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... Freshwater ecosystems are exposed to an increasing number of anthropogenic pressures (Birk et al., 2020;Reid et al., 2019) and unprecedented rates of change in natural stressors (Cañedo-Argüelles, 2020;Döll & Schmied, 2012). Currently, 39 % of EU water bodies are affected by two or more anthropogenic pressures (e.g., hydromorphological alteration, diffuse pollution, pointsource pollution, invasive species) (Birk et al., 2020;Nõges et al., 2016), causing a widespread degradation of freshwater ecosystems (Grizzet-ti et al., 2017) and challenging their monitoring and management (Brown, Saunders, Possingham, & Richardson, 2013;Feld et al., 2018;Soria et al., 2020). To reverse this situation and apply successful mitigation actions, it is fundamental to better quantify and understand the combined effects of multiple-stressors and their variation across different types of experimental approaches, aquatic systems, types of organisms and modelled responses. ...
... During the last decade, there has been a growing interest in exploring multiple-stressor effects on freshwaters (Côté et al., 2016;Nõges et al., 2016). Profiting such increase in multiple-stressor literature, recent meta-analyses and syntheses have contributed to identify some consistent patterns across ecosystems and stressor pairs (Birk et al., 2020;Jackson et al., 2016;Lemm et al., 2021;Nõges et al., 2016;Sabater et al., 2018;Manuel Villar-Argaiz et al., 2018). ...
... During the last decade, there has been a growing interest in exploring multiple-stressor effects on freshwaters (Côté et al., 2016;Nõges et al., 2016). Profiting such increase in multiple-stressor literature, recent meta-analyses and syntheses have contributed to identify some consistent patterns across ecosystems and stressor pairs (Birk et al., 2020;Jackson et al., 2016;Lemm et al., 2021;Nõges et al., 2016;Sabater et al., 2018;Manuel Villar-Argaiz et al., 2018). For example, a recent pan-European study showed that nutrient stress exerts a dominant effect on lakes, overriding the presence of a second stressor (Birk et al., 2020). ...
Article
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Freshwater ecosystems are exposed to an increasing number of stressors, challenging their biomonitoring and management. Despite recent advances in multiple-stressor research, regional-scale assessments in areas with high freshwater biodiversity and increasing anthropogenic pressure are urgently needed. We reviewed 61 studies focused on freshwater individuals, populations and communities from the Iberian Peninsula to (i) quantify the frequency of experimental approaches used (manipulative, observational), aquatic systems, biological organization levels, and types of organisms and modelled responses, (ii) identify key individual stressors and the frequency of significant positive (increase in response magnitude) and negative (decrease) effects and (iii) determine types of interacting stressors and the frequency of their combined effects. Our dataset comprised 409 unique responses to 13 types of individual stressors, 34 stressor pairs and 12 high-order interactions (3- and 4-way). We found a higher prevalence of manipulative (85 %) respect to observational studies, and a greater focus on lotic systems (59 %) and heterotrophic organisms (58 %). The most studied stressors were nutrient (Nutr), thermal (Therm), hydrologic (Hydr), ultraviolet radiation (UVR), toxic (Toxic) and salinity (Sal) stress and land-use pressure. Individual stressors showed a higher proportion of negative (34 %) than positive effects (26 %). Nutr × UVR, Toxic × Toxic, Therm × Toxic, Hydr × Toxic, Sal × Therm, and Nutr × Therm were the most studied stressor pairs. Non-interactive (50 %) and interactive responses (50 %) were balanced. Antagonistic effects (18 %) were slightly more common than synergisms (15 %), reversal or opposing (13 %) and high-order interactions (4 %). Such proportions varied within experimental approaches, biological organization levels and organism types. Our findings are helpful to manage certain stressor combinations in Iberian freshwaters. Further efforts in Iberian multiple-stressor research should be directed to (i) intensify the study of lentic systems, (ii) explore more observational data, (iii) autotrophic organisms and (vi) biodiversity-ecosystem functioning responses, and (v) cover a wider range of stressors and (vi) more complex interacting stressor scenarios.
... such that their joint effect is the sum of the individual effects (additive effects); and (3) one stressor either strengthens or weakens the effects of the other (interaction). There is a striking lack of information on the frequencies of occurrence of these effect types across spatial scales (that is, from individual water bodies to whole continents) and ecosystem types (rivers versus lakes) 8 . ...
... Impact of ecosystem type on stressor effect types. Stressor interactions are regularly reported in synthesis papers on multiple stressors in freshwater ecosystems 8,10 . We therefore hypothesized that high proportions of both lake and river case studies would indicate additive or interactive paired-stressor relationships. ...
... Though we are not aware of other studies comparing the effects of spatial scale on the explanatory power of stressor interaction models, the observed differences in the frequencies of stressor interactions between experiments and field studies are in line with the synthesis studies of ref. 8 and ref. 10 . While the study of Jackson et al. 10 included only experiments and observed interactive or additive effect types in all cases considered, the study by Nõges et al. 8 focused on field studies, and interactive or additive effect types were given for only 50% of the river and 15% of the lake cases. ...
... Other systems typically take into account eutrophication and hydromorphological modifications (Petriki et al., 2017;Ritterbusch and Brämick, 2015) but in many cases also fisheries pressure and/or non-native species (Gassner et al., 2014;Specziár and Eros, 2020;Virbickas and Stakenas, 2016). We argue that the value of lake fish systems lies in their capacity to capture the effect of many different pressures and their interactions (Nõges et al., 2016) which is lacking for most of the other lake assessment systems. ...
... Responses to fisheries and non-native species are always demonstrated via combined pressure indices. Furthermore, Nõges et al. (2016) have shown that, across all aquatic environments, explanatory power of fish-based pressure-response models increased only under multi-stress conditions, thus qualifying fish communities as a most useful indicator of multi-stress effects. The high mobility and complex life history of fish exposes different life stages to different lake zones, making them useful as holistic indicators in multiple stress situations. ...
Article
Triggered by the adoption of the Water Framework Directive, a variety of fish-based systems were developed throughout Europe to assess the ecological status of lakes. This paper provides a comprehensive overview of all existing systems and summarizes sampling methods, fish community traits (metrics) and the relevant anthropogenic pressures assessed by them. Twenty-one European countries developed fish-based assessment systems. Three countries each developed two distinct systems to approach different ecoregions, either to use different data, or to assess different lake types leading to a total number of 24 systems. The most common approach for the setting of reference conditions, used in seventeen systems, was the utilisation of fish communities in comparably undisturbed natural lakes as reference. Eleven used expert judgment, nine historical data and eight modelled relationships. Fourteen systems combined at least two approaches. The most common fish sampling method was a standardized fishing procedure with multimesh-gillnets. Many countries applied combinations of fishing methods, e.g. non-standard gillnets, fyke nets and electrofishing. Altogether 177 metrics were used for index development and each system combined 2–13 metrics. The most common ones were total standardized catches of number and biomass, relative abundance of Perca fluviatilis, Rutilus rutilus, and Abramis brama, feeding preferences, sensitive species, and non-natives. The pressure-response-relationships for these metrics were supported with both correlations established during system development and scientific publications. However, the metrics and their combinations were highly diverse and no metric was applied universally. Our analysis reveals that most fish-based assessment systems address multiple pressures (eutrophication, hydromorphological alterations, fishery pressure and occurrence of non-natives), whilst few are pressure-specific, tackling only eutrophication or acidification. We argue that the value of fish-based systems for lakes lies in their capacity to capture the effect of many different pressures and their interactions which is lacking for most assessment systems based on other biota.
... The Water Framework Directive (WFD) [1] specifies that for surface waters to be at "Good Ecological Status (GES)", nutrient concentrations should not exceed the levels established so as to ensure the functioning of the ecosystem and the achievement of the values specified for the Biological Quality Elements (BQEs) [1]. Based on the review delivered by MARS project [2] about the stressors affecting European rivers, lakes, groundwater and transitional-coastal waters [3], it becomes clear that nutrient loading was a predominant stressor occurring in more than 70% of multiple stress situations [4], underlining the need for reduction of nutrient stress [5]. ...
... Nutrient enrichment adversely affects both structure and function of the Greek lentic systems since most of them act as sinks mainly due to low water renewal time, among others, which in turns affects the restoration and PoMs [2,10,18]. Approaches to assess the eutrophication risk based on detailed site-specific (water body) information obviously may be applied, but they are of limited use in terms of management since the mode of the BQEs responses has a high level of uncertainty [4,56,57]. At least it is not the appropriate approach for the early stages of any national monitoring strategy. ...
Article
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Eutrophication caused by nutrient enrichment is a predominant stressor leading to lake degradation and, thus, the set-up of boundaries that support good ecological status, the Water Framework Directive’s main target, is a necessity. Greece is one of the Member States that have recorded delays in complying with the coherent management goals of European legislation. A wide range of different statistical approaches has been proposed in the Best Practice Guide for determining appropriate nutrient thresholds. To determine the nutrient thresholds supporting the good status of natural Greek lakes, the phytoplankton dataset gathered from the national monitoring programme (2015–2020) was used for shallow and deep natural lakes. The regression analyses were sufficient and robust in order to derive total phosphorus thresholds that ranged from 20 to 41 μg/L in shallow and 15–32 μg/L in deep natural lake types. Nutrient boundaries that encompass the stressors these lakes are subject to, are essential in proper lake management design.
... The links between hydrological and water quality parameters are generally determined by the catchment and lake own morphometry (Fichot et al., 2011;Nõges et al., 2016). For shallow lakes, like Lake Võrtsjärv, the water level, area and volume can strongly affect seasonal DOC fluxes, CDOM, chlorophyll-a and other parameters (Table 3 and Fig. 6). ...
... Seasonal monitoring revealed that hydrological processes were dominant in lake CDOM levels (WL and CDOM, r = 0.80 ** ) and inflowing DOC fluxes (I DOCAlloch , WL and A, r > 0.50 ** ) ( Fig. 6 and Fig. 8). Such relationships in Lake Võrtsjärv were reported also by Cremona et al. (2014), Toming et al. (2013) and Nõges et al. (2016). Previous studies demonstrated that in Estonian rivers, CDOM is positively correlated with discharge. ...
