Article

Macroinvertebrate short-term responses to flow variation and oxygen depletion: A mesocosm approach

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Abstract

In Mediterranean rivers, water scarcity is a key stressor with direct and indirect effects on other stressors, such as water quality decline and inherent oxygen depletion associated with pollutants inputs. Yet, predicting the responses of macroinvertebrates to these stressors combination is quite challenging due to the reduced available information, especially if biotic and abiotic seasonal variations are taken under consideration. This study focused on the response of macroinvertebrates by drift to single and combined effects ofwater scarcity and dissolved oxygen (DO) depletion over two seasons (winter and spring). A factorial design of two flowvelocity levels - regular and low (vL) - with three levels of oxygen depletion - normoxia, medium depletion (dM) and higher depletion (dH) - was carried out in a 5-artificial channels system, in short-term experiments. Results showed that both stressors individually and together had a significant effect on macroinvertebrate drift ratio for both seasons. Single stressor effects showed that macroinvertebrate drift decreased with flow velocity reduction and increased with DO depletion, in both winter and spring experiments. Despite single stressors opposing effects in drift ratio, combined stressors interaction (vL × dM and vL × dH) induced a positive synergistic drift effect for both seasons, but only in winter the drift ratio was different between the levels of DO depletion. Stressors interaction in winter seemed to intensify drift response when reached lower oxygen saturation. Also, drift patterns were different between seasons for all treatments, which may depend on individual's life stage and seasonal behaviour. Water scarcity seems to exacerbate the oxygen depletion conditions resulting into a greater drifting of invertebrates. The potential effects of oxygen depletion should be evaluated when addressing the impacts of water scarcity on river ecosystems, since flow reductions will likely contribute to a higher oxygen deficit, particularly in Mediterranean rivers.

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... This is further complicated by the fact that environmental stressors are highly interrelated and may act directly as well as indirectly on macroinvertebrate assemblages. Therefore a key challenge is to disentangle the contribution of individual and combined stressors to the overall effect on macroinvertebrate assemblages (Calapez et al., 2017;Elbrecht et al., 2016;Smeti et al., 2019;Tockner et al., 2010;Villeneuve et al., 2018). ...
... Synergistic and antagonistic effects may occur when stressors act simultaneously (Coors and de Meester, 2008;Jackson et al., 2016). Examples include the synergistic effects of low flow and oxygen depletion on macroinvertebrate communities, causing increased drift rates (Calapez et al., 2017), and the increased negative impact of sediment input at reduced flow on benthic invertebrates (Matthaei et al., 2010). These multiple-stressor interactions have not yet been accounted for in macroinvertebrate-simulation models, instead, stressors are treated one by one and their effects are subsequently combined additively. ...
... Interactions are specific per stressor combination, water body type, assemblage, and region. A number of these interactions has been described (Calapez et al., 2017;Davis et al., 2018;Elbrecht et al., 2016;Matthaei et al., 2010), but understanding of the mechanisms behind these interactions is still limited (Friberg, 2010;Ormerod et al., 2010). Therefore, it is not possible yet to fully represent stressor interactions in models for simulating macroinvertebrate responses to multiple stressors, even though an ideal future model would answer to this requirement. ...
Article
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Simulating macroinvertebrate responses to multiple environmental stressors is an important tool for water quality management, by predicting ecological effects of both stressors and restoration practices. Currently, existing modelling approaches fall short in simulating the responses of macroinvertebrate assemblages to environmental constraints, lacking incorporation of the multiple spatial and temporal scales on which stressors act, including their mutual interactions and uncertainties associated with input data. In answer to these shortcomings, this study aimed to design a conceptual multiscale model for simulating responses of macroinvertebrate assemblages to multiple environmental stressors. To this purpose, we drew up model requirements, selected model building blocks and assembled these into a conceptual model, also documenting the challenges that remain to be solved. This conceptual model offers a direction for simulating responses of macroinvertebrate assemblages to multiple stressors, which in turn can be used to better focus management resources and restoration practices.
... Compared with other aquatic organisms, benthic macroinvertebrates have important advantages. They not only have large abundances and relatively long life cycle, and are easy to collect, but also are highly sensitive to deterioration or improvements in aquatic ecological conditions (Pan et al., 2015c;Calapez et al., 2017). Studies based on benthic macroinvertebrates to evaluate river ecological health have been published (Kerans and Karr, 1994;Meng et al., 2009;Shi et al., 2017;Zhang et al., 2018b;Zhao et al., 2019). ...
... Aquatic ecosystems are often subject to a variety of anthropogenic activities stresses that interfere with the behavior of aquatic species (Fausch et al., 2010;Schinegger et al., 2012;Giorgio et al., 2016; https://doi.org/10.1016/j.ecoleng.2019.105595 Received 27 March 2019; Received in revised form 1 September 2019; Accepted 9 September 2019 T Calapez et al., 2017). One such example is river channel management, which influences the morphological processes in riverbeds and indirectly affects the habitat condition of benthic macroinvertebrate (Bylak et al., 2009;Wyżga et al., 2014;Bylak et al., 2017). ...
... Flow velocity played an important role in macroinvertebrate distribution. For example, Chironomidae, Corixidae and Psychodidae were positively related to velocity in normal flow season (Fig. 8a), while a slow flow velocity is considered a stressor to rheophilic taxa, which can be expected to enhance the habitat suitability (Calapez et al., 2017;Juras et al., 2018). Chironomidae, Corixidae and Psychodidae showed a negative correlation with the high flow rate during high flow season. ...
Article
Macroinvertebrates are sensitive to changes in the river environment and ecological status. Ecological variables over multi-spatial scales and macroinvertebrate community data were collected in June (normal flow season) and September (high flow season) of 2017 in the Weihe River Basin (WRB). A total of 14,377 individuals were identified, which were classified into 7 classes, 18 orders and 59 families. Macroinvertebrate community composition, density, biomass, the values of Pielou evenness index (E), Simpson diversity index (λ) were significantly different between normal flow season and high flow season. The dominant species (Tubificidae, Chironomidae and Baetidae) were the same in both seasons. The highest richness, abundance, density and biomass occurred at a stream bed depth of 0–10 cm. The results of canonical correspondence analyses (CCA) showed that ecological factors explained the major variation in macroinvertebrate community composition. Specifically, the increased nitrogen concentrations favored tolerant species, whereas high velocity and dissolved oxygen (DO) benefitted community taxa richness and biodiversity. The reduction of taxa richness, abundance, density and biomass in high flow season was related to the summer flood. Increased nutrient concentrations and macroinvertebrate habitat damage contributed to more tolerant, yet less diverse stream macroinvertebrate assemblages.
... Several factors may influence the distribution and changes in macroinvertebrates composition. Slow current velocities can trigger different drift responses, including lower (Dewson et al., 2007), higher (Acuña et al., 2005) or no change (James et al., 2008) in abundance/density in local communities, whereas large oxygen deficits in the water have been consistently found as a deleterious factor for such organisms (Burnett and Stickle, 2001;Cox, 2003;Pardo and Garcia, 2016;Calapez et al., 2017). Nevertheless, taxonomically based metrics are often limited in classifying mechanisms of impact (e.g. ...
... Nevertheless, experimental ex-situ studies that explore in a more controlled way (i.e. mesocosm assays) the trait level response of aquatic organisms to multiple pressures, such as water scarcity and the presence of hypoxia conditions are, to our knowledge, still lacking, despite some efforts had been recently made (Calapez et al., 2017). Thus, in this study we use a mesocosm system to test the single and combined effect of flow reduction and oxygen depletion on macroinvertebrate community's functional response. ...
... Oxygen depletion was induced by adding sodium sulphite (Na 2 SO 3 ) (Park et al., 2014) into the water of each mesocosm channel, following the same procedure used in a previous parallel study (see Calapez et al., 2017 for further details). As oxygen scavenger (Lewis Jr., 1970), Na 2 SO 3 has been formerly used in the setting of oxygen-deficit conditions in animal and water research (Crampton, 1998;Peay et al., 2006;Branco et al., 2016;Calapez et al., 2017), and was employed in the present study as a proxy for the reduction of DO in rivers due to the degradation of organic loads into the system. ...
Article
River ecosystems are most often subject to multiple co-occurring anthropogenic stressors. Mediterranean streams are particularly affected by water scarcity and organic loads that commonly lead to a simultaneous reduction in flow and increasing depletion of dissolved oxygen. In the present study, the single and combined effects of water scarcity (flow velocity reduction) and dissolved oxygen depletion were used to evaluate alterations of drifting macroinvertebrates on a channel mesocosm system, by employing a multiple trait-based approach. Our main findings confirmed that the impact of the two combined stressors can be implicated in alterations of ecosystem functions as result of the changes in proportions of biological traits. Overall, our results showed that, individually, flow velocity reduction and a severe oxygen depletion promoted a shift in community traits. In more detail, biological traits describing the dispersal of organisms and their respiration showed the strongest responses. The respiration mode responded to low flow with drift increase of gill breathers and decrease of individuals with tegument, whereas dispersal was clearly affected by the combination of stressors. Resistance through eggs was higher with the single effect of flow reduction, while swimmers´ relative abundance increased in individuals that drift after exposure to the combination of stressors. Thus, while flow reduction alone is expected to specifically filter out the gill breathers and the egg producers, the combination of stressors will impact more drastically organism's dispersal and swimmers. Such changes in biological traits can result in variations in ecosystem functioning through, for example, local changes in biomass, secondary production, stream metabolism as well as resulting in biodiversity losses or alterations of its distribution patterns.
... In recent years, much effort has been focused on the effect of flow alterations on macroinvertebrate assemblages (e.g. Chessman et al. 2010;Santos and Stevenson 2011;Li et al. 2012;Storey 2016;Calapez et al. 2017;Salmaso et al. 2018;White et al. 2018;Piano et al. 2019). Several of these flow alterations are natural, as occur in intermittent or seasonal streams from Mediterranean regions (Hershkovitz and Gasith 2013), but many others are human-induced due to water abstraction. ...
... During this period, the ditch filled up of sediments brought from upstream, and so this had a detrimental effect on the macroinvertebrates inhabiting there. Due to the direct effect of flow on dissolved oxygen (Calapez et al. 2017(Calapez et al. , 2018, oxygen also groups macroinvertebrate communities from ''Source'' and ''Irrigation ditch'' and separates those from ''Downstream''. Points representing communities in the latter site are exposed to higher levels of dissolved oxygen than those from the other two sites. ...
