Chapter

Detecting and Quantifying the Impact of Multiple Stress on River Ecosystems

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Abstract

Freshwater ecosystems are among the most imperiled on earth, with rivers being particularly susceptible to anthropogenic stress. Environmental monitoring across Europe reveals that 45% of rivers are affected by more than one human-driven pressure. Detecting and quantifying the impact of multiple stressors exerted from these pressures thus represent important scientific tasks in support of aquatic ecosystem management. This chapter reviews the scientific literature on experimental and field-based observational studies investigating into multistressor effects. Forty experimental and 48 field-based observational studies were covered, dealing with 72 and 151 paired stressor combinations, respectively. Morphological stress paired with either nutrient or hydrological stress was most frequently addressed in both study types. While experiments focused on a broad range of receptor organisms including phytobenthos, benthic invertebrates, fish, microorganisms (e.g., bacteria and fungi) and related processes (e.g., leaf decomposition), field studies mainly investigated the effects on benthic invertebrates and fish. Stressor interactions were more relevant in the experimental studies, with almost 50% of phytobenthos receptor metrics featuring interactions, as compared to the field studies, where stressor interactions were often not specified. Unknown stressor interactions challenge aquatic ecosystem management by posing risks of unwanted “ecological surprises.” Future scientific efforts need to concentrate on classifying the relevance and strength of interactive effects across types of stressors, receptors, and existing ecosystems, considering the specific local conditions of the water bodies to be managed. River basin management will benefit from ecosystem modeling to diagnose the causes of detrimental ecological effects, or to predict the benefits and trade-offs of management strategies in multistressor contexts.

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... Impact of ecosystem type and spatial scale on the models' explanatory power. European lakes are generally in a better condition than European rivers 20 and are affected by a lower number of stressors 30 . We therefore expected the explanatory power of our models to be lower for rivers because of the greater impacts of stressors that have not been regarded (that is, confounding factors) 8,31 . ...
... In this study, we considered a stressor as any external factor modified by human intervention that potentially moves a receptor (that is, a response variable) out of its normal operating range 46 . The analysed stressor variables belonged to six stress categories (see also ref. 30 ): (1) nutrient stress (142 cases), including the experimental addition or field sampling of phosphorus or nitrogen compounds in the water; (2) hydrological stress (57 cases), including the experimental manipulation or field measurement of high flow (for example, high flow pulse duration), low flow (for example, residual flow), water level change, non-specific flow alteration (for example, the mean summer precipitation as a proxy) and hydropeaking; (3) morphological stress (61 cases), including experimental treatment or field survey of river channel, bank and floodplain modification, and river connectivity disruption; (4) thermal stress (54 cases), including experimental heating or field measurement of water temperature (or air temperature as a proxy); (5) toxic stress of mixtures of xenobiotic compounds (18 cases), expressed as the multisubstance potentially affected fraction 40 , toxic units 47 or runoff potential 48 ; and (6) other chemical stress (16 cases), including the experimental application of humic substances and field samples of water quality determinants (for example, dissolved oxygen, chloride and biological oxygen demand). ...
... 29 Department of Ecohydrology, Leibniz-Institute of Freshwater Ecology and Inland Fisheries (IgB), Berlin, germany. 30 Center for Hydrology and Informatics, National technical university of Athens, Athens, greece. 31 Institute of Marine Biological Resources and Inland Waters, Hellenic Centre for Marine Research, Anavissos Attikis, greece. ...
... Despite an increasing number of studies on multiple stressor effects in aquatic systems (Birk, 2019;Nõges et al., 2016), the state of knowledge remains incomplete. Inconclusive evidence, for instance on the appearance of interactions (Côté et al., 2016;Crain et al., 2008;Jackson et al., 2016), necessitates increased research efforts (Orr et al., 2020). ...
... Such experimental results, however, do not necessarily upscale well in space and time since they only are a snapshot of a particular context at a particular time. In addition, most water bodies are oftentimes affected by more than three stressors (Birk, 2019;EEA, 2018a). Field studies at regional scale have delivered contradictory results, even when targeting the same area. ...
Article
Full-text available
The biota of European rivers are affected by a wide range of stressors impairing water quality and hydro‐morphology. Only about 40% of Europe’s rivers reach ‘good ecological status’, a target set by the European Water Framework Directive (WFD) and indicated by the biota. It is yet unknown how the different stressors in concert impact ecological status and how the relationship between stressors and status differs between river types. We linked the intensity of seven stressors to recently measured ecological status data for more than 50,000 sub‐catchment units (covering almost 80% of Europe’s surface area), which were distributed among twelve broad river types. Stressor data were either derived from remote sensing data (extent of urban and agricultural land use in the riparian zone) or modelled (alteration of mean annual flow and of base flow, total phosphorous load, total nitrogen load and mixture toxic pressure, a composite metric for toxic substances), while data on ecological status were taken from national statutory reporting of the second WFD River Basin Management Plans for the years 2010 to 2015. We used Boosted Regression Trees to link ecological status to stressor intensities. The stressors explained on average 61% of deviance in ecological status for the twelve individual river types, with all seven stressors contributing considerably to this explanation. On average 39.4% of the deviance was explained by altered hydro‐morphology (morphology: 23.2%; hydrology: 16.2%), 34.4% by nutrient enrichment and 26.2% by toxic substances. More than half of the total deviance was explained by stressor interaction, with nutrient enrichment and toxic substances interacting most frequently and strongly. Our results underline that the biota of all European river types are determined by co‐occurring and interacting multiple stressors, lending support to the conclusion that fundamental management strategies at the catchment‐scale are required to reach the ambitious objective of good ecological status of surface waters.
... Originally designed to assess the relevance of indicators for policymakers, it has been central in the application of the WFD (Hering et al., 2015). The DPSIR indeed recognizes the chain of effects departing from drivers to societal responses and impacts on freshwater ecosystems, and therefore considers the physical and societal components of the sources and effects associated to stressors (Birk, 2019). The DPSIR has been applied to multiple freshwater ecosystems through the EU-funded project MARS, where it was used in connection to risk assessment and ecosystem services workflows (Hering et al., 2015;Segurado et al., 2018;Birk, 2019). ...
... The DPSIR indeed recognizes the chain of effects departing from drivers to societal responses and impacts on freshwater ecosystems, and therefore considers the physical and societal components of the sources and effects associated to stressors (Birk, 2019). The DPSIR has been applied to multiple freshwater ecosystems through the EU-funded project MARS, where it was used in connection to risk assessment and ecosystem services workflows (Hering et al., 2015;Segurado et al., 2018;Birk, 2019). ...
