Assessing ecological quality of shallow lakes: Does knowledge of transparency suffice?

The European Water Framework Directive (WFD) requires that all aquatic ecosystems in their member states should reach ‘good’ ecological quality by 2015. To assess ecological quality, the WFD requires the definition of reference conditions using biological, physical and chemical indicators and the assignment of each water body to one of five quality classes using these indicators. Elaborate assessment schemes using large sets of variables are now being developed. Here we address the question whether all this is really needed and what the simplest assessment approach would be for the case of shallow lakes. We explore the relationships between the quality class assigned to a lake by experts in shallow lake ecology and a rich set of biological, physical, and chemical data. Multinomial logistic regression analyses were carried out based on data from 86 shallow lakes throughout Europe that were sampled in 2000 and/or 2001. Ecological quality of shallow lakes judged by experts was strongly correlated to physical and chemical variables associated with light regime and nutrients and much less to biological variables.Our regression model showed that ecological quality of this set of shallow lakes judged by experts could be predicted quite well from water transparency expressed as Secchi depth and that other variables did not contribute to it significantly. According to the WFD, lakes should at least have a ‘good’ ecological quality. Quality judged by experts and predicted quality were similar for 78% of the lakes with respect to meeting this standard. As a cautionary note we stress that Secchi depth alone will be a less useful indicator if effects of stressors other than eutrophication (e.g. lake acidification and toxic pollution) are to be considered.     

Potential conflicts between environmental legislation and conservation exemplified by aquatic macrophytes

It is important that legislation on water quality issues of freshwaters is not in conflict with nature conservation purposes. So far, it is however unknown how the assessment of ecological status according to for example the Water Framework Directive (WFD) of the European Community relates to the status of lakes according to the Habitat Directive (HD) or to national environmental objectives including, e.g., the protection of important wetland areas and red-listed species. We used lake macrophyte classification schemes of Norway, Sweden, and Finland and a total of 1,014 lakes to evaluate the possible conflict between these directives and national legislation. The classification schemes represent mainly trophic indices penalizing lakes with elevated phosphorous concentrations. In general, high ecological status according to the WFD did not mean high number of red-listed species or high status according to the HD or other national environmental objectives. In Sweden 78%, in Norway 47%, and in Finland 29% of lakes with red-listed species were classified as lakes of moderate or worse ecological status based on the macrophyte classification scheme. These lakes thus did not fulfill the demands of the WFD. Restoration of surface water toward fulfilling the demands requires in practice a reduction of the trophic status. This might potentially result in for example the loss of red-listed species. To avoid such potential conflicts, we primarily suggest revising the national quality assessment systems toward implicitly incorporating nature conservation aspects, e.g., the number of red-listed species in a multi-metric assessment system.     

Biological indicators track differential responses of pelagic and littoral areas to nutrient load reductions in German lakes

External nutrient loading was reduced over the past decades as a measure for improving the water quality of eutrophic lakes in western Europe, and has since been accelerated by the adoption of the European Water Framework Directive (WFD) in 2000 (EC, 2000). A variety of eutrophication-related metrics have indicated that the response of biological communities to this decreased nutrient loading has been diverse. Phytoplankton, a major component of the pelagic community, often responded rapidly, whereas a significant delay was observed for submerged macrophytes colonizing littoral areas. In this study we tested whether assessment methods developed for phytoplankton and macrophytes in lakes during Germany's implementation of the WFD reflect this differential response. An assessment of 263 German lakes confirmed that a lower ecological state was recorded when based on the biological quality element (BQE) for macrophytes than the BQE for phytoplankton during the investigated period (2003–2012). On average, lakes had a moderate ecological status for both phytoplankton and macrophyte BQEs, but differences of up to three classes were observed in single cases. Long-term data were available for five lowland lakes subject to strong reductions in phosphorus loading. Their phytoplankton-based assessments indicated a constant improvement of the ecological status in parallel to decreasing water phosphorus concentrations. In contrast, macrophyte-based assessments indicated a 10–20 year delay in their ecological recovery following nutrient load reduction. This delay was confirmed by detailed data on the temporal development of macrophyte species diversity and maximum colonization depths of two lakes after nutrient load reduction. We conclude that the available WFD assessment methods for phytoplankton and macrophyte BQEs are suitable to track the differential response of pelagic and littoral areas to nutrient load reductions in German lakes.     