Article
Full-text available
ion for irrigation has an important effect on stream organisms in general and aquatic macroinvertebrates in particular. The alteration of flow modifies the habitat conditions and creates important ecological constraints for many of these animals, so shaping the communities and affecting their diversity. With the aim to assess the impact of flow and habitat changes due to water abstraction for agriculture on the macroinvertebrate community of a Mediterranean stream, we characterized physicochemically three sampling sites representing three habitat types and collected the macroinvertebrate assemblage of each one. The three sites were a spring, an irrigation ditch 90 m downstream from the spring that diverge all the water from the natural channel and return it downstream, and a site after an area of agriculture 500 m downstream of the spring. Our hypothesis was that the highest diversity would be found in the irrigation ditch, where conditions were more constant along the year and that could act as a refuge for some organisms, followed by the spring and, afterwards, the downstream site, which would have a very poor community. Nonetheless, although our results showed that the irrigation ditch had the highest values of diversity, the spring and the downstream site did not differ significantly. When analysing the effect of the measured physicochemical parameters on macroinvertebrate communities, the most important was discharge. Thus, our study underlines the effect that water diversion may have on the macroinvertebrate communities even at a small watershed scale.
... We reduced oxygen values by adding sodium sulfite (Na 2 SO 3 ). This compound is a recognized oxygen scavenger [23] that has been used to create oxygen-deficient conditions in fish research [18,24], as well as in aquatic research more generally [25,26]. Each experiment lasted for eight minutes (six min acclimation [27] plus two min video-tracking) and was replicated five times, whereby a new subset of fish was used for each trial, giving a total of 75 tested fish. ...
... In our experiments, the addition of sodium sulfite not only reduced DO levels but also led to an increase in water temperature, conductivity, and pH, making it difficult to completely disentangle the effects of lowered DO from the increase of the other parameters. Nevertheless, similar changes in these variables can often occur with the release of organic stressors, such as sewage, into rivers [18,25]. To increase understanding of fish resistance to oxygen-depleted conditions and its implications for aquatic ecosystems, future studies should investigate the effects of long-term DO depletion on riverine fish species. ...
Article
Full-text available
Numerous anthropogenic stressors impact rivers worldwide. Hypoxia, resulting from organic waste releases and eutrophication, occurs very commonly in Mediterranean rivers. Nonetheless, little is known about the effects of deoxygenation on the behavior of Mediterranean freshwater fish. To fill this knowledge gap, we assessed the impact of three different dissolved oxygen levels (normoxia, 48.4%, 16.5% saturation) on kinematics indicators (swimming velocity, acceleration, distance traveled) and shoaling cohesion of adult Iberian barbel, Luciobarbus bocagei, a widespread cyprinid species inhabiting a broad range of lotic and lentic habitats. We conducted flume experiments and video-tracked individual swimming movements of shoals of five fish. Our results reveal significant differences between the treatments regarding kinematics. Swimming velocity, acceleration, and total distance traveled decreased stepwise from the control to each of the two oxygen depletion treatments, whereby the difference between the control and both depletion levels was significant, respectively, but not between the depletion levels themselves. Shoaling cohesion showed dissimilarities between the treatments regarding the maximum distance between fish, as the high depletion treatment differed from each of the other two, indicating that under severe oxygen depletion some individuals move away from the shoal. Overall, our results show how oxygen depletion changes fish behavior, which may entail ecological responses, highlighting the need to maintain an unfragmented river network to ensure movement dispersal among habitats, thus providing conditions for species escapement from hypoxia.
... Monitoring aquatic reservoirs have been traditionally based on measuring physical and chemical variables and bioindicator aquatic organisms (Lakhloufi et al., 2021). Benthic macroinvertebrates are good indicators due to their life history characteristics, such as a long enough lifecycle to reflect environmental changes, high abundance and diversity (Calapez et al., 2017;Everall et al., 2019). Their persistence requires optimal environmental conditions that vary depending on the species ability to cope with those conditions and thus reflects on their sensitivity or tolerance to different environmental stressor gradients (Everall et al., 2019;Lakhloufi et al., 2021). ...
Article
Reservoirs are aquatic ecosystems created by humans to supply water needs. They can impair aquatic diversity due to the lack of connectivity, reduced water volume, and pressures exerted by surrounding human activities. These changes are expected to produce abrupt fluctuations in the reservoirs' environment, thus influencing the structure and functioning of aquatic communities. Therefore, this study aimed to understand the impact of a range of environmental stressors in reservoirs on benthic macroinvertebrates by analyzing their functional threshold response. Biological data were collected in six reservoirs from the semi-arid region of Northeast Brazil, as case study. A total of 37.874 benthic macroinvertebrates belonging to 35 taxa were collected. Nevertheless, almost 90% of this abundance belonged to three species alone, considered generalists, with multivoltine reproduction and from the gatherer-collectors feeding group. Increases in environmental stressors such as salinity, nitrate, ammonia, and dissolved solids led to the selection of macroinvertebrates with specific traits (e.g., protected body, gill respiration, and large body size). These functional traits showed differences in their threshold response depending on the stressors and are indicators of the effects of these stressors on the reservoirs. Some of the potential sensitive traits (with a negative threshold response to the stressor) could also associate with other stressors, demonstrating that tolerance of benthic macroinvertebrates is defined by a set of functional characteristics. Overall, the increase in stressor' gradients selected functionally tolerant organisms with high resistance capacity, but these were represented by dominant species. This resulted in low diversity in the reservoirs, which may compromise ecosystem functioning, and raises concerns about adequate management of the systems.
... Monitoring aquatic reservoirs have been traditionally based on measuring physical and chemical variables and bioindicator aquatic organisms (Lakhloufi et al., 2021). Benthic macroinvertebrates are good indicators due to their life history characteristics, such as a long enough lifecycle to reflect environmental changes, high abundance and diversity (Calapez et al., 2017;Everall et al., 2019). Their persistence requires optimal environmental conditions that vary depending on the species ability to cope with those conditions and thus reflects on their sensitivity or tolerance to different environmental stressor gradients (Everall et al., 2019;Lakhloufi et al., 2021). ...
Article
Reservoirs are aquatic ecosystems created by humans to supply water needs. They can impair aquatic diversity due to the lack of connectivity, reduced water volume, and pressures exerted by surrounding human activities. These changes are expected to produce abrupt fluctuations in the reservoirs’ environment, thus influencing the structure and functioning of aquatic communities. Therefore, this study aimed to understand the impact of a range of environmental stressors in reservoirs on benthic macroinvertebrates by analyzing their functional threshold response. Biological data were collected in six reservoirs from the semi-arid region of Northeast Brazil, as case study. A total of 37.874 benthic macroinvertebrates belonging to 35 taxa were collected. Nevertheless, almost 90% of this abundance belonged to three species alone, considered generalists, with multivoltine reproduction and from the gatherer-collectors feeding group. Increases in environmental stressors such as salinity, nitrate, ammonia, and dissolved solids led to the selection of macroinvertebrates with specific traits (e.g., protected body, gill respiration, and large body size). These functional traits showed differences in their threshold response depending on the stressors and are indicators of the effects of these stressors on the reservoirs. Some of the potential sensitive traits (with a negative threshold response to the stressor) could also associate with other stressors, demonstrating that tolerance of benthic macroinvertebrates is defined by a set of functional characteristics. Overall, the increase in stressor’ gradients selected functionally tolerant organisms with high resistance capacity, but these were represented by dominant species. This resulted in low diversity in the reservoirs, which may compromise ecosystem functioning, and raises concerns about adequate management of the systems.
... Mesocosms are outdoor experimental systems that incorporate natural variations (such as natural photoperiod and air temperature) while allowing the manipulation of other variables, thus providing a link between field surveys and highly controlled laboratory experiments (Calapez et al., 2017;Gonino et al., 2019;Mameri et al., 2020). ...
Article
Rivers are experiencing increasing anthropogenic pressures and salinity has shown to affect freshwater fish behaviour, potentially disrupting ecological processes. In this study, the aim was to determine the sub-lethal effects of salinization on freshwater fish behaviour, using a widespread native cyprinid species, the Iberian barbel (Luciobarbus bocagei) as the model species. Behavioural trials in a mesocosms setting were performed to assess the effects of three levels of a salinity gradient – control (no salt added to the water, 0.8 mS/cm), low (9 mS/cm), and high concentration (18 mS/cm) – on fish routine activity, shoal cohesion and boldness. Upon increasing the salinity levels in the flume-channels, fish showed a significant reduction on their i) swimming activity (76% of searching behaviour in the control vs. 57% in high salinity), and ii) shoal cohesion (0.95 shoal cohesion ratio in the control vs. 0.76 in high salinity), while iii) an increase of bolder individuals, measured by a higher number of attempts to escape the altered environment (106 total jumps in the control vs. 262 in high salinity), was simultaneously observed. Behavioural changes in fish can reflect shifts in ecological condition. Thus, the behavioural responses of fish caused by salinization stress should be further researched, in addition to the interaction with other environmental stressors, in order to understand the true scope of the consequences of salinization for fish species.
... It is unlikely the short-term reductions in mean oxygen concentrations will have had significant detrimental impacts on ecological communities, as evidenced by the relatively modest changes in fish populations during this study. Further, it is reasonable to assume that macroinvertebrates may have drifted downstream (Calpez et al., 2017) and fish moved within the channel (Burleson et al., 2001)probably vertically within the water columnto avoid potentially harmful conditions, which we assume were more extreme at the bed than near the surface (where water physicochemistry measurements were made). However, future research should seek to quantify physical and chemical changes throughout the water column. ...
