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Changes in climate are causing floods to occur more often and more intensely in many parts of the world, including agricultural landscapes of southern Wisconsin (U.S.A.). How flooding and greater flood frequency affect stream carbon dioxide (CO2) and methane (CH4) fluxes and concentrations is not obvious. Thus, we asked how diffusive fluxes of CO2 and CH4 varied over time, particularly in response to floods, in agricultural streams, and what were likely causes for observed flood responses.We measured concentrations and diffusive fluxes of CO2 and CH4 at 10 stream sites in mixed agricultural and suburban catchments in southern Wisconsin (U.S.A.) during the growing season (March–November) in a year that experienced multiple floods. Habitat, hydrologic, and water chemistry attributes were also quantified to determine likely drivers of changes in gas concentrations and fluxes.Habitat and water chemistry, as well as CO2 and CH4 concentrations and fluxes were temporally erratic and lacked any seasonality. Carbon dioxide and CH4 concentrations and fluxes were higher during floods along with increased water velocity, turbidity, and dissolved organic carbon and decreases in dissolved oxygen, soft sediment depth, and macrophyte cover.Increased gas concentrations and fluxes were probably due to flushing of gases from soils, respiration of organic matter in the channel, and increased gas exchange velocities during floods.Flooding alleviated both supply and transfer limits on CO2 and CH4 emissions in these agricultural streams, and frequent and prolonged flooding during the growing season led to sustained high emissions from these streams. We hypothesise that such persistent increases in emissions during floods may be a common response to high precipitation periods for many agricultural streams. [ABSTRACT FROM AUTHOR]

In some regions, climate change is increasing the variability of rainfall and the frequency of extreme events such as drought. Consequently, non‐flow periods have grown in length and frequency, both in temporary and in formerly permanent streams. Water abstraction for human use may further prolong these dry periods.We analysed the resistance and resilience of biofilms from permanent and temporary streams to non‐flow conditions. This was achieved by exposing cobbles (collected from permanent and temporary streams) with intact biofilm to 31 days of non‐flow, followed by 20 days of stream flow in artificial stream channels. Biofilm resistance and resilience were assessed at a structural (algal biomass, pigment composition, and algae and cyanobacteria composition) and functional level (photosynthetic efficiency and community metabolism).Algal taxa in biofilms from permanent and temporary streams differed throughout the experiment. Biofilms from permanent streams were less resistant to non‐flow than those from temporary streams at structural level. Permanent stream biofilms also presented lower resilience at a structural level, but responded similarly to temporary stream biofilms at a functional level.Our investigation shows how the non‐flow period disturbed permanent stream biofilms, and suggests that temporary stream biofilms will have greater adaptive capacity as hydroperiod becomes shorter due to climate change. [ABSTRACT FROM AUTHOR]

Biotic interactions affect species distributions, and environmental factors that influence these interactions can play a key role when range shifts in response to environmental change are modelled.In a field experiment using enclosures, we studied the effects of the thermal habitat on intra‐ versus inter‐specific competition of juvenile Dolly Varden Salvelinus malma and white‐spotted charr Salvelinus leucomaenis, as measured by differences in specific growth rates during summer in allopatric and sympatric treatments. Previous laboratory experiments have shown mixed results regarding the importance of temperature‐dependent competitive abilities as a main driver for spatial segregation in stream fishes, and no study so far has confirmed its existence in natural streams.Under natural conditions in areas where the two species occur in sympatry, Dolly Varden dominate spring‐fed tributaries (cold, stable thermal regime), whereas both species often coexist in non‐spring‐fed tributaries (warm, unstable thermal regime). Enclosures (charr density = 6 per m2) were placed in non‐spring‐fed (10–14°C) and spring‐fed (7–8°C) tributaries.In enclosures placed in non‐spring‐fed tributaries, Dolly Varden grew 0.81% per day in allopatry and had negative growth (−0.33% per day) in sympatry, whereas growth rates were similar in allopatry and sympatry in spring‐fed tributaries (0.68 and 0.58% per day). White‐spotted charr grew better in sympatry than in allopatry in both thermal habitats. In non‐spring‐fed tributaries, they grew 0.17 and 0.79% per day and in spring‐fed tributaries 0.46 and 0.75% per day in allopatry and sympatry, respectively.The negative effect of inter‐specific competition from white‐spotted charr on Dolly Varden thus depended on the thermal habitat. However, there was no strong evidence of a temperature‐dependent effect of intra‐ and inter‐specific competition on white‐spotted charr growth.Multiple factors may shape species distribution patterns, and we show that temperature may mediate competitive outcomes and thus coexistence in stream fish. These effects of temperature will be important to incorporate into mechanistic and dynamic species distribution models. [ABSTRACT FROM AUTHOR]

