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Monitoring the condition (water quality, biodiversity, hydromorphology) of small water bodies presents a challenge for the relevant authorities in terms of time and resources (labour and financial) due to the extensive length of the stream network or the sheer number of small standing water bodies. Citizen science can help address information gaps, but the effort required should not be underestimated if such projects are to generate reliable and sustained data collection. The overall aim of this paper is to propose a framework for operationalisation of citizen science targeting collection of data from small water bodies. We first consider the data gaps and the elements (water chemistry, ecology, hydromorphology) to be addressed, in order to define where citizen science could best make an impact. We review examples of tools and methods that are appropriate for small water bodies, based on experience from a selection of freshwater citizen science projects, and the support that is needed for effective and sustained small water body projects across Europe. [ABSTRACT FROM AUTHOR]

Lake Balaton, the largest lake in Central Europe, underwent severe eutrophication from the 1960s to the 1990s, due to phosphorus loadings from external anthropogenic sources. The subsequent and complex eutrophication control and lake restoration program resulted in a significant decrease in the external phosphorus loading to the lake. Consequently, Lake Balaton has been returning to its former meso-eutrophic character. In this paper, we explore the long-term dynamics of chlorophyll a (Chl a) concentration, a proxy for phytoplankton biomass, and zooplankton biomass in Lake Balaton during its re-oligotrophication period from 2001 to 2017, and attempt to draw some conclusions on the subsequent changes in the fish stock. We found a proportional decrease in zooplankton and phytoplankton biomasses at moderate phytoplankton levels. However, below a certain phytoplankton concentration (< 10 μg l−1 Chl a), the decrease in phytoplankton biomass was not coupled with a further decline in zooplankton biomass because the fraction of small phytoplankton, edible for zooplankton, showed a much smaller decrease in biomass compared with large non-edible phytoplankton. Thus, improvements in water quality (i.e., reduced nutrient loading), partly via concomitant changes in the phytoplankton size distribution, did not cause a large difference in the fish stock in this shallow lake. [ABSTRACT FROM AUTHOR]

This introductory paper presents 20 river restoration cases throughout Europe that were investigated in the EU-funded research project REFORM. In the following, this special issue provides seven specific papers that highlight and discuss the effects of restoration on the investigated river-floodplain systems. Additionally, restoration success was estimated from a socio-economic perspective. The first part of this paper presents the overall study concept and the general sampling design of the field investigations. Each study site was examined with the same array of methods, covering habitat composition in the river and its floodplain, three aquatic and two floodplain-related organism groups, as well as food web composition and 'aquatic terrestrial' interactions as reflected by stable isotopes. An overview of the rivers and the study sites summarizes main attributes of all investigated sites, with emphasis on the large-scale restoration projects. Some of the projects represent the 'state of the art' restoration approaches for two major European river types: gravel-bed mountain rivers and sand-bed lowland rivers. Concluding, restoration efforts had positive effects even in the small restoration projects investigated but did not increase with project size. No 'single best' measure could be identified, but river widening generally had a larger effect compared to other restoration measures. [ABSTRACT FROM AUTHOR]

In Europe, ponds are an exceptionally numerous and widely distributed landscape feature forming a major part of the continental freshwater resource and contributing significantly to freshwater biodiversity conservation. This has been reflected by a growing scientific concern over the first few years of the twenty-first century and is evidenced by an increasing number of academic publications on pond related topics, particularly those relating to biodiversity. It is essential, however, that this expanding scientific knowledge is widely disseminated to those involved with pond management and is then rapidly translated into action. Inevitably, the task of transferring science to practice remains a significant challenge. As a first step towards meeting this challenge the European Pond Conservation Network (EPCN), at its biennial meeting in 2008 in Valencia (Spain), made this the main theme of the conference together with two special workshops further encouraging exchanges between scientists, practitioners and policy makers. The papers selected for this special issue of Hydrobiologia (from over 120 communications presented) are all from the conference. They represent a diverse collection of themes from across the continent and North Africa and present new and original insights into topics as wide ranging as: pond biodiversity; human disturbance; landscape ecology; ecological assessment and monitoring; practical management measures; ecological restoration; hydrology and climate change; invasive species and threatened species. In all cases, the papers demonstrate an overriding need for the development of a tight link between scientific knowledge and management. Furthermore, scientific advances have to be beneficial for on the ground management and, vitally, have to be disseminated, communicated and implemented into local, national and international policy. As such, national and international networks (such as the EPCN) have a central role to play and have to develop a robust information and communication strategy which will enable the dissemination of best practice materials and advice across the continent and beyond. The work contained in this volume represents a step in the right direction and will help to ensure that ponds remain a characteristic and highly visible feature of the European landscape in the twenty-first century. [ABSTRACT FROM AUTHOR]