Article
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Subaqueous dredging is a management activity undertaken globally to improve navigation, remove contaminants, mitigate flood risk and/or generate aggregate. Water Injection Dredging (WID) is a hydrodynamic technique involving the turbation and downstream displacement of fine sediments using vessel-mounted water jets. Despite the technique being widely applied internationally, the environmental and ecological effects of WID are poorly understood. For the first time, this study used a Before-After-Control-Impact (BACI) experimental design to assess the effects of WID on water physicochemistry, and macroinvertebrate and fish communities within a 5.7 km-long reach of tidal river. WID targeted the central channel (thalweg) to avoid disturbance of the channel margins and banks. Mean but not peak turbidity levels were substantially elevated, and dissolved oxygen levels were reduced during periods of WID, although effects were relatively short-lived (≈3 h on average). Dredging resulted in significant reductions in benthic macroinvertebrate community abundance (particularly taxa that burrow into fine sediments), taxonomic richness and diversity. In contrast, minor changes were detected in marginal macroinvertebrate communities within and downstream of the dredged reach following WID. Reductions in fish taxonomic richness and diversity were recorded downstream of the dredged reach most likely due to behavioural avoidance of the sediment plume. No visibly stressed or dead fish were sampled during dredging. Results suggest that mobile organisms and marginal communities were largely unaffected by thalweg WID and that the technique represents a more ecologically sensitive alternative to traditional channel margin mechanical dredging techniques.
... These effects were attributed primarily to high BOD leading to oxygen depletion. Although the focus of the present study is on N and P from a WFD reporting perspective, the potential impacts of other stressors (oxygen depletion [Calapez et al., 2017], sediment [Davis et al., 2018], etc.) on stream ecology may be pronounced. ...
Article
Farmyards present potential point sources of phosphorus loss to watercourses, affecting their ecological quality and attainment of environmental goals. Unlike many relatively simple point sources, farmyards are complex sub-systems within the wider agricultural setting, including individual runoff, management and infrastructure factors which influence the risk (likelihood and magnitude) of phosphorus loss. Comparison across these factors is confounded by heterogeneity in farmyard design and management, however, weighting of individual factors will support estimation of the relative riskiness of farmyards. This will allow identification of appropriate mitigation measures and evaluation of cost-benefit ratios. The aim of this study is to evaluate the riskiness of runoff, management, and infrastructure factors on phosphorus loss from farmyards to water, using expert opinion and to evaluate whether those estimates are supported by the literature. A survey of research, advisory and policy stakeholders was conducted (147 respondents) in which individuals rated the importance of individual factors from 0 (having no impact) to 10 (having critical impact) on phosphorus loss from farmyards. The most highly ranked factors were within the infrastructure category, followed by runoff and finally management factors. Factors relating to silage effluent and slurry storage were assigned the greatest risk (≥8.4). Runoff factors were also high risk but may be difficult to mitigate compared to infrastructure. Management factors were rated lower by all stakeholder groups but may offer low cost options to offset more intransigent risks. High consensus was observed between stakeholder groups, with significant differences in risk ratings for only 8 out of 29 individual factors.
... The effects of the experimental heatwave on fish behaviour were assessed in the mesocosm facility located at the School of Agriculture campus, University of Lisbon, Portugal. Mesocosms are outdoor experimental systems that examine the natural environment under controlled conditions, where a variable can be manipulated while controlling for confounding factors and incorporating natural variations (such as photoperiod and air temperature), thus providing a link between field surveys and highly controlled laboratory experiments (Calapez et al., 2017;Gonino et al., 2019). ...
Article
Heatwaves, which can be defined as increases of at least 5 °C in air temperature for more than five consecutive days for a specified reference period, are expected to become more frequent under the ongoing climate change, with freshwater organisms being particularly vulnerable to high temperature fluctuations. In Mediterranean-climate areas, depending on the extent of summer droughts and loss of longitudinal connectivity, river segments may become isolated, maintaining fish populations confined to a series of disconnected pools, with no possibility to move to thermal refugia and thus becoming more prone to thermal stress. In this study, we evaluated the effect of a simulated heatwave on the swimming behaviour of juvenile stages of a potamodromous native cyprinid fish, the Iberian barbel Luciobarbus bocagei, under experimental mesocosm conditions. Behavioural traits included fish activity, boldness and shoal cohesion and were continuously measured at a constant flow velocity of 18 cm s⁻¹, which is typical of riffle habitats. Overall, results show that the behaviour of juvenile Iberian barbel is likely to be affected by heatwaves, with fish displaying lower activity and boldness, while no clear difference was observed in shoal cohesion. This study highlights the importance of managing thermal refugia that are crucial for fish to persist in intermittent rivers. Future studies should focus on the interaction of heatwaves with other stressors, such as oxygen depletion, for a broader understanding of the perturbation affecting freshwater fishes under a changing climate.
... Even the creation of lateral habitats by inundation may be severely limited in the urbanization landscape given the disconnection of streams with their floodplains by the impermealization of surfaces and the construction of stormwater drainage systems and cut of riparian vegetation (Gurnell et al. 2007;Vietz and Hawley 2019). On the other hand, flow reduction and droughts reduce the area of benthic habitat and available feeding resources, reduce dissolved oxygen and increase nutrients concentrations in the water, leading to smaller populations and reduced community diversity (Konrad and Booth 2005;Nakano and Nakamura 2006;Calapez et al. 2017Calapez et al. , 2018. In consequence of these multiple-stressors, invertebrate communities of urban streams become impoverished and lose sensitive taxa, leading to a lower functional diversity and richness and consequently alterations in the ecosystem functioning, that further translate in an even poorer resistance and resilience to disturbances (Feio et al. 2015a;Pyne and Poff 2017). ...
Article
Full-text available
Urban streams provide important ecosystem services to cities’ population, from the maintenance of urban biodiversity, temperature, humidity and air quality to improving aesthetics and provision of natural areas for recreation. However, these streams are under multiple-stressors, including artificialization of the channel and flow, poor water quality and cut of riparian vegetation which puts in risk their ecological integrity and consequently their services. In this study, we aimed to understand variations in macroinvertebrate communities and in biological condition as a response to flow and water quality, by following a Mediterranean urban stream over 8 months (December–July). With a monthly periodicity, we sampled invertebrate communities and characterized in situ water physicochemical parameters. The urban stream studied showed a high variation of environmental factors over time. Invertebrate communities were generally poor, with some Ephemeroptera (Baetis sp.) but was dominated by Chironomidae and Oligochaeta that changed over time alongside with environmental conditions. Biological quality based on the Portuguese Invertebrates Index (IPtIS) varied between poor and bad. Multivariate community patterns (at genus level) showed variations in communities over time, as well as in their biological trait patterns (invertebrates’ maximal size, reproduction mode, resistance form, feeding habits and locomotion mode). Periods displaying worse biological quality, less diverse communities and lower functional richness corresponded to peaks of discharge, higher conductivity and hardness while the best quality communities were found under lower nitrate concentrations. Our study points out that the detection of impacts or recovery in urban streams through invertebrate communities might require at least the use of genus level as family level does not detect smoother changes. Communities reflect the complex interplay of environmental variables affecting structural and functional natural patterns and ultimately the biological condition of this urban stream. Rehabilitation measures should carefully consider this complex interplay of variables to enhance quality and ecosystem services.
... In particular, the typical sequence of hydrological conditions from low flows, to flow cessation and gradual drying can reduce oxygen concentrations, and intermittence and organic pollution can therefore have comparable effects by eliminating sensitive invertebrates (Pardo and García, 2016). Moreover, a reduction in oxygen availability and low flow can have synergistic effects on benthic invertebrates (Calapez et al., 2017). Disentangling the effects of stream drying and anthropogenic stressors (including organic pollution) is therefore challenging, but consideration of the Biodrought index alongside physico-chemical quality elements may improve the accuracy of ecological status assessments that might otherwise incorrectly classify IRES as polluted. ...
Article
Many streams in the extensive Central European region have an intermittent flow regime. Conventional hydrological methods used to identify zero-flow conditions, and in particular drying events, have limited use when assessing large areas dominated by low-order streams. We developed a novel multimetric index to recognise antecedent stream drying based on the analysis of benthic macroinvertebrate communities. The data used to develop the index were collected in pristine streams with different flow permanence regimes between 2012 and 2014, using standard sampling methods for ecological status assessment. The data include 64 perennial, 19 near-perennial and 27 intermittent benthic macroinvertebrate samples. Metrics considered for the index included variables based on (i) the occurrence of indicator taxa, (ii) the proportion of biological and ecological traits, and (iii) structural community metrics. Linear discriminant analysis identified the metric combinations that best discriminated among the three flow permanence categories. Different metrics were used in the final multimetric index calculation for the autumn and spring season that followed stream drying. In both seasons, the index included the proportion of indicator taxa and the proportion of taxa with high body flexibility. In addition, the autumn index included the proportion of taxa with a preference for organic substrates, whereas in spring the index included total abundance. Independent data from regulatory monitoring activity were used to validate the accuracy of the index. The correct classification of independent samples was 92% and 96% for samples from perennial and non-perennial sites, respectively. The index can be calculated using data collected by routine monitoring programmes used to assess ecological status and provides information about stream intermittence where conventional hydrological monitoring is limited. As intermittent streams increase in extent in global regions including Central Europe, the tool may be of particular interest to those who use invertebrates to monitor or manage these ecosystems.
... ,23 . De facto, em Portugal, como em muitos países europeus, a maioria das perturbações estão interligadas25. Por exem- plo, um açude tem efeito sobre a conectividade fluvial e o caudal mas também provoca alterações nos habitats disponíveis, alterando a sequência de riffles (zonas de corrente) e pools (zonas de reman- so), ou depósitos de sedimentos finos (que passam a ficar retidos a montante do açude), e levando ainda à diminuição da qualidade da água e à oxigenação da mesma. Por isso, há presentemente um grande investimento 25-27 em tentar perceber como interagem essas pressões sobre as comunidades, que podem resultar em efeitos adi- tivos, sinergísticos ou antagonísticos. ...
... The experiment durations were aligned to the receptor metrics in the study. For instance the trails on fish behavior and invertebrate drift rates only took between 30min and 5 h (Branco et al., 2016;Bruno et al., 2013;Sch€ ulting et al., 2016;Calapez et al., 2017). The experiment on invertebrate community response in natural stream reaches lasted for 334 days (Baumgartner and Robinson, 2015). ...