Article
Dissolved organic carbon (DOC) is an important fraction of organic carbon (OC) that together with colored dissolved organic matter (CDOM) plays a key role in the carbon cycling of lakes. Lake Võrtsjärv is a large and shallow eutrophic lake where water quality measurements have been carried out for a long time. The monthly characteristics of DOC and CDOM in Võrtsjärv and its input/output rivers were traced in 5-years observations. We attempted to link the hydro-morphological indices as lake area (A), water level (WL) and volume variations (Qc) with lake DOC fluxes and CDOM-DOC relationships to improve understanding of carbon fluxes in a very shallow, large and highly eutrophic lake, as well as of the possibility to estimate DOC fluxes by CDOM via remote sensing. The research questions were: how the properties and quantity of DOC, its fluxes and CDOM-DOC relationship in a very shallow, large and highly eutrophic lake are responding to 1) variable proportions of allochthonous and autochthonous processes and 2) changing hydrological conditions. The increased lake volume variation in spring caused the higher level of CDOM, signifying the terrestrial (allochthonous) DOC (DOCAlloch) domination in Lake Võrtsjärv. The proportion of DOCAlloch increased together with increasing WL, A and CDOM concentration. Although the generally high proportion of DOCAlloch in Võrtsjärv, the autochthonous DOC determines the water color (CDOM/DOC) in this highly productive ecosystem with short residence time (280-365 days). Our study on DOC flux revealed that the internal carbon sources, driven by hydrological factors, contribute significantly to the role of large and shallow lakes in global carbon cycling. The further development of water color remote sensing could provide novel directions for understand the feedbacks of lake DOC flux and changing hydrology.
... Most, if not all, ecosystems are being impacted by multiple cooccurring stressors (e.g., climate change, invasive species, pollution), which are predominately anthropogenic in origin (Beauchesne et al., 2021;Halpern et al., 2015), and are capable of affecting individuals through to entire ecosystems Simmons et al., 2021;Sokolova, 2021). At the individual level, responses to multiple stressors might be assessed by their joint effect on the physiology of an organism, e.g., a decline in feeding, growth, or fecundity, or a biochemical change (Nõges et al., 2016), and may also be measured on survival rates (e.g., bee health responses to agrochemicals, Siviter et al., 2021). Population responses to multiple stressors may be assessed by monitoring densities, biomass, or other markers such as chlorophyll concentrations (e.g., freshwater population responses to combinations of invasive species, pesticides, temperature, or UV changes, , whereas ecosystem responses might be measured through multiple stressor effects on functional and taxonomic diversity (e.g., coral reef species richness responses to warming and acidification, Timmers et al., 2021), or through other measures of ecosystem integrity (e.g., stability, Polazzo et al., 2021). ...
... Our discussions of null models and sample sizes have been restricted to investigations of pairs of stressors, yet we know many ecosystems are being challenged with more than two stressors (Halpern et al., 2015). For example, Nõges et al. (2016) identified ...
Article
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As most ecosystems are being challenged by multiple, co‐occurring stressors, an important challenge is to understand and predict how stressors interact to affect biological responses. A popular approach is to design factorial experiments that measure biological responses to pairs of stressors and compare the observed response to a null model expectation. Unfortunately, we believe experiment sample sizes are inadequate to detect most non‐null stressor interaction responses, greatly hindering progress. Using both real and simulated data, we show sample sizes typical of many experiments (<6) can (i) only detect very large deviations from the additive null model, implying many important non‐null stressor‐pair interactions are being missed, and (ii) potentially lead to mostly statistical outliers being reported. Computer code that simulates data under either additive or multiplicative null models is provided to estimate statistical power for user‐defined responses and sample sizes, and we recommend this is used to aid experimental design and interpretation of results. We suspect that most experiments may require 20 or more replicates per treatment to have adequate power to detect nonadditive. However, estimates of power need to be made while considering the smallest interaction of interest, i.e., the lower limit for a biologically important interaction, which is likely to be system‐specific, meaning a general guide is unavailable. We discuss ways in which the smallest interaction of interest can be chosen, and how sample sizes can be increased. Our main analyses relate to the additive null model, but we show similar problems occur for the multiplicative null model, and we encourage similar investigations into the statistical power of other null models and inference methods. Without knowledge of the detection abilities of the statistical tools at hand or the definition of the smallest meaningful interaction, we will undoubtedly continue to miss important ecosystem stressor interactions. Determining adequate sample size for experiments investigating how multiple ecosystem stressors interact need to consider (i) costs; (ii) statistical ability to detect a deviation from the null expectation; and (iii) prior determination of what constitutes a biologically important deviation. Currently, only costs have been considered and this leads to experimental designs that are likely to miss important stressor interactions.
... Man-made flow modifications belong to the dominant stressor group in rivers (Nõges et al., 2016), affecting 41% of European running waters (Schinegger et al., 2012). Hydrological stressors can originate from different sources such as dams and reservoirs, hydropower, water diversions and inter-basin water transfers, urbanization and surface sealing, levees and river channelization, or groundwater extraction (de Graaf et al., 2019;Poff et al., 1997;Rosenberg et al., 2000;Shumilova et al., 2018;Stewardson et al., 2017). ...
... Rivers are often affected by multiple stressors that can act in concert. To answer the question on primary influences, it is, therefore, required to take up the challenge of disentangling the main and interacting factors affecting riverine biota (Birk et al., 2020;Nõges et al., 2016;Schinegger et al., 2016). So, considering the European grayling (Thymallus thymallus) introduced in CHAPTER 1 as an indicator species for an entire fish region (Smialek et al., 2019), the first study of this thesis assessed which environmental factors influence this keystone species. ...
Thesis
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Free-flowing rivers support diverse, complex and dynamic ecosystems, as well as provide societal and economic services. Globally, however, the water flow of many rivers has been regulated by hydropower or other sources. Flow modification affects crucial ecosystem functions and processes, and organism’s capacity to fulfil its life cycle requirements. In light of these widespread effects, it is urgent to mitigate ecological impacts caused by existing water infrastructures. To achieve environmental objectives, as well as to manage water uses in a sustainable way, a thorough understanding of ecological responses to hydrological alterations on different temporal levels (e.g., environmental flow, hydropeaking) is essential. This work aims to establish holistic approaches for restoring flows in modified rivers, and to develop environmental flows able to sufficiently mitigate the ecological effects of short-term and annual flow modifications in fluvial ecosystems. This thesis disentangles the effects of multiple stressors and shows that flow regulation is a primary predictor of fish populations. Moreover, by assessing flow-ecology relationships on annual, seasonal, and sub-daily levels, this work identifies fundamental principles to implement flow restoration measures in rivers affected by water abstraction and hydropeaking. While more dynamic flows are generally recommended as environmental flows, flow restrictions are needed for hydropeaking mitigation. Regarding the latter, a seasonal framework for hydrological mitigation based on fish life-history stages is established, and thresholds are synthesized. Overall, this thesis advances the establishment of guidelines for successful flow restoration in river systems affected by competing water uses by establishing holistic flow restoration schemes and by subsuming quantitative and qualitative hydropeaking thresholds. Moreover, this thesis sets the topic of flow restoration into the broader context of hydromorphological river rehabilitation. Hence, this work contributes to a more balanced discussion on trade-offs between societal and environmental water uses.
... Most of the monitoring and assessment methods are linked to nutrient pollution, while only a few assess the impact of hydromorphological and multiple stressors [5]. A recent review of papers dedicated to aquatic ecology revealed that nutrient stress was studied in 71% to 98% of multi-stress situations [6]. Despite an increasing number of scientific investigations, there are still open questions regarding pathways between stressors, biota, and ecological status. ...
... Our observations highlight two further requirements: First, monitoring and assessment schemes should be based on environment-biology relationships considering multiple stressors and possible interactive effects. For instance, hydromorphological stress could alter the sensitivity to nutrient stress [6]. Second, aquatic communities under undisturbed conditions should be documented in order to better understand the mechanisms of stressor effects when compared against undisturbed conditions. ...
Article
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Upland rivers across Europe still exhibit undisturbed conditions and represent a treasure that we cannot afford to lose. We hypothesize that the combination of pristine and modified conditions could demonstrate biological responses along the stressor gradients. Thus, the response of aquatic macrophyte communities to anthropogenic stressors along upland rivers in Bulgaria was studied. Six stressors were selected out of 36 parameters grouped into hydromorphological, chemical variables and combined drivers (catchment land use). The stressors strongly affected species richness on the basis of biological type (bryophytes vs. vascular plants) and ecomorphological type (hydrophytes vs. helophytes). Hydrological alteration expressed by the change of the river’s base flow and altered riparian habitats has led to a suppression of bryophytes and a dominance of riverbank plant communities. Seventy-five percent of mountain sites were lacking bryophytes, and the vegetation at semi-mountainous sites was dominated by vascular plants. It can be concluded that hydropeaking, organic and inorganic pollution, and discontinuous urban structures caused important modifications in the aquatic macrophyte assemblages. Macrophyte abundance and the biological and ecomorphological type of aquatic macrophytes reflect multi-stressor effects in upland rivers.
... land use change can cause toxicant contamination, nutrification and sedimentation) and stressors will often co-occur . Understanding the major causes of environmental degradation among multiple co-occurring stressors is a challenge because their ecological effects and interactions among stressors are poorly understood (Nõges et al., 2016), and may be scale (Kath et al., 2018) and species dependent (Tockner et al., 2010). ...
... An improved understanding of whether the net effects of multiple interacting stressors differ from their individual effects is central to advancing our ability to address management challenges (Jackson et al., 2016;Nõges et al., 2016). However, establishing cause and effect and predicting consequences on freshwater systems is difficult and currently underexplored because stressors can potentially interact to produce effects that are greater (synergistic) or less (antagonistic) than the sum of each stressor (additive) (Folt et al., 1999). ...
Article
Environmental degradation of rivers in agricultural landscapes is typically caused by multiple co-occurring stressors, but how interactions among stressors affect freshwater ecosystems is poorly understood. Therefore, we investigated the sensitivity and specificity of several measures of benthic macroinvertebrate community response to the individual and combined effects of the pesticide sulfoxaflor (SFX), increased sand sedimentation and elevated nutrients using outdoor recirculating mesocosms. Among the single stressor treatments, nutrients had no observable impact and sand only affected one community response measure compared to controls. High SFX levels had the largest effects on benthic macroinvertebrate communities, negatively affecting six of seven macroinvertebrate response measures. Sulfoxaflor had similar adverse effects on biota when in combination with sand and nutrients in the multi-stressor treatment, suggesting that generally SFX has overwhelming and pervasive effects irrespective of the presence of the other stressors. In contrast to SFX, elevated nutrients had no detectable effect on macroinvertebrate communities, likely as a consequence of nutrients being rapidly taken up by bacteria rather than by benthic algae. Elevated sand sedimentation increased the negative effects of SFX on sediment sensitive taxa, but generally had limited biological effects. This was despite the levels of sedimentation in our treatments being at concentrations that have caused large impacts in other studies. This research points to direct and rapid toxic effects of SFX on stream macroinvertebrates, contrasting with effects of the other stressors. This study emphasises that pesticide effects could be misattributed to other common freshwater stressors, potentially focussing restoration actions on a stressor of lesser importance.
