Article

Multiple stress response of lowland stream benthic macroinvertebrates depends on habitat type

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Abstract

Worldwide, lowland stream ecosystems are exposed to multiple anthropogenic stress due to the combination of water scarcity, eutrophication, and fine sedimentation. The understanding of the effects of such multiple stress on stream benthic macroinvertebrates has been growing in recent years. However, the interdependence of multiple stress and stream habitat characteristics has received little attention, although single stressor studies indicate that habitat characteristics may be decisive in shaping the macroinvertebrate response. We conducted an experiment in large outdoor flumes to assess the effects of low flow, fine sedimentation, and nutrient enrichment on the structure of the benthic macroinvertebrate community in riffle and run habitats of lowland streams. For most taxa, we found a negative effect of low flow on macroinvertebrate abundance in the riffle habitat, an effect which was mitigated by fine sedimentation for overall community composition and the dominant shredder species (Gammarus pulex) and by nutrient enrichment for the dominant grazer species (Baetis rhodani). In contrast, fine sediment in combination with low flow rapidly affected macroinvertebrate composition in the run habitat, with decreasing abundances of many species. We conclude that the effects of typical multiple stressor scenarios on lowland stream benthic macroinvertebrates are highly dependent on habitat conditions and that high habitat diversity needs to be given priority by stream managers to maximize the resilience of stream macroinvertebrate communities to multiple stress.

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... Land use also significantly impacts the biological community structure of streams [17][18][19][20][21]. For example, the rapid urbanization in the watersheds of Jialing and Yangtze Rivers in China predominantly contributed toward the degradation of aquatic ecosystems in streams [22]. ...
... Agricultural and urban areas are concentrated downstream and cover approximately 20% and 4% of the total area, respectively. The urban areas significantly impact river water quality, despite their low coverage in the watershed [17]. Of particular concern are the high concentrations of harmful compounds such as phosphorus and nitrogen sourced from livestock wastewater and agricultural activity in the surrounding watershed. ...
... We found BOD to be an important water quality variable that regulates the health of benthic macroinvertebrates. In general, urban land use accounts for a low proportion of the total watershed area, but wastewater and domestic sewage emissions from urban/industrial activities and dense settlements have a significant impact on river water quality and benthic macroinvertebrates [11,17]. Jabbar and Grote [5] found that water quality parameters, including nitrogen and phosphorus, were more closely correlated with urban areas as opposed to agricultural areas, as most of the effluents from urban sewage treatment plants are discharged to stream tributaries, causing a rise in BOD [25]. ...
Article
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The extent of anthropogenic land use in watersheds determines the amount of pollutants discharged to streams. This indirectly and directly affects stream water quality and biological health. Most studies have therefore focused on ways to reduce non-point pollution sources to streams from the surrounding land use in watersheds. However, the mechanistic pathways between land use and the deterioration of stream water quality and biological assemblages remain unclear. This study estimated a structural equation model (SEM) representing the impact of agricultural and urban land use on water quality and the benthic macroinvertebrate index (BMI) using IBM AMOS in the Nam-Han river systems, South Korea. The estimated SEM showed that the percent of urban and agricultural land in the watersheds significantly affected both the water quality and the BMI of the streams. Specifically, a higher percent of urban land use had directly increased the biochemical oxygen demand (BOD) and total phosphorus (TP), and deteriorated the BMI of streams. Similarly, higher proportions of agricultural land use had also directly increased the BOD, total nitrogen (TN), and total phosphorus (TP) concentrations, and lowered the BMI of streams. In addition, it was observed that the percent of urban and agricultural land use had indirectly deteriorated the BMI through increased BOD. However, we were not able to observe any significant indirect effect of the percent of urban and agricultural land use through increased nutrients including TN and TP. These results indicate that increased urban and agricultural land use in the watersheds had directly and indirectly affected the physicochemical characteristics and benthic macroinvertebrate communities in streams. Our findings emphasize the need to develop more elaborate environmental management and restoration strategies to improve the water quality and biological status of streams.
... Factorial experiments are essential to understand and quantify the effects of certain pressures and stressors in the environment. In particular in a multi-stressor environment, experiments need to be able to disentangle individual stressors and their interactions (Graeber et al. 2017;Piggott et al. 2015). Mesocosms can bridge laboratory and field experiments by reducing environmental complexity while maintaining essential background conditions (Fig. 1, reviewed by Stewart et al. 2013). ...
... In the case of diffuse, temporal or spatial episodes of stressors, their experimental investigation is often difficult because the short-term transfer of experiments or their operation at multiple sites is often not possible. It is thus a challenge to develop suitable test systems that are flexible enough to analyse a wide range of both constant and pulsed stressors, and that can account for possible environmental gradients in river networks (Beermann et al. 2018;Graeber et al. 2017;Piggott et al. 2015). ...
... For example, a manipulation of basal resources by nutrient enrichment can be crossed with altered hydromorphology through siltation (Beermann et al. 2018;Graeber et al. 2017). Such settings help to elucidate the unique and joint effects of multiple stressors on key ecosystem processes and consequently ecosystem functioning. ...
Article
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A key research aim for lotic ecosystems is the identification of natural and anthropogenic pressures that impact ecosystem status and functions. As a consequence of these perturbations, many lotic ecosystems are exposed to complex combinations of non‐chemical and chemical stressors. These stressors comprise temperature fluctuations, flow alterations, elevated solute loads, or xenobiotics, and all these factors can pose stress upon aquatic ecosystems on different temporal, spatial and biological scales. Factorial experiments are essential to reveal causal relationships especially between combined stressors and their effects in the environment. However, experimental tools that account for the complexity of running waters across different ecosystem compartments, levels of biological organization, natural or anthropogenic environmental gradients, and replicability are rare. Here we present a new research infrastructure consisting of streamside mobile mesocosms (MOBICOS) that allows analysing the effects of stressors and stressor combinations through multifactorial experiments in near‐natural settings and across anthropogenic pressure gradients. Consisting of eight container‐based running water laboratories operated as bypasses to running surface waters, MOBICOS combines in situ real‐time monitoring of physicochemical and biological parameters with manipulative experiments across ranges of environmental conditions. Different flume types can be set up within MOBICOS to separate and combine different ecosystem compartments (pelagic, epibenthic and hyporheic zones) in a flexible and modular way. Due to its compact design, the MOBICOS units can be shifted easily to particular sites of interest. Furthermore, simultaneous operation of multiple MOBICOS units at different sites allows the integration of natural gradients in multi‐factorial experiments. We highlight the versatility of the MOBICOS experimental infrastructure with two case studies addressing 1) hydraulic control of lotic biofilms and 2) pollution‐induced community tolerance of biofilms along an environmental gradient. The modular and mobile MOBICOS units have the potential to significantly advance our understanding of causal relationships between natural environmental oscillations, anthropogenic stressors, and their combined ecological impacts on lotic aquatic ecosystems beyond existing stream mesocosm approaches. This article is protected by copyright. All rights reserved.
... Moreover, temperature was measured throughout the experiment in each channel using HOBO TidBit temperature loggers (logging interval 30 min). Macroinvertebrates were introduced to the channels on April 12th, 2010 using the procedure described in Graeber et al. (2017). In brief, macroinvertebrates were collected from Lemming stream using kick sampling along a reach of approximately 500 m. ...
... In total, 120 kick samples were transferred to each mesocosm channel. Graeber et al. (2017) showed that this method provided a community structure in the mesocosm channels that was comparable to Lemming stream. ...
Article
We exposed twelve mesocosm stream channels and four instream channels to one, two, and four pulses of the insecticide lambda-cyhalothrin (0.1 ug L⁻¹) applied at two day intervals, each pulse lasting 90 minutes. Unexposed controls were included. We monitored macroinvertebrate taxonomic composition in the channels and in deployed leaf packs one day before and 29 days after the first exposure. Further, we measured drift in and out of the channels and leaf litter decomposition. Lambda-cyhalothrin exposures induced significantly increased drift in both experiments especially for Gammarus pulex, Amphinemura standfussi, and Leuctra spp. Macroinvertebrate taxonomic composition increasingly changed with increasing number of lambda-cyhalothrin exposures being most pronounced in the mesocosm channels. Further, leaf decomposition significantly decreased with increasing number of exposures in the mesocosm channels. Our study showed that species with predicted highest sensitivity to lambda-cyhalothrin were primary drivers of significant changes in taxonomic composition lasting for at least one month despite continuous recolonization of exposed channels from upstream parts of the natural stream and from the water inlet in the mesocosm channels. The overall results highlight the importance of sequential exposures to insecticides for understanding the full impact of insecticides on macroinvertebrates at the community level in streams.
... Tackling multiple stressor effects requires a set of different approaches. Factorial experimental approaches have a strong potential to identify stressor effects and often highlight the role of stressor interactions (e.g., Townsend et al., 2008;Rotter et al., 2013;Schmitt-Jansen et al., 2016;Graeber et al., 2017;Beermann et al., 2018;Polst et al., 2018). Data-driven statistical analyses of large monitoring programs from catchment to national and continental scale (e.g., Leps et al., 2015;Feld et al., 2016;Birk et al., 2020) have significantly advanced our understanding of multiple stressor effects in real-world scenarios. ...
... Our study design is not suitable to detect the types of interactions between stressors. This would require experimental testing (e.g., Graeber et al., 2017;Beermann et al., 2018;Polst et al., 2018) in addition to the field data analyses as performed here. However, by revealing likely interconnections between stressors, our study provides a set of different stressor and response variables as relevant candidates for an experimental testing of interactions in multi-factorial experiments in the future. ...
Article
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Meeting ecological and water quality standards in lotic ecosystems is often failed due to multiple stressors. However, disentangling stressor effects and identifying relevant stressor-effect-relationships in complex environmental settings remain major challenges. By combining state-of-the-art methods from ecotoxicology and aquatic ecosystem analysis, we aimed here to disentangle the effects of multiple chemical and non-chemical stressors along a longitudinal land use gradient in a third-order river in Germany. We distinguished and evaluated four dominant stressor categories along this gradient: (1) Hydromorphological alterations: Flow diversity and substrate diversity correlated with the EU-Water Framework Directive based indicators for the quality elements macroinvertebrates, which deteriorated at the transition from near-natural reference sites to urban sites. (2) Elevated nutrient levels and eutrophication: Low to moderate nutrient concentrations together with complete canopy cover at the reference sites correlated with low densities of benthic algae (biofilms). We found no more systematic relation of algal density with nutrient concentrations at the downstream sites, suggesting that limiting concentrations are exceeded already at moderate nutrient concentrations and reduced shading by riparian vegetation. (3) Elevated organic matter levels: Wastewater treatment plants (WWTP) and stormwater drainage systems were the primary sources of bioavailable dissolved organic carbon. Consequently, planktonic bacterial production and especially extracellular enzyme activity increased downstream of those effluents showing local peaks. (4) Micropollutants and toxicity-related stress: WWTPs were the predominant source of toxic stress, resulting in a rapid increase of the toxicity for invertebrates and algae within only one order of magnitude below the acute toxic levels. This toxicity correlates negatively with the contribution of invertebrate species being sensitive towards pesticides (SPEARpesticides index), probably contributing to the loss of biodiversity recorded in response to WWTP effluents. Our longitudinal approach highlights the potential of coordinated community efforts in supplementing established monitoring methods to tackle the complex phenomenon of multiple stress.