Chapter
Freshwater ecosystems are among the most imperiled on earth, with rivers being particularly susceptible to anthropogenic stress. Environmental monitoring across Europe reveals that 45% of rivers are affected by more than one human-driven pressure. Detecting and quantifying the impact of multiple stressors exerted from these pressures thus represent important scientific tasks in support of aquatic ecosystem management. This chapter reviews the scientific literature on experimental and field-based observational studies investigating into multistressor effects. Forty experimental and 48 field-based observational studies were covered, dealing with 72 and 151 paired stressor combinations, respectively. Morphological stress paired with either nutrient or hydrological stress was most frequently addressed in both study types. While experiments focused on a broad range of receptor organisms including phytobenthos, benthic invertebrates, fish, microorganisms (e.g., bacteria and fungi) and related processes (e.g., leaf decomposition), field studies mainly investigated the effects on benthic invertebrates and fish. Stressor interactions were more relevant in the experimental studies, with almost 50% of phytobenthos receptor metrics featuring interactions, as compared to the field studies, where stressor interactions were often not specified. Unknown stressor interactions challenge aquatic ecosystem management by posing risks of unwanted “ecological surprises.” Future scientific efforts need to concentrate on classifying the relevance and strength of interactive effects across types of stressors, receptors, and existing ecosystems, considering the specific local conditions of the water bodies to be managed. River basin management will benefit from ecosystem modeling to diagnose the causes of detrimental ecological effects, or to predict the benefits and trade-offs of management strategies in multistressor contexts.
... DO concentration strongly affects macroinvertebrate and fish assemblages in aquatic ecosystems (Pollock et al. 2007;Calapez et al. 2017;Mwedzi et al. 2017), because most animal taxa are highly sensitive to hypoxic conditions (Dean and Richardson 1999;Gilmore et al. 2018). Therefore, fewer hypoxic episodes, together with other improvements in water quality, likely enabled more invertebrate taxa (including pollution-sensitive EPT taxa, i.e., Ephemeroptera, Plecoptera, and Trichoptera) and fish (most of the species in the region) to recolonize the river from the tributaries, many of which maintained good ecological quality in reaches upstream from the confluence (Province Government of Gipuzkoa 2015). ...
Article
Human activities have altered the environmental controls on river metabolism, i.e., gross primary production (GPP) and ecosystem respiration (ER). These coupled processes affect water quality, CO2 emissions, and biodiversity. Efforts to mitigate these impacts often lack long‐term, high‐resolution data needed to assess their success. Here, we estimated a 20‐yr time series of daily metabolism from dissolved oxygen (DO) data following pollution abatement (sewage treatment) in the Oria River, Spain. Ammonium concentration declined immediately after sewage abatement, whereas dissolved organic matter absorbance (proxy for concentration) declined slowly. Summer GPP declined with ammonium concentration. ER declined more strongly but more gradually than GPP and was driven by lower rates of autotrophic respiration (AR) and heterotrophic respiration following sewage treatment. Reduced AR reflected a decrease in the fraction of daily GPP being respired by algae themselves. Decline in ER caused net ecosystem production to increase from highly negative to approximately zero. Diel DO swings also declined and episodes of hypoxia nearly disappeared following reduced metabolic rates, and were paralleled by lower benthic chlorophyll a, increased macroinvertebrate indices, and a recovery of fish assemblages. Overall, wastewater treatment plants installation constrained river metabolism, greatly improved water quality, and enabled invertebrates and fish to recolonize the river. However, most variables responded gradually and these changes would not have been evident with short‐term DO data. These gradual responses revealed the need of long‐term, high‐resolution data to gain insight into long‐temporal scale responses superimposed on short‐temporal scale metabolic variation, especially in the current context of climate and land‐use change.
... Water resource development (WRD) can alter riverine habitat and flow regimes and, in turn, impact on important life-history stages of aquatic species (Bunn and Arthington 2002;Olden and Kennard 2010;Calapez et al. 2017). WRD has affected freshwater turtle populations around the world (Bodie 2001;Clark et al. 2009) with impacts most evident around water storages (Tucker 2000). ...
Article
The Mary River turtle (Elusor macrurus) is an endemic, monotypic species with multiple impacts across its life-history, including overharvesting of eggs, nest predation and habitat degradation. Long-Term recruitment failure has led to protection measures established under state, federal and international authority. Previous research has demonstrated that E. macrurus lives instream but nests on river banks, requiring specific habitat for breeding, nesting and recruitment. Ecohydrological rules represent the critical water requirements contributing to a species' life history and can be used to develop and assess environmental flow strategies for species affected by water resource development. This study investigated the nesting behaviour of E. macrurus, including the environmental drivers that affect nest inundation. Monitoring showed that nesting by E. macrurus peaked in October and November, driven by rainfall events (>10 mm), with potential impacts from flow events (20% of nests established <2.5 m above water level at time of nesting). These ecohydrological rules were modelled against 109 years of simulated natural flow and rainfall data. The 'potential nesting and nest inundation' (PNNI) indicator revealed that nesting for E. macrurus was assured in a majority of years under the natural flow scenario. The results of this study will inform the development and assessment of e-flow strategies for nesting by E. macrurus in terms of current, and future water resource development, along with climate change impacts.
... This would result in communities with low numbers of hypoxia tolerant taxa (Yuan, 2010). These types of community responses can be seen in the results of this study, which are further consistent with previous studies (Calapez et al., 2017;Friberg et al., 2010). ...
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.
... Another important factor affecting DO is the concentration of nutrients, which is provided both by nutrient-rich agriculture return flows (Jalali and Kolahchi, 2009) and by organic loads, the latter in the case of a concurrent alteration of electrical conductivity (Daniel et al., 2002;Ortiz et al., 2005;Calapez et al., 2017). In fact, nutrients promote biological activity, creating dead and decaying biomass which consumes DO as respiration (Odum, 1956;Null et al., 2017). ...
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This study analyses how indicators of water quality (thirteen physico-chemical variables) and drivers of change (i.e., monthly aggregated air temperature and streamflow, population density, and percentage of agricultural land use) coevolve in three large European river basins (i.e., Adige, Ebro, Sava) with different climatic, soil and water use conditions. Spearman rank correlation, Principal Component Analysis, and Mann-Kendall trend tests were applied to long-term time series of water quality data during the period 1990-2015 in order to investigate the relationships between water quality parameters and the main factors controlling them. Results show that air temperature, considered as a proxy of climatic change, has a significant impact, in particular in the Adige and Ebro: positive trends of water temperature and negative of dissolved oxygen are correlated with upward trends of air temperatures. The aquatic ecosystems of these rivers are, therefore, experiencing a reduction in oxygen, which may exacerbate in the future given the projected further increase in temperature. Furthermore, monthly streamflow has been shown to reduce in the Ebro, thereby reducing the beneficial effect of dilution, which appears evident from the observed upward patterns of chloride concentrations and electrical conductivity. Upward trends of chloride and biological oxygen demand in the Adige and Sava, and of phosphate in the Adige appears to be related to increasing human population density, whereas phosphates in the Sava and biological oxygen demand in the Ebro are highly correlated with agricultural land use, considered as a proxy of the impact of agricultural practises. The present study shows the complex relationships between drivers and observed changes in water quality parameters. Such analysis can represent, complementary to a deep knowledge of the investigated systems, a reliable tool for decision makers in river basin planning by providing an overview of the potential impacts on the aquatic ecosystem of the three basins.
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Climate change is causing pronounced shifts during winter in the US, including shortening the snow season, reducing snowpack, and altering the timing and volume of snowmelt-related runoff. These changes in winter precipitation patterns affect in-stream freeze-thaw cycles, including ice and snow cover, and can trigger direct and indirect effects on in-stream physical, chemical, and biological processes in ~60% of river basins in the Northern Hemisphere. We used high-resolution, multi-parameter data collected in a headwater stream and its local environment (climate and soil) to determine interannual variability in physical, chemical, and biological signals in a montane stream during the winter of an El Niño and a La Niña year. We observed ~77% greater snow accumulation during the El Niño year, which caused the formation of an ice dam that shifted the system from a primarily lotic to a lentic environment. Water chemistry and stream metabolism parameters varied widely between years. They featured anoxic conditions lasting over a month, with no observable gross primary production (GPP) occurring under the ice and snow cover in the El Niño year. In contrast, dissolved oxygen and GPP remained relatively high during the winter months of the La Niña year. These redox and metabolic changes driven by changes in winter precipitation have significant implications for water chemistry and biological functioning beyond the winter. Our study suggests that as snow accumulation and hydrologic conditions shift during the winter due to climate change, hot-spots and hot-moments for biogeochemical processing may be reduced, with implications for the downstream movement of nutrients and transported materials.
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The aim of this study was to investigate the effects of agricultural land use and periods of hydrological variability on the environmental variables, as well as macrophyte and macroinvertebrate assemblages in lowland riverine wetlands. As a case study, we compared two periurban wetlands with intensive agricultural land use against two others with extensive livestock, considered references for the region during a normal and a dry flow period. Nutrient concentrations were significantly higher in agricultural riverine wetlands (total phosphorus and total nitrogen 30% higher). These wetlands exhibited higher relative coverage of floating anchored macrophytes and the absence of submerged vegetation. They showed significantly lower taxonomic richness and 40% lower density of macroinvertebrates, and a higher relative abundance of scrapers and predators. Wetlands of both land uses had a lower total density of macroinvertebrates and a higher abundance of tolerant desiccation taxa in the dry period. Particular differences between land uses, such as lower dissolved oxygen concentrations and lower macroinvertebrate diversity in agricultural wetlands, were found during the dry period. These findings indicate that the differences between land uses seemed to increase during the aforementioned period. Further studies in riverine wetlands of both land uses must be carried on to generalize the results found. Despite this limitation, this study provides evidence of the effects of the surrounding landscape and hydrologic periods in the environmental characteristics, as well as the macrophyte and macroinvertebrate assemblages of the riverine wetlands studied.
