Multiple Stressor Scenarios Research Articles

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

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.

Embracing interactions in ocean acidification research: confronting multiple stressor scenarios and context dependence.

Changes in the Earth's environment are now sufficiently complex that our ability to forecast the emergent ecological consequences of ocean acidification (OA) is limited. Such projections are challenging because the effects of OA may be enhanced, reduced or even reversed by other environmental stressors or interactions among species. Despite an increasing emphasis on multifactor and multispecies studies in global change biology, our ability to forecast outcomes at higher levels of organization remains low. Much of our failure lies in a poor mechanistic understanding of nonlinear responses, a lack of specificity regarding the levels of organization at which interactions can arise, and an incomplete appreciation for linkages across these levels. To move forward, we need to fully embrace interactions. Mechanistic studies on physiological processes and individual performance in response to OA must be complemented by work on population and community dynamics. We must also increase our understanding of how linkages and feedback among multiple environmental stressors and levels of organization can generate nonlinear responses to OA. This will not be a simple undertaking, but advances are of the utmost importance as we attempt to mitigate the effects of ongoing global change.

Climate change and multiple stressors in small tropical streams

Despite the importance of small tropical streams for maintaining freshwater biodiversity and providing essential ecosystem services to humans, relatively few studies have investigated multiple-stressor effects of climate and land-use change on these ecosystems, and how these effects may interact. To illustrate these knowledge gaps, we reviewed the current state of knowledge regarding the ecological impacts of climate change and catchment land use on small tropical streams. We consider the effects of predicted changes in streamflow dynamics and water temperatures on water chemistry, habitat structure, aquatic biota, and ecosystem processes. We highlight the pervasive individual effects of climate and land-use change on algal, macroinvertebrate, and fish communities, and in stream metabolism and decomposition processes. We also discuss potential responses of tropical streams in a multiple-stressor scenario, considering higher temperatures and shifts in hydrological dynamics. Finally, we identify six key knowledge gaps in the ecology of low-order tropical streams and indicate future research directions that may improve catchment management in the tropics to help alleviate climate-change impacts and biodiversity losses.

Environmental impact and risk assessments and key factors contributing to the overall uncertainties

There is a significant number of nuclear and radiological sources that have contributed, are still contributing, or have the potential to contribute to radioactive contamination of the environment in the future. To protect the environment from radioactive contamination, impact and risk assessments are performed prior to or during a release event, short or long term after deposition or prior and after implementation of countermeasures. When environmental impact and risks are assessed, however, a series of factors will contribute to the overall uncertainties.To provide environmental impact and risk assessments, information on processes, kinetics and a series of input variables is needed. Adding problems such as variability, questionable assumptions, gaps in knowledge, extrapolations and poor conceptual model structures, a series of factors are contributing to large and often unacceptable uncertainties in impact and risk assessments. Information on the source term and the release scenario is an essential starting point in impact and risk models; the source determines activity concentrations and atom ratios of radionuclides released, while the release scenario determine the physico-chemical forms of released radionuclides such as particle size distribution, structure and density. Releases will most often contain other contaminants such as metals, and due to interactions, contaminated sites should be assessed as a multiple stressor scenario. Following deposition, a series of stressors, interactions and processes will influence the ecosystem transfer of radionuclide species and thereby influence biological uptake (toxicokinetics) and responses (toxicodynamics) in exposed organisms. Due to the variety of biological species, extrapolation is frequently needed to fill gaps in knowledge e.g., from effects to no effects, from effects in one organism to others, from one stressor to mixtures. Most toxtests are, however, performed as short term exposure of adult organisms, ignoring sensitive history life stages of organisms and transgenerational effects.To link sources, ecosystem transfer and biological effects to future impact and risks, a series of models are usually interfaced, while uncertainty estimates are seldom given. The model predictions are, however, only valid within the boundaries of the overall uncertainties. Furthermore, the model predictions are only useful and relevant when uncertainties are estimated, communicated and understood. Among key factors contributing most to uncertainties, the present paper focuses especially on structure uncertainties (model bias or discrepancies) as aspects such as particle releases, ecosystem dynamics, mixed exposure, sensitive life history stages and transgenerational effects, are usually ignored in assessment models. Research focus on these aspects should significantly reduce the overall uncertainties in the impact and risk assessment of radioactive contaminated ecosystems.