... Benthic macroinvertebrates in nature are affected by various concurrently occurring environmental factors operating at multiple spatio-temporal scales. Some of these factors include physicochemical parameters (Collier et al., 1998), hydrological regimes (White et al., 2018), land use patterns (Helms et al., 2009), habitat type (Graeber et al., 2017), sediment characteristics (Jones et al., 2012), biotic interaction (Verschut et al., 2015) etc. This complex interaction makes it difficult to characterize the individual effects of each factor (Rempel et al., 2000). ...
... The high residual value showed that the parameters studied here had little influence on macroinvertebrate assemblages. The other parameters which could explain the variation in macroinvertebrate assemblages could be sediment type (Peeters et al., 2004), habitat characteristics (Graeber et al., 2017), biological factors (Verschut et al., 2015) etc. Besides, the study only considered headwaters and used local environmental conditions in explaining the variation in the BMIs assemblages. Moreover, the scale of analysis could also have yielded such high residual value. ...
Article
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The distribution of benthic macro invertebrates (BMIs) is affected by various environmental factors. Understanding their response to these factors is a key to assessing freshwater quality. The aim of this research is to understand the influence of different environmental parameters on BMIs assemblages in the headwaters of Bagmati River. The BMIs were sampled following a multi-habitat sampling protocol and the – hydrological and physico-chemical parameters were measured using standard methods. The relationship between environmental parameters and macro invertebrate assemblages was analyzed through Multivariate analysis - Redundancy Analysis and Variation Partitioning. Stream discharge, pH and Dissolved Oxygen were selected for multivariate analysis through backward elimination method. pH and Dissolved Oxygen were important contributing factors explaining the variation in BMIs community. Physico-chemical parameters were found to be the most important group of variables explaining the variation in macro invertebrate assemblages. Only about twenty-five per cent of the variation in the BMIs community was explained by the model so the parameters studied here do not have a high degree of explanatory power.
... 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). ...
... Had the manipulative period been longer than 18 days, the negative effects of chronic N and P enrichment which appeared in the drift after two weeks might have also manifested themselves in the benthos. Longer multiple-stressor mesocosm experiments (ideally over several months) would allow one to more comprehensively assess the effects of nutrient enrichment on stream macroinvertebrate communities, even though one of the first such experiments, conducted by Graeber et al. (2017) in Denmark, found no significant response of macroinvertebrate community composition to eight weeks of nutrient enrichment. ...
Article
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.
... For instance, Von Bertrab et al. (2013) found that the chemical composition of fine deposited sediment, especially the C/N ration, was able to effectively alter the species composition and community structure. Similar findings were reported by Sponseller et al. (2001), Stoll et al. (2016) and Graeber et al. (2017), who depicted habitat structure and geomorphological features strongly affected benthic communities and spatial distribution. In our study, the variations of macroinvertebrate communities and biotic indices could be partly explained by sedimental parameters, however, the explanatory variation could also be alternatively interpreted by water parameters. ...
Article
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Urban estuaries are amongst the most severely altered systems worldwide and undergo a wide range of ecological crises such as habitat destruction, nutrient enrichment and hydrodynamic alterations, resulting in an irreversible loss of biodiversity as well as a further environmental deterioration. Differentiating the main driving forces of multiple stressors is of utmost importance to provide beneficial insights for environmental restoration and management. In the present study, comprehensive investigations and multivariate approaches were performed to reveal the spatio-temporal variations of benthic macroinvertebrate communities and biotic indices and to examine their responses to environmental alterations within a highly urbanized fluvial-estuarine system. The nutrient levels gradually dwindled from urban fluvial sections to estuarine sections, meanwhile, macro-invertebrate community composition and dominant species considerably varied along the estuarine gradient. Overall, environmental parameters, macroinvertebrate communities and biotic indices varied significantly among sections and seasons. Salinity, dissolved oxygen, ammonia, total nitrogen, chemical oxygen demand and total organic carbon significantly explained the spatio-temporal variations of macroinvertebrate communities and biotic indices. Despite some inconsistencies in assessment outcomes, all indices revealed that urban fluvial sections of the Pearl River Estuary were disturbed, more or less severe depending upon the index. Among the tested indices, AMBI, BENTIX and average taxonomic distinctness (Δ +) presented better performance in assessing the ecological quality status and showed high responses to environmental stresses. More importantly, the relative contribution of water parameters vastly overrode sediment parameters in shaping variations of macro-invertebrate communities and biotic indices, demonstrating that anthropogenic activities (e.g., discharge of municipal and industrial sewage) directly altered the benthic community composition and diversity.
... They are also taxonomically diverse and relatively easy to identify (at least at the genus or family level). Invertebrate assemblages integrate environmental changes over several months [26], and examining the structure and composition of such assemblages has the potential to relevantly inform on the ecological status of water bodies [19,[27][28][29][30][31] and to demonstrate the effects of past and present environmental degradation [31,32]. ...
Article
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Tropical rivers are strongly influenced by stormwaters, pollutants and agro-pastoral activities. These systems are no longer able to maintain their native biota. Therefore, it seems important to understand how biological assemblages are driven by environmental gradients at different spatial scales. However, information on the relationships between the distribution of aquatic macroinvertebrates and environmental variables remains scarce in Cameroon. To improve our knowledge on the drivers of such distributions, a study was carried out at 11 contrasted sites from three catchments located in West Cameroon. This study aimed at understanding the spatio-temporal variations of 19 taxonomic metrics calculated for the benthic macroinvertebrate assemblages of these sites sampled during 13 months, concurrently with physico-chemical analyses of water quality. Two hundred and twelve taxa were caught. Diptera(rf-S), Shannon-Wiener diversity, 1–GOLD, total richness, Pielou evenness and Heteroptera(rf-S) revealed their high ability to respond to anthropogenic pressures or disturbances. Conductivity, water temperature, dissolved oxygen, nitrates, total hardness and alkalinity were identified as the main physico-chemical drivers of the taxonomic structure of benthic assemblages. These results will allow further exploration of the implementation of a tool for monitoring the ecological quality of West Cameroon rivers.
... It has also been shown that in-stream nitrate removal by denitrification is higher under high hyporheic exchange than low hyporheic exchange when there is sufficient organic matter and anoxic microzones (Harvey et al., 2013;Sjodin et al., 1997). Fine sediment (FS) (grain size < 0.2 mm) clogging -defined as deposition and intrusion of suspended sediments into the hyporheic zone -was found to have a substantial impact on the aquatic community, including the microbial community and their habitat (Graeber et al., 2017;Matthaei et al., 2010;Townsend et al., 2008). However, its effects on the nutrient net-change of the hyporheic zone have not yet been systematically assessed. ...
Article
The hyporheic zone underneath stream channels is considered a biogeochemical hotspot reducing nutrient loads being transported downstream due to its high surface-to-volume ratio in combination with the hyporheic exchange. However, the effect of environmental stressors such as high amounts of fine sediment (FS; grain size <0.2 mm) on nutrient cycling in the hyporheic zone are not well understood. Physical clogging caused by fine sediment (FS) decreases the hyporheic exchange, thus, diminishing its potential to reduce nutrient loads despite increasing its surface-to-volume ratio. We determined the effect of physical clogging on nutrient cycling based on net change rates of dissolved inorganic nitrogen (DIN; nitrate-N, ammonium-N), soluble reactive phosphorus (SRP), and dissolved organic carbon (DOC) for a sand and gravel hyporheic zone. We performed three experimental runs in 12 flumes with four-week duration each following a factorial design. First, we determined nutrient cycling in sand and gravel in absence of clogging, and then tested the clogging effect for each sediment type under increasing clogging (0-480 g of FS addition increasing by 60 g per level). Without clogging, gravel acted as a source of nitrate-N; and both sand and gravel released SRP. Regardless of the clogging level and the resulting reduced hyporheic exchange, we found no changes in DOC and nitrate-N dynamics but net-release of ammonium-N and SRP for gravel. In contrast, in sand, physical clogging inhibited DOC release for flumes with the higher FS. We propose that not physical clogging but DOC availability limited the nutrient uptake, as molar ratios of DOC to DIN and SRP ranged 1.2–1.5 and 77–191, respectively, indicating severe C limitation of N-uptake and partial C limitation of P-uptake. Our results suggest an interplay between nutrient molar ratios and physical clogging, which emphasize the interactions between hydrology and the stoichiometry of organic carbon, nitrogen and phosphorus in the hyporheic zone.
... Example: Hydrological stress (river low flow) but not nutrient enrichment showed a significant effect on the benthic macroinvertebrate community composition in a lowland stream experiment (Graeber et al., 2017). ...
Chapter
The article serves to introduce the environmental issue of ever-increasing multiple stressors acting on streams and rivers globally. It presents the most relevant stressors and outlines the state of knowledge in multi-stressor research. Stressor interactions are well documented, but full understanding of the cause-effect relationships remains scarce. This poses high uncertainties to predicting and effectively managing multi-stressor effects. Both a refined analytical approach and integrative, adaptive environmental management offer solutions to this intricate problem.
... In other words, altered flow regime will affect water quality (e.g., nutrient concentrations, oxygen saturation, and water temperature), which in turn will impact the biota (Lobanova et al., 2016;Stefanidis et al., 2018). In general, interactions between flow and flow-related factors may result in unexpected ecological responses, as many scientists have recently pointed out (Calapez et al., 2018;Graeber et al., 2017;Segurado et al., 2018) with experimental and other studies focused on multiple stressor interactions and their effects on aquatic biota. What this means for estimating ecological flows is that in cases where other factors act in concert with hydrologic change, identifying possible significant interactions is important for providing more accurate thresholds of ecologically meaningful flow regime. ...
... In other words, altered flow regime will affect water quality (e.g., nutrient concentrations, oxygen saturation, and water temperature), which in turn will impact the biota (Lobanova et al., 2016;Stefanidis et al., 2018). In general, interactions between flow and flow-related factors may result in unexpected ecological responses, as many scientists have recently pointed out (Calapez et al., 2018;Graeber et al., 2017;Segurado et al., 2018) with experimental and other studies focused on multiple stressor interactions and their effects on aquatic biota. What this means for estimating ecological flows is that in cases where other factors act in concert with hydrologic change, identifying possible significant interactions is important for providing more accurate thresholds of ecologically meaningful flow regime. ...
