| 1. |
- Bruder, Andreas, et al.
(författare)
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Biotic interactions modify multiple-stressor effects on juvenile brown trout in an experimental stream food web
- 2017
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Ingår i: Global Change Biology. - : John Wiley & Sons. - 1354-1013 .- 1365-2486. ; 23:9, s. 3882-3894
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Tidskriftsartikel (refereegranskat)abstract
- Agricultural land use results in multiple stressors affecting stream ecosystems. Flow reduction due to water abstraction, elevated levels of nutrients and chemical contaminants are common agricultural stressors worldwide. Concurrently, stream ecosystems are also increasingly affected by climate change. Interactions among multiple co-occurring stressors result in biological responses that cannot be predicted from single-stressor effects (i.e. synergisms and antagonisms). At the ecosystem level, multiple-stressor effects can be further modified by biotic interactions (e.g. trophic interactions). We conducted a field experiment using 128 flow-through stream mesocosms to examine the individual and combined effects of water abstraction, nutrient enrichment and elevated levels of the nitrification inhibitor dicyandiamide (DCD) on survival, condition and gut content of juvenile brown trout and on benthic abundance of their invertebrate prey. Flow velocity reduction decreased fish survival (−12% compared to controls) and condition (−8% compared to initial condition), whereas effects of nutrient and DCD additions and interactions among these stressors were not significant. Negative effects of flow velocity reduction on fish survival and condition were consistent with effects on fish gut content (−25% compared to controls) and abundance of dominant invertebrate prey (−30% compared to controls), suggesting a negative metabolic balance driving fish mortality and condition decline, which was confirmed by structural equation modelling. Fish mortality under reduced flow velocity increased as maximal daily water temperatures approached the upper limit of their tolerance range, reflecting synergistic interactions between these stressors. Our study highlights the importance of indirect stressor effects such as those transferred through trophic interactions, which need to be considered when assessing and managing fish populations and stream food webs in multiple-stressor situations. However, in real streams, compensatory mechanisms and behavioural responses, as well as seasonal and spatial variation, may alter the intensity of stressor effects and the sensitivity of trout populations.
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| 2. |
- Bruder, Andreas, et al.
(författare)
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Multiple-stressor effects on leaf litter decomposition and fungal decomposers in agricultural streams contrast between litter species
- 2016
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Ingår i: Functional Ecology. - : John Wiley & Sons. - 0269-8463 .- 1365-2435. ; 30:7, s. 1257-1266
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Tidskriftsartikel (refereegranskat)abstract
- Agricultural land use commonly exerts multiple stressors on the functioning of stream ecosystems, including leaf litter decomposition and the utilization of this resource in stream food webs. If stressors interact, their cumulative effects on biotic responses cannot be predicted from knowledge of individual stressor effects, posing challenges for management and restoration of ecosystems. We examined the individual and interactive effects of four common agricultural stressors and the role of litter quality on leaf litter decomposition and fungal decomposers. In 128 outdoor, flow-through mesocosms, we manipulated levels of nutrients, a nitrification inhibitor (dicyandiamide), deposited fine sediment and flow velocity. Interactions among these stressors can ensue because, for instance, they jointly affect physicochemical conditions around leaf litter colonized by fungi such as concentrations of dissolved oxygen and nutrients. The two litter species used, deciduous birch and evergreen mahoe, showed contrasting decomposition dynamics, and these differences influenced their response to stressors. Fungi were important for birch litter decomposition but played a minor role for mahoe. Overall, flow velocity reduction and deposited fine sediment had the strongest, mainly negative effects on fungi and litter decomposition, probably as a consequence of reductions in dissolved oxygen available to fungi. However, fine sediment substantially increased mahoe litter mass loss, pointing at fungi-independent processes being relevant for its decomposition. Although interactions among stressors were uncommon, they showed effects of the same magnitude as stressor main effects. Potential mechanisms underlying interactions included reductions in dissolved oxygen and changes in microbial community composition. Knowledge of the effects of multiple agricultural stressors and of litter quality on litter decomposition and litter-associated fungi is crucial for management of forested riparian corridors, which have been shown to efficiently mitigate impacts of agricultural stressors on streams. The contrasting responses of the litter species used in our study warrant consideration of species composition of the riparian vegetation.
