Biomonitoring of Human Impacts in Freshwater Ecosystems

Towards stressor-specific macroinvertebrate indices: Which traits and taxonomic groups are associated with vulnerable and tolerant taxa?

Monitoring of macroinvertebrate communities is frequently used to define the ecological health status of rivers. Ideally, biomonitoring should also give an indication on the major stressors acting on the macroinvertebrate communities supporting the selection of appropriate management measures. However, most indices are affected by more than one stressor. Biological traits (e.g. size, generation time, reproduction) could potentially lead to more stressor-specific indices. However, such an approach has rarely been tested. In this study we classify 324 macroinvertebrate taxa as vulnerable (decreasing abundances) or tolerant (increasing abundances) along 21 environmental gradients (i.e. nutrients, major ions, oxygen and micropollutants) from 422 monitoring sites in Germany using Threshold Indicator Taxa Analysis (TITAN). Subsequently, we investigate which biological traits and taxonomic groups are associated with taxa classified as vulnerable or tolerant with regard to specific gradients. The response of most taxa towards different gradients was similar and especially high for correlated gradients. Traits associated with vulnerable taxa across most gradients included: larval aquatic life stages, isolated cemented eggs, reproductive cycle per year <1, scrapers, aerial and aquatic active dispersal and plastron respiration. Traits associated with tolerant taxa included: adult aquatic life stages, polyvoltinism, ovoviviparity or egg clutches in vegetation, food preference for dead animals or living microinvertebrates, substrate preference for macrophytes, microphytes, silt or mud and a body size >2-4cm. Our results question whether stressor-specific indices based on macroinvertebrate assemblages can be achieved using single traits, because we observed that similar taxa responded to different gradients and also similar traits were associated with vulnerable and tolerant taxa across a variety of water quality gradients. Future studies should examine whether combinations of traits focusing on specific taxonomic groups achieve higher stressor specificity.

TREHS: An open-access software tool for investigating and evaluating temporary river regimes as a first step for their ecological status assessment

When the regime of a river is not perennial, there are four main difficulties with the use of hydrographs for assessing hydrological alteration: i) the main hydrological features relevant for biological communities are not quantitative (discharges) but qualitative (phases such as flowing water, stagnant pools or lack of surface water), ii) stream flow records do not inform on the temporal occurrence of stagnant pools, iii) as most of the temporary streams are ungauged, their regime has to be evaluated by alternative methods such as remote sensing or citizen science, and iv) the biological quality assessment of the ecological status of a temporary stream must follow a sampling schedule and references adapted to the flow- pool-dry regime. To overcome these challenges within an operational approach, the freely available software tool TREHS has been developed within the EU LIFE TRIVERS project. This software permits the input of information from flow simulations obtained with any rainfall-runoff model (to set an unimpacted reference stream regime) and compares this with the information obtained from flow gauging records (if available) and interviews with local people, as well as instantaneous observations by individuals and interpretation of ground-level or aerial photographs. Up to six metrics defining the permanence of water flow, the presence of stagnant pools and their temporal patterns of occurrence are used to determine natural and observed river regimes and to assess the degree of hydrological alteration. A new regime classification specifically designed for temporary rivers was developed using the metrics that measure the relative permanence of the three main phases: flow, disconnected pools and dry stream bed. Finally, the software characterizes the differences between the natural and actual regimes, diagnoses the hydrological status (degree of hydrological alteration), assesses the significance and robustness of the diagnosis and recommends the best periods for biological quality samplings.

Environmental DNA metabarcoding: Transforming how we survey animal and plant communities

The genomic revolution has fundamentally changed how we survey biodiversity on earth. High-throughput sequencing ("HTS") platforms now enable the rapid sequencing of DNA from diverse kinds of environmental samples (termed "environmental DNA" or "eDNA"). Coupling HTS with our ability to associate sequences from eDNA with a taxonomic name is called "eDNA metabarcoding" and offers a powerful molecular tool capable of noninvasively surveying species richness from many ecosystems. Here, we review the use of eDNA metabarcoding for surveying animal and plant richness, and the challenges in using eDNA approaches to estimate relative abundance. We highlight eDNA applications in freshwater, marine and terrestrial environments, and in this broad context, we distill what is known about the ability of different eDNA sample types to approximate richness in space and across time. We provide guiding questions for study design and discuss the eDNA metabarcoding workflow with a focus on primers and library preparation methods. We additionally discuss important criteria for consideration of bioinformatic filtering of data sets, with recommendations for increasing transparency. Finally, looking to the future, we discuss emerging applications of eDNA metabarcoding in ecology, conservation, invasion biology, biomonitoring, and how eDNA metabarcoding can empower citizen science and biodiversity education.

