Intercalibrating classifications of ecological status: Europe's quest for common management objectives for aquatic ecosystems

Has climate change over the last ten years caused a banalisation of diatom communities in Cypriot streams?

To unveil possible changes in diatom communities in Cypriot streams over the last ten years or so, we selected samples from the years 2020, 2021, and 2022 for the "recent" dataset (N = 119) and samples from the years 2010 and 2011 for the "historical" dataset (N = 108). Biotic homogenization has become a truly global phenomenon. Here we show that, over the last ten years, in response to increased water temperature, conductivity, and discharge variability due to climate-change, Cypriot stream diatom communities include a higher number of trivial (= widespread, tolerant, and opportunistic), aerial, and thermophilic species, have reduced β-diversity and increased nestedness. Moreover, IndVal analysis shows that indicator species from the historical dataset were characteristic, often relatively rare species, while the indicators of the recent dataset were a group of typical trivial, eutraphentic, and thermophilic species. As is almost always the case, the diatom communities we studied were subjected to multiple stressors, often affecting them in opposite ways. Besides the increase in trivial species, the reduction in β-diversity, and the rise in nestedness mentioned above, the diatom assemblages we studied also showed an increase in α-diversity that could be due to a moderate reduction in nutrients in several sites. High-ecological-integrity ecosystems, such as springs, waterfalls, and dripping rock-walls, in particular springs that were shown to be excellent hydrologic refugia in climates heavily affected by climate change, and the stream sites close to them should be carefully protected, as they can be refugia for sensitive and characteristic species that can recolonize the adjacent streams after adverse climatic events.

Setting nutrient boundaries to protect aquatic communities: The importance of comparing observed and predicted classifications using measures derived from a confusion matrix

Defining nutrient thresholds that protect and support the ecological integrity of aquatic ecosystems is a fundamental step in maintaining their natural biodiversity and preserving their resilience. With increasing catchment pressures and climate change, it is more important than ever to develop clear methods to establish thresholds for status classification and management of waters. This must often be achieved using complex data and should be robust to interference from additional pressures as well as ameliorating or confounding conditions. We use both artificial and real data to examine challenges in setting nutrient thresholds in unbalanced and skewed data. We found significant advantages to using binary logistic regression over other techniques. However, one of the key challenges is objectively selecting a probability from which to derive the nutrient threshold. For this purpose, the examination of the proportions of matching and mismatching status classifications of nutrients and a biological quality element using a confusion matrix is a key step that should be more widely adopted in threshold selection. We examined a large array of statistical measures of classification accuracy and their performance over combinations of skewness and imbalance in the data. The most appropriate threshold probability is a compromise between maximising overall classification accuracy and reducing mismatches expressed as commission (false positives) without excessive omission (false negatives). An application to a lake type indicated total phosphorus thresholds that would be around 50 μg l-1 lower than the threshold achieved by an 'unguided' approach, indicating that this approach is a very significant development meriting attention from national authorities responsible for water management.

Ecosystem health evaluation of urban rivers based on multitrophic aquatic organisms

The ecosystem health evaluation method of urban rivers is significantly different from natural rivers, because of intensive human interferences and ecological restoration measures. Biotic integrity index (IBI) provides a method to quantify the response of aquatic organisms to environmental stress. Multi-trophic aquatic organisms may exhibit different responses and sensitivities to stress factors, which affects the reliability of the IBIs. This study proposed a hypothesis that the biota with the higher trophic level (whose habitat was not completely destroyed) or that of the biota with the shorter life cycle would be more sensitive in urban rivers. To prove the above hypothesis, the ecosystem health status of urban rivers was evaluated by the IBIs across multitrophic groups, including benthic invertebrates, zooplankton, phytoplankton, periphyton algae and microorganisms. The reliability of the IBIs was assessed by estimating their relationship with water quality index (WQI). The spatial distribution differences of the IBIs were distinguished by spatial autocorrelation analysis. The results showed that the IBI based on benthic invertebrates cannot mask the effects of dredging. Compared with the IBIs from other trophic groups, the correlation coefficients between the IBIs based on zooplankton and microorganisms and WQI were higher. Moreover, the evaluation results of Z (Zooplankton)-IBI and M (Microorganism)-IBI were able to discriminate the least, medium and highly impaired site groups divided by WQI. For the spatial response mode, Z-IBI and M-IBI could identify the high-value river sections under ecosystem restoration projects, and Z-IBI could also identify the low-value river sections under intensive human interferences. Therefore, Z-IBI and M-IBI could be recommended as the priority application in urban rivers. The constructed ecosystem health evaluation framework for urban rivers would play a guiding role in reducing impairments and restoring water ecosystem quality.

Striving for consistent bioassessment across diverse landscapes: Using land use matters for classifying reference and disturbed sites for index development

Consistency in ecological assessments is challenging across large diverse landscapes because natural geological, climatic, and hydrological factors vary greatly. As a result, large landscapes are often subdivided into ecoregions and assessments are based on ecoregion specific indices. In the present study, we developed and compared multimetric indices (MMIs) using benthic diatom data from the 2008-2009 dataset from the United States (US) National Rivers and Streams Assessment. Nationwide and separate ecoregion specific MMIs were developed with reference, moderately disturbed, and highly disturbed sites selected using criteria based on physicochemical condition of the habitat or based on watershed land use (% agriculture and % urban). Metrics were adjusted to account for variation in natural conditions when needed. We found only land use criteria selected reference sites with consistently low median % watershed disturbance (%WD) and large differences in %WD between reference and highly disturbed sites. <38 % of sites were identified as reference or highly disturbed by both physicochemical and land use criteria. All MMIs displayed substantial discrimination ability between reference and highly disturbed sites. At the national scale, MMIs based on land use outperformed MMIs based on physicochemical conditions for all performance attributes tested. When national scale MMIs were applied to ecoregions, MMIs based on land use were again better than MMIs based on physicochemical conditions for most performance attributes and even had better or comparable performance to the land use MMIs developed separately for each ecoregion. Our findings show that developing MMIs using land use criteria and adjusting metrics for natural variation could improve assessment consistency without losing MMI performance across large, diverse landscapes as in the US National Rivers and Streams Assessment.

Bacterial bioindicators enable biological status classification along the continental Danube river

Despite the importance of bacteria in aquatic ecosystems and their predictable diversity patterns across space and time, biomonitoring tools for status assessment relying on these organisms are widely lacking. This is partly due to insufficient data and models to identify reliable microbial predictors. Here, we show metabarcoding in combination with multivariate statistics and machine learning allows to identify bacterial bioindicators for existing biological status classification systems. Bacterial beta-diversity dynamics follow environmental gradients and the observed associations highlight potential bioindicators for ecological outcomes. Spatio-temporal links spanning the microbial communities along the river allow accurate prediction of downstream biological status from upstream information. Network analysis on amplicon sequence veariants identify as good indicators genera Fluviicola, Acinetobacter, Flavobacterium, and Rhodoluna, and reveal informational redundancy among taxa, which coincides with taxonomic relatedness. The redundancy among bacterial bioindicators reveals mutually exclusive taxa, which allow accurate biological status modeling using as few as 2-3 amplicon sequence variants. As such our models show that using a few bacterial amplicon sequence variants from globally distributed genera allows for biological status assessment along river systems.