Article
Urbanization, agriculture, and the manipulation of the hydrological cycle are the main drivers of multiple stressors affecting river ecosystems across the world. Physical, chemical, and biological stressors follow characteristic patterns of occurrence, intensity, and frequency, linked to human pressure and socio-economic settings. The societal perception of stressor effects changes when moving from broad geographic regions to narrower basin or waterbody scales, as political and ecologically based perspectives change across scales. Current approaches relating the stressor effects on river networks and human societies fail to incorporate complexities associated to their co-occurrence, such as: i) the evidence that drivers can be associated to different stressors; ii) their intensity and frequency may differ across spatial and temporal scales; iii) their differential effects on biophysical receptors may be related to their order of occurrence; iv) current and legacy stressors may produce unexpected outcomes; v) the potentially different response of different biological variables to stressor combinations; vi) the conflicting effects of multiple stressors on ecosystem services; and, vii) management of stressor effects should consider multiple occurrence scales. We discuss how to incorporate these aspects to present frameworks considering biophysical and societal consequences of multiple stressors, to better understand and manage the effects being caused on river networks.
... Among freshwater ecosystems, rivers are particularly susceptible to anthropogenic disturbance (Birk, 2019). Rivers have supplied drinking water, energy (hydropower), food, means of navigation, and fertile riparian soils (Sabater et al., 2019). ...
Chapter
Freshwater ecosystems are some of the most diverse and imperiled of the Earth. The ecosystems in this biome face numerous anthropogenic threats including invasive alien species; the modification, degradation, and fragmentation of habitats; overexploitation; climate change; and pollution. These ecosystems depend on the quality, quantity, and timing of freshwater; an increasingly scarce resource. The difficulty of sustaining adequate supplies of clean freshwater to support human needs is recognized as a central challenge to achieving the UN Sustainable Development Goals. Current and future policies and management strategies must have a greater focus on the unique ecological relationships of freshwater and the multiple threats facing them. Now is the critical time to work to achieve this.
... Therefore, on the one hand, it is possible to detect and quantify the ecological role of fish in an ecosystem by manipulating their densities 2016a), and on the other hand, to detect and quantify structural and functional responses of stream communities to environmental stressors effects (Townsed et al. 2008). From a managerial perspective, the findings provide valuable insights for possible mitigation actions (Birk, 2019). ...
Thesis
Community structure and ecosystem functions are determined by physical and chemical conditions, food resources and biotic interactions. Mediterranean-climate streams are intrinsically variable in streamflow, with marked flow reduction in summer and floods in autumn and spring according to regional precipitation patterns. Riverine species are adapted to cope with natural and predictable disturbances, and their responses are in a large part determined by their physiological and behavioral adaptations. As for fish, swimming performance can determine their ability to use habitats differing in water velocity, to obtain food and avoid predation, etc. Today, the intense use of water by human demands causes longer low-flow periods in streams, thereby producing a certain degree of water stress. In addition, nutrient enrichment and water pollution are also common anthropogenic stressors that threaten ecological integrity of freshwater ecosystems. Metal pollution is of particular concern due to its high potential toxicity, perdurability and bioaccumulation through the food chain. At the bottom of the food chain, periphyton communities serve as food and energy sources for many organisms (e.g. macroinvertebrate grazers), so any stressor affecting periphyton is likely to indirectly affect organisms of a higher trophic level (“bottom-up control”). On the contrary, periphytic algal biomass can be affected by shifts in grazing pressure, e.g. resulting from predator-induced changes in grazer density (“top-down control”). Periphyton communities are also involved in important ecosystem functions (e.g. nutrient cycling), and are important bioindicators for habitat degradation. Field mesocosm experiments, from which we can modify the density of certain consumers (e.g. fishes), have become an invaluable tool in ecotoxicology and ecology for increasing mechanistic understanding of stressor effects. This thesis aimed to assess the responses of stream biota to flow alterations, in terms of water velocity increments and reductions of discharge, and to metal pollution. The investigations performed encompassed (i) respirometry studies using swim-tunnel respirometers to evaluate swimming capabilities, as indicative of water velocity tolerance, and physiological responses (energetic costs of swimming) of several freshwater fishes, as well as the drivers (morphological features) of variation within and among species; and (ii) field observational and mesocosm studies were carried out to evaluate the role of the threatened fish B. meridionalis as modulator of the response of stream ecosystem structure and function to anthropogenic stressors, such as hydrologic alterations (e.g. resulting from the water diversion) and metal pollution. Our results showed that there exist a high intra-and interspecific variation in absolute critical swimming speed and metabolic traits in fish. Generally, swimming performance and aerobic metabolism scaled positively with body size. The study that compared the invasive mosquitofish (Gambusia holbrooki) with the native Spanish toothcarp (Aphanius iberus) revealed that mosquitofish can swim faster (i.e. higher critical swimming speed) and more efficiently than Spanish toothcarp, as it showed lower cost of transport at a comparable workload. Both sexes of mosquitofish showed a better hydrodynamic body shape, i.e. streamlined body and thiner caudal peduncle, both of which were positively correlated with swimming performance. The second study revealed that, after accounting for body size effects, critical swimming speed was independently affected by total length or maximal metabolic rate within certain fish species. At the interspecific level, variation in critical swimming speed was partly explained by the variation in the interrelated traits of maximal metabolic rate, and fineness and muscle ratios, when accounting for up to eight freshwater fish species. Field observational and mesocosm studies showed that the top-down control by grazers was largely responsible for the variation in structural responses of periphyton, such as biomass and nutrient content, and in functional responses, such as nutrient uptake rates. Generally, when grazer densities were higher the periphyton biomass (ash-free dry mass or chlorophyll-a) was lower, whereas the nitrogen content of periphyton increased (i.e. lower C:N). The higher phosphate uptake capacity by periphyton was likely due to a more rejuvenated and active periphyton community. In addition, the variation in macroinvertebrate and fish densities were directly related to the impacts of natural (floods) and anthropogenic stressors. In metal-polluted reaches, we found that direct negative effects of metals on grazers led to indirect positive effects on periphyton biomass. Our studies also provided evidence about the important functional role of the Mediterranean barbel (Barbus meridionalis) in streams because shifts in their densities can lead to large ecosystem changes. The absence of this predatory fish triggered trophic-cascade responses on periphyton biomass in low impacted streams, and led to modify phosphate uptake rates by periphyton through biotic interactions. On the contrary, this benthic fish markedly reduced periphyton biomass via bioturbation impacts, and the greatest consumption effects on macroinvertebrates were found in larvae of Chironomidae. Finally, it was discussed (i) the importance of fish swimming capabilities, metabolism and morphological traits in influencing patterns of species distributions in Mediterranean streams with hydrologic alterations; and (ii) the context dependency of stream community responses to anthropogenic stressors. A number of management actions and future research prospects in relation to our findings were also raised throughout this thesis.
... Almost 45% of rivers in Europe have been affected by multiple attributes which have roots in human-driven pressure functions and societal decisions (Birk, 2019). Added to these disturbances is climatic variability which has altered flood characteristics in river systems in Europe. ...
