Quantifying uncertainties in biologically-based water quality assessment: A pan-European analysis of lake phytoplankton community metrics

Lake phytoplankton are adopted world-wide as a sensitive indicator of water quality. European environmental legislation, the EU Water Framework Directive (WFD), formalises this, requiring the use of phytoplankton to assess the ecological status of lakes and coastal waters. Here we provide a rigorous assessment of a number of proposed phytoplankton metrics for assessing the ecological quality of European lakes, specifically in response to nutrient enrichment, or eutrophication, the most widespread pressure affecting lakes. To be useful indicators, metrics must have a small measurement error relative to the eutrophication signal we want them to represent among lakes of different nutrient status. An understanding of variability in metric scores among different locations around a lake, or due to sampling and analytical variability can also identify how best this measurement error is minimised.To quantify metric variability, we analyse data from a multi-scale field campaign of 32 European lakes, resolving the extent to which seven phytoplankton metrics (including chlorophyll a, the most widely used metric of lake quality) vary among lakes, among sampling locations within a lake and through sample replication and processing. We also relate these metrics to environmental variables, including total phosphorus concentration as an indicator of eutrophication.For all seven metrics, 65–96% of the variance in metric scores was among lakes, much higher than variability occurring due to sampling/sample processing. Using multi-model inference, there was strong support for relationships between among-lake variation in three metrics and differences in total phosphorus concentrations. Three of the metrics were also related to mean lake depth. Variability among locations within a lake was minimal (<4%), with sub-samples and analysts accounting for much of the within-lake metric variance. This indicates that a single sampling location is representative and suggests that sub-sample replication and standardisation of analyst procedures should result in increased precision of ecological assessments based upon these metrics.For three phytoplankton metrics being used in the WFD: chlorophyll a concentration, the Phytoplankton Trophic Index (PTI) and cyanobacterial biovolume, >85% of the variance in metric scores was among-lakes and total phosphorus concentration was well supported as a predictor of this variation. Based upon this study, we can recommend that these three proposed metrics can be considered sufficiently robust for the ecological status assessment of European lakes in WFD monitoring schemes.     

Incorporating invasive weeds into a plant indicator method (LakeSPI) to assess lake ecological condition

The use of lake macrophytes for ecological quality assessments usually seeks to indicate the degree of anthropogenic impact, but few of these schemes implicitly consider impacts of alien weeds. LakeSPI (submerged plant indicators) uses indicators of habitat degradation for macrophytes but also incorporates the degree of impact from alien weeds. Application of LakeSPI to 195 New Zealand lakes provided a dataset to examine how component metrics responded over gradients of anthropogenic pressures, and consider whether weed invasion was merely a ‘passenger’ of habitat degradation, or represented an additional pressure. As expected, metrics measuring depth, and diversity of native vegetation negatively correlated with independent measures of lake eutrophy and were also relatively well explained (69–78% variation) by multiple regression with lake and catchment attributes that included proxies for anthropogenic pressure. In contrast, metrics for invasive impact were largely de-coupled from eutrophication, and poorly explained (31%) by the multiple regression. The response of native vegetation metrics to invasive impact measures varied, with the strongest detected interaction relating to native displacement by increased weed occupation of the vegetated zone. Interactions between invasion and lake trophic status were also discerned, with the extent of weed occupation having a more substantial outcome for the presence of charophyte meadows in low productivity lakes than in more productive lakes. These results suggest weed invasion should be considered as an additional source of anthropogenic pressure, and incorporated in macrophyte bioassessment schemes for a more complete differentiation of lake ecological condition.     

