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1.
  • Hladyz, Sally, et al. (author)
  • Stream ecosystem functioning in an agricultural landscape : the importance of terrestrial-aquatic linkages
  • 2011
  • In: Ecosystems in a human-modified landscape. - San Diego : Academic Press. - 9780123747945 ; 44, s. 211-276
  • Book chapter (peer-reviewed)abstract
    • The loss of native riparian vegetation and its replacement with non-native species or grazing land for agriculture is a worldwide phenomenon, but one that is prevalent in Europe, reflecting the heavily-modified nature of the continent's landscape. The consequences of these riparian alterations for freshwater ecosystems remain largely unknown, largely because bioassessment has traditionally focused on the impacts of organic pollution on community structure. We addressed the need for a broader perspective, which encompasses changes at the catchment scale, by comparing ecosystem processes in woodland reference sites with those with altered riparian zones. We assessed a range of riparian modifications, including clearance for pasture and replacement of woodland with a range of low diversity plantations, in 100 streams to obtain a continental-scale perspective of the major types of alterations across Europe. Subsequently, we focused on pasture streams, as an especially prevalent widespread riparian alteration, by characterising their structural (e.g. invertebrate and fish communities) and functional (e.g. litter decomposition, algal production, herbivory) attributes in a country (Ireland) dominated by this type of landscape modification, via field and laboratory experiments. We found that microbes became increasingly important as agents of decomposition relative to macrofauna (invertebrates) in impacted sites in general and in pasture streams in particular. Resource quality of grass litter (e.g., carbon : nutrient ratios, lignin and cellulose content) was a key driver of decomposition rates in pasture streams. These systems also relied more heavily on autochthonous algal production than was the case in woodland streams, which were more detrital based. These findings suggest that these pasture streams might be fundamentally different from their native, ancestral woodland state, with a shift towards greater reliance on autochthonous-based processes. This could have a destabilizing effect on the dynamics of the food web relative to the slower, detrital-based pathways that dominate in woodland streams.
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2.
  • Chauvet, Eric, et al. (author)
  • Litter decomposition as an indicator of stream ecosystem functioning at local-to-continental scales : insights from the European RivFunction project
  • 2016
  • In: Large-scale ecology. - London : Academic Press. - 9780081009352 ; 55, s. 99-182
  • Book chapter (peer-reviewed)abstract
    • RivFunction is a pan-European initiative that started in 2002 and was aimed at establishing a novel functional-based approach to assessing the ecological status of rivers. Litter decomposition was chosen as the focal process because it plays a central role in stream ecosystems and is easy to study in the field. Impacts of two stressors that occur across the continent, nutrient pollution and modified riparian vegetation, were examined at > 200 paired sites in nine European ecoregions. In response to the former, decomposition was dramatically slowed at both extremes of a 1000-fold nutrient gradient, indicating nutrient limitation in unpolluted sites, highly variable responses across Europe in moderately impacted streams, and inhibition via associated toxic and additional stressors in highly polluted streams. Riparian forest modification by clear cutting or replacement of natural vegetation by plantations (e.g. conifers, eucalyptus) or pasture produced similarly complex responses. Clear effects caused by specific riparian disturbances were observed in regionally focused studies, but general trends across different types of riparian modifications were not apparent, in part possibly because of important indirect effects. Complementary field and laboratory experiments were undertaken to tease apart the mechanistic drivers of the continental scale field bioassays by addressing the influence of litter, fungal and detritivore diversity. These revealed generally weak and context-dependent effects on decomposition, suggesting high levels of redundancy (and hence potential insurance mechanisms that can mitigate a degree of species loss) within the food web. Reduced species richness consistently increased decomposition variability, if not the absolute rate. Further field studies were aimed at identifying important sources of this variability (e.g. litter quality, temporal variability) to help constrain ranges of predicted decomposition rates in different field situations. Thus, although many details still need to be resolved, litter decomposition holds considerable potential in some circumstances to capture impairment of stream ecosystem functioning. For instance, species traits associated with the body size and metabolic capacity of the consumers were often the main driver at local scales, and these were often translated into important determinants of otherwise apparently contingent effects at larger scales. Key insights gained from conducting continental scale studies included resolving the apparent paradox of inconsistent relationships between nutrients and decomposition rates, as the full complex multidimensional picture emerged from the large-scale dataset, of which only seemingly contradictory fragments had been seen previously.
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4.
  • Löfgren, Stefan, et al. (author)
  • Long-term effects on water chemistry and macroinvertebrates of selective thinning along small boreal forest streams
  • 2023
  • In: Forest Ecology and Management. - 0378-1127 .- 1872-7042. ; 549
  • Journal article (peer-reviewed)abstract
    • The maintenance of narrow strips of trees (forest buffers) along the shorelines of surface water bodies during logging is a common measure to protect freshwater habitats. The functionality of forest buffers may be improved by actively managing the streamside forest early in the rotation for their eventual function as buffers, including by increasing the proportion of broadleaf trees in spruce-dominated stands. In this study, long-term effects of different selective thinning regimes along two small forest streams were investigated in south-central Sweden. In a young coniferous forest, a c. 10 m-wide band along the streams was selectively thinned in 1998 to create a band with purely broadleaf trees along one of the streams and purely conifers along the other. Forest stand characteristics, water chemistry and benthic macroinvertebrates data were collected during 1996-2003 (before and after selective thinning). The streams were re-investigated 20-22 years after thinning, together with three streams representing operational forest management. The forest adjacent to all five streams was inventoried and litterfall, stream water chemistry, and benthic macroinvertebrates composition were monitored between spring and late autumn during 2018-2020. Twenty years after thinning, the thinned bands beside the streams were still dominated by either broadleaf trees or conifers, depending on the stream. Over the longer term, the differences in water chemistry between the streams with selective thinning were mainly related to lower pH, ANC, Tot-P and Tot-N concentrations in the stream bordered by mainly broadleaf trees. Analysis of benthic macroinvertebrates was based on environmental quality indices (ASPT and EPT), diversity and abundance metrics, and relative abundances of functional feeding groups. Streams with higher broadleaf litter inputs tended to score better on the ASPT and EPT indices than those with lower broadleaf inputs, as well as supporting higher relative abundances of one or more groups of invertebrate detritivores (leaf shredders, collector-gatherers and/or passive filter feeders). This suggests that management of the density of broadleaf trees beside these streams might support higher ecological status and will support a greater proportion of detritivores in benthic food webs.
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5.
  • Angeler, David, et al. (author)
  • Assessing and managing freshwater ecosystems vulnerable to environmental change
  • 2014
  • In: AMBIO: A Journal of the Human Environment. - : Springer Science and Business Media LLC. - 0044-7447 .- 1654-7209. ; 43, s. 113-129
  • Journal article (peer-reviewed)abstract
    • Freshwater ecosystems are important for global biodiversity and provide essential ecosystem services. There is consensus in the scientific literature that freshwater ecosystems are vulnerable to the impacts of environmental change, which may trigger irreversible regime shifts upon which biodiversity and ecosystem services may be lost. There are profound uncertainties regarding the management and assessment of the vulnerability of freshwater ecosystems to environmental change. Quantitative approaches are needed to reduce this uncertainty. We describe available statistical and modeling approaches along with case studies that demonstrate how resilience theory can be applied to aid decision-making in natural resources management. We highlight especially how long-term monitoring efforts combined with ecological theory can provide a novel nexus between ecological impact assessment and management, and the quantification of systemic vulnerability and thus the resilience of ecosystems to environmental change.
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6.
  • Angeler, David, et al. (author)
  • The recovery of European freshwater biodiversity has come to a halt
  • 2023
  • In: Nature. - 0028-0836 .- 1476-4687. ; 620, s. 582-
  • Journal article (peer-reviewed)abstract
    • Owing to a long history of anthropogenic pressures, freshwater ecosystems are among the most vulnerable to biodiversity loss(1). Mitigation measures, including wastewater treatment and hydromorphological restoration, have aimed to improve environmental quality and foster the recovery of freshwater biodiversity(2). Here, using 1,816 time series of freshwater invertebrate communities collected across 22 European countries between 1968 and 2020, we quantified temporal trends in taxonomic and functional diversity and their responses to environmental pressures and gradients. We observed overall increases in taxon richness (0.73% per year), functional richness (2.4% per year) and abundance (1.17% per year). However, these increases primarily occurred before the 2010s, and have since plateaued. Freshwater communities downstream of dams, urban areas and cropland were less likely to experience recovery. Communities at sites with faster rates of warming had fewer gains in taxon richness, functional richness and abundance. Although biodiversity gains in the 1990s and 2000s probably reflect the effectiveness of water-quality improvements and restoration projects, the decelerating trajectory in the 2010s suggests that the current measures offer diminishing returns. Given new and persistent pressures on freshwater ecosystems, including emerging pollutants, climate change and the spread of invasive species, we call for additional mitigation to revive the recovery of freshwater biodiversity.
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7.
  • Bjelke, Ulf, et al. (author)
  • Dieback of riparian alder caused by the Phytophthora alni complex: projected consequences for stream ecosystems
  • 2016
  • In: Freshwater Biology. - : Wiley. - 0046-5070 .- 1365-2427. ; 61, s. 565-579
  • Research review (peer-reviewed)abstract
    • 1. Alder trees (Alnus spp.) are key nitrogen-fixing riparian species in the northern hemisphere. Inputs of nitrogen-rich leaf litter from alder into stream food webs can contribute significantly to nitrogen dynamics at local and landscape scales. Alder trees also provide habitats for terrestrial and aquatic organisms, and help stabilize river banks.  2. Recently, substantial declines in alder stands have occurred along streams in Europe, with damages observed in some parts of North America also. A major driver has been the invasive oomycete pathogen Phytophthora alni species complex, which can spread rapidly along stream networks.  3. This review synthesises information on the pathogen, processes of spread and infection, and its impacts on alder. We further address the potential ecosystem-level and management consequences of the decline of alder, and highlight research needs.  4. The alder dieback caused by P. alni is associated with reductions in shade and quality and quantity of leaf litter. A decline in the structural integrity of branches and roots further threatens bank stability. Stream banks dominated by other tree species or no trees at all will result in ecosystem-level changes both above and below the waterline.  5. The P. alni taxonomic complex includes different species with varying phenotypes. An improved understanding of their environmental tolerances, virulence and evolution, along with the processes regulating the spread and impacts of the pathogen, would assist in identification of the riparian and stream systems most vulnerable not only to invasion but also to the heaviest disease outbreaks and ecosystem-level impacts.  6. Within the P. alni complex, the highly pathogenic hybrid species P. x alni is favoured by mild winters and warm, but not excessively hot summer temperatures suggesting possible changes in distribution and level of impact under future global climate change.
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8.