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Freshwater ecosystems are exposed to an increasing number of stressors, challenging their biomonitoring and management. Despite recent advances in multiple-stressor research, regional-scale assessments in areas with high freshwater biodiversity and increasing anthropogenic pressure are urgently needed. We reviewed 61 studies focused on freshwater individuals, populations and communities from the Iberian Peninsula to (i) quantify the frequency of experimental approaches used (manipulative, observational), aquatic systems, biological organization levels, and types of organisms and modelled responses, (ii) identify key individual stressors and the frequency of significant positive (increase in response magnitude) and negative (decrease) effects and (iii) determine types of interacting stressors and the frequency of their combined effects. Our dataset comprised 409 unique responses to 13 types of individual stressors, 34 stressor pairs and 12 high-order interactions (3- and 4-way). We found a higher prevalence of manipulative (85 %) respect to observational studies, and a greater focus on lotic systems (59 %) and heterotrophic organisms (58 %). The most studied stressors were nutrient (Nutr), thermal (Therm), hydrologic (Hydr), ultraviolet radiation (UVR), toxic (Toxic) and salinity (Sal) stress and land-use pressure. Individual stressors showed a higher proportion of negative (34 %) than positive effects (26 %). Nutr × UVR, Toxic × Toxic, Therm × Toxic, Hydr × Toxic, Sal × Therm, and Nutr × Therm were the most studied stressor pairs. Non-interactive (50 %) and interactive responses (50 %) were balanced. Antagonistic effects (18 %) were slightly more common than synergisms (15 %), reversal or opposing (13 %) and high-order interactions (4 %). Such proportions varied within experimental approaches, biological organization levels and organism types. Our findings are helpful to manage certain stressor combinations in Iberian freshwaters. Further efforts in Iberian multiple-stressor research should be directed to (i) intensify the study of lentic systems, (ii) explore more observational data, (iii) autotrophic organisms and (vi) biodiversity-ecosystem functioning responses, and (v) cover a wider range of stressors and (vi) more complex interacting stressor scenarios.
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Farmyards are commonly conceptualised as point sources of nutrient pollution nested within the wider agricultural landscape. However, within farmyards there are individual sources and delivery pathways, each of which are impacted by a range of management practices and infrastructure. Rainfall mobilizes these nutrients, which may then be delivered to a receptor or to the wider drainage network. As such, the nutrient transfer continuum (NTC) which has been established as a framework to understand and mitigate nutrient loss at a landscape scale can be similarly applied to disentangle the stages of nutrient transfer from farmyards. The NTC differentiates nutrient transfer into source, mobilization, delivery, and impact stages. This differentiation allows targeting of mitigation measures and evaluation of costs and benefits. This review paper applies the nutrient transfer continuum template to farmyard nitrogen and phosphorus transport to conceptualise causative factors and to identify mitigation options. This article is protected by copyright. All rights reserved The nutrient transfer continuum framework is applied to farmyard N and P losses. Nutrient sources include urine, faeces, silage effluent, and parlour washings. Mobilization is controlled by the timing and magnitude of rainfall. Delivery is controlled by connectivity of the farmyard with the drainage network. Mitigation measures include management and infrastructure.
Thesis
Freshwaters provide essential ecosystem services. Particularly, the use of plant protection products in agricultural areas and other chemicals used in industry might influence the aquatic food web. Within the prospective risk assessment of plant protection products, higher-tier studies with semi-field aquatic mesocosms can provide further information on the risk of a pesticide on ecosystem level. Hereby, it is important that vulnerable species are represented within the tested aquatic biocenosis, e. g. macroinvertebrates with long generation times or minor fecundity. The number of vulnerable species is often higher in lotic waterbodies compared to lentic ones. Furthermore, microorganisms play an important role in running waters, because they e.g. decompose leaf litter and in doing so they make nutrients available for other aquatic organisms. However, within the current ecotoxicological risk assessment of plant protection products no direct and indirect effect on microorganism community apart from algae will be assessed in laboratory and semi-field studies. In the present work approaches were developed to assess the risk of plant protection products on representative lotic waterbody biocenosis. Here, newly constructed stream mesocosms were used for conducting two higher-tier studies. Close attention was focused on macroinvertebrates and microorganisms. In the first study the plant protection products carbaryl with insecticidal mode of action was used as a model pesticide. Focus of the second study was the risk assessment of fungicides on the aquatic biocenosis and simultaneously develop new suitable methods for the risk assessment of fungicides within higher-tier studies on aquatic microorganisms. Tebuconazole was used as model fungicide. For both case studies the newly constructed stream mesocosms were realistically assembled representing a small lotic waterbody within an agricultural area and pesticide related effects on macroinvertebrates and microorganisms were observed. The newly constructed stream mesocosms possess a high ecological force of expression and can be used within aquatic risk assessment of plant protection products and other chemicals for higher-tier testing.
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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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RESUMO - As características do escoamento influenciam diretamente a fauna bentônica de um riacho. Este estudo tem como objetivos avaliar (i) se micro-habitats artificiais colonizados em um riacho alcançam composição, riqueza e abundância similares da assembleia no riacho e (ii) a resposta de comunidade bentônica a alterações de vazão em um canal hidráulico em termos de propensão à deriva. Água e invertebrados do manancial de Taboões, Parque Estadual da Serra do Rola Moça, Belo Horizonte, MG foram coletados e transferidos para o canal hidráulico do CEFET-MG, para identificar os efeitos de alterações hidráulicas sobre a estrutura da comunidade de (i) invertebrados que colonizaram micro-habitats artificiais durante 71 dias e (ii) invertebrados transferidos diretamente do riacho (sem pré-colonização). Os resultados permitem concluir que a colonização de micro-habitats experimentais foi eficaz, e que as alterações de vazão modificaram a densidade de indivíduos Ephemeroptera e Diptera no drift dos experimentos. A composição e a riqueza de macroinvertebrados em drift não sofreu alteração evidenciando que os organismos coletados estão adaptados a mudanças bruscas de vazão. Estes experimentos subsidiarão futuros experimentos eco-hidráulicos em mesocosmos in situ para testar os efeitos de mudanças globais sobre biodiversidade e processos ecológicos em riachos de cabeceira. ABSTRACT-The river flow characteristics influence directly the benthic fauna of a stream. This study aims to evaluate (i) if artificial microhabitats colonized in a stream reach similar composition, richness, and abundance of the instream assemblages and (ii) the response of a benthic community to flow changes in terms of propensity to drift. Water and invertebrates were collected on the Taboões spring, Serra do Rola Moça State Park, Belo Horizonte (MG) and transferred to hydraulic channel of CEFET-MG in order to identify the effects of hydraulic changes on the community structure of (i) invertebrates that colonized artificial micro-habitats for 71 days and (ii) invertebrates transferred directly from the stream (no pre-colonization). The results allow concluding that the process of colonization was effective, and the flow changes modified the density of Ephemeroptera and Diptera individuals in drift. The composition and richness of macroinvertebrates in the drift did not change, evidencing that benthic organisms are adapted to sudden changes of flow. These experiments will support future eco-hydraulic experiments in mesocosms in situ to test the effects of global changes on biodiversity and ecological processes in headwater streams. Palavras-chave-experimentos eco-hidráulicos, mesocosmos, bioindicadores bentônicos.
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Anthropogenic water turbidity derived from suspended solids (SS) is caused by reservoir sediment management practices such as drawdown flushing. Turbid water induces stress in many aquatic organisms, but the effects of turbidity on oxidative stress responses in aquatic insects have not yet been demonstrated. Here, we examined antioxidant responses, oxidative damage, and energy reserves in caddisfly (Stenopsyche marmorata) larvae exposed to turbid water (0 mg SS L⁻¹, 500 mg SS L⁻¹, and 2000 mg SS L⁻¹) at different temperatures. We evaluated the combined effects of turbid water and temperature by measuring oxidative stress and using metabolic biomarkers. No turbidity level was significantly lethal to S. marmorata larvae. Moreover, there were no significant differences in antioxidant response or oxidative damage between the control and turbid water treatments at a low temperature (10 °C). However, at a high temperature (25 °C), turbid water modulated the activity of the antioxidant enzymes superoxide dismutase and catalase and the oxygen radical absorbance capacity as an indicator of the redox state of the insect larvae. Antioxidant defenses require energy, and high temperature was associated with low energy reserves, which might limit the capability of organisms to counteract reactive oxygen species. Moreover, co-exposure to turbid water and high temperature caused fluctuation of antioxidant defenses and increased the oxidative damage caused by the production of reactive oxygen species. Furthermore, the combined effect of high temperature and turbid water on antioxidant defenses and oxidative damage was larger than the individual effects. Therefore, our results demonstrate that exposure to both turbid water and high temperature generates additive and synergistic interactions causing oxidative stress in this aquatic insect species.
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Abstract This work addresses human stressors and their impacts on fish assemblages at pan-European scale by analysing single and multiple stressors and their interactions. Based on an extensive dataset with 3105 fish sampling sites, patterns of stressors, their combination and nature of interactions, i.e. synergistic, antagonistic and additive were investigated. Geographical distribution and patterns of seven human stressor variables, belonging to four stressor groups (hydrological-, morphological-, water quality- and connectivity stressors), were examined, considering both single and multiple stressor combinations. To quantify the stressors' ecological impact, a set of 22 fish metrics for various fish assemblage types (headwaters, medium gradient rivers, lowland rivers and Mediterranean streams) was analysed by comparing their observed and expected response to different stressors, both acting individually and in combination. Overall, investigated fish sampling sites are affected by 15 different stressor combinations, including 4 stressors acting individually and 11 combinations of two or more stressors; up to 4 stressor groups per fish sampling site occur. Stressor-response analysis shows divergent results among different stressor categories, even though a general trend of decreasing ecological integrity with increasing stressor quantity can be observed. Fish metrics based on density of species ‘intolerant to water quality degradation’ and ‘intolerant to oxygen depletion” responded best to single and multiple stressors and their interactions. Interactions of stressors were additive (40%), synergistic (30%) or antagonistic (30%), emphasizing the importance to consider interactions in multi-stressor analyses. While antagonistic effects are only observed in headwaters and medium-gradient rivers, synergistic effects increase from headwaters over medium gradient rivers and Mediterranean streams to large lowland rivers. The knowledge gained in this work provides a basis for advanced investigations in European river basins and helps prioritizing further restoration and management actions.
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Spatial and temporal changes in water quality and in the macroinvertebrate community were investigated in a Mediterranean drainage chronically exposed to domestic sewage effluents. Organic pollution levels at some sampling stations were extremely high. However, selfpurification significantly reduced organic load in some stream reaches. From a temporal point of view rainfall strongly diminished organic pollution, especially in the most polluted stream sections. The macroinvertebrate community was greatly impoverished in comparison with other nearby catchments. Macroinvertebrate relative density, richness and Shannon diversity index, significantly increased with a reduction in organic pollution. At the same time, these macroinvertebrate community indexes were negatively correlated to temporal heterogeneity in physico-chemical conditions. The use of a higher taxonomic level classification is discussed as a rapid and effective mean of organic pollution monitoring in Mediterranean streams.