Running waters in Mediterranean regions are strongly regulated by dams, which produce significant alterations to natural flow regimes. Climate change will reduce discharge and increase flow intermittence in Mediterranean streams, which will lead to an intensified flow regulation to meet water demands. Very little is known about how the functional features of aquatic communities vary along combined anthropogenic flow alteration and natural intermittence gradients.As intermittent streams are subjected to natural stress (droughts and flash floods), the flow regime alteration effect may differ from that observed in perennial rivers. Consequently, studies that aim to determine the effects of flow regulation on the functioning of aquatic communities in a global change context are crucial.By applying linear mixed‐effect models and null models to the macroinvertebrate communities from 65 stream sites in the Segura River Basin (south‐east Spain), we assessed the separate effects of natural flow intermittence and flow regulation, as well as their interaction, on biological traits and functional diversity indices.Natural flow intermittence and flow regulation were mainly associated with loss of taxa with semivoltine or univoltine cycles and more sensitive aquatic stages (i.e. eggs), and with the replacement by taxa with multivoltine cycles and more resistant aquatic stages (i.e. adults). Flow regulation intensified the impact of natural flow intermittence on some biological traits, producing synergistic effects (i.e. decreasing interstitial taxa and tegument breathers and increasing taxa with aquatic adult stages). At the same time, antagonistic (life cycle) and opposing (shredders) interaction effects were also observed. Functional diversity, functional dispersion, and functional redundancy underwent a non‐random decrease as the flow regime alteration increased, and a significant antagonistic interaction was also found between both stressors for functional redundancy.In general, flow regulation effects were stronger in perennial than in intermittent streams because natural intermittence imposes a previous eco‐evolutionary pressure on aquatic biota by selecting those resistant or recovery traits that confer resilience to anthropogenic flow regime alterations. Thus, the natural flow regime influences the functional sensibility of communities to anthropogenic flow alteration. [ABSTRACT FROM AUTHOR]

We studied benthic macroinvertebrate communities in 12 mid‐elevation mountain streams in the Sierra Nevada, California. Data were collected at nine times (seven springs and two autumns) over a 14‐year period of variable hydrological conditions, including years of flood and extreme unprecedented drought.The taxonomic and trait structures of communities were similar during wet and average springs but became increasingly different as drought continued and smaller streams became intermittent.The density of total invertebrates, primarily chironomids, increased during the drought years, but the richness and abundance of mayfly, stonefly, and caddisfly (EPT) taxa declined during the late drought. During the late drought, the proportions of rheophilic, semivoltine taxa with clinger or swimmer behavioural habits decreased, whereas small, stress‐tolerant taxa with burrower and climber habits increased. Collector–gatherers dominated in all periods, but during the severe drought the relative abundance of micropredators increased and filterers, shredders, and grazers decreased.We also found greater changes in community structure between spring runoff and autumn base flow conditions in an average than a wet year. However, spring to autumn population growth rates were much greater during the wet than average year.Invertebrate richness and EPT abundance decreased and community structure showed large changes when stream discharge fell below 1–10 L/s, but remained relatively constant across a range of higher flows. During the severe drought, there were significant declines in the densities of 40% of the common EPT taxa compared to average and wet years, but chironomid, mite, and other invertebrate taxa showed variable responses.Invertebrate diversity, community structure, and ecosystem functions in small, headwater streams are especially vulnerable to drought conditions, which are expected to increase in frequency and intensity with climate change in the Sierra Nevada and other mountainous regions. [ABSTRACT FROM AUTHOR]