River doctors: Learning from medicine to improve ecosystem management

Effective ecosystem management requires a robust methodology to analyse, remedy and avoid ecosystem damage. Here we propose that the overall conceptual framework and approaches developed over millennia in medical science and practice to diagnose, cure and prevent disease can provide an excellent template. Key principles to adopt include combining well-established assessment methods with new analytical techniques and restricting both diagnosis and treatment to qualified personnel at various levels of specialization, in addition to striving for a better mechanistic understanding of ecosystem structure and functioning, as well as identifying the proximate and ultimate causes of ecosystem impairment. In addition to applying these principles, ecosystem management would much benefit from systematically embracing how medical doctors approach and interview patients, diagnose health condition, select treatments, take follow-up measures, and prevent illness. Here we translate the overall conceptual framework from medicine into environmental terms and illustrate with examples from rivers how the systematic adoption of the individual steps proven and tested in medical practice can improve ecosystem management.

Trophic availability buffers the detrimental effects of clogging in an alpine stream

Clogging, the streambed colmation by fine sediments, is an important widespread source of impact affecting freshwaters. Alterations in stream morphology and hydrology, added to the effects of global climate change, are responsible for this phenomenon, that is particularly pernicious in mountainous lotic systems naturally characterized by coarse substrates. Among the studies investigating this issue some were descriptive, while others used artificial substrates to compare ongoing fine sediment accumulation and macroinvertebrate assemblage recruitment. Other studies used from the outset artificial substrates arranged with different levels of clogging. Our study fits into this line, but adding an innovative element simulating different availability of coarse particulate organic matter, i.e. the main trophic input in low-order, mountainous stream. To investigate how clogging and CPOM can influence macroinvertebrate communities, we placed 135 artificial substrates in the upper Po river (NW Italy). We set up a three way factorial design with three different levels of sedimentation and terrestrial leaf material. Artificial substrates were removed on three different dates. Benthic invertebrates were identified and classified according to their bio-ecological traits. We also measured macroinvertebrate dry mass and CPOM degradation in the different trap types. Our findings show that clogging acts as a selective filter influencing taxa richness, density, functional composition and biomass of benthic assemblage. Moreover, fine sediments affect the energetic dynamics in the river ecosystem, decreasing the mass loss rate of terrestrial leaves. Interestingly, our results clearly demonstrate that high availability of CPOM can buffer the negative effect of clogging, suggesting that an adequate input of allochthonous organic matter may lessen the impact of fine sediment deposition. Because land use transformation and removal of wooded riparian areas increase clogging and simultaneously reduces the input of CPOM, our findings stress the importance to include the management of river basins in the conservation strategies of mountainous streams.

Benthic macroinvertebrate field sampling effort required to produce a sample adequate for the assessment of rivers and streams of Neuquén Province, Argentina

This multi-year pilot study evaluated a proposed field method for its effectiveness in the collection of a benthic macroinvertebrate sample adequate for use in the condition assessment of streams and rivers in the Neuquén Province, Argentina. A total of 13 sites, distributed across three rivers, were sampled. At each site, benthic macroinvertebrates were collected at 11 transects. Each sample was processed independently in the field and laboratory. Based on a literature review and resource considerations, the collection of 300 organisms (minimum) at each site was determined to be necessary to support a robust condition assessment, and therefore, selected as the criterion for judging the adequacy of the method. This targeted number of organisms was collected at all sites, at a minimum, when collections from all 11 transects were combined. Subsequent bootstrapping analysis of data was used to estimate whether collecting at fewer transects would reach the minimum target number of organisms for all sites. In a subset of sites, the total number of organisms frequently fell below the target when fewer than 11 transects collections were combined.Site conditions where < 300 organisms might be collected are discussed. These preliminary results suggest that the proposed field method results in a sample that is adequate for robust condition assessment of the rivers and streams of interest. When data become available from a broader range of sites, the adequacy of the field method should be reassessed.

Multibiomarker responses in aquatic insect Belostoma elegans (Hemiptera) to organic pollution in freshwater system

The present study analyzes a battery of biomarkers in the water bug Belostoma elegans from a stream polluted with organic matter (OMS), and another one considered as reference site (RS) during spring-summer season (December to March). Biochemical parameters of glucidic, lipidic and oxidative metabolic pathways were analyzed in males and females of this insect. In general, no significant differences were observed in all biomarkers assayed between both sexes, except lactate concentration which was higher in males than in females (p < 0.0006) in the first three months. About carbohydrate metabolism parameters, only pyruvate-kinase showed significant differences between insects collected in both streams (p < 0.05) during December. However, the total lipid content, saturated fatty acid, and mainly triacylglycerol were higher in insects from RS compared to those from OMS (p < 0.002) in all sampled months. Levels of lipoperoxidation, protein oxidation, reduced glutathione and glutathione-S-transferase activity showed no differences between insects collected from both streams. Nevertheless, the significant increase observed in superoxide dismutase and catalase activities (p < 0.004) could be due to the elevated oxidative metabolism in insects from RS compared to those from OMS with lower dissolved oxygen. Regarding those responding parameters, males accounted for the differences between the two sites during the study period. In conclusion, our results support that lipidic energetic reserves and antioxidant enzyme activities in B. elegans could be used as biomarkers of environmental pollution by organic matter.