... In other words, altered flow regime will affect water quality (e.g., nutrient concentrations, oxygen saturation, and water temperature), which in turn will impact the biota (Lobanova et al., 2016;Stefanidis et al., 2018). In general, interactions between flow and flow-related factors may result in unexpected ecological responses, as many scientists have recently pointed out (Calapez et al., 2018;Graeber et al., 2017;Segurado et al., 2018) with experimental and other studies focused on multiple stressor interactions and their effects on aquatic biota. What this means for estimating ecological flows is that in cases where other factors act in concert with hydrologic change, identifying possible significant interactions is important for providing more accurate thresholds of ecologically meaningful flow regime. ...
Chapter
Mountains and mountain rivers provide a multitude of invaluable goods and services to a profound portion of the planet’s population. As “water towers” of the Earth mountains are sources of the mightiest world rivers and play a pivotal role for global biodiversity, freshwater, and sediment supply. Distinct morphological, climatic, hydrological, hydrochemical, and biological features of mountainous river ecosystems, compared to lowland ones, make them particularly fragile and vulnerable to human interference. Despite a number of remote mountain areas and rivers still remaining intact from direct human pressures, the majority of mountain ecosystems, are being increasingly threatened by adverse local and global changes driven by market economy. To efficiently conserve and sustainably use mountain ecosystems and contribute to the survival of the planet, it is critical to change our standards and life attitudes by realizing and appreciating our immediate connection to the global ecosystem, change attitudes and current consumption patterns, and stimulate the ways our global society functions and interacts with the natural environment.
... In other words, altered flow regime will affect water quality (e.g., nutrient concentrations, oxygen saturation, and water temperature), which in turn will impact the biota (Lobanova et al., 2016;Stefanidis et al., 2018). In general, interactions between flow and flow-related factors may result in unexpected ecological responses, as many scientists have recently pointed out (Calapez et al., 2018;Graeber et al., 2017;Segurado et al., 2018) with experimental and other studies focused on multiple stressor interactions and their effects on aquatic biota. What this means for estimating ecological flows is that in cases where other factors act in concert with hydrologic change, identifying possible significant interactions is important for providing more accurate thresholds of ecologically meaningful flow regime. ...
Chapter
The modification of sediment and flow regimes caused by damming and river regulation has deleterious effects on the ecological and morphological river processes. This alteration of river systems triggered the implementation of safeguarding environmental flows (e-flows) defined as “the quantity, timing, and quality of water flows required to sustain freshwater and estuarine ecosystems and the human livelihoods and wellbeing that depend on these ecosystems”. In the last decades, physical habitat simulation approaches emerged as fundamental stand-alone or supplementary methods for e-flow assessment. These approaches combine three main components: (1) hydraulic simulation, (2) habitat suitability modeling, to determine the quality of the available habitat, and (3) hydrological analyses (under current and climate change scenarios). E-flow regimes are finally defined, by assessing the spatial and temporal habitat variability for the target taxa or community, after combining these three components. During the process of physical habitat simulation some river processes, such as sediment transport and morphological changes, are often neglected while uncertainties arise from every component. We reviewed the elements that should be considered in every component of the physical habitat simulation to reduce uncertainties with emphasis on the actual trends on the topic and how sediment transport and river morphodynamics can be included within this methodological framework.
... In other words, altered flow regime will affect water quality (e.g., nutrient concentrations, oxygen saturation, and water temperature), which in turn will impact the biota (Lobanova et al., 2016;Stefanidis et al., 2018). In general, interactions between flow and flow-related factors may result in unexpected ecological responses, as many scientists have recently pointed out (Calapez et al., 2018;Graeber et al., 2017;Segurado et al., 2018) with experimental and other studies focused on multiple stressor interactions and their effects on aquatic biota. What this means for estimating ecological flows is that in cases where other factors act in concert with hydrologic change, identifying possible significant interactions is important for providing more accurate thresholds of ecologically meaningful flow regime. ...
Chapter
In all available methodologies for the assessment of the environmental flow requirements, a sufficient knowledge of the natural hydrological regime is essential. In this chapter the hydrological data that are required in environmental flow assessment studies, their main characteristics, and their importance as well as the specific challenges in the case of mountainous areas are analyzed. The various available data sources, the measurement and processing of hydrological data, and the utilization of modeling techniques for the estimation of streamflow data in the case of ungauged or poorly gauged watersheds and for the naturalization of streamflow data are also presented. A short description of hydrological data series analysis for the determination of environmental water requirements is provided as well. Finally, sources for further reading are provided in each section.
... Macroinvertebrate abundance and composition were also affected by the discharge, with more macroinvertebrates and higher abundances of shredders to higher velocities. More macroinvertebrates, and particularly of periphyton grazers may potentially affect periphyton biomass and composition (Allan and Castillo, 2007;Feminella et al., 1989;Graeber et al., 2017;Rosemond et al., 2000). However, our results did not indicate an effect of grazer macroinvertebrates on periphyton biomass or life form composition. ...
Article
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Climate-induced changes in precipitation and land-use intensification affect the discharge of streams worldwide, which, together with eutrophication and loss of riparian canopy, can affect periphyton biomass and composition, and therefore, ultimately the stream functioning. We investigated the responses of periphyton biomass and life-forms (i.e., high profile, low profile and motile) to these changes applying an experimental approach by modulating nutrients (nutrient diffusion substrates enriched with 0.5 M NH4NO3 + 0.031 M KH2PO4 and without nutrient enrichment) and light availability (50% shade and full light) along a gradient in discharge ranging from 0.46 to 3.89 L/s (0.7 to 6.5 cm/s) in twelve large-sized (12- m long) outdoor flumes resembling lowland streams. We also analysed the potential effects of other environmental variables including macroinvertebrates on the responses of periphyton to discharge, nutrients, and light. Light and nutrient availability drastically affected periphyton biomass and composition responses to discharge. Periphyton biomass decreased with increasing discharge when shaded but this did not happen when exposed to full light. Under full light conditions, nutrient enrichment mediated an increase in the periphyton biomass with increasing discharge, possibly reflecting an increased metabolism, but this did not happen under non-enriched conditions. Enrichment further affected the compositional responses of periphyton to discharge, with an increase in the biomass of motile, fast-growing, small-sized flagellated at low discharge conditions, and mitigating a loss of high profile periphyton under higher discharges. Light did not affect periphyton composition, and the abundance or feeding-group composition of the macroinvertebrates did not affect biomass or composition of the periphyton either. Our results suggest that nutrient enrichment and light play an important synergistic role in the responses of the periphyton biomass and composition to discharge and emphasize the relevance of riparian canopy conservation and eutrophication control to avoid periphyton growth under increased discharge scenarios in small lowland streams.
... Functional groups with near zero species weights show either no response or one that is unrelated to the patterns represented in the PRC. Furthermore, the direction of the species weights determines the direction of the response of the species to the treatments (Van den Brink and Ter Braak, 1998;Graeber et al., 2017). Separate PRC were performed for pelagic and benthic mesocosms; the respective reference mesocosms were used as control. ...
Article
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A mesocosm experiment was conducted in a temperate eutrophic lake with the hypotheses: 1) the addition of a labile form of DOC would trigger a more pronounced response in phytoplankton biomass and composition compared with a non-labile form; 2) DOC addition would increase phytoplankton biomass by co-inserting organic nutrients for phytoplankton growth; 3) DOC addition would change phytoplankton composition, in particular towards mixotrophic taxa due to higher DOC availability; and that 4) there would be differences in phytoplankton responses to DOC addition, depending on whether sediment was included or not. We used two types of mesocosms: pelagic mesocosms with closed bottom, and benthic mesocosms open to the sediment. The experiment ran for 29 days in total. The DOC addition occurred once, at Day 1. Besides the control, there were two treaments: HuminFeed® (non-labile DOC) at a concentration of 2 mg L−1 , and a combination of 2 mg L−1 HuminFeed® and 2 mg L−1 DOC from alder leaf leachate (labile). Responses were detected only in the treatment with alder leaf extract. Ecosystem processes responded immediately to DOC addition, with the fall in dissolved oxygen and pH indicating an increase in respiration, relative to primary production (Day 2). In contrast, there was a delay of a few days in structural responses in the phytoplankton community (Day 6). Phytoplankton biomass increased after DOC addition, probably boosted by the phosphorus released from alder leaf extract. Changes in phytoplankton composition towards mixotrophic taxa were not as strong as changes in biomass, and happened only in the pelagic mesocosms. With the DOC addition, diatoms prevailed in benthic mesocosms, while the contribution of colonial buoyant cyanobacteria increased in the pelagic ones. This study points towards the necessity to look in greater detail at specific responses of phytoplankton to DOC concentration increases considering lake-habitat and sediment influence-
... The approach taken has been to design flow-biota relationships (Graeber et al., 2014(Graeber et al., ,2017Poff and Zimmermann, 2010) between flow regime variables and the ecological quality ratio for three biotic indices for macroinvertebrates, macrophytes and fish based on a number of Danish stream sites. Based on 72 flow regime variables, symbolic regression was used to develop a number of models that could potentially predict the relationship between flow regime variables and EQR for fish, macroinvertebrates and macrophytes (Graeber et al., 2014). ...
Article
Study region Two large-scale catchments in Denmark: Ringkøbing fiord and Mid-Zealand catchments. Study focus Future changes in hydrological regime, extremes, groundwater levels and ecological quality ratio (EQR) for fish were assessed. Based on an ensemble of 17 bias-corrected regional climate models forced by the emission scenario RCP8.5, a dry, a medium and a wet model were identified for the future period 2071–2100. Changes in water balances for catchments, impacts on groundwater level and fish ecological quality ration (fish EQR) were evaluated. The impact changes were based on an integrated, transient, coupled groundwater and surface-water flow model, set up with a horizontal resolution of 200m × 200m for the two catchments. New hydrological insights for the region Strengths and weaknesses of EQR assessments based on symbolic regression methods compared to expert assessments based on flow calendar and max flow changes in percent exceedance thresholds (Q95) were identified. While the modelled impact of climate change on monthly flow and flow calendar follows the same pattern at all monitoring stations, the impact on groundwater level and fish EQRs are more complex, and somewhat ambiguous across realisations and catchments.
... Hydroperiod is critical for ecological process in wetland and effects of water level fluctuation on macroinvertebrates have attracted much attention in recent years (Steinman et al., 2003). Cross-regional water diversion have significant adverse effects on aquatic habitats, affecting the abundance and richness of macroinvertebrate community , Fierro et al., 2017, Graeber et al., 2017, Monroy et al., 2017, Schneider and Petrin, 2017. And the effects in lake ecosystems are the greatest in shallow areas, where even small changes can result in the conversion of a standing-water environment to one where sediments are exposed to air, or vice versa. ...