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| 3. |
- Effenberger, Michael, et al.
(författare)
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Patchy bed disturbance and fish predation independently influence the distribution of stream invertebrates and algae
- 2011
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Ingår i: Journal of Animal Ecology. - : Wiley. - 0021-8790 .- 1365-2656. ; 80:3, s. 603-14
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Tidskriftsartikel (refereegranskat)abstract
- 1. The identification of factors determining the patchy distribution of organisms in space and time is a central concern of ecology. Predation and abiotic disturbance are both well-known drivers of this patchiness, but their interplay is still poorly understood, especially for communities dominated by mobile organisms in frequently disturbed ecosystems. 2. We investigated the separate and interactive influences of bed disturbance by floods and predation by fish on the benthic community in a flood-prone stream. Electric fields excluded fish predators from half of 48 stream bed patches (area 0·49 m(2) ) with contrasting disturbance treatments. Three types of bed disturbance were created by either scouring or filling patches to a depth of 15-20 cm or by leaving the patches undisturbed, thus mimicking the mosaic of scour and fill caused by a moderate flood. Benthic invertebrates and algae were sampled repeatedly until 57 days after the disturbance. 3. Disturbance influenced all ten investigated biological response variables, whereas predation affected four variables. Averaged across time, invertebrate taxon richness and total abundance were highest in stable patches. Algal biomass and densities of five of the seven most common invertebrate taxa (most of which were highly mobile) were higher in fill than in scour patches, whereas two taxa were more abundant in scour and stable than in fill patches. Furthermore, two common invertebrate grazers were more abundant and algal biomass tended to be reduced in fish exclusion patches, suggesting a patch-scale trophic cascade from fish to algae. 4. Our results highlight the importance of patchy physical disturbance for the microdistribution of mobile stream organisms and indicate a notable, but less prevalent, influence of fish predation at the patch scale in this frequently disturbed environment. Disturbance and predation treatments interacted only once, suggesting that the observed predation effects were largely independent of local bed disturbance patterns.
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| 4. |
- Lange, Katharina, et al.
(författare)
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Light, nutrients and grazing interact to determine stream diatom community composition and functional group structure
- 2011
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Ingår i: Freshwater Biology. - : Wiley. - 0046-5070 .- 1365-2427. ; 56:2, s. 264-278
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Tidskriftsartikel (refereegranskat)abstract
- P>1. Benthic algal communities are shaped by the availability of nutrients and light and by herbivore consumption. Many studies have examined how one of these factors affects algal communities, but studies simultaneously addressing all three are rare. 2. We investigated the effects of nutrients, light and a herbivore (the snail Potamopyrgus antipodarum) on benthic stream algae in a fully factorial experiment in 128 circular streamside channels. Four nutrient levels (none added to highly enriched), four snail grazing pressures (no snails to 777 individuals m-2) and two light levels (ambient and 65% reduced) were applied. Colonising algae were dominated by diatoms (Bacillariophyta), which were determined to species using acid-cleaned samples and assigned to functional groups according to their physiognomic growth form. 3. Diatom community structure changed considerably in response to our manipulations. Light had the strongest influence (as indicated by manova effect size), whereas nutrients had an intermediate effect and grazing was fairly weak. Relative abundances of six common diatom taxa decreased under reduced light, whereas five others became more prevalent. Eight taxa benefitted from nutrient enrichment, while three became rarer. Grazing affected the relative density of only one common taxon, which increased at higher grazing pressure. 4. Diatom functional groups also responded strongly. 'Low profile' taxa dominated at low resource levels (nutrients and especially light), whereas 'high profile' and 'motile' taxa became markedly more prevalent at higher resource levels. 5. Two-way interactions between experimental factors were quite common. For example, Planothidium lanceolatum and Rossithidium petersenii responded more strongly to nutrient enrichment at reduced than at ambient light, whereas Cocconeis placentula responded more strongly at ambient light. For diatom functional groups, the benefit of nutrient enrichment for 'motile' diatoms was greater at ambient than at reduced light. 6. Our results imply that multifactor experiments are required to determine the main forces driving the composition of benthic algal communities. Further, our findings highlight the considerable potential of using functional algal groups as indicators of changing environmental conditions to complement the traditional taxonomic approach.
