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Identification and interaction of multiple stressors in central European lowland rivers
Abstract
Interactions of multiple stressors in lotic systems have received growing interest and have been analysed in a growing number of studies using experiment and survey data. In this study, we present a protocol to identify, display and analyse stressors of rivers and their interactions (additive, synergistic or antagonistic). We used a dataset of 125 samples of central European lowland rivers comprising hydromorphological, physico-chemical and land use stressor and pressure variables as well as benthic macroinvertebrate traits as biological response variables. To identify and visualise multiple stressor combinations jointly operating in the data set, we applied social network analysis. The main co-occurring stressor combination was fine sediment accumulation (hydromorphological stress) and enhanced phosphorus concentration (nutrient stress). Agricultural (cropland) and urban land use were identified as the main large scale environmental pressures. Stressor interactions were analysed using generalised linear regression modelling (GLM) including pairwise interaction terms. Altogether, 14 macroinvertebrate response variables were tested on six stressor combinations and revealed predominantly additive effects (80% of all significant models with absolute standardised effect sizes > 0.1). Significant antagonistic and synergistic interactions occurred in almost 20% of the models. Fine sediment stress was more influential and frequent than nutrient stress. The methodology presented here is standardisable and thus could help inform practitioners in aquatic ecosystem monitoring about prominent combinations of multiple stressors and their interactions. Yet, further understanding of the mechanisms behind the biological responses is required to be able to derive appropriate guidance for management. This applies to rather complex stressors and pressures, such as land use, for which more detailed data (e.g. nutrient concentrations, fine sediment entry, pesticide pollution) is often missing.
... smaller than the sum of the effects) ways (Cote et al., 2016;Jackson et al., 2016;Piggott et al., 2015). While freshwater ecosystems often integrate environmental effects over several scales and are hence sensitive to multiple stressors, only in recent years have increased efforts been made to comprehensively and systematically quantify these (Jackson et al., 2016;Lemm and Feld, 2017;. How multiple environmental stressors interact in their effects on freshwater communities and how these can be optimally assessed for ecosystem management decisions are important fields of ongoing research . ...
... Elbrecht et al. (2016) found "triple" additive effects of nutrient enrichment, sediment addition and reduced flow velocity on several disturbance-sensitive stream macroinvertebrate taxa. Field survey data from European lowland rivers show that additive interactions of hydromorphological, physico-chemical and land use stressors on benthic macroinvertebrates prevailed with 80% of the studied interactions (Lemm and Feld, 2017). Antagonistic and synergistic interactions were, in accordance with , approximately equally common (Lemm and Feld, 2017). ...
... Field survey data from European lowland rivers show that additive interactions of hydromorphological, physico-chemical and land use stressors on benthic macroinvertebrates prevailed with 80% of the studied interactions (Lemm and Feld, 2017). Antagonistic and synergistic interactions were, in accordance with , approximately equally common (Lemm and Feld, 2017). Ortho-phosphate and fine sediment addition were the most commonly found interactions and most of these were synergistic in nature (Lemm and Feld, 2017). ...
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.
... Therefore, freshwater biota increasingly suffer from exposure to multiple abiotic and biotic stressors that threaten biodiversity (e.g., Vinebrook et al. 2004;Dewson et al. 2007;Gérard et al. 2008;Strayer 2010;Nunes et al. 2015;Botana 2016). Stressors can be punctual, recurrent or continuous; consequently, organisms usually undergo combined mixtures of interacting stressors, whose effects may be synergistic, but are often unknown or difficult to predict (Holmstrup et al. 2010;Lemm and Feld 2017). Because of the health hazard for biota induced by exposure to multiple stressors, there is a growing interest on this research topic (Fischer et al. 2013;Lemm and Feld 2017). ...
... Stressors can be punctual, recurrent or continuous; consequently, organisms usually undergo combined mixtures of interacting stressors, whose effects may be synergistic, but are often unknown or difficult to predict (Holmstrup et al. 2010;Lemm and Feld 2017). Because of the health hazard for biota induced by exposure to multiple stressors, there is a growing interest on this research topic (Fischer et al. 2013;Lemm and Feld 2017). Unfortunately, we still poorly understand to what extent interactive effects of multiple recurrent and concomitant stressors (and related stresses) influence the dynamics of community structure, potentially inducing resistance, resilience or decline of the populations depending on their sensitivity (Connell and Sousa 1983). ...
... Disentangle intricate effects of multiple interacting stressors, and related stresses, on freshwater biota over time in the field are challenging and of growing interest for scientists (Fischer et al. 2013;Lemm and Feld 2017). Our field survey contributes to study responses of gastropods to two frequent combined stressors recurrent in stagnant waters, i.e., toxic Gérard et al. 2008). ...
Freshwater biota increasingly undergo multiple stressors, but we poorly understand to what extent they influence the dynamics of community structure. Here, we study the impact of combined stressor exposure on gastropods at 9-year interval, through a monthly 1-year (2013) monitoring, also providing data on the occurrence of other macroinvertebrate taxa. Previous study in 2004 showed the occurrence of cyanobacterial proliferations, drought, trematode parasites and invasive non-native pulmonate Physa acuta. During the year 2013, we always detected cyanobacterial microcystins (MCs) in gastropods, from 59 to 4149 ng g⁻¹ fresh mass (vs. 0–246 ng g⁻¹ in 2004), suggesting a continuous and increased MC intoxication. Environmental intracellular MC concentrations were high (8–41 µg L⁻¹) from August to October 2013, whereas they were detected only in August 2004 (17 µg L⁻¹). In 2013, we recorded no trematodes among the 2490 sampled gastropods, and P. acuta represented 94% of gastropods (vs. 58% in 2004). After August 2013, nearly all gastropods disappeared as most other macroinvertebrates (except Chironomidae, Ephemeroptera and Trichoptera). The whole decline of gastropods and other macroinvertebrates, and the absence of trematodes strongly suggest adverse conditions in the study site. Despite acute stressful conditions suggested above, gastropod abundance was 13-fold higher in June 2013 (vs. 2004), reflecting successful recolonization and efficient breeding. Most gastropods exposed to drought and toxic bloom were young vulnerable stages. Thus, we supposed alternation of local gastropod extinctions versus recolonization that could induce, on a long term, a loss of diversity to the detriment of the most sensitive species.
... The use of species identification in the assessment of water quality was criticized and then refined considering biological and ecological traits [18][19][20][21][22][23], suggesting that nontaxonomic aggregation of taxa as similar as possible in their species traits could aid in the interpretation of information given by a taxonomic list of species. For example, biological traits were preferable to taxonomic species lists in analyzing the response of multiple stressors in central European lowland rivers [24]. ...
... For example, hemoglobin content, tube building ability, feeding habit, voltinism, and body size of Chironomid larvae suggested that hemoglobin-rich species, with tube building capacity and short generation time, may be dominant in disturbed sites, while the reverse should be expected in less disturbed sites. However, this approach gave some unexpected results, such as the presence of: 1-hemoglobin-rich species in less disturbed sites; 2-species with long generation time in disturbed sites [47], and/or 3-small body-sized species in less disturbed habitats [24]. These apparently conflicting results were explained by positing that oxygen deficit was not the only factor determining disturbed conditions. ...
Simple Summary
Benthic macroinvertebrates of inland waters, including running waters and lakes, are frequently used in biomonitoring. Sometimes, environmental data associated with species lists are not available; in this situation traits or functional adaptations of species to environment can be considered as a tool to translate the list of species into a useful index to evaluate the environmental quality a body of water.
Abstract
Chironomids are the species-richest family among macroinvertebrates and are often used as indicators of ecological conditions in inland waters. High taxonomic expertise is needed for identification and new species are still being described even in the well-known West Palearctic region. Our Microsoft Access relational database comprises data on Chironomid species collected in rivers and lakes in Italy and some other European countries over a period of about 50 years, often associated with physical-chemical data, but in some cases, only data on Chironomids are available with no associated environmental data. The aim of the present paper was to propose the calculation of ecological traits of Chironomid species as a tool to derive information on water quality, when only data on Chironomid species composition are present, while environmental data are lacking. Traits summarizing the species’ response to environmental variables were evaluated, with emphasis on natural and man-influenced factors: current velocity, water temperature, conductivity, dissolved oxygen, and nutrients. Traits calculations were carried out in the R environment using a subset of our data, including both environmental data and Chironomid abundances. The relations between sites, Chironomid, species and traits were evaluated using correspondence analysis and other multivariate methods. The response of species showed an interaction among different factors, with the possibility of ordering species along a single environmental gradient, extending from cold running waters to warm standing waters, with few exceptions.
... A stressor is a measurable variable that exceeds its normal variation range (e.g., high nutrient concentrations such as from sewage discharges (Matthaei et al., 2010) and which negatively affects stream ecosystems. The assessment of multiple stressors can be complex because effects may differ depending on the aquatic organism, ecological indicators, ecosystem type, spatial scale, ecoregion, and stressor type (Birk et al., 2020;Feld et al., 2016a;Gieswein et al., 2017;Lemm and Feld, 2017;Wiederkehr et al., 2020). Also, multiple individual stressors may be additive or interactive, resulting in synergistic or opposing outcomes that have a larger or smaller combined effect than the individual effects (Piggott et al., 2015). ...
... Four out of the five relevant interactions observed were attributed to aquatic invertebrate metrics indicating their suitability for detecting complex interactions in urbanised streams. The study of the interactions of multiple stressors in streams is a growing and current topic worldwide and understanding the most driving combinations of stressors will substantially improve the monitoring of lotic ecosystems (Lemm and Feld, 2017). Below, we provide insights about what kinds of interactions should be considered and which biological metrics may respond better when monitoring efforts should be optimized for tropical Andean streams under the urban stream syndrome. ...
However, knowledge about multiple-stressors effects on urbanised Andean streams is lacking. In southern Ecuador, we assessed how multiple stressors determine the structural (aquatic invertebrate metrics) and functional (organic matter breakdown and delta N of primary consumers) attributes of streams in a densely populated watershed without wastewater treatment and with contrasting land uses. We found that urbanised streams exhibited individual-stressor effects and that stressor interactions were rare. While structural and function attributes responded negatively to urbanisation, ecosystem functioning metrics were influenced most. Stream ecosystem functions were influenced by water-chemistry stressors, whereas aquatic invertebrate metrics were influenced by physical-habitat stressors. We suggest that managers of urbanised streams in the Andes immediately focus on the most important stressors by reducing inputs of inorganic N and P, re-establishing stream flow and substrate heterogeneity, and restoring riparian vegetation instead of attempting to elucidate intricate interactions among stressors. Our result also demonstrate that stream biomonitoring programs would benefit from a combination of structural and functional indicators to assess anthropogenic effects in a multiple-stressors scenario.
... The expectations must be set in the context of catchment condition and processes and should consider restoring both structural complexity and functional integrity [39] (Figure 1). Setting expectations or targets in a catchment context allows the interactions with other anthropogenic stressors to be considered [32,40,41]. Expectations should also consider projected future changes within the catchments of restored rivers including climate change and likely land use changes such as urban development. ...
... Post-restoration recovery time is influenced by a number of factors including the type of restoration activity (Figure 3), morphological response [108], sources of colonisers [80,109], spatial scale of restoration [110], and the presence of other pressures [40,41,111]. Understanding and anticipating these influences will help identify the appropriate temporal scale for monitoring [13]. ...
Nature-based solutions are widely advocated for freshwater ecosystem conservation and restoration. As increasing amounts of river restoration are undertaken, the need to understand the ecological response to different measures and where measures are best applied becomes more pressing. It is essential that appraisal methods follow a sound scientific approach. Here, experienced restoration appraisal experts review current best practice and academic knowledge to make recommendations and provide guidance that will enable practitioners to gather and analyse meaningful data, using scientific rigor to appraise restoration success. What should be monitored depends on the river type and the type and scale of intervention. By understanding how habitats are likely to change we can anticipate what species, life stages, and communities are likely to be affected. Monitoring should therefore be integrated and include both environmental/habitat and biota assessments. A robust scientific approach to monitoring and appraisal is resource intensive. We recommend that appraisal efforts be directed to where they will provide the greatest evidence, including ‘flagship’ restoration schemes for detailed long-term monitoring. Such an approach will provide the evidence needed to understand which restoration measures work where and ensure that they can be applied with confidence elsewhere.
... The method of assessing relationships can include water quality and pollution variables, such as electrical conductivity and herbicides (Berger et al. 2017). It can also include land use coverage variables, such as agriculture or urban coverage (Baumgartner and Robinson 2017), habitat variables (Fierro et al. 2019), or a combination of the above (Lemm and Feld 2017). Environmental gradients are useful to examine the spatial variability of natural ecosystems (Whittaker 1967) and environments that are anthropogenically altered (McDonnell and Pickett 1990). ...
... This is important because it suggests that relationships among environmental variables can often co-occur, confounding analyses of their influences on aquatic communities. For instance, a study in German lowland rivers found that fine sediment cover and high phosphorus concentrations often co-occur (Lemm and Feld 2017). These cooccurring relationships could cause difficulties when trying to narrow focus on a single environmental variable that is impacting aquatic communities. ...
Background
Urban areas are often built along large rivers and surrounded by agricultural land. This may lead to small tributary streams that have agricultural headwaters and urbanized lower reaches. Our study objectives assessed are as follows: (1) landscape, geomorphic, and water quality variables that best explained variation in aquatic communities and their integrity in a stream system following this agricultural-to-urban land use gradient; (2) ways this land use gradient caused aquatic communities to differ from what would be expected for an idealized natural stream or other longitudinal gradients; and (3) whether the impacts of this land use gradient on aquatic communities would grow larger in a downstream direction through the agricultural and urban developments. Our study area was an impaired coldwater stream in Michigan, USA.
Results
Many factors structured the biological communities along the agricultural-to-urban land use gradient. Instream woody debris had the strongest relationship with EPT (Ephemeroptera, Plecoptera, and Trichoptera) abundance and richness and were most common in the lower, urbanized watershed. Fine streambed substrate had the strongest relationship with Diptera taxa and surface air breather macroinvertebrates and was dominant in agricultural headwaters. Fish community assemblage was influenced largely by stream flow and temperature regimes, while poor fish community integrity in lower urban reaches could be impacted by geomorphology and episodic urban pollution events. Scraping macroinvertebrates were most abundant in deforested, first-order agricultural headwaters, while EPT macroinvertebrate richness was the highest downstream of agricultural areas within the urban zone that had extensive forest buffers.