... Moreover, biotic metrics do not allow the evaluation of species-specific thresholds (Wagenhoff et al., 2017;Waite and Van Metre, 2017). Furthermore, it is well documented that the biotic responses to stressors can be different across diatoms, macroinvertebrates (invertebrates), and fish assemblages and thus different assemblages may provide different information about relevant stressors (Schinegger et al., 2016;Graeber et al., 2017;Kuzmanovic et al., 2016;Waite et al., 2019). ...
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This study is part of the regional stream-quality assessment (RSQA) conducted by the U.S. Geological Survey (USGS) National Water Quality Assessment (NAWQA) project. The purpose of this study is to examine small streams along land-use and stressor gradients at the regional scale and to evaluate the relative importance of instream stressors on diatom, macroinvertebrate, and fish assemblages. In 2015, the RSQA project assessed stream quality in 82 wadeable streams that were selected along an urban land-use gradient in the Pacific Northwest Region (PNW) of the United States. This study evaluates the effects of four major categories of measured instream stressors-flow (i.e. alteration), water quality, habitat, and contaminants (in water and sediment)-on stream biota. We used gradient forest (GF) models to evaluate taxon specific responses to the various stressors for the three biotic assemblages. Results for diatom, invertebrate and fish assemblages showed that several environmental variables including substrate size, dissolved oxygen, and two or more different contaminants were selected in each of the GF models. In general, all three assemblages were negatively associated with any contaminant measures above zero, except the more tolerant taxa in each assemblage, which responded positively to contaminants. Total nitrogen (TN) and total phosphorus (TP) were important in both the diatom and invertebrate GF models but not in the fish models, which were related to temperature and stream flow. TP and TN were the top two variables for diatom GF models and various taxa responded at a range of nutrient concentrations; however, some taxa responded at low concentrations, for example around 0.02 for TP and 0.5 mg/L for TN. In general, the three biotic assemblages responded to multiple stressors following general patterns of known sensitive versus tolerant taxa for each of the biotic groups studied, yet the GF models allow us to explore taxon specific responses. For example, most of the sensitive Ephemeroptera, Plecoptera, Trichoptera invertebrate taxa (EPT) responded negatively when any contaminant increased above zero; yet some taxa such as the tolerant Trichoptera Cheumatopsyche responded positively to contaminants and many of the other stressors. The findings of this study demonstrate the value of using multiple assemblages to monitoring stressor gradients associated with urban stream systems and the importance of evaluating the responses of individual taxa to stressors.
... For example, natural banks provide necessary structures for macroinvertebrate assemblages, like habitat in the form of hollow banks and tree roots, and habitat elements like wet-dry gradients and associated vegetation (Flecker and Allan, 1984;Garcia et al., 2012;Tolkamp, 1980). High habitat diversity may mitigate the effects of multiple stressors such as low flow and fine sedimentation (Graeber et al., 2017). These morphological structures can act as stressors when they are in a non-natural state or even absent. ...
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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.
... Elevated nutrient levels can lead to eutrophication which can have indirect impacts on macroinvertebrate communities through degradation of habitat structure and reduced oxygen levels (Correll, 1998;Smith et al., 1999;Cook et al., 2018). At very high concentrations, nutrients have also been shown to have direct toxic effects on aquatic macroinvertebrates (Camargo et al., 2005;Dalu et al., 2017;Graeber et al., 2017;Zhang et al., 2018). Agricultural practices which increase catchment erosion can lead to the deposition of fine sediment in streams (Jones et al., 2012). ...
Article
Multiple stressors affect stream ecosystems worldwide and their interactions are of particular concern, with gaps existing in understanding stressor impacts on stream communities. Addressing these knowledge gaps will aid in targeting and designing of appropriate mitigation measures. In this study, the agricultural stressors fine sediment (ambient, low, medium, high), phosphorus (ambient, enriched) and nitrogen (ambient, enriched) were manipulated simultaneously in 64 streamside mesocosms to determine their individual and combined effects on the macroinvertebrate community (benthos and drift). Stressor levels were chosen to reflect those typically observed in European agricultural streams. A 21-day colonisation period was followed by a 14-day manipulative period. Results indicate that added sediment had the most pervasive effects, significantly reducing total macroinvertebrate abundance, total EPT abundance and abundances of three common EPT taxa. The greatest effect was at high sediment cover (90%), with decreasing negative impacts at medium (50%) and low (30%) covers. Added sediment also led to higher drift propensities for nine of the twelve drift variables. The effects of nitrogen and phosphorus were relatively weak compared to sediment. Several complex and unpredictable 2-way or 3-way interactions among stressors were observed. While sediment addition generally reduced total abundance at high levels, this decrease was amplified by P enrichment at low sediment, whereas the opposite effect occurred at medium sediment and little effect at high sediment. These results have direct implications for water management as they highlight the importance of managing sediment inputs while also considering the complex interactions which can occur between sediment and nutrient stressors.
... Similar association between macroinvertebrate communities and the sediment particle size has been obtained from field and experimental studies (Connolly et al., 2016;Milesi et al., 2017). Substrate is generally recognized as an important factor influencing the macroinvertebrate community structure (Beermann et al., 2017;Graeber et al., 2017). In the current study, sites in the headwater streams were characterized by high substrate heterogeneity with streambeds made of boulder and cobble whereas the sites located in the lower reaches of the rivers were characterized by lower levels of heterogeneity with streambeds made mostly of sand. ...
Article
Rapid agricultural development has induced severe environmental problems to freshwater ecosystems. In this study, we aimed to examine the structure and environmental determinants of macroinvertebrate assemblages in an agriculture dominated Lake Chaohu Basin, China. A cluster analysis of the macroinvertebrate communities identified four groups of sites that were characterized by significantly different macroinvertebrate species. These four groups of sites had concentric spatial distribution patterns that followed the variation in the environmental conditions from the less anthropogenically disturbed headwaters towards the more anthropogenically disturbed lower reaches of the rivers and the Lake Chaohu. Moreover, taxa richness decreased from the headwaters towards the Lake Chaohu. The increasing practice of agriculture has reduced the abundances and richness of pollution sensitive species while opposite effects on pollution tolerant species. The study identified substrate heterogeneity and nutrient concentrations as the key environmental factors regulating the changes in the macroinvertebrate communities. We propose that particular attentions should be paid to reduce the nutrient enrichment and habitat degradation in the Lake Chaohu Basin and similar agriculture dominated basins.
... For each flume, the benthic macroinvertebrates were taken from the source stream by standardised kick sampling along a reach of c. 500 m to construct a realistic stream environment (more details on the kick sampling can be found in Appendix S1). This macroinvertebrate colonisation approach has been shown to result in a macroinvertebrate composition similar to the one of the source stream (Graeber et al., 2017). ...
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Summary 1. Lowland stream ecosystems are subjected to multiple anthropogenic stressors, usually nutrient enrichment in combination with sedimentation of fine particles and low flow periods in summer. Here, we investigated the temporal development of the benthic algae community in response to these three stressors and linkages to the trait characteristics of the community to explore the mechanisms responsible for stress-induced community changes. 2. We investigated the response of benthic algae species composition, traits (life forms, cell size categories), biovolume and chlorophyll a (Chl-a) concentration to low flow in combination with nutrient enrichment and fine sedimentation in twelve large outdoor stream flumes (12 m long) resembling small streams in size and habitat characteristics. The experiment consisted of two phases: a normalflow phase followed by a low-flow phase (90% current velocity reduction), each spanning 4 weeks. We applied a eutrophication scenario (mean increases of 1.14–5.48 mg N/L and 0.01–0.06 mg P/L in the flumes for dissolved inorganic nitrogen and phosphate respectively) throughout the experiment. Under low flow, we supplemented this with a fine sedimentation scenario (>90% stream bed cover). We took samples once in the normal-flow phase and every week during the low-flow phase. 3. We observed strong responses in the benthic algae community to sudden changes in low flow and fine sedimentation, mediating rapid species turnover with a decreased algal biovolume and increased abundance of large, motile species. However, we did not observe any pronounced responses to nutrient enrichment. In contrast to the observations for other variables, we found a continuous increase in Chl-a concentration during low flow. This was likely due to continuous fine sedimentation during this phase, reducing light availability which probably resulted in an increase of cell-level Chl-a concentration in response to light limitation and lower rates of light-induced Chl-a degradation. 4. The rapid response of the benthic algal community to the applied stressors suggests that even short periods of major stressor exposure may significantly affect benthic algae in lowland systems. We suggest that short-term stress events may have cascading effects on several important ecosystem processes given the importance of benthic algae for the productivity of these systems.
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Although chalk aquifers are not too often associated with conduit flow, they are highly productive groundwater systems and, like limestone aquifers, they can be vulnerable to contamination when exposed to land use activities. The Danish carbonate rocks are generally recognized to be highly fractured and covered by thick Quaternary sediments. Fissure flow is pronounced, occurring in the upper 50–100 m due to Pleistocene glaciations. According to recently published maps of the distribution of karst in Europe, Denmark has no karst. However, this study concludes that karstified chalk and limestone aquifers are an important source of freshwater in Denmark. Four national datasets on karst features, groundwater flow, groundwater chemistry, and fish ecological quality ratio (EQR) data now indicate more heterogeneous structures and preferential flow pathways in the chalk and limestone aquifers than had been conceptualized and modelled with a national water resources groundwater/surface-water model in the recent past. This study provides new qualitative evidence that rapid and preferential flow of water and agrochemicals from the surface through thinner parts of the Quaternary cover layers, sinkholes and solution-enlarged fractures may likely impact the vulnerability of chalk and limestone aquifers. Additionally, due to the preferential flow system, some gaining streams discharged by karstified chalk and limestone aquifers show increased fish EQR values when using observed river daily discharge data instead of simulated daily discharge.