The major results and conclusions of the two papers in the hydromorphology section of the Hydrobiologia special issue on the EU STAR project are summarised. Several key findings have emerged from this research. Firstly, the hydromorphological characteristics of rivers between different geographical regions of Europe were found to vary considerably with rivers in each region possessing distinctive hydromorphological characteristics. Secondly, the hydromorphological attributes that most strongly influence two existing hydromorphological indices (the Habitat Quality Assessment and the Habitat Modification Score) were identified and attention was drawn to the accurate definition and recording of these attributes in field surveys and training courses. Thirdly, links between hydromorphological characteristics and macroinvertebrate quality indices were investigated. Two types of bank modification (resectioning and reinforcement) were significantly correlated with two biotic indices (EPT taxa and MTS), while channel modifications were negatively correlated with ASPT. While biotic indices were often strongly correlated with Habitat Quality Assessment they were less strongly related to Habitat Modification Score suggesting that physical habitat diversity may be more important in determining macroinvertebrate community structure than morphological alteration. The papers in this section provide important underpinning research for the implementation of the European Water Framework Directive. In both papers suggestions are made for further research on the hydromorphology of European rivers. [ABSTRACT FROM AUTHOR]

The Water Framework Directive (WFD) requires estimates of the confidence and precision associated with any scheme for assessing and monitoring the ecological status class of any European rivers, lakes, transitional or coastal waters. This is a complex important issue, especially for waterbody assessments based on multiple metrics and/or two or more taxonomic groups. This paper aims to contribute towards improving understanding and providing practical approaches to assessing confidence of class by (i) discussing the various sources and causes of uncertainty, (ii) using UK rivers macroinvertebrate datasets to illustrate the estimation of replicate, temporal and spatial variance components and the implications for water body metric precision, confidence of class and optimal sampling design, (iii) introducing new freely available general software WISER Bioassessment Uncertainty Guidance Software (WISERBUGS) which uses prior sampling uncertainty estimates with user-specified metrics, class limits and metric combination rules to simulate the joint sampling uncertainty in metric EQR values and provide estimates of confidence of class based on individual metrics, (optionally weighted) multi-metric indices and/or multi-metric classification rules (worst case, mean or median class) based on one or more WFD biological quality elements. [ABSTRACT FROM AUTHOR]

The implementation of the Water Framework Directive has required intense research in applied aquatic ecology in Europe, and thus created challenges for data management in international research projects. In the project Waterbodies in Europe: Integrative Systems to assess Ecological status and Recovery (WISER), biological and environmental data from rivers, lakes, transitional and coastal waters in 26 European countries were collated. More than one million records of biological observations were stored in the project's central database, representing phytoplankton, macrophytes, macroalgae, angiosperms, phytobenthos, invertebrates and fish. The central database includes new data from the WISER field campaign in lakes and transitional/coastal waters during 2009-2010 (more than 6,000 biological samples from 58 waterbodies in 14 countries). The purpose of this paper is to provide an overview of the data collated within WISER, in order to facilitate future re-use of these data by other scientists. More specifically, the objectives are to (1) describe the data management in WISER, (2) describe the structure and content of the WISER central database and (3) share experiences and give recommendations for data management in large ecological research projects. [ABSTRACT FROM AUTHOR]

Despite improvements in wastewater treatment systems, the impact of anthropogenic nutrient sources remains a key issue for the management of European lakes. The Water Framework Directive (WFD) provides a mechanism through which progress can be made on this issue. The Directive requires a classification of the ecological status of phytoplankton, which includes an assessment of taxonomic composition. In this paper, we present a composition metric, the plankton trophic index, that was developed in the WISER EU FP7 project and demonstrate how it has been used to compare national phytoplankton classification systems in Northern and Central Europe. The metric was derived from summer phytoplankton data summarised by genus from 1,795 lakes, covering 20 European countries. We show that it is significantly related to total phosphorus concentrations, but that it is also sensitive to alkalinity, lake size and climatic variables. Through the use of country-specific reference values for the index, we demonstrate that it is significantly related to other national phytoplankton assessment systems and illustrate for a single European (intercalibration) lake type how it was used to intercalibrate WFD boundaries from different countries. [ABSTRACT FROM AUTHOR]