Fish and macroinvertebrate assemblages reveal extensive degradation of the world's rivers

Rivers suffer from multiple stressors acting simultaneously on their biota, but the consequences are poorly quantified at the global scale. We evaluated the biological condition of rivers globally, including the largest proportion of countries from the Global South published to date. We gathered macroinvertebrate- and fish-based assessments from 72,275 and 37,676 sites, respectively, from 64 study regions across six continents and 45 nations. Because assessments were based on differing methods, different systems were consolidated into a 3-class system: Good, Impaired, or Severely Impaired, following common guidelines. The proportion of sites in each class by study area was calculated and each region was assigned a Köppen-Geiger climate type, Human Footprint score (addressing landscape alterations), Human Development Index (HDI) score (addressing social welfare), % rivers with good ambient water quality, % protected freshwater key biodiversity areas; and % of forest area net change rate. We found that 50% of macroinvertebrate sites and 42% of fish sites were in Good condition, whereas 21% and 29% were Severely Impaired, respectively. The poorest biological conditions occurred in Arid and Equatorial climates and the best conditions occurred in Snow climates. Severely Impaired conditions were associated (Pearson correlation coefficient) with higher HDI scores, poorer physico-chemical water quality, and lower proportions of protected freshwater areas. Good biological conditions were associated with good water quality and increased forested areas. It is essential to implement statutory bioassessment programs in Asian, African, and South American countries, and continue them in Oceania, Europe, and North America. There is a need to invest in assessments based on fish, as there is less information globally and fish were strong indicators of degradation. Our study highlights a need to increase the extent and number of protected river catchments, preserve and restore natural forested areas in the catchments, treat wastewater discharges, and improve river connectivity.

Harnessing aquatic plant growth forms to apply European nutrient-enrichment bioindicators to Canadian waters

Premise

Aquatic macrophyte species abundance and nutrient affinity are used in metrics to assess the trophic condition of lakes and rivers. The development of these indices is often regional, with inter-regional comparisons being complicated by the lack of taxonomic overlap. Here, we use a traits-based approach to expand the geographic scope of existing metrics.

Methods

We generalized European trophic affinity values using the response of plant growth form to the light-nutrient gradient, then applied these values to sites in Canada. We evaluated the method's performance against the measured total phosphorus concentration (TP).

Results

Free-floating and emergent growth forms were associated with enriched waters (>0.2 mg/L TP), whereas rosette forms were associated with oligotrophic conditions (<0.05 mg/L TP). The responses were longitudinally consistent, and the site scores among indices were highly collinear. Growth form-based scores were more strongly correlated with TP than were species-based scores (0.42-0.56 versus 0.008-0.25).

Discussion

We leveraged the ecological relationship between increased surface water nutrient enrichment and the dominance of particular aquatic plant growth forms to generalize aquatic plant trophic indices. We demonstrated an approach for adapting species-based indices to plant traits to facilitate a broader geographic application and simpler data collection, which could be used to develop an easily applied trait-based method of assessing water nutrient status.

Ecological quality status assessment of tropical estuaries with benthic indices using differently derived reference conditions

Setting appropriate reference conditions (RCs) is critical for classifying the Ecological Quality Status (EcoQS) which is extremely challenging, considering the present-day estuaries. The EcoQS of three tropical estuaries was assessed by applying five different RCs to identify the best applicable method for the area. The AZTI's indices (AMBI and M-AMBI) categorised areas with sharper pollution gradient with ease, while classification of moderate-low polluted areas was ambiguous. Indices responded to chemical stressors more clearly in the impacted estuary compared to the less polluted estuaries. Ecological status assigned by the default RC (lowest AMBI and highest diversity and richness values) were more accurate than those obtained on application of other four types of RCs, owing to various estuarine constraints that are discussed herewith. Thus, prior to application, caution should be exercised while setting area-specific RCs. The inclusion of combination of AZTI's indices with professional judgment for successful appraisal of ecosystem is recommended.

River and lake nutrient targets that support ecological status: European scale gap analysis and strategies for the implementation of the Water Framework Directive

Eutrophication caused by an excessive presence of nutrients is affecting large portions of European waters with more than 60% of the surface water bodies failing to achieve the primary ambition of water management in Europe, that of good ecological status (GES) with diffuse emission from agriculture being the second most important pressure affecting surface waters. We developed EU wide and regional nutrient targets that define the boundary concentrations between good and moderate status for river and lake total P (TP) and total N (TN) and assessed the gap between actual nutrient concentrations and these targets and considered strategies of nutrient reductions necessary to achieve GES and deliver ecosystem services. The nutrient targets established for rivers ranged from 0.5-3.5 mg/L TN and 11-105 μg/L TP and for lakes 0.5-1.8 mg/L TN and 10-60 μg/L TP. Based on the EU wide targets, 59% of the TN and 57% of the TP river monitoring sites and 64% of the TN and 61% of the TP lake monitoring sites exceed these value and are thus at less than GES. The PCA and step-wise regression for EU basins clearly showed that the basin nutrient export is predominantly related to agricultural inputs. In addition, the step-wise regression models for TN and TP provided the ability to extrapolate the results and quantify the input reductions necessary for reaching the nutrient targets at the EU level. The results suggest that a dual water management strategy would be beneficial and should focus a) on those less polluted rivers and lakes that can easily attain the GES goal and b) on the more highly polluted systems that will improve the delivery of ecosystem services.

Establishing ecologically-relevant nutrient thresholds: A tool-kit with guidance on its use

One key component of any eutrophication management strategy is establishment of realistic thresholds above which negative impacts become significant and provision of ecosystem services is threatened. This paper introduces a toolkit of statistical approaches with which such thresholds can be set, explaining their rationale and situations under which each is effective. All methods assume a causal relationship between nutrients and biota, but we also recognise that nutrients rarely act in isolation. Many of the simpler methods have limited applicability when other stressors are present. Where relationships between nutrients and biota are strong, regression is recommended. Regression relationships can be extended to include additional stressors or variables responsible for variation between water bodies. However, when the relationship between nutrients and biota is weaker, categorical approaches are recommended. Of these, binomial regression and an approach based on classification mismatch are most effective although both will underestimate threshold concentrations if a second stressor is present. Whilst approaches such as changepoint analysis are not particularly useful for meeting the specific needs of EU legislation, other multivariate approaches (e.g. decision trees) may have a role to play. When other stressors are present quantile regression allows thresholds to be established which set limits above which nutrients are likely to influence the biota, irrespective of other pressures. The statistical methods in the toolkit may be useful as part of a management strategy, but more sophisticated approaches, often generating thresholds appropriate to individual water bodies rather than to broadly defined "types", are likely to be necessary too. The importance of understanding underlying ecological processes as well as correct selection and application of methods is emphasised, along with the need to consider local regulatory and decision-making systems, and the ease with which outcomes can be communicated to non-technical audiences.

Cyprus' diatom diversity and the association of environmental and anthropogenic influences for ecological assessment of rivers using DNA metabarcoding

Human activities are the leading cause of environmental impairments. Appropriate biomonitoring of ecosystems is needed to assess these activities effectively. In freshwater ecosystems, periphytic and epilithic biofilms have diatom assemblages. These assemblages respond rapidly to environmental changes, making diatoms valuable bioindicators. For this reason, freshwater biomonitoring programs are currently using diatoms (e.g., Water Framework Directive). In the past ten years, DNA metabarcoding coupled with next-generation sequencing and bioinformatics represents a complementary approach for diatom biomonitoring. In this study, this approach is used for the first time in Cyprus by considering the association of environmental and anthropogenic pressures to diatom assemblages. Statistical analysis was then applied to identify the environmental (i.e., river types, geo-morphological) and anthropogenic (i.e., physicochemical, human land-use pressures) variables' role in the observed diatom diversity. Results indicate differences in diatom assemblages between intermittent and perennial rivers. Achnanthidium minutissimum was more abundant in intermittent rivers; whereas Amphora pediculus and Planothidium caputium in perennial ones. Additionally, we could demonstrate the correlation between nutrients (e.g., nitrogen, phosphorus), stations' local characteristics (e.g., elevation), and land use activities on the observed differences in diatom diversity. Finally, we conclude that multi-stressors and anthropogenic pressures together as multiple stressors have a significant statistical relationship to the observed diatom diversity and play a pivotal role in determining Cyprus' rivers' ecological status.