Chapter
Water scarcity can weaken economic development by disrupting natural flow regimes of rivers, hampering ecosystem functioning and jeopardizing food security. More than half of the world's large river systems are affected by large dams and diversions, and many large tropical river basins are hotspots for future impacts by proposed dams. Many of the large river basins of the world are characterized by over-abstraction of surface and groundwater triggered by rapid urbanization, expansion of irrigated agriculture and industrial growth with present withdrawals of total water reaching 3650 km³ year− 1. This has serious implications on global freshwater ecosystems including biodiversity. With higher water withdrawals than the desirable environmental flows, every populated river basin is impacted by water stress. This article presents a global synthesis of imperiled river ecosystems, detailing risk, rarity and endangerment, the major drivers of loss, areas of conservation importance, and restoration strategies.
... Fresh waters provide vital services to society, including the provision of clean drinking water, recreation and tourism, pollutant processing, biodiversity, food provision, and energy (Reynaud and Lanzanova 2017). These services generally rely on good water quality, underpinned by stable ecological processes, which are threatened globally by multiple and potentially interacting stressors (Dodds et al. 2013), including excess nutrients, hydrological modification, toxic chemicals, and non-native invasive species (Birk 2019). Among these, climate change and nutrient stressors are expected to act across large scales, although management of nutrients might be achievable at local scales to relieve effects of both in freshwater ecosystems (Moss et al. 2011). ...
Article
Interactions between stressors in freshwater ecosystems, including those associated with climate change and nutrient enrichment, are currently difficult to detect and manage. Our understanding of the forms and frequency of occurrence of such interactions is limited; assessments using field data have been constrained as a result of varying data forms and quality. To address this issue, we demonstrate a statistical approach capable of assessing multiple stressor interactions using contrasting data forms in 3 European catchments (Loch Leven Catchment, UK: assessment of phytoplankton response in a single lake with time series data; Pinios Catchment, Greece: macroinvertebrate response across multiple rivers using spatial data; and Lepsämänjoki Catchment, Finland: phytoplankton response across multiple rivers using spatiotemporal data). Statistical models were developed to predict the relative and interactive effects of climate change and nutrient enrichment sensitive indicators (stressors) on indicators of ecological quality (ecological responses) within the framework of linear mixed effects models. In all catchments, indicators of nutrient enrichment were identified as the primary stressor, with climate change-sensitive indicators causing secondary effects (Loch Leven: additive, total phosphorus [TP] × precipitation; Pinios: additive, nitrate × dissolved oxygen; Lepsämänjoki: synergistic, TP × summer water temperature), the intensity of which varied between catchments and along the nutrient stressor gradient. Simple stressor change scenarios were constructed for each catchment and used in combination with mechanistic models to explore potential management responses. This approach can be used to explore the need for multiple stressor management in freshwaters, helping practitioners navigate a complex world of environmental change.
... While conceptual understanding and experimental demonstration of these interactions are now well established ( Schäfer and Piggott, 2018 ), a major challenge remains to develop approaches to detect, quantify and manage stressor in-teractions in the real world ( Feld et al., 2016 ). To inform this development, various attempts have been made to assess the frequency of stressor interactions across a broad range of freshwater ecosystems ( Birk, 2019 ). These endeavours have identified issues that limit our capacity to generalise and predict undesirable ecological responses to single stressor reduction strategies. ...
Article
Despite advances in conceptual understanding, single-stressor abatement approaches remain common in the management of fresh waters, even though they can produce unexpected ecological responses when multiple stressors interact. Here we identify limitations restricting the development of multiple-stressor management strategies and address these, bridging theory and practice, within a novel empirical framework. Those critical limitations include that (i) monitoring schemes fall short of accounting for theory on relationships between multiple-stressor interactions and ecological responses, (ii) current empirical modelling approaches neglect the prevalence and intensity of multiple-stressor interactions, and (iii) mechanisms of stressor interactions are often poorly understood. We offer practical recommendations for the use of empirical models and experiments to predict the effects of freshwater degradation in response to changes in multiple stressors, demonstrating this approach in a case study. Drawing on our framework, we offer practical recommendations to support the development of effective management strategies in three general multiple-stressor scenarios.
... Waterbodies are generally subjected to multiple stressors ( Birk, 2018 ). This creates a complex task for water managers who aim to improve the ecological status of stream ecosystems. ...
Article
Full-text available
Aquatic ecosystems are affected by multiple environmental stressors across spatial and temporal scales. Yet the nature of stressor interactions and stressor-response relationships is still poorly understood. This hampers the selection of appropriate restoration measures. Hence, there is a need to understand how ecosystems respond to multiple stressors and to unravel the combined effects of the individual stressors on the ecological status of waterbodies. Models may be used to relate responses of ecosystems to environmental changes as well as to restoration measures and thus provide valuable tools for water management. Therefore, we aimed to develop and test a Bayesian Network (BN) for simulating the responses of stream macroinvertebrates to multiple stressors. Although the predictive performance may be further improved, the developed model was shown to be suitable for scenario analyses. For the selected lowland streams, an increase in macroinvertebrate-based ecological quality (EQR) was predicted for scenarios where the streams were relieved from single and multiple stressors. Especially a combination of measures increasing flow velocity and enhancing the cover of coarse particulate organic matter showed a significant increase in EQR compared to current conditions. The use of BNs was shown to be a promising avenue for scenario analyses in stream restoration management. BNs have the capacity for clear visual communication of model dependencies and the uncertainty associated with input data and results and allow the combination of multiple types of knowledge about stressor-effect relations. Still, to make predictions more robust, a deeper understanding of stressor interactions is required to parametrize model relations. Also, sufficient training data should be available for the water type of interest. Yet, the application of BNs may now already help to unravel the contribution of individual stressors to the combined effect on the ecological quality of water bodies, which in turn may aid the selection of appropriate restoration measures that lead to the desired improvements in macroinvertebrate-based ecological quality.
... Population growth and unsustainable economic development are the main drivers of biodiversity loss (Slingenberg et al., 2009). Rivers are particularly vulnerable to degradation (Palmer and Hondula, 2014), given their crucial role in the human history and being natural recipients of pollutants from the surrounding landscape (Birk, 2019). Multiple anthropogenic pressures, including point and diffuse pollution, alteration of flow regime caused by abstraction or regulation, and hydromorphological degradation are increasingly threatening the health of river ecosystems . ...