Conclusion
Environmental variables and aquatic communities would often not conform with what we would expect from an idealized natural stream. EPT richness improved downstream of agricultural areas. This shows promise for the recovery of aquatic systems using well-planned management in watersheds with this agricultural-to-urban land use pattern. Small patches of forest can be the key to conserving aquatic biodiversity in urbanized landscapes. These findings are valuable to an international audience of researchers and water resource managers who study stream systems following this common agricultural-to-urban land use gradient, the ecological communities of which may not conform with what is generally known about land use impacts to streams.
... Here, overall, higher effect activities were assessed for the non-restored sections. This difference in toxicity levels may be attributed to the variation in flow velocities and the stony-sandy bed substrate of the studied sites (Ahlf & Heise 2007;Pottgiesser 2018), whereas in Brettschneider et al. (2019), the increased toxicity was probably mainly due to the input of fine sediments that alters the water quality of rivers as suspended particles (Lemm & Feld 2017). However, whether this higher toxicity is related to the input of fine sediment at the restored river sections or whether there are other causes for these findings remains to be determined. ...
Aquatic ecosystems are affected by multiple stressors, including hydrological and morphological degradation, high nutrient loading, and chemical pollution. To improve freshwater habitats, hydromorphological restorations have been increasingly implemented. However, follow‐up assessments often show little to no improvement in ecological status, even years after restoration measures have been implemented. The success of restoration projects can be compromised by other stressors, such as insufficient water and sediment quality, which often receive less attention compared to nonchemical stressors. In this study, the impact of chemical stress on the outcome of five river restorations was evaluated ecologically, chemically, and ecotoxicologically. Overall, the habitat structure was considerably improved through the restoration measures, whereas the species communities did not show a consistent trend toward an improved ecological status. Effect‐based methods were used for an integrative assessment of the exposure to chemical mixtures in water and sediment samples of restored stream sections. Differences in toxicity between restored and non‐restored sections were found but did not show a consistent trend among the applied assays. In contrast, the chemical analysis showed that the sections of the same stream were similar in their chemical composition, and differences within a stream were primarily due to sediment contamination. The results of this study suggest that chemical pollution is a relevant factor preventing the success of restoration measures and, ultimately, the improvement of the ecological status of rivers. They also demonstrate the applicability of EBMs in water quality monitoring to detect mixture toxicity in streams and link chemical and ecological assessment.
... The identification and implementation of measures on such sites are also of enormous importance for the achievement of good ecological status of water bodies, as washed-off fine particles, as well as nutrients and pollutants associated with them, are seen as driving factors in most multi-stressed river ecosystems in Central Europe [21,22]. All biological quality elements mentioned in the Water Framework Guidelines are affected by human increased fine sediment loads. ...
Socio-economic changes, technical progress, and a variety of funding and planning interventions have significantly changed land use in Central Europe since World War II. The aim of this study was to illustrate these changes in the Alpine foothills in Bavaria and to calculate the effects of these changes on soil erosion. This was performed in a two-step procedure: a GIS-based orthophoto evaluation and a cause–effect model using the revised universal soil loss equation (RUSLE). Key findings were that field sizes (+370%) and lengths (+35%) have changed significantly since the 1960s. Moreover, the uninterrupted runoff paths on arable land have increased in length by about 70% on average, with corresponding effects on soil erosion. The discussion shows that the possibilities for erosion control measures in the field are already severely limited due to the effects of the climate crisis and structural changes in agriculture. Furthermore, the often-assumed rule, according to which only a small part of the arable land causes a large share of the eroded material, was largely confirmed. The findings underline the overlapping impacts of land use change and climate crisis on agriculture erosions rates with the need for integrative and adaptive management.
... Freshwater ecosystems are particularly sensitive to the effects of urbanisation, industrialisation or agriculture because they receive and transport water and materials from the entire catchment area. The major anthropogenic pressure that impacts freshwater ecosystems globally is pollution, which includes an elevated nutrient concentration in the water, organic substances that are constantly released into the environment, hydrological changes and hydromorphological alterations [1][2][3][4]. ...
The objectives of our survey were to determine the most important environmental factors within buffer zones that influenced mollusc communities and to evaluate the ecological conservation value of natural aquatic habitats (NAHs) that support mollusc species. Analysis of the spatial structure of buffer zones and catchments was based on a set of landscape metrics. Land cover classes were determined, and buffer zones within a radius of 500 m from a sampling point were marked out. Mollusc samples were collected from each NAHs. Our results showed that the number of patches and mean patch size were most associated with the distribution of mollusc species. Within patches of buffer zones, the length of the catchment boundaries with low-density housing, an increasing area of forest and pH of the water were also significant. Our results proved that landscape metrics provide essential information about catchment anthropogenic transformation. Therefore, landscape metrics and the designated buffer zones should be included in restoration plans for the river, water bodies and adjacent habitats as elements of modern, sustainable water management. NAHs located along a valley of a lowland river provide refuges for molluscs, play an essential role in the dispersal of IAS, create important protective biogeochemical barriers for rivers, constitute necessary sources of moisture and water and support microhabitats for distinct mollusc communities, especially in the context of global warming.
... Although our knowledge of the combined impacts is limited, stressors can interact in different ways (Schäfer and Piggott, 2018): by exerting a combined pressure on ecosystems (Holmstrup et al., 2010;Stampfli et al., 2013;Link et al., 2017), by influencing the sensitivity of organisms towards other stressors (Holmstrup et al., 2010), and by differentially affecting age stages, populations or species within an ecosystem, triggering disruptions in the population dynamics Van den Brink et al., 2019). Pesticides frequently co-occur (Matthaei et al., 2010;Moschet et al., 2014;Lemm and Feld, 2017;Szöcs et al., 2017) and interact with other stressors (Holmstrup et al., 2010), (Lange et al., 2011;Magbanua et al., 2013;Piggott et al., 2015;Elbrecht et al., 2016;Jackson et al., 2016;Liess et al., 2016;Magbanua et al., 2016;Chará-Serna and Richardson, 2018;Davis et al., 2018;European Environment Agency, 2018;Bray et al., 2019;Chará-Serna et al., 2019;Juvigny-Khenafou et al., 2020), often in a synergistic way (Holmstrup et al., 2010;Jackson et al., 2016;Liess et al., 2016). Maps of pesticide concentrations as discussed here may support the assessment of combinations of stressors on aquatic ecosystems, which so far have struggled to disentangle the effect of chemical pollutants (Vigiak et al., 2021). ...
Pesticides can be an important stressor to aquatic ecosystems, and their use is strictly regulated in the European Union (EU). However, data on the use of pesticides are rather limited and poorly available, and monitoring is often insufficient to characterize their actual exposure and impact. The aim of the work presented here is to harness the limited data available and assess, for the first time, the distribution of concentrations and toxicity of 148 pesticide active substances (AS) for the whole EU. Starting from available estimates of pesticide use in agriculture and a simple screening-level model of their fate and transport, we quantify pesticide concentrations in soil and water. A comparison with monitoring data shows that predicted water concentrations are in plausible orders of magnitude, hence the model can be regarded as a first-approximation representation of the distribution of pesticides in the environment. The toxicity of individual pesticide active substances (AS) is characterized by their concentrations divided by the respective no observed effect concentrations (NOEC) for aquatic organisms, which represents the “toxic units” (TU) of each AS. The cumulative toxicity of pesticides in soils and streams of the EU is obtained by summing the TU of individual AS. We estimate that the toxicity of individual AS is generally well below 0.1 TU, indicating relatively safe environmental exposure. However, the cumulative toxicity of a mixture of AS can exceed 0.1 toxic units (TU) for more than 27% of the length of the EU’s stream network, and 1 TU for more than 4%. The cumulative toxicity at a given location is driven by only a handful of AS, but these differ from site to site reflecting the variability of pesticide use. Still, we estimate that only about 20 AS out of 148 appear among the top contributors to cumulative toxicity in most cases. While our assessment suggests a relatively widespread risk due to pesticide pollution, it also points to the important limitations concerning knowledge of pesticide use and monitoring of pesticide occurrence in the environment. These limitations need to be addressed in order to evaluate more accurately the effectiveness of EU pesticide policies. The assessment represents a proof-of-concept of a method that can be applied in support of the monitoring of pesticide policies implementation in the EU and elsewhere, once pesticide use can be estimated.
... Because of the very high number of micropollutants, however, a comprehensive monitoring of these substances and their complex mixtures remains laborious and very resource-intensive, which may explain, why this stressor group remained underaddressed-or even unaddressed-in previous multiplestressor studies (e.g. Lemm [11][12][13], but see Lemm et al. 2021, Liess et al. 2021 for multiple-stressor studies including micropollutants). So far, there is still little knowledge about effects of micropollutants in a multiple-stressor context, but evidence from previous studies suggests that ecotoxicological effects of these substances pose a significant risk to riverine biota [15][16][17][18][19]. ...
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.
... The use of species identification in the assessment of water quality was criticized and refined considering biological and ecological traits [15,16,17,18,19,20], suggesting that non-taxonomic aggregation of taxa as similar as possible in their species traits could aid in interpretation of information given by taxonomic list of species. For example, biological traits were preferred to taxonomic species lists in analysing the response of multiple stressors in central European lowland rivers [21] The problem is that the possibility to translate a list of species into biological and ecological traits needs basic research to prepare this translation. ...
Chironomids are the species richest family among macroinvertebrates and are often used as indicators of ecological condition in inland waters. High taxonomic expertise is needed for identification and new species are still described even in the well-known West Palaearctic region. Data were filed in a Microsoft Access relational database and analysed using the R environment. Our database comprises data on Chironomid species collected in rivers and lakes in Italy and some other European countries over a period of about 50 years, often associated with physical-chemical data, but in some cases only benthic macroinvertebrates are available with no associated environmental data. In this case, the possibility of estimating water quality with only species composition available is discussed. Traits summarizing the species response to environmental variables were evaluated, with emphasis on natural and man influenced factors: current velocity, water temperature, conductivity, dissolved oxygen, nutrients. Traits calculations was possible using the subset of database including both environmental data and Chironomid abundances. The relations between sites, species and traits were evaluated using correspondence analysis and other multivariate methods. The response of species showed an interaction among different factors, with the possibility to order species along a single environmental gradient, extending from cold running waters to warm standing waters, with few exceptions. The utility and limits of the use of ecological traits are discussed.
... In a study of 230 British agricultural streams, Naden et al. (2016) determined that bed sedimentation was driven by stream power and agricultural intensity, meaning that both must be considered in rehabilitation projects. Through use of network analysis, cropland and urbanization were associated with increased fine sediments in stream bottoms and decreased shading of 125 lowland European rivers sites (Lemm and Feld, 2017). Using path modeling for 1200 French sites, the variability in streambed substrate among sites that was explained by land use ranged from 21 to 35% for small-sized non-limestone sites and medium-sized limestone sites, respectively (Villeneuve et al., 2018). ...
Rigorous assessments of the ecological condition of water resources and the effect of human activities on those waters require quantitative physical, chemical, and biological data. The U.S. Environmental Protection Agency’s river and stream surveys quantify river and stream bed particle size and stability, instream habitat complexity and cover, riparian vegetation cover and structure, and anthropogenic disturbance activities. Physical habitat is strongly controlled by natural geoclimatic factors that co-vary with human activities. We expressed the anthropogenic alteration of physical habitat as O/E ratios of observed habitat metric values divided by values expected under least-disturbed reference conditions, where site-specific expected values vary given their geoclimatic and geomorphic context. We set criteria for good, fair, and poor condition based on the distribution of O/E values in regional least-disturbed reference sites. Poor conditions existed in 22–24% of the 1.2 million km of streams and rivers in the conterminous U.S. for riparian human disturbance, streambed sediment and riparian vegetation cover, versus 14% for instream habitat complexity. Based on the same four indicators, the percentage of stream length in poor condition within 9 separate U.S. ecoregions ranged from 4% to 42%. Associations of our physical habitat indices with anthropogenic pressures demonstrate the scope of anthropogenic habitat alteration; habitat condition was negatively related to the level of anthropogenic disturbance nationally and in nearly all ecoregions. Relative risk estimates showed that streams and rivers with poor sediment, riparian cover complexity, or instream habitat cover conditions were 1.4 to 2.6 times as likely to also have fish or macroinvertebrate assemblages in poor condition. Our physical habitat condition indicators help explain deviations in biological conditions from those observed among least-disturbed sites and inform management actions for rehabilitating impaired waters and mitigating further ecological degradation.
... In a study of 230 British agricultural streams, Naden et al. (2016) determined that bed sedimentation was driven by stream power and agricultural intensity, meaning that both must be considered in rehabilitation projects. Through use of network analysis, cropland and urbanization were associated with increased fine sediments in stream bottoms and decreased shading of 125 lowland European rivers sites (Lemm and Feld, 2017). Using path modeling for 1200 French sites, the variability in streambed substrate among sites that was explained by land use ranged from 21 to 35% for small-sized non-limestone sites and medium-sized limestone sites, respectively (Villeneuve et al., 2018). ...
Anthropogenic alteration of physical habitat structure in streams and rivers is increasingly recognized as a major cause of impairment worldwide. As part of their assessment of the status and trends in the condition of rivers and streams in the U.S., the U.S. Environmental Protection Agency’s (USEPA) National Aquatic Resource Surveys (NARS) quantify and monitor channel size and slope, substrate size and stability, instream habitat complexity and cover, riparian vegetation cover and structure, anthropogenic disturbance activities, and channel-riparian interaction. Like biological assemblages and water chemistry, physical habitat is strongly controlled by natural geoclimatic factors that can obscure or amplify the influence of human activities. We developed a systematic approach to estimate the deviation of observed river and stream physical habitat from that expected in least-disturbed reference conditions. We applied this approach to calculate indices of anthropogenic alteration of three aspects of physical habitat condition in the conterminous U.S. (CONUS): streambed sediment size and stability, riparian vegetation cover, and instream habitat complexity. The precision and responsiveness of these indices led the USEPA to use them to evaluate physical habitat condition in CONUS rivers and streams. The scores of these indices systematically decreased with greater anthropogenic disturbance at river and stream sites in the CONUS and within ecoregions, which we interpret as a response of these physical habitat indices to anthropogenic influences. Although anthropogenic activities negatively influenced all three physical habitat indices in the least-disturbed sites within most ecoregions, natural geoclimatic and geomorphic factors were the dominant influences. For sites over the full range of anthropogenic disturbance, analyses of observed/expected sediment characteristics showed augmented flood flows and basin and riparian agriculture to be the leading predictors of streambed instability and excess fine sediments. Similarly, basin and riparian agriculture and non-agricultural riparian land uses were the leading predictors of reduced riparian vegetation cover complexity in the CONUS and within ecoregions. In turn, these reductions in riparian vegetation cover and complexity, combined with reduced summer low flows, were the leading predictors of instream habitat simplification. We conclude that quantitative measures of physical habitat structure are useful and important indicators of the impacts of human activities on stream and river condition.