Evaluation of the impact of heterogeneous environmental pollutants on benthic macroinvertebrates and water quality by long-term monitoring of the buyuk menderes river basin

Biomonitoring is a significant method for evaluating aquatic life forms and their environments. The longer the process continues, the results of it become more precise. Benthic macroinvertebrates' exposure to changes in environmental conditions makes them an important part of any biomonitoring program. This paper reviews a long-term water quality of the Buyuk Menderes River Basin which is the biggest river basin spread across the western Anatolia (Turkey). The study area was divided into three regions (Usak, Aydin, Denizli), primarily considering the provincial borders in the basin. A total of 40 sampling sites from the main river and its tributaries were selected. The prominent agricultural and industrial pollutants (textile, tannery and sugar factories) from each region have been taken into account. The most common and current biotic indices (BMWP Spanish version, ASPT, RBPIII, MMIF, EPT%, Diversity and Evenness) based on the pollution tolerance of benthic macroinvertebrates have been used to track water quality changes. The relationships between environmental variables (sO₂, dO₂, water temp., salinity, flow, TDS, Cond, pH, NO₃-N, NO₂-N, PO₄-P, Fe⁺³, NH₄-N) and bioindicators have been revealed by using multivariate analyses (NMDS, CCA). The region-based variations in water quality were compared with the Kruskal-Wallis test. The one-way variance analysis test (ANOVA) was used for the contrast between the biotic indices. Significant differences (p < 0.05) were found among the regions in terms of Shannon-Wiener, Evenness, BMWP and MMIF indices. Regions were separated according to pollution sources, and the impact of provinces on water quality may vary according to their industry types. It has been observed that pollutants can spread across a basin for very long distances and reinstatement of the environmental conditions may require long periods.

Setting the Phosphorus Boundaries for Greek Natural Shallow and Deep Lakes for Water Framework Directive Compliance

Eutrophication caused by nutrient enrichment is a predominant stressor leading to lake degradation and, thus, the set-up of boundaries that support good ecological status, the Water Framework Directive’s main target, is a necessity. Greece is one of the Member States that have recorded delays in complying with the coherent management goals of European legislation. A wide range of different statistical approaches has been proposed in the Best Practice Guide for determining appropriate nutrient thresholds. To determine the nutrient thresholds supporting the good status of natural Greek lakes, the phytoplankton dataset gathered from the national monitoring programme (2015–2020) was used for shallow and deep natural lakes. The regression analyses were sufficient and robust in order to derive total phosphorus thresholds that ranged from 20 to 41 μg/L in shallow and 15–32 μg/L in deep natural lake types. Nutrient boundaries that encompass the stressors these lakes are subject to, are essential in proper lake management design.

Assessing the Ecological Status of European Rivers and Lakes Using Benthic Invertebrate Communities: A Practical Catalogue of Metrics and Methods

The Water Framework Directive requires that the ecological status of surface waters be monitored and managed if necessary. A central function in ecological status assessment has the Biological Quality Elements—organisms inhabiting surface waters—by indicating human impact on their habitat. For benthic invertebrates, a wide array of national methods are used, but to date no comprehensive summary of metrics and methods is available. In this study, we summarize the benthic invertebrate community metrics used in national systems to assess the ecological status of rivers, (very) large rivers, and lakes. Currently, benthic invertebrate assemblages are used in 26 national assessment systems for rivers, 13 assessment systems for very large rivers, and 21 assessment systems for lakes in the EU. In the majority of systems, the same metrics and modules are used. In the Red Queen’s race of ecosystem management this may be a disadvantage as these same metrics and module likely depict the same stressors but there is growing evidence that aquatic ecosystems are subject to highly differentiated, complex multiple stressor impacts. Method development should be fostered to identify and rank impacts in multi-stressor environments. DNA-based biomonitoring 2.0 offers to detect stressors with greater accuracy—if new tools are calibrated.

Limno-ecological assessment of lentic ecosystems in the western Mediterranean basin (Turkey) using phytoplankton indices

Great attention has been given to freshwater ecosystems worldwide due to the increased exploitation of water resources and the degradation of water quality. This study was aimed to demonstrate the phytoplankton-stressor interactions using multivariate approaches and assess the ecological conditions of 28 sampling stations of 12 lentic ecosystems (five lakes and seven reservoirs) in the western Mediterranean basin using phytoplankton indices in dry and rainy seasons 2018. Freshwater and brackish water systems were separately ordinated by canonical correspondence analysis. The brackish ecosystems were under pressures of Ar (arsenic), N-N[Formula: see text] (nitrite), Ca (calcium), EC (electrical conductivity), Cl (chloride), B (boron), etc., whereas shallow freshwater ecosystems were associated with total organic carbon. These factors had significant effects on phytoplankton distribution among lentic ecosystems on the basin. Ecological associations of phytoplankton assemblages varied in the western Mediterranean basin during the study. Pseudanabaena catenata and Palatinus apiculatus, considered tolerant taxa, are associated with higher Ar, EC, and V (vanadium) while Desmodesmus abundans and Microcystis flos-aquae are related to total organic carbon. The modified PTI (phytoplankton trophic index) had the highest correlation coefficient value. Scores of the PTI varied from 2.02 in Çavdır Reservoir to 2.59 in Lake Kocagöl. Results of phytoplankton indices indicated that two (Gölhisar and Yazır) lakes and two (Yapraklı and Çavdır) reservoirs were classified as Good, and three lakes and five reservoirs were classified as Moderate condition. Other predicted classifications (high, poor, and bad) by phytoplankton metrics were not represented. The modified PTI could be a suitable phytoplankton metric for assessing the ecological status of lentic ecosystems in the Mediterranean system according to its highest correlation coefficient value. Overall, the results of this limno-ecological study demonstrated that responses of phytoplankton taxa to explanatory factors provide crucial ecological information about their ecology and to estimate the ecological status of lentic ecosystems.

Translational Molecular Ecology in practice: Linking DNA-based methods to actionable marine environmental management

Molecular-based approaches can provide timely biodiversity assessments, showing an immense potential to facilitate decision-making in marine environmental management. However, the uptake of molecular data into environmental policy remains minimal. Here, we showcase a selection of local to global scale studies applying molecular-based methodologies for environmental management at various stages of implementation. Drawing upon lessons learned from these case-studies, we provide a roadmap to facilitate applications of DNA-based methods to marine policies and to overcome the existing challenges. The main impediment identified is the need for standardized protocols to guarantee data comparison across spatial and temporal scales. Adoption of Translational Molecular Ecology - the sustained collaboration between molecular ecologists and stakeholders, will enhance consensus with regards to the objectives, methods, and outcomes of environmental management projects. Establishing a sustained dialogue among stakeholders is key to accelerating the adoption of molecular-based approaches for marine monitoring and assessment.

A comparative analysis of the application of water quality exemptions in the European Union: The case of nitrogen

Freshwater ecosystems and water uses may be jeopardized by the degradation of water quality. The Water Framework Directive of the European Union (EU) sets environmental objectives for water bodies but foresees the establishment of exemptions under some circumstances. The criteria used to justify these exemptions, however, are not fully developed, leaving their application open to some arbitrariness. Our study explores the relations between the magnitude of pressures affecting continental surface water bodies and the declared exemptions on the permitted concentration of nitrogen. It identifies different approaches to declare exemptions to nitrogen environmental objectives across six EU Member States and discusses the underlying criteria. A better understanding of the pressures-impact-measures/exemptions relation helps compare water policy decisions across different regions subject to the same legal obligations and set priorities for mitigation measures.

Ecoregions, climate, topography, physicochemical, or a combination of all: Which criteria are the best to define river types based on abiotic variables and macroinvertebrates in neotropical rivers?