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| 5. |
- Liess, Antonia, et al.
(författare)
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Landuse intensity in stream catchments affects the benthic food web : consequences for nutrient supply, periphyton C:nutrient ratios, and invertebrate richness and abundance
- 2012
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Ingår i: Freshwater Science. - : University of Chicago Press. - 2161-9549 .- 2161-9565. ; 31:3, s. 813-824
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Tidskriftsartikel (refereegranskat)abstract
- Anthropogenic nutrient enrichment increases the supply ratio of N and P to aquatic ecosystems and can affect the identity of the limiting nutrient. Here we focus on how stream communities change along gradients of N and P supply and stream catchment landuse intensity. We used a survey approach in 41 southern New Zealand tributaries to investigate how much changes in water N and P concentrations are reflected in periphyton C:nutrient ratios (C:N or C:P) and how much food quality (high food quality corresponds to low periphyton C:nutrient) is reflected in the abundance and taxonomic richness of benthic invertebrate primary and secondary consumers. We measured streamwater nutrient state, periphyton nutrient ratios, biomass (as chlorophyll a in mu g/cm(2)), algal taxon richness, and macroinvertebrate abundance, taxonomic composition, and richness. We also estimated stream habitat and catchment characteristics, such as current velocity, shading, substrate, geology, and landuse intensity. We calculated the Akaike information criterion (AIC) for each possible multiple linear regression model to select the best predictive models for each response variable. C:nutrient ratios were more strongly negatively related to water-column N than P availability. Neither N nor P availability covaried with periphyton biomass. Lower periphyton C:N partly explained higher grazer, but not predator, abundance. Increased % runoff from pasture and periphyton N:P co-occurred with a decrease in invertebrate taxon richness. For example, a 4x increase in periphyton N:P was related to the loss of similar to 1/2 of invertebrate species, but with high uncertainty (R-2 = 0.13). We conclude landuse intensity affects these southern New Zealand streams, and these effects are mediated by agricultural N runoff into streams (among other factors). Further shifts toward high-intensity farming within stream catchments may lead to losses of benthic species at all trophic levels.
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| 6. |
- Liess, Antonia, et al.
(författare)
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Light, nutrients and grazing interact to determine diatom species richness via changes to productivity, nutrient state and grazer activity
- 2009
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Ingår i: Journal of Ecology. - : Wiley. - 0022-0477 .- 1365-2745. ; 97:2, s. 326-336
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Tidskriftsartikel (refereegranskat)abstract
- 1. Productivity and grazing pressure interact in determining autotroph diversity, because high productivity increases the capability of a plant community to compensate for grazing losses. However, further factors may play a role in shaping diversity, including primary producer nutrient stoichiometry and grazer activity. 2. Our study focuses on the interactions between light, nutrients and grazing in determining species richness and evenness of stream diatoms. By measuring primary producer productivity and nutrient content as well as grazer activity, we attempt to disentangle the different pathways by which the three factors affect diatom species richness and evenness. 3. We hypothesized that high light intensities and nutrient addition would increase species richness by increasing primary productivity and that higher levels of light and nutrients would compensate for negative grazer effects on species richness of primary producers. We also hypothesized that high light intensities would decrease the nutrient content of primary producers, especially when nutrients are limiting, whereas nutrient addition would increase primary producer nutrient content. Last, in addition to changing primary producer nutrient content, light and nutrients would also change grazer activity, thus modifying the interactions between light, nutrients and grazing. 4. We used periphyton and gastropod grazers in an experiment with circular stream channels with four nutrient, two light and four grazing levels to determine individual and combined effects on benthic diatom richness and evenness. After 3 weeks, we determined algal biomass, periphyton nutrient content, diatom species richness and evenness as well as grazer activity. 5. Our results showed that light and nutrients increased species richness and primary producer productivity and nutrient content. Grazing decreased species richness but only at low light levels, possibly because high light levels reduced grazer activity. Evenness was not affected by any single factor alone, but was influenced by nutrient-light and grazing-light interactions. 6. Synthesis. Light, nutrients and grazing interacted in determining primary producer species richness. Their effects were mainly mediated through changes in productivity but primary producer nutrient content and grazer activity also played important roles.