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.     

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.     

Biodiversity in eutrophicated shallow lakes: determination of tipping points and tools for monitoring

Nutrient-rich freshwater ecosystems are generally considered as having low ecological quality and low associated biodiversity. In such systems we analysed the effects of water quality on biodiversity of several species groups, to determine tipping points and tools for monitoring. We investigated the water quality of 99 eutrophic and hypertrophic shallow lakes with extensive fish culture during a 3-year study, through the measures of physico-chemical parameters, phytoplankton biomass and structure. In a second step, we related the water quality with richness of aquatic plants, macroinvertebrates and dragonflies. With concentrations of chlorophyll-a above 30 or 70 μg l^?1, shallow lakes are normally classified, respectively, in a poor or bad ecological state. However, our results show that chlorophyll-a concentrations up to 78 μg l^?1 could be found together with relatively high species or family richness of aquatic plants, invertebrates and dragonflies. We identified most tipping points with 50–60 μg l^?1 of chlorophyll-a, values above which a significant decrease of species diversity was found. For monitoring of these shallow lakes we propose to use chlorophyll-a concentrations in combination with water transparency during spring. These parameters are easily applicable and cheap and they yield a good forecast of the biodiversity for the species groups studied.     

A fish-based index for the assessment of the ecological quality of temperate lakes

A fish – based index for the assessment of the ecological quality of natural temperate lakes was developed, in accordance to the requirements of the Water Framework Directive (WFD) 2000/60/EC. As a case study, 11 natural lakes located at northern and western Greece were selected. Fish surveys were conducted during mid summer to mid autumn in 2010, 2011 and 2012 using Nordic gillnets and electrofishing. Environmental parameters and anthropogenic pressures were assessed for each lake. Fish species richness, abundance, trophic, reproductive and habitat functional guilds were used for extracting a set of 107 metrics, meeting the requirements of the WFD. All metrics were initially tested as candidates for the index development. A stepwise linear regression of each metric against environmental parameters (lake area, altitude, maximum depth, alkalinity) and anthropogenic pressures (drainage area covered by non-natural land uses – NNLC, water total phosphorus concentrations – TP, Lake Habitat Modification Score – LHMS) was initially conducted for ensuring pressure-response relationships. Reference conditions for each lake were estimated by the hindcasting procedure and the ecological quality for each lake was expressed as the ecological quality ratio (EQR) by a value ranging from 0 (poor quality) to 1 (excellent quality). Two fish fauna metrics, the relative numerical abundance of introduced species (Introduced_a) and the relative biomass of omnivorous species (OMNI_b) were finally extracted as the most significant, responding to LHMS and TP, respectively. The final index was expressed as the mean values of the EQRs of these two metrics. The multimetric fish index presented herein could serve as a tool for assessing the ecological quality of natural lakes at broad geographical scale and generally, in the Mediterranean temperate lakes with similar hydromorphological characteristics.     

Central European water quality indices applied to long-term data from peri-alpine lakes: test and possible improvements

We tested the applicability of two available Water Framework Directive (WFD) compliant phytoplankton indices on three large peri-alpine lakes to analyze their suitability for trophic classification. We show that the indices vary in their final resulting Ecological Quality Ratios (EQRs) and are only appropriate to roughly distinguish lakes of different water quality according to OECD criteria (OECD, 1982). Annual mean TP concentration in Lake Geneva was 0.03 mg l^?1 in 2006 (Lazzarotto &; Rapin, 2007), which marks mesotrophic conditions. According to the tested indices, the lake is of ‘good’ (0.60–0.80) quality after the German WFD method (PSI) and of ‘moderate’ quality according to the Austrian WFD method (BI). We prove that the way how to derive the per annum value of the metric ‘Brettum Index’ (BI) in the Austrian WFD method significantly influences the resulting index and the scatter of long-term data. We focused on improvement strategies for this index in terms of calculation and sampling frequency. Contrary to the tested bin, the modified index presents no significant differences between four and six sampling dates per year. In order to improve the significance of the available indices, we propose to modify the way of per annum index calculation for the Austrian WFD method as well as to focus on species composition to achieve a high relative proportion of indicator species. A phytoplankton index alone may not be sensitive enough to track the changes that occur within a lake. The results confirm the need to take into account other biological elements such as fish, macrophytes, attached diatoms and macrozoobenthos as suggested by the WFD.     