Using a polymer probe characterized by MALDI-TOF/MS to assess river ecosystem functioning: From polymer selection to field tests

Characterization of river ecosystems must take into consideration both structural and functional aspects. For the latter, a convenient and simple approach for routine monitoring is based on the decomposition of organic matter measured in terms of breakdown of natural organic substrates like leaf litter, wood sticks. Here we extended the method to a synthetic organic material using polymer probes characterized by MALDI-TOF/MS. We first characterized several commercial available polymers, and finally selected polycaprolactonediol 1250 (PCP 1250), a polyester oligomer, as the most convenient for further studies. PCP 1250 was first tested at mesocosms scale under conditions simulating those of the river, with and without nutrient addition for up to 4weeks. Differences to the starting material measured in terms of changes in the relative ion peak intensities were clearly observed. Ions exhibited a different pattern evolution along time depending on their mass. Greatest changes were observed at longest exposure time and in the nutrient addition treatment. At shorter times, the effect of nutrients (addition or not) was indistinguishable. Finally, we performed an experiment in 11 tributaries of the Ebro River during 97days of exposure. Principal Component Analysis confirmed the different behavior of ions, which were clustered according to their mass. Exposed samples were clearly different to the standard starting material, but could not be well distinguished among each other. Polymer mass loss rates, as well as some environmental variables such as conductivity, temperature and flow were correlated with some peak intensities. Overall, the interpretation of field results in terms of environmental conditions remains elusive, due to the influence of multiple concurrent factors. Nevertheless, breakdown of synthetic polymers opens an interesting field of research, which can complement more traditional breakdown studies to assess river ecosystem functioning.

Eco-epidemiology of aquatic ecosystems: Separating chemicals from multiple stressors

A non-toxic environment and a good ecological status are policy goals guiding research and management of chemicals and surface water systems in Europe and elsewhere. Research and policies on chemicals and water are however still disparate and unable to evaluate the relative ecological impacts of chemical mixtures and other stressors. This paper defines and explores the use of eco-epidemiological analysis of surveillance monitoring data sets via a proxy to quantify mixture impacts on ecosystems. Case studies show examples of different, progressive steps that are possible. Case study data were obtained for various regions in Europe and the United States. Data types relate to potential stressors at various scales, concerning landscape, land-use, in-stream physico-chemical and pollutant data, and data on fish and invertebrates. The proxy-values for mixture impacts were quantified as predicted (multi-substance) Potentially Affected Fractions of species (msPAF), using Species Sensitivity Distribution (SSD) models in conjunction with bioavailability and mixture models. The case studies summarize the monitoring data sets and the subsequent diagnostic bioassessments. Variation in mixture toxic pressures amongst sites appeared to covary with abundance changes in large (50-86%) percentages of taxa for the various study regions. This shows that an increased mixture toxic pressure (msPAF) relates to increased ecological impacts. Subsequent multi-stressor evaluations resulted in statistically significant, site-specific diagnosis of the magnitudes of ecological impacts and the relative contributions of different stress factors to those impacts. This included both mixtures and individual chemicals. These results allow for ranking stressors, sites and impacted species groups. That is relevant information for water management. The case studies are discussed in relation to policy and management strategies that support reaching a non-toxic environment and good ecological status. Reaching these goals requires not only focused sectoral policies, such as on chemical- or water management, but also an overarching and solution-focused view.

Functional Response (FR) and Relative Growth Rate (RGR) Do Not Show the Known Invasiveness of Lemna minuta (Kunth)