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Streams generally are affected by multiple stressors acting at different timescales. Periphyton, often the most important primary producer in these ecosystems , may respond to short-term impacts as well as to different long-term environmental conditions with potentially various changes in community structure. Here, we experimentally investigated the effects of sudden flow pulses on peri-phyton communities as a way to mimic extreme precipitation events in lowland streams that are predicted to occur more often with climate change in some regions. Using outdoor flumes, we allowed periphyton to colonise nutrient-diffusion substrates under two light conditions (50% shade and fully open) and nutrient availabilities (control, with access only to stream nutrients, and N-P-enriched) along a gradient in baseflows (0.43 to 2.17 L/s). After one month, we exposed the communities to a flow pulse (two-fold peak flow increase to simulate conditions of a potentially high disturbance) and analysed the responses of biomass and taxonomic composition. Flow pulse promoted periphyton growth in the lowest range of the baseflow but led to biomass reduction in the highest range. Light was the second major driver of biomass accrual, whereas nutrient enrichment had a strong effect on community composition both before and after the pulse (i.e., diatom dominance vs. green algae dominance in scenarios without and with enrichment, respectively). In all treatments, the flow pulse promoted a higher taxonomic richness, suggesting a partial reset of the succession of the periphyton communities. However, independent of flow and resources, periphyton communities showed low ecological resistance against the pulse with changes in chlorophyll a, biovolume and taxonomic richness to the pulse. We demonstrated that the effects of pulses on periphyton are similar in terms of biomass but varied strongly regarding composition depending on their initial structure, which is in turn mediated by the baseflow normally experienced by the systems, and on light and nutrient availability. Our results highlight the importance of testing multiple stressors, such as an increase in extreme events, under a wide range of environmental conditions
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• Environmental DNA (eDNA) from water samples is increasingly used to detect the presence and distribution of species in aquatic ecosystems. However, before implementing eDNA in monitoring programmes, various species-specific sampling or analytical issues remain to be resolved in order to minimize frequencies of false-positive and -negative results. For example, empty shells from freshwater pearl mussels (Margaritifera margaritifera) contain extractable DNA (chemical extraction from ground-up shells) suggesting a risk of false-positive samples at stream sites with extinct populations but with empty shell material remaining. • The aim of this study was to investigate whether empty and naturally degrading shells from M. margaritifera can cause false-positive eDNA signals in water samples. • Water samples were collected from outdoor stream channels (in Lemming, Denmark) with living freshwater pearl mussels or empty shell material (density ~10 individuals m⁻²) during a 3-week experimental period. Living freshwater pearl mussels were collected from Hemgravs stream in Sweden and transported to Denmark according to permissions granted by the Swedish and Danish authorities. • All water samples from stream channels containing empty shells were negative for eDNA indicating that eDNA traces in stream water are most likely to originate from living individuals located upstream of the sampling site. Water samples collected from stream channels containing living individuals of M. margaritifera were consistently positive for eDNA except for one sample (interpreted as a false negative). • The study shows that positive eDNA signals for freshwater pearl mussels most likely reflect the presence of living individuals. Consequently, we suggest that eDNA should be used to locate remaining population fragments of M. margaritifera in deep and turbulent streams, providing a platform for faster and more efficient decision making when launching investigative and mitigation initiatives.
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Despite the fact that leaf decomposition constitutes an important function in rivers, how multiple environmental stressors simultaneously affect it remains largely unknown. This study investigated the interactive effects of fine sediments (particle size: <2 mm; experimentally manipulated) and a specific nutrient (i.e., nitrate) on subsurface (hyporheic) leaf litter decomposition rate and macroinvertebrates in a gravel-bed river and its tributary in eastern Hokkaido, Japan. The experiment was conducted by measuring leaf litter decomposition of dried Alnus japonica leaves (3 ± 0.05 g) in benthic and hyporheic zones with and without sediment treatments at four sites that had a gradient of nitrate concentration. The decomposition rate was comparable between the two zones but was slowed down by sediment addition in the hyporheic zone. The functional responses were highly predictable for the individual stressors. Detritivore invertebrates were the main driving component of decomposition in the decreased leaf litter decomposition rate under a higher fine sediment condition, whereas higher nitrate accelerated the leaf litter decomposition rate by stimulated microbe-driven decomposition as well as detritivore feeding. Overall, the negative effect of fine sediment could be offset in the presence of nitrate while considering gross functional responses. We demonstrated the additive effects of fine sediment and nitrate on leaf litter decomposition in the hyporheic zone.
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Stream macroinvertebrates, as non-target organisms, may face with either a single or a complex stressor during a restoration treatment. We quantified the structural, phylogenetic, and functional responses to both single (water retention) and complex (water retention and grazing) stressors and analysed how the ecological quality changes, in order to reveal the potential unwanted consequences in a soda pan restoration. Species composition has been restructured and taxonomic diversity decreased significantly as a response to the complex stressor, while they did not change under the single stress. Neither the single nor the complex stressor influenced the phylogenetic diversity. Functional diversity showed mainly no or reversible changes. Changes in diversity metrics induced changes in Ecological Quality Ratios, but the ecological state decreased only under the complex stressor. Our results suggest that different facets of alpha diversity (taxonomic, functional and phyloge-netic) are complementary and provide different information about community assembly against different stresses. We can support the opinion that taxon, phylogenetic and functional diversity are proper metrics in their own way to assess the impact of stress, but it is necessary to apply them together. Ecological knowledge of this paper could be considered throughout future conservation planning and enhance restoration success in aquatic environments.
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The quality of the aquatic environment of high Andean lagoons was evaluated by means of multivariate statistical methods in two contrasting climatic periods. The water samples and benthic macroinvertebrates were collected in 22 sampling sites during the rainy and dry seasons. In each lagoon DO, DTS, EC, temperature and pH were determined in situ. The results revealed that the physicochemical parameters comply with the environmental quality standards for water, except COD and BOD5. In the PCA of the physicochemical parameters, the first two axes explained 73% of the total variation. The gradual analysis in pairs showed significant differences. The SIMPER analysis determined an average of four families of benthic macroinvertebrates per lagoon that showed more than 70% contribution. The ANOSIM revealed that Tragadero lagoon differs significantly from the others. The DistLM showed a value of 0.46 of coefficient of determination. Therefore, the quality of the environment of high Andean lagoons evaluated by means of multivariate statistical methods presents important differences or dissimilarities not only in the physicochemical characteristics of the water, but also in the composition of the benthic macroinvertebrate communities. Keywords: aquatic environment, high Andean lagoons, benthic macroinvertebrates, water quality.
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Changes in catchment land cover can impact stream ecosystems through altered hydrology and subsequent increases in sedimentation and nonpoint-source pollutants. These stressors can affect habitat suitability and water quality for aquatic invertebrates. We studied the impact of a range of physical and chemical stressors on aquatic insects, and tested whether the effects of these stressors differed in 3 habitat types: riffles, pools, and banks. Our study was conducted in Piedmont streams in Georgia (USA) where catchment development pressure and the potential for aquatic biodiversity loss are high. We sampled 3 replicates of riffle, pool, and bank habitats within a 100-m reach of 29 streams (11-126 km(2)) that varied in catchment land cover. Correlations between environmental variables and aquatic insects (both richness and density) within habitat types indicated that riffle habitats (vs pool and bank habitats) exhibited the strongest relations with environmental variables. Riffle assemblages were negatively affected by both physical (e.g., bed mobility) and chemical (e.g., specific conductance, nutrient concentrations) variables. The density of aquatic insects in pools was also correlated to physical and chemical variables, but there were few relationships with pool or bank richness or bank density. Because of greater relative impacts of disturbance in riffles versus banks, we found greater differences between riffle and bank richness in streams with greater sediment disturbance. The proportion of bank richness (bank richness/bank + riffle richness) increased with finer bed sediment (r(2) = 0.43) and increased bed mobility (r(2) = 0.35). We compared richness of facultative taxa (found in multiple habitats) between sites we characterized as minimally impacted and sediment-impacted. In riffles, richness of facultative taxa was lower in sediment-impacted vs minimally impacted sites (11.0 vs 20.2, p 0.002, t-test), but was similar for both disturbance groups in banks (20.1 vs 22.7, p > 0.05, t-test). Our results suggest that taxa richness may be retained in bank habitats when riffle quality is poor and banks may serve as a refuge in highly disturbed systems. Such shifts in the distribution of benthos may be an early warning indicator of biotic impairment and have implications for biomonitoring and maintenance of habitat.
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Re-meandering of degraded rivers is a frequently implemented measure in river restoration. A simple solution is reconnection of old meanders; however, its success likely depends on the reconnection method. We conducted a field study to analyze the benefits of a fullyreconnected (fully opened meander, blocked main channel) and a partially reconnected meander (opened downstream, pipe bypass from main channel upstream, still open main channel) for macroinvertebrate communities in a German lowland river. Immediately upon reconnection of the two meanders, habitat diversity, and macroinvertebrates were recorded for three years with sampling in spring and in summer each year. The results of a principal response curve analysis show that the macroinvertebrate community in the fully reconnected meander reflected main channel reference conditions after 1.5 years. The macroinvertebrate community composition was not improved relative to in-stream reference conditions within the partially reconnected meander, which could be attributed to the almost complete lack of flow changes that resulted in missing improvements of substrate diversity. Our results show that the meander reconnection method must sufficiently affect the basic hydromorphological requirements to achieve reference macroinvertebrate community composition. Measures including hydromorphological conditions are therefore recommended for employment in environmental management.
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Dissolved organic matter (DOM) is an important factor in aquatic ecosystems, which is involved in a large variety of biogeochemical and ecological processes, and recent literature suggests that it could be strongly affected by agriculture in different climates. Based on novel monitoring techniques, we investigated the interaction of climate and agriculture effects on DOM quantity and quality. To examine this, we took water samples over 2 years in two paired intensive and extensive farming catchments in each of Denmark (temperate climate) and Uruguay (subtropical climate). We measured dissolved organic carbon (DOC) and nitrogen (DON) concentrations and DOC and DON molecular fractions with size-exclusion chromatography. Moreover, we characterized DOM quality with absorbance and fluorescence measurements, as well as parallel factor analysis (PARAFAC). We also calculated the DOC and DON loads based on daily discharge measurements, as well as measured precipitation and air temperature. The fluvial DOM in the catchments in Uruguay was characterized by higher temporal variability of DOC and DON loads which were clearly to a higher temporal variability of precipitation and a DOM composition with rather plant-like character relative to the Danish catchments. Moreover, we found a consistently higher temporal variability of DOC and DON loads in the intensive farming catchments than in the extensive farming catchments, with highest temporal variability in the Uruguayan intensive farming catchment. Furthermore, the composition of DOM exported from the intensive farming catchments was consistently complex and always related to microbial processing in both Denmark and Uruguay. This was indicated by low C : N ratios, several spectroscopic DOM composition indices and PARAFAC fluorescence components. We propose that the consistent effect of intensive farming on DOM composition and the temporal variability of DOC and DON loads is related to similarities in the management of agriculture, which may have widescale implications for fluvial DOM composition, as well as related ecological processes and biogeochemical cycles.
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Surface and subsurface sediments in river ecosystems are recognized as refuges that may promote invertebrate survival during disturbances such as floods and streambed drying. Refuge use is spatiotemporally variable, with environmental factors including substrate composition, in particular the proportion of fine sediment (FS), affecting the ability of organisms to move through interstitial spaces. We conducted a laboratory experiment to examine the effects of FS on the movement of Gammarus pulex Linnaeus (Crustacea: Amphipoda) into subsurface sediments in response to surface water loss. We hypothesized that increasing volumes of FS would impede and ultimately prevent individuals from migrating into the sediments. To test this hypothesis, the proportion of FS (1–2 mm diameter) present within an open gravel matrix (4–16 mm diameter) was varied from 10 to 20% by volume in 2.5% increments. Under control conditions (0% FS), 93% of individuals moved into subsurface sediments as the water level was reduced. The proportion of individuals moving into the subsurface decreased to 74% at 10% FS, and at 20% FS no individuals entered the sediments, supporting our hypothesis. These results demonstrate the importance of reducing FS inputs into river ecosystems and restoring FS-clogged riverbeds, to promote refuge use during increasingly common instream disturbances.