The baseline conditions for a particular river or stream type are essential to classify aquatic ecosystems based on physical and biological characteristics. In this study, we proposed a river typology for different ecoregions, climate and topography of northwestern Argentina using parameters, and combined key variables to establish reference conditions. A set of geographical, hydro-morphological, hydrological, geological (pedology and sedimentology) and physicochemical variables were measured from different rivers and analyzed with clustering and ordination techniques to develop a typology. We analyzed the correspondence of the physical river conditions and benthic macroinvertebrate assemblages using non-metric multidimensional scaling analysis, dissimilarity among assemblages, ANOSIM approach and envfit analysis in order to make an ecological validation of the classification. Our results allowed us to classify the neotropical rivers studied, according to typological systems adapted from the European Water Framework Directive. The combination of ecoregions and topography along with other variables associated (system B), was better corresponded with biological arrangements. Hence, ecoregions and topography combined turned out to be more precise as a criterion to define river types and their local abiotic and biotic reference conditions. Macroinvertebrate distribution corresponded with the classifications proposed and was related with abiotic features of the rivers. The physical variables as altitude, grain size, water temperature and turbidity were key parameters to develop a schematic model to define river types that could be implemented and tested in other countries of the region. Five river types have been identified, characterized, and included in three large groups: Mountains, Foothills, and Lowlands (Plains). Our results showed that topography and climate are two aspects that strongly influence South American freshwater biota. We propose the schematic model developed in our study as a baseline to define freshwater biomes based on altitude (topography), ecoregions (climate) and biological functional traits at a broad spatial scale (continental or global).

Understanding divergences between ecological status classification systems based on diatoms

A large number of diatom-based classification systems have been developed worldwide in recent years. These new systems, together with the oldest, emerged on the need to assess the water quality of rivers, but knowledge on possible divergences resulting from their simultaneous application within a territory is limited. This study aimed to compare the ecological status classification provided by conceptually different methodological approaches, of use or potential use within the same region. 402 monitoring samples were collected from Atlantic siliceous streams (NW-Iberian Peninsula) and temporary Mediterranean streams (Balearic Islands, Spain). Two multimetric indices specifically developed for these areas (MDIAT and DIATMIB, respectively) were calculated, as well as the Specific Polluosensitivity Index (IPS). Multimetric indices were more sensitive methods at diagnosing degradation than IPS since they took directly account of abundance (i.e. chlorophyll a in DIATMIB) or indirectly by its proved inverse relationship with Chl a (MDIAT), together with their use of the regional reference diatom community. Alteration gradients were identified in both studied regions based on the distribution of diatoms, with the first axis of distance-based redundancy analyses (dbRDA) being related to nutrient enrichment and organic loads. Threshold Indicator Taxa ANalysis (TITAN) performed on diatoms sampled along environmental (dbRDA axis 1 and phosphate) and biological gradients (as Ecological Quality Ratio scores of classifications), pointed to lower than current Good/Moderate boundaries for phosphate maximum values (e.g. 22.5 and 71.6 μg L^-1 for Galicia and the Balearic Islands, respectively) as well as for higher Good/Moderate boundaries for the MDIAT and IPS classifications. A 'transition group' of species was classified as sensitive or as tolerant depending on the regional nutrients range. Findings of the present study highlight the need to perform auto-ecological studies to increase the knowledge on regional diatoms and their optimal survival ranges across regions prior to adopt other non-regional diatom indices.

Chemical pollution imposes limitations to the ecological status of European surface waters

Aquatic ecosystems are affected by man-made pressures, often causing combined impacts. The analysis of the impacts of chemical pollution is however commonly separate from that of other pressures and their impacts. This evolved from differences in the data available for applied ecology vis-à-vis applied ecotoxicology, which are field gradients and laboratory toxicity tests, respectively. With this study, we demonstrate that the current approach of chemical impact assessment, consisting of comparing measured concentrations to protective environmental quality standards for individual chemicals, is not optimal. In reply, and preparing for a method that would enable the comprehensive assessment and management of water quality pressures, we evaluate various quantitative chemical pollution pressure metrics for mixtures of chemicals in a case study with 24 priority substances of Europe-wide concern. We demonstrate why current methods are sub-optimal for water quality management prioritization and that chemical pollution currently imposes limitations to the ecological status of European surface waters. We discuss why management efforts may currently fail to restore a good ecological status, given that to date only 0.2% of the compounds in trade are considered in European water quality assessment and management.

Use of Aquatic Biota to Detect Ecological Changes in Freshwater: Current Status and Future Directions

Freshwater ecosystems have been severely damaged worldwide by a multitude of human pressures, such as pollution, nutrient enrichment, damming or overexploitation, and this has been more intense over the past five decades. It is therefore important that the impacts of such stressors can be effectively detected, monitored and assessed in order to provide adequate legislative tools and to protect and restore freshwater ecosystems. The use of aquatic biota to detect, measure and track changes in the environment is often known as freshwater biomonitoring and is based on the premise that the presence or absence of biotic assemblages at a given site reflects its degree of environmental quality. For over a century, since the early pollution-oriented indicators, freshwater monitoring has been developing and testing progressively more complex indicator systems, and increasing the plethora of pressures addressed, using different biological groups, such as benthic macroinvertebrates, macrophytes, fish, phytoplankton and phytobenthos. There is an increasing demand for precision and accuracy in bioassessment. In this Special Issue, five high-quality papers were selected and are briefly presented herein, that cover a wide range of issues and spatial contexts relevant to freshwater biomonitoring.

Changes in invertebrate community composition allow for consistent interpretation of biodiversity loss in ecological status assessment

Biological communities change in response to human alteration. The response of individual taxa and the community can be used to establish preventive criteria to halt further biodiversity deterioration. Here we explore how consistent are the boundaries between Good and Moderate ecological status derived from classification systems used in North-NW Spain: NORThern Spain Indicators system (NORTI), River type specific multimetric (METI) and Iberian Bio-monitoring Working Party (IBMWP), by using common interpretation of normative definitions of Water Framework Directive. We applied the three classifications to a monitoring dataset of Nalón River basin, comprising samples from different stream types and reference conditions. We applied Threshold Indicator Taxa ANalysis to the invertebrate community along the most relevant environmental pressures and biological impairment gradients represented by the Ecological Quality Ratio (EQR) scores of the classification systems. Only NORTI provided a true community ecological threshold and the change point (cp) 95% quantile (Q95%) range of 0.760 was assumed to be the boundary from Good to Moderate (G/M) status, used to standardize the number of taxa loss in all systems. Since the average number of taxa at reference sites was 34, the estimated loss of sensitive taxa was up to 97.1% in IBMWP, 73.5% in METI and 52.9% in NORTI when passing from Good to Moderate status, revealing very permissive boundaries. The loss of common sensitive taxa in NORTI at Q95% was used as G/M threshold and applied to the other classifications, resulting all in a common biodiversity loss of 21% of sensitive taxa richness at values of NORTI-EQR = 0.760, METI-EQR = 0.818 and IBMWP-EQR = 0.753. Results indicate that significant community changes along pressure gradients allow for establishing quantitative criteria consistent with normative definitions. This understanding derived from Directive monitoring programs can assess the risk that invertebrate communities face in terms of species loss derived from anthropogenic pressures.

Ecological status assessment based on benthic macrofauna of three Mediterranean ports: Comparisons across seasons, activities and regions

The present study aimed to compare anthropogenic impacts in three Mediterranean ports (Cagliari-Italy, Heraklion-Greece, El-Kantatoui-Tunisia) employing benthic macrofaunal indices, used in the context of the European Water Framework Directive. Sampling stations were selected within ports according to sector usage categorization and sampled over three seasons. Benthic indices calculated include M-AMBI, BENTIX, BQI and BQI_Family. Comparisons were made between the indices values and ecological status (ES) of each station within and between ports. Overall, few statistically significant differences were observed across different seasons or different stations with the same usage within or across ports. The ES of sampling stations in the leisure/fishing and passenger/cargo ships sectors was mostly "good" or "moderate", while the shipyard sector had "poor" ES. The results suggest that the indices used were suitable for assessing the ES of Mediterranean ports, led to comparable results even across different countries and contribute to the adaptation of specific port monitoring guidelines.