  • Boyero, Luz, et al. (author)
  • Riparian plant litter quality increases with latitude
  • 2017
  • In: Scientific Reports. - : Nature Publishing Group. - 2045-2322. ; 7
  • Journal article (peer-reviewed)abstract
    • Plant litter represents a major basal resource in streams, where its decomposition is partly regulated by litter traits. Litter-trait variation may determine the latitudinal gradient in decomposition in streams, which is mainly microbial in the tropics and detritivore-mediated at high latitudes. However, this hypothesis remains untested, as we lack information on large-scale trait variation for riparian litter. Variation cannot easily be inferred from existing leaf-trait databases, since nutrient resorption can cause traits of litter and green leaves to diverge. Here we present the first global-scale assessment of riparian litter quality by determining latitudinal variation (spanning 107 degrees) in litter traits (nutrient concentrations; physical and chemical defences) of 151 species from 24 regions and their relationships with environmental factors and phylogeny. We hypothesized that litter quality would increase with latitude (despite variation within regions) and traits would be correlated to produce 'syndromes' resulting from phylogeny and environmental variation. We found lower litter quality and higher nitrogen: phosphorus ratios in the tropics. Traits were linked but showed no phylogenetic signal, suggesting that syndromes were environmentally determined. Poorer litter quality and greater phosphorus limitation towards the equator may restrict detritivore-mediated decomposition, contributing to the predominance of microbial decomposers in tropical streams.
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9.
  • Bundschuh, Mirco, et al. (author)
  • An ecological and ecotoxicological perspective on fine particulate organic matter in streams
  • 2016
  • In: Freshwater Biology. - : Wiley. - 0046-5070 .- 1365-2427. ; 61, s. 2063-2074
  • Research review (peer-reviewed)abstract
    • Fine particulate organic matter (FPOM) provides a key longitudinal link within stream networks, and is the predominant food source for filter- and deposit-feeding invertebrates, collectively classified as collectors'. Organisms involved in producing and using FPOM are sensitive to chemical and other anthropogenic stressors, but information on such impacts, and on FPOM dynamics in general, is limited. Here, we review information on the ecological role of FPOM in streams, and discuss potential impacts on FPOM dynamics of organic and inorganic chemical stressors, including metals and pesticides. Emphasis is placed on faecal particles produced within the leaf-litter processing chain. Key biological factors controlling the resource quality of FPOM for collectors include the identity of the invertebrates producing FPOM, and the nutritional quality of their food resources. FPOM nutrient content is also strongly influenced by microbial colonisation and activity, and FPOM processing rates are thus likely to be sensitive to the impacts of stressors affecting microbes, including nutrients and antimicrobial chemicals. The potential for FPOM to bind and subsequently transport chemical stressors is high, particularly for hydrophobic compounds, but the extent of such effects and impacts on collectors consuming contaminated particles has attracted only limited attention. Combining concepts and research approaches from ecotoxicology and basic stream ecology would facilitate development of a common integrated framework for understanding the role of FPOM, and assessing anthropogenic impacts on FPOM dynamics in stream networks.
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10.
  • Bundschuh, Mirco, et al. (author)
  • Effects of mosquito control using the microbial agent Bacillus thuringiensis israelensis (Bti) on aquatic and terrestrial ecosystems: a systematic review
  • 2023
  • In: Environmental Evidence. - 2047-2382. ; 12
  • Research review (peer-reviewed)abstract
    • Background The bacterium Bacillus thuringiensis serovar israelensis (Bti) is commercially produced in various formulations for use as a larvicide worldwide, targeting especially the aquatic larval stage of mosquitoes. However, there is a concern that repeated Bti treatments may have both direct and indirect impacts on non-target organisms (NTOs) and the ecosystems they inhabit. This review evaluates the evidence for such impacts.Methods Literature was searched using six bibliographic databases, two search engines, and on specialist web sites. Eligibility screening was performed in two steps on (1) title/abstract, with consistency among reviewers assessed by double-screening 557 articles and (2) full text. Articles included after full text screening were critically appraised independently by two reviewers. Disagreements were reconciled through discussions. Key parameters of included studies are presented in narrative synthesis tables, including risk of bias assessments. Meta-analyses comparing treated with untreated ecosystems and using either the raw mean difference or log response ratio as effect size were performed.Review findings Ninety-five articles covering 282 case studies were included in the review. From these, we identified 119 different response variables, which were divided into nine outcome categories. Most studies investigated NTO abundance or life history (reproduction related outcomes), but diversity and community composition are also well represented as outcome categories. The studies are highly variable in methodology, rigor, and spatiotemporal scale, spanning 1 day to 21 years and from < 1m(2) to > 10,000 m(2). Our metanalyses revealed a consistent negative effect of Bti treatment on abundances of Chironomidae and Crustacea, and also on chironomid emergence, although from a more restricted set of studies and regions. For most remaining response variables, we judged meta-analysis unfeasible, due to low study numbers or insufficient reporting of methods and results.Conclusions There is now a significant body of studies documenting effects of mosquito control using Bti on NTOs or other ecosystem properties, especially associated with negative effects on Chironomidae, as apparent from our meta-analyses. Accordingly, we suggest the potential for negative NTO or other ecosystem effects of Bti treatment should not be discounted a priori. Once a decision to proceed with Bti treatment has been taken, priority should be given to a well-designed program of ongoing monitoring and assessment. The paucity of rigorous studies conducted with low bias risk for most response variables undermines our capacity for evaluating how common many of the effects documented might be. Future research would benefit from a rigorous and well-replicated approach to studying Bti impacts in semi-field mesocosms or in the field, combined with a greater rigor in reporting key methodological details. A greater focus is needed on understanding the environmental factors which regulate the wider effects of mosquito control using Bti on NTOs and ecosystems, to enhance our capacity for predicting where and when Bti is most likely to have additional, negative and indirect ecological impacts.
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11.
  • Bundschuh, Mirco, et al. (author)
  • What are the effects of control of mosquitoes and other nematoceran Diptera using the microbial agent Bacillus thuringiensis israelensis (Bti) on aquatic and terrestrial ecosystems? A systematic review protocol
  • 2019
  • In: Environmental Evidence. - : Springer Science and Business Media LLC. - 2047-2382. ; 8
  • Research review (peer-reviewed)abstract
    • Background The bacterium Bacillus thuringiensis serovar israelensis (Bti) is used in many countries as a biological larvicide to control dipteran insects of the suborder Nematocera, especially mosquitoes and black flies. Bti is generally accepted to be target-specific and efficient, with low potential for development of resistance among the target species. However, even though Bti may have minimal direct effects on non-target organisms, it might potentially be associated with knock-on effects on food webs and other ecosystem properties, including biodiversity and ecosystem functioning. Evidence from previous research is mixed, with some finding no evidence for indirect effects on biodiversity and ecosystem-level properties, but others indicating that such effects are possible. The fact that many studies have been conducted by organisations coordinating the control programs, and that many of those studies have been published outside peer reviewed scientific journals, highlights the challenges for decision makers and others to assess the results of the existing studies. In this protocol we outline how we aim to systematically and transparently synthesise all available evidence in a forthcoming systematic review. Methods We will use six bibliographic databases/platforms and the online search engines Google and Google Scholar in searches for literature. Searches will also be made on specialist websites. We will screen the search results for eligibility in stage one based on title and abstract, and in stage two based on the full text of the material. At stage one, after testing and clarifying the eligibility criteria, two reviewers will split and single screen the search results. At stage two the articles will be screened independently by two reviewers. We have developed a preliminary critical appraisal tool that will be used as basis for assessing study validity. Each study will be critically appraised independently by two reviewers. Disagreements will be reconciled through discussions seeking to reach consensus. It is unclear whether a quantitative synthesis based on meta-analysis will be feasible. A narrative synthesis will include descriptive statistics outlining the evidence base in terms of bibliographic information and study metadata. A narrative synthesis table in the form of an Excel spreadsheet will be provided.
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12.
  • Burdon, Francis, et al. (author)
  • A Bayesian Belief Network learning tool integrates multi-scale effects of riparian buffers on stream invertebrates
  • 2022
  • In: Science of the Total Environment. - : Elsevier BV. - 0048-9697 .- 1879-1026. ; 810
  • Journal article (peer-reviewed)abstract
    • Riparian forest buffers have multiple benefits for biodiversity and ecosystem services in both freshwater and terrestrial habitats but are rarely implemented in water ecosystem management, partly reflecting the lack of information on the effectiveness of this measure. In this context, social learning is valuable to inform stakeholders of the efficacy of riparian vegetation in mitigating stream degradation. We aim to develop a Bayesian belief network (BBN) model for application as a learning tool to simulate and assess the reach-and segment-scale effects of riparian vegetation properties and land use on instream invertebrates. We surveyed reach-scale riparian conditions, extracted segment-scale riparian and subcatchment land use information from geographic information system data, and collected macroinvertebrate samples from four catchments in Europe (Belgium, Norway, Romania, and Sweden). We modelled the ecological condition based on the Average Score Per Taxon (ASPT) index, a macroinvertebrate-based index widely used in European bioassessment, as a function of different riparian variables using the BBN modelling approach. The results of the model simulations provided insights into the usefulness of riparian vegetation attributes in enhancing the ecological condition, with reach-scale riparian vegetation quality associated with the strongest improvements in ecological status. Specifically, reach-scale buffer vegetation of score 3 (i.e. moderate quality) generally results in the highest probability of a good ASPT score (99-100%). In contrast, a site with a narrow width of riparian trees and a small area of trees with reach-scale buffer vegetation of score 1 (i.e. low quality) predicts a high probability of a bad ASPT score (74%). The strengths of the BBN model are the ease of interpretation, fast simulation, ability to explicitly indicate uncertainty in model outcomes, and interactivity. These merits point to the potential use of the BBN model in workshop activities to stimulate key learning processes that help inform the management of riparian zones.
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13.
  • Burdon, Francis, et al. (author)
  • Assessing the Benefits of Forested Riparian Zones: A Qualitative Index of Riparian Integrity Is Positively Associated with Ecological Status in European Streams
  • 2020
  • In: Water. - : MDPI AG. - 2073-4441. ; 12
  • Journal article (peer-reviewed)abstract
    • Developing a general, predictive understanding of ecological systems requires knowing how much structural and functional relationships can cross scales and contexts. Here, we introduce the CROSSLINK project that investigates the role of forested riparian buffers in modified European landscapes by measuring a wide range of ecosystem attributes in stream-riparian networks. CROSSLINK involves replicated field measurements in four case-study basins with varying levels of human development: Norway (Oslo Fjord), Sweden (Lake Malaren), Belgium (Zwalm River), and Romania (Arge River). Nested within these case-study basins include multiple, independent stream-site pairs with a forested riparian buffer and unbuffered section located upstream, as well as headwater and downstream sites to show cumulative land-use impacts. CROSSLINK applies existing and bespoke methods to describe habitat conditions, biodiversity, and ecosystem functioning in aquatic and terrestrial habitats. Here, we summarize the approaches used, detail protocols in supplementary materials, and explain how data is applied in an optimization framework to better manage tradeoffs in multifunctional landscapes. We then present results demonstrating the range of riparian conditions present in our case-study basins and how these environmental states influence stream ecological integrity with the commonly used macroinvertebrate Average Score Per Taxon (ASPT) index. We demonstrate that a qualitative index of riparian integrity can be positively associated with stream ecological status. This introduction to the CROSSLINK project shows the potential for our replicated study with its panoply of ecosystem attributes to help guide management decisions regarding the use of forested riparian buffers in human-impacted landscapes. This knowledge is highly relevant in a time of rapid environmental change where freshwater biodiversity is increasingly under pressure from a range of human impacts that include habitat loss, pollution, and climate change.