... The upstream catchments for the sampling sites and the stream network were derived from the European digital elevation model with a cell size of 25 m × 25 m (EEA, 2016) using the free open-source software R, version 4.0.5, (R Core Team, 2021) and the R-package openSTARS (Kattwinkel and Szöcs, 2020). The fraction of land use types in each catchment was calculated by intersecting the derived catchments with the Corine Land Cover data (CLC, 2020;Lemm and Feld, 2017). The land use types were aggregated into three groups, 1) arable land (representing arable land and permanent crops), 2) pastures also including heterogeneous agricultural areas, and 3) forest. ...
Traditional forms of agriculture have created and preserved heterogeneous landscapes characterized by semi-natural meadows and pastures, which have high conversation value for biodiversity. Landscapes in Central and Eastern European countries with traditional agriculture are a stronghold for pollinators, butterflies and amphibians, which have declined in other parts of Europe. Despite different landscape structures, agriculture-associated pesticide exposure in streams can be similarly high as in Western Europe. This raises the question whether the heterogeneous landscape can buffer a temporary water quality decline by agriculture. We investigated the influence of landscape heterogeneity and water quality, in particular pesticide exposure, on macroinvertebrate communities in 19 small streams in Central Romania. We sampled the macroinvertebrate community, assessed the ecosystem function of leaf litter decomposition and analyzed the parasite prevalence in Baetis sp. and Gammarus balcanicus. No association between pesticide toxicity towards macroinvertebrates and several macroinvertebrate metrics was found. However, the level of pesticide toxicity was generally high, constituting a rather short gradient, and the pesticide indicator SPEARpesticides implied pesticide-driven community change in all sites. Landscape heterogeneity and forested upstream sections were among the most important drivers for the macroinvertebrate metrics, indicating increased dispersal and recolonization success. Agricultural land use in the catchment was negatively associated with vulnerable macroinvertebrate taxa such as Ephemeroptera, Plecoptera and Trichoptera. G. balcanicus dominated the shredder taxa and its abundance was positively associated with the pesticide indicator SPEARpesticides. Parasite prevalence in G. balcanicus increased with extensive land use (pastures and forests), whereas it decreased with arable land. Our results suggest that heterogeneous landscapes with structures of low-intensive land use may buffer the effects of agricultural land use and facilitate dispersal and recolonization processes of pesticide-affected macroinvertebrate communities.
... The upstream catchments for the sampling sites and the stream network were derived from the European digital elevation model with a cell size of 25 m × 25 m (EEA, 2016) using the free open-source software R, version 4.0.5, (R Core Team, 2021) and the R-package openSTARS (Kattwinkel and Szöcs, 2020). The fraction of land use types in each catchment was calculated by intersecting the derived catchments with the Corine Land Cover data (CLC, 2020;Lemm and Feld, 2017). The land use types were aggregated into three groups, 1) arable land (representing arable land and permanent crops), 2) pastures also including heterogeneous agricultural areas, and 3) forest. ...
... However, the history of the ecological success of restoration activities is inconsistent, with some researchers reporting success (e.g., [7]), whilst others report mixed results (e.g., [14,15]). Differences have been attributed to restoration activity not being undertaken at the same scale as the causes of degradation [15,16], varying timescales of ecological response [17], proximity to sources of colonists [18], limiting factors degrading riverine ecosystems not being addressed [16] and/or interactions with other anthropogenic stressors [19,20]. ...
River ecosystems have been heavily degraded globally due to channel hydromorphological modifications or alterations to catchment-wide processes. Restoration actions aimed at addressing these changes and restoring ecological integrity are increasing, but evidence of the effectiveness of these actions is variable. Using a rare 7-year before-after-control-impact (BACI) study of restoration of a lowland groundwater-fed river in England, UK, we explore changes in the macroinvertebrate community following the removal of impoundments and channel narrowing to aid restoration of physical processes. Restoration activity prompted significant taxonomic and functional responses of benthic invertebrate communities in the 4 years post-restoration. Specifically, significant gains in taxonomic and functional richness were evident following restoration, although corresponding evenness and diversity measures did not mirror these trends. Restoration activities prompted a shift to more rheophilic taxa and associated traits matching the physical changes to the channel and habitat composition. Temporal changes were clearer for taxonomic compositions compared to the functional properties of macroinvertebrate communities, indicating a functional redundancy effect of new colonists inhabiting restored reaches following restoration. The results highlight the value of long-term BACI studies in river restoration assessments, as well as project appraisals incorporating both taxonomic and functional observations. We highlight the urgent need of such studies to provide evidence to inform effective river restoration strategies to address future changes such as adaption to climate change and the biodiversity crisis.
... Short term salinity tolerance of zebra mussels is quite high (Ellis and MacIsaac 2008), and zebra mussel populations can persist in estuaries with salinities of 8-12 ppt (Karatayev et al. 1998). However, salinity is still likely to act as a stressor, particularly when interacting with other stressors (Lemm and Feld 2017). Zebra mussel growth rates are lower at low food concentrations, but extremely high concentrations also negatively affect growth rate, due to increased clogging of the gills (Lei et al. 1996), reduced food quality (Vanderploeg et al. 2009), and stoichiometric imbalances (Morehouse et al. 2013). ...
... More specifically, we expected nutrient enrichment to be particularly relevant for the ecological status of lowland rivers, whose catchments are often characterized by high agricultural intensities (Hypothesis 2.1; e.g. Lemm & Feld, 2017); hydrological alteration to be particularly relevant for river types with small and F I G U R E 1 Overview of the locations of 52,847 sub-catchment units and their ecological status class (grey area: no data available) medium size catchments or rivers in the Mediterranean, which are frequently affected by damming or water abstraction for irrigation (Hypothesis 2.2; Couto & Olden, 2018;Huđek et al., 2020;Panagopoulos et al., 2019); and toxic substances to mainly affect small streams in intensively used areas (Hypothesis 2.3;Beketov et al., 2013;Schäfer et al., 2013). We furthermore expected that riparian land use particularly impacts ecological status of small streams, which are more strongly affected by the immediate surrounding as compared to larger rivers, for which cumulative stressors at catchment scale are more relevant (Hypothesis 2.4;Fuller & Death, 2018). ...
The biota of European rivers are affected by a wide range of stressors impairing water quality and hydro‐morphology. Only about 40% of Europe’s rivers reach ‘good ecological status’, a target set by the European Water Framework Directive (WFD) and indicated by the biota. It is yet unknown how the different stressors in concert impact ecological status and how the relationship between stressors and status differs between river types. We linked the intensity of seven stressors to recently measured ecological status data for more than 50,000 sub‐catchment units (covering almost 80% of Europe’s surface area), which were distributed among twelve broad river types. Stressor data were either derived from remote sensing data (extent of urban and agricultural land use in the riparian zone) or modelled (alteration of mean annual flow and of base flow, total phosphorous load, total nitrogen load and mixture toxic pressure, a composite metric for toxic substances), while data on ecological status were taken from national statutory reporting of the second WFD River Basin Management Plans for the years 2010 to 2015. We used Boosted Regression Trees to link ecological status to stressor intensities. The stressors explained on average 61% of deviance in ecological status for the twelve individual river types, with all seven stressors contributing considerably to this explanation. On average 39.4% of the deviance was explained by altered hydro‐morphology (morphology: 23.2%; hydrology: 16.2%), 34.4% by nutrient enrichment and 26.2% by toxic substances. More than half of the total deviance was explained by stressor interaction, with nutrient enrichment and toxic substances interacting most frequently and strongly. Our results underline that the biota of all European river types are determined by co‐occurring and interacting multiple stressors, lending support to the conclusion that fundamental management strategies at the catchment‐scale are required to reach the ambitious objective of good ecological status of surface waters.
... We measured several physicochemical and habitat-specific variables during the period where the rainfall events occurred (June 2016). These variables included the buffer width and the ratio of stream substrate smaller than 2 mm which can be used as a proxy for sediment input caused by erosion ( Lemm and Feld, 2017 ). Additionally, we measured the average field size in a 200 m long section lateral to the sampling site, which was used as a proxy for the intensity of agricultural land use ( Pe'er et al., 2014 ), based on Google Earth images ( Google Earth, 2019 ) that were temporally closest to the field study. ...
Pesticide contamination of agricultural streams has widely been analysed in regions of high intensity agriculture such as in Western Europe or North America. The situation of streams subject to low intensity agriculture relying on human and animal labour, as in parts of Romania, remains unknown. To close this gap, we determined concentrations of 244 pesticides and metabolites at 19 low-order streams, covering sites from low to high intensity agriculture in a region of Romania. Pesticides were sampled with two passive sampling methods (styrene-divinylbenzene (SDB) disks and polydimethylsiloxane (PDMS) sheets) during three rainfall events and at base flow. Using the toxic unit approach, we assessed the toxicity towards algae and invertebrates. Up to 50 pesticides were detected simultaneously, resulting in sum con- centrations between 0.02 and 37 μg L -1 . Both, the sum concentration as well as the toxicities were in a similar range as in high intensity agricultural streams of Western Europe. Different proxies of agricultural intensity did not relate to in-stream pesticide toxicity, contradicting the assumption of previous studies. The toxicity towards invertebrates was positively related to large scale variables such as the catchment size and the agricultural land use in the upstream catchment and small scale variables including riparian plant height, whereas the toxicity to algae showed no relationship to any of the variables. Our results suggest that streams in low intensity agriculture, despite a minor reported use of agrochemicals, exhibit similar levels of pesticide pollution as in regions of high intensity agriculture.
... Therefore, these approaches can improve the ability to understand the structure and dynamics of ecological communities and potentially predict their sensitivity and recovery potential to natural or human disturbances (Keddy, 1992;Díaz and Cabido, 1997;Dray et al., 2014). In fact, biological traits have been widely used in the field of ecological risk assessment (ERA) and biomonitoring of aquatic ecosystems to reveal impacts of various types of human disturbance on invertebrate communities, including organic pollution, heavy metal pollution, cargo-ship traffic, eutrophication, land use and hydrological alterations (e.g., Dolédec and Statzner, 2008;Statzner and Beche, 2010;Culp et al., 2011;De Castro-Català et al., 2015;Rico and Van den Brink, 2015;Kuzmanović et al., 2017;Lemm and Feld, 2017), especially in the temperate zone where biological attributes of invertebrates are well documented (Tachet et al., 2010). For example, Kuzmanović et al. (2017) found that pesticides, high metal pollution, nutrients and flow alterations significantly affected trait composition of benthic macroinvertebrate assemblages in polluted Iberian rivers. ...
Benthic macroinvertebrate communities are used as indicators for anthropogenic stress in freshwater ecosystems. To better understand the relationship between anthropogenic stress and changes in macroinvertebrate community composition, it is important to understand how different stressors and species traits are associated, and how these associations influence variation in species occurrence and abundances. Here, we show the capacity of the multivariate technique of double constrained correspondence analysis (dc-CA) to analyse trait-environment relationships, and we compare it with the redundancy analysis method on community weighted mean values of traits (CWM-RDA), which is frequently used for this type of analysis. The analyses were based on available biomonitoring data for macroinvertebrate communities from the Danube River. Results from forward selection of traits and environmental variables using dc-CA analyses showed that aquatic stages, reproduction techniques, dispersal tactics, locomotion and substrate relations, altitude, longitudinal and transversal distribution, and substrate preferendum were significantly related to habitat characteristics, hydromorphological alterations and water quality measurements such as physico-chemical parameters, heavy metals, pesticides and pharmaceuticals. Environmental variables significantly associated with traits using the CWM-RDA method were generally consistent with those found in dc-CA analysis. However, the CWM-RDA does neither test nor explicitly select traits, while dc-CA tests and selects both traits and environmental variables. Moreover, the dc-CA analysis revealed that the set of environmental variables was much better in explaining the community data than the available trait set, a kind of information that can neither be obtained from CWM-RDA nor from RLQ (Environment, Link and Trait data), which is a close cousin of dc-CA but not regression-based. Our results suggest that trait-based analysis based on dc-CA may be useful to assess mechanistic links between multiple anthropogenic stressors and ecosystem health, but more data sets should be analysed in the same manner.
... This study stands out as it investigates quantitatively the links between pressures, looking more closely into the relationships between pressures and bioconcentrated contamination in gammarids. Numerous studies focused on multiple pressures and more specifically its effect on ecological communities and their responses (Dahm et al., 2013;Grizzetti et al., 2017;Lemm and Feld, 2017;Rico et al., 2016;Schmidt et al., 2019;Villeneuve et al., 2018). Comparing this paper's results to large-scale pressure-impact studies is not possible since different inputs (various multiple pressures) and outputs (bioconcentration versus ecological response) were considered. ...
Active biomonitoring permits the quantification of biological exposure to chemicals through measurements of bioavailable concentrations in biota and biological markers of toxicity in organisms. It enables respective comparison of the levels of contamination between sites and sampling campaigns. Caged gammarids are recently proposed as relevant probes for measuring bioavailable contamination in freshwater systems. The purpose of the present study was to develop a multi-pressure and multiscale approach, considering metallic contamination levels (from data based on active biomonitoring) as a response to pressures (combination of individual stressors). These pressures were anthropogenic land cover, industry density, wastewater treatment plant density, pressures on stream hydromorphological functioning, riverside vegetation and bioavailability factors. A dataset combining active biomonitoring and potentially related pressures was established at the French national scale, with 196 samplings from 2009 to 2016. The links between pressures and metallic contamination were defined and modelled via structural equation modeling (more specifically partial least squares – path modeling). The model enabled the understanding of the respective influences of pressures on metallic bioconcentration in caged sentinel organisms. Beyond validating the local influence of industries and wastewater treatment plants on metallic contamination, this model showed a complementary effect of driving forces of anthropogenic land cover (leading to human activities). It also quantified a significant influence of pressures on stream hydromorphological functioning, presence of vegetation and physico-chemical parameters on metal bioconcentration. This hierarchical multi-pressure approach could serve as a concept on how pressures and contamination (assessed by active biomonitoring) can be connected. Its future application will enable better understanding of environmental pressures leading to contamination in freshwater ecosystems.