Freshwater aquatic ecosystems are in decline due to intensifying land use, salinisation, water abstraction and climate change. Understanding compositional patterns in aquatic biota is a useful step towards better management of aquatic ecosystems., We used generalised dissimilarity modelling (GDM) to predict compositional turnover in riverine invertebrate fauna (primarily insects) as a function of environment. Conceptual understanding of major drivers of aquatic invertebrate species distribution helped decide which predictor variables to source and include. Five groups of environmental variables-waterscape, local habitat, climate, landscape and disturbance-were derived from either spatial layers or in situ (site) measurements., Predictive models and variance partitioning tests of variable groups demonstrated the importance of representing all conceptual drivers of ecological pattern and process. As expected, waterscape variables were independently the most important group, followed by local habitat and landscape variables; with complex interactions between groups. Climate variables independently contributed the least., To determine the information content for mapping patterns, we investigated the independent and combined contribution of site-measured and spatial predictors. Even though predictive models developed using only site-measured variables or only spatial variables explained around the same amount of deviance (DE), combined they increased explained model DE by 11.2%. Compositional dissimilarities between the 51 surveyed site pairs predicted by the model using only spatial variables were highly correlated ( r2 = .85) with dissimilarities predicted using site and spatial variables. These results support the use of the spatial model for conservation decisions., The spatial model was used to evaluate representativeness of both the conservation reserve network and biological monitoring locations. The location of aquatic monitoring sites was uneven, with comprehensive coverage south and coastward, and less representative of inland environments. Proportional protection of ecological environments (scaled by riverine invertebrate taxa) was found to vary between 20% and 30%, being higher in southern parts where more land has been allocated to reserves and less in northern and inland parts. This demonstrated local progress towards achieving the Convention on Biological Diversity's Aichi Target 11 for inland waters., These results provide a focus for improving the robustness of information used in decisions affecting the conservation of aquatic biodiversity, including places to target to fill gaps in the reserve network and additional aquatic monitoring locations (supporting Convention on Biological Diversity's Aichi Target 19). The GDM-based approach to characterising ecological environments, provided a first quantitative foundation for comprehensively evaluating the conservation status of freshwater ecosystems in south-western Australia. Potential future applications include assessing the ecological implications of land use and climate change. [ABSTRACT FROM AUTHOR]

1. Although more than half the world's river networks comprise channels that periodically cease to flow and dry [intermittent rivers (IRs)], river ecology was largely developed from and for perennial systems. Ecological knowledge of IRs is rapidly increasing, so there is a need to synthesise this knowledge and deepen ecological understanding. 2. In this Special Issue, we bring together 13 papers spanning observational case studies, field and laboratory experiments and reviews to guide research and management in this productive field of freshwater science. We summarise new developments in IR ecology, identify research gaps and needs, and address how the study of IRs as highly dynamic ecosystems informs ecological understanding more broadly. 3. This series of articles reveals that contemporary IR ecology is a multifaceted and maturing field of research at the interface between aquatic and terrestrial ecology. This research contributes to fresh water and general ecology by testing concepts across a range of topics, including disturbance ecology, metacommunity ecology and coupled aquatic-terrestrial ecosystems. 4. Drying affects flow continuity through time and flow connectivity across longitudinal, lateral and vertical dimensions of space, which aligns well with the recent emphasis of mainstream ecology on meta-system perspectives. Although most articles here focus on the wet phase, there is growing interest in dry phases, and in the terrestrial vegetation and invertebrate assemblages living in and along IR channels. We encourage interdisciplinary studies on IRs to further blur the demarcation between aquatic and terrestrial ecosystems and develop more integrated perspectives. 5. As a result of climate change and human modification of landscapes and waterways, flooding and drought are expected to become more extreme and widespread. Shifts in streamflow regimes from perennial to intermittent may exacerbate the duration and frequency of dry phases in IRs with serious implications for river ecosystems and the quality and diversity of services they provide. [ABSTRACT FROM AUTHOR]