... Multiple stressors are damaging ecosystems worldwide. Hence, for successful conservation and restoration of surface waters, these need to be addressed in concert (Nõges et al., 2016). Human-induced stressors operate locally (e.g. ...
Article
Multiple stressors are continuously deteriorating surface waters worldwide, posing many challenges for their conservation and restoration. Combined effect types of multiple stressors range from single-stressor dominance to complex interactions. Identifying prevalent combined effect types is critical for environmental management, as it helps to prioritise key stressors for mitigation. However, it remains unclear whether observed single and combined stressor effects reflect true ecological processes unbiased by sample size and length of stressor gradients. Therefore, we examined the role of sample size and stressor gradient lengths in 158 paired-stressor response cases with over 120,000 samples from rivers, lakes, transitional and marine ecosystems around the world. For each case, we split the overall stressor gradient into two partial gradients (lower and upper) and investigated associated changes in single and combined stressor effects. Sample size influenced the identified combined effect types, and stressor interactions were less likely for cases with fewer samples. After splitting gradients, 40 % of cases showed a change in combined effect type, 30 % no change, and 31 % showed a loss in stressor effects. These findings suggest that identified combined effect types may often be statistical artefacts rather than representing ecological processes. In 58 % of cases, we observed changes in stressor effect directions after the gradient split, suggesting unimodal stressor effects. In general, such non-linear responses were more pronounced for organisms at higher trophic levels. We conclude that observed multiple stressor effects are not solely determined by ecological processes, but also strongly depend on sampling design. Observed effects are likely to change when sample size and/or gradient length are modified. Our study highlights the need for improved monitoring programmes with sufficient sample size and stressor gradient coverage. Our findings emphasize the importance of adaptive management, as stress reduction measures or further ecosystem degradation may change multiple stressor-effect relationships, which will then require associated changes in management strategies.
... This is a critical limitation as the effects of pressing human disturbances, such as land use or anthropogenic climate change, often develop over multidecadal time scales (Smol, 2019). The problem is further exacerbated as lakes are increasingly confronted with multiple interacting human pressures that may superimpose or amplify the effect of one another (Nõges et al., 2016;Bruel et al., 2018). Approaches incorporating the long-term temporal perspective are therefore needed to elicit patterns and control of lake CO 2 under growing human perturbation. ...
Article
Global change transforms processes regulating carbon dioxide (CO2) concentrations in lakes, yet our understanding of the broad scale responses of lake CO2 to global and local human perturbation across heterogeneous landscapes and multidecadal time scales is limited. We examined decadal scale variability in the carbon isotope (δ¹³C) composition of subfossil zooplankton (Branchiopoda: Cladocera) in seven large clear perialpine lakes, including three previously studied sites, to decipher different patterns in summer surface CO2 concentrations. Generalized additive models were used to examine whether and how these patterns connect to changing nutrient regimes and anthropogenic warming over the past century. In all but one of the lakes shifts in cladoceran δ¹³C values coincided with turning points in the eutrophication history, broadly implying decreasing summer surface CO2 concentrations driven by phosphorus fertilization of pelagic primary production. Yet where nutrient concentrations remained below mesotrophic levels, the positive relationship between δ¹³C and phosphorus diminished indicating that the strong biotic control of CO2 concentrations was overwritten, probably by catchment inorganic carbon inputs and internal biochemical processes. Even under extensive nutrient loading, the connection was further weakened in lakes with high catchment to lake area ratio attributable to increased catchment interference and shorter water residence times. Warming of the perialpine region was also imprinted in the isotopic records, yet the temperature effects appeared modest and were restricted to three smaller lakes with lower drainage ratios. In these lakes, warming contributed to declining cladoceran δ¹³C values likely partially driven by epilimnetic deepening increasing CO2 in surface waters. Overall, our results manifest the broad heterogeneity of lake responses to global change and point to the importance of hydrogeomorphic context in shaping the sensitivity and responses of lake CO2 to changing nutrient regimes and warming at the regional scale.
... Frequent occurrences of hypoxic or anoxic conditions in the bottom water influence the distribution of macrobenthic animals, causing catastrophic disturbances to macrobenthic communities (e.g., Diaz and Rosenberg, 1995;Seitz et al., 2009), and are the main driver of eutrophication-associated dead zones around the world (Diaz and Rosenberg, 2008). Thus, negative effects from anthropogenic impacts can remain in benthic ecosystems over a long time, even after the removal of those impacts (Borja et al., 2010;Nõges et al., 2016). Benthic invertebrates are useful indicators for assessing such effects on the benthic environment (Dauer, 1993). ...
Article
Deterioration of the sediment environment and benthic ecosystem is an undesirable effect of eutrophication, but little is known about the response of macrobenthic communities to eutrophication and their long-term recovery. In the present study, temporal changes in benthic ecological status, associated with reductions in anthropogenic impacts on a largest semi-enclosed sea in Japan, were determined using long-term monitoring data from water and sediment quality based on the multivariate AZTI Marine Biotic Index (M-AMBI), focusing on spatial differences in anthropogenic impacts. Several sub-areas were classified based on Chlorophyll a (Chl.a) concentrations in surface water during the 1980s. Chl.a concentrations decreased in all sub-areas except the sub-area with <2 μg Chl.a L⁻¹ from the 1990s–2010s. On the other hand, total organic carbon contents in sediment decreased and M-AMBI values increased in all sub-areas during this period may be due to reduced lateral organic matter advection from surrounding areas.
... In contrast to index totals, 'average score per taxon' (ASPT) indices describe community sensitivity to impacts independent of taxonomic richness, and may thus experience less pronounced decreases in response to stressors (Wilding et al., 2018;Figure 1b). However, research is needed to inform the development of metrics that respond independently to impacts and natural stressors (Gutiérrez-Cánovas et al., 2015), and thus to enable effective biomonitoring in ecosystems responding to environmental change (Nõges et al., 2016). ...
Article
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Rivers are dynamic ecosystems in which both human impacts and climate‐driven drying events are increasingly common. These anthropogenic and natural stressors interact to influence the biodiversity and functioning of river ecosystems. Disentangling ecological responses to these interacting stressors is necessary to guide management actions that support ecosystems adapting to global change. We analysed the independent and interactive effects of human impacts and natural drying on aquatic invertebrate communities—a key biotic group used to assess the health of European freshwaters. We calculated biological response metrics representing communities from 406 rivers in eight European countries: taxonomic richness, functional richness and redundancy, and two biomonitoring indices that indicate ecological status. We analysed metrics based on the whole community and a group of taxa with traits promoting resistance and/or resilience (‘high RR’) to drying. We also examined how responses vary across Europe in relation to climatic aridity. Most community metrics decreased independently in response to impacts and drying. A richness‐independent biomonitoring index (the average score per taxon; ASPT) showed particular potential for use in biomonitoring, and should be considered alongside new metrics representing high RR diversity, to promote accurate assessment of ecological status. High RR taxonomic richness responded only to impacts, not drying. However, these predictors explained little variance in richness and other high RR metrics, potentially due to low taxonomic richness. Metric responsiveness could thus be enhanced by developing region‐specific high RR groups comprising sufficient taxa with sufficiently variable impact sensitivities to indicate ecological status. Synthesis and applications. Metrics are needed to assess the ecological status of dynamic river ecosystems—including those that sometimes dry—and thus to identify priority sites requiring action to tackle the causes of environmental degradation. Our results inform recommendations guiding the development of such metrics. We propose concurrent use of richness‐independent ‘average score per taxon’ indices and metrics that characterize the richness of resistant and resilient taxa. We observed interactions between aridity, impacts and drying, highlighting that these new metrics should be region‐specific, type‐specific and adaptable, promoting their ability to inform management actions that protect biodiversity in river ecosystems responding to climate change.
... European rivers, for instance, are mainly threatened by the interplay of physical and chemical stressors including hydrological, morphological and nutrient stress (EEA, 2018). Accordingly, these stressor combinations are investigated most often in the scientific literature (Nõges et al., 2016). ...
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.
... Much attention in recent years has focussed on interactions between stressors, recognising that part of the uncertainty observed in relationships with a single stressor is due to interactions (additive, synergistic or antagonistic) with other stressors (Nõges et al., 2016;Torres et al., 2017). Subsequently, models have begun to incorporate this complexity within catchment-level decision making processes (Spears et al., 2021). ...
Article
One key component of any eutrophication management strategy is establishment of realistic thresholds above which negative impacts become significant and provision of ecosystem services is threatened. This paper introduces a toolkit of statistical approaches with which such thresholds can be set, explaining their rationale and situations under which each is effective. All methods assume a causal relationship between nutrients and biota, but we also recognise that nutrients rarely act in isolation. Many of the simpler methods have limited applicability when other stressors are present. Where relationships between nutrients and biota are strong, regression is recommended. Regression relationships can be extended to include additional stressors or variables responsible for variation between water bodies. However, when the relationship between nutrients and biota is weaker, categorical approaches are recommended. Of these, binomial regression and an approach based on classification mismatch are most effective although both will underestimate threshold concentrations if a second stressor is present. Whilst approaches such as changepoint analysis are not particularly useful for meeting the specific needs of EU legislation, other multivariate approaches (e.g. decision trees) may have a role to play. When other stressors are present quantile regression allows thresholds to be established which set limits above which nutrients are likely to influence the biota, irrespective of other pressures. The statistical methods in the toolkit may be useful as part of a management strategy, but more sophisticated approaches, often generating thresholds appropriate to individual water bodies rather than to broadly defined “types”, are likely to be necessary too. The importance of understanding underlying ecological processes as well as correct selection and application of methods is emphasised, along with the need to consider local regulatory and decision-making systems, and the ease with which outcomes can be communicated to non-technical audiences.
... In contrast, riverine ecosystems remain relatively understudied in this respect and it is likely that cumulative stressor effects display complex threshold behaviors, where synergism or antagonism may occur at certain values of stressors and initial environmental conditions Johnson et al., 2017;Nõges et al., 2016). ...
