihue. Species diversity was significantly related to species richness in all lakes. Discriminant analysis based on the occurrence and abundances of species throughout the year revealed that the rotifer assemblage in Lake Llanquihue was different from that in the rest of the Araucanian lakes. Furthermore, the same analysis using environmental variables showed that this lake is clearly discriminated from the others on the basis of the ionic composition of the water (i.e. Cl^–, Na⁺, Mg²⁺). Rotifer abundances in these lakes were significantly influenced by a number of abiotic variables, including those related to water ionic composition. These relationships may imply that the small differences in chemical characteristics of these lakes influence the structure of the rotifer community.     

Impacts of introduced brown and rainbow trout on benthic invertebrate communities in shallow New Zealand lakes

1. Brown and rainbow trout have been introduced to many inland waters in New Zealand, but research on the impacts on native communities has focused mainly on streams. The purpose of this study was to compare the benthic communities of trout and troutless lakes. Based on previous studies in North America and Europe, we predicted that the benthic biomass, and especially the abundance of large invertebrates, would be lower in lakes with trout as compared to those without. We surveyed the invertebrate fauna of 43 shallow, high‐elevation lakes (26 with and 17 without trout) in four geographic clusters on the central South Island and then conducted a detailed quantitative study of invertebrate biomass and community structure in 12 of these lakes. 2. Benthic community composition and diversity of lakes with and without trout were nearly identical and biomass was as high or higher in the lakes with as without trout. There was no evidence that trout have caused local extinctions of benthic invertebrates. Although the proportional abundance of large‐bodied aquatic was slightly lower in lakes with than without trout, the abundance of several groups of large‐bodied benthic taxa (dragonflies, caddisflies and water bugs) did not differ. 3. Our findings are in contrast to those in North American and Europe where trout introductions into previously troutless lakes have led to declines in the abundance of benthic invertebrates, especially large‐bodied taxa. We propose that the modest effects of trout in New Zealand could be explained by (i) the high areal extent of submergent vegetation that acts as a benthic refuge, (ii) low intensity of trout predation on benthic communities and/or (iii) characteristics of the benthic invertebrates that make them relatively invulnerable to fish predation. 4. Regardless of the relative importance of these hypotheses, our results emphasise that the same invertebrates occurred in all of the lakes, regardless of size, elevation and presence of trout, suggesting habitat generalists dominate the benthic fauna in shallow New Zealand lakes.     

Characterization of bacterial communities in four freshwater lakes differing in nutrient load and food web structure

The phylogenetic composition of bacterioplankton communities in the water column of four shallow eutrophic lakes was analyzed by partially sequencing cloned 16S rRNA genes and by PCR-DGGE analysis. The four lakes differed in nutrient load and food web structure: two were in a clearwater state and had dense stands of submerged macrophytes, while two others were in a turbid state characterized by the occurrence of phytoplankton blooms. One turbid and one clearwater lake had very high nutrient levels (total phosphorus > 100 microg/l), while the other lakes were less nutrient rich (total phosphorus < 100 microg/l). Cluster analysis, multidimensional scaling and ANOSIM (analysis of similarity) were used to investigate differences among the bacterial community composition in the four lakes. Our results show that each lake has its own distinct bacterioplankton community. The samples of lake Blankaart differed substantially from those of the other lakes; this pattern was consistent throughout the year of study. The bacterioplankton community composition in lake Blankaart seems to be less diverse and less stable than in the other three lakes. Clone library results reveal that Actinobacteria strongly dominated the bacterial community in lake Blankaart. The relative abundance of Betaproteobacteria was low, whereas this group was dominant in the other three lakes. Turbid lakes had a higher representation of Cyanobacteria, while clearwater lakes were characterized by more representatives of the Bacteroidetes. Correlating our DGGE data with environmental parameters, using the BIOENV procedure, suggests that differences are partly related to the equilibrium state of the lake.     

Direct measurement of spatial autocorrelation at the community level in four plant communities

Abstract. Four sites were sampled to determine spatial autocorrelation in vegetation at the community level. All were in western New Zealand, but on different substrates and of different physiognomy: a terrace forest, a floodplain forest, a mire and the middle of a logging road. In ‘dissimograms’the four communities all showed steady increases in dissimilarity with distance, but with shoulders in the curve for some sites, which could be related to plant morphology. Most of the increase in dissimilarity occurred over very short distances: less than 0.5 m in the forests, less than 1 m in the mire and less than 2 m in the road. Separate analyses of the woody and herbaceous guilds in the floodplain forest showed that herbaceous dissimilarities remained low at distances up to 20 m, probably because of clonal structure in some species. The mire showed low overall dissimilarity, which is attributed to the uniform substrate and the small species pool. Simulations showed that the approach is capable of indicating structure when it is present. Although the dissimogram was clearest when analysing a simulated grid of patches, other types of simulated patchiness showed dissimograms that were clearly distinguishable from those obtained from the vegetation studied. The almost continuous rise in dissimilarity with distance found in the four sites offers no support to the Hierarchy theory, fitting much more closely the alternative Continuum theory.     

城市河湖生态系统健康评价——以北京市“六海”为例

健康的城市河湖才能发挥生态环境功能,体现景观和人文价值。城市河湖健康评价是城市河湖科学管理和生态恢复的前提和基础。对城市河湖生态系统健康概念和内涵进行了探讨,建立了评价指标体系和评价模型。以北京“六海”为例,对各子湖的健康状况进行比较评价。结果表明,中海和南海处于不健康向临界转化的状态,其余4个湖均处于不健康状态;水环境质量、水生态系统结构和功能以及水滨空间结构是影响“六海”健康水平的制约因素;除南海外,各湖的健康程度都处于很差的级别。中海和南海的整体生态环境好于其余4湖,对健康和临界状态的隶属度之和接近0.6,可恢复程度处于中等水平;其余4湖对健康和临界状态的隶属度之和均小于0.3,恢复困难。对“六海”的生态恢复和科学管理提出建议:①控制点源、面源污染,改善入湖和湖水水质;②改善“六海”的水文条件;③恢复水生态系统结构和水滨空间。