1. Differences in the composition of ecological communities among rivers with contrasting flow regimes have been detected in many regions worldwide. However, we know little of how climatic variation alters these spatial patterns for constituent species with varying dispersal modes and strengths. 2. We predicted that beta diversity (spatial variation in composition) of macro in vertebrate and fish assemblages among streams with near-perennial, mildly intermittent and highly intermittent flow regimes would be greater during prolonged drought than under wetter climate conditions. We hypothesised that changes in beta diversity between these climate phases would be greater for taxa with stronger dispersal ability. We tested these predictions with biomonitoring data from Australian subtropical rivers. 3. Differences in average community composition among flow regimes were statistically significant for six groups of macroinvertebrates with differing dispersal (non-swimmers, weak swimmers, strong swimmers, non-fliers, weak fliers and strong fliers) and two groups of fish (potamodromous and diadromous), but not for locally dispersing fish. For each of these biotic groups, shifts in assemblage composition between supra-seasonal drought and a subsequent non-drought period were either statistically non-significant or of similar magnitude among flow regimes. Therefore, beta diversity among flow regimes did not change significantly with climate phase. 4. Beta diversity within flow-regime classes was greater during the drought than afterwards or not significantly different between climate phases, depending on the flow regime and biotic group. Stronger powers of flight were associated with greater change in beta diversity between climate phases in near-perennial streams, but stronger powers of swimming were not. Within-regime beta diversity was driven more by replacement of taxa among samples than by nestedness, except for diadromous fish in near-perennial streams. 5. Our findings are consistent with the hypothesis that decreasing hydrological connectivity and greater environmental heterogeneity during prolonged drought increase beta diversity of stream communities. However, changes in beta diversity between climate phases were not as pronounced as we expected. The communities may have been somewhat drought resistant because the magnitude and duration of the drought were within the range of historical variability and because surface water persisted at study sites during drought-imposed flow cessations. Our findings suggest that maintenance of refuge pools will be critical to lessening drought impacts on river biodiversity at landscape scales, particularly if drought duration and intensity increase in the future. [ABSTRACT FROM AUTHOR]

We review the predicted changes in extreme events following climate change in flowing waters in arctic and subarctic regions. These regions are characterised by tundra or taiga ecosystems in either erosional or depositional glacial landforms or presently glacierised areas of the Northern Hemisphere., The ecological and geomorphic effects of extreme meteorological and hydrological events, such as episodes of strongly increased precipitation, temperatures and flows, can be exacerbated by altered base conditions. For example, winter temperature variations between frost and thaw will become more frequent at many places because mean temperature during the winter is closer to 0 °C, potentially leading to changes in the production of ice and intensified disturbance of riparian and aquatic habitats during extreme floods. Additionally, thawing of permafrost and glaciers can lead to increased bank erosion because of thaw slump and glacial outburst floods., We discuss the abiotic and biotic effects of these and other extreme events, including heavy precipitation, floods, drought and extreme air or water temperatures, and summarise our findings in a model that aims to stimulate further research in this field. [ABSTRACT FROM AUTHOR]

1. Temperature is a major driver of ecological processes in stream ecosystems, yet the dynamics of thermal regimes remain poorly described. Most work has focused on relatively simple descriptors that fail to capture the full range of conditions that characterise thermal regimes of streams across seasons or throughout the year. 2. To more completely describe thermal regimes, we developed several descriptors of magnitude, variability, frequency, duration and timing of thermal events throughout a year. We evaluated how these descriptors change over time using long-term (1979-2009), continuous temperature data from five relatively undisturbed cold-water streams in western Oregon, U.S.A. In addition to trends for each descriptor, we evaluated similarities among them, as well as patterns of spatial coherence, and temporal synchrony. 3. Using different groups of descriptors, we were able to more fully capture distinct aspects of the full range of variability in thermal regimes across space and time. A subset of descriptors showed both higher coherence and synchrony and, thus, an appropriate level of responsiveness to examine evidence of regional climatic influences on thermal regimes. Most notably, daily minimum values during winter-spring were the most responsive descriptors to potential climatic influences. 4. Overall, thermal regimes in streams we studied showed high frequency and low variability of cold temperatures during the cold-water period in winter and spring, and high frequency and high variability of warm temperatures during the warm-water period in summer and autumn. The cold and warm periods differed in the distribution of events with a higher frequency and longer duration of warm events in summer than cold events in winter. The cold period exhibited lower variability in the duration of events, but showed more variability in timing. 5. In conclusion, our results highlight the importance of a year-round perspective in identifying the most responsive characteristics or descriptors of thermal regimes in streams. The descriptors we provide herein can be applied across hydro-ecological regions to evaluate spatial and temporal patterns in thermal regimes. Evaluation of coherence and synchrony of different components of thermal regimes can facilitate identification of impacts of regional climate variability or local human or natural influences. [ABSTRACT FROM AUTHOR]