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Numerous anthropogenic stressors, including river regulation, excess loadings of nutrients and sediment, channelisation, as well as thermal and hydrological stressors driven by climate change impact riverine ecosystems worldwide. In a time when freshwater degradation and the rate of global warming are faster than ever, understanding the potential interactive effects of local and catchment‐scale stressors with large‐scale climatic conditions is essential to enhance our ability to plan effective conservation, restoration, and mitigation measures. In this study we analysed a dataset spanning the whole of Sweden using a space‐for‐time approach to investigate interactive effects of land use, river regulation, and climate on brown trout (Salmo trutta) abundance in streams. We found that in warmer regions trout populations were negatively affected in catchments with more intense river regulation by hydropower dams (i.e. ≥10 m3/km2 total reservoir storage volume). In such catchments, a 7°C warmer mean summer air temperature was associated with an average between 44% and 83% decline in trout abundance. In catchments with less intense river regulation, trout abundance instead increased moderately with increasing temperature. We also found that brown trout abundance declined with increasing areal extent of urban areas when found in combination with ≥20% agricultural land use. When agricultural land use reached maximum values (84%), brown trout abundance decreased from an average of 13 individuals per 100 m2 in catchments with no urban areas to values ≤1 in catchments with ≥5% urban land use. Also, brown trout abundance declined with increasing agricultural land use in catchments with ≥3% urban land use. Our study brings innovative empirical evidence of interactive effects between river regulation, land use and climate on brown trout populations. From a management perspective our findings suggest that: (1) restoring natural flows (e.g. through dam removal) and riparian vegetation could mitigate adverse effects of climate change; and (2) restoration measures that minimise the effects of agriculture and urban land use (e.g. reduction of nutrient levels and restored riparian buffer zones) could help rehabilitate brown trout in catchments with high anthropogenic land use change. However, given the large observed variation between streams, we advise for bespoke management actions stemming from sound knowledge of local habitat conditions and target populations, whenever possible, using an ecosystem management‐based approach.
... Then, although the number of topics is often set a priori by the user (e.g., Kane et al. (2016)), in this study, the number of topics for each dataset was determined based on the ldatuning package (Murzintcev 2020). This package calculates different metrics to estimate the preferable number of topics for LDA model (Arun et al. 2010;Cao et al. 2009;Deveaud et al. 2014;Griffiths and Steyvers 2004). ...
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Anthropogenic land use change (ALUC) satisfies human needs but also impacts aquatic ecosystems. Aquatic ecosystems are intrinsically linked with terrestrial landscapes, an association that is already recognized as a key factor to address future research and effective governance. However, the complexity and range of the impact of ALUC in aquatic ecosystems have been fundamental challenges and have implicitly routed the analysis to particular segments, drivers, management, or effects of the theme. In this study, we present an attempt to frame the subject in a broader context through a topic-based bibliometric analysis. Our aim is to identify possible biases and gaps in the current scientific literature and detect the main topics that have characterized the theme. Our results show an unequal distribution of articles by country when we analyzed the authors’ affiliation and also a slight increase in contributions from social and economic disciplines, although they are still underrepresented. Moreover, we distinguish topics whose prevalence seems to change, especially those topics where the use of scenario analysis and multi-stressors are considered. We discuss the main biases and gaps revealed by our results, concluding that future studies on the impact of ALUC on aquatic ecosystems should better integrate social and economic disciplines and expand geographic frontiers.
... Pollution is a major threat for freshwater ecosystems; particularly, environmental degradation is depleting water resources, whether because the surface waters contain higher amounts of pollutants, or because pollutants through the soil attain even the underground water reserves [21]. Apart from industrial discharging in large river basins, a huge impact is determined by organic civil pollution that may not only affect small streams and creeks but also groundwaters through percolation, with cascading detrimental effects for humans and for a large part of the overall biodiversity. ...
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Assessing the effects of pollution in groundwaters is recently considered among the most relevant aims for subterranean biology; with this perspective, we aim to provide examples of the most relevant effects that pollution may cause on stygofauna community and underline patterns deserving further investigations. We retrieved different cases in which pollution caused alteration of groundwater trophic webs, favored invasions by epigean mesopredators, damaged stygobiont keystone species, and promoted interspecific competition between stygobionts and epigean animals. The results and the remarks derived from our perspective review underline that pollution may play multifaceted effects on groundwaters communities, and the paucity of information that exists on community-level changes and threats underlines the necessity for further studies.
... Species diversity is an important attribute of ecological communities (Cardinale et al. 2006). Its loss as a result of warming, particularly when combined with other stressors, may erode ecological network functioning (Piggott et al. 2015, Nõges et al. 2016, White et al. 2018. For example, aerial taxa abundance, richness, and diversity in heated sections of the river in summer were significantly lower than in the unheated adjacent section. ...
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Warm discharges from industrial processes have the potential to impact benthic invertebrate communities and undermine river functioning as well as inform climate change impacts. We evaluated the effects of heated cooling waters from 2 power plants across 2 River Shannon locations (Ireland) in summer and in winter. The overall multivariate community composition differed significantly between heated and unheated river sections in both seasons. In summer, overall invertebrate taxon richness and diversity were significantly lower in heated than in unheated sections. This finding was coupled with a striking decrease in Ephemeroptera, Plecoptera, and Trichoptera (EPT) abundance, taxon richness, and diversity in heated sections. Furthermore, aerial taxon richness and diversity were significantly lower in the heated sections. We also observed that the abundance of grazers was lower in heated sections. Winter patterns were similar to summer, but with lower invertebrate community abundance and decreased functional representation of shredders, gatherers, and predators in heated sections. Such impacts likely have strong implications for river functioning, including depressed connectivity with riparian habitats, and may impair the performance of eutrophication biomonitoring tools that rely on EPT taxa. Our results highlight the impact of warming of thermal plumes and other ubiquitous triggers of heating and may indicate climate change-driven trajectories.
... On the other hand, biotic assessments indicate both water quality and overall ecosystem health [55]. This suggests that using both biotic and abiotic metrics, as we did, provides a deeper understanding of water quality, and may be useful to inform fisheries or ecosystem management [56,57]. ...
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The Mekong River is one of the world’s largest rivers, unparalleled in terms of its biodiversity and ecosystem services. As in other regions, sufficient water quality is required to support diverse organisms, habitats, and ecosystems, but in the Mekong region, water quality has not been well studied. Based on biological and physical-chemical data collected over the last two decades, we evaluated spatial-temporal water quality of the Lower Mekong Basin (LMB) using biotic and abiotic assessment metrics. We found that during the 2000s, water quality in the LMB was unpolluted, with “very good” metrics for tributary rivers and “good” status for mainstem rivers. However, during the last decade, water quality has been degraded in the LMB, particularly near Vientiane City; the Sekong, Sesan, and Srepok (3S) Rivers; the Tonle Sap Lake system; and the Mekong Delta. Water quality degradation likely corresponds to flow alteration, erosion, sediment trapping, and point and non-point wastewater, which have occurred from rapid hydropower development, deforestation, intensive agriculture, plastic pollution, and urbanization. Regular biomonitoring, physical-chemical water quality assessment, transparent data sharing, and basin-wide water quality standards or management are needed to sustain water quality to support biodiversity and ecosystem function in the LMB.
... On top of that, ecosystems may shift abruptly in response to environmental perturbations (Oprandi et al., 2020;Scheffer and Carpenter, 2003), but very little information on critical thresholds and on their variability across space and time is available (Boada et al., 2017;Rindi et al., 2017). Our limited knowledge regarding the response of specific structural and functional features of ecosystems to multiple stressors and disturbances (Gissi et al., 2021;Micheli et al., 2013), the inherent spatial and temporal variability in the distribution of ecological features and stressors, and the challenging detection of critical thresholds that lead to regime shifts, are still restraining our potential to quantify and, consequently, achieve and maintain good ecological conditions (Nõges et al., 2016). ...
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Local, regional and global targets have been set to halt marine biodiversity loss. Europe has set its own policy targets to achieve Good Environmental Status (GES) of marine ecosystems by implementing the Marine Strategy Framework Directive (MSFD) across member states. We combined an extensive dataset across five Mediterranean ecoregions including 26 Marine Protected Areas (MPAs), their reference unprotected areas, and a no-trawl case study. Our aim was to assess if MPAs reach GES, if their effects are local or can be detected at ecoregion level or up to a Mediterranean scale, and which are the ecosystem components driving GES achievement. This was undertaken by using the analytical tool NEAT (Nested Environmental status Assessment Tool), which allows an integrated assessment of the status of marine systems. We adopted an ecosystem approach by integrating data from several ecosystem components: the seagrass Posidonia oceanica, macroalgae, sea urchins and fish. Thresholds to define the GES were set by dedicated workshops and literature review. In the Western Mediterranean, most MPAs are in good/high status, with P. oceanica and fish driving this result within MPAs. However, GES is achieved only at a local level, and the Mediterranean Sea, as a whole, results in a moderate environmental status. Macroalgal forests are overall in bad condition, confirming their status at risk. The results are significantly affected by the assumption that discrete observations over small spatial scales are representative of the total extension investigated. This calls for large-scale, dedicated assessments to realistically detect environmental status changes under different conditions. Understanding MPAs effectiveness in reaching GES is crucial to assess their role as sentinel observatories of marine systems. MPAs and trawling bans can locally contribute to the attainment of GES and to the fulfillment of the MSFD objectives. Building confidence in setting thresholds between GES and non-GES, investing in long-term monitoring, increasing the spatial extent of sampling areas, rethinking and broadening the scope of complementary tools of protection (e.g., Natura 2000 Sites), are indicated as solutions to ameliorate the status of the basin.
... The mechanisms through which adaptive traits improve fitness are complex given that the value of adaptive traits may vary based on the magnitude and duration of exposure as well as the presence of additional stressors that often lead to unpredictable responses. Anthropogenic activities have been shown to increase the severity, frequency, and co-occurrence of stressors, therefore, untangling the interactive effects of multiple stressors and the strategies employed by organisms to tolerate them is critical for increasing our basic understanding of ecological interactions as well as managing ecosystems (Nõges et al. 2016). ...
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Anthropogenic impacts are expected to increase the co-occurrence of stressors that can fundamentally alter ecosystem structure and function. To cope with stress, many organisms locally adapt, but how such adaptations affect the ability of an organism to manage co-occurring stressors is not well understood. In aquatic ecosystems, elevated temperatures and harmful algal blooms are common co-stressors. To better understand the role and potential trade-offs of local adaptations for mitigating the effects of stressors, Daphnia pulicaria genotypes that varied in their ability to consume toxic cyanobacteria prey (i.e., three tolerant and three sensitive) were exposed to five diets that included combinations of toxic cyanobacteria, Microcystis aeruginosa, and a green alga, Ankistrodesmus falcatus, under two temperatures (20 °C vs. 28 °C). A path analysis was conducted to understand how local adaptations affect energy allocation to intermediate life history traits (i.e., somatic growth, fecundity, survival) that maximize Daphnia fitness (i.e., population growth rate). Results from the 10-day study show that tolerant Daphnia genotypes had higher fitness than sensitive genotypes regardless of diet or temperature treatment, suggesting toxic cyanobacteria tolerance did not cause a decrease in fitness in the absence of cyanobacteria or under elevated temperatures. Results from the path analysis demonstrated that toxic cyanobacteria had a stronger effect on life history traits than temperature and that population growth rate was mainly constrained by reduced fecundity. These findings suggest that local adaptations to toxic cyanobacteria and elevated temperatures are synergistic, leading to higher survivorship of cyanobacteria-tolerant genotypes during summer cyanobacterial bloom events.