Effects of benthic filamentous algae on the sediment–water interface in an acidic mining lake

Natural alkalinity generation by microbial sulphate reduction in acidic lakes is usually inhibited by the low pH and a low primary production which results in a lack of suitable organic carbon sources. In some acidic mining lakes mass developments of filamentous benthic algae occur. The effects of this periphyton layer on the biogeochemistry of the sediment–water interface were investigated by in situ microsensor measurements and laboratory incubations in Mining Lake Grünewalder Lauch (Germany). Microsensor measurements showed that the oxic–anoxic boundary was located in the periphyton layer and was moving up and down depending on light triggered photosynthesis. The sediment itself was permanently anoxic. The diurnal redox shift and the maintenance of neutral conditions in the periphyton layer lead to an effective precipitation of iron and phosphorus. Under the periphyton layer very high sulphate reduction rates up to 265 nmol cm⁻³ d⁻¹ were measured in the sediment. These are the highest rates reported for mining lakes so far. The microbial activity was high enough to keep the pH in the surface sediment neutral and contributed to natural alkalinity production. Handling editor: L. Naselli-Flores     

Effects of counting variances on water quality assessments: implications from four benthic diatom samples,each counted by 40 diatomists

The European Water Framework Directive (EU WFD) aims to improve and maintain the water quality of lakes and rivers. Diatoms play an important role for implementing the EU WFD as they are widely used to assess water quality. To asses and use diatom-based evaluations in practice, it is essential to know and to minimize the analyst-dependent variability of the primary diatom results. We compare the counting results of benthic diatoms from two river and two lake samples as identified by 40 participants of the first German benthic diatom intercalibration exercise. Differences among participants and auditors are calculated with the Bray-Curtis distance, and similarities are graphically displayed by detrended correspondence analyses. Additionally, this study identifies the effects of counting variances on the ecological water assessment with the German PHYLIB method for implementing the EU WFD using the above dataset. Counting result differences among participants may have a significant impact on the assessed water quality. Some taxonomically problematic taxa do not have indicator values (no impact), sometimes, several taxonomic mistakes counterbalance each other during assessment (no or minor impact), and sometimes, taxonomic differences greatly influence the assessment due to highly deviating taxon abundances and/or strongly differing indicator values between mistaken taxa. Intercalibration exercises promote discussion about taxonomy, identify problematic taxa, and harmonize taxonomic concepts among diatomists. Thus, the shown analyst-induced variability of diatom counts may be reduced with an intercalibration exercise, thereby further refining the accuracy of water quality assessments.     

Use of marker pigments and functional groups for assessing the status of phytoplankton assemblages in lakes

Phytoplankton is a key biological quality element for the establishment of the Water Framework Directive (WFD) ecological status in reservoirs and lakes. In freshwaters, inverted microscope examination is the traditional standard method for estimating phytoplankton and assessing taxonomic composition. Based on the enumeration of algal units and measurements for biovolume calculation, this technique is cumbersome and time-consuming. In large monitoring programmes, such as the application of the WFD in lakes and reservoirs, chemotaxonomy (HPLC pigment analysis and CHEMTAX treatment) is ideally suited as an alternative method because it allows the rapid processing of large numbers of samples from numerous locations and depths, thereby providing ideal temporal and spatial resolution. The low taxonomical detail obtained by HPLC and CHEMTAX (phytoplankton classes or phyla) can easily be overcome by a rapid inverted microscope screening with identification of the dominant species. Combining HPLC and microscopy provides a useful method for monitoring phytoplankton assemblages, which can be used to implement the WFD with respect to phytoplankton. Here, we present the application of a method combining marker pigments and microscopy to phytoplankton samples from 12 Belgian reservoirs. This method substantially reduced the workload and enabled us to assess the status of the phytoplankton assemblage in these lakes. The method complies with the WFD, as it takes into account taxonomic composition, assesses abundance and biomass of the phytoplankton taxa, and easily detects blooms. Additionally, a set of templates of probability of occurrence of phytoplankton functional groups at the maximal ecological potential for reservoirs from the Central/Baltic region is presented, based on reference conditions defined for natural lakes from other regions.     