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14.
  • Burdon, Francis, et al. (author)
  • Forested Riparian Zones Provide Important Habitat for Fish in Urban Streams
  • 2021
  • In: Water. - : MDPI AG. - 2073-4441. ; 13
  • Journal article (peer-reviewed)abstract
    • Riparian zones form a boundary between aquatic and terrestrial ecosystems, with disproportionate influences on food web dynamics and ecosystem functioning in both habitats. However, riparian boundaries are frequently degraded by human activities, including urbanization, leading to direct impacts on terrestrial communities and indirect changes that are mediated through altered connectivity with adjacent aquatic ecosystems. We investigated how riparian habitat influences fish communities in an urban context. We electrofished nine urban site pairs with and without forested riparian buffers, alongside an additional 12 sites that were located throughout the river networks in the Oslo Fjord basin, Norway. Brown trout (Salmo trutta) were the dominant fish species. Riparian buffers had weak positive effects on fish densities at low to moderate levels of catchment urbanization, whereas fish were absent from highly polluted streams. Subtle shifts in fish size distributions suggested that riparian buffers play an important role in metapopulation dynamics. Stable isotopes in fish from buffered reaches indicated dietary shifts, pointing to the potential for a greater reliance on terrestrial-sourced carbon. Combining these results, we postulate that spatially-mediated ontogenetic diet shifts may be important for the persistence of brown trout in urban streams. Our results show that using a food web perspective is essential in understanding how riparian buffers can offset impacts in urban catchments.
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15.
  • Burdon, Francis, et al. (author)
  • Latitude dictates plant diversity effects on instream decomposition
  • 2021
  • In: Science Advances. - : American Association for the Advancement of Science (AAAS). - 2375-2548. ; 7
  • Journal article (peer-reviewed)abstract
    • Running waters contribute substantially to global carbon fluxes through decomposition of terrestrial plant litter by aquatic microorganisms and detritivores. Diversity of this litter may influence instream decomposition globally in ways that are not yet understood. We investigated latitudinal differences in decomposition of litter mixtures of low and high functional diversity in 40 streams on 6 continents and spanning 113 degrees of latitude. Despite important variability in our dataset, we found latitudinal differences in the effect of litter functional diversity on decomposition, which we explained as evolutionary adaptations of litter-consuming detritivores to resource availability. Specifically, a balanced diet effect appears to operate at lower latitudes versus a resource concentration effect at higher latitudes. The latitudinal pattern indicates that loss of plant functional diversity will have different consequences on carbon fluxes across the globe, with greater repercussions likely at low latitudes.
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16.
  • Burdon, Francis, et al. (author)
  • Riparian reforestation on the landscape scale: Navigating trade-offs among agricultural production, ecosystem functioning and biodiversity
  • 2022
  • In: Journal of Applied Ecology. - : Wiley. - 0021-8901 .- 1365-2664. ; 59, s. 1456-1471
  • Journal article (peer-reviewed)abstract
    • Stream-riparian networks are subject to multiple human pressures that threaten key functions of aquatic and terrestrial ecosystems, drive habitat and diversity losses, affect riparian connectivity and cause stakeholder conflicts. Designing riparian landscapes in a way that they can simultaneously meet multiple competing demands requires a clear understanding of existing trade-offs, and a landscape-scale perspective on the planning of reforestation measures. This study applied a landscape optimization algorithm for allocating riparian forest management measures in the intensively used agricultural catchment of the Zwalm River (Belgium). We optimized forest allocation to improve stream ecological quality (EPT index), functional diversity (diatoms) and riparian carbon processing (cotton-strip assay), while minimizing losses in agricultural production potential. Regression models were developed to predict the target indicators for 489 segments of the Zwalm riparian corridor, using spatial variables on three different scales. For each riparian segment, we developed spatially explicit management measures, representing different intensities of riparian reforestation. The allocation and combination of these measures in the riparian corridor were optimized to identify (a) trade-offs among the target indicators, (b) priority regions for reforestation actions and (c) the required reforestation intensity. The results showed that all target indicators were affected by the area share of riparian forests and its landscape-scale configuration. Reforestation of the Zwalm riparian corridor could significantly improve indicators for biodiversity and ecosystem functioning (e.g. up to +96% for EPT index), but would lead to a strong trade-off with agricultural production. By optimizing the placement of management measures, we showed how these trade-offs could be best balanced. The headwater regions of the Zwalm were identified as priority regions for reforestation actions. Facilitating connectivity among and further expansion of existing forest patches in the Zwalm headwaters showed to improve ecosystems with minimized trade-offs. Synthesis and applications. This study demonstrates, for the first time, the potential of landscape optimization algorithms to support the management and design of multifunctional stream-riparian networks. We identified riparian reforestation solutions that minimized trade-offs between specific natural values and societal needs. Our spatially explicit approach allows for an integration into spatial planning and can inform policy design and implementation.
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17.
  • Burdon, Francis, et al. (author)
  • Riparian Vegetation Structure Influences Terrestrial Invertebrate Communities in an Agricultural Landscape
  • 2021
  • In: Water. - : MDPI AG. - 2073-4441. ; 13
  • Journal article (peer-reviewed)abstract
    • Stream and terrestrial ecosystems are intimately connected by riparian zones that support high biodiversity but are also vulnerable to human impacts. Landscape disturbances, overgrazing, and diffuse pollution of agrochemicals threaten riparian biodiversity and the delivery of ecosystem services in agricultural landscapes. We assessed how terrestrial invertebrate communities respond to changes in riparian vegetation in Romanian agricultural catchments, with a focus on the role of forested riparian buffers. Riparian invertebrates were sampled in 10 paired sites, with each pair consisting of an unbuffered upstream reach and a downstream reach buffered with woody riparian vegetation. Our results revealed distinct invertebrate community structures in the two site types. Out of 33 invertebrate families, 13 were unique to either forested (6) or unbuffered (7) sites. Thomisidae, Clubionidae, Tetragnathidae, Curculionidae, Culicidae, and Cicadidae were associated with forested buffers, while Lycosidae, Chrysomelidae, Staphylinidae, Coccinellidae, Tettigoniidae, Formicidae, and Eutichuridae were more abundant in unbuffered sites. Despite statistically equivocal results, invertebrate diversity was generally higher in forested riparian buffers. Local riparian attributes significantly influenced patterns in invertebrate community composition. Our findings highlight the importance of local woody riparian buffers in maintaining terrestrial invertebrate diversity and their potential contribution as a multifunctional management tool in agricultural landscapes.
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18.
  • Burdon, Francis, et al. (author)
  • Small Patches of Riparian Woody Vegetation Enhance Biodiversity of Invertebrates
  • 2020
  • In: Water. - : MDPI AG. - 2073-4441. ; 12
  • Journal article (peer-reviewed)abstract
    • Patches of riparian woody vegetation potentially help mitigate environmental impacts of agriculture and safeguard biodiversity. We investigated the effects of riparian forest on invertebrate diversity in coupled stream-riparian networks using a case study in the Zwalm river basin (Flanders, Belgium). Agriculture is one of the main pressures in the basin and riparian forest is limited to a number of isolated patches. Our 32 study sites comprised nine unshaded “unbuffered” sites which were paired with nine shaded “buffered” sites on the same stream reach, along with five ‘least-disturbed’ sites and nine downstream sites. We sampled water chemistry, habitat characteristics and stream and riparian invertebrates (carabid beetles and spiders) at each site. Three methods were used to quantify riparian attributes at different spatial scales: a visually-assessed qualitative index, quantitative estimates of habitat categories in six rectangular plots (10 × 5 m) and geographic information system (GIS)-derived land cover data. We investigated relationships between invertebrates and riparian attributes at different scales with linear regression and redundancy analyses. Spiders and carabids were most associated with local riparian attributes. In contrast, aquatic macroinvertebrates were strongly influenced by the extent of riparian vegetation in a riparian band upstream (100–300 m). These findings demonstrate the value of quantifying GIS-based metrics of riparian cover over larger spatial scales into assessments of the efficacy of riparian management as a complement to more detailed local scale riparian assessments in situ. Our findings highlight the value of even small patches of riparian vegetation in an otherwise extensively disturbed landscape in supporting biodiversity of both terrestrial and freshwater invertebrates and emphasize the need to consider multiple spatial scales in riparian management strategies which aim to mitigate human impacts on biodiversity in stream-riparian networks.
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19.
  • Burrows, Ryan, et al. (author)
  • Nitrogen limitation of heterotrophic biofilms in boreal streams
  • 2015
  • In: Freshwater Biology. - : Wiley. - 0046-5070 .- 1365-2427. ; 60:7, s. 1237-1251
  • Journal article (peer-reviewed)abstract
    • Nutrient limitation of the biofilm is fundamental to stream ecosystem processes, as microbial activity shapes the biological availability and biogeochemical cycling of carbon and nutrients. We used nutrient-diffusing substrata (NDS) to investigate heterotrophic nutrient limitation of microbial respiration (MR) across 20 streams draining boreal landscapes in northern Sweden. We also explored variation in microbial biomass and community structure of biofilms that developed on NDS using phospholipid fatty acid (PLFA) biomarkers. Limitation was determined as a significant response of MR and biomass production on cellulose surfaces to enrichment with nitrogen (N), phosphorus (P) or N+P, relative to controls. Microbial respiration was N-limited, with an average 3.3-fold increase on N-amended NDS. Nitrogen limitation decreased, and control rates of MR increased, with greater background concentrations of inorganic N across the sites. In contrast to MR, microbial biomass was primarily N-limited but was greatest for the N+P NDS. Accordingly, differences in respiratory versus biomass responses to nutrient addition resulted in significantly greater biomass-specific MR on N-amended NDS compared to all other treatments. In addition, PLFA biomarkers indicated distinct microbial communities on N and N+P NDS compared to controls and/or P NDS. Greater MR and biomass, and the development of distinct microbial communities, when supplied with inorganic N suggest that factors which alter aquatic N loading during autumn may have important implications for ecosystem processes and the biogeochemistry of boreal streams and rivers. Our findings add to a growing body of evidence that the productivity of Fennoscandian boreal landscapes is constrained by N availability.
  •  
20.
  • Burrows, Ryan, et al. (author)
  • Seasonal resource limitation of heterotrophic biofilms in boreal streams
  • 2017
  • In: Limnology and Oceanography. - : WILEY-BLACKWELL. - 0024-3590 .- 1939-5590. ; 62:1, s. 164-176
  • Journal article (peer-reviewed)abstract
    • Unraveling the potentially shifting controls over microbial activity among habitats and across seasonal transitions is critical for understanding how freshwater ecosystems influence broader elemental cycles, and how these systems may respond to global changes. We used nutrient-diffusing substrates to investigate seasonal patterns and constraints on microbial activity of biofilms in streams draining distinct landscape features of the boreal biome (forests, mires, and lakes). Microbial respiration (MR) largely mirrored spatial and temporal variation in water temperature. However, limitation by labile carbon (C) was a constraint to microbial activity during ice-covered periods, when MR of control nutrient-diffusing substrates fell below rates predicted from stream temperature alone. Variation in C limitation among the study streams was reflective of putative organic C availability, with C limitation of biofilms weakest in the dissolved organic C (DOC)-rich, mire-outlet stream and greatest in the relatively DOC-poor, forest stream. Incidences of nutrient limitation were only observed during warmer months. Our study illustrates how variation in processes mediated by heterotrophic biofilms and seasonal shifts in resource limitation can emerge in a stream network draining a heterogeneous landscape. In addition, our results show that, for a large portion of the year, heterotrophic processes in boreal streams can be strongly limited by the availability of labile C, despite high DOC concentrations. Metabolic constraints to dissolved organic matter processing at near-freezing temperatures, coupled with hydrological controls over the delivery of more labile organic resources to streams (e.g., soil freezing and flooding), have potentially strong influences on the productivity of boreal streams.