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| 7. |
- Macher, Jan N., et al.
(författare)
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Multiple-stressor effects on stream invertebrates : DNA barcoding reveals contrasting responses of cryptic mayfly species
- 2016
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Ingår i: Ecological Indicators. - : Elsevier. - 1470-160X .- 1872-7034. ; 61:January, s. 159-169
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Tidskriftsartikel (refereegranskat)abstract
- Most freshwater ecosystems are subject to multiple anthropogenic stressors, which commonly reduce biodiversity across all levels. Existing freshwater bioassessment programmes aim at identifying responses of aquatic biota to stressors. For practical reasons, higher-level taxonomic groups (e.g. genus or family) are often used in these programmes. This approach, however, may bias assessment results as different species can differ substantially in their biological traits, thus emphasising the need for species-level data. DNA barcoding can reliably generate species-level data for animals by sequencing a fragment of the mitochondrial cytochrome c oxidase subunit I gene (COI). This allows investigating species-specific responses to environmental stressors. In this study, we sampled 43 stream sites in southern New Zealand spanning wide gradients of agricultural stressors (fine sediment and nutrient levels). We first used conventional morphological assessment to determine stream invertebrate responses to the stressors, focusing on two important indicator taxa, the mayfly Deleatidium and the snail Potamopyrgus. We then tested for the presence of cryptic species in Deleatidium and Potamopyrgus using DNA barcoding of the COI gene for 520 and 305 specimens, respectively. While all Potamopyrgus specimens belonged to a single species, Deleatidium consisted of 12 distinct molecularly identified clades that likely represent distinct species. Finally, we compared stressor responses assessed at genus and species level. While overall Deleatidium abundance was unrelated to stressor levels, some of the individual clades differed clearly in the magnitude and direction of their responses to nutrient and sediment stress. While the most abundant cryptic Deleatidium clade (clade 1) showed no relationship to sediment or nutrient levels, clades 2 and 3 responded negatively to nutrient or sediment increases, respectively. These contrasting patterns indicate that individual freshwater invertebrate species, often merged to a higher taxonomic level for biomonitoring purposes, can differ substantially in their tolerance to stressors and respond in more complex ways than observed at genus level. Overall, our results highlight the considerable potential and importance of including DNA barcoding into freshwater ecosystem assessment and biomonitoring programmes.
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| 8. |
- Piggott, Jeremy J., et al.
(författare)
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Climate warming and agricultural stressors interact to determine stream periphyton community composition
- 2015
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Ingår i: Global Change Biology. - : John Wiley & Sons. - 1354-1013 .- 1365-2486. ; 21:1, s. 206-222
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Tidskriftsartikel (refereegranskat)abstract
- Lack of knowledge about how the various drivers of global climate change will interact with multiple stressors already affecting ecosystems is the basis for great uncertainty in projections of future biological change. Despite concerns about the impacts of changes in land use, eutrophication and climate warming in running waters, the interactive effects of these stressors on stream periphyton are largely unknown. We manipulated nutrients (simulating agricultural runoff), deposited fine sediment (simulating agricultural erosion) (two levels each) and water temperature (eight levels, 0-6 °C above ambient) simultaneously in 128 streamside mesocosms. Our aim was to determine the individual and combined effects of the three stressors on the algal and bacterial constituents of the periphyton. All three stressors had pervasive individual effects, but in combination frequently produced synergisms at the population level and antagonisms at the community level. Depending on sediment and nutrient conditions, the effect of raised temperature frequently produced contrasting response patterns, with stronger or opposing effects when one or both stressors were augmented. Thus, warming tended to interact negatively with nutrients or sediment by weakening or reversing positive temperature effects or strengthening negative ones. Five classes of algal growth morphology were all affected in complex ways by raised temperature, suggesting that these measures may prove unreliable in biomonitoring programs in a warming climate. The evenness and diversity of the most abundant bacterial taxa increased with temperature at ambient but not with enriched nutrient levels, indicating that warming coupled with nutrient limitation may lead to a more evenly distributed bacterial community as temperatures rise. Freshwater management decisions that seek to avoid or mitigate the negative effects of agricultural land use on stream periphyton should be informed by knowledge of the interactive effects of multiple stressors in a warming climate.