Article
Anthropogenic activities are seriously endangering the conservation of biodiversity worldwide, calling for urgent actions to mitigate their impact on ecosystems. We applied machine learning techniques to predict the response of freshwater ecosystems to multiple anthropogenic pressures, with the goal of informing the definition of water policy targets and management measures to recover and protect aquatic biodiversity. Random Forest and Gradient Boosted Regression Trees algorithms were used for the modelling of the biological indices of macroinvertebrates and diatoms in the Tagus river basin (Spain). Among the anthropogenic stressors considered as explanatory variables, the categories of land cover in the upstream catchment area and the nutrient concentrations showed the highest impact on biological communities. The model was then used to predict the biological response to different nutrient concentrations in river water, with the goal of exploring the effect of different regulatory thresholds on the ecosystem status. Specifically, we considered the maximum nutrient concentrations set by the Spanish legislation, as well as by the legislation of other European Union Member States. According to our model, the current nutrient thresholds in Spain ensure values of biological indices consistent with the good ecological status in only about 60% of the total number of water bodies. By applying more restrictive nutrient concentrations, the number of water bodies with biological indices in good status could increase by almost 40%. Moreover, coupling more restrictive nutrient thresholds with measures that improve the riparian habitat yields up to 85% of water bodies with biological indices in good status, thus proving to be a key approach to restore the status of the ecosystem.
... The combination of such diverse stressors on biological and functional responses of stream biota often result in interactions that leads to unexpected ecosystem behaviour with synergisms (amplified effects) or antagonisms (reduced effects) (Folt et al., 1999;Piggott et al., 2015). Those represent a relevant lack of knowledge that poses difficulties and challenges for environmental management and ecological restoration (Birk, 2019). Particularly, in arid and semi-arid regions, such as the Mediterranean, water scarcity along with aquatic pollution resulting from effluent discharges and other sources, represent two major co-occurrent pressures that strongly decrease water quality (Navarro-Ortega et al., 2014;Vörösmarty et al., 2010). ...
Article
Freshwaters are constantly facing ecosystem functioning alterations and loss of biodiversity driven by multiple anthropogenic and natural stressors, that by acting simultaneously create complex interactions, affecting the quantity and quality of water resources. Stream biofilms are complex communities, which are exposed to these alterations and, in addition, are naturally stressed by invertebrate grazing. Therefore, they are expected to reflect these impacts through shifts in community structure, composition and function. Here we used a mesocosm system to assess the single and interacting effect of major anthropogenic stressors acting in Mediterranean streams (i.e. flow stagnation and sewage contamination) in combination with a biological natural stressor (i.e. grazing) on the main assemblages composing biofilm (i.e. bacteria, fungi and algae) by assessing communities’ relative abundance through Denaturing Gradient Gel Electrophoresis (DGGE) operational taxonomic units (OTUs). Biofilm was submitted to the three stressors, in a full-factorial design (2 flow conditions × 2 contamination conditions × 2 grazing settings) in a 5-week experiment. Molecular data showed that the combined effect of anthropogenic stressors (flow stagnation and sewage contamination) induced unequal OTUs responses on biofilm assemblages, with antagonistic effects for bacteria, synergistic for fungi and additive for algae. Sewage and grazing interaction were significant for all groups revealing a negative effect (antagonistic) on bacteria and algae diversity but positive on fungi diversity (synergistic). The same overall response pattern was also found for the triple co-occurring stressors, which increased fungi diversity while decreasing algae and bacteria. In stream ecosystems in which low flow conditions and sewage contamination prevail in the presence of natural herbivory, algae and bacterial diversity may be severely affected, while fungal diversity may be surprisingly enhanced. Consequently, shifts in the relative proportions could led to the unbalancing of ecosystem processes (e.g., photosynthesis, nutrient mineralization) defined by the microbial communities.
... altered ecological status or ecosystem services) may then induce a political or societal 'Response' (e.g. ecosystem mitigation; Birk, 2019;Hering et al., 2015). Then, the specific modeling strategy for each basin was developed based on these conceptual models, and the availability of empirical data and PMs. ...
Article
There are infinite possible future scenarios reflecting the impacts of anthropogenic multiple stress on our planet. These impacts include changes in climate and land cover, to which aquatic ecosystems are especially vulnerable. To assess plausible developments of the future state of European surface waters, we considered two climate scenarios and three storylines describing land use, management and anthropogenic development (‘Consensus’, ‘Techno’ and ‘Fragmented’, which in terms of environmental protection represent best-, intermediate- and worst-case, respectively). Three lake and four river basins were selected, representing a spectrum of European conditions through a range of different human impacts and climatic, geographical and biological characteristics. Using process-based and empirical models, freshwater total nitrogen, total phosphorus and chlorophyll-a concentrations were projected for 2030 and 2060. Under current conditions, the water bodies mostly fail good ecological status. In future predictions for the Techno and Fragmented World, concentrations further increased, while concentrations generally declined for the Consensus World. Furthermore, impacts were more severe for rivers than for lakes. Main pressures identified were nutrient inputs from agriculture, land use change, inadequately managed water abstractions and climate change effects. While the basins in the Continental and Atlantic regions were primarily affected by land use changes, in the Mediterranean/Anatolian the main driver was climate change. The Boreal basins showed combined impacts of land use and climate change and clearly reflected the climate-induced future trend of agricultural activities shifting northward. The storylines showed positive effects on ecological status by classical mitigation measures in the Consensus World (e.g. riparian shading), technical improvements in the Techno World (e.g. increasing wastewater treatment efficiency) and agricultural extensification in the Fragmented World. Results emphasize the need for implementing targeted measures to reduce anthropogenic impacts and the importance of having differing levels of ambition for improving the future status of water bodies depending on the societal future to be expected.
... Aquatic ecosystems have historically attracted human settlements and their activities, resulting in a long-term exposure to the associated multiple pressures threatening these natural systems (Nõges et al., 2016;Hein et al., 2018;Birk, 2019;Borgwardt et al., 2019). Aquatic ecosystems have specificities that underline their role in ES provision, but no evidence of differences in services provision between different types of aquatic systems have been found (Boulton et al., 2016). ...
Article
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Global initiatives have been increasingly focusing on mainstreaming the values of biodiversity and ecosystem services into decision-making at all levels. Due to the accelerated rate at which biodiversity is declining and its consequences for the functioning of ecosystems and subsequently, the services they provide, there is need to develop comprehensive assessments of the services and the benefits nature delivers to society. Based on expertevaluation, we identified relevant flow linkages in the supply-side of the socio-ecological system, i.e. from biodi- versity to ecosystem services supply for eight case studies across European aquatic ecosystems covering freshwater, transitional, coastal and marine waters realms. Biological mediated services were considered, as well as those reliant on purely physical aspects of the ecosystem, i.e. abiotic outputs, since both have implications for spatial planning, management and decision-making. Due to the multidimensional nature of ecosystems and their biodiversity, our approach used ecosystem components such as habitats and biota as proxies for biodiversity and as the focal point for linkage identification. Statistical analysis revealed the importance of considering mobile biota in the spatial assessment of habitats. Contrary to literature evidences so far, our results showed signifi cantly different and complementary ecosystem services supply patterns across the continuum of aquatic realms. The implemented score of ecosystem services supply has a high potential for integrated aquatic ecosystem service supply assessments in the context of ecosystem-based management. <br/
... The effects of stressors other than nutrient enrichment can also add to uncertainty and influence the setting of reliable nutrient criteria, especially when interacting with nutrient stress: synergism may prompt overly protective values, while antagonism could lead to values being too relaxed (Côté et al., 2016). With only 26% of lake water bodies in Europe being affected by more than one pressure, multi-stressor effects are perhaps less relevant in lakes than rivers or transitional waters (Birk, 2019). However, hydromorphological pressures (e.g. ...