  •  
21.
  • Carlson, Peter, et al. (author)
  • Optimizing stream bioassessment: habitat, season, and the impacts of land use on benthic macroinvertebrates
  • 2013
  • In: Hydrobiologia. - : Springer Science and Business Media LLC. - 0018-8158 .- 1573-5117. ; 704, s. 363-373
  • Journal article (peer-reviewed)abstract
    • Bioassessment of running waters should ideally be optimized to include sampling of the biota when and where they are most sensitive to anthropogenic disturbances, but direct comparisons of the responses of biota across habitats and seasons are lacking. We sampled benthic macroinvertebrates from nine boreal streams situated along an agricultural land use gradient in two seasons (spring and autumn) and two habitats (pools and riffles). Univariate (e.g., diversity) and multivariate (ordination scores) metrics, as well as biological traits, were used to assess changes in assemblage composition associated with agricultural land use. Abundances were generally higher in agricultural compared to forested streams, and in riffles compared to pools. Spring samples had lower mean abundances of several insect taxa (e.g., chironomid midges) compared to autumn samples, while abundances of non-insects (e.g., oligochaetes and Pisidium spp.) remained unchanged. Community turnover (correspondence analysis) had higher precision and sensitivity compared to diversity metrics, and samples from the spring and from riffles responded more to the land use gradient than those from autumn and pool habitats, respectively. The finding that catchment land use resulted in macrohabitat differences and, ultimately, differences in taxonomic composition between agricultural and forested streams and between pool and riffle habitats can be used to optimize future bioassessment based on macroinvertebrates.
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22.
  • Carlson, Peter, et al. (author)
  • Strong land-use effects on the dispersal patterns of adult stream insects: implications for transfers of aquatic subsidies to terrestrial consumers
  • 2016
  • In: Freshwater Biology. - : Wiley. - 0046-5070 .- 1365-2427. ; 61, s. 848-861
  • Journal article (peer-reviewed)abstract
    • The dispersal of terrestrial adults of freshwater insects is a key process regulating the transfer resources from aquatic habitats to terrestrial consumers, including high-quality lipids synthesised in the aquatic environment. However, the efficiency of these transfers depends strongly on both subsidy production in the aquatic source habitat and permeability of the aquatic-terrestrial boundary. We assessed how land use (agriculture versus forest) affects stream riparian habitats and the dispersal of adult aquatic insects. Flying insects were sampled alongside eight streams (four agricultural, four forested) in central Sweden using sticky traps, placed from 1 up to 100m from the stream edge. Environmental variables including temperature, wind, vegetation structure and canopy cover were also quantified. Abundances of adult aquatic insects were greater at agricultural than at forested sites, but most (64%) were caught close to the stream edge. In contrast, catches of adult aquatic insects declined relatively little with increasing distance from the forest streams. Overall, dispersal of the dominant aquatic insect order (Diptera) was positively associated with greater tree density and canopy shading and negatively associated with higher wind speeds and soil temperatures, more open habitats and steeper topographies. Taxonomic differences among assemblages, reflecting differing dispersal capacities, were also important, but less so than environmental factors. Our results indicate that adult aquatic insects in our forested landscapes are more likely to subsidise near-ground food webs at a greater distance from stream channels, whereas the abundant subsidy emerging from the agricultural sites is likely to be most influential near the stream channel. A key question for future research is whether the deposition of large quantities of aquatic subsidy in agricultural riparian habitats exceeds the resource requirements and processing capacities of terrestrial consumers.
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23.
  • Chauvet, Eric, et al. (author)
  • Litter decomposition as an indicator of stream ecosystem functioning at local-to-continental scales : insights from the European RivFunction project
  • 2016
  • In: Large-scale ecology. - London : Academic Press. ; 55, s. 99-182
  • Book chapter (pop. science, debate, etc.)abstract
    • RivFunction is a pan-European initiative that started in 2002 and was aimed at establishing a novel functional-based approach to assessing the ecological status of rivers. Litter decomposition was chosen as the focal process because it plays a central role in stream ecosystems and is easy to study in the field. Impacts of two stressors that occur across the continent, nutrient pollution and modified riparian vegetation, were examined at > 200 paired sites in nine European ecoregions. In response to the former, decomposition was dramatically slowed at both extremes of a 1000-fold nutrient gradient, indicating nutrient limitation in unpolluted sites, highly variable responses across Europe in moderately impacted streams, and inhibition via associated toxic and additional stressors in highly polluted streams. Riparian forest modification by clear cutting or replacement of natural vegetation by plantations (e.g. conifers, eucalyptus) or pasture produced similarly complex responses. Clear effects caused by specific riparian disturbances were observed in regionally focused studies, but general trends across different types of riparian modifications were not apparent, in part possibly because of important indirect effects. Complementary field and laboratory experiments were undertaken to tease apart the mechanistic drivers of the continental scale field bioassays by addressing the influence of litter, fungal and detritivore diversity. These revealed generally weak and context-dependent effects on decomposition, suggesting high levels of redundancy (and hence potential insurance mechanisms that can mitigate a degree of species loss) within the food web. Reduced species richness consistently increased decomposition variability, if not the absolute rate. Further field studies were aimed at identifying important sources of this variability (e.g. litter quality, temporal variability) to help constrain ranges of predicted decomposition rates in different field situations. Thus, although many details still need to be resolved, litter decomposition holds considerable potential in some circumstances to capture impairment of stream ecosystem functioning. For instance, species traits associated with the body size and metabolic capacity of the consumers were often the main driver at local scales, and these were often translated into important determinants of otherwise apparently contingent effects at larger scales. Key insights gained from conducting continental scale studies included resolving the apparent paradox of inconsistent relationships between nutrients and decomposition rates, as the full complex multidimensional picture emerged from the large-scale dataset, of which only seemingly contradictory fragments had been seen previously.
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24.
  • Choudhury, Maidul, et al. (author)
  • Disentangling the roles of plant functional diversity and plaint traits in regulating plant nitrogen accumulation and denitrification in freshwaters
  • 2022
  • In: Functional Ecology. - : Wiley. - 0269-8463 .- 1365-2435. ; 36, s. 921-932
  • Journal article (peer-reviewed)abstract
    • 1. There is a growing recognition that functional measures of diversity, based on quantification of functionally important species traits, are useful for explaining variation in ecosystem processes. However, the mechanisms linking functional diversity to different processes remain poorly understood, hindering development of a predictive framework for ecosystem functioning based on species traits.2. The current understanding of how the functional traits of aquatic plants (macrophytes) affect nitrogen (N) cycling by regulating microbial communities and their activity in freshwater habitats is particularly limited. Denitrifying bacteria are typically associated with the roots of both aquatic and terrestrial plants and denitrification is the main cause of loss of N from ecosystems. Disentangling the interplay between plants and microbial denitrifiers is key to understanding variation in rates of denitrification from local to landscape scales.3. In a mesocosm experiment, we varied the species richness (monocultures or two-species mixtures) and composition of macrophytes. We quantified effects of both macrophyte functional diversity, quantified as functional trait dissimilarity, and functional trait composition, quantified as community weighted mean trait values, on N removal in wetlands. We used structural equation modelling to disentangle the direct and indirect influences of traits on N accumulation in plant biomass, denitrification activity and abundance of key bacterial denitrification genes (nirS and nirK).4. Both functional diversity and functional trait composition regulated N removal, explaining 70%-94% variation in the underlying ecosystem processes. Increased macrophyte functional diversity increased plant N accumulation, and indirectly enhanced denitrification by increasing denitrification gene abundance. Among traits, greater plant relative growth rates, specific leaf area and above-ground biomass increased plant N accumulation. Denitrification activity increased with increasing below-ground biomass but decreased with increasing root diameter.5. These findings improve our understanding of N removal in freshwater wetlands dominated by macrophytes, and have broad ecological implications for wetland management targeting enhanced ecosystem services. Our results highlight the potential for optimizing denitrification and plant N accumulation in wetlands and thereby improving water purification by increasing macrophyte functional diversity and ensuring the presence of key traits in macrophyte assemblages.
  •  
25.
  • Choudhury, Maidul, et al. (author)
  • Importance of plant species for nitrogen removal using constructed floating wetlands in a cold climate
  • 2019
  • In: Ecological Engineering. - : Elsevier BV. - 0925-8574 .- 1872-6992. ; 138, s. 126-132
  • Journal article (peer-reviewed)abstract
    • Constructed floating wetlands (CFWs) have been tested in different climatic regions and aquatic habitat types for nitrogen (N) removal from surface water, but there is limited knowledge about their applicability for N removal in cold climate regions. Most CFWs studies are conducted at the micro- or mesocosm scale, while the application of CFWs at in situ is rare. Moreover, most CFWs studies have focused on plant N accumulation without considering macrophyte root-associated denitrification as a possible N removal pathway. Here, we study the N removal potential of CFWs through N accumulation by macrophytes and potential denitrification activity (PDA) associated with plants. At a mining area in the sub-arctic region of Sweden receiving N-rich mine effluents, we tested the concept of CFWs and evaluated the performance of six native, emerging macrophyte species planted in CFWs. The CFWs were deployed in two types of systems: in situ in the recipient lake, subjected to ambient N concentrations, and CFWs placed in water-side "eco-tanks", subjected to higher N concentrations. We showed that macrophyte establishment in CFWs is feasible under cold climatic conditions, both in situ and eco-tanks. The standing biomass of macrophytes, bulk N accumulation in plant biomass and PDA in mesocosms were 0.54-2.25 kg m(-2), 7.56-24.75 mg N m(-2) d(-1) and 31.82-2250.77 mg N2O-N m(-2) d(-1), respectively. In the recipient, the variation was larger and the values were higher (standing biomass, 0.37-6.74 kg m(-2); bulk N accumulation, 8.09-106.93 mg N m(-2) d(-1); PDA, 11.89-8446.15 mg N m(-2) d(-1)). Macrophyte root-associated denitrification was the main N removal pathway in the CFWs. Given the demonstrated applicability of CFWs and the high denitrification rates that can be obtained, future studies should focus on designing CFWs to enhance denitrification as this process leads to permanent removal of N from the water phase.
  •  
26.