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We examined how wastewater treatment plant (WWTP) inputs affect fluvial biofilm functioning and structure developing on river surface sediments in two different reaches characterized by different anthropogenic pressures. The upper reach includes one site before and one after Palautordera WWTP (Pref and P, respectively); the lower reach includes one site before and one after Tordera WWTP (Tref and T, respectively). We performed an ex situ translocation experiment which resulted in four treatments (Pref-P, Pref-T, Tref-T, Tref-P) and in three different impact grades according to a translocation gradient defined by water chemical changes between sites, being Tref-T the lowest translocation gradient, Pref-P and Tref-P the medium translocation gradient, and Pref-T the highest translocation gradient. After receiving WWTP inputs, upper reach communities (Pref-P and Pref-T treatments) had a decrease in live bacteria and an inhibition of extracellular enzyme activities, while lower reach communities (Tref-T and Tref-P treatments) showed an increase of enzyme activities. Treatments with the highest and lowest translocation gradients resulted in different metabolic fingerprints. Results suggest that the origin and sensitivity of the receiving community determines its functional response and also reinforce the idea that the impact level is an influential aspect to consider when analyzing community responses to anthropogenic impacts.
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The potential for complex synergistic or antagonistic interactions between multiple stressors presents one of the largest uncertainties when predicting ecological change but, despite common use of the terms in the scientific literature, a consensus on their operational definition is still lacking. The identification of synergism or antagonism is generally straightforward when stressors operate in the same direction, but if individual stressor effects oppose each other, the definition of synergism is paradoxical because what is synergistic to one stressor's effect direction is antagonistic to the others. In their highly cited meta-analysis, Crain et al. (Ecology Letters, 11, 2008: 1304) assumed in situations with opposing individual effects that synergy only occurs when the cumulative effect is more negative than the additive sum of the opposing individual effects. We argue against this and propose a new systematic classification based on an additive effects model that combines the magnitude and response direction of the cumulative effect and the interaction effect. A new class of “mitigating synergism” is identified, where cumulative effects are reversed and enhanced. We applied our directional classification to the dataset compiled by Crain et al. (Ecology Letters, 11, 2008: 1304) to determine the prevalence of synergistic, antagonistic, and additive interactions. Compared to their original analysis, we report differences in the representation of interaction classes by interaction type and we document examples of mitigating synergism, highlighting the importance of incorporating individual stressor effect directions in the determination of synergisms and antagonisms. This is particularly pertinent given a general bias in ecology toward investigating and reporting adverse multiple stressor effects (double negative). We emphasize the need for reconsideration by the ecological community of the interpretation of synergism and antagonism in situations where individual stressor effects oppose each other or where cumulative effects are reversed and enhanced.
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We analyzed long-term changes in macroinvertebrate communities in a Mediterranean temporary stream in southern Portugal over 15 y (1993-2008) at 10 locations with 3 degrees of physicochemical disturbance (reference, high disturbance, and mild disturbance). We related year-to-year variation of macroinvertebrate communities to long-term (59 y) information on precipitation and temperature. Our goals were to: 1) determine the stability of macroinvertebrate communities in the stream, 2) establish the influence of physicochemical disturbance on community stability, 3) assess the influence of climate change on the macroinvertebrate communities, and 4) assess the interactive effects of climate change and disturbance level on macroinvertebrate communities. Community structure varied naturally from year to year, but changes in taxon richness and evenness were much stronger and more unpredictable in disturbed than in other sites. In the long term, the more diverse (reference) and the poorest (disturbed) communities were stable, whereas communities affected by mild disturbance slowly decreased in taxon richness (slope = -0.07, r(2) = 0.38). This decrease could be a response to the continuous stress or to climate change. The multivariate patterns over time of invertebrate communities at mildly disturbed sites were the only patterns significantly correlated with climatic patterns. In the past 59 y in this Mediterranean area (southeastern Europe), winter temperature has increased 1 degrees C and precipitation has decreased 1.5 mm/d. Marked changes in community composition (70-80% Bray-Curtis dissimilarity) occurred only in years of extremely low precipitation or temperature. In years of climatic extremes and at chemically disturbed sites, Orthocladiinae and Simuliidae became dominant. In this stream, a shift in community equity occurs before species elimination. This shift might be useful as an early warning for biodiversity loss because of disturbance or climate change. We recommend continued sampling of reference sites for monitoring purposes so that effects of climate change can be established and so that contemporary human disturbance can be assessed relative to an adjusted reference condition.
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Running water ecosystems of Europe are affected by various human pressures. However, little is known about the prevalence, spatial patterns, interactions with natural environment and co-occurrence of pressures. This study represents the first high-resolution data analysis of human pressures at the European scale, where important pressure criteria for 9330 sampling sites in 14 European countries were analysed. We identified 15 criteria describing major anthropogenic degradation and combined these into a global pressure index by taking additive effects of multiple pressures into account. Rivers are affected by alterations of water quality (59%), hydrology (41%) and morphology (38%). Connectivity is disrupted at the catchment level in 85% and 35% at the river segment level. Approximately 31% of all sites are affected by one, 29% by two, 28% by three and 12% by four pressure groups; only 21% are unaffected. In total, 47% of the sites are multi-impacted. Approximately 90% of lowland rivers are impacted by a combination of all four pressure groups.
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Maintenance of suitable conditions in lowland rivers for both fish passage and resident species is crucial to ensuring the long-term sustainability of fish populations. The dissolved oxygen concentration of water is a key factor controlling habitat quality for fish and a critical measure of stream health. Continued land use intensification and greater exploitation of water resources has contributed towards increasing the frequency and duration of low dissolved oxygen events in lowland rivers and the associated risk of adverse effects on fish communities. Revised guidelines are therefore proposed to support setting of biologically relevant dissolved oxygen limits for the protection of New Zealand freshwater fish communities. These guidelines account for both event magnitude and duration, identify different protection levels based on the risk of negative impacts and are based on current scientific knowledge on the tolerances of New Zealand fish species.
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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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River impoundments and waste water discharge are a serious threat to the integrity and biodiversity of river ecosystems, especially in central Italy. Benthic macroinvertebrates were sampled in autumn and summer along the Aniene River to assess the cumulative biological effect of the numerous dams and sewage treatment plants that affect its middle and lower course. We hypothesized that (i) increasing habitat impairment would promote the formation of nestedness in species assemblage, where species poor locations support only a sub-set of organisms from richer sites; (ii) specific life-history traits would confer sensitivity to habitat degradation. Patterns of macroinvertebrate richness and diversity along the river tracked the distribution of dams and sewage treatment plants. Partial Mantel test showed that dissimilarity in assemblages increased with the number of dams and treatment plants between reaches after controlling for longitudinal distance. Assemblages were significantly nested, and nestedness appeared related to both water quality gradients (phosphorous, turbidity) that reflected anthropogenic inputs, and to natural gradient in altitude. Reaches with nested assemblages (supporting a sub-set of the species pool) were characterized by greater representations of taxa with shorter life cycles, while, in contrast, species rich sites supported taxa with longer life cycles and lower dispersal ability. These results suggest that the cumulative effect of dams and sewage treatment plants promoted the formation of nested subsets in species distribution. Moreover, it appeared that certain functional traits that conferred sensitivity also dictated the progressive non-random loss of taxa in face of multiple anthropogenic stressors. These findings have conservation implications in the regions, but need to be considered preliminary since anthropogenic and natural factors co-varied systematically along the study river precluding the identification of single factor effects.
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The effect of different dissolved oxygen (DO) concentrations on the macroinvertebrate assemblages from 2 Australian tropical streams (1 upland, 1 lowland) was measured using artificial stream mesocosms. Responses to 5-d exposures were tested. Both the upland and lowland assemblages showed a similar response. Most taxa tolerated all but very low DO levels (<10% saturation), although a reduction in emergence of insect taxa at intermediate levels (25–35% and 10–20% saturation) was observed. Mayflies showed the highest sensitivity to low oxygen conditions, and lethal effects were observed at DO levels <20% saturation for several upland and lowland species. For other taxa, including several Chironomidae, mortality was observed when oxygen concentrations were below 8% saturation. A drift response was observed only when oxygen concentrations reached near lethal levels (≤10% saturation). The lack of a drift response at DO concentrations of 25 to 35% and 10 to 20% saturation indicates that, in moderately poor oxygen conditions, macroinvertebrates will remain at a location and, hence, experience sublethal effects such as suppressed emergence. It is clear that these animals can persist in hypoxic conditions in the short term. However, because of sublethal effects, understanding how low DO concentrations affect natural assemblages of aquatic macroinvertebrates may require studies of populations over several generations.
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Drift in the River Negro (Asturias, Spain) was dominated by terrestrial invertebrates, chironomid larvae, simuliid larvae, water mites and the mayfly Baetis rhodani. Trichopterans and Leuctra spp. (plecopterans) occasionally exhibited increased abundances related to events in their life cycle (hatching, emergence). Total numbers of drifting macroinvertebrates increased after sunset, and on some dates a second, pre-dawn peak appeared. Baetis spp., plecopterans, adult aquatic Coleoptera and simuliid larvae drifted mostly at night. Terrestrial invertebrates and water mites were more abundant during the day, whereas trichopterans, chironomid larvae and naidid oligochaetes showed no consistent diel pattern. Drift composition changed seasonally and daily. Seasonal changes appeared to be determined mainly by seasonal shifts in the assemblage of benthic macroinvertebrates. The combined use of UPGMA cluster analysis and detrended correspondence analysis showed that seasonal variation was the major factor influencing overall drift composition, but that diel changes were only slightly less important. The degree of diel variation also changed seasonally. In January and March, day and night samples from a given date were quire similac In contrast, in May and October, diel variation was greater and the dissimilarity between day and night samples was comparable to that between samples from different dates.
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Hypoxia can have profound effects on individual organisms. This chapter focuses on the mechanisms different kinds of animals possess to avoid, tolerate, and adapt to low levels of oxygen in water; selected examples illustrate these mechanisms. While some organisms can detect and avoid hypoxic water, avoidance is not always possible, especially in the case of sessile organisms. When an organism cannot avoid hypoxia, its response may depend on the intensity and thz duration of the bout of low oxygen. Examples of responses to hypoxia include a depression in feeding as well as a decrease in molting and growth rates. During acute exposures to hypoxia some organisms can maintain aerobic metabolism by making effective use of a respiratory pigment, or increasing ventilation rates, or increasing the flow of blood past the respiratory surfaces or combinations of all three. Responses to chronic hypoxia are different and include the production of greater quantities of respiratory pigment and changing the structure of the pigment to one with an adaptive higher oxygen affinity. Many organisms respond to hypoxia by switching fiom aerobic to anaerobic metabolism and some simply reduce their overall metabolism. Hypoxia is often accompanied by hypercapnia (an elevation in water C02), which produces an acidification of the body tissues, including the blood, and has physiological implications that can also be profound and separate from the effects of low oxygen. Finally, there is evidence that hypoxia can inhibit immune responses, causing greater mortality than would otherwise occur when organisms are challenged with a pathogen.