Summary 1. Spring-fed streams, with temperatures ranging from 7.1 to 21.6 °C, in an alpine geothermal area in SW Iceland were chosen to test hypotheses on the effects of nutrients and temperature on stream primary producers. Ammonium nitrate was dripped into the lower reaches of eight streams, with higher reaches being used as controls, during the summers of 2006 and 2007. Dry mass of larger primary producers, epilithic chlorophyll a and biovolumes of epilithic algae were measured. 2. Bryophyte communities were dominated by Fontinalis antipyretica, and biomass was greatest in the warmest streams. Jungermannia exsertifolia, a liverwort, was found in low densities in few samples from cold streams but this species was absent from the warmest streams. 3. Nutrient enrichment increased the biomass of bryophytes significantly in warm streams. No effects of the nutrient addition were detected on vascular plants. The biomass of larger filamentous algae (mainly Cladophora spp.) was significantly increased by nutrient enrichment in cold streams but reduced by nutrients in warm streams. Thalloid cyanobacteria ( Nostoc spp.) were not affected by nutrients in cold streams but decreased with nutrient addition in warm streams. Epilithic algal chlorophyll a was increased by nutrients in all streams and to a greater extent in 2007 than in 2006. Nutrient addition did not affect the epilithic chlorophyll a differently in streams of different temperatures. 4. There were small differential effects of nutrients, influenced by pH and conductivity, on different epilithic algal groups. 5. As global temperatures increase, animal husbandry and perhaps crop agriculture are likely to increase in Iceland. Temperature will directly influence the stream communities, but its secondary effects, manifested through agricultural eutrophication, are likely to be much greater. [ABSTRACT FROM AUTHOR]

Summary 1. Freshwater ecosystems will be profoundly affected by global climate change, especially those in mountainous areas, which are known to be particularly vulnerable to warming temperatures. We modelled impacts of climate change on the distribution ranges of 38 species of benthic stream macroinvertebrates from nine macroinvertebrate orders covering all river zones from the headwaters to large river reaches. 2. Species altitudinal shifts as well as range changes up to the year 2080 were simulated using the A2a and B2a Intergovernmental Panel on Climate Change climate-warming scenarios. Presence-only species distribution models were constructed for a stream network in Germany's lower mountain ranges by means of consensus projections of four algorithms, as implemented in the BIOMOD package in R (GLM, GAM, GBM and ANN). 3. Species were predicted to shift an average of 122 and 83 m up in altitude along the river continuum by the year 2080 under the A2a and B2a climate-warming scenarios, respectively. No correlation between altitudinal shifts and mean annual air temperature of species' occurrence could be detected. 4. Depending on the climate-warming scenario, most or all (97% for A2a and 100% for B2a) of the macroinvertebrate species investigated were predicted to survive under climate change in the study area. Ranges were predicted to contract for species that currently occur in streams with low annual mean air temperatures but expand for species that inhabit rivers where air temperatures are higher. 5. Our models predict that novel climate conditions will reorganise species composition and community structure along the river continuum. Possible effects are discussed, including significant reductions in population size of headwater species, eventually leading to a loss of genetic diversity. A shift in river species composition is likely to enhance the establishment of non-native macroinvertebrates in the lower reaches of the river continuum. [ABSTRACT FROM AUTHOR]

1. Freshwater systems are subject to multiple stressors that include changing climate, changing land use, changing demands on water resources and changing nutrient cycles. Global trends suggest these stressors that impact on water availability will increase over the coming decades, and – without action – will constrain opportunities to sustain ecosystem services to deliver the Millennium Development Goals. 2. Although a key ‘service’ freshwaters provide is buffering inputs from the land system, predicting ecosystem response through observation and modelling is complex because nonlinear and dynamic interactions amongst a large number of constituents operate to regulate biogeochemical transformations in freshwater systems. 3. Reductionist approaches have been successful at unravelling many of the processes and some of the interactions in freshwater systems. However, reductionist approaches cannot provide the concepts or methods to understand how system properties will emerge in response to a changing climate (particularly the changing spatial and temporal distribution of precipitation); to the consequent change in water availability and water quality in the context of social drivers on the demand for water; and to feedbacks arising from nutrient cycling across a range of scales. 4. This study presents a review of the evidence for landscape-scale filtering of nutrient delivery to receiving waters and examines the role of the internal processing of nutrients at critical interfaces such as the hyporheic in attenuating nutrient loads. Analysis of research on the spatial scales and time step appropriate for catchment and water quality observations indicates the importance of small scale and short time step data for unravelling nutrient cycling in freshwater ecosystems. 5 . Thematic implications: leading work in the catchment and aquatic sciences on the importance of diffuse nutrient losses from land, and on nutrient cycling in freshwaters, in governing water quality and protecting water availability, is making an increasing contribution to mainstream environmental science. Critically, the evidence base is starting to grow to inform policy-related debates with respect to food security, to climate change adaptation and for sustaining ecosystem services in freshwater environments. [ABSTRACT FROM AUTHOR]