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Small, permanent streams are at risk of becoming stagnant or intermittent because of hydrological changes induced by climate change, which can be further intensified by anthropogenic disruptions, such as water abstraction. Macroinvertebrate communities are vulnerable to such changes because they depend on stream hydromorphological regime. We conducted a fully controlled field experiment in 1 impacted and 1 unimpacted Danish lowland stream with contrasting nutrient availability. We used dams and diversions to create short-term (2-10 wk) stagnant and drought conditions, and we installed pools in the drought area to test their value as refugia for benthic macroinvertebrates. After 2 wk, community composition had changed significantly in all treatments in both streams. The abundance of Chironomidae increased and the abundance of mayflies (Baetis rhodani), stoneflies (Amphinemura standfussi, Leuctra nigra), caddisflies (Silo pallipes, Sericostorna personatum), the amphipod Gammarus pulex, and some Diptera taxa (Simuliidae, Dicranota sp.) decreased relative to the control. Diversity and total abundance did not change in the stagnant or drought treatments, so we do not consider these variables sensitive to effects of short-term flow reductions. Diversity decreased (unimpacted stream) or was not affected (impacted stream) in pools relative to the drought treatment. Thus, pools did not act as a substantial refugium for macroinvertebrates under extreme low-flow conditions. Current velocity and amount of deposited organic material explained most of the change in the macroinvertebrate community. Nutrient availability did not influence the response of the macroinvertebrate community to the treatments, probably because the physicochemical changes were exacerbated in the impacted stream and outweighed the expected higher resilience of this community. Our results clearly demonstrate that short-term stagnation and droughts in lowland streams can cause strong alteration of species composition.
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In this paper a novel multivariate method is proposed for the analysis of community response data from designed experiments repeatedly sampled in time. The long-term effects of the insecticide chlorpyrifos on the invertebrate community and the dissolved oxygen (DO)–pH–alkalinity–conductivity syndrome, in outdoor experimental ditches, are used as example data. The new method, which we have named the principal response curve method (PRC), is based on redundancy analysis (RDA), adjusted for overall changes in community response over time, as observed in control test systems. This allows the method to focus on the time-dependent treatment effects. The principal component is plotted against time, yielding a principal response curve of the community for each treatment. The PRC method distills the complexity of time-dependent, community-level effects of pollutants into a graphic form that can be appreciated more readily than the results of other currently available multivariate techniques. The PRC method also enables a quantitative interpretation of effects towards the species level.
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Reduction of flow constitutes one of the most severe human alterations to rivers, as it affects the key abiotic feature of these ecosystems. While there has been considerable progress in understanding the effects of reduced flow on benthic macroinvertebrates, cascading effects of flow reduction on dissolved oxygen concentrations (DO) have not yet received much attention. We compared the macroinvertebrate composition between reference conditions and a situation after several years of discharge reduction in the Spree River (Brandenburg, Germany). Community composition shifted from rheophilic species to species indifferent to flow conditions. Filter feeders were partially replaced by collector/gatherers, which likely reduces the retention of organic matter, and thus the self-purification capacity of the river section. These shifts were associated with low discharge during summer, cascading into daily DO concentration minima of less than 5 mg l−1 which prevailed 74% of the days in summer. This depletion of DO after flow reduction presumably caused the observed species turnover. Hence, flow reduction in lowland rivers may not only directly impair the ecological functions provided by benthic macroinvertebrates but may also act indirectly by depleting DO concentrations.
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Changes in the microdistribution of benthic macroinvertebrates were observed, between patches identified as refugia from high flow and the remaining benthic habitat, over a range of discharges in a small stream with prominent flow refugia. Total invertebrate abundances were similar across all patch types at baseflow, but local densities were higher in flow refugia after periods of high and fluctuating flow. Different species- and size-specific responses were observed: microdistributions of larval Chironomidae and small nymphs of the stonefly Leuctra nigra did not change with discharge. Conversely, the stonefly Nemurella pictetii and large nymphs of L. nigra were most abundant in refugia, relative to the remaining benthic habitat, during periods of high and fluctuating discharge. The interactive effects of leaf litter and local flow conditions on species microdistributions were investigated. In some seasons, some species may respond indirectly to hydraulic conditions through their direct response to litter mass. Observed microdistribution changes probably do not reflect very short-term reactions to individual flow events, but perhaps a longer-term response to seasonal flow conditions. These are some of the first field data implicating the role of in-stream flow refugia in macroinvertebrate community structure.
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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.
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Catchment riparian areas are considered key zones to target mitigation measures aimed at interrupting the movement of diffuse substances from agricultural land to surface waters. Hence, unfertilized buffer strips have become a widely studied and implemented "edge of field" mitigation measure assumed to provide an effective physical barrier against nitrogen (N), phosphorus (P), and sediment transfer. To ease the legislative process, these buffers are often narrow mandatory strips along streams and rivers, across different riparian soil water conditions, between bordering land uses of differing pollution burdens, and without prescribed buffer management. It would be easy to criticize such regulation for not providing the opportunity for riparian ecosystems to maximize their provision for a wider range of ecosystem goods and services. The scientific basis for judging the best course of action in designing and placing buffers to enhance their multifunctionality has slowly increased over the last five years. This collection of papers aims to add to this body of knowledge by giving examples of studies related to riparian buffer management and assessment throughout Europe. This introductory paper summarizes discussion sessions and 13 selected papers from a workshop held in Ballater, UK, highlighting research on riparian buffers brought together under the EU COST Action 869 knowledge exchange program. The themes addressed are (i) evidence of catchment- to national-scale effectiveness, (ii) ecological functioning linking terrestrial and aquatic habitats, (iii) modeling tools for assessment of effectiveness and costs, and (iv) process understanding enabling management and manipulation to enhance pollutant retention in buffers. The combined understanding led us to consider four principle key questions to challenge buffer strip research and policy.
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We provide a global assessment, with detailed multi-scale data, of the ecological and toxicological effects generated by inorganic nitrogen pollution in aquatic ecosystems. Our synthesis of the published scientific literature shows three major environmental problems: (1) it can increase the concentration of hydrogen ions in freshwater ecosystems without much acid-neutralizing capacity, resulting in acidification of those systems; (2) it can stimulate or enhance the development, maintenance and proliferation of primary producers, resulting in eutrophication of aquatic ecosystems; (3) it can reach toxic levels that impair the ability of aquatic animals to survive, grow and reproduce. Inorganic nitrogen pollution of ground and surface waters can also induce adverse effects on human health and economy.
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The Danish Monitoring Programme reveals that diffuse sources are currently the major source of nutrient input to the aquatic environment. Nutrient concentration and loading data for about 50 small agricultural catchments and seven undisturbed catchments reveal that agriculture is the major diffuse source, average annual nitrogen (N) and phosphorus (P) concentration and loading being respectively, 5.1- and 6.8-fold, and 2.7- and 3.9-fold greater in streams draining agricultural catchments than in streams draining undisturbed catchments during the period 1989–96. A statistical trend analysis (discharge adjusted Mann-Kendall seasonal test) applied to long-term time series (1967–96) in three streams revealed an upward trend in nitrate concentration in Skjern Å (p<0.1%), Odense Å (p=5.7%) and GudenÅ (p=11%) during the 15-year period 1967-81, whereas there was no significant trend during the following 15-year period (1982-96). There was a significant downward trend in P concentration in all three streams over the 30-year period. Statistical analysis of recent trends (1989-96) in 77 (N) and 40 (P) streams draining small agricultural catchments revealed a median annual decrease of 0.073 mg N 1−1 and 0.0034 mg P 1−1 (Sen's slope estimator). The observed trend was only significant in 6 of the streams tested at the 5% level and 27 at the 10% level, however. The median annual decrease in N and P concentrations was higher in streams draining loamy catchments (0.092 mg N 1−1 and 0.0035 mg P 1−1) than in streams draining sandy catchments (0.040 mg N 1−1 and 0.0005 mg P 1−1).
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The saturated interstices below and adjacent to the riverbed (i.e., the hyporheic zone) can be a refuge for biota during low flows, flow cessation and river drying. Prior to complete drying, organisms are constrained by abiotic and biotic factors (e.g., water temperature, competition) and may respond through vertical migration into the hyporheic zone. However, it remains unclear when temperature and competition become harsh enough to trigger migration. Furthermore, potential consequences of using the hyporheic zone, which is often food-limited, on the survival, effects on ecosystem function and physiology of organisms are unknown. We tested the hypotheses that (1) Gammarus pulex, a widespread detritivore, migrates into the hyporheic zone to avoid increasing surface water temperature and intraspecific competition and (2) that these factors would reduce their survival, leaf mass consumption and energy stores. Using 36 mesocosms, three temperature (15, 20, 25 °C) and species density levels (low, medium, high) were manipulated in a factorial design over 15 days. Increasing temperature to 25 °C and a threefold increase in density both caused G. pulex to vertically migrate, and the interaction of these factors was additive, rather than antagonistic or synergistic. Importantly, survival, leaf consumption and glycogen content were reduced in high temperature and density treatments, suggesting tradeoffs between tolerating harsh surface conditions and limitations of inhabiting the hyporheic zone. Identifying that the hyporheic zone is used by G. pulex to avoid high water temperature and intraspecific competition is a key finding considering the global-scale increases in temperature and flow intermittence.
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Streams are extremely vulnerable to water abstraction across the world because of increasing water demand from humans, as well as because precipitation is decreasing in many areas. To determine how water abstraction affects water chemistry, hydromorphological variables and invertebrate assemblages, we conducted an experiment in which we mimicked two levels of disturbance: stagnation and drought. The experiment was performed at two lowland streams in Galicia (northwest Spain), which were similar in physical conditions but differed in trophic status (high v. low P). Samples were taken both before and after manipulation at the upstream control and downstream-disturbed stretches. There was a significant overall effect of water abstraction on both disturbed stretches, but invertebrate assemblages responded differently between streams and within stretches. In the low-P stream, invertebrate densities remained unchanged in the drought stretch but declined in the stagnation stretch relative to the control. At the same time, the high-P stream exhibited a strong loss of diversity in both the stagnation and drought stretches. These results suggest that short-term flow reductions driven by increasing water scarcity and abstraction put benthic communities in lowland streams at risk, and that risk would be greater (in terms of biodiversity loss) in streams that are initially impaired by high-P loading.
