First steps in the Central-Baltic intercalibration exercise on lake macrophytes: where do we start?

The Water Framework Directive (WFD 2000) defines macrophytes as one of the biological groups required for the ecological assessment of European surface waters. Several indices for macrophyte assessment have been proposed or are currently in use by different European states. As a first step towards performing an intercalibration of these indices a common dataset was developed. This dataset contains abundance data on 789 macrophyte species from 316 different lake sites in ten European countries. Various common species and genera were identified as indicators of reference and impacted conditions within the dataset. Cluster analysis of macrophyte data, supported by non-metric multidimensional scaling, indicated that clusters formed were more reflective of their source country rather than lake type. This might be caused by differences in regional climate, biogeography, monitoring techniques, or a combination of these factors. A total of six national indices were applied to assign quality classes to the lakes. However, this produced results that often differed by one or two quality classes for the same site. We foresee that a more precise intercalibration exercise is necessary, and it should be based on more detailed data considering both seasonality and the latitudinal differences within the area covered.     

A review on the ecological quality status assessment in aquatic systems using community based indicators and ecotoxicological tools: what might be the added value of their combination?

The European Water Framework Directive (WFD) represents a transformation of the guidelines for water quality assessment and monitoring across all EU Member States. At present, it is widely accepted that the WFD requires holistic and multidisciplinary ecological approaches by integrating multiple lines of evidence. Within the scope of the WFD, the scientific community identified clear opportunities to take advantage of an ecotoxicological line of evidence. In this context, ecotoxicological tools, namely biomarkers and bioassays, were proposed to contribute to the integration of the chemical and biological indicators, and thus to provide an overall insight into the quality of a water body. More than one decade after the publication of the WFD, we reviewed the studies that have attempted to integrate ecotoxicological tools in the assessment of surface water bodies. For this purpose, we reviewed studies providing an ecological water status assessment through more conventional community based approaches, in which biomarkers and/or bioassays were also applied to complement the evaluation. Overall, from our review emerges that studies at community level appear suitable for assessing the ecological quality of water bodies, whereas the bioassays/biomarkers are especially useful as early warning systems and to investigate the causes of ecological impairment, allowing a better understanding of the cause–effect-relationships. In this sense, community level responses and biomarkers/bioassays seem to be clearly complementary, reinforcing the need of combining the approaches of different disciplines to achieve the best evaluation of ecosystem communities’ health.     

The M-NIP: a macrophyte-based Nutrient Index for Ponds

In Swiss ponds, eutrophication represents one of the major threats to biodiversity. A biological method to assess the trophic state would, therefore, be particularly useful for monitoring purposes. Macrophytes have already been successfully used to evaluate the trophic state of rivers and lakes. Considering their colonizing abilities and their roles in pond ecosystem structure and function, macrophytes should be included in any assessment methods as required by the European Water Framework Directive. Vegetation survey and water quality data for 114 permanent ponds throughout Switzerland were analysed to define indicator values for 113 species including 47 with well-defined ecological response to total water phosphorus (TP). Using indicator values and species cover, a Macrophyte Nutrient Index for Ponds (M-NIP) was calculated for each site and assessed with both the original pond data set and a limited validation data set. The resulting index performed better when considering only species with narrow responses to TP gradient and was more applicable, but less accurate when including all species. Despite these limitations, the M-NIP is a valuable and easy tool to assess and monitor the nutrient status of Swiss ponds and was shown to be robust and relatively sensitive to slight changes in phosphorus loading with a validation subset. Guest editors: B. Oertli, R. Cereghino, A. Hull & R. Miracle Pond Conservation: From Science to Practice. 3rd Conference of the European Pond Conservation Network, Valencia, Spain, 14–16 May 2008     

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.     

Validation of the Macrophyte Quality Index (MaQI) set up to assess the ecological status of Italian marine transitional environments

The paper couples the results obtained by applying the expert and the rapid Macrophyte Quality Indices set up to assess the ecological status of the Italian transitional environments according to the requirements by the Water Framework Directive (2000/60/CE). The indices were validated by comparing the composition of the macrophyte assemblages and the values of some bio-physico-chemical parameters of the water column of 20 stations of the Venice lagoon sampled monthly for one year between 2003 and 2005. In 5 stations out of the 20, the ones which fall within the 5 classes of ecological status suggested by the Water Framework Directive, sedimentation rates, sediment grain-size, and nutrient and pollutant (metals, Polychloro-Dibenzo-Dioxins/Furans, Polycyclic Aromatic Hydrocarbons, Pesticides and Polychlorinated Biphenils) concentrations in surface sediments were also determined. Results showed strong relationships between the trends of these environmental parameters and the composition and structure of macrophyte associations, as well as with the Macrophyte Quality Index assessment. Chlorophyceae showed a trend opposite to Rhodophyceae whose presence was concentrated in oxygenated and transparent environments. Chlorophyceae and the species characterised by low scores prevailed in turbid areas where nutrient and pollutant concentrations were high. Results allowed the identification of the conditions of the “reference sites” (confinement areas and sites with high water renewal) and the integration of the dichotomic key used for the application of the R-MaQI. Handling editor: S. M. Thomaz     