... Many studies (Rask et al. 2011;Nõges et al. 2016;Huo et al. 2018;Phillips et al. 2018a) show that there is a significant relationship between stressors (such as nutrients and hydromorphology) and the condition of biological quality element (BQEs). On the other hand, studies proved that the pressure-response relationships are very complex (Lyche-Solheim et al. 2013), therefore deriving nutrient criteria might require more refined methods. ...
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The objective of the Water Framework Directive (WFD) is to achieve good ecological status in surface waters by 2027. To make a proper evaluation of the ecological status of watercourses, it is necessary to harmonize class boundaries for chemical and biological quality elements (BQEs). This paper aims to explore the linkages between physicochemical parameters and BQEs and set river nutrient threshold concentrations that support good ecological status. Regression and mismatch methods were applied to find the relationship between phytoplankton (PP) and phytobenthos (PB) ecological quality ratio and mean total phosphorus (TP) and total nitrogen (TN) concentrations. Nutrient thresholds have been suggested for several water types, which are varied in the case of highland rivers 1.8–6.2 mg TN/l, 180–400 μg TP/l; in the case of lowland rivers 1.4–5.0 mg TN/l, and 100–350 μg TP/l. These values are similar to what other studies found, but the relationship between biology and nutrients was weaker. Besides nutrients, additional data of measured dissolved organic carbon, 5-day biochemical oxygen demand, chemical oxygen demand with potassium permanganate method, and information about hydromorphological features were involved in the analysis. The research demonstrates that random forest can be used as a nonlinear, multiparametric model for predicting biological class from five variables with 35–81% error for PP and with 18–47% error for PB. HIGHLIGHTS Statistical analysis demonstrated in the paper will be the first publication of Hungarian ecological monitoring data processing.; The research pointed out some failures in the implementation of the Water Framework Directive, namely that considering every biological quality element throughout criteria development might be a mistake.; The paper demonstrates how random forests can be used for biological classification.;
... This creates huge challenges for both science and policy, as most of the past century of ecotoxicology and biomonitoring has focused on single stressors, and the much smaller subset of studies on two or more stressors has typically assumed additivity by default [23][24][25]. This is a gross oversimplification, as global meta-analyses and reviews have revealed that nonadditive effects are common [26,27] in both the aquatic [10,[28][29][30][31] and terrestrial [32,33] realms, although we still do not fully understand how and why they arise [25]. Some initial evidence suggests that when stressors occur simultaneously, nonadditive effects are the rule rather than the exception [34]. ...
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Multiple stressors, such as warming and invasions, often occur together and have nonadditive effects. Most studies to date assume that stressors operate in perfect synchrony, but this will rarely be the case in reality. Stressor sequence and overlap will have implications for ecological memory – the ability of past stressors to influence future responses. Moreover, stressors are usually defined in an anthropocentric context: what we consider a short-term stressor, such as a flood, will span multiple generations of microbes. We argue that to predict responses to multiple stressors from individuals to the whole ecosystem, it is necessary to consider metabolic rates, which determine the timescales at which individuals operate and therefore, ultimately, the ecological memory at different levels of ecological organization.
... In contrast to micropollutants, there is a huge body of literature on the effects of hydrological and morphological stressors on riverine biota [1,12,[20][21][22][23]. The European Environment Agency recently listed hydromorphological impacts, such as channelisation, disconnection of floodplains or flow regulation, among the top stressor groups affecting Europe's rivers [24]. ...
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Background A variety of anthropogenic stressors influences the ecological status of rivers wordwide. Important stressors include elevated concentrations of nutrients, salt ions, heavy metals and other pollutants, habitat degradation and flow alteration. Some stressors tend to remain underrepresented in multiple-stressor studies, which in particular is apparent for micropollutants (e.g. pesticides, pharmaceuticals) and alterations of the flow regime. This case study analysed and compared the effects of 19 different stressor variables on benthic macroinvertebrates in the two German rivers Erft and Niers (Federal State of North Rhine-Westphalia, Germany). The stressors variables were assigned to four stressor groups (physico-chemical stress, mixture toxicity of 42 micropollutants, hydrological alteration and morphological degradation) and were put into a hierarchical context according to their relative impact on the macroinvertebrate community using redundancy analysis and subsequent variance partitioning. Results The results suggest a strong and unique effect of physico-chemical stress, yet at the same time reveal also a strong joint effect of physico-chemical and hydrological stressor variables. Morphological degradation showed subordinate effects. Notably, only a minor share of the explained variance was attributed to the mixture toxicity of micropollutants in these specific catchments. Conclusions The stressor hierarchy indicates that management measures for improving the ecological status still need to address water quality issues in both rivers. The strong joint effect of physico-chemical stress and hydrological alteration might imply a common source of both stressor groups in these two catchment areas: lignite mining drainage, urban area and effluents of wastewater treatment plants. The findings point at the important role of alterations in the flow regime, which often remain unconsidered in hydro-morphological surveys.
... However, these impacts are being increasingly exacerbated by concurrent climate change effects acting on similar pathways [2••]. In response to the deepening biodiversity crisis, there is a growing, substantial body of research dedicated to understanding drivers of freshwater biodiversity change, including syntheses of the overall evidence base [5,6]. However, translating this growing knowledge base into meaningful conservation action remains a significant challenge in part due to the vast complexity and diversity of real-world ecosystems [7]. ...
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Purpose of Review Multiple stressor studies conducted in real-world environments play an important role in discovering how stressor pathways may vary relative to ecological complexity and study scale. We reviewed the evidence for climate and landscape change impacts on freshwater biodiversity in real-world ecosystems at the global scale. Using our compiled database of 150 studies, we asked (1) what are the study characteristics within the available evidence base and (2) what are the main knowledge gaps and recommendations for future research? Recent Findings Most studies employed an observational design and examined climatic and landscape change trends over a broad regional spatial scale (median = 97 sites/study). Ecological complexity was well represented in studies with a median of 11 predictor variables that characterized the relevant climate, landscape condition, and many other environmental attributes. Community-level metrics were common response types across all biota including larger, more mobile organisms such as fish that are challenging to examine in an ecologically-relevant context within controlled laboratory settings. Summary We identified several knowledge gaps including the need for more published time-series data, particularly with respect to understanding climate change impacts. Other opportunities for improved future research included incorporating more stressor and biological interactions, examining potential climate stressors over multiple seasons and streamlining methods for dealing with the pervasive challenges of multicollinearity in real-world systems. We emphasize the unique role of ‘natural experiments’ in validating experimental findings and provide a suite of recommendations for creating more strategic field studies to inform conservation efforts.
... Among these, only one study considered five ecosystem elements 33 . This represents a shortcoming in the analysis of wind energy devices impacts, since it is well-known that human activities can produce several co-occurring pressures, which can result in cumulative, synergistic or antagonistic impacts on the ecosystem [34][35][36] . Investigating multiple interactions between human activities and ecosystem elements is urgent, given that future wind energy developments will add to the cumulative impacts already produced by existing activities and climate change 37 . ...
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Offshore wind energy is widely regarded as one of the most credible sources for increasing renewable energy production towards a resilient and decarbonised energy supply. However, current expectations for the expansion of energy production from offshore wind may lead to significant environmental impacts. Assessing ecological risks to marine ecosystems from electricity production from wind is both timely and vital. It will support the adoption of management measures that minimize impacts and the environmental sustainability of the offshore wind energy sector.
... A recent review of the effects of multiple stressors on aquatic ecosystems revealed that most limnological studies considered time periods between 7.5 to 9 years (based on a targeted search from the Web of Science citation databases that yielded 219 papers ;Nõges et al., 2016). However, in many cases, such relatively short timescales will fail to include baseline conditions prior to the onset of multiple stressors and instead examine what are already changing and transient conditions. ...
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While it is now well accepted that human activities are having pronounced effects on natural ecosystems, regional variation in the rate and magnitude of various human impacts is unclear. Moreover, the effects of land use change on natural aquatic communities have only relatively recently begun to be explored. Our goal was to understand how and where assemblages of a central food web component of freshwater lakes have changed over the course of industrialization in relation to land use. Canada. Pre‐1880 AD to present. Cladoceran zooplankton. As part of the Natural Sciences and Engineering Research Council (NSERC) Canadian Lake Pulse Network, we selected 101 lakes across Canada along a gradient of human impact to analyse subfossil cladoceran assemblages from sediment cores. We examined relationships between taxonomic and functional indicators of cladoceran assemblage change among lakes and through time. Contemporary assemblages were taxonomically and functionally less diverse locally relative to pre‐industrial assemblages (α‐diversity) and were structured by the degree of human impact in watersheds. Local α‐diversity losses were greatest in highly impacted lakes where agriculture and pasture are prevalent. While spatial homogenization (spatial β‐diversity) did not increase since pre‐industrial times as expected, temporal turnover (temporal β‐diversity) showed a non‐significant but increasing trend in highly impacted lakes, especially in urbanized watersheds. Cladoceran assemblages have changed significantly over the course of the Industrial period, and especially in more highly impacted watersheds, underscoring the important role of watershed land use in shaping diversity. However, indicators of cladoceran function have remained relatively conserved over time and land use change showed little impact on β‐diversity, despite important environmental variation. Overall, this research furthers our understanding of the health status of Canadian lakes and the consequences of human activities, especially agriculture and urbanization, on lake zooplankton.
... Several efforts to summarize general trends of how stressors interact with each other have been carried out in recent years, with a main focus on freshwater systems (C.J. Brown et al., 2013;Jackson et al., 2016;Côté et al., 2016). However, despite these efforts, patterns and processes that may lead to interactive effects among multiple stressors remain poorly understood (Nöges et al., 2016). In addition, it remains unclear how the detection and classification of multiple stressor effects may vary under biased coverage of stressor gradients in the context of empirical data from field surveys and biomonitoring programmes. ...