Article
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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 ʽgoodʼ 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 ʽgoodʼ to ‘moderate’ ecological status. LCB1 lakes achieved ʽgoodʼ 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 ʽgoodʼ ecological status in the lakes of Europe.
Chapter
The article serves to introduce the environmental issue of ever-increasing multiple stressors acting on streams and rivers globally. It presents the most relevant stressors and outlines the state of knowledge in multi-stressor research. Stressor interactions are well documented, but full understanding of the cause-effect relationships remains scarce. This poses high uncertainties to predicting and effectively managing multi-stressor effects. Both a refined analytical approach and integrative, adaptive environmental management offer solutions to this intricate problem.
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Environmental policies fall short in protecting freshwater ecosystems, which are heavily threatened by human pressures and their associated stressors. One reason is that stressor effects depend on the context in which they occur and it is difficult to extrapolate patterns to predict the effect of stressors without these being contextualized in a general frame. This study aims at improving existing decision-making frameworks such as the DPSIR approach (Driver-Pressure-State-Impact-Response) or ERA (Environmental Risk Assessment) in the context of stressors. Here, we delve into stressor-impact relationships in freshwater ecosystems and develop a guideline which includes key characteristics such as stressor type, stressor duration, location, the natural levels of environmental variables to which each ecosystem is used to, among others. This guideline is intended to be useful in a wide range of ecosystem conditions and stressors. Incorporating these guidelines may favor the comparability of scientific results and may lead to a substantial advancement in the efficacy of diagnosis and predictive approaches of impacts.
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Running water ecosystems of Europe are affected by various human pressures. However, little is known about the prevalence, spatial patterns, interactions with natural environment and co-occurrence of pressures. This study represents the first high-resolution data analysis of human pressures at the European scale, where important pressure criteria for 9330 sampling sites in 14 European countries were analysed. We identified 15 criteria describing major anthropogenic degradation and combined these into a global pressure index by taking additive effects of multiple pressures into account. Rivers are affected by alterations of water quality (59%), hydrology (41%) and morphology (38%). Connectivity is disrupted at the catchment level in 85% and 35% at the river segment level. Approximately 31% of all sites are affected by one, 29% by two, 28% by three and 12% by four pressure groups; only 21% are unaffected. In total, 47% of the sites are multi-impacted. Approximately 90% of lowland rivers are impacted by a combination of all four pressure groups.
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Freshwater ecosystems are impacted by a range of stressors arising from diverse human-caused land and water uses. Identifying the relative importance of single stressors and understanding how multiple stressors interact and jointly affect biology is crucial for River Basin Management. This study addressed multiple human-induced stressors and their effects on the aquatic flora and fauna based on data from standard WFD monitoring schemes. For altogether 1095 sites within a mountainous catchment, we used 12 stressor variables covering three different stressor groups: riparian land use, physical habitat quality and nutrient enrichment. Twenty-one biological metrics calculated from taxa lists of three organism groups (fish, benthic invertebrates and aquatic macrophytes) served as response variables. Stressor and response variables were subjected to Boosted Regression Tree (BRT) analysis to identify stressor hierarchy and stressor interactions and subsequently to Generalised Linear Regression Modelling (GLM) to quantify the stressors standardised effect size. Our results show that riverine habitat degradation was the dominant stressor group for the river fauna, notably the bed physical habitat structure. Overall, the explained variation in benthic invertebrate metrics was higher than it was in fish and macrophyte metrics. In particular, general integrative (aggregate) metrics such as % Ephemeroptera, Plecoptera and Trichoptera (EPT) taxa performed better than ecological traits (e.g. % feeding types). Overall, additive stressor effects dominated, while significant and meaningful stressor interactions were generally rare and weak. We concluded that given the type of stressor and ecological response variables addressed in this study, river basin managers do not need to bother much about complex stressor interactions, but can focus on the prevailing stressors according to the hierarchy identified.
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The operation of storage hydropower plants is commonly linked to frequent fluctuations in discharge and water level (hydropeaking) of downstream river stretches and is often accompanied by cooling or warming of the water body downstream (cold or warm thermopeaking, respectively). The objective of this study is to assess the single and combined effects of hydropeaking and cold thermopeaking on the drift of selected aquatic macroinvertebrates in experimental flumes. The study specifically aims to (1) investigate the macroinvertebrate drift induced by hydropeaking, (2) identify taxon-specific drift patterns following combined hydropeaking and cold thermopeaking and (3) quantify diurnal drift differences under both impact types. Overall, hydropeaking induced significantly higher drift rates of most macroinvertebrate taxa. Combined hydropeaking and cold thermopeaking, however, revealed reduced total drift rates, however with strong taxon-specific response patterns. Hydropeaking during night led to significantly higher drift rates than during daytime, while in combination with thermopeaking the same trend was observable, although insignificant. Taxon-specific analysis revealed lower drift rates following hydropeaking for rheophilic and interstitial taxa (e.g. . Leuctra sp., . Hydropsyche sp.), whereas many limnophilic taxa adapted to low current showed markedly increased drift (e.g. . Lepidostoma hirtum and Leptoceridae). In line with previous studies, our results confirm a significant loss of limnophilic macroinvertebrate taxa following hydraulic stress. The mitigating effect of cold thermopeaking might be explained by behavioural patterns, but requires further investigation to clarify if macroinvertebrates actively avoid drift and intrude into the interstitial, when cold water is discharged. Our results imply that river restoration projects must address the hydrological regime and, if necessary need to include suitable management schemes for hydropower plants. Besides operative management measures, the construction of reservoirs to buffer hydropeaks or the diversion of hydropeaks into larger water bodies could mitigate hydropeaking effects and foster biological recovery including limnophilic taxa.
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Water resources globally are affected by a complex mixture of stressors resulting from a range of drivers, including urban and agricultural land use, hydropower generation and climate change. Understanding how stressors interfere and impact upon ecological status and ecosystem services is essential for developing effective River Basin Management Plans and shaping future environmental policy. This paper details the nature of these problems for Europe's water resources and the need to find solutions at a range of spatial scales. In terms of the latter, we describe the aims and approaches of the EU-funded project MARS (Managing Aquatic ecosystems and water Resources under multiple Stress) and the conceptual and analytical framework that it is adopting to provide this knowledge, understanding and tools needed to address multiple stressors. MARS is operating at three scales: At the water body scale, the mechanistic understanding of stressor interactions and their impact upon water resources, ecological status and ecosystem services will be examined through multi-factorial experiments and the analysis of long time-series. At the river basin scale, modelling and empirical approaches will be adopted to characterise relationships between multiple stressors and ecological responses, functions, services and water resources. The effects of future land use and mitigation scenarios in 16 European river basins will be assessed. At the European scale, large-scale spatial analysis will be carried out to identify the relationships amongst stress intensity, ecological status and service provision, with a special focus on large transboundary rivers, lakes and fish. The project will support managers and policy makers in the practical implementation of the Water Framework Directive (WFD), of related legislation and of the Blueprint to Safeguard Europe's Water Resources by advising the 3rd River Basin Management Planning cycle, the revision of the WFD and by developing new tools for diagnosing and predicting multiple stressors.