  • Choudhury, Maidul, et al. (author)
  • Mixtures of macrophyte growth forms promote nitrogen cycling in wetlands
  • 2018
  • In: Science of the Total Environment. - : Elsevier BV. - 0048-9697 .- 1879-1026. ; 635, s. 1436-1443
  • Journal article (peer-reviewed)abstract
    • The importance of aquatic plant diversity in regulating nutrient cycling in wetlands remains poorly understood. We investigated how variation in macrophyte growth form (emerging, submerged and bryophyte) combinations and species mixtures affect nitrogen (N) removal from the water and N accumulation in plant biomass. We conducted a wetland mesocosm experiment for 100 days during July-September 2015. Twelve species were grown in mono- and in two-species mixed cultures for a total of 32 single and two-growth form combinations. Nitrogen removal from the water was quantified on three occasions during the experiment, while N accumulation in plant biomass was determined following termination of the experiment. The number of species and growth forms present increased N removal and accumulation. The growth form combinations of emerging and bryophyte species showed the highest N accumulation and N removal from water, followed by combinations of emerging species. By contrast, submerged species growing in the presence of emerging or other submerged species showed the lowest levels of N accumulation and N removal. Temporal variation in N removal also differed among growth form combinations: N removal was highest for emerging-bryophyte combinations in July, but peaked for the emerging-submerged and emerging-bryophyte combinations in August. Indeed, the occurrence of complementarity among macrophyte species, particularly in combinations of bryophyte and emerging species, enhanced N removal and uptake during the entire growing season. Our study highlights the importance of bryophytes, which have been neglected in research on nutrient cycling in wetlands, for aquatic N cycling, especially given their worldwide distribution across biomes. Overall, our findings point towards the potential important role of the diversity of macrophyte growth forms in regulating key ecosystem processes related to N cycling in wetlands. (C) 2018 Elsevier B.V. All rights reserved.
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27.
  • Costello, David M., et al. (author)
  • Global patterns and controls of nutrient immobilization on decomposing cellulose in riverine ecosystems
  • 2022
  • In: Global Biogeochemical Cycles. - : John Wiley & Sons. - 0886-6236 .- 1944-9224. ; 36:3
  • Journal article (peer-reviewed)abstract
    • Microbes play a critical role in plant litter decomposition and influence the fate of carbon in rivers and riparian zones. When decomposing low-nutrient plant litter, microbes acquire nitrogen (N) and phosphorus (P) from the environment (i.e., nutrient immobilization), and this process is potentially sensitive to nutrient loading and changing climate. Nonetheless, environmental controls on immobilization are poorly understood because rates are also influenced by plant litter chemistry, which is coupled to the same environmental factors. Here we used a standardized, low-nutrient organic matter substrate (cotton strips) to quantify nutrient immobilization at 100 paired stream and riparian sites representing 11 biomes worldwide. Immobilization rates varied by three orders of magnitude, were greater in rivers than riparian zones, and were strongly correlated to decomposition rates. In rivers, P immobilization rates were controlled by surface water phosphate concentrations, but N immobilization rates were not related to inorganic N. The N:P of immobilized nutrients was tightly constrained to a molar ratio of 10:1 despite wide variation in surface water N:P. Immobilization rates were temperature-dependent in riparian zones but not related to temperature in rivers. However, in rivers nutrient supply ultimately controlled whether microbes could achieve the maximum expected decomposition rate at a given temperature. Collectively, we demonstrated that exogenous nutrient supply and immobilization are critical control points for decomposition of organic matter.
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28.
  • Dawoud, Mohab, et al. (author)
  • Interactive effects of an insecticide and a fungicide on different organism groups and ecosystem functioning in a stream detrital food web
  • 2017
  • In: Aquatic Toxicology. - : Elsevier BV. - 0166-445X .- 1879-1514. ; 186, s. 215-221
  • Journal article (peer-reviewed)abstract
    • Freshwater ecosystems are often affected by cocktails of multiple pesticides targeting different organism groups. Prediction and evaluation of the ecosystem-level effects of these mixtures is complicated by the potential not only for interactions among the pesticides themselves, but also for the pesticides to alter biotic interactions across trophic levels. In a stream microcosm experiment, we investigated the effects of two pesticides targeting two organism groups (the insecticide lindane and fungicide azoxystrobin) on the functioning of a model stream detrital food web consisting of a detritivore (Ispoda: Asellus aquaticus) and microbes (an assemblage of fungal hyphomycetes) consuming leaf litter. We assessed how these pesticides interacted with the presence and absence of the detritivore to affect three indicators of ecosystem functioning - leaf decomposition, fungal biomass, fungal sporulation - as well as detritivore mortality. Leaf decomposition rates were more strongly impacted by the fungicide than the insecticide, reflecting especially negative effects on leaf processing by detritivores. This result most like reflects reduced fungal biomass and increased detritivore mortality under the fungicide treatment. Fungal sporulation was elevated by exposure to both the insecticide and fungicide, possibly representing a stress-induced increase in investment in propagule dispersal. Stressor interactions were apparent in the impacts of the combined pesticide treatment on fungal sporulation and detritivore mortality, which were reduced and elevated relative to the single stressor treatments, respectively. These results demonstrate the potential of trophic and multiple stressor interactions to modulate the ecosystem-level impacts of chemicals, highlighting important challenges in predicting, understanding and evaluating the impacts of multiple chemical stressors on more complex food webs in situ. (C) 2017 Elsevier B.V. All rights reserved.
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29.
  • Donadi, Serena, et al. (author)
  • Interactive effects of land use, river regulation, and climate on a key recreational fishing species in temperate and boreal streams
  • 2021
  • In: Freshwater Biology. - : Wiley. - 0046-5070 .- 1365-2427. ; 66, s. 1901-1914
  • Journal article (peer-reviewed)abstract
    • Numerous anthropogenic stressors, including river regulation, excess loadings of nutrients and sediment, channelisation, as well as thermal and hydrological stressors driven by climate change impact riverine ecosystems worldwide. In a time when freshwater degradation and the rate of global warming are faster than ever, understanding the potential interactive effects of local and catchment-scale stressors with large-scale climatic conditions is essential to enhance our ability to plan effective conservation, restoration, and mitigation measures. In this study we analysed a dataset spanning the whole of Sweden using a space-for-time approach to investigate interactive effects of land use, river regulation, and climate on brown trout (Salmo trutta) abundance in streams. We found that in warmer regions trout populations were negatively affected in catchments with more intense river regulation by hydropower dams (i.e. >= 10 m(3)/km(2) total reservoir storage volume). In such catchments, a 7 degrees C warmer mean summer air temperature was associated with an average between 44% and 83% decline in trout abundance. In catchments with less intense river regulation, trout abundance instead increased moderately with increasing temperature. We also found that brown trout abundance declined with increasing areal extent of urban areas when found in combination with >= 20% agricultural land use. When agricultural land use reached maximum values (84%), brown trout abundance decreased from an average of 13 individuals per 100 m(2) in catchments with no urban areas to values <= 1 in catchments with >= 5% urban land use. Also, brown trout abundance declined with increasing agricultural land use in catchments with >= 3% urban land use. Our study brings innovative empirical evidence of interactive effects between river regulation, land use and climate on brown trout populations. From a management perspective our findings suggest that: (1) restoring natural flows (e.g. through dam removal) and riparian vegetation could mitigate adverse effects of climate change; and (2) restoration measures that minimise the effects of agriculture and urban land use (e.g. reduction of nutrient levels and restored riparian buffer zones) could help rehabilitate brown trout in catchments with high anthropogenic land use change. However, given the large observed variation between streams, we advise for bespoke management actions stemming from sound knowledge of local habitat conditions and target populations, whenever possible, using an ecosystem management-based approach.
  •  
30.
  • Ecke, Frauke, et al. (author)
  • Meta-analysis of environmental effects of beaver in relation to artificial dams
  • 2017
  • In: Environmental Research Letters. - : IOP Publishing. - 1748-9326. ; 12
  • Research review (peer-reviewed)abstract
    • Globally, artificial river impoundment, nutrient enrichment and biodiversity loss impair freshwater ecosystem integrity. Concurrently, beavers, ecosystem engineers recognized for their ability to construct dams and create ponds, are colonizing sites across the Holarctic after widespread extirpation in the 19th century, including areas outside their historical range. This has the potential to profoundly alter hydrology, hydrochemistry and aquatic ecology in both newly colonized and recolonized areas. To further our knowledge of the effects of beaver dams on aquatic environments, we extracted 1366 effect sizes from 89 studies on the impoundment of streams and lakes. Effects were assessed for 16 factors related to hydrogeomorphology, biogeochemistry, ecosystem functioning and biodiversity. Beaver dams affected concentrations of organic carbon in water, mercury in water and biota, sediment conditions and hydrological properties. There were no overall adverse effects caused by beaver dams or ponds on salmonid fish. Age was an important determinant of effect magnitude. While young ponds were a source of phosphorus, there was a tendency for phosphorus retention in older systems. Young ponds were a source methylmercury in water, but old ponds were not. To provide additional context, we also evaluated similarities and differences between environmental effects of beaver-constructed and artificial dams (767 effect sizes from 75 studies). Both are comparable in terms of effects on, for example, biodiversity, but have contrasting effects on nutrient retention and mercury. These results are important for assessing the role of beavers in enhancing and/or degrading ecological integrity in changing Holarctic freshwater systems.
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31.
  • Frainer, André, 1982- (author)
  • Ecosystem functioning in streams : Disentangling the roles of biodiversity, stoichiometry, and anthropogenic drivers
  • 2013
  • Doctoral thesis (other academic/artistic)abstract
    • What will happen to ecosystems if species continue to go extinct at the high rates seen today? Although ecosystems are often threatened by a myriad of physical or chemical stressors, recent evidence has suggested that the loss of species may have impacts on the functions and services of ecosystems that equal or exceed other major environmental disturbances. The underlying causes that link species diversity to ecosystem functioning include species niche complementarity, facilitative interactions, or selection effects, which cause process rates to be enhanced in more diverse communities. Interference competition, antagonistic interactions, or negative selection effects may otherwise reduce the efficiency or resource processing in diverse communities. While several of these mechanisms have been investigated in controlled experiments, there is an urgent need to understand how species diversity affects ecosystem functioning in nature, where variability of both biotic and abiotic factors is usually high. Species functional traits provide an important conceptual link between the effects of disturbances on community composition and diversity, and their ultimate outcomes for ecosystem functioning. Within this framework, I investigated relationships between the decomposition of leaf litter, a fundamental ecosystem process in stream ecosystems, and the composition and diversity of functional traits within the detritivore feeding guild. These include traits related to species habitat and resource preferences, phenology, and size. I focused on disentangling the biotic and abiotic drivers, including functional diversity, regulating ecosystem functioning in streams in a series of field experiments that captured real-world environmental gradients. Leaf decomposition rates were assessed using litter-bags of 0.5 and 10 mm opening size which allow the quantification of microbial and invertebrate + microbial contributions, respectively, to litter decomposition. I also used PVC chambers where leaf litter and a fixed number of invertebrate detritivores were enclosed in the field for a set time-period. The chemical characterisation of stream detritivores and leaf litter, by means of their nitrogen, phosphorus, and carbon concentration, was used to investigate how stoichiometric imbalance between detritivores and leaf litter may affect consumer growth and resource consumption. I found that the diversity and composition of functional traits within the stream detritivore feeding guild sometimes had effects on ecosystem functioning as strong as those of other major biotic factors (e.g. detritivore density and biomass), and abiotic factors (e.g. habitat complexity and agricultural stressors). However, the occurrence of diversity-functioning relationships was patchy in space and time, highlighting ongoing challenges in predicting the role of diversity a priori. The stoichiometric imbalance between consumers and resource was also identified as an important driver of functioning, affecting consumer growth rates, but not leaf decomposition rates. Overall, these results shed light on the understanding of species functional diversity effect on ecosystems, and indicate that the shifts in the functional diversity and composition of consumer guilds can have important outcomes for the functioning of stream ecosystems.