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Although sedimentation is a naturally occurring phenomenon in rivers, land-use changes have resulted in an increase in anthropogenically induced fine sediment deposi-tion. Poorly managed agricultural practices, mineral extraction , and construction can result in an increase in suspended solids and sedimentation in rivers and streams, leading to a decline in habitat quality. The nature and origins of fine sediments in the lotic environment are reviewed in relation to channel and nonchannel sources and the impact of human activity. Fine sediment transport and deposition are outlined in relation to variations in streamflow and particle size characteristics. A holistic approach to the problems associated with fine sediment is outlined to aid in the identification of sediment sources, transport, and deposition processes in the river catchment. The multiple causes and deleterious impacts associated with fine sediments on river-ine habitats, primary producers, macroinvertebrates, and fisheries are identified and reviewed to provide river managers with a guide to source material. The restoration of rivers with fine sediment problems are discussed in relation to a holistic management framework to aid in the planning and undertaking of mitigation measures within both the river channel and surrounding catchment area.
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Cladophora glomerata (a filamentous chlorophyte) and Nostoc parmeloides (a colonial cyanobacterium) are strongly associated with rough substrates in Rattlesnake Creek, Santa Barbara County, California. The dominant grazer, the caddisfly Agapetus celatus, was excluded from tiles. In the absence of Agapetus, Cladophora was found nearly equally on rough and smooth surfaces. Grazers strongly reduced Cladophora establishment on all surfaces; texture did not generally influence grazing effects in autumn, but refuges (pits) greatly increased algal survival in spring when recruitment was greater. Two other grazing insects (Baetis spp. and Micrasema) increased on exclusion tiles, apparently due to competitive release, but did not eliminate effects of Agapetus. Manual disturbance at 3- and 7-wk intervals kept Cladophora densities much lower than on control and once-scoured tiles. Densities were higher on rough tiles, but the interaction between disturbance and texture was not significant for macroalgae; basal filaments, and new sporelings, were protected within depressions. Nostoc attained densities in autumn of 50-100 colonies/100 cm2 on rough tiles and was virtually absent from smooth tiles. It was little affected by grazing, but was greatly reduced by disturbance. Rough texture provided minor protection, but mature Nostoc formed basal crusts that resisted disturbance, thereby maintaining space in the absence of severe scour. -from Authors
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Fresh waters have seen the largest decline in biodiversity of any ecosystem, with lotic ecosystems particularly impacted by human activities. The main drivers of environmental change relate primarily to agriculture, urbanization, and industrial production that have resulted in severe habitat degradation in streams and rivers worldwide. The increasing impact of climate change and invasive species has put further pressure on these systems. For more than a century, status of rivers and streams has been assessed using biological indicators and represents a prime example of applying ecological knowledge to address societal issues. Today, legislative regulations and water management rely primarily on measurements of ecological status through the assessment of biotic communities. There has been a continuous development of these biological indicators but primarily based on fundamental approaches that date back to the original assessment systems. The indicators used today ignore large parts of what is occurring in the ecosystem and cannot, in most cases, diagnose the cause of degradation with a reasonable precision. There is clearly a need to improve existing assessment systems through new and innovative approaches that, as an example, include ecosystem processes and can be linked more closely to the services that lotic ecosystems provide. This article critically reviews the use of biological indicators in the context of inherent properties of lotic ecosystems and types of degradation, and suggests how assessment could be refined through applying a number of additional approaches to those already used.For further resources related to this article, please visit the WIREs website.Conflict of interest: The author has declared no conflicts of interest for this article.
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Note: In March 2016 this paper won the International Society of Limnology (SIL) inaugural “best paper” award for students or early career scientists. It was selected by 9 international judges as the best of the papers entered from 19 countries. Lack of knowledge about how the various drivers of global climate change will interact with multiple stressors already affecting ecosystems is the basis for great uncertainty in projections of future biological change. Despite concerns about the impacts of changes in land use, eutrophication and climate warming in running waters, the interactive effects of these stressors on stream periphyton are largely unknown. We manipulated nutrients (simulating agricultural runoff), deposited fine sediment (simulating agricultural erosion) (2 levels each) and water temperature (8 levels, 0-6°C above ambient) simultaneously in 128 streamside mesocosms. Our aim was to determine the individual and combined effects of the three stressors on the algal and bacterial constituents of the periphyton. All three stressors had pervasive individual effects, but in combination frequently produced synergisms at the population level and antagonisms at the community level. Depending on sediment and nutrient conditions, the effect of raised temperature frequently produced contrasting response patterns, with stronger or opposing effects when one or both stressors were augmented. Thus, warming tended to interact negatively with nutrients or sediment by weakening or reversing positive temperature effects or strengthening negative ones. Five classes of algal growth morphology were all affected in complex ways by raised temperature, suggesting that these measures may prove unreliable in biomonitoring programs in a warming climate. The evenness and diversity of the most abundant bacterial taxa increased with temperature at ambient but not with enriched nutrient levels, indicating that warming coupled with nutrient limitation may lead to a more evenly distributed bacterial community as temperatures rise. Freshwater management decisions that seek to avoid or mitigate the negative effects of agricultural land use on stream periphyton should be informed by knowledge of the interactive effects of multiple stressors in a warming climate.
Article
1. The factors underlying population and community dynamics are almost invariably multivariate, and ecosystems worldwide are affected by many anthropogenic stressors. Inorganic dissolved nutri-ents and deposited fine sediment are common stressors in agricultural streams and can be expected to influence benthic algae and cyanobacteria. 2. 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 peri-phyton attributes. 3. 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 pro-duce proportional increases in both motile and high-profile forms. 4. Unimodal subsidy-stress patterns along the sediment gradient were found only for densities of two common Nitzschia 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 dif-ferent. As a notable exception from this rule, potentially harmful cyanobacteria (Phormidium and Oscillatoria species) responded synergistically to the stressors. Our hypothesis about the representa-tion of ecological guilds across the sediment gradient was fully supported, whilst the hypothesis regarding nutrients received partial support. 5. 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.
Article
The effects of drought on stream invertebrates have been reviewed, but the effects of artificially reduced flows have not. We addressed this knowledge gap by reviewing the literature on the effects of natural low flows and artificially reduced flows (without complete cessation of flow). We considered the effects of low water volume on habitat conditions and on invertebrate community structure, behavior, and biotic interactions. Decreases in discharge usually cause decreased water velocity, water depth, and wetted channel width; increased sedimentation; and changes in thermal regime and water chemistry. Invertebrate abundance increases or decreases in response to decreased flow, whereas invertebrate richness commonly decreases because habitat diversity decreases. Invertebrates differ in their environmental tolerances and requirements, and any loss of habitat area or alteration of food resources from decreased flow can influence organism behavior and biotic interactions. Invertebrate drift often increases immediately after flow reduction, although some taxa are more responsive to changes in flow than others. Natural low flows and artificially reduced flows have similar effects on invertebrates, but the severity (duration and magnitude) of the flow decrease can influence invertebrate responses. Certain invertebrate taxa are especially sensitive to flow decreases and might be useful indicators for reduced flows or flow restoration. The effect of low flow on streams is an important issue, but few empirical studies of the impacts of decreased flow on stream ecosystems have been done, and more manipulative experiments are needed to understand the ecological consequences of decreased flow.
Article
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.
Article
The Danish Monitoring Programme reveals that diffuse sources are currently the major source of nutrient input to the aquatic environment. Nutrient concentration and loading data for about 50 small agricultural catchments and seven undisturbed catchments reveal that agriculture is the major diffuse source, average annual nitrogen (N) and phosphorus (P) concentration and loading being respectively, 5.1- and 6.8-fold, and 2.7- and 3.9-fold greater in streams draining agricultural catchments than in streams draining undisturbed catchments during the period 1989–96. A statistical trend analysis (discharge adjusted Mann-Kendall seasonal test) applied to long-term time series (1967–96) in three streams revealed an upward trend in nitrate concentration in Skjem Å (p<0.1%), Odense Å (p=5.7%) and Gudenå (p=11%) during the 15-year period 1967–81, whereas there was no significant trend during the following 15-year period (1982–96). There was a significant downward trend in P concentration in all three streams over the 30-year period. Statistical analysis of recent trends (1989–96) in 77 (N) and 40 (P) streams draining small agricultural catchments revealed a median annual decrease of 0.073 mg N 1−1 and 0.0034 mg P 1−1 (Sen's slope estimator). The observed trend was only significant in 6 of the streams tested at the 5% level and 27 at the 10% level, however. The median annual decrease in N and P concentrations was higher in streams draining loamy catchments (0.092 mg N 1−1 and 0.0035 mg P 1−1) than in streams draining sandy catchments (0.040 mg N 1−1 and 0.0005 mg P 1−1).
Article
1. Many ecosystems are influenced simultaneously by multiple stressors, and the consequences of stressors are often unpredictable on the basis of knowledge of single effects. Agriculture affects streams world-wide via nutrient enrichment, elevated fine sediment and water abstraction for irrigation, but the combined impacts of these stressors are unknown. 2. We manipulated all three stressors simultaneously in an 18-day experiment and determined their individual and pair-wise combined effects on benthic invertebrates, algal biomass and leaf decay. We added nutrients (phosphorus plus nitrogen) and/or fine sediment (grain size 0·2 mm) to 18 experimental stream channels (dimensions 250 × 15 × 15 cm) supplied with water from a nearby stream. Three sediment and three nutrient treatments (high, intermediate, natural) were applied to each of six channels while flow was reduced by 80% in half the channels. Invertebrates (composition, abundance) and algae (chlorophyll a) were assayed using ceramic tile substrata and leaf decay was assayed using bundled leaves of a native shrub. Invertebrates colonizing leaf packs were also sampled. 3. Effects of sediment addition and flow reduction on biological response parameters were twice as common as nutrient enrichment effects. Nutrient enrichment increased total invertebrate abundance on tiles, algal biomass accrual and leaf decay rates, whereas both sediment addition (at the highest level) and flow reduction had mostly negative effects (e.g. reduced algal biomass, invertebrate abundance and/or taxonomic richness). 4. Stressors interacted often, and interactions between sediment and flow were particularly common. The negative impact of added sediment on aquatic biota was stronger at reduced flow, especially on tile substrata that were more exposed to the current than leaf-pack substrata. 5. Synthesis and applications. Our key findings imply that abstracting water from a stream already subjected to high fine sediment inputs may have far worse effects on the invertebrate fauna than abstraction from a similar stream with lower sediment levels. Aquatic resource managers should be aware of this important interaction between multiple stressors.
Article
1. 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.
Article
The sedimentological connectivity of agricultural catchments may be affected by anthropogenic structures (land management practices) established to reduce sediment exportation from agricultural plots to water streams. Distributed erosion models may in theory provide information about where and how these structures should be installed in catchments to reduce sediment exportation. The interaction between sediment exportation and land management practices is very complex from both theoretical and experimental points of view. Vegetated filters are a widely used land management practice. They interact with water flow, change turbulence conditions, and ultimately affect sediment transport and deposition processes. Experimental results have shown that the efficiency of sediment trapping in vegetated filters is influenced by flow characteristics, sediment size, and vegetation type, as well as by the slope and width of the filter in the streamwise direction. At the catchment scale, the spatial organisation of management practices is crucial for the global sedimentological connectivity. Present-day erosion models propose different approaches to simulate the influence of management practices on soil loss and sediment export for agricultural catchments. Some of them use the Sediment Delivery Ratio (SDR) or P-factor to describe sediment transport from source to sink areas. Others, such as in the TRAVA and VSFMOD, rely on process-based descriptions involving changes in roughness and infiltrability along flow paths to study the effect of management practices. From the literature review conducted herein, we identified the lack of an approach of intermediate complexity, that would be more physically relevant than SDR and P-factor approaches, but simpler and easier to spatialise than TRAVA and VSFMOD-type models. Copyright © 2010 John Wiley and Sons, Ltd.