... Nitrogen and phosphorous concentrations are of concern because they cause eutrophication that threatens the ecological status of the aquatic ecosystem (Lemm and Feld, 2017). Nutrients commonly generate an increase in algal biomass, which can result in increased diel swings in oxygen concentrations, thereby stressing some aquatic species (Correll, 1998). ...
Pollution from human activities is a major threat to the ecological integrity of fluvial ecosystems. Microbial communities are the most abundant organisms in biofilms, and are key indicators of various pollutants. We investigated the effects some human stressors (nutrients and heavy metals) have on the structure and activity of microbial communities in seven sampling sites located in the Ter River basin (NE Spain). Water and biofilm samples were collected in order to characterize physicochemical and biofilm parameters. The 16S rRNA gene was analysed out from DNA and RNA extracts to obtain α and β diversity. Principal coordinates analyses (PCoA) of the operational taxonomic units (OTUs) in the resident microbial community revealed that nutrients and conductivity were the main driving forces behind the diversity and composition. The effects of mining have had mainly seen on the taxonomic composition of the active microbial community, but also at the OTUs level. Remarkably, metal-impacted communities were very active, which would indicate a close link with the stress faced, that is probably related to the stimulation of detoxification.
... Nitrogen and phosphorous concentrations are of concern because they cause eutrophication that threatens the ecological status of the aquatic ecosystem (Lemm and Feld, 2017). Nutrients commonly generate an increase in algal biomass, which can result in increased diel swings in oxygen concentrations, thereby stressing some aquatic species (Correll, 1998). ...
Pollution from human activities is a major threat to the ecological integrity of fluvial ecosystems. Microbial communities are the most abundant organisms in biofilms, and are key indicators of various pollutants. We investigated the effects some human stressors (nutrients and heavy metals) have on the structure and activity of microbial communities in seven sampling sites located in the Ter River basin (NE Spain). Water and biofilm samples were collected in order to characterize physicochemical and biofilm parameters. The 16S rRNA gene was analysed out from DNA and RNA extracts to obtain α and β diversity. Principal coordinates analyses (PCoA) of the operational taxonomic units (OTUs) in the resident microbial community revealed that nutrients and conductivity were the main driving forces behind the diversity and composition. The effects of mining have had mainly seen on the taxonomic composition of the active microbial community, but also at the OTUs level. Remarkably, metal-impacted communities were very active, which would indicate a close link with the stress faced, that is probably related to the stimulation of detoxification.
... The cumulative stress scores may change when synergistic or antagonistic interactions between stressors are included in the calculation (Piggott et al., 2015;Schäfer and Piggott, 2018). A possible synergistic interaction is the combined effect of elevated nutrient concentrations and hydromorphological stress (Lemm and Feld, 2017), a possible antagonistic interaction is the combined lower stress levels for Daphnia exposed to a toxicant at low temperatures (Folt et al., 1999). ...
Macroinvertebrates in lowland streams are exposed to multiple stressors from the surrounding environment. Yet, quantifying how these multiple stressors impact macroinvertebrate assemblages is challenging. The aim of this study was to develop a novel method to quantify the cumulative stress acting on macroinvertebrate assemblages in lowland streams. To this purpose, we considered 22 stressors from different stressor categories such as hydrological, morphological and chemical stressors, acting over multiple spatial scales ranging from instream to the catchment scale. Stressor intensity was categorized into classes based on impact on the macroinvertebrate assemblages. The main stream was divided into segments, after which for each stream segment, the cumulative stressor contribution from headwater catchments, from the riparian zone and from upstream was calculated. To validate the cumulative stress quantification method, the lowland stream Tungelroyse Beek in the Netherlands was used as a case study. For this stream it was shown that independently derived ecological quality scores based on macroinvertebrate samples collected at multiple sites along the stream decreased with increasing calculated cumulative stress scores, supporting the design of the cumulative stress quantification method. Based on the contribution of each specific stressor to the cumulative stress scores, the reasons for the absence and presence of macroinvertebrate species may be elucidated. Hence, the cumulative stress quantification method may help to identify and localize the most stringent stressors limiting macroinvertebrate assemblages, and can thereby provide a better focus for management resources.
... Most river catchments are affected to some degree by agricultural activities (Allan, 2004), which leads to impacts from nutrient enrichment, principally nitrogen (N) and phosphorus (P), and increased fine sediment deposition (Allan, 2004;Matthaei et al., 2010). The effects of stressors acting on freshwater ecosystems has received much attention in recent years (Beermann et al., 2018;Graeber et al., 2017;Lemm and Feld, 2017;Ormerod et al., 2010). The emerging consensus is that there are a multitude of influential stressors, which often interact in complex and unexpected ways (Jackson et al., 2016;Nõges et al., 2016). ...
Freshwaters worldwide are affected by multiple stressors. Timing of inputs and pathways of delivery can influence the impact stressors have on freshwater communities. In particular, effects of point versus diffuse nutrient inputs on stream macroinvertebrates are poorly understood. Point-source inputs tend to pose a chronic problem, whereas diffuse inputs tend to be acute with short concentration spikes. We manipulated three key agricultural stressors, phosphorus (ambient, chronic, acute), nitrogen (ambient, chronic, acute) and fine sediment (ambient, high), in 112 stream mesocosms (26 days colonisation, 18 days of manipulations) and determined the individual and combined effects of these stressors on stream macroinvertebrate communities (benthos and drift). Chronic nutrient treatments continuously received high concentrations of P and/or N. Acute channels received the same continuous enrichment, but concentrations were doubled during two 3-hour periods (day 6, day 13) to simulate acute nutrient inputs during rainstorms. Sediment was the most pervasive stressor in the benthos, reducing total macroinvertebrate abundance and richness, EPT (mayflies, stoneflies, caddisflies) abundance and richness. By contrast, N or P enrichment did not affect any of the six studied community-level metrics. In the drift assemblage, enrichment effects became more prevalent the longer the experiment went on. Sediment was the dominant driver of drift responses at the beginning of the experiment. After the first acute nutrient pulse, sediment remained the most influential stressor but its effects started to fade. After the second pulse, N became the dom- inant stressor. In general, impacts of either N or P on the drift were due to chronic exposure, with acute nutrient pulses having no additional effects. Overall, our findings imply that cost-effective management should focus on mitigating sediment inputs first and tackle chronic nutrient inputs second. Freshwater managers should also take into account the length of exposure to high nutrient concentrations, rather than merely the concentrations themselves.
... The availability of differently structured habitats ("habitat mosaics", Pander et al., 2018), both inside and outside the main channel is of key importance for riverine fishes (e.g., Pander et al., 2018;Pander and Geist, 2018). Multiple mitigation measures addressing hydromorphology, navigation traffic and additional habitat availability would result in multiple benefits for also other aquatic organisms (e.g., macroinvertebrates; Brabender et al., 2016;Lemm and Feld, 2017;Shell and Collier, 2018;Stoll et al., 2016) and such living at the aquatic-terrestrial borderline (e.g., apex predators; , aquatic vegetation (e.g., Seer et al., 2018) as well as stipulate positive feedbacks amongst organisms and ecosystems (e.g., Lusardi et al., 2018). ...
English Abstract here, German below / Deutsche Zusammenfassung weiter unten
European large rivers have been tremendously modified over centuries and transformed into waterways for inland navigation. Extensive river modifications such as river regulation, channel straightening and flood protection have resulted in multiple pressures. However, inland navigation has not been considered as a potential pressure yet. This thesis aimed to assess the role of inland navigation among the most prevailing pressures in large rivers under field conditions. A worldwide unique and complementary dataset, the Large River Fish Database (LRDB) was compiled. The LRDB consists of 2693 fish samples assessed at 358 sampling sites in 16 European large rivers. Sites were characterized by various pressure variables and frequencies of ship traffic. To derive representative samples of large rivers fish assemblages, performance of various fishing gears applied was assessed. Electrofishing samples represented highest densities of fish and highest overall biodiversity. Therefore, electrofishing is suitable for fish-based assessments of large rivers and only electrofishing samples were selected to assess multiple pressures and inland navigation. Commercial cargo navigation appeared as the most influential pressures on large rivers fish assemblages among increased velocities and the loss of floodplains. Starting at already eight passing vessels per day, densities of particularly habitat-sensitive spawners significantly declined. Moreover, recreational navigation such as river cruises and motorized sport boats had distinct ecological consequences to those of cargo vessels. Inland navigation is as detrimental as the hydromorphological degradation of the river channel and requires specific attention in river management and rehabilitation. Pleasure boating (river cruises and sport boats) will counteract river rehabilitation also in smaller waterways and delimit ecological success of the Blue Band initiative in Germany.
German / Deutsch:
Europäische große Flüsse wurden über Jahrhunderte entscheidend verändert und zu Wasserstraßen für die Schifffahrt ausgebaut. Flussregulierung, Begradigung und Hochwasserschutz tragen zu multiplen Stressoren bei, wobei die Schifffahrt bislang keine Beachtung als potentieller zusätzlicher Einflussfaktor (Stressor) fand. Die zentrale Fragestellung dieser Arbeit befasste sich mit der Rolle der Schifffahrt zwischen multiplen Stressoren und deren Auswirkungen auf die Fischgemeinschaften großer Flüsse. Hierzu wurde die „Large River Fish Database“ (LRDB), ein weltweit einzigartiger Datensatz zusammengestellt, der 2693 Befischungen an 358 Probestellen in 16 europäischen großen Flüssen enthält. Die Probestellen sind durch verschiedene Einflussfaktoren (Stressoren) und Schiffsverkehr beschrieben. Um ein für große Flüsse repräsentatives Abbild der Fischgemeinschaften zu erhalten, wurden zunächst die angewendeten Fischfangmethoden analysiert. Mit der Elektrofischerei wurden die höchsten Fischdichten und die höchste Biodiversität erfasst. Die Elektrofischerei ist daher für eine repräsentative Erfassung der Fischgemeinschaften großer Flüsse geeignet und wurde für weitere Analysen ausgewählt. Die kommerzielle Frachtschifffahrt trat als einer der einflussreichsten Stressoren hervor, zusammen mit erhöhter Fließgeschwindigkeit und dem Verlust von Überschwemmungsflächen. Dichten von insbesondere Habitat-sensitiven Fischen sanken bereits ab acht Frachtschiffen pro Tag signifikant ab. Darüberhinaus hatte auch die Freizeitschifffahrt (Flusskreuzfahrten und motorisierte Sportboote) deutliche und zu Frachtschiffen unterscheidbare ökologische Konsequenzen. Die Wirkungen der Schifffahrt sind ebenso verheerend wie die der hydromorphologischen Degradierung und benötigen eine gesonderte Beachtung im Flussmanagement und der Flussrevitalisierung. Freizeitboote und Flussdampfer wirken der Flussrenaturierung kleinerer Wasserstraßen entgegen und gefährden den ökologischen Erfolg des Blauen Bandes.
... In scale experiments might dramatically stray from real situation. Mesocosms and field assays provide 250 information about real ecological effects ( Tarazona and Vega, 2002) ( Szöcs et al., 2015) (Hasenbein et 251 al., 2017) ( Lemm and Feld, 2017). A critical aspect may consist in the multi-faceted scenario of 252 responses, which can present non-monotonic trends and can be affected by hormesis and adaptation 253 phenomena (Calabrese and Blain, 2011). ...
... Velocity of climate change represents the speed at which animals must disperse to maintain populations at suitable habitat (Burrows et al., 2011;Hamann et al., 2015;Loarie et al., 2009 (Clapcott, Collier, & Death, 2012). Global-and watershedscale investigations especially illustrate the asymmetric distribution of indicators and pressures (Halpern et al., 2015;Kalogianni et al., 2017;Lemm & Feld, 2017). There are numerous analytical techniques to uncover the effects of multiple pressures (Feld et al., 2016;Ferguson, Carvalho, & Scott, 2008), yet few options exist to address the inherent correlations of these often broadly distributed data. ...
The expanding human global footprint and growing demand for freshwater have placed tremendous stress on inland aquatic ecosystems. Aichi Target 10 of the Convention on Biological Diversity aims to minimize anthropogenic pressures affecting vulnerable ecosystems, and pressure interactions are increasingly being incorporated into environmental management and climate change adaptation strategies. In this study, we explore how climate change, overfishing, forest disturbance, and invasive species pressures interact to affect inland lake walleye (Sander vitreus) populations. Walleye support subsistence, recreational, and commercial fisheries and are one of most sought‐after freshwater fish species in North America. Using data from 444 lakes situated across an area of 475 000 km² in Ontario, Canada, we apply a novel statistical tool, R‐INLA, to determine how walleye biomass deficit (carrying capacity—observed biomass) is impacted by multiple pressures. Individually, angling activity and the presence of invasive zebra mussels (Dreissena polymorpha) were positively related to biomass deficits. In combination, zebra mussel presence interacted negatively and antagonistically with angling activity and percentage decrease in watershed mature forest cover. Velocity of climate change in growing degree days above 5°C and decrease in mature forest cover interacted to negatively affect walleye populations. Our study demonstrates how multiple pressure evaluations can be conducted for hundreds of populations to identify influential pressures and vulnerable ecosystems. Understanding pressure interactions is necessary to guide management and climate change adaptation strategies, and achieve global biodiversity targets.
... In freshwater lake and river systems, excessive P has been clearly linked with eutrophication (Correll, 1998), including harmful algal blooms (Steffen et al., 2017). Phosphorus is a representative nutrient stressor for freshwater macroinvertebrate communities in European rivers (Lemm and Feld, 2017). Excessive P may also have cascading effects on stream food webs; for example, elevated P concentrations in agricultural streams were shown to affect diatom quality (Shore et al., 2017). ...
... Thus, laboratory scale experiments might dramatically stray from real situation. Mesocosms and field assays provide information about real ecological effects (Tarazona and Vega, 2002;Szöcs et al., 2015;Hasenbein et al., 2017;Lemm and Feld, 2017). A critical aspect may consist in the multi-faceted scenario of responses, which can present nonmonotonic trends and can be affected by hormesis and adaptation phenomena (Calabrese and Blain, 2011). ...
This opinion paper focuses on the role of eco-toxicological tools in the assessment of possible impacts of emerging contaminants on the aquatic ecosystem, hence, on human health. Indeed, organic trace pollutants present in raw and treated wastewater are the pivot targets: a multidisciplinary approach allows defining the basic principles for managing this issue, from setting a proper monitoring campaign up to evaluating the optimal process treatment. Giving hints on trace pollutants fate and behaviour, attention is focused on the choice of the bioassay(s), by analysing the meaning of possible biological answers. Data interpretation and exploitation are detailed with the final goal of providing criteria in order to be able to select the best targeted treatment options. The manuscript deals with conventional and innovative analytical approaches for assessing toxicity, by reviewing laboratory and field assays; illustrative real scale and laboratory applications integrate and exemplify the proposed approach.