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AbstractMany surface waters in Europe suffer from the adverse effects of multiple stresses. The Otra River, southernmost Norway, is impacted by acid deposition, hydropower development and increasingly by climate change. The river holds a unique population of land-locked salmon and anadromous salmon in the lower reaches. Both populations have been severely affected by acidification. The decrease in acid deposition since the 1980s has led to partial recovery of both populations. Climate change with higher temperatures and altered precipitation can potentially further impact fish populations. We used a linked set of process-oriented models to simulate future climate, discharge, and water chemistry at five sub-catchments in the Otra river basin. Projections to year 2100 indicate that future climate change will give a small but measureable improvement in water quality, but that additional reductions in acid deposition are needed to promote full restoration of the fish communities. These results can help guide management decisions to sustain key salmon habitats and carry out effective long-term mitigation strategies such as liming. The Otra River is typical of many rivers in Europe in that it fails to achieve the good ecological status target of the EU Water Framework Directive. The programme of measures needed in the river basin management plan necessarily must consider the multiple stressors of acid deposition, hydropower, and climate change. This is difficult, however, as the synergistic and antagonistic effects are complex and challenging to address with modelling tools currently available.
Article
Rivers are impacted by multiple stressors that can interact to create synergistic, additive or antagonistic effects, but experimental studies on fish encompassing more than one stressor are seldom found. Thus, there is the need to study stressors through multifactorial approaches that analyse the impact of fish exposure to multiple stressors and evaluate fish sensitivity to stressor combinations. Some of the most common impacts to Mediterranean rivers are of two natures: i) water abstraction and ii) diffuse pollution. Therefore, the present study aims at studying the responses of potamodromous fish facing combinations of: 1) a primary stressor (two levels of connectivity reduction due to water scarcity), and 2) a secondary stressor (three levels of oxygen depletion due to increase organic load - of anthropogenic nature). Schools of five wild fish from a cyprinid species (Luciobarbus bocagei) were placed in a flume, equipped with see-through sidewalls to allow for behavioural analysis, and subjected to different combinations of the stressors. Results show that at the unconnected level the primary stressor (lack of connectivity) overrode the effect of the secondary stressor (oxygen depletion), but when connectivity existed oxygen depletion caused a reduction of fish movements with decreasing oxygen concentrations. This multifactorial study contributes to improved prediction of fish responses upon actual or projected pressure scenarios.
Article
The accelerating rate of global change has focused attention on the cumulative impacts of novel and extreme environmental changes (i.e., stressors), especially in marine ecosystems. As integrators of local catchment and regional processes, freshwater ecosystems are also ranked highly sensitive to the net effects of multiple stressors, yet there has not been a large-scale quantitative synthesis. We analysed data from 88 papers including 286 responses of freshwater ecosystems to paired stressors, and discovered that overall, their cumulative mean effect size was less than the sum of their single effects (i.e., an antagonistic interaction). Net effects of dual stressors on diversity and functional performance response metrics were additive and antagonistic, respectively. Across individual studies, a simple vote-counting method revealed that the net effects of stressor pairs were frequently more antagonistic (41%) than synergistic (28%), additive (16%) or reversed (15%). Here, we define a reversal as occurring when the net impact of two stressors is in the opposite direction (negative or positive) from that of the sum of their single effects. While warming paired with nutrification resulted in additive net effects, the overall mean net effect of warming combined with a second stressor was antagonistic. Most importantly, the mean net effects across all stressor pairs and response metrics were consistently antagonistic or additive, contrasting the greater prevalence of reported synergies in marine systems. Here, a possible explanation for more antagonistic responses by freshwater biota to stressors is that the inherent greater environmental variability of smaller aquatic ecosystems fosters greater potential for acclimation and co-adaptation to multiple stressors. This article is protected by copyright. All rights reserved. This article is protected by copyright. All rights reserved.
Article
The historical reduction in habitat heterogeneity and water quality of running waters is an ongoing challenge being addressed by resource managers worldwide. The persistent legacy of past land use, reflected in part by depauperate macroinvertebrate assemblages, is likely to affect the responses of macroinvertebrate assemblages to novel anthropogenic stressors and amendments (e.g. river restoration).The response of macroinvertebrate assemblages differing in the abundance of sensitive taxa to stressors was investigated using a mesocosm experiment conducted at five sites within two sub-basins that differed in historic land-use impacts. The sub-basins were similar in morphology and water quality, but a higher dissolved organic carbon (DOC) level in the sub-basin with a less sensitive assemblage reflected a greater agricultural influence.Macroinvertebrate assemblages were assessed monthly over an annual cycle in replicated in situ mesocosms manipulated with respect to substratum heterogeneity (fine, coarse) and water quality (nutrient amendments) following a full-factorial design. Due to relatively high background nutrient levels, there was no effect of nutrient amendment on macroinvertebrate colonisation of mesocosms.In the sub-basin harbouring a more sensitive macroinvertebrate assemblage, higher total and EPT taxa richness was found in coarse (heterogeneous) substratum than that in fine (homogeneous) substratum mesocosms, whereas this response was not observed in the sub-basin with a less sensitive assemblage. In the former sub-basin, coarse substratum mesocosms were more favourable for sensitive taxa, as they had more diverse flow patterns, less clogging of interstitial spaces and more benthic organic matter than fine substratum mesocosms.These results suggest that past land-use legacies influencing current macroinvertebrate assemblages can underlie differential response patterns of macroinvertebrates to habitat mitigation measures in human-dominated catchments.
Article
Global climate change is likely to modify the ecological consequences of currently acting stressors, but potentially important interactions between climate warming and land-use related stressors remain largely unknown. Agriculture affects streams and rivers worldwide, including via nutrient enrichment and increased fine sediment input. We manipulated nutrients (simulating agricultural runoff), deposited fine sediment (simulating agricultural erosion) (2 levels each) and water temperature (8 levels, 0-6°C above ambient) simultaneously in 128 streamside mesocosms to determine the individual and combined effects of the three stressors on macroinvertebrate community dynamics (community composition and body size structure of benthic, drift and insect emergence assemblages). All three stressors had pervasive individual effects, but in combination often produced additive or antagonistic outcomes. Changes in benthic community composition showed a complex interplay among habitat quality (with or without sediment), resource availability (with or without nutrient enrichment) and the behavioural/physiological tendency to drift or emerge as temperature rose. The presence of sediment and raised temperature both resulted in a community of smaller organisms. Deposited fine sediment strongly increased the propensity to drift. Stressor effects were most prominent in the benthic assemblage, frequently reflected by opposite patterns in individuals quitting the benthos (in terms of their propensity to drift or emerge). Of particular importance is that community measures of stream health routinely used around the world (taxon richness, EPT richness and diversity) all showed complex three-way interactions, with either a consistently stronger temperature response or a reversal of its direction when one or both agricultural stressors were also in operation. The negative effects of added fine sediment, which were often stronger at raised temperatures, suggest that streams already impacted by high sediment loads may be further degraded under a warming climate. However, the degree to which this will occur may also depend on in-stream nutrient conditions. This article is protected by copyright. All rights reserved.