Ecological status assessment of European lakes: a comparison of metrics for phytoplankton, macrophytes, benthic invertebrates and fish

Data on phytoplankton, macrophytes, benthic invertebrates and fish from more than 2000 lakes in 22 European countries were used to develop and test metrics for assessing the ecological status of European lakes as required by the Water Framework Directive. The strongest and most sensitive of the 11 metrics responding to eutrophication pressure were phytoplankton chlorophyll a, a taxonomic composition trophic index and a functional traits index, the macrophyte intercalibration taxonomic composition metric and a Nordic lake fish index. Intermediate response was found for a cyanobacterial bloom intensity index (Cyano), the Ellenberg macrophyte index and a multimetric index for benthic invertebrates. The latter also responded to hydromorphological pressure. The metrics provide information on primary and secondary impacts of eutrophication in the pelagic and the littoral zone of lakes. Several of these metrics were used as common metrics in the intercalibration of national assessment systems or have been incorporated directly into the national systems. New biological metrics have been developed to assess hydromorphological pressures, based on aquatic macrophyte responses to water level fluctuations, and on macroinvertebrate responses to morphological modifications of lake shorelines. These metrics thus enable the quantification of biological impacts of hydromorphological pressures in lakes.     

Patterns in freshwater diatom taxonomic distinctness along an eutrophication gradient

1. A variety of species richness measures have been used to assess the effects of environmental degradation on biodiversity. Such measures can be highly influenced by sample size, sampling effort, habitat type or complexity, however, and typically do not show monotonic responses to human impact. In addition to being independent of the degree of sampling effort involved in data acquisition, effective measures of biodiversity should reflect the degree of taxonomical relatedness among species within ecological assemblages and provide a basis for understanding observed diversity for a particular habitat type. Taxonomic diversity or distinctness indices emphasize the average taxonomic relatedness (i.e. degree of taxonomical closeness) between species in a community. 2. Eutrophication of freshwater ecosystems, mainly due to the increased availability of nutrients, notably phosphorus, has become a major environmental problem. Two measures of taxonomic distinctness (Average Taxonomic Distinctness and Variation in Taxonomic Distinctness) were applied to surface sediment diatoms from 45 lakes across the island of Ireland to examine whether taxonomic distinctness and nutrient enrichment were significantly related at a regional scale. The lakes span a range of concentrations of epilimnic total phosphorus (TP) and were grouped into six different types, based on depth and alkalinity levels, and three different categories according to trophic state (ultra‐oligotrophic and oligotrophic; mesotrophic; and eutrophic and hyper‐eutrophic). 3. The taxonomic distinctness measures revealed significant differences among lakes in the three different classes of trophic state, with nutrient‐rich lakes generally more taxonomically diverse than nutrient‐poor lakes. This implies that enrichment of oligotrophic lakes does not necessarily lead to a reduction in taxonomic diversity, at least as expressed by the indices used here. Furthermore, taxonomic distinctness was highly variable across the six different lake types regardless of nutrient level. 4. Results indicate that habitat availability and physical structure within the study lakes also exert a strong influence on the pattern of taxonomic diversity. Overall the results highlight problems with the use of taxonomic diversity measures for detecting impacts of freshwater eutrophication based on diatom assemblages.     

Identifying resilience mechanisms to recurrent ecosystem perturbations

The complex nature of ecological systems limits the unambiguous determination of mechanisms that drive resilience to natural disturbance or anthropogenic stress. Using eight-year time series data from boreal lakes with and without bloom formation of an invasive alga (Gonyostomum semen, Raphidophyceae), we studied resilience of phytoplankton communities in relation to recurring bloom impacts. We first characterized phytoplankton community dynamics in both lake types using univariate metrics of community structure (evenness, species richness, biovolume and Simpson diversity). All metrics, except species richness, were substantially altered and showed an inherent stronger variability in bloom lakes relative to reference lakes. We assessed resilience mechanisms using a multivariate time series modelling technique. The models captured clear successional dynamics of the phytoplankton communities in all lakes, whereby different groups of species were substituted sequentially over the ice-free period. The models also identified that G. semen impacts in bloom lakes were only manifested within a single species group, not across species groups, highlighting the rapid renewal of the phytoplankton communities upon bloom collapse. These results provide empirical support of the cross-scale resilience model. Cross-scale resilience could provide an explanation for the paradox that similar species richnesses are seen in bloom-forming lakes and reference lakes despite the clear difference between the community features of the two different sets of lakes investigated.     