Tissue-specific effects of acute aluminium exposure on the radiation-induced bystander effect in rainbow trout (Oncorhynchus mykiss, Walbaum)

Purpose: To investigate if aluminium (Al) modifies the rainbow trout response to radiation exposure and/or the induction of a radiation-induced bystander effect.Methods: Rainbow trout were exposed to 100 or 200 μg l−1 Al (for 3 h), a 0.5 Gy X-ray dose or Al followed immediately by irradiation. The exposed fish were then swum with completely untreated bystander fish. A human reporter cell clonogenic assay was used to determine whether Al exposure modified the effects of irradiation on the skin and gills from directly exposed fish and also the radiation-induced bystander effect in untreated fish.Results: Al exposure did not modify the response to direct irradiation by the skin, or the gill. Al did not modify the bystander effect in the skin. However Al did modify the bystander effect in the gill. Gills of bystander fish swum with fish exposed to 200 μg l−1 Al, followed by irradiation, caused a greater reduction in HPV-G cell survival than was caused by irradiation only. Interestingly Al exposure only also caused a bystander effect (reduced HPV-G survival) in the gill.Conclusion: This study shows that, in a multiple stressor scenario, the communication of radiation-induced stress signals is modified on a tissue-specific basis by acute Al exposure. Aside from the implications this has for radiological protection this response may also have potential for environmental monitoring where detection of the bystander effect could act as an indicator of radiation exposure when direct exposure responses are not evident.

Resilience of the macroinvertebrate community of a small mountain river (Mau River, Portugal) subject to multiple stresses

Freshwaters commonly face human pressure, which produces multiple stressor scenarios that may threaten their ecological status. Biotic community assessments are useful tools to monitor such changes, and the European Water Framework Directive (WFD) has brought this into the legislative framework. The present study focused on a small mountain river facing multiple stresses, with the purpose of (1) evaluating the sensitivity of the macroinvertebrate community to the stresses, (2) assessing whether the ecological status was impaired in different years and (3) comparing the WFD approach with more refined community analyses. The river was generally in a very good ecological state. Despite seasonal and inter-annual fluctuations, no evident stressor-related effects were detected. We hypothesise that the observed resilience was the result of (1) the current dormant state of the abandoned mining areas (the most relevant potential source of contamination) and (2) the naturalness and strong current of the river, which buffered the impacts of contamination. Such a pattern may be generally valid for small mountain rivers, making them therefore more resilient to stresses. Nevertheless, small changes in community structure in the lowest reach of the river – undetected by the WFD assessment scheme – suggest that some disturbance was present, signalling the need for intervention by managers.

Beyond taxonomy: a review of macroinvertebrate trait‐based community descriptors as tools for freshwater biomonitoring

Summary 1. Species traits have been frequently used in ecological studies in an attempt to develop a general ecological framework linking biological communities to habitat pressures. The trait approach offers a mechanistic alternative to traditional taxonomy‐based descriptors. This review focuses on research employing traits as biomonitoring tools for freshwater ecosystems, although the lessons learned have wider application in the assessment of other ecosystem types. 2. We review the support from ecological theory to employ species traits for biomonitoring purposes (e.g. the habitat templet concept, landscape filtering hypothesis), and the subsequent studies that test the hypotheses arising from these theories, and apply this knowledge under real freshwater biomonitoring scenarios. We also include studies that deal with more specific issues such as trait trade‐offs and trait syndromes. 3. We highlight the functional trait approach as one of the most promising tools emerging for biomonitoring freshwater ecosystems. Several technical issues are addressed and solutions are proposed. We discuss the need for: a broader unified trait biomonitoring tool; a more accurate understanding of the natural variation of community patterns of trait expression; approaches to diminish the effects of trait trade‐offs and trait syndromes; additional life history and ecological requirement studies; and the detection of specific impacts under multiple stressor scenarios. 4. Synthesis and applications. This review provides biologists with the conceptual underpinning for the use of species traits as community descriptors and for freshwater biomonitoring and management. We expect that the functional trait approach will ultimately improve communication to managers and legislators of the importance of protecting freshwater ecosystem functions.