1. Streams are highly connected to their landscapes and so are easily altered by multiple stressors that affect both uplands and riparian zones, and the streams themselves. These include dams and diversions, channelisation, deforestation, water pollution, biological invasions and climate change. 2. We review research conducted in Hokkaido Island, northern Japan, which measured the effects of many of these stressors on both stream food webs and fluxes of invertebrates to and from the riparian zone that feed aquatic and terrestrial consumers. About half the energy that sustains fish falls directly into streams as terrestrial invertebrates, and a quarter of the energy needs for riparian birds is supplied by adult aquatic insects emerging from the stream. 3. Single stressors in these Hokkaido streams, including deforestation, channelisation, erosion-control dams, biological invasions and climate change, have drastic effects on stream food webs, the fishes they support and riparian predators (spiders, birds, and bats). Most stressors caused 30–90% declines in foraging, growth, or abundance of aquatic or terrestrial predators. Indirect effects of stressors also cascaded throughout stream food webs and across the aquatic–terrestrial boundary. 4. Effects of individual stressors were largely concordant across spatial scale, through time during years of different productivity and among different food web components. 5. Two studies of multiple stressors revealed that each stressor alone reduced food web components like abundance of stream benthos or riparian spiders to low levels (35–83% reduction; mean 59%), beyond which an additional stressor had little effect. Synergism and antagonism are less relevant when individual stressors have such large effects. 6. Thematic implications: small streams in Hokkaido are highly sensitive to many individual stressors and have little resistance or resilience to their effects. Moreover, each stressor alone can reduce biota strongly, indicating that restoration will need to consider all simultaneously to protect biotic diversity. [ABSTRACT FROM AUTHOR]

1. Both the clearance rates (CR) and abundances of the freshwater sponge Ephydatia muelleri and the bryozoans Plumatella emarginata and Fredericella sultana were investigated from autumn to spring under different temperature regimes. The experiments were performed in bypass channels of the River Rhine (Cologne, Germany) in which temperature could be manipulated. 2. The impact of temperature increase on CRs depends upon the grazer: E. muelleri showed a clear increase in CRs with increasing temperature whereas P. emarginata was not significantly affected by experimental warming. 3. Distinct differences in food preference were found for the sponge (which is an efficient grazer of bacteria and small algae) and for the bryozoan P. emarginata (which feeds primarily on large algae, and with no significant grazing on bacteria). 4. In contrast to their temperature-related patterns in CR, respiration of both P. emarginata and E. muelleri increased with temperature between 19 and 32 °C, suggesting that the risk of experiencing energy deficiency at high temperatures due to increased metabolic rates is particularly high for the bryozoan. 5. A temperature elevation of 3 °C above the natural Rhine temperature resulted in a delay in the disappearance of active tissue and formation of resting stages for E. muelleri in autumn. This delay ranged from 8 (beginning of gemmulation) to 22 days (termination of gemmulation). In contrast, there was no distinct effect of warming on the disappearance of active zooids of the two bryozoan species in autumn. However, warming can positively affect the maintenance of active zooids during winter in F. sultana. In spring, the appearance of active zooids of P. emarginata was clearly stimulated by temperature elevations, whereas the hatching of both F. sultana and E. muelleri was hardly affected by warming. 6. The study demonstrated different patterns in the thermal ecology of the two freshwater bryozoans and the sponge in comparison to other filter feeders, particularly mussels. Such patterns need to be considered when predicting the impact of temperature on pelagic-benthic coupling in aquatic habitats. [ABSTRACT FROM AUTHOR]