Ecological classification of lakes: Uncertainty and the influence of year-to-year variability

Regular monitoring of lakes is important to determine their ecological state and development and of key significance when deciding whether action should be taken to improve their quality, for instance by reducing the external loading of nutrients. Imprecise or inadequate knowledge of the ecological state increases the risk of misclassification and of wrong management decisions. Based on Danish lake data, we aimed to determine temporal variations, in particular natural year-to-year differences, and to describe the uncertainty in assessing the ecological state of lakes. We analysed environmental data from ca. 350 Danish lakes (1100 lake years), including three case studies, with long-term data series (up to 24 years), with no significant changes in external nutrient loading. We used summer means of selected water chemical variables, phytoplankton and submerged macrophytes as indicators of ecological state and found considerable variations in all indicators, which could not be ascribed alone to meteorological variation. In shallow lakes, chlorophyll a concentrations exhibited large year-to-year variations, especially at TP ranging between 0.05 and 0.15 mg L⁻¹ where the lakes may shift between a macrophyte- and a phytoplankton-dominated state. For example, chlorophyll a varied by a factor 5–10 between years and was particularly low when submerged macrophyte coverage exceeded 20% compared with lakes without macrophytes. Use of a multimetric index including four phytoplankton indicators reduced the coefficient of variation. Generally, the 95% confidence interval of ecological classification was approximately 50% lower when the assessment of ecological state was based on 4–5 years’ measurements than if based on only one year's measurements. Knowledge and awareness of the uncertainty of indicators used in ecological classification are highly relevant for lake managers and policy makers when defining efficient monitoring and restoration strategies.     

Assessment of eutrophication pressure on lakes using littoral invertebrates

Until the E.U. Water Framework Directive listed benthic invertebrates as a biotic element to be used for ecological classification of lakes, techniques for the assessment of the response of littoral invertebrates to anthropogenic pressures were extremely limited compared with those of rivers and lake profundal zones. We describe here the development of an ecological classification model based on changes of littoral invertebrate assemblages across a gradient of eutrophication, which is the most widespread anthropogenic pressure on lakes across Europe. The model comprises three derived parameters, two of which were developed from taxon-specific optima along a total phosphorus gradient calculated using canonical correspondence analysis, and the third based on invertebrate abundance. Combining the parameter metrics, we can estimate the ecological quality ratio (EQR), relative to those from paleolimnologically-confirmed reference lakes. The model was tested using independent samples collected from both hard and soft substrata and across two seasons from 45 lakes, comprising three alkalinity groups (n = 15 in each), and across gradients in water column total phosphorus concentrations. For hard substrata, EQRs were related consistently and highly significantly to water column concentrations of total phosphorus, accounting for the majority of the variance in every alkalinity group. For samples taken from soft substrata, a significant relationship was found only for high alkalinity lakes, accounting for a moderate proportion of the variability in water column total phosphorus concentrations. Our results compare highly favourably with those from other aquatic ecological assessment methods, irrespective of the faunal or floral group upon which they are based, demonstrating that littoral invertebrate assemblages can provide a statistically robust prediction of nutrient status when samples are collected from hard substrata. While the method was developed specifically to assess nutrient pressures on littoral invertebrates, many lakes are subject to multiple pressures. The development of classification models that incorporate multiple pressures presents a particularly significant challenge for the implementation of the Water Framework Directive, requiring both reliable identification of minimally-impacted reference states and incorporation of pressures that are unlikely to interact in predictable ways.     