Post-project appraisal is a key component of river restoration scheme. It allows the success and failure of a project to be evaluated and provides essential information for proper adaptive management. This chapter presents a set of indicators whose objective is to evaluate the hydromorphological effectiveness of the actions included in the River Manzanares Restoration Project, in the area surrounding the Real Sitio de El Pardo (Madrid). All the proposed indicators evaluate variables indicative of processes, are based on the hydromorphological and ecological characteristics, have a precise and relatively simple estimation method, and their results are easily interpretable. The results obtained show the usefulness of the indicators (i) to evaluate the hydromorphological effect of the restoration actions carried out, (ii) as an adaptive management tool that will allow us to propose improvements and generate guidelines for other similar projects.
Multiple stressors affect freshwater systems and cause a deficient ecological status according to the European Water Framework Directive (WFD). To select effective mitigation measures and improve the ecological status, knowledge on the stressor hierarchy and individual and joined effects is necessary. However, compared to common stressors like nutrient enrichment and morphological degradation, the relative importance of micropollutants such as pesticides and pharmaceuticals is largely unaddressed. We used WFD monitoring data from Saxony (Germany) to investigate the importance of 85 environmental variables (including 34 micropollutants) for 18 benthic invertebrate metrics at 108 sites. The environmental variables were assigned to five groups (natural factors, nutrient enrichment, metals, micropollutants and morphological degradation) and were ranked according to their relative importance as group and individually within and across groups using Principal Component Analyses (PCAs) and Boosted Regression Trees (BRTs). Overall, natural factors contributed the most to the total explained deviance of the models. This variable group represented not only typological differences between sampling sites but also a gradient of human impact by strongly anthropogenically influenced variables such as electric conductivity and dissolved oxygen. These large-scale effects can mask the individual importance of the other variable groups, which may act more specifically at a subset of sites. Accordingly, micropollutants were not represented by a few dominant variables but rather a diverse palette of different chemicals with similar contribution. As group, micropollutants contributed similarly as metals, nutrient enrichment and morphological degradation. However, the importance of micropollutants might be underestimated due to limitations of the current chemical monitoring practices.
We have implemented a specific data mining process to explore the relationship between biological indices and physico-chemical pressures in rivers. Data were collected in the framework of the French National monitoring network set up to assess the ecological status of rivers under the European Water Framework Directive (WFD). Chemical parameters and biological indices were collected regularly from 1.781 locations in metropolitan France from 2007 to 2013. The sequential pattern mining process generates closed partially ordered patterns representing a succession of physico-chemical events that precede a given biological index in a given status, validated using a subset of data. This paper focuses on the patterns and their occurrence. We showed that biological statuses depend on these temporal successions of alterations and not only on the last alterations. The physico-chemical statuses of water bodies usually appeared to be higher than their biological statuses, suggesting synergism between toxicants and/or an additive impact of other stressors related to hydromorphology or hydrology. Patterns found in the highest biological status for the biological indices based on macroinvertebrates, diatoms, macrophytes or fish, were characterised by the constancy of a high physico-chemical status over time. By contrast, before indices based on macroinvertebrates and macrophytes, two types of patterns were observed for bad biological status: (1) a chronic multi-pressure pattern, in which pressure categories such as nitrates, pesticides and other organic hydrocarbons, in moderate, poor or bad status, repeated themselves several times over time, or (2) a single occurrence of a degraded pressure category, such as one moderate nitrogen, excluding nitrate, or one poor oxidizable organic matter, among other pressure categories in good status. Extracting such patterns is a promising solution both to disentangle the effects of the different stressors on water quality, and to identify the key temporal sequences among them in a context of multi-stress conditions, which is a challenge currently facing the WFD.
Rivers suffer from more severe decreases in species diversity compared to other aquatic and terrestrial ecosystems due to a variety of pressures related to human activities. Species provide different roles in the functioning of the ecosystem, and their loss may reduce the capacity of the ecosystems to respond to multiple stressors. The effects on diversity will differ based on the type, combination and severity of stressors, as well as on the characteristics of the community composition and tolerance. Multiple trait-based approaches (MTBAs) can help to unravel the effects of multiple stressors on communities, providing a mechanistic interpretation, and, thus, complementing traditional biodiversity assessments using community structure. We studied the relationships between diversity indexes and trait composition of macroinvertebrate and diatom communities, as well as environmental variables that described the hydrological and geomorphological alterations and toxic pollution (pesticides and pharmaceuticals) of three different European river basins: the Adige, the Sava, and the Evrotas. These river basins can be considered representative cases of different situations in European freshwater systems. Hydrological variables were the main drivers determining the community structure and function in the rivers, for both diatoms and macroinvertebrates. For diatom communities, pharmaceutical active compound (PhAC) toxic units were also identified as a very important driver of diversity changes, explaining up to 57% of the variance in taxonomic richness. For macroinvertebrates, river geomorphology was an important driver of structural changes, particularly affecting Plecoptera richness. In addition, PhAC and pesticide toxic units were also identified as stressors for macroinvertebrate communities. MTBA provided a detailed picture of the effects of the stressors on the communities and confirmed the importance of hydrological variables in shaping the functional attributes of the communities.
High loads of fine sediments are considered one of the most important causes of river ecosystem degradation worldwide. Especially in intensively used catchment areas changes in the sediment regime must be regarded as a key factor that prevents the achievement of the objectives of the European Water Framework Directive. To work on these problems, two comprehensive studies were carried out in Upper Austria to get a wider understanding of the causes of siltation, its current status, and its effects. The results revealed that fine sediments considerably degrade about one-third of the examined river sites in the pre-alpine foothills in Upper Austria and, only about a fifth of the stretches exhibit a natural sediment composition. It turned out that (A) human land uses and their changes over the last decades, (B) increased entry paths, (C) climate change, (D) local hydraulic conditions, and (E) lateral connectivity are key issues for siltation. Durable and valuable river restoration measures are determined by the consideration of these drivers. Moreover, pursuing investigations emphasized the determining processes and related chemical alterations, with further implications for aquatic biota.
This deliverable gives an overview of the functionality of the Freshwater Information System (FIS) through a number of screenshots and a short explanatory text. FIS is one of the tools that are developed within the MARS project. It is the web-based information system providing access to information and practical tools generated in MARS. FIS contains informative factsheets for DPSIR, stressors, ecosystem services and MARS case studies on the impact of multiple stressors for ecological status as well as a model selection tool for river basin management. The design and functionality has been discussed internally with MARS partners (Deltares, UDE, IGB) and with end-users during workshops in Delft (September 2015) and Den Helder (October 2016). FIS will be integrated in the Freshwater Information Platform, which aims at bringing together the results of many projects dealing with freshwater ecosystems in one a single platform.
While the assessment of the ecological status of surface water bodies has become quite straightforward nowadays, almost two decades after the WFD has been launched, the inference of appropriate management options from the assessment is still challenging. More precisely, water body managers face the ecological status assessment of a given water body that usually integrates over several or numerous (multiple) stressors impacting the water body. The challenge is to identify the most-impacting stressor(s) and to distinguish them from the minor ones. Such stressor hierarchies are required to infer the appropriate hierarchy of management options to address the relevant stressors. This report presents tools to assist water body managers in the inference of management options to address the impact of multiple stressors on surface water bodies.
The first chapter presents a conceptual model to visualise the published evidence of the impacts of combined stressors (here: nutrient enrichment and fine sediment pollution) on river organisms. The structured evaluation of published evidence can help identify potential interactions of stressors, which then require consideration in water body management.
The second chapter presents an approach to diagnose the causes of deterioration of lowland rivers based on the causes' (stressors') effects on selected diagnostic metrics derived from the macrozoobenthos community. The approach uses a Bayesian (Belief) Network (BN) to statistically infer the probabilities of the causes to be causal for the detected effects at the water body.
In the third chapter, we present an interactive online tool that builds upon the BN as presented in Chapter 2. The tool provides a graphical interface that allows the user to easily enter evidence (i.e. the states of selected effect variables) to the BN. The results are graphically displayed and accompanied by helpful background information and web links to relevant sources of information.
Abstract This work addresses human stressors and their impacts on fish assemblages at pan-European scale by analysing single and multiple stressors and their interactions. Based on an extensive dataset with 3105 fish sampling sites, patterns of stressors, their combination and nature of interactions, i.e. synergistic, antagonistic and additive were investigated. Geographical distribution and patterns of seven human stressor variables, belonging to four stressor groups (hydrological-, morphological-, water quality- and connectivity stressors), were examined, considering both single and multiple stressor combinations. To quantify the stressors' ecological impact, a set of 22 fish metrics for various fish assemblage types (headwaters, medium gradient rivers, lowland rivers and Mediterranean streams) was analysed by comparing their observed and expected response to different stressors, both acting individually and in combination. Overall, investigated fish sampling sites are affected by 15 different stressor combinations, including 4 stressors acting individually and 11 combinations of two or more stressors; up to 4 stressor groups per fish sampling site occur. Stressor-response analysis shows divergent results among different stressor categories, even though a general trend of decreasing ecological integrity with increasing stressor quantity can be observed. Fish metrics based on density of species ‘intolerant to water quality degradation’ and ‘intolerant to oxygen depletion” responded best to single and multiple stressors and their interactions. Interactions of stressors were additive (40%), synergistic (30%) or antagonistic (30%), emphasizing the importance to consider interactions in multi-stressor analyses. While antagonistic effects are only observed in headwaters and medium-gradient rivers, synergistic effects increase from headwaters over medium gradient rivers and Mediterranean streams to large lowland rivers. The knowledge gained in this work provides a basis for advanced investigations in European river basins and helps prioritizing further restoration and management actions.
The world's population is concentrated in urban areas. This change in demography has brought landscape transformations that have a number of documented effects on stream ecosystems. The most consistent and pervasive effect is an increase in impervious surface cover within urban catchments, which alters the hydrology and geomorphology of streams. This results in predictable changes in stream habitat. In addition to imperviousness, runoff from urbanized surfaces as well as municipal and industrial discharges result in increased loading of nutrients, metals, pesticides, and other contaminants to streams. These changes result in consistent declines in the richness of algal, invertebrate, and fish communities in urban streams. Although understudied in urban streams, ecosystem processes are also affected by urbanization. Urban streams represent opportunities for ecologists interested in studying disturbance and contributing to more effective landscape management.
Interactions between multiple ecosystem stressors are expected to jeopardize biological processes, functions and biodiversity. The scientific community has declared stressor interactions—notably synergies—a key issue for conservation and management. Here, we review ecological literature over the past four decades to evaluate trends in the reporting of ecological interactions (synergies, antagonisms and additive effects) and highlight the implications and importance to conservation. Despite increasing popularity, and ever-finer terminologies, we find that synergies are (still) not the most prevalent type of interaction, and that conservation practitioners need to appreciate and manage for all interaction outcomes, including antagonistic and additive effects. However, it will not be possible to identify the effect of every interaction on every organism’s physiology and every ecosystem function because the number of stressors, and their potential interactions, are growing rapidly. Predicting the type of interactions may be possible in the near-future, using meta-analyses, conservation-oriented experiments and adaptive monitoring. Pending a general framework for predicting interactions, conservation management should enact interventions that are robust to uncertainty in interaction type and that continue to bolster biological resilience in a stressful world. © 2016 The Author(s) Published by the Royal Society. All rights reserved.
The use of trait-based approaches to detect effects of land use and climate change on terrestrial plant and aquatic phytoplankton communities is increasing, but such a framework is still needed for benthic stream algae. Here we present a conceptual framework of morphological, physiological, behavioural and life-history traits relating to resource acquisition and resistance to disturbance. We tested this approach by assessing the relationships between multiple anthropogenic stressors and algal traits at 43 stream sites. Our "natural experiment" was conducted along gradients of agricultural land-use intensity (0-95% of the catchment in high-producing pasture) and hydrological alteration (0-92% streamflow reduction resulting from water abstraction for irrigation) as well as related physicochemical variables (total nitrogen concentration and deposited fine sediment). Strategic choice of study sites meant that agricultural intensity and hydrological alteration were uncorrelated. We studied the relationships of seven traits (with 23 trait categories) to our environmental predictor variables using general linear models and an information-theoretic model-selection approach. Life form, nitrogen fixation and spore formation were key traits that showed the strongest relationships with environmental stressors. Overall, FI (farming intensity) exerted stronger effects on algal communities than hydrological alteration. The large-bodied, non-attached, filamentous algae that dominated under high farming intensities have limited dispersal abilities but may cope with unfavourable conditions through the formation of spores. Antagonistic interactions between FI and flow reduction were observed for some trait variables, whereas no interactions occurred for nitrogen concentration and fine sediment. Our conceptual framework was well supported by tests of ten specific hypotheses predicting effects of resource supply and disturbance on algal traits. Our study also shows that investigating a fairly comprehensive set of traits can help shed light on the drivers of algal community composition in situations where multiple stressors are operating. Further, to understand non-linear and non-additive effects of such drivers, communities need to be studied along multiple gradients of natural variation or anthropogenic stressors.
The potential for complex synergistic or antagonistic interactions between multiple stressors presents one of the largest uncertainties when predicting ecological change but, despite common use of the terms in the scientific literature, a consensus on their operational definition is still lacking. The identification of synergism or antagonism is generally straightforward when stressors operate in the same direction, but if individual stressor effects oppose each other, the definition of synergism is paradoxical because what is synergistic to one stressor's effect direction is antagonistic to the others. In their highly cited meta-analysis, Crain et al. (Ecology Letters, 11, 2008: 1304) assumed in situations with opposing individual effects that synergy only occurs when the cumulative effect is more negative than the additive sum of the opposing individual effects. We argue against this and propose a new systematic classification based on an additive effects model that combines the magnitude and response direction of the cumulative effect and the interaction effect. A new class of “mitigating synergism” is identified, where cumulative effects are reversed and enhanced. We applied our directional classification to the dataset compiled by Crain et al. (Ecology Letters, 11, 2008: 1304) to determine the prevalence of synergistic, antagonistic, and additive interactions. Compared to their original analysis, we report differences in the representation of interaction classes by interaction type and we document examples of mitigating synergism, highlighting the importance of incorporating individual stressor effect directions in the determination of synergisms and antagonisms. This is particularly pertinent given a general bias in ecology toward investigating and reporting adverse multiple stressor effects (double negative). We emphasize the need for reconsideration by the ecological community of the interpretation of synergism and antagonism in situations where individual stressor effects oppose each other or where cumulative effects are reversed and enhanced.