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Rivers are impacted by multiple stressors that can interact to create synergistic, additive or antagonistic effects, but experimental studies on fish encompassing more than one stressor are seldom found. Thus, there is the need to study stressors through multifactorial approaches that analyse the impact of fish exposure to multiple stressors and evaluate fish sensitivity to stressor combinations. Some of the most common impacts to Mediterranean rivers are of two natures: i) water abstraction and ii) diffuse pollution. Therefore, the present study aims at studying the responses of potamodromous fish facing combinations of: 1) a primary stressor (two levels of connectivity reduction due to water scarcity), and 2) a secondary stressor (three levels of oxygen depletion due to increase organic load - of anthropogenic nature). Schools of five wild fish from a cyprinid species (Luciobarbus bocagei) were placed in a flume, equipped with see-through sidewalls to allow for behavioural analysis, and subjected to different combinations of the stressors. Results show that at the unconnected level the primary stressor (lack of connectivity) overrode the effect of the secondary stressor (oxygen depletion), but when connectivity existed oxygen depletion caused a reduction of fish movements with decreasing oxygen concentrations. This multifactorial study contributes to improved prediction of fish responses upon actual or projected pressure scenarios.
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Flow reduction generated by water abstraction can alter abiotic and biotic properties of stream ecosystems. We hypothesized that reducing stream flow will reduce oxygen levels affecting sensitive invertebrates. We experimentally suppressed flow with longitudinal barriers in two lowland streams of mesotrophic and eutrophic status In each stream we fixed an upstream free flowing control and two downstream disturbed stretches without flow: an initial stagnation stretch and a final drought stretch separated from the stagnation by sand bags to force a greater lowering of the water level. Invertebrates were sampled in control and disturbed stretches before and after the experimental setup for 10 weeks, and temperature and oxygen were recorded with data loggers. Flow reduction caused a significant decrease in oxygen, resulting in hypoxia (< 4 mg O2/L) in the stagnation stretches and anoxia (0 mg O2/L) in the drought stretches mainly at night, without influencing water temperature. Invertebrate responded with differential sensitivity to flow and oxygen reduction, some indicator taxa declined at 7.3 mg O2/L, others at 6.3 mg O2/L, while at 5.3 mg O2/L many taxa were severely reduced. Flow reduction generated oxygen depletion, reducing rheophilous and oxygen dependent taxa, while favouring tolerant limnophilous taxa with atmospheric respiration. Passive filterers and scrapers were significantly reduced. Our results indicate that flow reduction can cause hypoxia and anoxia in lowland streams and is an unforeseen effect not addressed in the assessment of flow reduction impacts to streams. Further research is required to evaluate if spatially extensive flow reductions and hypoxia result in long-term impairment of stream biodiversity and function.
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Spatial avoidance is a mechanism by which many organisms prevent their exposure to environmental stressors, namely chemical contaminants. Numerous studies on active avoidance and drift by aquatic organisms, as well as the main approaches used to measure both responses, were reviewed. We put forward a particular recommendation regarding methodological approaches: active avoidance should preferably be evaluated under a dilution gradient in a multi-compartmented system instead of in a bi-compartmented system. Available data on spatial avoidance from contamination indicate that emigration can occur at even lower contaminant concentrations than sub-individual noxious effects (assessed with the traditional forced-exposure assays), challenging the widely accepted paradigm in ecotoxicology that contaminant-driven adverse consequences at the population level result from a time delayed cascade of sequentially linked biochemical, cellular, physiological, and finally whole organism deleterious effects. Therefore, contaminants should not be viewed solely as potential toxicants at the individual level, but also as potential disturbers of habitats, by making the latter, at least partially, unsuited to accommodate life. Also, exposure to contamination is needed to trigger avoidance, but uptake is not mandatory, which demands the concept of exposure to be expanded, to include also the mere perception of the stressor. Since emigration eventually leads to local population extinction, and thus to severe implications for ecosystem structure and functioning, we then recommend that avoidance data be incorporated in environmental risk assessment schemes.
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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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Land-use changes have degraded ecosystems worldwide. A particular concern for freshwater biodiversity and ecosystem function are stressors introduced by intensified agriculture. Typically several stressors affect freshwater ecosystems simultaneously. However, the combined effects of these multiple stressors on streams and rivers are still poorly understood, yet of critical importance to improve freshwater management. We investigated responses of benthic macroinvertebrates to three globally important agricultural stressors affecting streams (nutrient enrichment, fine sediment deposition and reduced current velocity), using 64 stream mesocosms (full-factorial 2 × 2 × 2 design, eight replicates of each treatment combination) established on the banks of the Breitenbach Stream (Hesse, Germany). The experiment ran for 1 month (16 days of colonisation, 14 days of manipulations), and all invertebrates in the mesocosms were collected at the end of this period. Fourteen of the 17 studied invertebrate response variables were affected by one or more stressors each. Negative effects on richness or abundance of pollution-sensitive Ephemeroptera, Plecoptera and Trichoptera (EPT) taxa were particularly common. Overall, both sediment addition and stream flow velocity reduction had pervasive and strong effects. Responses to sediment addition were mostly negative, whereas decreased current velocity reduced several EPT metrics but increased the abundances of some of the other common taxa. Nutrient enrichment had few effects, but these were consistently negative. Combined stressor effects were mainly additive, with only two interactions found in total, both between reduced velocity and nutrients (on the crustacean Gammarus spp. and ceratopogonid midges). This finding implies that multiple-stressor responses may be predicted from knowledge of single-stressor effects in this stream community (unlike the often synergistic or antagonistic responses observed elsewhere). However, further taxon-specific responses and interactions among stressors may have been obscured by limited taxonomic resolution, especially for the numerically dominant Chironomidae. Genetic approaches are required to address this limitation in the future.
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The accelerating rate of global change has focused attention on the cumulative impacts of novel and extreme environmental changes (i.e., stressors), especially in marine ecosystems. As integrators of local catchment and regional processes, freshwater ecosystems are also ranked highly sensitive to the net effects of multiple stressors, yet there has not been a large-scale quantitative synthesis. We analysed data from 88 papers including 286 responses of freshwater ecosystems to paired stressors, and discovered that overall, their cumulative mean effect size was less than the sum of their single effects (i.e., an antagonistic interaction). Net effects of dual stressors on diversity and functional performance response metrics were additive and antagonistic, respectively. Across individual studies, a simple vote-counting method revealed that the net effects of stressor pairs were frequently more antagonistic (41%) than synergistic (28%), additive (16%) or reversed (15%). Here, we define a reversal as occurring when the net impact of two stressors is in the opposite direction (negative or positive) from that of the sum of their single effects. While warming paired with nutrification resulted in additive net effects, the overall mean net effect of warming combined with a second stressor was antagonistic. Most importantly, the mean net effects across all stressor pairs and response metrics were consistently antagonistic or additive, contrasting the greater prevalence of reported synergies in marine systems. Here, a possible explanation for more antagonistic responses by freshwater biota to stressors is that the inherent greater environmental variability of smaller aquatic ecosystems fosters greater potential for acclimation and co-adaptation to multiple stressors. This article is protected by copyright. All rights reserved. This article is protected by copyright. All rights reserved.
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Artificial reduction of stream discharge resulted in an increase in benthic invertebrates in the drift. Virtually all bottom-dwelling forms were affected. Entry into the drift seemed an active process initiated by changes in current velocity and depth, and resulting in reversal of the normal avoidance response to light.
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Significance It is generally assumed that shapes encountered in nature have evolved in a way as to maximize the robustness of a species. Nevertheless, given nature’s notoriously complex designs, it is often unclear what is being optimized. The lamellar pattern of fish gills is one of the few cases in which optimization in nature can be well defined. We demonstrate that the lamellar pattern of fish gills has been optimized, such that fish display interlamellar spaces of similar dimension regardless of body mass or species, thereby revealing the primary evolutionary pressure on fish gills. This natural optimization strategy demonstrates how control of the channel arrangement in microfluidic devices enhances heat and mass transfer.
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River regulation and altered land use are two common anthropogenic disturbances in rivers worldwide. Alteration of the stream bed, through processes such as siltation, or of hydrology through river regulation, are likely to modify hyporheic processes or clog interstitial space and thereby affect both hyporheic invertebrates and nutrient dynamics.We tested the separate and combined effects of increased flow and increased fine sediment on hyporheic water quality and invertebrates in flume mesocosms. Each mesocosm contained two bed sediment types: clean sediment in the upstream section and experimentally colmated (EC) sediment (10% by weight of fine sediment) in the downstream section. Two flow rates were established, a higher flow rate to create turbulent flow in six mesocosms and a lower flow rate to create a transitional flow between turbulent and laminar flows in the remaining six mesocosms. Invertebrates and physicochemistry were sampled after 30 days at three depths (5, 11 and 18 cm), and the flows in six of twelve mesocosms were switched. The experiment was concluded after sampling invertebrates and physicochemistry on day 70.The addition of fine sediment to the mesocosm bed generally increased ammonium and decreased nitrate and soluble reactive phosphorus concentrations, decreased oxygen penetration and altered invertebrate assemblage structure. Increased flow rates generally lowered ammonium concentrations, increased soluble reactive phosphorus concentrations, increased oxygen penetration and altered invertebrate assemblage structure. Our hypothesis that higher flows would ameliorate any effects of added fine sediment was generally supported for oxygen penetration and nitrate concentration. However, we observed no differences in interaction effects of flow regime and sediment type either on other nutrient concentrations or invertebrate assemblage structure.The rates of flow used in our mesocosms did not appear to reach the threshold required to remove fine sediment. It is generally recognised that river hyporheic restoration requires a set of objectives against which the outcomes can be measured yet this is often overlooked. Our research provides preliminary guidelines that small amounts of fine sediment can have deleterious ecological effects. However, further research is required to evaluate whether lower percentages of bed fine sediment result in ecological impairment and to determine what flow rates are required to ameliorate colmation impacts.