Assessing relationships between chemical exposure, parasite infection, fish health, and fish ecological status: A case study using chub (Leuciscus cephalus) in the Bílina River, Czech Republic

Multiple stressor scenarios, as they are relevant in many watersheds, call for approaches extending beyond conventional chemical-focused approaches. The present study, investigated the fish population, represented by chub (Leuciscus cephalus), in the Bílina River (Czech Republic), which is impacted by various pollution sources and might pose a risk on the fish population. To confirm or reject this hypothesis it was examined whether there exists an association between abundance of chub and exposure to toxic chemicals as well as natural stressors, represented by parasites, and whether health-related suborganismal traits, namely, organ indices, tissue histopathology, and immune parameters, would help in revealing relationships between stressor impact and population status. Toxic pressure was assessed by the toxic unit approach, which gives an integrative estimate of toxic effect concentrations and by measuring the biomarkers cytochrome P4501A and vitellogenin, which indicate exposure to bioavailable arylhydrocarbon- or estrogen receptor ligands. Parasite pressure was estimated by determining abundance and species composition of ecto- and endoparasites of chub. Chub abundance was high upstream in the Bílina, low to zero in the middle stretches, and increased again downstream. Toxic pressure increased in the downstream direction, while parasite intensity decreased in this direction. Health status of chub did not differ clearly between up-, middle-, and downstream sites. Thus, it appears that neither toxic pressure nor parasite pressure nor their combination translates into a change of chub health status. By using varied assessment tools, this study provides evidence against a presumed causative role of toxicants impairing the fish ecological status of the Bílina River.

Intermountain basins use in subtropical regions and their influences on benthic fauna

AbstractConversion of high mountain forests into pastures or croplands and changes in land uses have produced changes in hydrology, vegetation cover and terrestrial aquatic linkages, resulting in increased nutrient loads on water bodies. The developing countries today need to obtain an indicator response signature under multiple stressor scenario, to identify causes of water bodies impairment. Intermountain land use impact on a Subtropical Andean River was studied in Tucumán province, Northwestern Argentina. Benthic macroinvertebrates were used as indicators of diffuse alterations produced by anthropic activities on a small valley at ca. 1000 m.a.s.l. The objectives were: (a) test the effect of land use on macroinvertebrate assemblages; (b) test the response of benthic fauna to diffuse organic pollution and (c) test the accuracy of the current biological water quality indices. Nutrient levels were higher than international standards. First axis in multivariate analysis shows an important upstream–downstream gradient meanwhile the second axis shows seasonal effects. These effects are specially produced by monsoonal regime of rainfall (ca. 80% in summer). No effect of the land use or diffuse pollution was detected on the macroinvertebrate assemblage structure, probably due to the good oxygen availability. Of the several biotic indices (BI) and metrics tested, only one worked on acceptable levels being ‘affected’ by small oxygen variations. Dry winter, dry and warm spring with high sunlight exposure plus high levels of nutrients could be an undesirable combination for standing waters of a reservoir projected in this watershed. A correct monitoring of water quality and alternatives as management of reforested margins is the right beginning. These actions and more studies represent interesting alternatives for poor regions of undeveloped countries. Copyright © 2008 John Wiley & Sons, Ltd.