The role of phytoplankton diversity metrics in shallow lake and river quality assessment

Ecological water quality problems are frequently connected to increment of phytoplankton productivity and overdominance of some phytoplankton species. Metrics that show monotonously increasing or decreasing tendencies along stressor gradients is recommended for ecological state assessment. Diversity metrics are influenced by various physical disturbances and show high within-year variability; thus, there is no agreement on the usefulness of these metrics as state indicators.To test the usefulness of phytoplankton diversity in ecological state assessment we investigated the productivity–diversity relationships for lakes and rivers in the Carpathian Basin (Hungary). We demonstrated that the shape of productivity–diversity relationship depends on the investigated water body type. Regarding lakes, hump-shaped relationship was found for all computed metrics. Parallel with the increase in phytoplankton productivity values, diversity metrics showed monotonously increasing tendencies in rhithral and decreasing tendencies in large potamal rivers. We found no systematic relationship in the case of small lowland rivers.Changes of diversity metrics calculated for species and functional groups showed similar tendencies within the types, only the slopes of regression lines differ each other.The use of diversity metrics as ecological state indicators should be restricted to water body types where diversity decreases or increases monotonously with phytoplankton biomass. Regarding the lakes the use of diversity metrics is not recommended for ecological state assessment. In rhithral and large potamal river assessment, application of diversity metrics should be strongly considered. We demonstrated that diversity metrics can be useful components of multimetric indices proposed to use by the Water Framework Directive.     

Using chlorophyll a and cyanobacteria in the ecological classification of lakes

Phytoplankton is one of the four key biological quality elements to be used in the ecological classification of lakes in Europe according to the Water Framework Directive (WFD). Chlorophyll a (Chla) has so far been used as the main – and sometimes only – metric to define class boundaries. Chla is often a key metric for lake managers and is used to determine whether and how much action should be taken to reduce the external nutrient loading. In this paper we present the analyses of empirical relationships between nutrient (total phosphorus, TP, total nitrogen, TN) concentrations versus Chla and the proportion of cyanobacteria of total phytoplankton biomass based on data from 440 Danish lakes (1800 lake years). These data represent one eco-region sampled using standardised methodology, thereby minimising the heterogeneity often seen in large datasets. Sampling frequency is important for the precision by which Chla can be determined and the precision is always low with less than 15 summer measurements. As expected Chla was related significantly to TP, but the variability was high, with R² reaching only 0.47, 0.59 and 0.61 in shallow, stratified and siliceous lakes, respectively, based on summer averages. The correlation was strongest in late summer (R² up to 0.80) and weak in winter. Chla is also related to TN, but the correlation coefficients were low throughout the year, and in a multiple regression with TP included, TN only added little to the total variability. Similarly, the proportion of cyanobacteria increased significantly with TP, but the correlation was weak. Seasonal and yearly data from five lakes with relatively stable TP show considerable variations in Chla and cyanobacteria abundance during a 20-year monitoring period. It is concluded that despite clear nutrient phytoplankton relationships it will be difficult to define the proposed WFD ecological classes – particularly regarding cyanobacteria. To ensure a high degree of certainty for meeting a specific water quality threshold, lake managers must reduce the external phosphorus loading more strongly than expected from existing simple empirical external loading-inlake TP–Chla relationships.     

Review of rotifers and crustaceans in highly acidic environments of pH values ≤3

A review of the literature on rotifers and crustacean zooplankton in highly acidic environments revealed that data from eleven aquatic environments on three continents (America, Europe, Japan) with a pH 3 are available. Seven sites are influenced by volcanism or weathering processes in the catchment area, four others originated from human mining activities. Species richness was generally low. Only 16 species are found and 1–11 species are reported for each area. These studies clearly show that small littoral or benthic rotifers predominate over crustaceans under highly acidic conditions. In the Lusatian mining area (Germany), all lakes are colonized by zooplankton, even the most acidic one with a pH of 2.3. The core community consists of the rotifers Cephalodella hoodi, C. gibba, Elosa worallii and Rotaria rotatoria, with C. hoodi and E. worallii the most abundant. Larger species, such as the rotifer Brachionus sericus or the cladoceran Chydorus sphaericus, occur at a pH close to 3. A similar pattern is reported from acidic mining lakes in Illinois, U.S.A. Many of these species can also be found in less acidic softwater or even alkaline environments due to the tolerance of a broad range of pH values. Elosa worallii and Brachionus sericus are probably the most acidophilic rotifer species, though at least the latter can also grow at neutral pH in the laboratory. Clear understanding of the pH limits of B. sericus in nature may also have been complicated by the fact that it has probably in the past been wrongly named as B. urceolaris (phenotype `sericus'). The typical B. urceolaris cannot tolerate extremely low pH. Overall, generalist species with a worldwide distribution seem to play the major role in the colonization of anthropogenic highly acidic lakes.     