A review of dystrophic lake and pool habitat in Europe: An Irish perspective

Freshwater lakes and pools contained within peatlands are unique habitats that support rare and specialised species. Despite this, these ecosystems have been overlooked in conservation and management practices. One of these habitats, ‘3160 Natural dystrophic lakes and ponds’, is protected under the European Union (EU) Habitats Directive with a concerning proportion of these habitats having an “unfavourable-bad” or an “unfavourable-inadequate” conservation status across Europe. Our current understanding of the key physico-chemical and ecological features of this habitat is inadequate which is hindering the implementation of effective conservation measures. This review summarises the current knowledge of this protected lake habitat as defined under the EU Habitats Directive. With a focus on Ireland, we demonstrate how the current monitoring and assessment methods used to characterise and assess the structure and function and conservation status of this habitat, which relies largely on the use of macrophyte community composition and surrogate physico-chemical data collected under the EU Water Framework Directive, is ineffective. We propose the incorporation of further or alternative ecological metrics including, but not limited to, algae and macroinvertebrates which are needed to improve our understanding of the structure and function of this priority lake habitat. In addition, application of such data via ecological metrics would allow for the quantification of biodiversity and species rarity metrics which would aid in identifying sites of conservation importance.     

中国中东部平原亚热带湿润区湖泊营养物生态分区

湖泊营养物生态分区是实现湖泊分区控制的前提和基础。以中国中东部平原亚热带湿润区为案例区,根据区域特点,从自然地理要素、生态系统和人类活动三方面建立指标体系,对各指标进行归一化得到各指标数据的分值;采用AHP方法确定各指标的权重值,结合各指标分值计算栅格尺度上湖泊营养物生态分区综合评价分值;根据研究区域DEM数据划分小流域,将栅格尺度的湖泊营养物生态分区综合评价分值投影到小流域尺度上,采用双约束空间聚类算法对小流域尺度上湖泊营养物生态分区评价分值进行聚类得到湖泊营养物生态分区结果。结果表明:(1)AHP可以用来确定复杂指标体系中各指标的权重,适合用于确定湖泊营养物生态分区指标体系中各指标的权重;(2)采用双约束空间聚类进行湖泊营养物生态分区,保证了分区结果在空间上的连续性和评价分值上的接近性;(3)根据自然地理条件、土地利用和人类活动强度的不同,可以将中东部平原亚热带湿润区划分为长江中下游平原湖区、湘赣平原丘陵湖区、湘渝山地湖区、四川盆地湖区、川西—大巴山山地湖区5个营养物生态区。     

The influence of variability in species trait data on community‐level ecological prediction and inference

Species trait data have been used to predict and infer ecological processes and the responses of biological communities to environmental changes. It has also been suggested that, in lieu of trait, data niche differences can be inferred from phylogenetic distance. It remains unclear how variation in trait data may influence the strength and character of ecological inference. Using species‐level trait data in community ecology assumes intraspecific variation is small in comparison with interspecific variation. Intraspecific variation across species ranges or within populations may lead to variability in trait data derived from different scales (i.e., local or regional) and methods (i.e., mean or maximum values). Variation in trait data across species can affect community‐level relationships. I examined variability in body size, a key trait often measured across taxa. I collected 12 metrics of fish species length (including common and maximum values) for 40 species from literature, online databases, museum collections, and field data. I then tested whether different metrics of fish length could consistently predict observed species range boundary shifts and the impacts of an introduced predator on inland lake fish communities across Ontario, Canada. I also investigated whether phylogenetic signal, an indicator of niche‐conservativism, changed among measures. I found strong correlations between length metrics and limited variation across metrics. Accordingly, length was a consistently significant predictor of the response of fish communities to environmental change. Additionally, I found significant evidence of phylogenetic signal in fish length across metrics. Limited variation in length across metrics (within species), in comparison with variation within metrics (across species), made fish species length a reliable predictor at a community‐level. When considering species‐level trait data from different sources, researchers should examine the potential influence of intraspecific trait variation on data derived by different metrics and at different scales.     