Water resources globally are affected by a complexmixture of stressors resulting from a range of drivers, including urban and agricultural land use, hydropower generation and climate change. Understanding how stressors interfere and impact upon ecological status and ecosystem services is essential for developing effective River Basin Management Plans and shaping future environmental policy. This paper details the nature of these problems for Europe'swater resources and the need to find solutions at a range of spatial scales. In terms of the latter, we describe the aims and approaches of the EU-funded project MARS (Managing Aquatic ecosystems and water Resources under multiple Stress) and the conceptual and analytical framework that it is adopting to provide this knowledge, understanding and tools needed to address multiple stressors. MARS is operating at three scales: At the water body scale, the mechanistic understanding of stressor interactions and their impact upon water resources,ecological status and ecosystem services will be examined through multi-factorial experiments and the analysis of long time-series. At the river basin scale, modelling and empirical approaches will be adoptedto characterise relationships between multiple stressors and ecological responses, functions, services and water resources. The effects of future land use and mitigation scenarios in 16 European river basinswill be assessed. At the European scale, large-scale spatial analysiswill be carried out to identify the relationships amongst stress intensity, ecological status and service provision, with a special focus on large transboundary rivers, lakes and fish. The project will support managers and policy makers in the practical implementation of theWater Framework Directive (WFD), of related legislation and of the Blueprint to Safeguard Europe's Water Resources by advising the 3rd River Basin Management Planning cycle, the revision of the WFD and by developing new tools for diagnosing and predicting multiple stressors.
Effective catchment management in the face of landuse alteration depends on our ability to quantify ecologically significant changes and to discriminate among varying levels of impact. We compared the efficiency of traditional structural indices of change (species composition) with functional measures based on species traits (including life-history, trophic, and morphological features) in an analysis of grassland streams along a gradient of agricultural development (ungrazed native tussock, grazed tussock, extensively grazed pasture, and intensive dairy and deer farming). Streams were categorized in relation to overall agricultural intensity, and separately in terms of increasing nutrient concentrations and fine sediments on the streambed. Only 5 of 60 individual species demonstrated a significant separation across the landuse gradient, whereas 14 of 53 trait categories did so. Traits associated with population resilience (short generation time, asexual reproduction) became more prevalent with more intense agricultural pressure, reflecting predicted increases in intensity and frequency of stream disturbance. We observed a shift away from a tendency to lay unattached eggs at the water surface of the stream, reflecting the increasing likelihood of smothering by sediment, as well as increases in highly flexible and streamlined body shapes. Principal components and correspondence analyses involving species or trait composition all were able to discriminate landuse practises, but more of the overall between-landuse variance was accounted for by trait composition than species composition. All biological measures (species or trait composition) were correlated with both nutrient concentrations and sedimentation. Nutrient concentrations were better related to species and trait-category densities, whereas sedimentation was related to trait-category relative abundances. Overall, species traits successfully complemented traditional structural measures by helping to differentiate the consequences of landuse intensification in grassland stream communities. Rather than simply recording a loss or reduction of species, our functional approach was able to identify sensitive life-history characteristics linked to the functioning of ecosystems, thereby facilitating the development of targeted management actions.
This study was designed to test for synergism (increased stress) or antagonism (decreased stress) among multiple environmental stressors using additive, multiplicative, and simple comparative effects models. Model predictions were compared to empirical results of laboratory experiments measuring interactions among thermal stress, toxin exposure, and low food on reproduction and survival of two species of cladoceran zooplankton. Stress was defined operationally as a reduction in reproduction or survival relative to optimal conditions over a 7-d period. These experiments are particularly applicable to episodic stresses such as those associated with short-term heat waves. Toxin or low food in combination with 30°C temperatures were generally more harmful than high temperature alone. However, most multiple stress effects were antagonistic, in that effects in combination were not as severe as predicted based on the sum or the product of their individual effects. In rare cases, interaction among stressors even diminished effects of the worst single stressor. Optimal conditions for reproduction and survival occurred at 25°C, high food and 0 mg liter-1 toxin (a surfactant, sodium dodecyl sulfate). Suppressive effects of stressors examined individually ranked: high temperature (30°C) > SDS (10 mg liter-1 ≥ low food (~100 μg C liter-1) > low temperature (20°C). Daphnia pulex isolated from a pond which experiences high summer temperatures throughout was more tolerant of 30°C conditions than Daphnia pulicaria isolated from a lake with a cold-water refuge. Differences were observed in individuals exposed as either adults or as 24-h neonates.
Changes to land use affect streams through nutrient enrichment, increased inputs of sediment and, where riparian vegetation has been removed, raised water temperature. We manipulated all three stressors in experimental streamside channels for 30 days and determined the individual and pair-wise combined effects on benthic invertebrate and algal communities and on leaf decay, a measure of ecosystem functioning. We added nutrients (phosphorus+nitrogen; high, intermediate, natural) and/or sediment (grain size 0.2 mm; high, intermediate, natural) to 18 channels supplied with water from a nearby stream. Temperature was increased by 1.4°C in half the channels, simulating the loss of upstream and adjacent riparian shade. Sediment affected 93% of all biological response variables (either as an individual effect or via an interaction with another stressor) generally in a negative manner, while nutrient enrichment affected 59% (mostly positive) and raised temperature 59% (mostly positive). More of the algal components of the community responded to stressors acting individually than did invertebrate components, whereas pair-wise stressor interactions were more common in the invertebrate community. Stressors interacted often and in a complex manner, with interactions between sediment and temperature most common. Thus, the negative impact of high sediment on taxon richness of both algae and invertebrates was stronger at raised temperature, further reducing biodiversity. In addition, the decay rate of leaf material (strength loss) accelerated with nutrient enrichment at ambient but not at raised temperature. A key implication of our findings for resource managers is that the removal of riparian shading from streams already subjected to high sediment inputs, or land-use changes that increase erosion or nutrient runoff in a landscape without riparian buffers, may have unexpected effects on stream health. We highlight the likely importance of intact or restored buffer strips, both in reducing sediment input and in maintaining cooler water temperatures.
1. The fundamental importance of freshwater resources, the rapid extinction rate among freshwater species and the pronounced sensitivity of freshwater ecosystems to climate change together signal a pre-eminent need for renewed scientific focus and greater resources. Against this background, the Freshwater Biological Association in 2008 launched a new series of ‘summit’ Conferences in Aquatic Biology intended to develop and showcase the application of ecological science to major issues in freshwater management.
2. This collection of studies arose from the first summit entitled ‘Multiple Stressors in Freshwater Ecosystems’. Although freshwater science and management are replete with mutiple-stressor problems, few studies have been designed explicitly to untangle their effects.
3. The individual case studies that follow reveal the wide array of freshwaters affected by multiple stressors, the spatial and temporal scales involved, the species and ecosystem processes affected, the complex interactions between ecology and socioeconomics that engender such effects, the approaches advocated to address the problems and the challenges of restoring affected systems. The studies also illustrate the extent to which new challenges are emerging (e.g. through climate change), but also they develop a vision of how freshwaters might be managed sustainably to offset multiple stressors in future.
4. More generically, these case studies illustrate (i) how freshwaters might be at particular risk of multiple-stressor effects because of conflicts in water use, and because the hydrological cycle vectors stressor effects so effectively and so extensively; (ii) that dramatic, nonlinear, ‘ecological surprises’ sometimes emerge as multiple-stressor effects develop and (iii) that good ecology and good ecologists add considerable value to other freshwater disciplines in understanding multiple stressors and managing their effects.
The objective of the current study was to identify hydromorphological variables that are suitable to define and describe hydromorphological degradation. Stream type-specific and spatial scale-dependent multivariate analysis (Non-metric Multidimensional Scaling, NMS) of 106 hydromorphological variables derived from 275 samples at 147 sites and indicator value analysis (IndVal) resulted in the identification of key factors describing hydromorphological differences in Central European lowland streams. Sample sites represented six European stream types from Sweden (1 stream type), The Netherlands (2 stream types), and Germany (3 stream types). The four large-scale hydro(geo)morphological variables: catchment size, geology (`% moraines', `% alluvial deposits'), and natural land use (`% natural forest') explained inter-stream type differences best. On the smaller site scale, riparian vegetation described inter-stream type differences best.
On catchment scale, `% natural forest', and `agricultural land use' illustrated inter-stream type hydromorphological degradation of all six stream types very well. Four site related variables (`% wooded riparian vegetation', `% shading', `average stream width', and `% macrolithal (cobbles, 20 to 40 cm long) account for hydromorphological degradation on the smaller reach-scale. An analysis of indicator variables restricted to German stream types only resulted in four factors, namely `% xylal' (tree trunks, branches, roots, etc.), `no of debris dams >0.3 m3', `no of logs >10 cm ∅', and `% fixed banks' as important descriptors of hydromorphological degradation. Intra-stream type hydromorphological degradation is illustrated for `mid-sized sand bottom streams in the German lowlands'. For this stream type, a clear gradient of degradation was revealed, and 25 variables were identified to entirely characterize reference conditions and degradation. The variables that described the degradation gradient best were combined to the new German Structure Index (GSI), which can be implemented to continuously measure hydromorphological degradation.
The main objective of the European Union (EU) funded project AQEM1was to develop a framework of an assessment system for streams in Europe based on benthic macroinvertebrates that fulfils the requirements of the EU Water Framework Directive. Initial assessment methods for 28 European stream types and more generally applicable tools for stream biomonitoring in Europe were generated.
The development of the system was based on a newly collected data set covering stream types in Austria, the Czech Republic, Germany, Greece, Italy, The Netherlands, Portugal and Sweden. Altogether, 901 benthic invertebrate samples were taken using a standardised multi-habitat sampling procedure and a large number of parameters describing the streams and their catchments was recorded for all sampling sites. From the stream and catchment characteristics measures of stress were derived. A large number of metrics was tested independently for each of the stream types, to identify the response of each metric to degradation of a site. This process resulted in up to 18 core metrics for the individual stream types, which were combined into a different multimetric index in each country. The multimetric AQEM assessment system is used to classify a stream stretch into an Ecological Quality Class ranging from 5 (high quality) to 1 (bad quality) and often provides information on the possible causes of degradation.
AQEM provides a taxa list of 9557 European macroinvertebrate taxa with associated autecological information, a software package for performing all the calculations necessary for applying the multimetric AQEM assessment system and a manual describing all aspects of the application of the system from site selection to data interpretation.
The main objective of the European Union (EU) funded project AQEM1was to develop a framework of an assessment system for streams in Europe based on benthic macroinvertebrates that fulfils the requirements of the EU Water Framework Directive. Initial assessment methods for 28 European stream types and more generally applicable tools for stream biomonitoring in Europe were generated.
The development of the system was based on a newly collected data set covering stream types in Austria, the Czech Republic, Germany, Greece, Italy, The Netherlands, Portugal and Sweden. Altogether, 901 benthic invertebrate samples were taken using a standardised multi-habitat sampling procedure and a large number of parameters describing the streams and their catchments was recorded for all sampling sites. From the stream and catchment characteristics measures of stress were derived. A large number of metrics was tested independently for each of the stream types, to identify the response of each metric to degradation of a site. This process resulted in up to 18 core metrics for the individual stream types, which were combined into a different multimetric index in each country. The multimetric AQEM assessment system is used to classify a stream stretch into an Ecological Quality Class ranging from 5 (high quality) to 1 (bad quality) and often provides information on the possible causes of degradation.
AQEM provides a taxa list of 9557 European macroinvertebrate taxa with associated autecological information, a software package for performing all the calculations necessary for applying the multimetric AQEM assessment system and a manual describing all aspects of the application of the system from site selection to data interpretation.
Land‐use changes have degraded ecosystems worldwide. A particular concern for freshwater biodiversity and ecosystem function are stressors introduced by intensified agriculture. Typically several stressors affect freshwater ecosystems simultaneously. However, the combined effects of these multiple stressors on streams and rivers are still poorly understood, yet of critical importance to improve freshwater management.
We investigated responses of benthic macroinvertebrates to three globally important agricultural stressors affecting streams (nutrient enrichment, fine sediment deposition and reduced current velocity), using 64 stream mesocosms (full‐factorial 2 × 2 × 2 design, eight replicates of each treatment combination) established on the banks of the Breitenbach Stream (Hesse, Germany). The experiment ran for 1 month (16 days of colonisation, 14 days of manipulations), and all invertebrates in the mesocosms were collected at the end of this period.
Fourteen of the 17 studied invertebrate response variables were affected by one or more stressors each. Negative effects on richness or abundance of pollution‐sensitive Ephemeroptera, Plecoptera and Trichoptera ( EPT ) taxa were particularly common. Overall, both sediment addition and stream flow velocity reduction had pervasive and strong effects. Responses to sediment addition were mostly negative, whereas decreased current velocity reduced several EPT metrics but increased the abundances of some of the other common taxa. Nutrient enrichment had few effects, but these were consistently negative.
Combined stressor effects were mainly additive, with only two interactions found in total, both between reduced velocity and nutrients (on the crustacean Gammarus spp. and ceratopogonid midges). This finding implies that multiple‐stressor responses may be predicted from knowledge of single‐stressor effects in this stream community (unlike the often synergistic or antagonistic responses observed elsewhere). However, further taxon‐specific responses and interactions among stressors may have been obscured by limited taxonomic resolution, especially for the numerically dominant Chironomidae. Genetic approaches are required to address this limitation in the future.
Urban impacts on streams are mediated by alteration of land cover and subsurface drainage. Understanding interactions of these 2 effects is critical for urban land and water management. We used boosted regression trees to analyze relationships between environmental predictors, including land-cover measures that indicate urban impacts, and Stream Invertebrate Grade Number Average Level (SIGNAL) or the occurrence of 60 macroinvertebrate families across the Melbourne (Australia) region. SIGNAL and 51 families were negatively correlated with attenuated imperviousness (AI). Twenty-four families exhibited a steep decline in probability of occurrence between 0 and �3% AI, consistent across the range of natural discharge (Q). Responses to attenuated forest cover (AF) were more variable among families (39 positive, 15 negative). AF had a less positive influence on SIGNAL at high than at low AI because the many (high SIGNAL-grade) families that were strongly negatively correlated with AI were likely to be absent at high AI. Interactions that suggested a modification of response to AI or AF as a result of the influence of another variable were restricted to 19 families. For 4 families with occurrences that were positively correlated with AF, the negative effect of AI was reduced in streams with high AF. For 14 families, responses of occurrence to AI or AF varied with Q or antecedent discharge in multiple ways. A reduced effect of AI was observed in low-Q streams or after very dry antecedent conditions for 10 families. Despite strong effects of the regional gradient in rainfall and vegetation across our study area, catchment-scale urban stormwater drainage was consistently associated with reduced occurrence of most families. The relative number of families predicted to be lost at low levels of AI underestimated relative loss of genera or species. Urban stormwater runoff probably is a strong driver of species loss in streams, but riparian forest can increase the probability of occurrence of a small number of tolerant families.