Towards ecological goals for the heavily modified lakes in the IJsselmeer area,The Netherlands

The European Water Framework Directive (WFD) obliges EU member states to define ecological goals for water bodies and, if necessary, to take measures to achieve these goals by 2015. The goals and measures for the water bodies in the IJsselmeer area of The Netherlands are elaborated in this study, following an approach described by Irmer &; Pollard (2006, Alternative methodology for defining Good Ecological Potential (GEP) for Heavily Modified Water Bodies (HMWB) and Artificial Water Bodies (AWB). ECOSTAT). With the closure of the Afsluitdijk in 1932, the former Southern Sea estuary was transformed into the freshwater Lake IJsselmeer. Subsequently, a string of so-called border lakes and Lake Markermeer were created by land reclamation projects and the construction of dams. These alterations serve safety, provide drinking water supplies and created agricultural land. Owing to the change in category, the lakes are by (WFD) definition heavily modified. A natural lake rather than an estuary will be the starting point for determining ecological potential. However, damming and fixing the water table prevented the development of emergent vegetation and caused steep water-land gradients. The Maximum Ecological Potential includes the effect of these hydromorphological changes after all mitigation measures have been considered. Other pressures on the lakes are high nutrient loads, which cause phytoplankton blooms, the disappearance of aquatic macrophytes and intensive fishery, which overexploites the pikeperch and eel populations and causes indirect negative effects on water quality. Good Ecological Potential for these lakes is derived by estimating the effects of all effective hydromorphological measures that have no significant negative impact on existing functions or the wider environment, and the effects of all other measures. The suggested main measures are: construction of fish passages, adaptation of shore-lines, wind sheltered areas, reduction of nutrient load, reduction of fishery pressure and reduction of the bream stock. The effects of these measures are calculated from multivariate analyses that establish the relationships between (a) nutrients and chlorophyll-a, (b) chlorophyll-a and water transparency, (c) water transparency, depth distribution and vegetation coverage and (d) vegetation coverage and fish community. The proposed goals will be refined using new scientific insights and further discussions with stakeholders, and will finally be reported in the River Basin Management Plan 2009. It is expected that exemptions will be used for a phased achievement of the objectives.     

Transitional and coastal waters ecological status assessment: advances and challenges resulting from implementing the European Water Framework Directive

The derivation, performance, sensitivity and inherent uncertainty of ecological quality indicators have become major topics in developing tools for the management of marine, transitional and coastal waters. In reviewing the advances in these waters, related to an ecological status assessment, we show the future challenges to be addressed within the European Water Framework Directive (WFD). Using new analyses carried out under the research project ‘Water Bodies in Europe: Integrative Systems to Assess Ecological status and Recovery’, we provide a complete set of assessments for the biological quality elements (BQEs) (phytoplankton, macroalgae-seagrasses, macroinvertebrates and fish) to be assessed, as well as the validation of existing indicators and multimetric indices and, in some cases, the development of new assessment indices. We show that these indices respond differently to different human pressures and they each have challenges in defining reference conditions against which future changes are judged. In investigating good ecological potential, as the response to heavily modified water bodies, we show that there are flaws in the Directive, not least in its definitions. Our analyses have also focussed on uncertainty in using the indices and we emphasise the problems of defining ecological class boundaries based on indices which themselves may be combined indices (multimetrics). The analysis shows that some of those multimetrics are redundant and/or are inter-correlated and thus may reduce the sensitivity in defining ecological class boundaries. If this is related to the drivers-pressures-state change-impacts-response approach then there are lessons for management measures aimed at achieving good ecological status and even the potential for legal challenges to decisions based on uncertain indices under the WFD. Hence, we conclude the continued need for advances in assessing pressures and gradients, and defining reference conditions for state change, index development, impact assessment and the validation of indices for each BQE.