Diatoms as indicators of water quality in some English urban lakes

SUMMARY. 1. The paper describes diatom communities from a series of linked urban lakes in relation to water chemistry and uses multivariate statistical techniques to show how indicator groups can he defined.
2. Diatoms are classified into ecological groups using two-way species indicator analysis (TWINSPAN). Each ecological group is associated with a specific range of water-quality conditions. The headwater stream environments are differentiated from the lake habitats at level 1. At level 2 of TWINSPAN. the sampling sites are grouped into five ecological groups, according to their water chemistry and irrespective of the time of year.
3. Detrended correspondence analysis (DCA) and principal components analysis (PCA) provide two statistically independent methods of assessing the environmental gradients along which the ecological groups are distributed. The most important physico-chemical parameters are total hardness, specific conductance and pH, followed by phosphates and nitrates.
4. Ecological groups I-V correspond to an environmental gradient ranging from the forested headwaters, which are acidic, of low specific conductance, total hardness and nutrient content, through the urban lakes, which are alkaline and of relatively high total hardness, specific conductance and nutrient content.
5. Twelve site groups are identified at level 3 of TWINSPAN, each of which corresponds to a narrower range of water-quality conditions within the ecological groupings. A specific diatom assemblage is associated with each site group.
6. Benthic diatoms form an integral part of the diatom assemblages found in the water column and this is identified as a topic for further study.     

Effects of Introduced Groundwater on Water Chemistry and Fish Assemblages in Central Florida Lakes

We assessed effects of groundwater pumping to elevate lake levels on lake water chemistry and fish population metrics at seven Florida lakes. Following groundwater pumping, lake level fluctuation was reduced and lake water samples increased in mean pH, total alkalinity, total phosphorus, chloride and Secchi depth compared to historical means, indicating a close resemblance to the chemistry of aquifer water in the region. Fish community metrics from the augmented lakes were compared to 36 non-augmented lakes in Florida. The mean values for catch per unit effort, species richness and biomass of harvestable fishes, determined by electrofishing, were lower in augmented lakes compared to non-augmented lakes. Canonical correspondence analysis (CCA) indicated a high probability of a low abundance of individual species in augmented lakes compared to a majority of non-augmented lakes. The augmented lake with the lowest pumping rate exhibited less of a shift in limnological variables from historical values, and had fish population characteristics more closely resembling those of non-augmented lakes. Thus, reduced volumes of groundwater introduction could lower impacts to limnological and fish population characteristics. Augmentation allows for lakes to be utilized for recreational activities, and without augmentation some lakes in central Florida would likely go dry due to groundwater withdrawals for water supply. Therefore, allowing more natural water level fluctuations and possible reductions in total pumpage are recommended to reduce impacts to limnological and fish population characteristics, while still allowing sufficient groundwater pumping to preserve lake habitats.     

Network parameters quantify loss of assemblage structure in human‐impacted lake ecosystems

Lake biodiversity is an incomplete indicator of exogenous forcing insofar as it ignores underlying deformations of community structure. Here, we seek a proxy for deformation in a network of diatom assemblages comprising 452 species in 273 lakes across China. We test predictions from network theory that nodes of similar type will tend to self‐organize in an unstressed system to a positively skewed frequency distribution of nodal degree. The empirical data reveal shifts in the frequency distributions of species associations across regions, from positive skew in lakes in west China with a history of low human impacts, to predominantly negative skew amongst lakes in highly disturbed regions in east China. Skew values relate strongly to nutrient loading from agricultural activity and urbanization, as measured by total phosphorus in lake water. Reconstructions through time show that positive skew reduces with temporal intensification of human impacts in the lake and surrounding catchments, and rises as lakes recover from disturbance. Our study illustrates how network parameters can track the loss of aquatic assemblage structure in lakes associated with human pressures.     

Zooplankton as indicators in lakes: a scientific-based plea for including zooplankton in the ecological quality assessment of lakes according to the European Water Framework Directive (WFD)

With the implementation of the EU Water Framework Directive (WFD), the member states have to classify the ecological status of surface waters following standardised procedures. It was a matter of some surprise to lake ecologists that zooplankton were not included as a biological quality element (BQE) despite their being considered to be an important and integrated component of the pelagic food web. To the best of our knowledge, the decision of omitting zooplankton is not wise, and it has resulted in the withdrawal of zooplankton from many so-far-solid monitoring programmes. Using examples from particularly Danish, Estonian, and the UK lakes, we show that zooplankton (sampled from the water and the sediment) have a strong indicator value, which cannot be covered by sampling fish and phytoplankton without a very comprehensive and costly effort. When selecting the right metrics, zooplankton are cost-efficient indicators of the trophic state and ecological quality of lakes. Moreover, they are important indicators of the success/failure of measures taken to bring the lakes to at least good ecological status. Therefore, we strongly recommend the EU to include zooplankton as a central BQE in the WFD assessments, and undertake similar regional calibration exercises to obtain relevant and robust metrics also for zooplankton as is being done at present in the cases of fish, phytoplankton, macrophytes and benthic invertebrates.     