  •  
32.
  • Frainer, André, et al. (author)
  • Enhanced ecosystem functioning following stream restoration : The roles of habitat heterogeneity and invertebrate species traits
  • 2018
  • In: Journal of Applied Ecology. - : Wiley-Blackwell Publishing Inc.. - 0021-8901 .- 1365-2664. ; 55:1, s. 377-385
  • Journal article (peer-reviewed)abstract
    • 1. Habitat restoration is increasingly undertaken in degraded streams and rivers to help improve biodiversity and ecosystem functioning. Follow-up assessments focused on outcomes for biodiversity have often found scant evidence for recovery, raising concerns about the efficacy of habitat restoration for improving ecological integrity. However, responses of other ecological variables, such as ecosystem process rates and the functional trait composition of biological assemblages, have been little evaluated.2. We assessed how the restoration of habitat heterogeneity affected multiple functional parameters in 20 boreal stream reaches encompassing both more and less extensively restored sites, as well as channelised and natural reference sites. We further assessed relationships between our functional parameters and a fluvial geomorphic measure of habitat heterogeneity.3. Leaf decomposition was positively related to habitat heterogeneity. This was associated with shifts in the functional composition of detritivore assemblages, with the most obligate litter consumers more prominent in reaches showing higher habitat heterogeneity. The deposition of fine particulate organic matter was consistently higher in restored than channelised sites, and was positively related to the heterogeneity gradient. Algal biomass accrual per unit area did not vary either with restoration or the heterogeneity gradient.4. Synthesis and applications. Our findings demonstrate that restoration of river habitat heterogeneity can enhance retention and decomposition of organic matter, key ecosystem properties underpinning ecosystem functioning and service delivery. Significantly, enhanced litter decomposition was linked with a change in the functional composition rather than diversity of detritivore assemblages. Future evaluation of the success of habitat restorations should incorporate quantification of ecosystem processes and the functional traits of biota, in addition to measures of fluvial geomorphology and more traditional biotic metrics, to facilitate a more comprehensive and mechanistic assessment of ecological responses.
  •  
33.
  • Frainer, André, 1982-, et al. (author)
  • Is ecosystem functioning enhanced when habitat complexity increases? : River restoration and the functioning of algal and detrital food webs
  • Other publication (other academic/artistic)abstract
    • Stream restoration is a multi-million dollar business that aims at rehabilitating systems impacted by hydrogeomorphological modifications, such as channelization, and ameliorating physical or ecological degradation caused by catchment-scale impacts, such as agriculture or urbanization. Despite extensive programs aimed at restoring habitat complexity in channelized streams, there is little evidence for a recovery of biological diversity, and functional responses have been little assessed. Notably large-scale habitat restorations have recently been undertaken in a river catchment in northern Sweden, including rehabilitation of large habitat structures (massive boulders, large woody debris) originally removed to facilitate timber floating. Based on a hydrogeomorphological measure of habitat complexity, we characterised variability in habitat complexity across 20 stream reaches in the catchment, including reference, channelised and restored sites. We assessed whether increased habitat complexity following restoration affected retention of organic matter (FPOM), the functional diversity and organisation of the detritivore feeding guild, and two ecosystem processes: algal productivity and litter decomposition. Deposition of FPOM increased along the complexity gradient, as did leaf litter decomposition mediated by invertebrates. The increase in invertebrate-mediated decomposition was associated with shifts in the functional composition of detritivore assemblages, with feeding traits associated with more efficient decomposition more prominent in the restored reaches. There was no change in algal productivity at local scales, but increases in shallow, well- lit habitats favourable for algal growth indicate a possible increase in algal productivity at the stream reach scale. Increases in habitat complexity enhanced functioning within the detritital foodweb at local scales, without any changes in the biodiversity of detritivores. Our findings indicate that aspects of functional diversity and ecosystem functioning may be better than measures of community structure for assessing stream restoration projects.
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34.
  • Frainer, André, et al. (author)
  • Parasitism and the Biodiversity-Functioning Relationship
  • 2018
  • In: Trends in ecology & evolution. - : Elsevier BV. - 0169-5347 .- 1872-8383. ; 33, s. 260-268
  • Research review (peer-reviewed)abstract
    • Species interactions can influence ecosystem functioning by enhancing or suppressing the activities of species that drive ecosystem processes, or by causing changes in biodiversity. However, one important class of species interactions - parasitism - has been little considered in biodiversity and ecosystem functioning (BD-EF) research. Parasites might increase or decrease ecosystem processes by reducing host abundance. Parasites could also increase trait diversity by suppressing dominant species or by increasing within-host trait diversity. These different mechanisms by which parasites might affect ecosystem function pose challenges in predicting their net effects. Nonetheless, given the ubiquity of parasites, we propose that parasite-host interactions should be incorporated into the BD-EF framework.
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35.
  • Frainer, André, 1982-, et al. (author)
  • Shifts in ecosystem functioning of a detritus-based foodweb explained by imbalances between resource and consumer stoichiometry
  • Other publication (other academic/artistic)abstract
    • The stoichiometric imbalance between consumers and resources can affect both resource processing rates and consumer growth, and thus constitutes a potentially important driver of ecosystem functioning. We hypothesized that imbalances in nitrogen (N), phosphorus (P), and carbon (C) concentrations between detritus and detritivores would have contrasting effects on two related ecosystem processes, with stronger imbalances triggering compensatory feeding while simultaneously constraining detritivore growth. In a stream field experiment, we found that growth of detritivores was constrained by stoichiometric imbalances mostly driven by N limitation, but there was no evidence for compensatory feeding. However, when offered diets of mixed litter with varying N:P and C:N, detritivores preferred the litter species showing the closest match to their own N:P and C:N, which drove accelerated processing of the preferred species in mixture. Our results highlight the role of stoichiometric imbalances between consumers and resources in regulating ecosystem processes.
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36.
  • Frainer, André, et al. (author)
  • Shifts in the Diversity and Composition of Consumer Traits Constrain the Effects of Land Use on Stream Ecosystem Functioning
  • 2015
  • In: Advances in Ecological Research. - : Elsevier. - 0065-2504. ; 52, s. 169-200, s. 169-200
  • Research review (peer-reviewed)abstract
    • Species functional traits provide an important conceptual link between the effects of disturbances on community composition and diversity, and their ultimate outcomes for ecosystem functioning. Across 10 boreal streams covering a gradient of increasing intensity of land-use management, from forested to agricultural sites, we analysed relationships between leaf decomposition, the feeding traits of detritivores and measures of anthropogenic disturbances in two seasons. The direct effect of increasing land-use intensity on decomposition was positive and was associated with increases in nutrient concentrations and current velocities. However, this relationship was countered by negative effects associated with a loss of detritivore functional diversity along the gradient during autumn and shifts in species trait composition during spring, limiting the net change in functioning associated with increasing land-use management overall. Our results highlight the key roles that trait identity and diversity can play in mediating the effects of human disturbance on ecosystem functioning.
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37.
  • Frainer, André, 1982-, et al. (author)
  • Shifts in the diversity and composition of consumer traits limit the effects of land use on stream ecosystem functioning
  • Other publication (other academic/artistic)abstract
    • Abiotic disturbances that directly affect ecosystem functioning may also affect the distribution and composition of functional traits within a community. Shifts in trait composition may further enhance or even limit those effects caused by the abiotic stressors. In this work we asked whether an agricultural landuse gradient would affect both invertebrate detritivore functional diversity and leaf litter decomposition in streams. We further asked how the landuse effect on functional traits would relate to ecosystem functioning, and if their relationship would change across seasons. Using Structural Equation Modelling, which allows the partitioning of both direct and indirect relationships, we show that in the autumn land use had a positive effect on functioning, but this relationship was counteracted by a negative indirect effect on leaf decomposition. Landuse positively affected the presence of detritivore traits that were negatively related to functioning and also promoted trait dominance, which was negatively related to functioning. These results contrast with direct linear regressions between disturbance and functioning, which did not yield any relationship between the two variables. In spring, landuse had no effect on functioning, which is explained by the reduced impact of agricultural disturbances in our boreal streams. Our results emphasise the key role played by trait identity and diversity in mediating the effects of human disturbance on ecosystem functioning. Furthermore, our findings highlight the value of distinguishing the direct effects of human disturbances on ecosystem processes from those mediated through changes in the structure of trophic webs.
  •  
38.
  • Frainer, André, et al. (author)
  • Stoichiometric imbalances between detritus and detritivores are related to shifts in ecosystem functioning
  • 2016
  • In: Oikos. - : Wiley. - 0030-1299 .- 1600-0706. ; 125:6, s. 861-871
  • Journal article (peer-reviewed)abstract
    • How are resource consumption and growth rates of litter-consuming detritivores affected by imbalances between consumer and litter C:N:P ratios? To address this question, we offered leaf litter as food to three aquatic detritivore species, which represent a gradient of increasing body N: P ratios: a crustacean, a caddisfly and a stonefly. The detritivores were placed in microcosms and submerged in a natural stream. Four contrasting leaf species were offered, both singly and in two-species mixtures, to obtain different levels of stoichiometric imbalance between the resources and their consumers. The results suggest that detritivore growth was constrained by N rather than C or P, even though 1) the N: P ratios of the consumers' body tissue was relatively low and 2) microbial leaf conditioning during the experiment reduced the N:P imbalance between detritivores and leaf litter. This surprisingly consistent N limitation may be a consequence of cumulative N-demand arising from the production of N-rich chitin in the exoskeletons of all three consumer species, which is lost during regular moults, in addition to N-demand for silk production by the caddisfly. These N requirements are not commonly quantified in stoichiometric analyses of arthropod consumers. There was no evidence for compensatory feeding, but when offered mixed-species litter varying in C:N:P ratios, detritivores consumed more of the litter species showing the highest N:P and lowest C:N ratio, accelerating the mass loss of the preferred leaf species in the litter mixture. These results show that imbalances in consumer-resource stoichiometry can have contrasting effects on coupled processes, highlighting a challenge in developing a mechanistic understanding of the role of stoichiometry in regulating ecosystem processes such as leaf litter decomposition.
  •  
39.