Freshwater organisms face numerous stressors, such as nutrient enrichment, contaminant pollution, sedimentation and alterations in stream hydrology and habitat structure. One of the most significant and widespread stressors in European freshwaters is expected to be water pollution from intensive land use. However, the information on critical threshold concentrations at which taxa decline or increase in frequency and abundance is missing for the large majority of river benthic invertebrate taxa. The main aim was to determine ecological change points for benthic invertebrate taxa at which rapid alterations in species frequency and abundance occur as a consequence of relatively small changes in the environmental gradient. These change points can be interpreted as critical threshold concentrations. A total of 468 river benthic invertebrate taxa and nine physico-chemical variables describing the daytime dissolved oxygen, chloride, nutrient concentrations and organic load were analyzed. We selected 751 river sites from a nationwide range of locations in Germany for this investigation. Depending on the physico-chemical variable, between 20.6% and 48.8% of the total number of tested taxa were assigned with a valid change point. All taxa were assigned to negative or positive response groups depending on the response direction. Except for daytime dissolved oxygen, negative responding taxa are referred to as decreasers and positive responding taxa as increasers, respectively. In total, 25.8–100% of the decreasers’ change points were below (and above in the case of daytime dissolved oxygen) the background values defined as quality criteria for German rivers by the water authorities. This indicates that stricter quality criteria may need to be set to reach the good ecological status according to the European Water Framework Directive. The calculated daytime dissolved oxygen change points were essentially in line with the species saprobic values and taxon-specific change points for physico-chemical variables fit well with the data provided in other international studies. We deliver valuable knowledge about the sensitivities and response schemes of river benthic invertebrate species. This information is especially useful for the development of efficient management and policy tools to predict the likelihood of occurrence of individual species under different levels of anthropogenic impact.
Multivariate data and multivariate analysis.- Looking at multivariate data: visualization.- Principal components analysis.- Multidimensional scaling.- Exploratory factor analysis.- Cluster analysis.- Confirmatory factor analysis and structural equation models.- The analysis of repeated measures data.-
1. Biological traits, which may give insights into the mechanisms driving the distribution of organ- isms along gradients of stressor intensities, have been proposed as a tool for disentangling the effects of multiple stressors acting simultaneously on scales ranging from climatic region to river basins, val- leys, reaches and microhabitats. However, the combined effects of farming intensity and flow reduc- tion on biological traits of stream invertebrates remain to be studied.
2. We assessed the benthic invertebrate community and physicochemistry at 43 stream sites along gradients of farming intensity (0–95% of the catchment in intensively managed grassland) and water abstraction (0–92% streamflow reduction). Using general linear models and an information-theoretic approach, we studied individual and combined effects of agricultural stressors on invertebrate traits and community composition.
3. Traits often followed predictable patterns along stressor gradients, and non-additive interactions between paired stressors were common. Farming intensity was more frequently related to life-his- tory, resistance and resilience traits, whereas water abstraction was correlated more often with gen- eral biological traits such as feeding habits, dietary preference and respiration. Further, traits and traditional measures of community structure, such as taxon relative abundances and community indices, offered a similar level of distinction along the gradients of stressor intensities.
4. Our findings indicate that invertebrate traits can differentiate the effects of multiple stressors and provide insights into potential mechanisms. At the landscape scale, farming intensity exerted stron- ger effects via invertebrate habitat quality and water abstraction via food availability. At the reach scale, both fine sediment and nutrients affected habitat quality, whereas nutrients showed more marked effects via food availability. Finally, we propose a suite of traits that may provide the strong- est differentiation of stressor intensities.
Lotic ecosystems worldwide are being increasingly modified hydromorphologically, for example, by damming, fragmentation, flow regulation and channel modification. Serious threats to riverine biodiversity are suspected, yet available field data are few and rarely address the various taxonomic, functional and phylogenetic components of biodiversity.
We examined benthic macroinvertebrate diversity along a gradient of hydromorphological alteration across 65 lowland river sites in the Netherlands, Germany and Poland. We calculated eight metrics describing taxonomic diversity (richness, rarefied richness, Shannon's and Simpson's diversity, Pielou's evenness), functional diversity (mean trait diversity) and phylogenetic diversity (mean taxonomic distinctness and its variance).
Threshold Indicator Taxa AN alysis ( TITAN ) and Non‐metric Multidimensional Scaling ( NMS ) showed detailed changes in taxonomic and trait composition, respectively, with increasing hydromorphological alteration. TITAN revealed a gradual turnover under increasing impact in which taxon losses were almost balanced by gains. NMS illustrated a high degree of concordance in the traits possessed by the taxa lost and gained at the gradient's end points.
Although a biologically meaningful hydromorphological gradient was evident, the biodiversity response was modest (Spearman's ρ < |0.32| for all metrics). Pielou's evenness and mean taxonomic distinctness actually increased at impaired sites.
Our results suggest that taxonomic and trait replacement with hydromorphological alteration is not followed by changes in whole‐community diversity. This implies some redundancy in these systems, with ecologically similar species replacing those lost through environmental change.
The results highlight how whole‐community‐based diversity, although frequently calculated and interpreted for decades in ecology and conservation biology, is not the all‐purpose concept to detect and assess the various facets of biodiversity loss. Therefore, we suggest that concerted effort is needed to develop and test novel indicators of biodiversity, capable of detecting biodiversity loss, or other changes, in response to the main environmental stressors of lotic ecosystems.
Concern is growing about the potential effects of interacting multiple stressors, especially as the global climate changes. We provide a comprehensive review of multiple stressor interactions in coral reef ecosystems, which are widely considered to be one of the most sensitive ecosystems to global change. First, we synthesized coral reef studies that examined interactions of two or more stressors, highlighting stressor interactions (where one stressor directly influences another) and potentially synergistic effects on response variables (where two stressors interact to produce an effect that is greater than purely additive). For stressor-stressor interactions, we found studies that examined at least 2 of the 13 stressors of interest. Applying network analysis to analyze relationships between stressors, we found that pathogens were exacerbated by more co-stressors than any other stressor, with ~78% of studies reporting an enhancing effect by another stressor. Sedimentation, storms, and water temperature directly affected the largest number of other stressors. Pathogens, nutrients, and crown-of-thorns starfish were the most-influenced stressors. We found 187 studies that examined the effects of two or more stressors on a third dependent variable. The interaction of irradiance and temperature on corals has been the subject of more research (62 studies, 33% of the total) than any other combination of stressors, with many studies reporting a synergistic effect on coral symbiont photosynthetic performance (n=19). Second, we performed a quantitative meta-analysis of existing literature on this most-studied interaction (irradiance and temperature). We found that the mean effect size of combined treatments was statistically indistinguishable from a purely additive interaction, although it should be noted that the sample size was relatively small (n=26). Overall, although in aggregate a large body of literature examines stressor effects on coral reefs and coral organisms, considerable gaps remain for numerous stressor interactions and effects, and insufficient quantitative evidence exists to suggest that the prevailing type of stressor interaction is synergistic. This article is protected by copyright. All rights reserved.
Agriculture affects streams worldwide, and multiple stressors are usually at work. The effects of farming intensification in the catchment are likely to interact with flow reduction due to abstraction for irrigation, but their combined effects on fish communities are unknown.
In a low‐rainfall, agricultural catchment, we sampled instream physicochemistry and fish populations (non‐native brown trout, Salmo trutta , and native upland bullies, Gobiomorphus breviceps , dominated the fish communities) at 36 stream sites chosen to cover wide gradients of % Farming Intensity (%FI) (% catchment in ‘high‐producing exotic grassland’) and % Water Abstraction (%WA) (estimated from a published hydrological model). These landscape variables were not well correlated, allowing us to unravel their individual and combined effects.
Presence of trout was best described by an additive multiple‐stressor model consisting of a unimodal response to %FI and a negative response to %WA. Trout density only showed a negative response to %FI. Upland bullies were unrelated to either landscape variable.
When populations were modelled using instream variables, trout presence was negatively related to fine sediment depth, while density was negatively related to both sediment depth and total nitrogen (themselves closely related to %FI). Upland bully presence and density showed unimodal responses to just total nitrogen. Ammonium concentration was the only measured instream variable related to %WA.
The final models for instream stressors explained more of the variation in fish density, whereas the final models for landscape stressors explained more of the variation in fish presence.
Overall, farming intensity showed stronger negative relationships with fish populations than water abstraction, and fish were absent from stream reaches whose upstream catchments contained more than 40% high‐producing exotic grassland. Resource managers considering intensifying water abstraction or agriculture in low‐rainfall river catchments should be aware of the interplay between these two agricultural stressors.
The factors underlying population and community dynamics are almost invariably multivariate, and ecosystems worldwide are affected by many anthropogenic stressors. Inorganic dissolved nutrients and deposited fine sediment are common stressors in agricultural streams and can be expected to influence benthic algae and cyanobacteria.
We determined population‐ and community‐level responses of phototrophic periphyton along twin‐stressor gradients of dissolved nutrients and deposited fine sediment after 20 days of exposure in stream mesocosms. Multiple linear regression and an information‐theoretic approach were used to select the best predictive models for each response variable, accounting for potential subsidy‐stress responses for each stressor (where at low stressor levels, an ecological variable responds positively up to an inflection point, beyond which the effect is negative) and for multiple‐stressor interactions. This approach enabled us to test the subsidy‐stress hypothesis for each stressor and to investigate whether the two stressors operated singly or in concert (additively or with an interaction) on periphyton attributes.
Focussing further on three ecological guilds of periphyton (low profile, high profile, motile), we also tested the specific hypotheses, that sediment augmentation would produce a proportional increase in motile and a decrease in high‐profile forms, and that nutrient augmentation would produce proportional increases in both motile and high‐profile forms.
Unimodal subsidy‐stress patterns along the sediment gradient were found only for densities of two common N itzschia species. By contrast, unimodal patterns along the nutrient gradient occurred frequently at both population and community levels, supporting the subsidy‐stress hypothesis for nutrient enrichment. Some single‐stressor responses were observed, but the twin stressors sediment and nutrients mainly acted in a simple, additive way, probably because their modes of action are different. As a notable exception from this rule, potentially harmful cyanobacteria ( P hormidium and O scillatoria species) responded synergistically to the stressors. Our hypothesis about the representation of ecological guilds across the sediment gradient was fully supported, whilst the hypothesis regarding nutrients received partial support.
Categorisation of periphyton taxa into physiognomic guilds revealed predictable response patterns to the stressors. The prevalence of motile taxa in stream communities may be suitable for detecting sedimentation impacts and early signs of nutrient enrichment. Finally, based on periphyton response shapes along the nutrient gradient, thresholds could be identified at which community variables changed abruptly.
Previous research on the combined action of various paired agricultural stressors in stream ecosystems has shown that non‐additive outcomes (i.e. synergisms or antagonisms) are more common than simple additive effects on communities, but the interplay between deposited fine sediment and widely used herbicides such as glyphosate as stressors is not well understood.
A 28‐day experiment in outdoor stream mesocosms simulated effects of varying levels of fine sediment and a glyphosate‐based herbicide on macroinvertebrates and ecosystem function (leaf breakdown) in a fully factorial repeated‐measures design. Our aim was to determine whether (i) increased levels of sediment and glyphosate had individual and/or additive combined effects on invertebrates and leaf breakdown, (ii) increased sediment reduced the toxicity of glyphosate (antagonistic multiple stressor interaction) or (iii) sediment‐adsorbed glyphosate prolonged the effects of exposure (synergistic interaction).
Sediment addition positively or negatively affected eight of the 10 most common invertebrate taxa colonising the mesocosms and increased or decreased the representation of 12 of 15 biological trait categories possessed by the invertebrates, while glyphosate addition negatively affected only two taxa and two invertebrate trait categories, indicating that glyphosate entering streams as a result of herbicide addition to farmland is less likely to be problematic for invertebrates than fine sediment from catchment erosion.
No significant overall sediment‐by‐glyphosate interaction was detected for invertebrate taxonomic or trait compositions or for any common individual taxon, trait or community metric, indicating that the two stressors were acting additively (i.e. without interaction), rather than synergistically or antagonistically.
Leaf breakdown rates (measured as mass and strength loss) were accelerated by sediment and glyphosate as individual stressors. Further, the two stressors interacted for leaf strength loss, with their combined effect being less than additive when both stressors were at their highest levels.
Population, community and ecosystem variables responded differently to multiple stressors, highlighting the value of combining structural, functional taxonomic and trait data to assess the effects of anthropogenic stressors.
1. Degradation of freshwater ecosystems is a major concern worldwide. Agriculture introduces multiple stressors to streams, presenting a challenge for freshwater managers who must understand the relative strengths of individual stressor effects and their combined multiple-stressor effects.
2. Using a replicated regression design, we manipulated levels of fine sediment and nutrients to create a broad eight-point gradient for each stressor across 128 stream mesocosms to determine the shapes of macroinvertebrate responses after 21 days of exposure.
3. Subsidy–stress response patterns occurred along both stressor gradients. Sediment addition provided an initial subsidy for some pollution-tolerant taxa and total macroinvertebrate density, but produced consistently negative effects for other taxa, total taxon richness and the density and richness of pollution-sensitive Ephemeroptera, Plecoptera, Trichoptera (EPT) taxa. Nutrient enrichment provided an initial subsidy for densities of two common EPT taxa, total EPT density, macroinvertebrate and EPT taxon richness.
4. Few macroinvertebrate variables were affected by a single stressor (always fine sediment). The majority of responses were additive multiple-stressor patterns, although Chironomidae density and EPT taxon richness followed complex synergistic patterns.
5. Fine sediment was a much more pervasive stressor than augmented nutrient concentrations. Overall, macroinvertebrate traits responded to stressors as strongly as community variables or individual taxa.
6. Synthesis and applications. Managing both fine sediment and nutrient inputs from agriculture is crucial to achieve good stream condition but priority should be given to minimizing fine sediment, which should be maintained below a threshold of 5% cover and 0·5-mm depth. Managers also need to be wary of interactive multiple-stressor effects because ecological outcomes of an increase in stressor load may be worse than predicted based on the knowledge of single-stressor effects.