A new broad typology for rivers and lakes in Europe: Development and application for large-scale environmental assessments

European countries have defined >1000 national river types and >400 national lake types to implement the EU Water Framework Directive (WFD). In addition, common river and lake types have been defined within regions of Europe for intercalibrating the national classification systems for ecological status of water bodies. However, only a low proportion of national types correspond to these common intercalibration types. This causes uncertainty concerning whether the classification of ecological status is consistent across countries. Therefore, through an extensive dialogue with and data provision from all EU countries, we have developed a generic typology for European rivers and lakes. This new broad typology reflects the natural variability in the most commonly used environmental type descriptors: altitude, size and geology, as well as mean depth for lakes. These broad types capture 60-70% of all national WFD types including almost 80% of all European river and lake water bodies in almost all EU countries and can also be linked to all the common intercalibration types. The typology provides a new framework for large-scale assessments across country borders, as demonstrated with an assessment of ecological status and pressures based on European data from the 2nd set of river basin management plans. The typology can also be used for a variety of other large-scale assessments, such as reviewing and linking the water body types to habitat types under the Habitats Directive and the European Nature Information System (EUNIS), as well as comparing type-specific limit values for nutrients and other supporting quality elements across countries. Thus, the broad typology can build the basis for all scientific outputs of managerial relevance related to water body types.

Adapting the (fast-moving) world of molecular ecology to the (slow-moving) world of environmental regulation: lessons from the UK diatom metabarcoding exercise

Development of effective metabarcoding-based tools for ecological assessment requires more than just detailed knowledge of ecology and molecular genetics. There is also a need to understand the context within which they will be used, and for the organisation that uses it to understand the techniques involved and, more especially, how the data that are produced differs from that generated by traditional ecological methods. Lessons learnt during the development of a metabarcoding tool for phytobenthos in the UK are set out in this paper. This attempted to develop a molecular “mirror” of the existing light microscopy-based approach to ecological assessment. Although this conservative approach does not exploit the full potential of metabarcoding data, it does mean that benchmarks exist against which performance and data can be judged. However, the pace of developments within molecular ecology means that regulators will need to find ways of incorporating new scientific insights whilst, at the same time, ensuring a stable regulatory regime. Installation of a metabarcoding technique within a regulatory organisation, in other words, is more than a transaction in which one approach is switched for another. A deeper transformation of the organisation is required.

Nutrient criteria for surface waters under the European Water Framework Directive: Current state-of-the-art, challenges and future outlook

The aim of European water policy is to achieve good ecological status in all rivers, lakes, coastal and transitional waters by 2027. Currently, more than half of water bodies are in a degraded condition and nutrient enrichment is one of the main culprits. Therefore, there is a pressing need to establish reliable and comparable nutrient criteria that are consistent with good ecological status. This paper highlights the wide range of nutrient criteria currently in use by Member States of the European Union to support good ecological status and goes on to suggest that inappropriate criteria may be hindering the achievement of good status. Along with a comprehensive overview of nutrient criteria, we provide a critical analysis of the threshold concentrations and approaches by which these are set. We identify four essential issues: (1) Different nutrients (nitrogen and/or phosphorus) are used for different water categories in different countries. (2) The use of different nutrient fractions (total, dissolved inorganic) and statistical summary metrics (e.g., mean, percentiles, seasonal, annual) currently hampers comparability between countries, particularly for rivers, transitional and coastal waters. (3) Wide ranges in nutrient threshold values within shared water body types, in some cases showing more than a 10-fold difference in concentrations. (4) Different approaches used to set threshold nutrient concentrations to define the boundary between "good" and "moderate" ecological status. Expert judgement-based methods resulted in significantly higher (less stringent) good-moderate threshold values compared with data-driven approaches, highlighting the importance of consistent and rigorous approaches to criteria setting. We suggest that further development of nutrient criteria should be based on relationships between ecological status and nutrient concentrations, taking into account the need for comparability between different water categories, water body types within these categories, and countries.

Establishing nutrient thresholds in the face of uncertainty and multiple stressors: A comparison of approaches using simulated datasets

Various methods have been proposed to identify threshold concentrations of nutrients that would support good ecological status, but the performance of these methods and the influence of other stressors on the underlying models have not been fully evaluated. We used synthetic datasets to compare the performance of ordinary least squares, logistic and quantile regression, as well as, categorical methods based on the distribution of nutrient concentrations categorised by biological status. The synthetic datasets used differed in their levels of variation between explanatory and response variables, and were centered at different positions along the stressor (nutrient) gradient. In order to evaluate the performance of methods in "multiple stressor" situations, another set of datasets with two stressors was used. Ordinary least squares and logistic regression methods were the most reliable when predicting the threshold concentration when nutrients were the sole stressor; however, both had a tendency to underestimate the threshold when a second stressor was present. In contrast, threshold concentrations produced by categorical methods were strongly influenced by the level of the stressor (nutrient enrichment, in this case) relative to the threshold they were trying to predict (good/moderate in this instance). Although all the methods tested had limitations in the presence of a second stressor, upper quantiles seemed generally appropriate to establish non-precautionary thresholds. For example, upper quantiles may be appropriate when establishing targets for restoration, but not when seeking to minimise deterioration. Selection of an appropriate threshold concentration should also attend to the regulatory regime (i.e. policy requirements and environmental management context) within which it will be used, and the ease of communicating the principles to managers and stakeholders.

Autonomous marine environmental monitoring: Application in decommissioned oil fields

Hundreds of Oil & Gas Industry structures in the marine environment are approaching decommissioning. In most areas decommissioning operations will need to be supported by environmental assessment and monitoring, potentially over the life of any structures left in place. This requirement will have a considerable cost for industry and the public. Here we review approaches for the assessment of the primary operating environments associated with decommissioning - namely structures, pipelines, cuttings piles, the general seabed environment and the water column - and show that already available marine autonomous systems (MAS) offer a wide range of solutions for this major monitoring challenge. Data of direct relevance to decommissioning can be collected using acoustic, visual, and oceanographic sensors deployed on MAS. We suggest that there is considerable potential for both cost savings and a substantial improvement in the temporal and spatial resolution of environmental monitoring. We summarise the trade-offs between MAS and current conventional approaches to marine environmental monitoring. MAS have the potential to successfully carry out much of the monitoring associated with decommissioning and to offer viable alternatives where a direct match for the conventional approach is not possible.

Protecting and restoring Europe's waters: An analysis of the future development needs of the Water Framework Directive

The Water Framework Directive (WFD) is a pioneering piece of legislation that aims to protect and enhance aquatic ecosystems and promote sustainable water use across Europe. There is growing concern that the objective of good status, or higher, in all EU waters by 2027 is a long way from being achieved in many countries. Through questionnaire analysis of almost 100 experts, we provide recommendations to enhance WFD monitoring and assessment systems, improve programmes of measures and further integrate with other sectoral policies. Our analysis highlights that there is great potential to enhance assessment schemes through strategic design of monitoring networks and innovation, such as earth observation. New diagnostic tools that use existing WFD monitoring data, but incorporate novel statistical and trait-based approaches could be used more widely to diagnose the cause of deterioration under conditions of multiple pressures and deliver a hierarchy of solutions for more evidence-driven decisions in river basin management. There is also a growing recognition that measures undertaken in river basin management should deliver multiple benefits across sectors, such as reduced flood risk, and there needs to be robust demonstration studies that evaluate these. Continued efforts in 'mainstreaming' water policy into other policy sectors is clearly needed to deliver wider success with WFD goals, particularly with agricultural policy. Other key policy areas where a need for stronger integration with water policy was recognised included urban planning (waste water treatment), flooding, climate and energy (hydropower). Having a deadline for attaining the policy objective of good status is important, but even more essential is to have a permanent framework for river basin management that addresses the delays in implementation of measures. This requires a long-term perspective, far beyond the current deadline of 2027.