1. In semi-arid climates, seasonally-flowing streams provide most of the water required for human use, but knowledge of how water extraction affects ecological processes is limited. Predicted alterations in stream flows associated with the impacts of climate change further emphasize the need to understand these processes. Benthic algae are an important base for stream food webs, but we have little knowledge of how algae survive dry periods or respond to altered flow regimes. 2. We sampled 19 streams within the Grampians National Park, south-eastern Australia and included four components: a survey of different drought refuges (e.g. permanent pools, dry biofilm on stones and dry leaf packs) and associated algal taxa; a survey of algal regrowth on stones after flows recommenced to determine which refuges contributed to regrowth; reciprocal transplant experiments to determine the relative importance of algal drift and regrowth from dry biofilm in recolonization; direct measurement of algal drift to determine taxonomic composition in relation to benthic assemblage composition. 3. Algae showed little specificity for drought refuges but did depend on them; no species were found that were not present in at least one of the perennial pool, dry biofilm or leaf pack refuges. Perennial pools were most closely correlated with the composition of algal assemblages once flows resumed, but the loss or gain of perennial pools that might arise from stream regulation is unlikely to affect the composition of algal regrowth. However, regulated streams were associated with strong increases in algal density in dry biofilm, including increased densities of Cyanobacteria. 4. A model for algal recolonization in seasonally-flowing streams identified three pathways for algal recolonization (drift-dependent, dry biofilm-dependent and contributions from both), depending on whether streams are diatom-dominated or dominated by filamentous algae. The model predicted the effects of changes to stream flow regimes on benthic algal recolonization and provides a basis for hypotheses testable in streams elsewhere. [ABSTRACT FROM AUTHOR]

1. Macroinvertebrate assemblages of five non-glacial intermittent high altitude headwater streams (above 1400 m – Serra da Estrela, Portugal), with dry periods of different lengths (0–3 months), were investigated in nearly undisturbed conditions to (i) examine spatial differences and identify environmental variables responsible for the observed invertebrate patterns, (ii) assess the association of dry period length with invertebrate community structure and (iii) determine the influence of using different taxonomic identification levels (order, family and genus) to assess invertebrate community patterns. 2. More than 100 macroinvertebrate genera were identified. Insects clearly dominated these communities with more than 95% of total captures and around 95% of the total richness. Diptera were the most rich and abundant group with chironomid occurrences comprising over 70% of macroinvertebrate captures. 3. The highest taxon richness, diversity, EPT (Ephemeroptera + Plecoptera + Trichoptera) and OCH (Odonata + Coleoptera + Heteroptera) genus richness, the greatest number of exclusive and characteristic taxa identified by the Indicator Value (IndVal), and a distinct community structure shown by Canonical Correspondence Analyses (CCA), were found in the only stream that was never totally dry, with pools lasting over summer. Environmental gradients that spatially structured the macroinvertebrate communities were always related to flow variations. 4. Over time, the highest abundances found in these systems were also related to flow variations and maximum genus richness occurred in the connected pools or in isolated pools. Streams with longer dry periods presented a distinct recolonization phase, with higher abundance of the stonefly larvae Nemoura sp. and the presence of the chironomid larvae Krenosmittia sp., possibly arriving from the hyporheos. 5. Taxonomic level of invertebrate identification was vital for recognizing the characteristic taxa (IndVal) of streams yet was not critical for identifying streams with the highest macroinvertebrate richness/diversity or structuring environmental gradients. 6. Overall, this study emphasizes the variability of high altitude intermittent streams macroinvertebrate communities, despite spatial proximity. This variability was probably related to flow intermittency and hydrologic permanence, different vegetation covers and riverbed substrata. Consequently, the establishment of reference conditions should involve long-term data collections and more detailed physical characterization. Also, these findings have significant implications for accurately predicting the ecological consequences of future climate change in high altitude scenarios. [ABSTRACT FROM AUTHOR]