Impacts of invasion by <Emphasis Type="Italic">Dreissena polymorpha</Emphasis> (Pallas, 1771) on the performance of macroinvertebrate assessment tools for eutrophication pressure in lakes

Aquatic ecosystems are experiencing increasing disturbance from multiple stressors caused by anthropogenic activities. The potential for multiple stressors to modify each others’ impacts is not well understood. Legislation such as the EU Water Framework Directive (WFD) requires the development of tools to assess human impacts in aquatic systems that incorporate ecological elements, such as macroinvertebrates. Nutrient enrichment and invasive species are major threats to freshwater systems. The invasive zebra mussel Dreissena polymorpha is a conspicuous invader in freshwater aquatic systems in Europe and North America, and has been linked to drastic changes in macroinvertebrate communities and lake ecology. In 31 lake sites varying in nutrient pressure and in the presence or absence of D. polymorpha we tested three ecological quality assessment tools based on macroinvertebrate assemblages (% Sensitive Taxa to Total Phosphorus (TP), TP Score and Indicator Taxa Metric) and two basic ecological metrics. There were highly significant changes in macroinvertebrate diversity, structure, and composition associated with the invasion by D. polymorpha. While the three metrics performed consistently well in non-invaded systems, they lost explanatory power for eutrophication pressure in invaded systems. Our results suggest that metrics may need to be developed separately for invaded and non-invaded systems, and that the interaction between alien species and nutrient enrichment requires further investigation.     

Correlation of surface sediment diatoms with the present lake water pH in 28 Algoma lakes,Ontario, Canada

The surface sediment diatom analysis of 28 Algoma lakes (pH 4.40–8.13) indicates that even though each lake has a widely different aquatic environment and characteristic diatom assemblage, a definite relationship exists between the lake water pH and their diatom assemblages. In the acidic lakes acidobiontic and acidophilous diatom species predominate whereas in circumneutral and alkaline lakes circumneutral and alkaliphilous diatoms were most common. Cluster analysis of the pH indicator diatom assemblages grouped the study lakes into three distinct cluster groups. These groups also closely corresponded to lake water pH. On the basis of published ecological information as well as their presence in our study lakes, the pH indicator status of a number of diatom taxa have been discussed. A detailed listing of the diatom taxa identified and their pH indicator status is provided in order to facilitate their use in future diatom-inferred pH studies.     

Variability in the functional role of Arctic charr Salvelinus alpinus as it relates to lake ecosystem characteristics

This study investigated how dietary habits vary with lake characteristics in a fish species that exhibits extensive morphological and ecological variability, the Arctic charr Salvelinus alpinus. Iceland is a hotspot of geological activity, so its freshwater ecosystems vary greatly in physical and chemical attributes. Associations of dietary items within guts of charr were used to form prey categories that reflect habitat-specific feeding behavior. Six prey categories were defined and dominated by snails (Radix peregra), fish (Gasterosteus aculeatus), tadpole shrimp (Lepidurus arcticus), chironomid pupae, pea clam (Pisidium spp.), and the cladoceran Bosmina sp.. These reflected different combinations of feeding in littoral stone, offshore benthic, and limnetic habitats. Certain habitat-specific feeding strategies consistently occurred alongside each other within lakes. For example, zooplanktivory occurred in the same lakes as consumption from offshore habitats; piscivory occurred in the same lakes as consumption from littoral benthic habitats. Redundancy analyses (RDA) were used to investigate how lake environment was related to consumption of different prey categories. The RDA indicated that piscivory exhibited by Arctic charr was reduced where brown trout were abundant and lakes were shallow, greater zooplanktivory occurred at lower latitudes and under decreased nutrient but higher silicon dioxide concentrations, and benthic resource consumption was associated with shallower lakes and higher altitudes. This study showed that trends previously observed across fish species were supported at the intraspecific level, indicating that a single species with flexible dietary habits can fill functional roles expected of multiple species in more diverse food webs.     