Article
This study aims at understanding how observed inconsistencies in the response of biotic indicators to multiple stressors may result from different stressor gradient lengths being represented at different areas or temporal windows, either as the result of intrinsic natural causes or as the result of sampling bias. We simulated a pool of sites showing five types of interactive responses of indicators to two co-occurring virtual stressors, as well as several sampling constraints, resulting in different portions of each stressor's gradient being covered. The sampled gradient length showed a strong influence on the detection of single stressor effects, both in terms of statistical significance and goodness-of-fit. Increasing constraints on gradient coverage also led to an increasingly deficient identification of stressor interactions. The fail in detecting significant interactions largely dominated over switches between interaction types. The simulations indicated that datasets not fully capturing stressor gradients may hinder the ability to unveil underlying multiple stressor effects. As distinct portions of stressor gradients may be present at different contexts and may change over time, our simulations stress the importance of adaptive management strategies based on robust sampling designs to minimize potential statistical artefacts and uncertainties.
... As with most aquatic ecosystems, estuaries are simultaneously exposed to a range of different human pressures that can have cumulative effects at different levels of biological organisation (Nõges et al. 2016). When caused by discrete activities, these pressures can be managed locally (e.g. ...
... En ce qui concerne les pressions anthropiques, les seuils trouvés par rapport à la tolérance de P. oceanica dans nos travaux sont similaires à ceux déjà trouvés par (Holon et al., 2018), avec l'indice de déclin (composition spatiale). L'interprétation des seuils liés aux multiples facteurs de stress anthropiques (Holon et al., 2018;Nõges et al., 2016;Houngnandan et al., 2020;Valerio et al., 2020) n'est souvent pas évidente étant donné que i) on sait que les différentes pressions anthropiques agissent soit en synergie soit en combinaison (Boudouresque et al., 2012;Jordà et al., 2012;Adams et al., 2020;Mecca et al., 2020), ii) l'influence des pressions anthropiques est soit directe par des dommages physiques (mouillage) soit indirecte par modification des conditions environnementales (agriculture, sédimentation, rejets urbains) (Marbà et al., 2014;Orth et al., 2006;Deter et al., 2017), iii) le processus de fragmentation de P. oceanica est d'abord induit par une réduction de la cohésion entre les patchs (configuration) qui précèdent par la suite une réduction de sa superficie (composition) (Boudouresque et al., 2012 Nos résultats montrent pourtant que ces activités humaines ralentissent l'invasion des deux EEE les plus dangereuses de la Méditerranée de façon directe par l'érosion côtière ou indirecte par les rejets urbains ou les cages de pisciculture qui bloquent l'accessibilité à la lumière. Cela pourrait être expliqué par le fait que des études expérimentales ont montré par exemple que ces deux EEE évitent la faible salinité et la forte turbidité (Carruthers et al., 1993;Creese, 2004b;West and West, 2007 , ce qui a été mal pris en compte par la plupart des pays de l'UE dans leurs efforts de mise en oeuvre de la DCSMM et la DCE . ...
Thesis
Les activités humaines sont la principale cause des changements globaux avec des conséquences néfastes sur l’ensemble de la biodiversité, aussi bien terrestre que marine. Dans ce contexte, de nombreux pays dont la France souhaite endiguer ce phénomène à travers l’amélioration des réseaux de surveillance et de gestion des écosystèmes à l’aide de nouvelles méthodes et approches qui visent, notamment l’atteinte d’un bon état écologique de leurs masses d’eaux. C’est l’objectif principal que s’est fixé ce projet de thèse, en se concentrant sur un écosystème sentinelle de Méditerranée, les herbiers de Posidonia oceanica. P. oceanica est une plante sous-marine endémique de méditerranée, indicatrice de la qualité de son environnement. En croisant sa distribution spatiale avec des données biologiques et de pressions anthropiques, il est possible de proposer des nouveaux indicateurs faciles à calculer à l’échelle de tout le littoral français (1800 km).Nous avons par une approche multidisciplinaire, mêlant cartographie participative, analyse d’images anciennes et données écologiques actuelles, pu localiser d’anciens herbiers aujourd’hui disparus et quantifier l’importance du déclin (70 % en 66 années par exemple à Agde et Rochelongue). Nos résultats montrent aussi que les indices de composition et de configuration paysagère reflètent bien l’état de conservation d’un herbier de P. oceanica. En utilisant ces indices paysagers, nous avons mis en place une nouvelle approche pour définir des zones de conservation clés pour la gestion de P. oceanica sur la base de l’influence de variables environnementales et d’activités humaines. Enfin nous avons aussi montré qu’en dégradant les herbiers de P. oceanica, les activités humaines favorisent l’installation d’algues exotiques envahissantes, mais peuvent aussi constituer un frein à ces mêmes invasions en modifiant les conditions locales environnementales et en les rendant défavorables aux espèces invasives.Ces résultats laissent présager de multiples applications pour améliorer la gestion et la surveillance du milieu marin en Méditerranée française.
... However, great uncertainty remains about the respective contribution of various stressors to ecosystem degradation. This debate also relates to agricultural pesticides as some investigations have identified strong impacts of nonpoint-source pesticide pollution on streams in Australia ( Beketov et al., 2013 ), Europe ( Beketov et al., 2013 ;Liess and Von Der Ohe, 2005 ), North America ( Chiu et al., 2016 ) and South America ( Hunt et al., 2017 ) while others only identified comparatively low impacts of pesticides ( Noges et al., 2016 ). Accordingly, the question remains how severe the effects of pesticides are compared to other stressors and, more specifically, at which concentrations ecosystem effects occur and which species and functional parameters are affected. ...
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Despite elaborate regulation of agricultural pesticides, their occurrence in non-target areas has been linked to adverse ecological effects on insects in several field investigations. Their quantitative role in contributing to the biodiversity crisis is, however, still not known. In a large-scale study across 101 sites of small lowland streams in Central Europe, Germany we revealed that 83% of agricultural streams did not meet the pesticide-related ecological targets. For the first time we identified that agricultural nonpoint- source pesticide pollution was the major driver in reducing vulnerable insect populations in aquatic in- vertebrate communities, exceeding the relevance of other anthropogenic stressors such as poor hydro- morphological structure and nutrients. We identified that the current authorisation of pesticides, which aims to prevent unacceptable adverse effects, underestimates the actual ecological risk as (i) measured pesticide concentrations exceeded current regulatory acceptable concentrations in 81% of the agricultural streams investigated, (ii) for several pesticides the inertia of the authorisation process impedes the incor- poration of new scientific knowledge and (iii) existing thresholds of invertebrate toxicity drivers are not protective by a factor of 5.3 to 40. To provide adequate environmental quality objectives, the authorisa- tion process needs to include monitoring-derived information on pesticide effects at the ecosystem level. Here, we derive such thresholds that ensure a protection of the invertebrate stream community.
... * Noé Ferreira-Rodríguez noeferreira@uvigo.es 1 3 40 Page 2 of 12 especially at lower latitudes (e.g., the Balkans and the Iberian Peninsula; Jarić et al. 2019). Aquatic systems are subject to multiple, cumulative, longterm pressures, including pollution, habitat alteration and destruction, and invasive species introduction (Birk et al. 2020;Carvalho et al. 2019;Nõges et al. 2016;Thrush et al. 2020). The European Water Framework Directive (WFD; European Commission 2000) mandates the characterization of water body types to set the biological reference conditions based on normative indicator parameters (e.g. ...
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Ecological status classification systems based on biological elements (e.g., macroinvertebrate communities) are dependent on their response to different pressures. However, there is a need to determine if invasive species should be incorporated to indicator parameters (i.e. metrics based on measurements of richness and diversity) or as a pressure affecting such parameters. Moreover, because ecosystem classification systems are lacking for northwestern Iberian estuaries, there is even the possibility to develop a new metric penalizing presence or abundance of invasive species. To increase our understanding on this topic, we analyze the taxonomic and functional responses of benthic macroinvertebrates to Corbicula invasion along the environmental gradient of 12 northwestern Iberian estuaries. Macroinvertebrate assemblages were described and compared between invaded and uninvaded sections. Additionally, to assess differences in community structure, macroinvertebrate assemblages’ similarity was examined between two distinct estuarine sections (freshwater and oligohaline vs transitional water and mesohaline) and among water body types, including and excluding Corbicula from the analysis. The salinity gradient was the main driver explaining changes in macroinvertebrate assemblages and in functional group distribution. Freshwater and transitional water sections clearly differed in macroinvertebrate assemblages and functional groups composition. In addition, differences among river types in macroinvertebrate composition were found. Corbicula inclusion or exclusion from multivariate community analysis significantly affected the results in functional feeding group composition in the Cantabric-Atlantic siliceous river axis type. Nevertheless, considering Corbicula as a pressure at the regional scale did not provide different results in diversity indices calculation. Hence, we argue that because Corbicula eradication is virtually impossible, it should be included as an additional metric evidencing its presence as a negative indication, or be included within other indicator metrics used in the assessment of the ecological status, for instance in invertebrate abundance metrics were its dominance should be indicative of invasion impairment.
... Nowadays, running waters are impaired by multiple stressors acting simultaneously [1][2][3][4] or sequentially [5]. Climate change, increasing urbanization and intensive agro-pastoral activities, which have adverse effects on stream biota [6,7], are the most important stressors of small tropical streams. ...
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Tropical rivers are strongly influenced by stormwaters, pollutants and agro-pastoral activities. These systems are no longer able to maintain their native biota. Therefore, it seems important to understand how biological assemblages are driven by environmental gradients at different spatial scales. However, information on the relationships between the distribution of aquatic macroinvertebrates and environmental variables remains scarce in Cameroon. To improve our knowledge on the drivers of such distributions, a study was carried out at 11 contrasted sites from three catchments located in West Cameroon. This study aimed at understanding the spatio-temporal variations of 19 taxonomic metrics calculated for the benthic macroinvertebrate assemblages of these sites sampled during 13 months, concurrently with physico-chemical analyses of water quality. Two hundred and twelve taxa were caught. Diptera(rf-S), Shannon-Wiener diversity, 1–GOLD, total richness, Pielou evenness and Heteroptera(rf-S) revealed their high ability to respond to anthropogenic pressures or disturbances. Conductivity, water temperature, dissolved oxygen, nitrates, total hardness and alkalinity were identified as the main physico-chemical drivers of the taxonomic structure of benthic assemblages. These results will allow further exploration of the implementation of a tool for monitoring the ecological quality of West Cameroon rivers.
... Marine monitoring programmes are generally recognised as important because they help scientists and conservation managers to characterise and understand coastal dynamics and vulnerabilities (Bastos et al., 2016). Marine monitoring enables environmental stressors to be identified, and in some cases, reduced or removed (Nõges et al., 2016) and is said to be "urgently required" for the protection of global marine biodiversity and ecosystem functioning (Danovaro et al., 2016). Bali's coral reefs have experienced an increase in active management measures over the last few decades (for example AR deployment, ecotourism activities and MPA establishment). ...