An ecological status indicator for all time: Are AMBI and M-AMBI effective indicators of change in deep time?

Increasingly environmental management seeks to limit the impacts of human activities on ecosystems relative to some 'reference' condition, which is often the presumed pre-impacted state, however such information is limited. We explore how marine ecosystems in deep time (Late Jurassic) are characterised by AZTI's Marine Biotic Index (AMBI), and how the indices responded to natural perturbations. AMBI is widely used to detect the impacts of human disturbance and to establish management targets, and this study is the first application of these indices to a fossil fauna. Our results show AMBI detected changes in past seafloor communities (well-preserved fossil deposits) that underwent regional deoxygenation in a manner analogous to those experiencing two decades of organic pollution. These findings highlight the potential for palaeoecological data to contribute to reconstructions of pre-human marine ecosystems, and hence provide information to policy makers and regulators with greater temporal context on the nature of 'pristine' marine ecosystems.

Deriving nutrient criteria to support 'good' ecological status in European lakes: An empirically based approach to linking ecology and management

European water policy has identified eutrophication as a priority issue for water management. Substantial progress has been made in combating eutrophication but open issues remain, including setting reliable and meaningful nutrient criteria supporting 'good' ecological status of the Water Framework Directive. The paper introduces a novel methodological approach - a set of four different methods - that can be applied to different ecosystems and stressors to derive empirically-based management targets. The methods include Ranged Major Axis (RMA) regression, multivariate Ordinary Least Squares (OLS) regression, logistic regression, and minimising the mismatch of classifications. We apply these approaches to establish nutrient (nitrogen and phosphorus) criteria for the major productive shallow lake types of Europe: high alkalinity shallow (LCB1; mean depth 3-15 m) and very shallow (LCB2; mean depth < 3 m) lakes. Univariate relationships between nutrients and macrophyte assessments explained 29-46% of the variation. Multivariate models with both total phosphorus (TP) and total nitrogen (TN) as predictors had higher R2 values (0.50 for LCB1 and 0.49 for LCB2) relative to the use of TN or TP singly. We estimated nutrient concentrations at the boundary where lake vegetation changes from 'good' to 'moderate' ecological status. LCB1 lakes achieved 'good' macrophyte status at concentrations below 48-53 μg/l TP and 1.1-1.2 mg/l TN, compared to LCB2 lakes below 58-78 μg/l TP and 1.0-1.4 mg/l TN. Where strong regression relationships exist, regression approaches offer a reliable basis for deriving nutrient criteria and their uncertainty, while categorical approaches offer advantages for risk assessment and communication, or where analysis is constrained by discontinuous measures of status or short stressor gradients. We link ecological status of macrophyte communities to nutrient criteria in a user-friendly and transparent way. Such analyses underpin the practical actions and policy needed to achieve 'good' ecological status in the lakes of Europe.

Macrophyte assessment in European lakes: Diverse approaches but convergent views of 'good' ecological status

The European Water Framework Directive has been adopted by Member States to assess and manage the ecological integrity of surface waters. Specific challenges include harmonizing diverse assessment systems across Europe, linking ecological assessment to restoration measures and reaching a common view on 'good' ecological status. In this study, nine national macrophyte-based approaches for assessing ecological status were compared and harmonized, using a large dataset of 539 European lakes. A macrophyte common metric, representing the average standardized view of each lake by all countries, was used to compare national methods. This was also shown to reflect the total phosphorus (r² = 0.32), total nitrogen (r² = 0.22) as well as chlorophyll-a (r² = 0.35-0.38) gradients, providing a link between ecological data, stressors and management decisions. Despite differing assessment approaches and initial differences in classification, a consensus was reached on how type-specific macrophyte assemblages change across the ecological status gradient and where ecological status boundaries should lie. A marked decline in submerged vegetation, especially Charophyta (characterizing 'good' status), and an increase in abundance of free-floating plants (characterizing 'less than good' status) were the most significant changes along the ecological status gradient. Macrophyte communities of 'good' status lakes were diverse with many charophytes and several Potamogeton species. A large number of taxa occurred across the entire gradient, but only a minority dominated at 'less than good' status, including filamentous algae, lemnids, nymphaeids, and several elodeids (e.g., Zannichellia palustris and Elodea nuttallii). Our findings establish a 'guiding image' of the macrophyte community at 'good' ecological status in hard-water lakes of the Central-Baltic region of Europe.

The future of biotic indices in the ecogenomic era: Integrating (e)DNA metabarcoding in biological assessment of aquatic ecosystems

The bioassessment of aquatic ecosystems is currently based on various biotic indices that use the occurrence and/or abundance of selected taxonomic groups to define ecological status. These conventional indices have some limitations, often related to difficulties in morphological identification of bioindicator taxa. Recent development of DNA barcoding and metabarcoding could potentially alleviate some of these limitations, by using DNA sequences instead of morphology to identify organisms and to characterize a given ecosystem. In this paper, we review the structure of conventional biotic indices, and we present the results of pilot metabarcoding studies using environmental DNA to infer biotic indices. We discuss the main advantages and pitfalls of metabarcoding approaches to assess parameters such as richness, abundance, taxonomic composition and species ecological values, to be used for calculation of biotic indices. We present some future developments to fully exploit the potential of metabarcoding data and improve the accuracy and precision of their analysis. We also propose some recommendations for the future integration of DNA metabarcoding to routine biomonitoring programs.

Implementation options for DNA-based identification into ecological status assessment under the European Water Framework Directive

Assessment of ecological status for the European Water Framework Directive (WFD) is based on "Biological Quality Elements" (BQEs), namely phytoplankton, benthic flora, benthic invertebrates and fish. Morphological identification of these organisms is a time-consuming and expensive procedure. Here, we assess the options for complementing and, perhaps, replacing morphological identification with procedures using eDNA, metabarcoding or similar approaches. We rate the applicability of DNA-based identification for the individual BQEs and water categories (rivers, lakes, transitional and coastal waters) against eleven criteria, summarised under the headlines representativeness (for example suitability of current sampling methods for DNA-based identification, errors from DNA-based species detection), sensitivity (for example capability to detect sensitive taxa, unassigned reads), precision of DNA-based identification (knowledge about uncertainty), comparability with conventional approaches (for example sensitivity of metrics to differences in DNA-based identification), cost effectiveness and environmental impact. Overall, suitability of DNA-based identification is particularly high for fish, as eDNA is a well-suited sampling approach which can replace expensive and potentially harmful methods such as gill-netting, trawling or electrofishing. Furthermore, there are attempts to replace absolute by relative abundance in metric calculations. For invertebrates and phytobenthos, the main challenges include the modification of indices and completing barcode libraries. For phytoplankton, the barcode libraries are even more problematic, due to the high taxonomic diversity in plankton samples. If current assessment concepts are kept, DNA-based identification is least appropriate for macrophytes (rivers, lakes) and angiosperms/macroalgae (transitional and coastal waters), which are surveyed rather than sampled. We discuss general implications of implementing DNA-based identification into standard ecological assessment, in particular considering any adaptations to the WFD that may be required to facilitate the transition to molecular data.