Article
Sudden instream releases of hypolimnetic water from hydropower plants [i.e. hydropeaking (HP)] can cause abrupt temperature variations [i.e. thermopeaking (TP)], typically on a daily basis. The propagation of discharge and thermal waves is asynchronous, causing the benthic community to undergo two different but consecutive impacts. Invertebrates respond to sudden increases in discharge with catastrophic drift, and respond to sudden changes of temperature with behavioural drift. Owing to the time lag separating discharge and thermal wave peaks, catastrophic and behavioural drift can occur as distinct events. We conducted simulations in a set of open air flumes directly fed by an Alpine stream, and analysed drift induction in benthic invertebrates caused by a HP wave followed by a cold TP wave, and compared it with drift induced only by a cold TP wave. Drift propensity increased during HP and TP simulations, with a synergic effect: drift was higher when the TP wave followed the HP one. We also recorded a selective effect: some taxa did not respond to the alterations, some taxa responded to the discharge variations and to the thermal variations, or to the thermal variations alone. The most abundant taxa in benthos were Chironomidae and Baetidae, followed by Simuliidae. Simuliidae and Chironomidae were the most abundant drifting taxa. Copyright © 2012 John Wiley & Sons, Ltd.
Article
Most studies dealing with the use of ecological indicators and other applied ecological research rely on some definition or concept of what constitutes least-, intermediate- and most-disturbed condition. Currently, most rigorous methodologies designed to define those conditions are suited to large spatial extents (nations, ecoregions) and many sites (hundreds to thousands). The objective of this study was to describe a methodology to quantitatively define a disturbance gradient for 40 sites in each of two small southeastern Brazil river basins. The assessment of anthropogenic disturbance experienced by each site was based solely on measurements strictly related to the intensity and extent of anthropogenic pressures. We calculated two indices: one concerned site-scale pressures and the other catchment-scale pressures. We combined those two indices into a single integrated disturbance index (IDI) because disturbances operating at both scales affect stream biota. The local- and catchment-scale disturbance indices were weakly correlated in the two basins (r = 0.21 and 0.35) and both significantly (p < 0.05) reduced site EPT (insect orders Ephemeroptera, Plecoptera, Trichoptera) richness. The IDI also performed well in explaining EPT richness in the basin that presented the stronger disturbance gradient (R2 = 0.39, p < 0.001). Natural habitat variability was assessed as a second source of variation in EPT richness. Stream size and microhabitats were the key habitat characteristics not related to disturbances that enhanced the explanation of EPT richness over that attributed to the IDI. In both basins the IDI plus habitat metrics together explained around 50% of EPT richness variation. In the basin with the weaker disturbance gradient, natural habitat explained more variation in EPT richness than did the IDI, a result that has implications for biomonitoring studies. We conclude that quantitatively defined disturbance gradients offer a reliable and comprehensive characterization of anthropogenic pressure that integrates data from different spatial scales.
Article
1. Modification of natural landscapes and land-use intensification are global phenomena that can result in a range of differing pressures on lotic ecosystems. We analysed national-scale databases to quantify the relationship between three land uses (indigenous vegetation, urbanisation and agriculture) and indicators of stream ecological integrity. Boosted regression tree modelling was used to test the response of 14 indicators belonging to four groups – water quality (at 578 sites), benthic invertebrates (at 2666 sites), fish (at 6858 sites) and ecosystem processes (at 156 sites). Our aims were to characterise the ecological response curves of selected functional and structural metrics in relation to three land uses, examine the environmental moderators of these relationships and quantify the relative utility of metrics as indicators of stream ecological integrity.
Article
Impending changes in climate will interact with other stressors to threaten aquatic ecosystems and their biota. Native Colorado River cutthroat trout (CRCT; Oncorhynchus clarkii pleuriticus) are now relegated to 309 isolated high-elevation (>1700 m) headwater stream fragments in the Upper Colorado River Basin, owing to past nonnative trout invasions and habitat loss. Predicted changes in climate (i.e., temperature and precipitation) and resulting changes in stochastic physical disturbances (i.e., wildfire, debris flow, and channel drying and freezing) could further threaten the remaining CRCT populations. We developed an empirical model to predict stream temperatures at the fragment scale from downscaled climate projections along with geomorphic and landscape variables. We coupled these spatially explicit predictions of stream temperature with a Bayesian Network (BN) model that integrates stochastic risks from fragmentation to project persistence of CRCT populations across the upper Colorado River basin to 2040 and 2080. Overall, none of the populations are at risk from acute mortality resulting from high temperatures during the warmest summer period. In contrast, only 37% of populations have a ≥90% chance of persistence for 70 years (similar to the typical benchmark for conservation), primarily owing to fragmentation. Populations in short stream fragments <7 km long, and those at the lowest elevations, are at the highest risk of extirpation. Therefore, interactions of stochastic disturbances with fragmentation are projected to be greater threats than warming for CRCT populations. The reason for this paradox is that past nonnative trout invasions and habitat loss have restricted most CRCT populations to high-elevation stream fragments that are buffered from the potential consequences of warming, but at risk of extirpation from stochastic events. The greatest conservation need is for management to increase fragment lengths to forestall these risks.
Article
1. Many ecosystems are influenced simultaneously by multiple stressors, and the consequences of stressors are often unpredictable on the basis of knowledge of single effects. Agriculture affects streams world-wide via nutrient enrichment, elevated fine sediment and water abstraction for irrigation, but the combined impacts of these stressors are unknown. 2. We manipulated all three stressors simultaneously in an 18-day experiment and determined their individual and pair-wise combined effects on benthic invertebrates, algal biomass and leaf decay. We added nutrients (phosphorus plus nitrogen) and/or fine sediment (grain size 0·2 mm) to 18 experimental stream channels (dimensions 250 × 15 × 15 cm) supplied with water from a nearby stream. Three sediment and three nutrient treatments (high, intermediate, natural) were applied to each of six channels while flow was reduced by 80% in half the channels. Invertebrates (composition, abundance) and algae (chlorophyll a) were assayed using ceramic tile substrata and leaf decay was assayed using bundled leaves of a native shrub. Invertebrates colonizing leaf packs were also sampled. 3. Effects of sediment addition and flow reduction on biological response parameters were twice as common as nutrient enrichment effects. Nutrient enrichment increased total invertebrate abundance on tiles, algal biomass accrual and leaf decay rates, whereas both sediment addition (at the highest level) and flow reduction had mostly negative effects (e.g. reduced algal biomass, invertebrate abundance and/or taxonomic richness). 4. Stressors interacted often, and interactions between sediment and flow were particularly common. The negative impact of added sediment on aquatic biota was stronger at reduced flow, especially on tile substrata that were more exposed to the current than leaf-pack substrata. 5. Synthesis and applications. Our key findings imply that abstracting water from a stream already subjected to high fine sediment inputs may have far worse effects on the invertebrate fauna than abstraction from a similar stream with lower sediment levels. Aquatic resource managers should be aware of this important interaction between multiple stressors.