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... In the middle section of the Danube River (the same section that was analyzed here), it was found that species diversity and the abundance of macrophyte assemblages increased in the downstream direction towards the dams (i.e., in the run of the river reservoirs), and were negatively correlated to the riparian zone width (Vukov et al., 2018). In the impoundments, discontinuity in flow imposed by anthropogenic alteration-damming, and loss of riparian shading, alleviate many of the constrains to the plant growth found in the free-running section (water velocity is lower, sedimentation is increased, transparency is higher), while the higher retention time leads to accumulation of nutrients and eutrophication that contribute to macrophyte biomass production (Smith et al., 2006;O'Hare et al., 2010;Nõges et al., 2016). It was concluded that macrophytic cover and species diversity in the main channel of the Danube River in its middle course indicates major anthropogenic impact-damming, and consequent eutrophication (Vukov et al., 2018). ...
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... As with most aquatic ecosystems, estuaries are simultaneously exposed to a range of different human pressures that can have cumulative effects at different levels of biological organisation (Nõges et al. 2016). When caused by discrete activities, these pressures can be managed locally (e.g. ...
Chapter
This chapter addresses the use of fish as indicators of environmental health. The main anthropogenic pressures impacting estuarine fishes are reviewed, as well as the main types of responses by fishes at different levels of biological organisation. Fishes have been widely used to assess estuarine health through different methodological approaches, namely comparisons with historical data or reference conditions, experimental approaches, environmental impact or risk assessment methods, as well as qualitative or quantitative indicators and models. A large number of multi‐metric indices based on fish have been proposed and are routinely used in environmental assessments, although to disentangle natural variability from anthropogenic pressures in a multi‐stress context of global change is still a major challenge.
... Adding one or more stressors increases complications to such governance processes, partly due to the difficulties of communicating complex science on multiple stressor interactions. The scientific community often struggles to "prove" or reach consensus on the cause-effect relationships and provide evidence of adverse effects 11 and then, summarize, translate and communicate these complex findings, with inherent uncertainties, to policy makers. Similarly, policy makers face challenges in transforming complex scientific findings into practical management measures and regulations. ...
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... Such interactions can be synergistic or antagonistic (Piggott et al., 2015; see Box 2 for a detailed description). In recent years, the study of multiple drivers has increased (Przeslawski et al., 2015;Nõges et al., 2016). Here we give an overview of recent research on the interaction of multiple drivers in intertidal rocky shore ecosystems with regard to climate change. ...
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Most intertidal rocky systems are exposed to severe tidal, diurnal, and seasonal changes in environmental parameters. In addition, they show extreme vulnerability to anthropogenic impacts. Research on multiple drivers is therefore crucial to understand the complexity of their potential interactions. Here, we first give an overview of the natural environment and impacts of climate change on rocky shore intertidal systems, and then focus on the impacts of multiple drivers. We further provide a summary of existing multiple driver studies in the literature with the aim for a better understanding of multiple driver interactions. As multiple drivers can affect rocky shore intertidal systems at different spatial and temporal scales, and the outcome of their effects are still more of an “ecological surprise,” we recommend a more widespread assessment of the environmental and biological context. We propose a new, integrated approach based on existing literature: this complements previous frameworks but with an improved understanding of co-occurring multiple driver systems of the rocky intertidal, in order to find management solutions based on accurate and informed predictions in these times of global change.
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The European Union adopted the Water Framework Directive (WFD) in the year 2000 to tackle the rapid degradation of freshwater systems. However, biological, hydromorphological, and physico-chemical water quality targets are currently not met, and identifying successful policy implementation and management actions is of key importance. We built a joint species distribution model for riverine fish in Flanders (Belgium) to better understand the response of fish communities to current environmental policy goals. Environmental covariates included physico-chemical variables and hydromorphological quality indices, while waterway distances accounted for spatial effects. We detected strong effects of physico-chemistry on fish species’ distributions. Evaluation of fish community responses to simulated policy scenarios revealed that targeting a ‘good’ status, following the WFD, increases average species richness with a fraction of species (0.13–0.69 change in accumulated occurrence probabilities). Targeting a ‘very good’ status, however, predicted an increase of 0.17–1.38 in average species richness. These simulations indicated that riverbed quality, nitrogen, and conductivity levels should be the focal point of policy. However, the weak response of species to a ‘good’ quality together with the complexity of nutrient-associated problems, suggest a challenging future for river restoration in Flanders.
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Within South Africa, the St. Lucia Basin, comprising the White Mfolozi, Black Mfolozi, Mfolozi Hluhluwe-Mkuze sub-basins, is an ecologically important region. However, the river ecosystems and their inherent biota, especially the ichthyofauna, are inadequately studied. Considering the anthropogenic land-use change currently occurring and the concomitant elevated resource-use, we sought to ascertain the composition of the fish species communities within the basin and the environmental drivers influencing the spatial shifts in these communities to provide baseline information. We collected data from 20 sites in the basin from 2016 to 2018. A total of 4 420 individuals representing 24 fish species, from eight families, were recorded. Using generalised linear modelling, species count data were fitted to sub-catchment factor variables and habitat variables. We observed significant differences in the structure of the ichthyofauna communities between the sub-catchments as well as the environmental drivers to be substrate, mean depth, mean velocity, overhanging vegetation and woody debris. The Hluhluwe sub-catchment was the most diverse, while the White Mfolozi was the least diverse. Continued unsustainable use of the basin's water resources and poor land management practices are likely to shift the ichthyofauna communities into uniform, species-depauperate communities, potentially leading to a loss in ecosystem services and functioning.
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Functional diversity metrics have been suggested as important indicators of ecosystem functioning. We investigated the effects of land use mediated by local environmental variables on the fish assemblages’ functional structure in 18 headwater streams distributed in the Upper Paraná and Iguaçu ecoregions. The species were characterized according to habitat use, food resource use, life history, and hypoxia tolerance. We calculated functional diversity indices [richness (FRic), evenness (FEve), divergence (FDiv), dispersion (FDis), diversity (RaoQ)] and functional rarity indices [distinctiveness (Disti), uniqueness (Uni)], and evaluated the effects of regional and local variables on these indices using generalized linear models. The results highlighted the occurrence of the most functionally distinct and unique species in the forested streams. Moreover, we observed higher FRic in streams sampled in argisol, with a high ammonia load and low habitat diversity. Forested and agricultural covers positively affected FDis and RaoQ. Urban cover had a negative effect on FDis and RaoQ, mainly due to the increase in generalist functional groups in urban streams. Our findings emphasize the importance of forested cover in maintaining specialized species in fish assemblages of streams and preserving functional diversity and ecosystem functioning. Furthermore, these results contribute to direct conservation and recovery measures in freshwater environments.
Chapter
Hydromorphological stressors, i.e. hydrological and morphological alterations, affect freshwater biota in running and standing waters in a multitude of ways. These vary depending on size, morphology and other abiotic characteristics of rivers and lakes and also the respective organism groups of which macroinvertebrates, macrophytes and fish are discussed in this chapter. Hydromorphological stressors interact with other stressors, most importantly eutrophication and acidification. Interactions can be characterized as additive, synergistic or antagonistic. Invasive species can modify the effects of hydromorphological alterations. Hydromorphological restorations projects vary considerably in scale, location and effectiveness and more efforts are necessary to design and evaluate these.
Chapter
Human life and other biotic organisms inhabiting Earth are endangered due to the vagaries of climate change, overexploitation and unsustainable use of natural resources like freshwater ecosystems, forests, genetic resources, wildlife and land use, etc. While emphasizing on the vitality of natural ecosystems and the goods and services accruing from them for human and other biotic organisms, focus is also reinforced on the conservation and sustainable use of natural resources to ward off adverse impacts of climate change and sustain the continuity of life cycle on Earth.
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In aquatic ecosystems, excessive nutrient loading is a global problem that can induce regime shifts from macrophyte- to phytoplankton-dominated states with severe consequences for ecosystem functions. Most agricultural landscapes are sites of nutrient and pesticide loading, which can interact with other stressors (e.g., warming) in additive, antagonistic, synergistic or reversed forms. The effects of multiple stressors on the resilience of macrophyte-dominated states and on critical thresholds for regime shifts are, however, unknown. We test the effects of individual and combined stressors of warming, nitrate, and various pesticides typically found in agricultural run-off (ARO) on the growth of macrophytes, periphyton, and phytoplankton in microcosms. We applied a one-level replicated design to test whether ARO induces a regime shift and a multifactorial dose–response design to model stressor thresholds and disentangle stressor interactions along a gradient. The individual stressors did not induce a regime shift, but the full ARO did. Nitrate and pesticides acted synergistically, inducing a shift with increasing phytoplankton biomass and decreasing macrophyte biomass. Warming amplified this effect and lowered critical thresholds for regime shifts. Shallow aquatic ecosystems in agricultural landscapes affected by global warming thus increasingly risk shifting to a turbid, phytoplankton-dominated state, and negatively impacting ecosystem service provisioning. Multiple stressor interactions must be considered when defining safe operating spaces for aquatic systems.
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The reservoir of the El Kansra dam contributes to the drinking water supply of the cities of Khemisset and Tiflet and also to the irrigation of more than 30,000 ha of cultivable land, as well as an annual electricity supply of approximately 13 million Kwh. This study aims to better understand the mechanisms and the factors that cause the eutrophication of this lake. 41 water samples (41 campaigns) per month were collected in the ONEP intake, from March 2005 to September 2015, in order to determine the degree of stratification, the trophic state and some trace elements (Iron and Magnesium) of this lake. Principal Component Analysis (PCA) was performed to process information on some of the most important physical and chemical tracers in dam eutrophication. According to the Trophy State Index (TSI) and the Vollenweider classification, the lake of this dam is classified in the mesotrophic category. The stratification and mixing regime of the water mass presents a monomictic water body with a thermal stratification, generally extending between April and November. Physico-chemically, the water of the El Kansra dam contains a relatively high concentration of total phosphorus, with a much-reduced transparency by phase and a significant deficit in oxygen in the hypolimnion. As for nitrates (NO3-), they present relatively high levels during the winter-spring period in relation to the good oxygenation of the water, combined with the importance of liquid inputs. The PCA showed a state dominated by water rich in chlorophyll favored by a good oxygenation, leading to high water turbidity, and an opposite state, generally during the summer and autumn period, marked by a deficit of dissolved oxygen, but with a strong mineral load (Manganese, iron). Résumé. La retenue du barrage d'El Kansra contribue à l'approvisionnement en eau potable de deux villes (Khémisset et Tiflet) et à l'irrigation de plus de 30.000 ha de terres cultivables tout en apportant un appoint annuel d'électricité d'environ 13 millions de Kwh. Cette étude est effectuée sur le lac de ce barrage afin d'acquérir une meilleure connaissance des mécanismes qui entrent en jeu et les facteurs qui conditionnent l'eutrophisation de ce lac. Un échantillonnage mensuel de 41 prélèvements (41 campagnes) d'eau du lac a été effectué entre le mois de mars 2005 et le mois de septembre 2015 au niveau de la prise de l'ONEP pour déterminer le degré de stratification, l'état trophique, et quelques éléments traces (Fer et Magnésium). L'analyse en composantes principales (ACP) a été effectuée pour traiter les informations relatives à certains traceurs physiques et chimiques les plus importants dans l'eutrophisation du barrage. Le statut trophique, selon Trophy State Index (TSI) et selon la classification de Vollenweider, ce lac est classée dans la catégorie Mésotrophe. Le régime de stratification et de mixage de la masse d'eau présente un plan d'eau monomictique avec une stratification thermique qui s'étend en général entre avril et novembre. Sur le plan physico-chimique, l'eau du barrage El Kansra a une concentration relativement importante en phosphore total, une transparence très réduite par phase et un déficit important en oxygène au niveau de l'hypolimnion. Quant aux nitrates (NO3-), ils présentent des teneurs relativement élevées en période hiverno-printanière en relation avec la bonne oxygénation de l'eau, conjuguée à l'importance des apports liquides. L'ACP a montré un état dominé par des eaux riches en chlorophylle du fait de la bonne oxygénation, entrainant une forte turbidité des eaux, et un état inverse, marqué par un déficit en oxygène dissous mais à forte charge minérale (Mn, fer) qui correspond généralement à la période estivale et automnale.