Growing travel and trade threatens biodiversity as it increases the rate of biological invasions globally, either by accidental or intentional introduction. Therefore, avoiding these impacts by forecasting invasions and impeding further spread is of utmost importance. In this study, three forecasting approaches were tested and combined to predict the invasive behaviour of the alien macrophyte Lemna minuta in comparison with the native Lemna minor: the functional response (FR) and relative growth rate (RGR), supplemented with a combined biomass-based nutrient removal (BBNR). Based on the idea that widespread invasive species are more successful competitors than local, native species, a higher FR and RGR were expected for the invasive compared to the native species. Five different nutrient concentrations were tested, ranging from low (4 mgN.L-1 and 1 mgP.L-1) to high (70 mgN.L-1 and 21 mgP.L-1). After four days, a significant amount of nutrients was removed by both Lemna spp., though significant differences among L. minor and L. minuta were only observed at lower nutrient concentrations (lower than 17 mgN.L-1 and 6 mgP.L-1) with higher nutrient removal exerted by L. minor. The derived FR did not show a clear dominance of the invasive L. minuta, contradicting field observations. Similarly, the RGR ranged from 0.4 to 0.6 d-1, but did not show a biomass-based dominance of L. minuta (0.5 ± 0.1 d-1 versus 0.63 ± 0.09 d-1 for L. minor). BBNR showed similar results as the FR. Contrary to our expectations, all three approaches resulted in higher values for L. minor. Consequently, based on our results FR is sensitive to differences, though contradicted the expectations, while RGR and BBNR do not provide sufficient power to differentiate between a native and an invasive alien macrophyte and should be supplemented with additional ecosystem-based experiments to determine the invasion impact.

Habitat Complexity in Aquatic Microcosms Affects Processes Driven by Detritivores

Habitat complexity can influence predation rates (e.g. by providing refuge) but other ecosystem processes and species interactions might also be modulated by the properties of habitat structure. Here, we focussed on how complexity of artificial habitat (plastic plants), in microcosms, influenced short-term processes driven by three aquatic detritivores. The effects of habitat complexity on leaf decomposition, production of fine organic matter and pH levels were explored by measuring complexity in three ways: 1. as the presence vs. absence of habitat structure; 2. as the amount of structure (3 or 4.5 g of plastic plants); and 3. as the spatial configuration of structures (measured as fractal dimension). The experiment also addressed potential interactions among the consumers by running all possible species combinations. In the experimental microcosms, habitat complexity influenced how species performed, especially when comparing structure present vs. structure absent. Treatments with structure showed higher fine particulate matter production and lower pH compared to treatments without structures and this was probably due to higher digestion and respiration when structures were present. When we explored the effects of the different complexity levels, we found that the amount of structure added explained more than the fractal dimension of the structures. We give a detailed overview of the experimental design, statistical models and R codes, because our statistical analysis can be applied to other study systems (and disciplines such as restoration ecology). We further make suggestions of how to optimise statistical power when artificially assembling, and analysing, 'habitat complexity' by not confounding complexity with the amount of structure added. In summary, this study highlights the importance of habitat complexity for energy flow and the maintenance of ecosystem processes in aquatic ecosystems.

A multiple index integrating different levels of organization

Many methods in freshwater biomonitoring tend to be restricted to a few levels of biological organization, limiting the potential spectrum of measurable of cause-effect responses to different anthropogenic impacts. We combined distinct organisational levels, covering biological biomarkers (histopathological and biochemical reactions in liver and fish gills), community based bioindicators (fish guilds, invertebrate metrics/traits and chironomid pupal exuviae) and ecosystem functional indicators (decomposition rates) to assess ecological status at designated Water Framework Directive monitoring sites, covering a gradient of human impact across several rivers in northern Portugal. We used Random Forest to rank the variables that contributed more significantly to successfully predict the different classes of ecological status and also to provide specific cut levels to discriminate each WFD class based on reference condition. A total of 59 Biological Quality Elements and functional indicators were determined using this procedure and subsequently applied to develop the integrated Multiple Ecological Level Index (MELI Index), a potentially powerful bioassessment tool.

Ecological impact and recovery of a Mediterranean river after receiving the effluent from a textile dyeing industry

The textile industry is one of the largest sectors globally, representing up to 20% of industrial water pollution. However, there is limited insight into how fluvial ecosystems respond and recover from this impact. From summer 2012 to spring 2013, we examined water quality and ecological status upstream and 1.5km downstream the input of a textile industry wastewater treatment plant (WWTP) in Ripoll River, NE Spain. The ecological status was determined via diversity measures and 10 biotic indices based on diatoms, macrophytes, macroinvertebrates and fish. Our results showed that the WWTP severely deteriorated water quality and biological communities at the discharge site, but that they improved at 1.5km downstream. Severity also varied across taxa and seasons, being fish the most affected taxa and spring the season with the best ecological status. The strong correlation amongst water quality variables and many biotic indices across taxa indicated that this is a chronic pollution event affecting multiple trophic levels. Thus, this study suggests that there is an urgent need to invest in wastewater treatment in this industry to preserve the ecological integrity of Ripoll River and especially its fish fauna. Likewise, it illustrates the diagnostic power of biotic indices based on diatoms, macroinvertebrates and fish, as driven by the European Water Framework Directive.