Response of fish communities to multiple pressures: Development of a total anthropogenic pressure intensity index

Lakes in Europe are subject to multiple anthropogenic pressures, such as eutrophication, habitat degradation and introduction of alien species, which are frequently inter-related. Therefore, effective assessment methods addressing multiple pressures are needed. In addition, these systems have to be harmonised (i.e. intercalibrated) to achieve common management objectives across Europe. Assessments of fish communities inform environmental policies on ecological conditions integrating the impacts of multiple pressures. However, the challenge is to ensure consistency in ecological assessments through time, across ecosystem types and across jurisdictional boundaries. To overcome the serious comparability issues between national assessment systems in Europe, a total anthropogenic pressure intensity (TAPI) index was developed as a weighted combination of the most common pressures in European lakes that is validated against 10 national fish-based water quality assessment systems using data from 556 lakes. Multi-pressure indices showed significantly higher correlations with fish indices than single-pressure indices. The best-performing index combines eutrophication, hydromorphological alterations and human use intensity of lakes. For specific lake types also biological pressures may constitute an important additional pressure. The best-performing index showed a strong correlation with eight national fish-based assessment systems. This index can be used in lake management for assessing total anthropogenic pressure on lake ecosystems and creates a benchmark for comparison of fish assessments independent of fish community composition, size structure and fishing-gear. We argue that fish-based multiple-pressure assessment tools should be seen as complementary to single-pressure tools offering the major advantage of integrating direct and indirect effects of multiple pressures over large scales of space and time.

The paradox of expert judgment in rivers ecological monitoring

A great investment has been done in the last decades in the development of numerical and qualitative assessment methods to classify the ecological quality of water bodies. Yet, in spite of all attempts to avoid subjectivity, expert judgment is still used at numerous steps of the ecological classification and is considered by some authors as indispensible for management purposes. Thus, the aim of this study is to test the hypothesis that expert judgment, when done by the adequate experts (limnologists/river ecologist) with experience in the study area (i.e., natural conditions and expected communities), could be as good as quantitative indices and measures (i.e., result in the same classification), but quicker and with lower cost. For that we compared the classifications (on 13 aspects of rivers ecosystems) attributed by two experts to 20 sites (10 each) located in their study areas, with the classifications of ecological quality based on biological indices (for invertebrates and diatoms), hydromorphology and water chemistry, calculated by an independent team. Our results show that assessments made by experts and those calculated through indices (biological quality and hydromorphology) are globally very similar (RELATE test; Rho = 0.442; p < 0.001, 999 permutations). Most differences were of one class and experts tended to attribute a better condition than indices to the best quality sites but a worse condition to the worse quality sites. A Principal Components Analysis revealed that sites to which experts attributed a moderate quality had higher nitrate concentration and pH but were well oxygenated. The sites classified as poor and bad where those with stronger modifications in their habitats (given by the higher values of HMS). The difference between experts and indices is small but still represents 15% of sites, and includes both situations: the experts or the indices lead to the need of measures (i.e., classifications below class Good). Experts' evaluations on hydromorphological conditions of the channel and margins are also significantly correlated with the quality assessments made by the field team that has no experience in the study area (Rh₀ = 0.518; p = 0.001; 999 permutation), indicating geographic independence in the expert judgment. We concluded that expert judgment could be used in the determination of streams and rivers ecological quality, saving money and time and helping to redirect monitoring funds to actual implementation of restoration measures. Yet, classification' scoring methods may still be useful for a better targeting of restoration measures.

RAPPER: A new method for rapid assessment of macroalgae as a complement to diatom-based assessments of ecological status

Most methods for ecological assessment developed since the onset of the Water Framework Directive require substantial effort by skilled analysts and are therefore expensive to use. RAPPER ("Rapid Assessment of PeriPhyton Ecology in Rivers") is a high level ecological "triage" method that enables rapid screening of sites within a water body to enable managers to identify areas subject to nutrient pressures. The method involves a survey of macroscopic algae within 10m lengths of watercourses, taking samples for subsequent identification, and assessing cover. Genus-level identification is used to ensure rapid assessment and comparability, and that the method can be used by a wide range of users. Genera of alga that form conspicuous growths recognisable with the naked eye are designated as either "stress-tolerant" ("S-taxa") or "competitive" taxa ("C-taxa"), depending on their preference for locations with low or high nutrient concentrations. Genera whose representatives span a wide range of nutrient conditions, or for which few data are available, are placed in a third class, "unclassified". The presence of S-taxa and the relative cover of C-taxa are then used to determine whether a site is at risk from eutrophication. Field trials in Scotland demonstrated that the method discriminates between sites with low and high nutrient concentrations. Significant differences were also observed in values of the Trophic Diatom Index between RAPPER classification categories. RAPPER can be used alone (allowing greater spatial or temporal coverage within water bodies at lower cost than conventional assessment methods) or to increase confidence in assessments of the condition of the phytobenthos by incorporating algae other than diatoms. The outcomes also relate directly to the experiences of non-technical stakeholders, and will have benefits for communicating ecosystem health concepts to the wider public, for example through "citizen science".

Benthic macroinvertebrates in lake ecological assessment: A review of methods, intercalibration and practical recommendations

Legislation in Europe has been adopted to determine and improve the ecological integrity of inland and coastal waters. Assessment is based on four biotic groups, including benthic macroinvertebrate communities. For lakes, benthic invertebrates have been recognized as one of the most difficult organism groups to use in ecological assessment, and hitherto their use in ecological assessment has been limited. In this study, we review and intercalibrate 13 benthic invertebrate-based tools across Europe. These assessment tools address different human impacts: acidification (3 methods), eutrophication (3 methods), morphological alterations (2 methods), and a combination of the last two (5 methods). For intercalibration, the methods were grouped into four intercalibration groups, according to the habitat sampled and putative pressure. Boundaries of the 'good ecological status' were compared and harmonized using direct or indirect comparison approaches. To enable indirect comparison of the methods, three common pressure indices and two common biological multimetric indices were developed for larger geographical areas. Additionally, we identified the best-performing methods based on their responsiveness to different human impacts. Based on these experiences, we provide practical recommendations for the development and harmonization of benthic invertebrate assessment methods in lakes and similar habitats.

Comparative test of ecological assessment methods of lowland streams based on long-term monitoring data of macrophytes

Ecological assessment of water courses is required by the European Water Framework Directive (WFD). Assessment by means of macrophytes is impeded by insufficient knowledge on the relations between assessment scores and the dynamics of environmental parameters. Data from a long-term observation of macrophyte dynamics over 21 years in two lowland rivers were used for testing the performance of six widely used assessment methods. Six sample sites situated in two lowland streams were selected. Four sites were classified as of moderate habitat quality and two sites as of poor habitat quality in the context of WFD. Assessment methods generally showed a poor performance in recognizing the ecological status of the annual observations. Status was more often over- than underestimated. Performance of methods differed among individual rivers and among river zones. Assessment scores mostly showed a steady decline, even though all sites obviously remained in the same habitat quality class throughout the observation period. Variation of most environmental factors was largely unrelated to assessment scores. Fluctuations of assessment scores were partly related to single natural disturbance events such as high discharge. Increased shading by marginal trees was reflected negatively by most assessment scores. Assessment scores were highly correlated with species richness and total abundance. The best overall performance was shown by the North-Rhine Westphalian (NRW) method. In contrast to single metric methods it can be adapted to individual properties of a reach in a flexible way. Macrophyte assessment based on the pressure-impact framework did not lead to a satisfying result in our case study. Improvement of species assessment scores and inclusion of functional properties such as growth form may help to overcome the present difficulties.