1. This study analysed changes occurring in Mediterranean stream fish assemblages over a sequence of dry years followed by a generally wet period (1991–98). Variations in assemblage attributes were quantified at the basin and stream reach scales, and related to variables reflecting the occurrence of unusually dry or wet conditions. 2. Assemblage variability increased along with the resolution of analysis, with little changes in species richness, composition and rank abundances, but significant variation in individual species abundances. Fluctuations in relative abundances were significantly affected by variables reflecting the severity of summer droughts and the occurrence of rainy springs. These patterns were evident at the basin scale, while variability at individual stream reaches tended to be higher and less related to rainfall patterns. 3. At least three response guilds to rainfall variation could be identified: two of the four abundant and widespread species (chub and loach) declined following dry years, whereas the two other core species (nase and eel) declined after rainy spring; one scarce native species (stickleback) increased in dry years. 4. Except at the two most upstream reaches, the assemblages tended to recover quickly to previous configuration after the changes occurring during the sequence of dry years. 5. Temporal variability of local assemblages was concordant among reaches but did not follow any consistent spatial pattern. Instead, spatial patterns in assemblage attributes changed over time in response to environmental variability, with a tendency for a disruption of upstream–downstream gradients following dry years. 6. Results supported the view that present-day droughts cause relatively small and transient changes to Mediterranean stream fish assemblages. However, longer and more severe droughts expected under altered future climates, may result in declines or local extinctions of the most sensitive species and their potential replacement by more resistant species. Changing drought regimes thus need to be duly considered in the development of conservation strategies for Mediterranean stream fish. [ABSTRACT FROM AUTHOR]

1. Relating processes occurring at a local scale to the natural variability of ecosystems at a larger scale requires the design of predictive models both to orientate stream management and to predict the effects of larger scale disturbances such as climate changes. Our study contributes to this effort by providing detailed models of the hydraulic preferences of 151 invertebrate taxa, mostly identified at the species level. We used an extensive data set comprising 580 invertebrate samples collected using a Surber net from nine sites of second and third order streams during one, two or three surveys at each site. We used nested non-linear mixed models to relate taxon local densities to bed shear stresses estimated from FliesswasserStammTisch hemisphere numbers. 2. An average model by taxon, i.e. independent from surveys, globally explained 25% of the density variations of taxa within surveys. A quadratic relationship existed between the average preferences and the niche breadth of taxa, indicating that taxa preferring extreme hemisphere numbers had a reduced hydraulic niche breadth. A more complete model, where taxa preferences vary across surveys, globally explained 38% of the variation of taxa densities within surveys. Variations in preferences across surveys were weak for taxa preferring extreme hemisphere numbers. 3. There was a significant taxonomic effect on preferences computed from the complete model. By contrast, season, site, average hemisphere number within a survey and average density of taxa within a survey used as covariates did not consistently explain shifts in taxon hydraulic preferences across surveys. 4. The average hydraulic preferences of taxa obtained from the extensive data set were well correlated to those obtained from two additional independent data sets collected in other regions. The consistency of taxon preferences across regions supports the use of regional preference curves for estimating the impact of river management on invertebrate communities. By contrast, the hydraulic niche breadths of taxa computed from the different data sets were not related. [ABSTRACT FROM AUTHOR]

1. The influence of 11 environmental variables on benthic macroinvertebrate communities was examined in seven glacier-fed European streams ranging from Svalbard in the north to the Pyrenees in the south. Between 4 and 11 near-pristine reaches were studied on each stream in 1996–97. 2. Taxonomic richness, measured at the family or subfamily (for Chironomidae) levels for insects and higher levels for non-insects, increased with latitude from Svalbard (3 taxa) to the Pyrenees (29 taxa). 3. A Generalized Additive Model (GAM) incorporating channel stability [Pfankuch Index (PFAN)], tractive force, Froude number (FROU), water conductivity (COND), suspended solids (SUSP) concentration, and maximum temperature explained 79% of the total deviance of the taxonomic richness per reach. Water temperature and the PFAN of stability made the highest contribution to this deviance. In the model, richness response to temperature was positive linear, whereas the response to the PFAN was bell-shaped with an optimum at an intermediate level of stability. 4. Generalized Additive Models calculated for the 16 most frequent taxa explained between 25 (Tipulidae) and 79% (Heptageniidae) of the deviance. In 10 models, more than 50% of the deviance was explained and 11 models had cross-validation correlation ratios above 0.5. Maximum temperature, the PFAN, SUSP and tractive force (TRAC) were the most frequently incorporated explanatory variables. Season and substrate characteristics were very rarely incorporated. 5. Our results highlight the strong deterministic nature of zoobenthic communities in glacier-fed streams and the prominent role of water temperature and substrate stability in determining longitudinal patterns of macroinvertebrate community structure. The GAMs are proposed as a tool for predicting changes of zoobenthic communities in glacier-fed streams under climate or hydrological change scenarios. [ABSTRACT FROM AUTHOR]