Article
1. Productivity and grazing pressure interact in determining autotroph diversity, because high productivity increases the capability of a plant community to compensate for grazing losses. However, further factors may play a role in shaping diversity, including primary producer nutrient stoichiometry and grazer activity. 2. Our study focuses on the interactions between light, nutrients and grazing in determining species richness and evenness of stream diatoms. By measuring primary producer productivity and nutrient content as well as grazer activity, we attempt to disentangle the different pathways by which the three factors affect diatom species richness and evenness. 3. We hypothesized that high light intensities and nutrient addition would increase species richness by increasing primary productivity and that higher levels of light and nutrients would compensate for negative grazer effects on species richness of primary producers. We also hypothesized that high light intensities would decrease the nutrient content of primary producers, especially when nutrients are limiting, whereas nutrient addition would increase primary producer nutrient content. Last, in addition to changing primary producer nutrient content, light and nutrients would also change grazer activity, thus modifying the interactions between light, nutrients and grazing. 4. We used periphyton and gastropod grazers in an experiment with circular stream channels with four nutrient, two light and four grazing levels to determine individual and combined effects on benthic diatom richness and evenness. After 3 weeks, we determined algal biomass, periphyton nutrient content, diatom species richness and evenness as well as grazer activity. 5. Our results showed that light and nutrients increased species richness and primary producer productivity and nutrient content. Grazing decreased species richness but only at low light levels, possibly because high light levels reduced grazer activity. Evenness was not affected by any single factor alone, but was influenced by nutrient-light and grazing-light interactions. 6. Synthesis. Light, nutrients and grazing interacted in determining primary producer species richness. Their effects were mainly mediated through changes in productivity but primary producer nutrient content and grazer activity also played important roles.
Article
Summary1. Accurately assessing the effects of multiple human-caused stressors on freshwater (and other) ecosystems is an essential step in the development of efficient decision support tools for environmental managers. Our objective is to review potentials and limitations of the use of biological traits as indicators (BTIs) of multiple stressor effects on running water (i.e. lotic) ecosystems.2. Pioneers in ecology provided mechanistic explanations for responses of alternative biological traits to a given stressor and for the action of habitat harshness as a trait filter. These ideas were subsequently integrated in theoretical ecological constructs (e.g. Habitat Templet Concept) that form the basis of the BTI approach.3. To resolve the effects of multiple stressors on running waters requires multiple traits of a biologically diverse group of organisms such as lotic invertebrates. To meet this goal, however, recently created databases on the biological traits of lotic invertebrates must be expanded and unified.4. Addressing the technical implementation of the BTI approach, we illustrate that anticipated problems with phylogenetic trait syndromes are seemingly less serious in reality and that presence–absence data of genera and few sample replicates are sufficient for accurate trait descriptions of invertebrate communities.5. Current trends in politics demand that biomonitoring tools be effective at large scales, i.e. large-scale trait patterns of natural communities (i.e. at reference conditions) should be relatively stable. The trait composition of natural invertebrate communities is relatively stable at the scale of Europe and North America because trait filters of natural lotic habitats act similarly across large biogeographical units.6. The mechanistic actions of stressors on the biological traits of invertebrates should facilitate a priori predictions, but the complexity of potential trait responses makes such predictions sometimes difficult.7. To illustrate potentials and limitations of BTIs to identify a given stressor acting exclusively (or primarily), we examine the (i) use of functional feeding groups to indicate the action of various stressors and (ii) trait responses to an indirectly acting stressor (discharge variation) and to a more directly acting stressor (near-bottom flow). If the excessive use of specific traits for the indication of too many different stressors is avoided and a given stressor acts directly on traits as a priori predicted, reliable interpretations of trait responses can be achieved.8. To illustrate how BTIs can identify individual stressors acting in combination, we examine three cases of multiple stressors: (i) heavy metal pollution in combination with cargo-ship traffic; (ii) eutrophication and fine sediment deposits associated with land use; and (iii) various stressors associated with climate change in combination with salinity. If the number of the assessed traits is sufficiently great and the action of each individual among the multiple stressors is not too weak, multiple traits can potentially resolve the effects of multiple stressors.9. Thematic implications: if the expansion and unification of existing trait databases can be achieved, the rapidly growing knowledge about biological trait responses of lotic invertebrates to individual and multiple stressors should enable the identification of management priorities focused on: (i) individually acting stressors (manage stressor A at site X prior to stressor B at site Y); (ii) multiple stressors acting in different combinations at different sites (manage stressors A & B at site X prior to stressors C & D at site Y); and (iii) individual stressors acting in combination (manage stressor A prior to stressor B at site X). Thus, the BTI approach has the potential to inaugurate a new era in the biomonitoring of lotic (and other) ecosystems.
Article
The field of ecotoxicology is in the early stages of a major paradigm shift driven by three interrelated forces: (1) the consideration of sustainable use of the planet, (2) the protection of ecosystem services (i.e., those ecological functions deemed useful by human society), and (3) the shift from emphasis on producing no deleterious effects to organisms and natural systems to maintaining them in robust health. This review examines present methodologies and information systems in the field of ecotoxicology and determines how suitable they are for making policy and management decisions related to the three developments just stated. Malone (1994) concluded that management of the environment to assure sustainability of its capacity to support human life is essentially a matter of managing human affairs in a manner that fosters sustainable human development. The concept of sustainable development asks whether present practices are suitable for longrange use of the planet.
Environmental Indicators: Typology and Overview
EEA [European Environment Agency], 1999. Environmental Indicators: Typology and Overview. Technical Report no 25, European Environment Agency, Copenhagen.
Individual and combined responses of stream ecosystems to multiple stressors
  • C R Townsend
  • S S Uhlmann
  • C D Matthaei
Townsend, C.R., Uhlmann, S.S., Matthaei, C.D., 2008. Individual and combined responses of stream ecosystems to multiple stressors. J. Appl. Ecol. 45, 1810-1819.
Risk and Resilience in a New Era
  • Wwf
WWF, 2016. Living Planet Report 2016. Risk and Resilience in a New Era. WWF, Gland, Switzerland.