Functional redundancy as a tool for bioassessment: A test using riparian vegetation

There is an urgent need to track how natural systems are responding to global change in order to better guide management efforts. Traditionally, taxonomically based metrics have been used as indicators of ecosystem integrity and conservation status. However, functional approaches offer promising advantages that can improve bioassessment performance. In this study, we aim to test the applicability of functional redundancy (FR), a functional feature related to the stability, resistance and resilience of ecosystems, as a tool for bioassessment, looking at woody riparian communities in particular. We used linear mixed-effect models to investigate the response of FR and other traditional biomonitoring indices to natural (drought duration) and anthropogenic stress gradients (flow regulation and agriculture) in a Mediterranean basin. Such indices include species richness, a taxonomic index, and the Riparian Quality Index, which is an index of ecological status. Then, we explored the ability of FR and the other indices to discriminate between different intensities of human alteration. FR showed higher explanatory capacity in response to multiple stressors, although we found significant negative relationships between all the biological indices (taxonomic, functional and ecological quality) and stress gradients. In addition, FR was the most accurate index to discriminate among different categories of human alteration in both perennial and intermittent river reaches, which allowed us to set threshold values to identify undisturbed (reference condition), moderately disturbed and highly disturbed reaches in the two types of river. Using these thresholds and the best-fitting model, we generated a map of human impact on the functional redundancy of riparian communities for all the stretches of the river network. Our results demonstrate that FR presents clear advantages over traditional methods, which suggests that it should be part of the biomonitoring toolbox used for environmental management so as to obtain better predictions of ecosystem response to environmental changes.

A stochastic dynamic model to assess land use change scenarios on the ecological status of fluvial water bodies under the Water Framework Directive

This method development paper outlines an integrative stochastic dynamic methodology (StDM) framework to anticipate land use (LU) change effects on the ecological status of monitored and non-monitored lotic surface waters under the Water Framework Directive (WFD). Tested in the Alto Minho River Basin District in North West Portugal, the model is an innovative step towards developing a decision-making and planning tool to assess the influence impacts such as LU change and climate change on these complex systems. Comprising a series of sequential steps, a Generalized Linear Model based, competing model Multi Model Inference (MMI) approach was used for parameter estimation to identify principal land use types (distal factors) driving change in biological and physicochemical support elements (proximal factors) in monitored water bodies. The framework integrated MMI constants and coefficients of selected LU categories in the StDM simulations and spatial projections to simulate the ecological status of monitored and non-monitored lotic waterbodies in the test area under 2 scenarios of (1) LU intensification and (2) LU extensification. A total of 100 simulations were run for a 50year period for each scenario. Spatially dynamic projections of WFD metrics were obtained, taking into account the occurrence of stochastic wildfire events which typically occur in the study region and are exacerbated by LU change. A marked projected decline to "Moderate" ecological status for most waterbodies was detected under intensification but little change under extensification; only a few waterbodies fell to "moderate" status. The latter scenario describes the actual regional socio-economic situation of agricultural abandonment due to rural poverty, partly explaining the projected lack of change in ecological status. Based on the WFD "one out all out" criterion, projected downward shifts in ecological status were due to physicochemical support elements, namely increased phosphorus levels. Little or no change in status was driven by Intercalibrated Biological Quality Elements, indicating innate resilience and raising questions concerning uncertainty, the effect of pressures other than land use and metric redundancy and the WFD classification process.

Quality control in public participation assessments of water quality: the OPAL Water Survey

Background

Public participation in scientific data collection is a rapidly expanding field. In water quality surveys, the involvement of the public, usually as trained volunteers, generally includes the identification of aquatic invertebrates to a broad taxonomic level. However, quality assurance is often not addressed and remains a key concern for the acceptance of publicly-generated water quality data. The Open Air Laboratories (OPAL) Water Survey, launched in May 2010, aimed to encourage interest and participation in water science by developing a ‘low-barrier-to-entry’ water quality survey. During 2010, over 3000 participant-selected lakes and ponds were surveyed making this the largest public participation lake and pond survey undertaken to date in the UK. But the OPAL approach of using untrained volunteers and largely anonymous data submission exacerbates quality control concerns. A number of approaches were used in order to address data quality issues including: sensitivity analysis to determine differences due to operator, sampling effort and duration; direct comparisons of identification between participants and experienced scientists; the use of a self-assessment identification quiz; the use of multiple participant surveys to assess data variability at single sites over short periods of time; comparison of survey techniques with other measurement variables and with other metrics generally considered more accurate. These quality control approaches were then used to screen the OPAL Water Survey data to generate a more robust dataset.

Results

The OPAL Water Survey results provide a regional and national assessment of water quality as well as a first national picture of water clarity (as suspended solids concentrations). Less than 10 % of lakes and ponds surveyed were ‘poor’ quality while 26.8 % were in the highest water quality band.

Conclusions

It is likely that there will always be a question mark over untrained volunteer generated data simply because quality assurance is uncertain, regardless of any post hoc data analyses. Quality control at all stages, from survey design, identification tests, data submission and interpretation can all increase confidence such that useful data can be generated by public participants.