Phytoplankton constitutes a diverse array of short-lived organisms which derive their nutrients from the water column of lakes. These features make this community the most direct and earliest indicator of the impacts of changing nutrient conditions on lake ecosystems. It also makes them particularly suitable for measuring the success of restoration measures following reductions in nutrient loads. This paper integrates a large volume of work on a number of measures, or metrics, developed for using phytoplankton to assess the ecological status of European lakes, as required for the Water Framework Directive. It assesses the indicator strength of these metrics, specifically in relation to representing the impacts of eutrophication. It also examines how these measures vary naturally at different locations within a lake, as well as between lakes, and how much variability is associated with different replicate samples, different months within a year and between years. On the basis of this analysis, three of the strongest metrics (chlorophyll- a, phytoplankton trophic index (PTI), and cyanobacterial biovolume) are recommended for use as robust measures for assessing the ecological quality of lakes in relation to nutrient-enrichment pressures and a minimum recommended sampling frequency is provided for these three metrics. [ABSTRACT FROM AUTHOR]

The EU-funded research project WISER ('Water bodies in Europe: Integrative Systems to assess Ecological status and Recovery') developed new assessment methods required by the EU Water Framework Directive (WFD) for lakes, coastal and transitional waters. WISER also addressed the recovery of biotic assemblages from degradation. The results are summarised in five key messages, supported by papers in this special issue and by WISER results published elsewhere: (1) Response to stress differs between organism groups, water types and stressors; a conceptual model is proposed summarising how the individual organism groups respond to different types of degradation in rivers, lakes, transitional and coastal waters. (2) The sources of uncertainty differ between BQEs and water types, leading to methodological suggestions on how to design WFD sampling programmes. (3) Results from about 300 current assessment methods indicate geographical variations in metrics but assessments are comparable at an aggregated level ('ecological status'). (4) Scale and time matter; restoration requires action at (sub)-basin levels and recovery may require decades. (5) Long-term trends require consideration; the effects of both degradation and restoration at the water body or river basin scales is increasingly superimposed by multiple stressors acting at large scales, in particular by climate change. [ABSTRACT FROM AUTHOR]

The literature on monitoring rivers using benthic algal communities is reviewed, especially that for Europe during the past 20 years. In particular, papers in a series of symposia at approximately 3-year intervals are considered to assess the extent to which aims and methods have shifted. A variety of methods were being tested in the early 1990s, and some put to practical use. However, the requirements of the EU Urban Waste Water Directive in 1991 have gradually narrowed procedures in most countries outside Scandinavia to the use of indices based on benthic diatoms to monitoring nutrients, especially phosphate. Most countries in Europe now adopt one of a few indices. The same indices are being used to deal with the requirements of the EU Water Framework Directive introduced in 2000 to achieve good ecological status by 2015. It is argued, however, that features of upland river sites require the development of revised indices for this purpose. Features of many sites include highly variable nutrient concentrations and ratios, and the greater importance of organic phosphate. Two possible approaches are suggested to developing a revised index. One is a diatom index which incorporates information about the environmental features important here. The other is to use an index which incorporates data on genera from all algal phyla, with emphasis on those which are long-lived. [ABSTRACT FROM AUTHOR]

The European Union (EU)’s Water Framework Directive (WFD) requires that all Member States participate in intercalibration exercises in order to ensure that ecological status concepts and assessment levels are consistent across the EU. This paper describes one such exercise, performed by the countries in the Central/Baltic Geographical Intercalibration Group stretching from Ireland in the west to Estonia in the east and from the southern parts of Scandinavia to the northern regions of Spain and Italy (but excluding alpine regions, which were intercalibrated separately). In this exercise, methods used to measure ecological status of rivers using benthic diatoms were compared. Ecological status is estimated as the ratio between the observed value of a biological element and the value expected in the absence of significant human impact. Approaches to defining the ‘reference sites’, from which these ‘expected’ values were derived, varied from country to country. Minimum criteria were established as part of the exercise but there was still considerable variation between national reference values, reflecting typological differences that could not be resolved during the exercise. A simple multimetric index was developed to compare boundary values using two widely used diatom metrics. Boundary values for high/good status and good/moderate status set by each participant were converted to their equivalent values of this intercalibration metric using linear regression. Variation of ±0.05 EQR units around the median value was considered to be acceptable and the exercise provided a means for those Member States who fell significantly above or below this line to review their approaches and, if necessary, adjust their boundaries. [ABSTRACT FROM AUTHOR]