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The reservoir of the El Kansra dam contributes to the drinking water supply of the cities of Khemisset and Tiflet and also to the irrigation of more than 30,000 ha of cultivable land, as well as an annual electricity supply of approximately 13 million Kwh. This study aims to better understand the mechanisms and the factors that cause the eutrophication of this lake. 41 water samples (41 campaigns) per month were collected in the ONEP intake, from March 2005 to September 2015, in order to determine the degree of stratification, the trophic state and some trace elements (Iron and Magnesium) of this lake. Principal Component Analysis (PCA) was performed to process information on some of the most important physical and chemical tracers in dam eutrophication. According to the Trophy State Index (TSI) and the Vollenweider classification, the lake of this dam is classified in the mesotrophic category. The stratification and mixing regime of the water mass presents a monomictic water body with a thermal stratification, generally extending between April and November. Physico-chemically, the water of the El Kansra dam contains a relatively high concentration of total phosphorus, with a much-reduced transparency by phase and a significant deficit in oxygen in the hypolimnion. As for nitrates (NO3-), they present relatively high levels during the winter-spring period in relation to the good oxygenation of the water, combined with the importance of liquid inputs. The PCA showed a state dominated by water rich in chlorophyll favored by a good oxygenation, leading to high water turbidity, and an opposite state, generally during the summer and autumn period, marked by a deficit of dissolved oxygen, but with a strong mineral load (Manganese, iron). Résumé. La retenue du barrage d'El Kansra contribue à l'approvisionnement en eau potable de deux villes (Khémisset et Tiflet) et à l'irrigation de plus de 30.000 ha de terres cultivables tout en apportant un appoint annuel d'électricité d'environ 13 millions de Kwh. Cette étude est effectuée sur le lac de ce barrage afin d'acquérir une meilleure connaissance des mécanismes qui entrent en jeu et les facteurs qui conditionnent l'eutrophisation de ce lac. Un échantillonnage mensuel de 41 prélèvements (41 campagnes) d'eau du lac a été effectué entre le mois de mars 2005 et le mois de septembre 2015 au niveau de la prise de l'ONEP pour déterminer le degré de stratification, l'état trophique, et quelques éléments traces (Fer et Magnésium). L'analyse en composantes principales (ACP) a été effectuée pour traiter les informations relatives à certains traceurs physiques et chimiques les plus importants dans l'eutrophisation du barrage. Le statut trophique, selon Trophy State Index (TSI) et selon la classification de Vollenweider, ce lac est classée dans la catégorie Mésotrophe. Le régime de stratification et de mixage de la masse d'eau présente un plan d'eau monomictique avec une stratification thermique qui s'étend en général entre avril et novembre. Sur le plan physico-chimique, l'eau du barrage El Kansra a une concentration relativement importante en phosphore total, une transparence très réduite par phase et un déficit important en oxygène au niveau de l'hypolimnion. Quant aux nitrates (NO3-), ils présentent des teneurs relativement élevées en période hiverno-printanière en relation avec la bonne oxygénation de l'eau, conjuguée à l'importance des apports liquides. L'ACP a montré un état dominé par des eaux riches en chlorophylle du fait de la bonne oxygénation, entrainant une forte turbidité des eaux, et un état inverse, marqué par un déficit en oxygène dissous mais à forte charge minérale (Mn, fer) qui correspond généralement à la période estivale et automnale.
Thesis
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Dans le milieu naturel, les poissons sont exposés à une multitude de facteurs de stress biotiques et abiotiques, mais leurs interactions sont encore mal connues. La hausse des températures et la contamination par les éléments trace métalliques (ETMs) sont des sources importantes de stress pour les poissons. Les parasites ont également des effets sur la physiologie de leur hôte, mais sont rarement considérés en tant que facteurs de stress. Ces trois facteurs de stress agissent via des voies physiologiques communes (immunité, stress oxydant, métabolisme) et sont donc susceptibles d'interagir de manière complexe (e.g. antagonisme, synergisme). De plus, il existe souvent une grande variabilité des réponses entre échelles biologiques, des molécules aux populations. Notamment, l'historique d'exposition des populations de poisson dans leur milieu naturel pourrait conditionner leur capacité de réponse au stress. La prise en compte de ces deux niveaux de variabilité (i.e. interactions entre stress et entre échelles d'organisation) représente donc un verrou scientifique majeur pour mieux comprendre les effets des stress multiples sur les populations de poissons d'eau douce. Cette thèse vise donc à évaluer les effets combinés de facteurs de stress abiotique (i.e. température, ETMs) et biotique (i.e. challenge immunitaire provoqué par le parasitisme) sur les réponses des poissons d'eau douce via une approche multi-échelles. Afin de remplir ces objectifs, le Goujon (Gobio occitaniae) a été utilisé comme espèce modèle dans le cadre de trois approches méthodologiques : (i) une approche transversale de terrain visant à comparer l'état de santé de population de poissons le long des gradients de stress ; puis, (ii) des expérimentations en conditions contrôlées afin de distinguer les effets des différents facteurs de stress simples dans différentes populations sauvages ; enfin (iii) une expérience de translocation réciproque (i.e. encagement sur le terrain) entre sites contaminés et peu contaminés afin de tester l'adaptation locale des populations. Les résultats montrent que les stress simples ont des effets importants aux échelles biologiques fines et induisent la mise en place de stratégies métaboliques de compensation : les poissons investissent dans les défenses immunitaires et antioxydantes, avec une réduction des réserves énergétiques. De plus, les ajustements comportementaux (i.e. activité de nage, recherche de nourriture) sont particulièrement importants sous stress simples, et permettent d'ajuster l'acquisition d'énergie ce qui limite les effets sur la survie et la croissance. Au contraire, les stress multiples ont peu d'effets aux échelles moléculaires et cellulaires, mais provoquent des réponses complexes à l'échelle individuelle, ce qui se traduit par des effets antagonistes sur le comportement et des effets négatifs sur la survie et la croissance. Ces résultats suggèrent que sous stress multiples, les capacités de réponse des poissons pourraient être dépassées, menant ainsi à une stratégie de conservation, avec des effets délétères sur la fitness. Cependant, les réponses observées étaient fortement variables selon la population considérée. [...]
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Marine organisms are simultaneously exposed to anthropogenic stressors with likely interactive effects, including synergisms in which the combined effects of multiple stressors are greater than the sum of individual effects. Early life stages of marine organisms are potentially vulnerable to the stressors associated with global change, but identifying general patterns across studies, species and response variables is challenging. This review represents the first meta-analysis of multi-stressor studies to target early marine life stages (embryo to larvae), particularly between temperature, salinity and pH as these are the best studied. Knowledge gaps in research on multiple abiotic stressors and early life stages are also identified. The meta-analysis yielded several key results: 1) Synergistic interactions (65% of individual tests) are more common than additive (17%) or antagonistic (17%) interactions. 2) Larvae are generally more vulnerable than embryos to thermal and pH stress. 3) Survival is more likely than sub-lethal responses to be affected by thermal, salinity, and pH stress. 4) Interaction types vary among stressors, ontogenetic stages, and biological responses, but they are more consistent among phyla. 5) Ocean acidification is a greater stressor for calcifying than non-calcifying larvae. Although more ecologically realistic than single-factor studies, multifactorial studies may still oversimplify complex systems, and so meta-analyses of the data from them must be cautiously interpreted with regard to extrapolation to field conditions. Nonetheless our results identify taxa with early life stages that may be particularly vulnerable (e.g. molluscs, echinoderms) or robust (e.g. arthropods, cnidarians) to abiotic stress. We provide a list of recommendations for future multiple stressor studies, particularly those focussed on early marine life stages.This article is protected by copyright. All rights reserved.
Technical Report
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The second MAES report presents indicators that can be used at European and Member State's level to map and assess biodiversity, ecosystem condition and ecosystem services according to the Common International Classification of Ecosystem Services (CICES v4.3). This work is based on a review of data and indicators available at national and European level and is applying the MAES analytical framework adopted in 2013.
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Nonlinear ecological responses to anthropogenic forcing are common, and in some cases, the ecosystem responds by assuming a new stable state. This article is an overview and serves as the introduction to several articles in this BRIDGES cluster that are directed toward managers interested in dealing with nonlinear responses in freshwaters, particularly streams. A threshold or breakpoint occurs where the system responds rapidly to a relatively small change in a driver. The existence of a threshold can signal a change in system configuration to an alternative stable state, although such a change does not occur with all thresholds. In general, a mechanistic understanding of ecological dynamics is required to predict thresholds, where they will occur, and if they are associated with the occurrence of alternative stable states. Thresholds are difficult to predict, although a variety of univariate methods has been used to indicate thresholds in ecological data. When we applied several methods to one type of response variable, the resulting threshold values varied 3-fold, indicating that more research on detection methods is necessary. Numerous case studies suggest that the threshold concept is important in all ecosystems. Managers should be aware that human actions might result in undesirable rapid changes and potentially an unwanted alternative stable state, and that recovery from that state might require far more resources and time than avoiding entering the state in the first place would have required. Given the difficulties in predicting thresholds and alternative states, the precautionary approach to ecosystem management is probably the most prudent.
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