Sedimentation is widely acknowledged as a major cause of degradation of instream habitats. However, macroinvertebrate burial by sediment has been poorly studied. Ex situ experiments were undertaken to examine the response of four common and abundant macroinvertebrate taxa (Baetis rhodani, Nemoura cambrica, Hydropsyche pellucidula, and Asellus aquaticus) to burial by six sediment size classes (range = 125 m 10 mm in size) and two depths of burial (5 mm and 10 mm). The nymphs of the ephemeropteran, Baetis rhodani, were unable to excavate themselves from any of the sediments. In contrast, the plecopteran nymphs of Nemoura cambrica were able to excavate themselves from all sediment classes and burial depths. Adults of the isopod, Asellus aquaticus, were able to excavate themselves rapidly from finer sediment classes (< 1 mm) but took significantly longer to escape from sediment > 1 mm in size and became trapped in coarser sediments (>4 mm in size at 5 mm burial depth and > 2 mm at 10 mm burial depth). The larvae of the trichopteran, Hydropsyche pellucidula, were able to excavate their heads from all sediment classes and both burial depths, but became trapped in particles < 500 m in size when buried under 10 mm of sediment. The results demonstrate that the response of individual taxa to burial with sediments is highly variable. Consequently, many of the documented changes to benthic macroinvertebrate community composition due to sedimentation probably mask a variety of individual faunal responses.
1. Many ecosystems are influenced simultaneously by multiple stressors, and the consequences of stressors are often unpredictable on the basis of knowledge of single effects. Agriculture affects streams world-wide via nutrient enrichment, elevated fine sediment and water abstraction for irrigation, but the combined impacts of these stressors are unknown.
2. We manipulated all three stressors simultaneously in an 18-day experiment and determined their individual and pair-wise combined effects on benthic invertebrates, algal biomass and leaf decay. We added nutrients (phosphorus plus nitrogen) and/or fine sediment (grain size 0·2 mm) to 18 experimental stream channels (dimensions 250 × 15 × 15 cm) supplied with water from a nearby stream. Three sediment and three nutrient treatments (high, intermediate, natural) were applied to each of six channels while flow was reduced by 80% in half the channels. Invertebrates (composition, abundance) and algae (chlorophyll a) were assayed using ceramic tile substrata and leaf decay was assayed using bundled leaves of a native shrub. Invertebrates colonizing leaf packs were also sampled.
3. Effects of sediment addition and flow reduction on biological response parameters were twice as common as nutrient enrichment effects. Nutrient enrichment increased total invertebrate abundance on tiles, algal biomass accrual and leaf decay rates, whereas both sediment addition (at the highest level) and flow reduction had mostly negative effects (e.g. reduced algal biomass, invertebrate abundance and/or taxonomic richness).
4. Stressors interacted often, and interactions between sediment and flow were particularly common. The negative impact of added sediment on aquatic biota was stronger at reduced flow, especially on tile substrata that were more exposed to the current than leaf-pack substrata.
5. Synthesis and applications. Our key findings imply that abstracting water from a stream already subjected to high fine sediment inputs may have far worse effects on the invertebrate fauna than abstraction from a similar stream with lower sediment levels. Aquatic resource managers should be aware of this important interaction between multiple stressors.
1. Large-scale comparative studies of ecological responses to anthropological stressors in rivers require measures that are consistent across a range of spatial scales. The biological trait profile of communities offers an alternative approach to traditional measures of macroinvertebrate taxonomic identity and is less constrained by biogeographic influences.
2. We compared the capacities of taxonomic composition and biological trait composition to discriminate the effects of land use (measured as percentage of the catchment in pasture) across a large geographic zone (the whole of New Zealand) in 30 sub-catchments grouped into five ecoregions throughout the North and South Islands of New Zealand. In addition, we investigated trait consistency (i.e. whether similar traits had similar trait responses to land use at local (catchment) and broad scales).
3. The analysis of taxonomic composition showed that community structure was indeed influenced by land-use intensity, but that relationships differed among ecoregions. In contrast, traditional assessment metrics (Macroinvertebrate Community Index, richness in Ephemeroptera, Plecoptera and Trichoptera taxa) and trait composition were uninfluenced by region. Trait responses were consistent at the broad and catchment scales, with similar traits responding to pastoral land use at both scales.
4. We used general linear modelling to investigate individual trait responses to land-use intensity, catchment area and region, focussing on 15 trait categories known to be influenced by land-use intensity at the catchment scale. Several trait categories varied with land-use intensity and demonstrated consistency at both catchment and broad scales. Of these, the representation of shorter generation time, asexual reproduction and hermaphroditism, ability to lay eggs beneath the water surface, egg protection and respiration types tolerant of oxygen depletion generally increased in assemblages exposed to more intense pastoral land use. At the same time, the representation of short life duration of adults, prevalence of laying eggs at the water surface, sexual reproduction and low body flexibility decreased in assemblages exposed to land-use intensification.
5. Our results highlight the value of developing predictive response measures that are relevant at multiple scales and provide the basis for new measures of river condition that are as effective as taxonomic identity in terms of response reliability.
The sustainable use of water resources requires clear guidelines for the management of diffuse pollution inputs to rivers. Without informed guidelines, management decisions are unlikely to deliver cost-effective improvements in the quality of rivers as required by current water policy. Here, we review the evidence available for deriving improved guidelines on the loading of fine sediment to rivers based on the impact on macro-invertebrates. The relationship between macro-invertebrates and fine sediments is poorly defined. Studies of the impacts of fine sediment on macro-invertebrates have been undertaken at various scales, which has an influence on the range of responses displayed and the reliability of the results obtained; results obtained from investigations at smaller scales may not manifest at the scale required to manage rivers and vice versa. Many of the identified effects of increased loading of fine sediment on macro-invertebrates occur as a consequence of deposition on the river bed, yet many current management guidelines are based on suspended sediment targets. On this basis, existing water quality guidelines for sediment management are unlikely to be appropriate. Copyright © 2011 John Wiley & Sons, Ltd.
1. Stream managers need to understand relationships between multiple stressors and ecological responses. We examined responses of benthic invertebrates and algae along two land-use-related stressor gradients of concern in running waters. Our correlative study of the consequences of augmented deposited fine sediment and nutrient concentrations was conducted in a regional set of streams and rivers monitored by a water management authority in New Zealand and incorporated a wide range of catchment geologies and stream orders.
2. We used multiple linear regression analysis and an information-theoretic approach to select the best predictive models for our biological response variables by testing multiple competing hypotheses that include nonlinear subsidy-stress relationships and interactive effects between the two stressors.
3. Patterns consistent with a subsidy-stress response to increasing dissolved inorganic nitrogen concentration were found for the relative abundances of the common invertebrate genera Pycnocentrodes and Deleatidium and for the relative abundance of total individuals in the EPT orders (Ephemeroptera, Plecoptera, Trichoptera).
4. Fine sediment seemed the more pervasive stressor, apparently counteracting and overwhelming any initial subsidy effect of increased nutrients, and accounting for more of the variance in biological response variables. Relationships with high nutrient concentrations were weaker and modelled with less certainty, probably reflecting the indirect modes of action of nutrients compared to those underlying sediment effects. Nevertheless, in several cases, the models indicated that nutrients interacted synergistically with fine sediment, lending further weight to the conclusion that managers need to address both stressors to achieve the best outcomes.
1. Increased fine sediment input caused by agricultural development is expected to act as a stressor for stream ecosystems. In a large‐scale field experiment, we added fine river sand to 50‐m reaches of three second‐order streams in each of four categories of catchment development (ungrazed tussock grasslands, grazed pasture, dairying and deer farming) and measured the responses of macroinvertebrates and aquatic moss.
2. Before addition, fine sediment cover differed between land uses, being lowest in tussock (7%), intermediate in pasture (30%) and dairy (47%) and highest in deer streams (88%). Sediment addition increased cover by one land‐use category (e.g. augmented sediment cover in tussock streams was similar to pre‐existing cover in pasture streams), and cover remained high in impact reaches (compared with controls) throughout the 5‐week experiment. Sediment addition did not change concentrations of phosphate, nitrate and ammonium, which were generally highest in dairy streams and lowest in tussock streams.
3. Aquatic mosses (most common in tussock, absent in dairy and deer), invertebrate density (highest in deer, lowest in tussock), taxon richness (highest in pasture, lowest in deer) and diversity (highest in pasture and tussock, lowest in dairy and deer) all differed between land uses. Sediment addition resulted in reductions of moss cover, invertebrate taxon richness and richness of Ephemeroptera, Plecoptera and Trichoptera in impact relative to control reaches.
4. The impact of sediment addition was strongest in pasture streams where pre‐existing sediment cover was moderate and richness and diversity of the invertebrate community highest. However, even in the already sediment‐rich and species‐poor deer streams, density of one common taxon was reduced significantly by sediment addition, and another two were affected in the same way in dairy streams, the second‐most intense land use.
5. Our experiment has disentangled the impact of sediment addition from other concomitant land‐use effects that could not be reliably distinguished in previous research, which has mainly consisted of correlative studies or unrealistically small‐scale experiments.
Key Words catchment, disturbance, stressor response, stream health, river ■ Abstract Local habitat and biological diversity of streams and rivers are strongly influenced by landform and land use within the surrounding valley at multiple scales. However, empirical associations between land use and stream response only varyingly succeed in implicating pathways of influence. This is the case for a number of reasons, including (a) covariation of anthropogenic and natural gradients in the landscape; (b) the existence of multiple, scale-dependent mechanisms; (c) nonlinear responses; and (d) the difficulties of separating present-day from historical influences. Further research is needed that examines responses to land use under different management strategies and that employs response variables that have greater diagnostic value than many of the aggregated measures in current use. In every respect, the valley rules the stream.
1. This study investigated the relation of benthic macroinvertebrates to environmental gradients in Central European lowland rivers. Taxonomic structure (taxa) and functional composition (metrics) were related to gradients at four different spatial scales (ecoregion, catchment, reach and site). The environmental variables at the catchment‐, reach‐ and site scales reflected the intensity of human impact: catchment and floodplain land use, riparian and floodplain degradation, flow regulation and river bank and bed modification.
2. Field surveys and GIS yielded 130 parameters characterising the hydromorphology and land use of 75 river sections in Sweden, the Netherlands, Germany and Poland. Two hundred and forty‐four macroinvertebrate taxa and 84 derived community metrics and biotic indices such as functional guilds, diversity and composition measures were included in the analysis.
3. Canonical Correspondence Analysis (CCA) and Redundancy Analysis (RDA) showed that hydromorphological and land use variables explained 11.4%, 22.1% and 15.8% of the taxa variance at the catchment (‘macro’), reach (‘meso’) and site (‘micro’) scales, respectively, compared with 14.9%, 33.2% and 21.5% of the variance associated with the derived metrics. Ecoregion and season accounted for 10.9% and 20.5% of the variance of the taxonomic structure and functional composition, respectively.
4. Partial CCA (pCCA) and RDA (pRDA) showed that the unique variance explained was slightly higher for taxa than for metrics. By contrast, the joint variance explained for metrics was much higher at all spatial scales and largest at the reach scale. Environmental variables explained 46.8% of metric variance and 32.4% of taxonomic structure.
5. Canonical Correspondence Analysis and RDA identified clear environmental gradients along the two main ordination axes, namely, land use and hydromorphological degradation. The impact of catchment land use on benthic macroinvertebrates was mainly revealed by the proportion of urban areas. At the reach scale, riparian and floodplain attributes (bank fixation, riparian wooded vegetation, shading) and the proportion of large woody debris were strong predictors of the taxonomic structure and functional composition of benthic macroinvertebrates. At the site scale, artificial substrata indicated human impact, particularly the proportion of macro‐ and mesolithal used for bank enforcement (rip–rap).
6. Our study revealed the importance of benthic macroinvertebrate functional measures (functional guilds, composition and abundance measures, sensitivity and tolerance measures, diversity measures) for detecting the impact of hydromorphological stress at different spatial scales.
Managers must understand the effects of stressors on ecosystems in order to identify thresholds of harm but, to be meaningful, thresholds will usually need to be defined for situations where multiple stressors are operating.
We investigated the individual and combined effects of the principal stressors (nutrient concentration and streambed fine sediment cover) operating in native grassland streams converted to pasture in New Zealand, using two different approaches: a survey of 32 small streams and an experiment involving nine streams where the stressors were manipulated in a factorial design. We investigated the consequences for populations of benthic invertebrates and for the structure of communities, including taxon richness and the representation of species traits.
Up to half the taxa and most community metrics responded to at least one stressor. Our results suggest that in these streams, an increase in fine sediment loading from anthropogenic causes had more widespread effects than augmented nutrient concentrations. Of most significance is our finding, both from the survey and, in particular, the experiment, of a variety of complex interactions among the stressors.
Synthesis and applications . The development of indices of stream health that distinguish the effects of sediment from those of nutrients should help prioritize catchment management actions. Of more general importance is our finding that the consequences of stressors are often unpredictable on the basis of knowledge of single effects; if managers only consider the effects of individual stressors, their assessment of risk may be higher or lower than reality.
Benthic macroinvertebrates samples were collected in spring and autumn 2000. Fifteen streams in southern Sweden were sampled twice both for chemical, physical, and biological parameters. Eighty-four macroinvertebrate `single' metrics were calculated and tested for their ability of detecting organic pollution of streams. A comparison of the `best' single metrics with two multimetric indices was also done. The Belgian Biotic Index (BBI), the Average Score Per Taxon (ASPT), the Saprobic Index (Zelinka & Marvan), the German Saprobic Index, percentage hypopotamal preferences, the Danish Stream Fauna Index (DSFI) and percentage pelal preferences were found to be good indicators of organic pollution. Both DSFI and ASPT are frequently used for detecting organic pollution in southern Sweden and could be recommended for further use. Although saprobic indices are not commonly used in Sweden, our results indicate that they may be appropriate. BBI, percentage hypopotamal preferences, and percentage pelal preferences are seldom used for detecting organic pollution of Swedish streams, but could maybe prove useful for future uses. Two multimetric indices recently developed for detecting the effects of organic pollution in southern Sweden, the AQEM Type S05 Index and the DJ Index, were compared to the `best' single metrics by determining their responses to total phosphorous concentration, conductivity, and percentage cropland. The comparison showed that the DJ Index proved to be a better indicator of the effects of organic pollution than the single metrics. The other multimetric index, the AQEM Type S05 Index, had slightly lower statistical power, but performed well in comparison to the other metrics.
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