Type-specific reference conditions that describe sites with no or only very minor anthropogenic disturbances are a basic requirement of the European Water Framework Directive. The reference condition approach implies a previous determination of criteria acceptable for the definition of near-natural stretches. In this paper, a methodology based on selection and validation procedures is applied to a Portuguese watershed to guide the identification of reference sites. The methodology consisted of three phases: (1) a preliminary site inspection through the use of maps, available data and an extensive screening field campaign that resulted in the selection of 52 potentially undisturbed small- and medium-sized rivers stretches, ranging from 43 to 1069 m in altitude, with catchment areas between 4 and 641 km2 and representing siliceous and calcareous riverbeds; (2) a detailed site selection based on ten pre-defined criteria involving physical/social/biological attributes that indicated catchment land use changes and alien vegetal riparian species as major human impacts; (3) a site validation procedure involving detailed investigation of benthic macroinvertebrate communities, riparian vegetation, in-stream habitat quality and chemical parameters that showed riparian wood-related problems as a major restriction to validate a stretch as a near-natural site. Only about 12% of all investigated river sites, accounting for 600 m of all 5200 m studied, could be considered as near-reference stretches or sites retaining essential natural functions. Selection and validation procedures can identify different sites as reference, which reinforces the need for applying both procedures. The results presented can help to accomplish the requirements of the EU – Water Framework Directive by selecting reference sites as the first step to establish biological reference conditions and, simultaneously, to form a basis for nature conservation strategies. [ABSTRACT FROM AUTHOR]

The main results of the STAR project on the intercalibration of boundaries of European assessment systems and comparison between assessment methods are summarized here. The main findings are outlined in the context of the Water Framework Directive that requires reliable instructions to be set up on how to use and harmonise assessment systems and methods for European rivers. The main papers published on these subjects by STAR partners are reviewed, with focus on major questions addressed and approaches used for investigation. The need for broad coverage of geographic ranges and pressure gradients, together with the goal of providing outcomes appropriate to the effective application of the WFD are emphasized. Extensive datasets from a wide range of countries, stream types and sites and a large number of methods, metrics and approaches are compared and tested and various cross-cutting themes emerged. Among these, the value of the use of benchmarking systems for comparison and intercalibration is highlighted. Two ways of looking for comparability of assessment systems results were analyzed: a) by adopting identical sampling techniques across Europe and b) by harmonizing the classification results of the national assessment systems. In addition, the need, in the intercalibration process, for a proper definition of the criteria for reference conditions is underlined. This is because their imprecision now represents one of the major weaknesses of the whole intercalibration process. Direct and indirect approaches to intercalibration are considered and commented on for their potential use in distinct circumstances. Finally, the use common metrics for the intercalibration process, which make comparability across Europe valid, is tested and indeed encouraged. [ABSTRACT FROM AUTHOR]

This short paper summarises the information developed in the EU funded research project STAR on autecology databases, metrics, multimetrics and community approaches. For Europe the WFD implementation gave an important stimulus for the development of ecology based assessment techniques. Along with the development of metrics and multimetrics indices taxalists and autecological information were strongly improved. Recommendations are given to further develop ecological assessment in European streams and rivers. [ABSTRACT FROM AUTHOR]

Lake Prespa and Lake Ohrid, located in south-eastern Europe, are two lakes of extraordinary ecological value. Although the upstream Lake Prespa has no surface outflow, its waters reach the 160 m lower Lake Ohrid through underground hydraulic connections. Substantial conservation efforts concentrate on oligotrophic downstream Lake Ohrid, which is famous for its large number of endemic and relict species. In this paper, we present a system analytical approach to assess the role of the mesotrophic upstream Lake Prespa in the ongoing eutrophication of Lake Ohrid. Almost the entire outflow from Lake Prespa is found to flow into Lake Ohrid through karst channels. However, 65% of the transported phosphorus is retained within the aquifer. Thanks to this natural filter, Lake Prespa does not pose an immediate threat to Lake Ohrid. However, a potential future four-fold increase of the current phosphorus load from Lake Prespa would lead to a 20% increase (+0.9 mg P m−3) in the current phosphorus content of Lake Ohrid, which could jeopardize its fragile ecosystem. While being a potential future danger to Lake Ohrid, Lake Prespa itself is substantially endangered by water losses to irrigation, which have been shown to amplify its eutrophication. [ABSTRACT FROM AUTHOR]