长江中下游四大淡水湖生态系统完整性评价

长江中下游地区是我国淡水湖泊集中分布区域,研究该区域湖泊生态系统完整性对于湖泊生态系统保护和恢复具有重要意义。物理、化学和生物完整性指标已经广泛应用于河湖生态系统健康评价,但是缺少物理、化学和生物完整性的综合评价方法。以历史调查状况为主要参照系统,构建了基于物理、化学和生物完整性的多参数湖泊完整性综合评价指标体系,结合近年来长江中下游四大淡水湖(洞庭湖、鄱阳湖、巢湖、太湖)生态系统调查数据,对四大淡水湖生态系统完整性进行了评价。结果表明,洞庭湖、鄱阳湖、巢湖和太湖的综合得分分别为66、71、57和57。根据评价等级划分标准,洞庭湖和鄱阳湖生态系统完整性状况都达到"好"的等级,而巢湖和太湖则处于"一般"等级;结果显示,该指标能够表征人类活动对于湖泊生态系统完整性不同方面的干扰,且能够反映四大淡水湖生态系统完整性历史变化状况。因此,该方法可以作为长江中下游淡水湖泊生态系统完整性综合评价的工具并能够为湖泊生态系统的保护和恢复提供科学支撑。     

Relevance of abiotic criteria used in German lake typology for macroinvertebrate fauna

For lake characterisation, top-down typologies are mostly used throughout Europe, including type criteria such as climate, lake area, catchment geology and conductivity. In Germany, a lake typology was applied comprising ecoregion, calcium concentration, Schindler’s ratio, stratification type and residence time. However, the relevance of these criteria for the macroinvertebrate fauna has not been conclusively demonstrated till now. Benthic invertebrate community data and related environmental parameters of pristine or near-pristine lakes in Germany were analysed by multivariate analysis techniques to elucidate which environmental parameters are reflected by invertebrate composition. Moreover, benthic invertebrate data were transformed to metrics expressing ecological attributes and species richness (summarising functional composition, diversity and sensitivity measures). Multivariate statistics were used to test whether information relevant to ordination was lost and whether variation decreases using metrics which combine data with ecological attributes. Analysis of lake-type criteria revealed that ecoregions and prevailing substrates were characterized by different taxonomic compositions of macroinvertebrates. In addition, a relationship was found between community composition and lake size. Creating a novel bottom-up lake typology based on ecoregions, lake size and prevailing substrate gives better separation of distinct macroinvertebrate communities and a higher level of homogeneity within groups compared to top-down typology or single environmental parameters alone, both on species and metrics data. Despite some data variation due to methodological differences (e.g. different sampling and sorting techniques) and interannual and seasonal variation in the data set, NMDS ordination presented well-separated groups of bottom-up lake types. Lake types were more precisely separated by species data than by metric data in both top-down and bottom-up typology. However, as information loss from species lists to calculated metrics is marginal, type-specific benthic invertebrate assemblages are reflected both on the species level and on the metric level. Species and metric data are both suitable for data ordination, while single environmental parameters affecting macroinvertebrate composition can best be obtained using metrics.     

The influence of anthropogenic shoreline changes on the littoral abundance of fish species in German lowland lakes varying in depth as determined by boosted regression trees

Residential development on lake shores is regularly associated with the conversion of natural littoral habitats to riprap, sheet piles, beaches, parks, or marinas. The subsequent loss of littoral vegetation induces a decline of structural diversity and impacts littoral fish communities. These impacts may be shaped by lake morphology. Using boosted regression trees (BRT) to relate fish abundance data from 57 north-east German lowland lakes to various factors characterizing trophic state, lake morphology, and shoreline development, we investigated the response of 11 fish species to shoreline development. The analyses revealed that mean depth followed by trophic level and shoreline length (SL) contributed most in explaining littoral fish abundance. BRT models built for deep and shallow lakes separately confirmed that primarily trophic level and SL influenced fish abundance but that littoral vegetation was relatively more important in deep compared to shallow lakes, indicating that the effects of shoreline development may be more pronounced in deep lakes where the littoral makes up a smaller proportion of the lake area as compared to shallow lakes. The BRT further demonstrated species-specific responses to shoreline degradation, indicating that the reliability of ecological quality assessments of lakes can be improved by applying separate metrics for individual species.     