The effects of climatic fluctuations and extreme events on running water ecosystems

Most research on the effects of environmental change in freshwaters has focused on incremental changes in average conditions, rather than fluctuations or extreme events such as heatwaves, cold snaps, droughts, floods or wildfires, which may have even more profound consequences. Such events are commonly predicted to increase in frequency, intensity and duration with global climate change, with many systems being exposed to conditions with no recent historical precedent. We propose a mechanistic framework for predicting potential impacts of environmental fluctuations on running-water ecosystems by scaling up effects of fluctuations from individuals to entire ecosystems. This framework requires integration of four key components: effects of the environment on individual metabolism, metabolic and biomechanical constraints on fluctuating species interactions, assembly dynamics of local food webs, and mapping the dynamics of the meta-community onto ecosystem function. We illustrate the framework by developing a mathematical model of environmental fluctuations on dynamically assembling food webs. We highlight (currently limited) empirical evidence for emerging insights and theoretical predictions. For example, widely supported predictions about the effects of environmental fluctuations are: high vulnerability of species with high per capita metabolic demands such as large-bodied ones at the top of food webs; simplification of food web network structure and impaired energetic transfer efficiency; and reduced resilience and top-down relative to bottom-up regulation of food web and ecosystem processes. We conclude by identifying key questions and challenges that need to be addressed to develop more accurate and predictive bio-assessments of the effects of fluctuations, and implications of fluctuations for management practices in an increasingly uncertain world.

Functional trait composition of aquatic plants can serve to disentangle multiple interacting stressors in lowland streams

Historically, close attention has been paid to negative impacts associated with nutrient loads to streams and rivers, but today hydromorphological alterations are considered increasingly implicated when lowland streams do not achieve good ecological status. Here, we explore if trait-abundance patterns of aquatic plants change along gradients in hydromorphological degradation and eutrophication in lowland stream sites located in Denmark. Specifically, we hypothesised that: i) changes in trait-abundance patterns occur along gradients in hydromorphological degradation and ii) trait-abundance patterns can serve to disentangle effects of eutrophication and hydromorphological degradation in lowland streams reflecting that the mechanisms behind changes differ. We used monitoring data from a total of 147 stream reaches with combined data on aquatic plant species abundance, catchment land use, hydromorphological alterations (i.e. planform, cross section, weed cutting) and water chemistry parameters. Traits related to life form, dispersal, reproduction and survival together with ecological preference values for nutrients and light (Ellenberg N and L) were allocated to 41 species representing 79% of the total species pool. We found clear evidence that habitat degradation (hydromorphological alterations and eutrophication) mediated selective changes in the trait-abundance patterns of the plant community. Specific traits could distinguish hydromorphological degradation (free-floating, surface; anchored floating leaves; anchored heterophylly) from eutrophication (free-floating, submerged; leaf area). We provide a conceptual framework for interpretation of how eutrophication and hydromorphological degradation interact and how this is reflected in trait-abundance patterns in aquatic plant communities in lowland streams. Our findings support the merit of trait-based approaches in biomonitoring as they shed light on mechanisms controlling structural changes under environmental stress. The ability to disentangle several stressors is particularly important in lowland stream environments where several stressors act in concert since the impact of the most important stressor can be targeted first, which is essential to improve the ecological status.

Ecological relevance of biomarkers in monitoring studies of macro-invertebrates and fish in Mediterranean rivers

Mediterranean rivers are probably one of the most singular and endangered ecosystems worldwide due to the presence of many endemic species and a long history of anthropogenic impacts. Besides a conservation value per se, biodiversity is related to the services that ecosystems provide to society and the ability of these to cope with stressors, including climate change. Using macro-invertebrates and fish as sentinel organisms, this overview presents a synthesis of the state of the art in the application of biomarkers (stress and enzymatic responses, endocrine disruptors, trophic tracers, energy and bile metabolites, genotoxic indicators, histopathological and behavioural alterations, and genetic and cutting edge omic markers) to determine the causes and effects of anthropogenic stressors on the biodiversity of European Mediterranean rivers. We also discuss how a careful selection of sentinel species according to their ecological traits and the food-web structure of Mediterranean rivers could increase the ecological relevance of biomarker responses. Further, we provide suggestions to better harmonise ecological realism with experimental design in biomarker studies, including statistical analyses, which may also deliver a more comprehensible message to managers and policy makers. By keeping on the safe side the health status of populations of multiple-species in a community, we advocate to increase the resilience of fluvial ecosystems to face present and forecasted stressors. In conclusion, this review provides evidence that multi-biomarker approaches detect early signs of impairment in populations, and supports their incorporation in the standardised procedures of the Water Frame Work Directive to better appraise the status of European water bodies.