Uncertainty in ecological status assessments of lakes and rivers using diatoms

The EU’s Water Framework Directive requires all surface water bodies to be classified according to their ecological status. As biological communities show both spatial and temporal heterogeneity, expressions of ecological status will, inevitably, have an element of uncertainty associated with them. A consequence of this environmental heterogeneity is that there is a risk that status inferred from one or more samples is different to the true status of that water body. In order to quantify the scale of temporal uncertainty associated with benthic diatoms, replicate samples were collected from sites across the ecological status gradient in lakes and rivers in the UK. Variability (expressed as standard deviation of temporal replicate samples from a single site) could be described using a polynomial function and this was then used to calculate the risk of placing a water body in the wrong ecological status class. This risk varied depending on the distance from the class boundaries and the number of replicates. Based on these data, we recommend that ecological status is determined from a number of samples collected from a site over a period of time.     

Performance of a new phytoplankton composition metric along a eutrophication gradient in Nordic lakes

A new phytoplankton metric is presented, which is developed from a large dataset of Norwegian lakes (>2,000 samples from >400 lakes). In contrast to previous metrics, this index is not built on selected ‘indicative’ taxa, but uses all available taxonomic information at genus and species level. Taxa optima with respect to lake trophic status (derived from total phosphorus concentrations) are used to calculate a phytoplankton trophic index (TI) for each sample. Analysis of the TI shows that phytoplankton communities exhibit highly non-linear responses to eutrophication in Norwegian lakes. Reference lakes are characterized by very similar TIs despite having considerable variation in total phosphorus and chlorophyll a concentrations. TI exhibits a non-linear distribution along the eutrophication gradient which separates unimpacted from impacted sites in the study area. We further show that TI exhibits smaller seasonal variations than chlorophyll a, making it a more reliable indicator for lake monitoring. Implications for its applicability within the WFD are discussed.     

Towards a multimetric index for ecological assessment of Mediterranean flatland ponds: the use of macroinvertebrates as bioindicators

Fifty-five macroinvertebrate metrics were tested for their response to pond condition in 41 ponds of northwest Spain to develop a preliminary multimetric index for ecological assessment of Mediterranean flatland ponds. Stressor specific response of individual attributes to eutrophication and habitat alteration was also investigated to identify differences in the responses of metrics to single stressors and elucidate how this might affect the performance of the final index. Several combinations were tested using discrimination efficiency (25th percentile of slightly impaired sites for metrics decreasing with perturbation and 75th percentile of slightly impaired sites for metrics increasing with perturbation) and Mann–Whitney U-test with Bonferroni adjustment (P < 0.001). The final index comprised five measures (generic richness of Chironominae, generic richness of Dytiscidae + Odonata + Tanypodinae, relative richness of Chironomidae, % Macropelopini and Shannon index) and discriminated between acceptable (good) and unacceptable (moderate) conditions with more than 86% efficiency. Moreover, all the five measures included in the final index showed unidirectional responses to eutrophication, decreasing as eutrophication increased. In contrast, the effect of habitat alteration was less clear, especially in ponds in best available conditions where a vegetation belt of shrubs and trees prevented growing of macrophitic vegetation on shores and consequently associated fauna. Interestingly, none of the functional groups (e.g. % predators and % collector–gatherers) were sensitive to degradation. Handling editor: K. Martens     

Validation of diatoms as proxies for phytobenthos when assessing ecological status in lakes

Research to develop tools to assess the ecological status of phytobenthos, as required in Annex V of the European Union Water Framework Directive, has focussed largely on diatoms. Diatoms are often the most abundant and diverse group of algae within the phytobenthos and have been used widely for other monitoring purposes. However, there is little empirical justification for the use of diatoms as proxies for the wider phytobenthos. In this paper, we re-examine an existing dataset compiled largely from littoral samples from standing waters in the English Lake District and compared transfer functions for total phosphorus, dissolved inorganic carbon, conductivity and calcium concentration generated from diatoms and non-diatoms separately and together. The results show that transfer functions generated from diatoms alone are as powerful as transfer functions generated from diatoms and non-diatoms combined, while transfer functions generated from non-diatoms alone are less effective. These results provide support for the use of diatoms as proxies for phytobenthos when ecological status is being assessed. Handling editor: J. Saros     

Ecological variation within Sellaphora species complexes (Bacillariophyceae): specialists or generalists?