Austrian Index Macrophytes (AIM-Module 1) for lakes: a Water Framework Directive compliant assessment system for lakes using aquatic macrophytes

We describe a new macrophyte-based assessment tool for Austrian lakes elaborated according to the requirements of the European Water Framework Directive. Data from 38 out of 45, WFD-relevant (≥50 ha) lakes in Austria collected with the help of a new mapping procedure form the basis for a macrophyte-based lake typology and the definition of reference conditions. Module 1 of the Austrian Index Macrophytes (AIM) focuses on the assessment of trophic state and general impairment of lakes. Several metrics were developed and applied in combination with existing indices to classify lakes into five ecological status classes. The metric “vegetation density” focuses on the overall abundance of macrophytes. Since the lower limit of the macrophyte vegetation in lakes is mainly regulated by the water transparency, the metric “vegetation limit” is closely related to the trophic state of the lake. In deep lakes, macrophytes normally form different vegetation zones. As a result of alteration of the shoreline, artificial water level fluctuations or wave action and even eutrophication, specific zones can be missing. The metric “characteristic zonation” helps to check, if all type-specific vegetation zones are present. The metric “trophic indication” uses the Macrophyte Index after Melzer (Hydrobiologia, 395/396: 181–190, 1999). This term indicates the lake trophic state but, in contrast to the metric “vegetation limit”, it tends to show not only the trophic state of the water column but also, in particular, the nutrient conditions in the sediment. With the help of the metric “species composition,” the species spectrum and the species abundances of the current transect are compared with the species composition at reference sites. The similarity of the datasets is measured as Bray–Curtis Distance (Beals, Advances in Ecological Research, 14: 1–55, 1984). The established metrics cover different aspects of macrophyte vegetation and allow analysing the prevailing pressure. Since the different metrics have a different temporal response to eutrophication and reoligotrophication, additional information on the current state of the lake in relation to these processes can be derived. The successful application of AIM-Module 1 is presented for two Austrian lakes and discussed in relation to other assessment tools. Guest editors: P. N?ges, W. van de Bund, A.C. Cardoso, A. Solimini & A.-S. Heiskanen Assessment of the Ecological Status of European Surface Waters     

Consideration of Geography and Wetland Geomorphic Type in the Development of Great Lakes Coastal Wetland Bird Indicators

We examined how geographic distribution of birds and their affinities to three geomorphic wetland types would affect the scale at which we developed indicators based on breeding bird communities for Great Lakes coastal wetlands. We completed 385 breeding bird surveys on 222 wetlands in the US portion of the basin in 2002 and 2003. Analyses showed that wetlands within two ecoprovinces (Laurentian Mixed Forest and Eastern Broadleaf Forest) had different bird communities. Bird communities were also significantly different among five lakes (Superior, Michigan, Huron, Erie, and Ontario) and among three wetland types (lacustrine, riverine, barrier-protected). Indicator values illustrated bird species with high affinities for each group (ecoprovince, lake, wetland type). Species with restricted geographic ranges, such as Alder and Willow Flycatchers (Empidonax alnorum and E. traillii), had significant affinities for ecoprovince. Ten bird species had significant affinities for lacustrine wetlands. Analyses on avian guild metrics showed that Lake Ontario wetlands had fewer long-distant migrants and warblers than other lakes. Numbers of short-distant migrants and total individuals in wetlands were higher in the Eastern Broadleaf Forest ecoprovince. Number of flycatchers and wetland obligate birds were not different among provinces, lakes, or wetland type. One potential indicator for wetland condition in Great Lakes wetlands, proportion of obligate wetland birds, responded negatively to proportion of developed land within 1 km of the wetland. We conclude that, although a guild approach to indicator development ameliorates species-specific geographic differences in distribution, individual species responses to disturbance scale will need to be considered in future indicator development with this approach.