A new framework for selecting environmental surrogates

Surrogate concepts are used in all sub-disciplines of environmental science. However, controversy remains regarding the extent to which surrogates are useful for resolving environmental problems. Here, we argue that conflicts about the utility of surrogates (and the related concepts of indicators and proxies) often reflect context-specific differences in trade-offs between measurement accuracy and practical constraints. By examining different approaches for selecting and applying surrogates, we identify five trade-offs that correspond to key points of contention in the application of surrogates. We then present an 8-step Adaptive Surrogacy Framework that incorporates cross-disciplinary perspectives from a wide spectrum of the environmental sciences, aiming to unify surrogate concepts across disciplines and applications. Our synthesis of the science of surrogates is intended as a first step towards fully leveraging knowledge accumulated across disciplines, thus consolidating lessons learned so that they may be accessible to all those operating in different fields, yet facing similar hurdles.

Development of a benthic diatom index of biotic integrity (BD-IBI) for ecosystem health assessment of human dominant subtropical rivers, China

As efforts intensify to address the issues of declining water quality and biodiversity losses in freshwater ecosystems, there have been great demands for effective methods of evaluating aquatic ecosystem health. In this study, benthic algae assemblages and water quality variables were analyzed to develop a benthic diatom-based index of biotic integrity (BD-IBI) for assessment of the aquatic environment in the upper Han River (China). Through the use of multivariate and multimetric approaches, four metrics - % prostrate individuals, % Amphora individuals, % polysaprob species, and diatom-based eutrophication/pollution index (EPI-D) - were identified from 98 candidate metrics to develop a BD-IBI. Application of the index revealed that water quality in 11% of the 31 sampled sites could be described as excellent condition, in 43% of the sites it could be described as good condition, in 25% as moderate condition, and in 21% as poor condition. The assessment further revealed that the main reason for degradation of the Han river ecosystem was nutrient enrichment through agricultural land use.

How stressor specific are trait-based ecological indices for ecosystem management?

Using macroinvertebrates as ecological indicators for different stressors has a long tradition. However, when applied to field data, one often observes correlations between different macroinvertebrate indices that can be attributed to both correlations of stressors and inherent correlations due to the sensitivity of taxa to different stressors. Ignoring the source of any given correlation leads to ambiguous conclusions about the impact of different stressors. Here, we demonstrate how to distinguish the causes of correlation by means of Monte Carlo simulations. We assessed to which degree trait-based indices are stressor-specific and whether this depends on the pool of taxa and its taxonomic resolution. Therefore, we (1) analysed the frequencies of "sensitive" and "insensitive" taxa for pairwise combinations of different indices, (2) analysed the inherent correlation of indices with random samples from different taxon pools derived from field samples and from a complete species list of a whole ecoregion, and (3) compared this inherent correlation with the actual correlation of the field samples. We exemplified this approach by analysing two existing indices (SPEARpesticides, Saprobic Index) and new indices for temperature, flow and pH stress. We used these new indices to illustrate our approach while in-depth testing of their applicability was not the focus of our study. We found strong correlations between several indices in our study area at the Swiss Plateau. The probability that this correlation is only due to inherent correlation in the taxa sensitivities was low (maximum of 0.34). The problem of inherent correlation between indices is more severe for the smaller taxon pool with lower taxonomic resolution. Correlation in the sensitivity of different taxa to different stressors leads to an inherent correlation in trait-based indices, which weakens their explanatory power. Our results highlight the importance of correlation analyses when using trait-based indices to guide ecosystem-management, especially in regions with reduced biodiversity.

Re-meandering of lowland streams: will disobeying the laws of geomorphology have ecological consequences?

We evaluated the restoration of physical habitats and its influence on macroinvertebrate community structure in 18 Danish lowland streams comprising six restored streams, six streams with little physical alteration and six channelized streams. We hypothesized that physical habitats and macroinvertebrate communities of restored streams would resemble those of natural streams, while those of the channelized streams would differ from both restored and near-natural streams. Physical habitats were surveyed for substrate composition, depth, width and current velocity. Macroinvertebrates were sampled along 100 m reaches in each stream, in edge habitats and in riffle/run habitats located in the center of the stream. Restoration significantly altered the physical conditions and affected the interactions between stream habitat heterogeneity and macroinvertebrate diversity. The substrate in the restored streams was dominated by pebble, whereas the substrate in the channelized and natural streams was dominated by sand. In the natural streams a relationship was identified between slope and pebble/gravel coverage, indicating a coupling of energy and substrate characteristics. Such a relationship did not occur in the channelized or in the restored streams where placement of large amounts of pebble/gravel distorted the natural relationship. The analyses revealed, a direct link between substrate heterogeneity and macroinvertebrate diversity in the natural streams. A similar relationship was not found in either the channelized or the restored streams, which we attribute to a de-coupling of the natural relationship between benthic community diversity and physical habitat diversity. Our study results suggest that restoration schemes should aim at restoring the natural physical structural complexity in the streams and at the same time enhance the possibility of re-generating the natural geomorphological processes sustaining the habitats in streams and rivers. Documentation of restoration efforts should be intensified with continuous monitoring of geomorphological and ecological changes including surveys of reference river systems.