The genus Sellaphora has become a model system for studies of the species concept, speciation and automated identification in diatoms. Three species, S. pupula, S. bacillum and S. laevissima, have proved to be complexes containing several or many species, which are difficult to distinguish morphologically but which are genetically differentiated and (where tested) reproductively isolated. Until now, however, there has been little information about the ecology of the species within this complex, except in relation to parasite sensitivity. In order to test whether semi- and pseudo-cryptic Sellaphora species are ecologically differentiated with respect to trophic status, we used tools recently developed in the UK in response to the EU Water Framework Directive (WFD). Diatom samples from three substrata (plants, rocks, sediment) were taken from 22 lakes in Scotland and England, covering a gradient from oligotrophic mountain lakes to eutrophic lowland ponds. The epilithic and epiphytic diatom assemblages were used to evaluate lake trophic status according to the UK WFD assessment system and showed that there was a strong environmental gradient in the dataset. Sellaphora species occurred in the sediment-derived epipelon and their distributions were analysed in relation to the trophic gradient. A total of 28 Sellaphora phenodemes (putative species) were found, and some of them differed in their environmental demands. Two groups were distinguished: (1) a group indicating rather oligotrophic conditions and containing several demes with linear valves and subcapitate or capitate poles (referred to here as S. [pupula] cap-A, cap-B and cap-C and (2) a group occurring in eutrophic lakes and containing the recently described species S. blackfordensis, S. capitata and S. obesa, as well as S. [pupula] Φ ‘small lanceolate’. The data obtained are also discussed with respect to Finlay’s hypothesis on microalgal cosmopolitanism. Handling editor: J. Padisak     

Stream characteristics and their implications for the protection of riparian fens and meadows

1. Running waters, including associated riparian areas, are embraced by international legal frameworks outlining targets for the preservation, protection and improvement of the quality of the environment. Interactions between stream and river processes and riparian habitats have not received much attention in the management of stream ecosystems, and integrated measures that consider both the ecological status of streams and rivers (sensu EU Water Framework Directive, WFD) and the conservation status of riparian habitats and species (sensu EU Habitats Directive, HD) are rare. 2. Here, we analysed the influence of stream size, morphology and chemical water characteristics for the distribution of water‐dependent terrestrial habitat types, i.e. alkaline fens, periodically inundated meadows and meadows in riparian areas in Denmark using an extensive data set covering a total of 254 stream reaches. A species‐based classification model was used to translate species lists into a standardised interpretation of habitat types protected by the HD in Denmark. 3. No size dependency was found regarding the distribution of fen and meadow vegetation. Instead, the distribution of fen and meadow vegetation was strongly affected by the morphology of the streams. Alkaline fens, periodically inundated meadows and meadows occurred six, five and four times, respectively, less frequently along channelised compared with natural stream reaches. Our results indicate that stream channelisation strongly interfered with the natural hydrology of riparian areas, affecting conditions needed to sustain protected fen and meadow communities. 4. We also found that water chemistry strongly influenced the occurrence of fen and meadow vegetation in riparian areas. The probability of finding fen and meadow vegetation was reduced when total phosphorus (TP) concentration exceeded 40–50 μg P L^?1, whereas meadow vegetation responded less strongly to TP. 5. Our findings highlight the importance of restoring hydrology of riparian areas to improve conditions for fen and meadow vegetation, but also that the water chemistry should be considered when measures that increase hydrological connectivity result in an increase in the probability of flooding.     

Extending the phytoplankton tool kit for the UK Water Framework Directive: indicators of phytoplankton community structure

The Water Framework Directive (WFD) demands consideration of normative definitions for assessing ecological state of marine waters. For phytoplankton, ‘deviations from the ideal’ need to be considered for species composition and abundance, average biomass and the occurrence of blooms. A combination of phytoplankton metrics has been developed which, when considered in combination, should provide a confident assessment of the ecological state of each water body under assessment. The aim of this study was to evaluate phytoplankton community structure in different coastal and estuarine water bodies within England and Wales, and to contribute evidence towards the development of a community-based phytoplankton indicator. Influences of seasonality on the species assemblage were tested using a long-term data set available from a long-term monitoring site just offshore of Plymouth, UK. There is a substantive seasonal influence to the data, with a maximum of 10–14 common species (out of a potential 20) reoccurring within the same calendar month over a 10-year time span. Comparisons between reference and test water bodies give a range of common species of between 3 and 11 species within water type and season. A statistical and qualitative approach for comparing the most common species occurring between a reference and test site were tested for development of a WFD phytoplankton assessment tool. Overall, the results indicate that there are distinct phytoplankton assemblages over seasons which could form the basis of a community assessment metric. However, differences in boundary conditions are negligible between the different areas. There is evidence that community populations may be ubiquitous across marine water types in England and Wales, and development of generic seasonal lists across typologies could be appropriate in the further development of this tool.     

Macrophytes and diatoms – major results and conclusions from the STAR project

The interactions between sensitivity and variability of macrophyte and diatom communities were evaluated as a research support of methodologies required by the Water Framework Directive. Slope and shading were identified as additional typological parameters improving links between unimpacted macrophyte communities and running water types. Two other studies demonstrated indication value of macrophytes for assessment of nutrient enrichment and hydromorphological degradation. The special exercises were realized within the STAR project to evaluate sources of variability/uncertainty in assessment methods based on macrophytes and diatoms. Sampling period and shading of the site were found as major factors affecting variability in macrophyte assessment results. Uncertainty of diatom assessment is predominantly associated with selection of site, substrate type and taxonomic identification. Further extension of indication systems and definition of macrophyte/diatom-specific typology of running waters are considered as the main aims of subsequent investigations.