  • Frainer, André, 1982-, et al. (author)
  • The legacy of forest disturbance on stream ecosystem functioning
  • 2021
  • In: Journal of Applied Ecology. - : John Wiley & Sons. - 0021-8901 .- 1365-2664. ; 58:7, s. 1511-1522
  • Journal article (peer-reviewed)abstract
    • Forest clearance is a pervasive disturbance worldwide, but many of its impacts are regarded as transient, diminishing in intensity as forest recovers. However, forests can take decades to centuries to recover after severe disturbances, and temporal lags in recovery of ecosystem properties for different forest habitats are mostly unknown. This includes forest streams, where most studies of the impacts of forest clearance are restricted to the first years of recovery, typically finding that temporary increases in light and nutrient run-off diminish as forest recovers. Implications of longer term changes remain little investigated.In a space-for-time substitution experiment, we assessed changes in organic matter processing and in the functional and taxonomic composition of litter-consuming detritivores along a riparian forest age gradient ranging from 1 to 120 years since last timber harvesting.Variation in organic matter processing and detritivore functional diversity along the forest succession gradient were both expressed as second-order polynomial relationships (peaking at ~50 years along the forest age gradient). Decomposition rates were lowest in both the more recently clear-cut and older riparian forest streams.Variation of litter decomposition rates among litter bags within streams, measured by the coefficient of variation, was lowest in recent clear-cuts and increased linearly along the succession gradient. This result indicates higher within-stream heterogeneity in decomposition rates in older forest streams.Synthesis and applications: We found that the decomposition of leaf litter, a component of carbon cycling in forests, was higher in streams flowing through intermediately aged forest, and that several key attributes of the organisms regulating litter decomposition also varied systematically with forest age. These findings highlight the longer term consequences of forest succession following forest clear-cutting for stream habitats. Our findings further illustrate complications arising from the use of forested sites as references for newly cleared sites without properly accounting for forest age, given conclusions regarding biotic responses will depend on the age of the reference forests. Finally, our results emphasise the potential of intensive forest management centred on vast, one-time clear-cutting events to drive long-term homogenisation not only in forest age structure but also in the functioning of associated forest stream habitats. ​.
  •  
40.
  • Frainer, André, 1982-, et al. (author)
  • When does diversity matter? : Species functional diversity and ecosystem functioning across habitats and seasons in a field experiment
  • 2014
  • In: Journal of Animal Ecology. - : John Wiley & Sons. - 0021-8790 .- 1365-2656. ; 83:2, s. 460-469
  • Journal article (peer-reviewed)abstract
    • Despite ample experimental evidence indicating that biodiversity might be an important driver of ecosystem processes, its role in the functioning of real ecosystems remains unclear. In particular, the understanding of which aspects of biodiversity are most important for ecosystem functioning, their importance relative to other biotic and abiotic drivers, and the circumstances under which biodiversity is most likely to influence functioning in nature, is limited. We conducted a field study that focussed on a guild of insect detritivores in streams, in which we quantified variation in the process of leaf decomposition across two habitats (riffles and pools) and two seasons (autumn and spring). The study was conducted in six streams, and the same locations were sampled in the two seasons. With the aid of structural equations modelling, we assessed spatiotemporal variation in the roles of three key biotic drivers in this process: functional diversity, quantified based on a spe- cies trait matrix, consumer density and biomass. Our models also accounted for variability related to different litter resources, and other sources of biotic and abiotic variability among streams. All three of our focal biotic drivers influenced leaf decomposition, but none was important in all habitats and seasons. Functional diversity had contrasting effects on decomposition between habitats and seasons. A positive relationship was observed in pool habitats in spring, associated with high trait dispersion, whereas a negative relationship was observed in riffle habitats during autumn. Our results demonstrate that functional biodiversity can be as significant for functioning in natural ecosystems as other important biotic drivers. In particular, variation in the role of functional diversity between seasons highlights the importance of fluctuations in the relative abundances of traits for ecosystem process rates in real ecosystems.
  •  
41.
  • Gardeström, Johanna, et al. (author)
  • Disturbance history influences stressor impacts : effects of a fungicide and nutrients on microbial diversity and litter decomposition
  • 2016
  • In: Freshwater Biology. - : Wiley. - 0046-5070 .- 1365-2427. ; 61:12, s. 2171-2184
  • Journal article (peer-reviewed)abstract
    • Streams draining agricultural catchments are severely degraded by multiple stressors, including nutrient enrichment and pesticides. The understanding of how such stressors interact to alter ecosystem structure and function, and how responses of biota reflect their longer-term disturbance history, remains limited. We conducted a multifactorial stream microcosm experiment to investigate how elevated nutrients and a fungicide (azoxystrobin) interact to affect multiple variables associated with leaf decomposition: the biomass, sporulation rate and diversity of aquatic hyphomycete decomposers, litter decomposition rates and detritivore growth. We further manipulated decomposer species composition by using three distinct fungal assemblages drawn from streams with contrasting histories of agricultural disturbance: a forest stream, a mixed land-use stream subject to nutrient enrichment but little pesticide use, and an agricultural stream subjected to both intensive nutrient and pesticide use. We also varied the presence of the detritivorous isopod Asellus aquaticus. The fungicide azoxystrobin reduced both biomass and diversity of aquatic hyphomycetes and growth of A.aquaticus, and had negative knock-on effects on leaf decomposition and fungal sporulation. These impacts further varied with nutrient concentration. Impacts of the fungicide differed markedly among the three fungal assemblages. The agricultural assemblages were dominated by tolerant species and showed some capacity for maintaining processes under pesticide exposure, whereas diversity and functioning were strongly suppressed in the forest stream assemblage, which was dominated by stress-intolerant species. Pesticides, in interaction with other agricultural stressors, can impact microbial diversity and key ecosystem processes underlying the delivery of ecosystem services from streams. The extent of such impacts vary according to the longer-term disturbance history of the biota, and might be most acute when agricultural activity expands into previously uncultivated catchments, as is currently occurring in many regions of the world.
  •  
42.
  • Göthe, Emma, et al. (author)
  • Flow restoration and the impacts of multiple stressors on fish communities in regulated rivers
  • 2019
  • In: Journal of Applied Ecology. - : John Wiley & Sons. - 0021-8901 .- 1365-2664. ; 56:7, s. 1687-1702
  • Journal article (peer-reviewed)abstract
    • River regulation for hydropower is undertaken worldwide, causing profound alterations to hydrological regimes and running water habitats. Regulated catchments are often subjected to additional stressors, arising inter alia from agriculture, forestry and industry, which are likely to interact with impacts of river regulation on fish and other biota. Such interactions are poorly understood, hindering planning of effective mitigation and restoration. We investigated fish responses to increased discharge (as a restoration measure) in regulated rivers in Sweden. We compiled electrofishing data from river channels downstream of hydropower dams, each of which either has or lacks a mandated minimum discharge corresponding to c. 5% of pre-regulation discharge. We further analysed interactions between flow restoration and co-occurring local and regional stressors. River channels without a mandated minimum discharge were characterized by a low diversity of fish species with traits favouring persistence under unpredictable environmental conditions, including omnivory, short life cycles and small size. Additional stressors further reduced diversity and increased dominance by broad-niched, opportunistic species. Both the presence and magnitude of a mandated minimum discharge were positively related to fish diversity and density, and the relative density of three economically and recreationally valuable species. However, the size of these relationships frequently varied with the presence of additional stressors. Increasing levels of hydrological degradation and reduced connectivity at the catchment scale reduced positive flow-ecology relationships and hindered the restoration of fish communities towards reference conditions. However, application of a mandated minimum discharge also assisted in mitigating impacts of some co-occurring stressors, especially reduced riparian integrity. Synthesis and applications. Additional stressors can strongly influence the outcomes of flow restoration for fish community diversity and composition. Our approach combining fish species and trait data from multiple flow restoration projects with information on additional stressors yielded valuable insights into factors affecting flow restoration success, useful for (a) identifying the systems most likely to benefit from mandated minimum flows, (b) modelling influences of multiple stressors on flow-ecology relationships, (c) prioritizing additional measures to manage co-occurring stressors and enhance outcomes from flow restoration.
  •  
43.
  • Handa, I. Tanya, et al. (author)
  • Consequences of biodiversity loss for litter decomposition across biomes
  • 2014
  • In: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 509:7499, s. 218-221
  • Journal article (peer-reviewed)abstract
    • The decomposition of dead organic matter is a major determinant of carbon and nutrient cycling in ecosystems, and of carbon fluxes between the biosphere and the atmosphere(1-3). Decomposition is driven by a vast diversity of organisms that are structured in complex food webs(2,4). Identifying the mechanisms underlying the effects of biodiversity on decomposition is critical(4-6) given the rapid loss of species worldwide and the effects of this loss on human well-being(7-9). Yet despite comprehensive syntheses of studies on how biodiversity affects litter decomposition(4-6,10), key questions remain, including when, where and how biodiversity has a role and whether general patterns and mechanisms occur across ecosystems and different functional types of organism(4,9-12). Here, in field experiments across five terrestrial and aquatic locations, ranging from the subarctic to the tropics, we show that reducing the functional diversity of decomposer organisms and plant litter types slowed the cycling of litter carbon and nitrogen. Moreover, we found evidence of nitrogen transfer from the litter of nitrogen-fixing plants to that of rapidly decomposing plants, but not between other plant functional types, highlighting that specific interactions in litter mixtures control carbon and nitrogen cycling during decomposition. The emergence of this general mechanism and the coherence of patterns across contrasting terrestrial and aquatic ecosystems suggest that biodiversity loss has consistent consequences for litter decomposition and the cycling of major elements on broad spatial scales.
  •  
44.
  • Hasselquist, Eliza Maher, et al. (author)
  • Contrasting effects of geomorphic complexity on diversity of three aquatic organism groups after stream restoration
  • Other publication (other academic/artistic)abstract
    • Ecological theory states that greater habitat heterogeneity should support higher biodiversity. Many stream restoration projects aim to increase geomorphic complexity, assuming that this increases habitat heterogeneity and, thus, biodiversity. However, little evidence has been published that supports this theory, especially with respect to stream restoration and aquatic organisms.Previous assessments of stream habitat restoration have suffered from four major limitations: (1) incomplete quantification of habitat complexity metrics, (2) assessment of the responses of only one organism group, most often macroinvertebrates, (3) mismatch between scale of restoration and scale of disturbance, and (4) limited number of restoration measures applied.We used 12 metrics of geomorphic complexity spanning five dimensions of complexity (sediment grain size distribution, longitudinal profile, cross section, planform, and instream wood) to evaluate if the diversity, abundance and community composition of three aquatic organism groups (benthic macroinvertebrates, diatoms and macrophytes) relate positively to complexity along near-natural, restored and channelised stream reaches in rural northern Sweden where disturbance to the streams has been primarily reach-scale channelisation to facilitate timber floating.We found that the variation in biodiversity and abundance within each of the three organism groups could be described by multiple regression models that included only geomorphic complexity metrics, but the variation within an organism group could rarely be described by only one metric of complexity in isolation. Rather, three metrics were needed on average to describe the variation in biodiversity and abundance, and rarely did all metrics relate positively to diversity. Sediment grain size distribution metrics were most often significant as explanatory variables, but were inconsistent in the direction of influence. The other four dimensions of complexity were less consistently significant but were nearly all positively related to our diversity metrics.Most of the variation in these metrics was driven by advanced restoration techniques and to a lesser extent older best practice techniques. Three complexity metrics were most often included in multiple regression models as well as described community composition in ordinations:  a metric quantifying heterogeneity of small sediment sizes, a metric that represents the variation in stream depth along the longitudinal profile, and instream wood metrics. Therefore, specifically these metrics could be targets for future restoration. The organism groups were not concordant in their patterns of diversity, abundance, or community composition; thus, none can be used as a surrogate in monitoring biodiversity of these sites.Synthesis and applications. Geomorphic complexity should be measured in multiple dimensions, and ideally in all five dimensions, to understand the full breadth of restoration impacts to which organisms could be responding. More than one organism group should be used in monitoring to ensure biodiversity goals are met. Finally, even though the scale of the restorations matched the scale of the disturbance at the reach scale, the older best practice methods of restoration rarely restored the large-scale features necessary to bring the sites up to their potential levels of complexity as these elements (large boulders, bedrock, log jams) had been destroyed or removed from the system. Although the advanced restoration sites were the youngest, advanced restoration techniques that added big boulders, coarse gravel and instream wood increased complexity to a level that elicited a biological response. Finally, the complexity level needed to elicit a biological response could be difficult to understand for a given system, so we suggest doing restoration work in an experimental way in collaboration with geomorphologists to determine what level of complexity is needed.