Benefits and limitations of an intercalibration of phytoplankton assessment methods based on the Mediterranean GIG reservoir experience

The status of European legislation regarding inland water quality after the enactment of the Water Framework Directive (WFD) originated scientific effort to develop reliable methods, primarily based on biological parameters. An important aspect of the process was to ensure that quality assessment was comparable between the different Member States. The Intercalibration process (IC), required in the WFD ensures the unbiased application of the norm. The presented results were developed in the context of the 2nd IC phase. An overview of the reservoir type definition of the Lake Mediterranean Geographical Intercalibration Group, where four types were considered divided by both alkalinity and climate, together with the results for selection of Maximum Ecological Potential sites (MEP) are presented. MEP reservoirs were selected based on pressure and biological variables. Three phytoplankton-based assessment methods were intercalibrated using data from Mediterranean countries. The Mediterranean Assessment System for Reservoirs Phytoplankton (Spain), the New Mediterranean Assessment System for Reservoirs Phytoplankton (Portugal and Cyprus) and the New Italian Method (Italy) were applied. These three methods were compared through option 3 of the Intercalibration Guide. The similarity of the assessments was quantified, and the Good/Moderate (GM) boundaries assessed. All three methods stood as comparable at the GM boundary except for the MASRP in siliceous wet reservoirs, which was slightly stricter. Finally, the main taxonomic groups represented in the phytoplankton community at MEP conditions were identified, as well as their main changes with an increasing trophic status. MEP sites are dominated by chrysophytes in siliceous wet reservoirs and by the diatoms Cyclotella and Achnanthes in calcareous ones. Cyanobacteria take over the community in both calcareous and siliceous wet reservoirs as eutrophication increases. In summary, the relevance and reliability of the quality assessment methods compared were confirmed both from an ecological perspective and a health risk management point of view.

Nationwide benthic macroinvertebrate assemblage multimetric indices: identifying inconsistencies and limitations in reporting stream impairment status, USA

The objective of this study was to identify the current status of stream water-quality assessment and reporting methods for four states in the Ohio River basin (Indiana, Ohio, Tennessee, and Virginia), as required by the 305(b) section of the United States (US) Clean Water Act. Specifically, we clarified the discrepancies that exist among stream-impairment status classified by benthic macroinvertebrate multimetric indices (MMIs) and depicted using Geographic Information Systems shapefiles. In addition, we provided guidance in solving some of the comparability problems that arise when developing state-specific MMIs and depicting stream-impairment status using Geographic Information Systems technology. The MMI variation among states and differences in shapefile formats resulted in a nationwide dataset, which cannot be directly compared. Incorporating the changes suggested in this study allow for a uniform assessment and reporting method nationwide. Successful implementation of these changes would strengthen the US Environmental Protection Agency efforts to identify impaired streams and sources of those impairments without the limitations of state-by-state .developed assessment methods.

Assessing the ecological status in the context of the European Water Framework Directive: where do we go now?

The Water Framework Directive (WFD) is now well established as the key management imperative in river basins across Europe. However, there remain significant concerns with the way WFD is implemented and there is now a need for water managers and scientists to communicate better in order to find solutions to these concerns. To address this, a Science-Policy Interface (SPI) activity was launched in 2010 led by Directorate-General for Research and Innovation and Onema (the French national agency for water and aquatic ecosystems), which provided an interactive forum to connect scientists and WFD end-users. One major aim of the SPI activity was to establish a list of the most crucial research and development needs for enhancing WFD implementation. This paper synthesises the recommendations from this event highlighting 10 priority issues relating to ecological status. For lakes, temporary streams and transitional and coastal waters, WFD implementation still suffers from a lack of WFD-compliant bioassessment methods. For rivers, special attention is required to assess the ecological impacts of hydromorphological alterations on biological communities, notably those affecting river continuity and riparian covering. Spatial extrapolation tools are needed in order to evaluate ecological status for water bodies for which no data are available. The need for more functional bioassessment tools as complements to usual WFD-compliant tools, and to connect clearly good ecological state, biodiversity and ecosystem services when implementing WFD were also identified as crucial issues.

FORUM: Ecological networks: the missing links in biomonitoring science

Monitoring anthropogenic impacts is essential for managing and conserving ecosystems, yet current biomonitoring approaches lack the tools required to deal with the effects of stressors on species and their interactions in complex natural systems.

Ecological networks (trophic or mutualistic) can offer new insights into ecosystem degradation, adding value to current taxonomically constrained schemes. We highlight some examples to show how new network approaches can be used to interpret ecological responses.

Synthesis and applications. Augmenting routine biomonitoring data with interaction data derived from the literature, complemented with ground‐truthed data from direct observations where feasible, allows us to begin to characterise large numbers of ecological networks across environmental gradients. This process can be accelerated by adopting emerging technologies and novel analytical approaches, enabling biomonitoring to move beyond simple pass/fail schemes and to address the many ecological responses that can only be understood from a network‐based perspective.

Augmenting routine biomonitoring data with interaction data derived from the literature, complemented with ground‐truthed data from direct observations where feasible, allows us to begin to characterise large numbers of ecological networks across environmental gradients. This process can be accelerated by adopting emerging technologies and novel analytical approaches, enabling biomonitoring to move beyond simple pass/fail schemes and to address the many ecological responses that can only be understood from a network‐based perspective.

Comparability of fish-based ecological quality assessments for geographically distinct Iberian regions

In this work we compare two Iberian and a pan-European fish-based methods to assess ecological quality in rivers: the Fish-based Index of Biotic Integrity for Portuguese Wadeable Streams (F-IBIP), the Mediterranean Index of Biotic Integrity (IBIMED) and the pan-European Fish Index (EFI+). The results presented herein were developed in the context of the 2nd phase of the Intercalibration Exercise (IC), as required by the Water Frame Directive (WFD). The IC is aimed at ensuring comparability of the quality boundaries among the different WFD assessment methods developed by the Member States for each biological quality element. Although the two national assessment methods were developed for very distinct regions of Iberia (Western and Eastern Iberian Peninsula) they share the same methodological background: both are type-specific and guild-based multimetric indices. EFI+ is a multimetric guild-based model, but it is site-specific and uses a predictive modelling approach. The three indices were computed for all sites included in the Iberian Intercalibration database to allow the direct comparison, by means of linear regressions, of the resulting three quality values per site. The quality boundary harmonization between the two Iberian methods was only possible through an indirect comparison between the two indices, using EFI+ as a common metric. The three indices were also shown to be responsive to a common set of human induced pressures. This study highlights the need to develop general assessment methods adapted to wide geographical ranges with high species turnover to help intercalibrating assessment methods tailored for geographically more restricted regions.

Water quality assessment of rivers using diatom metrics across Mediterranean Europe: a methods intercalibration exercise

The European Water Framework Directive establishes a framework for the protection of water resources. However, common water management tools demand common understanding of assessment methods, so quality goals are equally met. Intercalibration of methods ensures the comparability of biological elements across similar geographical areas. Many aspects can influence the outcome of intercalibration: data sampling, treatment methods, taxonomic reliability of databases, choice of metrics for ecological quality status classification, and criteria for selecting reference sites. This study describes the potentials and constraints of the intercalibration of indices using diatoms for assessment of Mediterranean rivers. Harmonisation of diatom taxonomy and nomenclature was based on a previous ring test which took place at the European level. Four diatom indices (Indice de Polluosensibilité Spécifique-IPS, Indice Biologique Diatomées-IBD 2007, Intercalibration Common Metric Italy-ICMi and Slovenian Ecological Status assessment system) were intercalibrated using data from six European Mediterranean countries (Cyprus, France, Italy, Portugal, Slovenia and Spain). Boundaries between High/Good and Good/Moderate quality classes were harmonised by means of the Intercalibration Common Metric (ICM). Comparability between countries was assured through boundary bias and class agreement. The national boundaries were adjusted when they deviated more than a quarter of a class equivalent (0.25) from the global mean. All national methods correlated well with the ICM, which was sensitive to water quality (negatively correlated to nutrients). Achnanthidium minutissimum sensu lato was the most discriminative species of Good ecological status class. Planothidium frequentissimum, Gomphonema parvulum and Nitzschia palea were the most contributive to Moderate ecological status class. Some taxa were discriminative for both Good and Moderate ecological status classes due to low indication and ecological discriminative power but also due to differences in taxonomy between countries. This intercalibration exercise allowed establishment of common water quality goals across Mediterranean Europe, which is substantiated with the ICM.