Article
Global climate change is likely to modify the ecological consequences of currently acting stressors, but potentially important interactions between climate warming and land-use related stressors remain largely unknown. Agriculture affects streams and rivers worldwide, including via nutrient enrichment and increased fine sediment input. We manipulated nutrients (simulating agricultural runoff), deposited fine sediment (simulating agricultural erosion) (2 levels each) and water temperature (8 levels, 0-6°C above ambient) simultaneously in 128 streamside mesocosms to determine the individual and combined effects of the three stressors on macroinvertebrate community dynamics (community composition and body size structure of benthic, drift and insect emergence assemblages). All three stressors had pervasive individual effects, but in combination often produced additive or antagonistic outcomes. Changes in benthic community composition showed a complex interplay among habitat quality (with or without sediment), resource availability (with or without nutrient enrichment) and the behavioural/physiological tendency to drift or emerge as temperature rose. The presence of sediment and raised temperature both resulted in a community of smaller organisms. Deposited fine sediment strongly increased the propensity to drift. Stressor effects were most prominent in the benthic assemblage, frequently reflected by opposite patterns in individuals quitting the benthos (in terms of their propensity to drift or emerge). Of particular importance is that community measures of stream health routinely used around the world (taxon richness, EPT richness and diversity) all showed complex three-way interactions, with either a consistently stronger temperature response or a reversal of its direction when one or both agricultural stressors were also in operation. The negative effects of added fine sediment, which were often stronger at raised temperatures, suggest that streams already impacted by high sediment loads may be further degraded under a warming climate. However, the degree to which this will occur may also depend on in-stream nutrient conditions. This article is protected by copyright. All rights reserved.
Article
Aquatic ecosystems are confronted with multiple stress factors. Current approaches to assess the risk of anthropogenic stressors to aquatic ecosystems are developed for single stressors and determine stressor effects primarily as a function of stressor properties. The cumulative impact of several stressors, however, may differ markedly from the impact of the single stressors, and can result in non-linear effects and ecological surprises. To meet the challenge of diagnosing and/or predicting multiple stressor impacts, assessment strategies should focus on properties of the biological receptors rather than on stressor properties. This change of paradigm is required because (i) multiple stressors affect multiple biological targets at multiple organizational levels, (ii) biological receptors differ in their sensitivities, vulnerabilities and response dynamics to the individual stressors, and (iii) biological receptors function as networks, so that actions of stressors at disparate sites within the network can lead via indirect or cascading effects, to unexpected outcomes.
Article
Streams and rivers in mediterranean-climate regions (med-rivers in med-regions) are ecologically unique, with flow regimes reflecting precipitation patterns. Although timing of drying and flooding is predictable, seasonal and annual intensity of these events is not. Sequential flooding and drying, coupled with anthropogenic influences make these med-rivers among the most stressed riverine habitat worldwide. Med-rivers are hotspots for biodiversity in all med-regions. Species in med-rivers require different, often opposing adaptive mechanisms to survive drought and flood conditions or recover from them. Thus, metacommunities undergo seasonal differences, reflecting cycles of river fragmentation and connectivity, which also affect ecosystem functioning. River conservation and management is challenging, and trade-offs between environmental and human uses are complex, especially under future climate change scenarios. This overview of a Special Issue on med-rivers synthesizes information presented in 21 articles covering the five med-regions worldwide: Mediterranean Basin, coastal California, central Chile, Cape region of South Africa, and southwest and southern Australia. Research programs to increase basic knowledge in less-developed med-regions should be prioritized to achieve increased abilities to better manage med-rivers.
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The Mediterranean and neighboring countries are already experiencing a broad range of natural and man-made threats to water security. According to climate projections, the region is at risk due to its pronounced susceptibility to changes in the hydrological budget and extremes. Such changes are expected to have strong impacts on the management of water resources and on key strategic sectors of regional economies. Related developments have an increased capacity to exacerbate tensions, and even intra- and inter-state conflict among social, political, ecological and economic actors. Thus, effective adaptation and prevention policy measures call for multi-disciplinary analysis and action.This review paper presents the current state-of-the-art on research related to climate change impacts upon water resources and security from an ecological, economic and social angle. It provides perspectives for current and upcoming research needs and describes the challenges and potential of integrating and clustering multi-disciplinary research interests in complex and interwoven human-environment systems and its contribution to the upcoming 5th assessment report of the IPCC.
Article
Water resources are directly and indirectly affected by anthropogenic activities (e.g., changes in land use) and natural factors (e.g., climate change), that is, global change. The Mediterranean basin is one of the most vulnerable regions of the world to global change, and one of the “hot spots” for forthcoming problems of water availability. The present review provides an overview about the relationship between chemical quality (especially concerning organic microcontaminants) and water scarcity, particularly in the Mediterranean area. We include an overview of environmental contaminants and analytical methodologies and consider the fate and the behavior of organic contaminants, and the effects of pollutants on ecosystems.
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Research highlights ► Managed flows in ephemeral creek channels can create hypoxic blackwater. ► Leaf litter is the major cause of DOC increase and DO decline following flooding. ► One month of peak litterfall provides sufficient C to cause hypoxia.
Article
The cladoceran Daphnia pulex was exposed to low oxygen concentration, a kairomone from the predator Chaoborus, and the pesticide carbaryl; the combined effects of these factors on Daphnia life-history characteristics were analyzed. Low oxygen reduced juvenile growth rate, mature size, clutch size, neonate body size, and neonatal necktccth development; the effects depended on size at birth (neonate size), with a stronger influence on smaller neonates. The kairomone and carbaryl had similar effects, apart from the effect on neonatal neckteeth development, which was enhanced. In all treatments, positive relationships were found between individual body size and clutch size, mother’s body size and neonate size, and neonate size and neonatal neckteeth development. The most important effect of the environmental factors is probably reduction in juvenile growth rate. Reduced growth rate induced small size at maturation and thus smaller adult sizes, leading to smaller clutch sizes and producing smaller neonates, which had poorer neckteeth. Synergism was detected statistically for the effects of any pair of the three factors and of all together, indicating that one factor reduces tolerance to the other factors. Daphnia is one of the most important components of freshwater planktonic communities. It is a significant herbivore that affects the composition and abundance of algal communities and is also a significant prey item for vertebrate and invertebrate predators (Larsson and Dodson 1993). The dynamics of Daphnia populations arc affected by numerous environmental factors (Peters and DeBernardi 1987; Dodson and Frey 1989). However, studies of these environmental factors have usually been single-factor studies. In nature, the population dynamics are likely to be influenced by many factors simultaneously, and there are likely to be synergistic interactions among the factors (Hanazato and Dodson 1992). The purpose of the present study was to analyze the combined effects of environmental factors known to affect Daphnia population dy
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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.
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A previously unrecognized morphological adaptation of fishes to oxygen depletion is described. Natural oxygen depletion was simulated by use of sodium sulfite. It was demonstrated that some fishes are adapted to permit use of an oxygen rich layer of water at the atmosphere-water interface. Representative cypronodontoids (Fundulus notatus, Gambusia affinis, and Poecilia reticulata) exhibited maximum adaptation and the greatest survival ability of the species tested. Notemigonus crysoleucas, Brachydanio rerio, Lepomis macrochirus, and L. cyanellus, representing other suborders, showed less adaptation to these conditions and correspondingly lower survival. Micropterus salmoides seemed unadapted for survival in oxygen depleted waters. Carassius auratus exhibited a physiological adaptation, but used the oxygen rich surface water as a supplement.
Article
Effluents produced by pulp mills and sewage plants on northern rivers have the potential for a variety of interacting effects on downstream benthic invertebrates via increased levels of toxicants and nutrients and decreased levels of dissolved oxygen (DO) in the substratum. We experimentally measured the combined effects of these stressors at low temperature (4.5°C) on a common northern river invertebrate, the mayfly Baetis tricaudatus Dodds. Mayflies were exposed in laboratory artificial streams to one of two DO levels (low (5 mg·L-1) versus high (11 mg·L-1)) in the presence and absence of pulp mill and sewage effluent from an Alberta, Canada, mixed-effluent outfall (control river water versus 1% effluent); the DO and effluent treatments bracketed typical field concentrations. In the low-DO treatment, grazing intensity was reduced by 80%, and after 2 weeks of exposure, survival was reduced by 60-90%. Furthermore, 250-350% more mayflies in the low-DO treatment moved upward into regions of greater current velocity close to the surface of the artificial streams, a behavior that would likely make them more susceptible to fish predation in the field. In contrast, the 1% effluent treatment increased mayfly survival (possibly due, in part, to stimulation of increased mayfly grazing intensity by the effluent), although this effect only partly compensated for the pronounced negative impact of low DO levels.
Article
The crustaceans studied were the isopod Asellus intermedius Forbes, and the amphipods Hyalella azteca (Saussure), Gammarus fasciatus Say, and Gammarus pseudolimnaeus Bousfield.Resistance to high temperature decreased with size in A. intermedius and G. fasciatus, but no difference was found for H. azteca. Female Gammarus, were more resistant than males, there was no difference for A. intermedius, and a variable relation in H. azteca. Acclimation temperature could be raised at rates of 2.5 to 5 °C per day, at temperatures above 14 °C. Raising acclimation from 10 to 20 °C increased the lethal temperature (50% mortality in 24 hours) by 1.9 °C in G. fasciatus, 1.3 °C in A. intermedius, 0.5 °C in G. pseudolimnaeus, and apparently not at all in H. azteca. There was no seasonal variation in resistance after A. intermedius was acclimated in the laboratory.Two difficulties encountered were mortality during acclimation and short survival of controls, but careful checking showed that neither greatly affected the reported resistance.Estimates of the ultimate 24-hour lethal temperatures were 34.6 °C for A. intermedius and G. fasciatus, 33.2 °C for H. azteca, and 29.6 °C for G. pseudolimnaeus. The concentrations of low oxygen causing 50% mortality in 24 hours, with acclimation and testing at 20 °C, were.0.03 mg/l for A. intermedius, 0.7 mg/l for H. azteca, 2.2 mg/l for G. pseudolimnaeus, and 4.3 mg/l for G. fasciatus. Lethal temperatures would seldom seem to affect distribution under natural conditions, but resistance to low oxygen fits field observations fairly closely.