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.

Impact of genomic diversity in river ecosystems

We propose that genomic diversity in aquatic macrophytes of rivers, driven by the underlying genomic processes of interspecific hybridization and polyploidy (whole-genome duplication), play a significant role in ecosystem functioning. These genomic processes generate individuals which might differ in their demands for nitrogen (N) and phosphorus (P). This is significant because (i) N and/or P are frequently limiting nutrients in freshwater ecosystems, and (ii) nucleic acids are demanding in N and P. We suggest that N and P availability will provide a selection pressure for genetic variants in macrophytes which will, in turn, influence the nutritional quality of plant biomass, and hence their consumption by herbivores and detritivores as well as the energy flux of their biomass through the food web.

The use of wooden sticks to assess stream ecosystem functioning: comparison with leaf breakdown rates

Breakdown of organic matter is a key process in streams and rivers, and thus, it has potential to assess functional impairment of river ecosystems. Because the litter-bag method commonly used to measure leaf breakdown is time consuming and expensive, several authors proposed to measure breakdown of wooden sticks instead. Nevertheless, currently there is little information on the performance of wooden sticks versus that of leaves. We compared the breakdown of tongue depressors made of untreated poplar wood, to that of six common leaf species in two large streams in the Basque Country (northern Spain), one polluted and the other unpolluted. Breakdown rates ranged from 0.0011 to 0.0120 day(-1), and were significantly lower in the polluted stream. Wooden sticks performed very similarly to leaves, but were less affected by flood-induced physical abrasion. The ranking of the materials according to their breakdown rate was consistent, irrespective of the stream. The experiments with leaves were 10 times more costly for breakdown rate, 4 times if we include the rest of the variables measured. Therefore wooden sticks offer a promising tool to assess river ecosystem functioning, although more research is necessary to define the thresholds for ecosystem functional impairment.

The importance of metacommunity ecology for environmental assessment research in the freshwater realm

Most bioassessment programs rest on the assumption that species have different niches, and that abiotic environmental conditions and changes therein determine community structure. This assumption is thus equivalent to the species sorting perspective (i.e. that species differ in their responses to environmental variation) in metacommunity ecology. The degree to which basing bioassessment on the species sorting perspective is reasonable is likely to be related to the spatial extent of a study and the characteristics of the organism groups (e.g. dispersal ability) with which the effects of anthropogenic changes are assessed. Recent findings in metacommunity research have stressed that community structure is determined not only by local abiotic environmental conditions but also by biotic interactions and dispersal-related effects. For example, dispersal limitation may prevent community structure recovery from the effects of a putative stressor, as organisms may not be able to disperse to all sites in a region. Mass effects (i.e. the presence of species in environmentally suboptimal sites due to high dispersal rates from environmentally suitable sites) may, in turn, obscure the effects of a stressor, as dispersal from source sites (e.g. an unaltered site) allows persistence at sink sites (e.g. an anthropogenically altered site). Better bioassessment should thus take both niche- and dispersal-related processes simultaneously into consideration, which can be accomplished by explicitly modelling spatial location as a proxy for dispersal effects. Such an integrated approach should be included in bioassessment programs using general multivariate approaches, predictive modelling, and multimetric indices.

Caddisflies as biomonitors identifying thresholds of toxic metal bioavailability that affect the stream benthos

It has been proposed that bioaccumulated concentrations of toxic metals in tolerant biomonitors be used as indicators of metal bioavailability that could be calibrated against the ecological response to metals of sensitive biotic assemblages. Our hypothesis was that metal concentrations in caddisfly larvae Hydropsyche siltalai and Plectrocnemia conspersa, as tolerant biomonitors, indicate metal bioavailability in contaminated streams, and can be calibrated against metal-specific ecological responses of mayflies. Bioaccumulated concentrations of Cu, As, Zn and Pb in H. siltalai from SW English streams were related to the mayfly assemblage. Mayflies were always sparse where bioavailabilities were high and were abundant and diverse where bioavailabilities of all metals were low, a pattern particularly evident when the combined abundance of heptageniid and ephemerellid mayflies was the response variable. The results offer promise that bioaccumulated concentrations of metals in tolerant biomonitors can be used to diagnose ecological impacts on stream benthos from metal stressors.