Article
1. Experimental channels were installed at the outlet of a small Canadian Shield lake to study the role of light and nutrients on the regulation of periphyton and invertebrate biomass and taxonomic composition. Light (93% reduction) and nutrients (four-fold increase of ambient total phosphorus (TP) concentration) were manipulated in a factorial design experiment. 2. Periphyton chlorophyll a (Chl a), measured four times during the 12-week experiment, increased due to higher irradiance but was unaffected by phosphorus enrichment. Over the experiment, periphyton biomass was, on average, three times higher in open than in shaded channels. 3. Algal taxonomic and growth form composition were affected by light and phosphorus enrichment. The proportion of cyanophytes was significantly higher in unenriched, shaded channels (45%) compared to the three other treatments. Single cells and colonial forms were dominant in shaded channels, whereas filamentous and chain-forming algae were prevalent in open channels. 4. Total invertebrate biomass remained unchanged over time and among treatments. At the beginning of the experiment, all the channels were dominated by Chironomidae and filter feeders (Simuliidae and Hydropsychidae). After 55 days, filter feeders became clearly dominant (60%) in all treatments except in the enriched, open channels where there was a significant shift in the functional group composition toward grazers (snails and oligochaetes). Among filter feeders, Simuliidae increased in shaded channels.
Article
Summary • 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.
Article
Leuctridae is the richest stonefly family on the European continent, with many species of Leuctra often coexisting in sympatry in the same lotic environment. In this work we studied the life cycle and feeding habits of two species, Leuctra fusca and L. hippopus, coexisting in a small Italian Apennine stream. The life cycles of the two species are non-overlapping, i.e., periods of nymphal growth and adult emergence are separated. Nymphs of both species feed mainly on detritus, but quantities of coarse particulate organic matter (CPOM) and diatoms are also ingested. Larger nymphs of both species ingest more CPOM and fewer diatoms. This suggests a similar trophic behaviour through their development. For example, they act as collector-gatherers in their earlier instars and as collector-gatherers or as shredders in their later instars (© 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
Article
The Danish National Aquatic Monitoring and Assessment Programme (NOVA) was launched in 1988 following the adoption of the first Danish Action Plan on the Aquatic Environment in 1987 with the aim to reduce by 50% the nitrogen (N) loading and by 80% the phosphorus (P) loading to the aquatic environment. The 14 years of experience gathered from NOVA have shown that discharges of total N (TN) and P (TP) from point sources to the Danish Aquatic Environment have been reduced by 69% (N) and 82% (P) during the period 1989–2002. Consequently, the P concentration has decreased markedly in most Danish lakes and estuaries. Considerable changes in agricultural practice have resulted in a reduction of the net N-surplus from 136 to 88 kg N ha−1 yr−1 (41%) and the net P-surplus from 19 to 11 kg P ha−1 yr−1 (42%) during the period 1985–2002. Despite these efforts Danish agriculture is today the major source of both N (>80%) and P (>50%) in Danish streams, lakes and coastal waters. A non-parametric statistical trend analysis of TN concentrations in streams draining dominantly agricultural catchments has shown a significant (p<0.05) downward trend in 48 streams with the downward trend being stronger in loamy compared to sandy catchments, and more pronounced with increasing dominance of agricultural exploitation in the catchments. In contrast, a statistical trend analysis of TP concentrations in streams draining agricultural catchments did not reveal any significant trends. The large reduction in nutrient loading from point and non-point sources has in general improved the ecological conditions of Danish lakes in the form of increased summer Secchi depth, decreased chlorophyll a and reduced phytoplankton biomass. Major changes have also occurred in the fish communities in lakes, with positive cascading effects on water quality. In Danish estuaries and coastal waters only a few significant improvements in the ecological quality have been observed, although it is expected that the observed reduced nutrient concentrations are likely to improve the ecological quality of estuaries and coastal waters in Denmark in the long term.
Article
Agricultural pesticides continue to impair surface water ecosystems, although there are few assessments of interactions with other modifications such as fine sediment and physical alteration for flood drainage. We, therefore, surveyed pesticide contamination and macroinvertebrates in 14 streams along a gradient of expected pesticide exposure using a paired-reach approach to differentiate effects between physically modified and less modified sites. Apparent pesticides effects on the relative abundance of SPEcies At Risk (SPEAR) were increased at sites with degraded habitats primarily due to the absence of species with specific preferences for hard substrates. Our findings highlight the importance of physical habitat degradation in the assessment and mitigation of pesticide risk in agricultural streams.
Article
This paper outlines the effects of climate change by the 2050s on hydrological regimes at the continental scale in Europe, at a spatial resolution of 0.5×0.5°. Hydrological regimes are simulated using a macro-scale hydrological model, operating at a daily time step, and four climate change scenarios are used. There are differences between the four scenarios, but each indicates a general reduction in annual runoff in southern Europe (south of around 50°N), and an increase in the north. In maritime areas there is little difference in the timing of flows, but the range through the year tends to increase with lower flows during summer. The most significant changes in flow regime, however, occur where snowfall becomes less important due to higher temperatures, and therefore both winter runoff increases and spring flow decreases: these changes occur across a large part of eastern Europe. In western maritime Europe low flows reduce, but further east minimum flows will increase as flows during the present low flow season – winter – rise. “Drought” was indexed as the maximum total deficit volume below the flow exceeded 95% of the time: this was found to increase in intensity across most of western Europe, but decrease in the east and north. The study attempted to quantify several sources of uncertainty, and showed that the effects of model uncertainty on the estimated change in runoff were generally small compared to the differences between scenarios and the assumed change in global temperature by 2050.
Article
Published data on nitrate (NO3-) toxicity to freshwater and marine animals are reviewed. New data on nitrate toxicity to the freshwater invertebrates Eulimnogammarus toletanus, Echinogammarus echinosetosus and Hydropsyche exocellata are also presented. The main toxic action of nitrate is due to the conversion of oxygen-carrying pigments to forms that are incapable of carrying oxygen. Nitrate toxicity to aquatic animals increases with increasing nitrate concentrations and exposure times. In contrast, nitrate toxicity may decrease with increasing body size, water salinity, and environmental adaptation. Freshwater animals appear to be more sensitive to nitrate than marine animals. A nitrate concentration of 10 mg NO3-N/l (USA federal maximum level for drinking water) can adversely affect, at least during long-term exposures, freshwater invertebrates (E. toletanus, E. echinosetosus, Cheumatopsyche pettiti, Hydropsyche occidentalis), fishes (Oncorhynchus mykiss, Oncorhynchus tshawytscha, Salmo clarki), and amphibians (Pseudacris triseriata, Rana pipiens, Rana temporaria, Bufo bufo). Safe levels below this nitrate concentration are recommended to protect sensitive freshwater animals from nitrate pollution. Furthermore, a maximum level of 2 mg NO3-N/l would be appropriate for protecting the most sensitive freshwater species. In the case of marine animals, a maximum level of 20 mg NO3-N/l may in general be acceptable. However, early developmental stages of some marine invertebrates, that are well adapted to low nitrate concentrations, may be so susceptible to nitrate as sensitive freshwater invertebrates.
Article
Nutrient availability and herbivory control the biomass of primary producer communities to varying degrees across ecosystems. Ecological theory, individual experiments in many different systems, and system-specific quantitative reviews have suggested that (i) bottom-up control is pervasive but top-down control is more influential in aquatic habitats relative to terrestrial systems and (ii) bottom-up and top-down forces are interdependent, with statistical interactions that synergize or dampen relative influences on producer biomass. We used simple dynamic models to review ecological mechanisms that generate independent vs. interactive responses of community-level biomass. We calibrated these mechanistic predictions with the metrics of factorial meta-analysis and tested their prevalence across freshwater, marine and terrestrial ecosystems with a comprehensive meta-analysis of 191 factorial manipulations of herbivores and nutrients. Our analysis showed that producer community biomass increased with fertilization across all systems, although increases were greatest in freshwater habitats. Herbivore removal generally increased producer biomass in both freshwater and marine systems, but effects were inconsistent on land. With the exception of marine temperate rocky reef systems that showed positive synergism of nutrient enrichment and herbivore removal, experimental studies showed limited support for statistical interactions between nutrient and herbivory treatments on producer biomass. Top-down control of herbivores, compensatory behaviour of multiple herbivore guilds, spatial and temporal heterogeneity of interactions, and herbivore-mediated nutrient recycling may lower the probability of consistent interactive effects on producer biomass. Continuing studies should expand the temporal and spatial scales of experiments, particularly in understudied terrestrial systems; broaden factorial designs to manipulate independently multiple producer resources (e.g. nitrogen, phosphorus, light), multiple herbivore taxa or guilds (e.g. vertebrates and invertebrates) and multiple trophic levels; and - in addition to measuring producer biomass - assess the responses of species diversity, community composition and nutrient status.
Ökologische Typisierung der aquatischen Makrofauna
  • M Colling
  • U Schmedtje
Colling, M., Schmedtje, U., 1996. Ökologische Typisierung der aquatischen Makrofauna (No. 4/96), Informationsberichte des Bayerischen Landesamtes für Wasserwirtschaft. Landesamt für Wasserwirtschaft, Bayerisches.
Rapid response of the benthic algae community to typical lowland-stream multiple stressor scenarios in a full-scale experiment
  • E M Neif
  • D Graeber
  • L Rodrigues
  • S R Leth
  • T M Jensen
  • P Wiberg-Larsen
  • F Landkildehus
  • A Baattrup-Pedersen
Neif, E.M., Graeber, D., Rodrigues, L., Leth, S.R., Jensen, T.M., Wiberg-Larsen, P., Landkildehus, F., Baattrup-Pedersen, A., 2016. Rapid response of the benthic algae community to typical lowland-stream multiple stressor scenarios in a full-scale experiment. Freshw. Biol. (submitted).
Individual and combined responses of stream ecosystems to multiple stressors
  • C R Townsend
  • S S Uhlmann
  • C D Matthaei
Townsend, C.R., Uhlmann, S.S., Matthaei, C.D., 2008. Individual and combined responses of stream ecosystems to multiple stressors. J. Appl. Ecol. 45, 1810-1819.
Rapid response of the benthic algae community to typical lowland-stream multiple stressor scenarios in a full-scale experiment
  • Neif
Individual and combined responses of stream ecosystems to multiple stressors
  • Townsend