  •  
45.
  • Hasselquist, Eliza Maher, et al. (author)
  • Contrasting Responses among Aquatic Organism Groups to Changes in Geomorphic Complexity Along a Gradient of Stream Habitat Restoration : Implications for Restoration Planning and Assessment
  • 2018
  • In: Water. - : MDPI. - 2073-4441. ; 10:10
  • Journal article (peer-reviewed)abstract
    • Many stream restoration projects aim to increase geomorphic complexity, assuming that this increases habitat heterogeneity and, thus, biodiversity. However, empirical data supporting these linkages remain scant. Previous assessments of stream restoration suffer from incomplete quantification of habitat complexity, or a narrow focus on only one organism group and/or one restoration measure, limiting learning. Based on a comprehensive quantification of geomorphic complexity in 20 stream reaches in northern Sweden, ranging from streams channelized for timber floating to restored and reference reaches, we investigated responses of macroinvertebrates, diatoms, and macrophytes to multiple geomorphic metrics. Sediment size heterogeneity, which was generally improved in restored sites, favored macroinvertebrate and diatom diversity and macroinvertebrate abundance. In contrast, macrophyte diversity responded to increased variation along the longitudinal stream profile (e.g., step-pools), which was not consistently improved by the restoration. Our analyses highlight the value of learning across multiple restoration projects, both in identifying which aspects of restoration have succeeded, and pinpointing other measures that might be targeted during adaptive management or future restoration. Given our results, a combination of restoration measures targeting not only sediment size heterogeneity, but also features such as step-pools and instream wood, is most likely to benefit benthic biota in streams.
  •  
46.
  • Hladyz, Sally, et al. (author)
  • Stream ecosystem functioning in an agricultural landscape : the importance of terrestrial-aquatic linkages
  • 2011
  • In: Ecosystems in a human-modified landscape. - San Diego : Academic Press. - 9780123747945 ; 44, s. 211-276
  • Book chapter (pop. science, debate, etc.)abstract
    • The loss of native riparian vegetation and its replacement with non-native species or grazing land for agriculture is a worldwide phenomenon, but one that is prevalent in Europe, reflecting the heavily-modified nature of the continent's landscape. The consequences of these riparian alterations for freshwater ecosystems remain largely unknown, largely because bioassessment has traditionally focused on the impacts of organic pollution on community structure. We addressed the need for a broader perspective, which encompasses changes at the catchment scale, by comparing ecosystem processes in woodland reference sites with those with altered riparian zones. We assessed a range of riparian modifications, including clearance for pasture and replacement of woodland with a range of low diversity plantations, in 100 streams to obtain a continental-scale perspective of the major types of alterations across Europe. Subsequently, we focused on pasture streams, as an especially prevalent widespread riparian alteration, by characterising their structural (e.g. invertebrate and fish communities) and functional (e.g. litter decomposition, algal production, herbivory) attributes in a country (Ireland) dominated by this type of landscape modification, via field and laboratory experiments. We found that microbes became increasingly important as agents of decomposition relative to macrofauna (invertebrates) in impacted sites in general and in pasture streams in particular. Resource quality of grass litter (e.g., carbon : nutrient ratios, lignin and cellulose content) was a key driver of decomposition rates in pasture streams. These systems also relied more heavily on autochthonous algal production than was the case in woodland streams, which were more detrital based. These findings suggest that these pasture streams might be fundamentally different from their native, ancestral woodland state, with a shift towards greater reliance on autochthonous-based processes. This could have a destabilizing effect on the dynamics of the food web relative to the slower, detrital-based pathways that dominate in woodland streams.
  •  
47.
  • Jabiol, Jeremy, et al. (author)
  • Diversity patterns of leaf-associated aquatic hyphomycetes along a broad latitudinal gradient
  • 2013
  • In: Fungal ecology. - : Elsevier. - 1754-5048 .- 1878-0083. ; 6:5, s. 439-448
  • Journal article (peer-reviewed)abstract
    • Information about the global distribution of aquatic hyphomycetes is scarce, despite the primary importance of these fungi in stream ecosystem functioning. In particular, the relationship between their diversity and latitude remains unclear, due to a lack of coordinated surveys across broad latitudinal ranges. This study is a first report on latitudinal patterns of aquatic hyphomycete diversity associated with native leaf-litter species in five streams located along a gradient extending from the subarctic to the tropics. Exposure of leaf litter in mesh bags of three different mesh sizes facilitated assessing the effects of including or excluding different size-classes of litter-consuming invertebrates. Aquatic hyphomycete evenness was notably constant across all sites, whereas species richness and diversity, expressed as the Hill number, reached a maximum at mid-latitudes (Mediterranean and temperate streams). These latitudinal patterns were consistent across litter species, despite a notable influence of litter identity on fungal communities at the local scale. As a result, the bell-shaped distribution of species richness and Hill diversity deviated markedly from the latitudinal patterns of most other groups of organisms. Differences in the body-size distribution of invertebrate communities colonizing the leaves had no effect on aquatic hyphomycete species richness, Hill diversity or evenness, but invertebrates could still influence fungal communities by depleting litter, an effect that was not captured by the design of our experiment. (C) 2013 Elsevier Ltd and The British Mycological Society. All rights reserved.
  •  
48.
  • Johnson, Richard, et al. (author)
  • Contrasting responses of terrestrial and aquatic consumers in riparian - stream networks to local and landscape level drivers of environmental change
  • 2021
  • In: Basic and Applied Ecology. - : Elsevier BV. - 1439-1791 .- 1618-0089. ; 57, s. 115-128
  • Journal article (peer-reviewed)abstract
    • The biodiversity of streams and riparian zones is highly interlinked by multiple cross-habitat flows of organisms, nutrients and materials, and are thus increasingly recognized as forming an extended "meta-ecosystem" network spanning both within and across entire catchments. However, current understanding of how these extended networks respond to environmental change is limited by the lack of studies quantifying the local and larger-scale drivers of biodiversity in both terrestrial and aquatic systems simultaneously. Using high-resolution species and environmental data from eight boreal riparian stream meta-ecosystems, half of which were situated in forest and half in agricultural catchments, we quantified land-use impacts and the importance of catchment and local (riparian, instream) scale variables on the diversity and community composition of three epigeal arthropod groups (spiders and staphylinid and carabid beetles) and aquatic macroinvertebrates. All four organism groups responded to quantifiable environmental variables. Staphylinid beetle and spider assemblages differed significantly between forested and agricultural sites and were strongly correlated with riparian variables such as vegetation type and soil properties, but also instream variables such as conductivity and floating macrophytes. By contrast, carabid beetle and aquatic macroinvertebrate assemblages did not differ between forested and agricultural sites and showed similar responses to catchment and local scale variables. Our results indicate that measures that only address local scale drivers of terrestrial biodiversity might be ineffective if the catchment-scale variables regulating aquatic biodiversity and aquatic terrestrial linkages are not adequately addressed in ecosystem management. (C) 2021 The Author(s). Published by Elsevier GmbH on behalf of Gesellschaft fur Okologie.
  •  
49.
  • Johnson, Richard, et al. (author)
  • Decomposing multiple pressure effects on invertebrate assemblages of boreal streams
  • 2017
  • In: Ecological Indicators. - : Elsevier BV. - 1470-160X .- 1872-7034. ; 77, s. 293-303
  • Journal article (peer-reviewed)abstract
    • Land use often results in multiple pressures affecting the structure and function of aquatic ecosystems. Understanding how pressures interact to affect the biology of aquatic ecosystems is therefore a major challenge for freshwater management. Using a field survey approach, we studied individual and combined effects of impacts arising from agricultural land use and alteration of hydrology and geomorphology (HYMO) on benthic invertebrate assemblages in boreal streams. Variation partitioning of species and trait composition to pressures characterizing agriculture and HYMO revealed significant joint effects on the biota. Changes in species composition were significantly and uniquely related to agricultural pressures, whilst the variance component characterizing HYMO effects was not significant, confounding separation of unique pressure effects. In line with our predictions, the effects of HYMO on species and trait composition were largely negative. However, in contrast to predictions, ranking pressure variables showed that agricultural impacts explained more of the variability in species composition than HYMO impacts. Disturbance of riparian habitats was a strong predictor of shifts in species and trait composition. Interestingly, community responses were less pronounced at sites affected by both loss of riparian integrity and elevated nutrients, suggesting that HYMO effects were mitigated by moderate levels of elevated nutrients. Collectively, our results showed ecologically realistic, impact-specific changes on biodiversity of riverine environments. This knowledge allows managers to rank the importance of individual and combined pressure impacts when designing rehabilitation strategies. (C) 2017 Elsevier Ltd. All rights reserved.
  •  
50.
  • Kahlert, Maria, et al. (author)
  • Benthic Diatom Communities in Urban Streams and the Role of Riparian Buffers
  • 2020
  • In: Water. - : MDPI AG. - 2073-4441. ; 12
  • Journal article (peer-reviewed)abstract
    • Urbanization impacts stream ecosystems globally through degraded water quality, altered hydrology, and landscape disturbances at the catchment and riparian scales, causing biodiversity losses and altered system functioning. Addressing the "urban stream syndrome" requires multiple mitigation tools, and rehabilitation of riparian vegetation may help improve stream ecological status and provide key ecosystem services. However, the extent to which forested riparian buffers can help support stream biodiversity in the face of numerous environmental contingencies remains uncertain. We assessed how a key indicator of stream ecological status, benthic diatoms, respond to riparian habitat conditions using 10 urban site pairs (each comprising of one unbuffered and one buffered reach), and additional urban downstream and forest reference upstream sites in the Oslo Fjord basin. Diatom communities were structured by multiple drivers including spatial location, land use, water quality, and instream habitat. Among these, riparian habitat condition independently explained 16% of variation in community composition among site pairs. Changes in community structure and indicator taxa, along with a reduction in pollution-tolerant diatoms, suggested tangible benefits of forested riparian buffers for stream biodiversity in urban environments. Managing urban impacts requires multiple solutions, with forested riparian zones providing a potential tool to help improve biodiversity and ecosystem services.
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