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| 9. |
- Salis, Romana K., et al.
(författare)
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Multiple-stressor effects of dicyandiamide (DCD) and agricultural stressors on trait-based responses of stream benthic algal communities
- 2019
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Ingår i: Science of the Total Environment. - : Elsevier. - 0048-9697 .- 1879-1026. ; 693
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Tidskriftsartikel (refereegranskat)abstract
- Agricultural practices often result in multiple stressors affecting stream ecosystems, and interacting stressors complicate environmental assessment and management of impacted streams. The nitrification inhibitor dicyandiamide (DCD) is used for nitrogen management on farmland. Effects of leached DCD on stream ecosystems are still largely unstudied, even though it could be relevant as a stressor on its own or in combination with other agricultural stressors. We conducted two experiments in 128 outdoor stream-fed mesocosms to assess stressor effects on biomass, cell density, taxon richness, evenness and functional trait composition of benthic algal communities. First, we examined responses to a wide DCD gradient (eight concentrations, 0–31 mg L−1) and two additional stressors, deposited fine sediment (none, high) and nutrient enrichment (ambient, enriched). Second, we determined algal responses to four stressors: DCD, sediment, nutrients, and reduced flow velocity. Here DCD treatments included controls, constant application (1.4 mg L−1) and two pulsed treatments mimicking concentration patterns in real streams (peaks 3.5 mg L−1, 2.2 mg L−1). Sediment and nutrient enrichment were influential stressors in both experiments, with fine sediment having the most pervasive effects. In Experiment 2, reduced flow velocity had pervasive effects and stressor interactions were mainly restricted to two-way interactions. DCD had few, weak stressor main effects, especially at field-realistic concentrations (Experiment 2). At the highest concentrations in Experiment 1 (above levels observed in real streams), DCD effects were still rare but some significant stressor interactions occurred. Analyses of functional traits were helpful in identifying potential mechanisms driving changes in densities and community composition. These findings suggest that, while DCD on its own may be a minor stressor, it could have adverse effects on algal communities already exposed to other stressors, a scenario common in agricultural streams.
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| 10. |
- Winkworth, Cynthia L., et al.
(författare)
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Interactive multiple-stressor effects of the antibiotic monensin, cattle effluent and light on stream periphyton
- 2015
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Ingår i: Freshwater Biology. - : John Wiley & Sons. - 0046-5070 .- 1365-2427. ; 60:11, s. 2410-2423
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Tidskriftsartikel (refereegranskat)abstract
- 1. Streams draining agricultural land are simultaneously exposed to multiple stressors including agri-cultural antibiotics and effluent from surface water run-off. The potential interactive effects of thesecontaminants on stream benthic communities are poorly understood.2. Using a streamside channel experiment with a full factorial, repeated-measures design, weassessed the individual and combined effects of the veterinary antibiotic monensin (four concentra-tions versus control), dairy cattle effluent (added versus control) and differing light levels (reducedversus ambient) on benthic stream periphyton (biomass accrual, community composition and ecolog-ical algal guilds). Antibiotic and effluent treatments were applied during a 24-hour pulse to simulaterun-off from farmland, while light was manipulated throughout the experiment, to mimic the pres-ence or absence of riparian shading.3. Periphyton taxon richness was decreased by the two highest antibiotic levels 8 days after thepulse. Multivariate community composition (relative abundances of the 15 most common periphytontaxa) was also affected by all three stressors 8 days post-pulse. However, the periphyton communityrecovered within 16 days post-pulse.4. Interactions among stressors were fairly common, occurring for two of three ecological algal guildsand six of the 15 common taxa. Nevertheless, interactions were generally subtle, without any strongsynergistic or antagonistic patterns.5. Our study shows that the antibiotic monensin can negatively affect stream periphyton communi-ties, but also implies short pulses may not have lasting impacts. The lack of strong synergistic orantagonistic interactions between monensin and light or effluent indicates monensin effects onstream periphyton may be predicted reasonably well based on single-stressor studies.
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