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Biodiversity loss is increasing worldwide, necessitating effective approaches to counteract negative trends. Here, we assessed aquatic macroinvertebrate biodiversity in two river catchments in Switzerland; one significantly degraded and associated with urbanisation and instream barriers, and one in a near-natural condition. Contrary to our expectations, environmental heterogeneity was lower in the near-natural stream, with enhanced productivity in the degraded system resulting in a greater range of environmental conditions. At face value, commonly employed alpha, beta and gamma biodiversity metrics suggested both catchments constituted healthy systems, with greater richness or comparable values recorded in the degraded system relative to the near-natural one. Further, functional metrics considered to be early indicators for anthropogenic disturbance, demonstrated no anticipated differences between degraded and near-natural catchments. However, investigating the identity of the taxa unique to each river system showed that anthropogenic degradation led to replacement of specialist, sensitive species indicative of pristine rivers, by generalist, pollution tolerant species. These replacements reflect a major alteration in community composition in the degraded system compared with the near-natural system. Total nitrogen and fine sediment were important in distinguishing the respective communities. We urge caution in biodiversity studies that employ numerical biodiversity metrics alone. Assessing just one aspect of diversity, such as richness, is not sufficient to track biodiversity changes associated with environmental stress. We advocate that biodiversity monitoring for conservation and management purposes must go beyond traditional richness biodiversity metrics, to include indices that incorporate detailed nuances of biotic communities that relates to taxon identity. [ABSTRACT FROM AUTHOR]

The loss of biodiversity in freshwater environments is becoming an increasing problem globally. As a result, many tools have been developed and improved to reduce this decline. However, there is still a need for the identification and evaluation of precise restoration measures to improve habitats and preserve sentinel freshwater species, such as brown trout. This paper provides an up‐to‐date viewpoint about the life history, habitat characteristics, suitability conditions, and metapopulation dynamic modelling of brown trout, aiming to identify and discuss gaps and propose possible improvements based on collating and reinterpreting literature data. Results suggest that habitat suitability curves for environmental and hydraulic variables possess some degree of universality, for spawning habitat, fry, juvenile and adult trout. Further, an improved method to estimate the amount of suitable area by including the role of stream obstacles (i.e., macro‐roughness with characteristic size in the order of the mean water depth) is proposed and discussed. This approach can be integrated into advanced metapopulation models and will allow experts to evaluate the best measures towards restoring and preserving freshwater riverine environments. [ABSTRACT FROM AUTHOR]

Alpine landscapes are notable regarding their sensitivity to environmental change. Surface waters are especially sensitive as many are influenced by glacial meltwaters that are diminishing with the retreat of glaciers worldwide. The Macun Lakes region, Swiss National Park, is an alpine cirque landscape housing a number of lakes interconnected by streams. The area has been non-glaciated for decades, although rock glaciers are still present in the south basin. Surface waters, 10 stream sites in the present study, have been monitored in mid-summer since the year 2001 for physico-chemistry, periphyton and macroinvertebrates (including 74 species of chironomids). Water physico-chemistry revealed that the two main basins in the catchment differed, reflecting the inputs of rock glacier waters in the south basin. However, trends suggest that waters are becoming more similar as rock glacier inputs diminish over time along with a general decrease in nitrogen levels in all waters. Periphyton biomass showed some spatial differences among sites and a general decrease after 2010. Macroinvertebrate assemblages, including chironomids, clearly differed among basins and spatially along the stream network in each basin. Notably, no significant temporal trend was observed in the long-term data for macroinvertebrates, including chironomids, at the monitored sites. The results suggest that lotic macroinvertebrates may be buffered by the interconnectedness of streams and lakes in the landscape, which mitigates major response patterns of running waters to environmental change. [ABSTRACT FROM AUTHOR]

Flow regulation of montane and alpine headwater streams can fundamentally alter food web structure and energy flows through changes in productivity, resource availability, and community assembly. Dam flow‐release schemes can be used to mitigate the environmental impacts of flow regulation via environmental flows, which can increase discharge variability and other ecologically important hydrological properties. In particular, managed floods can reintroduce disturbance to the system and stimulate the reactivation of physical habitat dynamics. However, how managed floods might restore ecosystem processes is virtually unknown. In this study, we examined patterns in potential energy fluxes before, during and after a long‐term experimental flood program on the river Spöl, a regulated alpine River in southeast Switzerland. We used benthic samples collected during long‐term monitoring and stable isotope analysis (δ13C and δ15N) of macroinvertebrates and their potential food sources to reconstruct secondary production, and potential energy fluxes, over a 20‐year study period. The experimental floods did not alter the relative importance of basal resources but resulted in a considerable decline in secondary production, which remained low after the discontinuation of the floods. Our data suggest that a lack of recolonization by mosses following the discontinuation of the experimental flood program on the river Spöl may have driven patterns in energy fluxes by limiting macroinvertebrates using mosses for habitat. The effects of environmental flows on energy flows in this system thus depend on flood disturbance and the environmental context following the discontinuation of floods. [ABSTRACT FROM AUTHOR]

This paper describes a new diatom species (Orthoseira helvetica sp. nov.) found in the Swiss Alps at an elevation over 2600 m a.s.l. The diatom was recorded at the Macun plateau, Swiss National Park, from samples of terrestrial and wet semi-terrestrial mosses near the stream splash zone. The diatom has a unique set of features and is easily recognized under light and scanning electron microscopy. The most distinctive feature is the presence of a prominent silica collar in a 'rose flower' shape rounding each carinoportulae and an additional silica collar on the areolae (first 3–4 rows) bordering the hyaline area. The valve diameter of O. helvetica sp. nov. is 7.5–26.5 µm and possesses 2–3 (usually 3) carinoportulae. Linking spines at the valve face/mantle junction are present, having a simple basis and being triangular in shape. [ABSTRACT FROM AUTHOR]

Flow regime is a major determinant of the structure and functioning of aquatic ecosystems. Under climate change, flow intermittency is becoming more prevalent in glaciated alpine catchments, but the effects of increasing dryness on aquatic biodiversity remain largely unknown.We characterised flow intermittency patterns in 30 streams of a glaciated alpine catchment over 15 months and separated these streams into four intermittency categories: perennial streams, winter‐drying streams, moderately intermittent streams with occasional drying in summer, and periodically intermittent streams with extensive dry periods throughout the year. We then examined how these drying patterns affected structural and functional properties of benthic macroinvertebrate communities, and whether these changes were primarily deterministic or stochastic.At the taxonomic level, we observed a response at the highest intermittency levels, with α diversity lower and β diversity higher in periodically intermittent streams than in other stream types. This result suggested that local biota were well adapted to intermediate intermittency levels (mostly during winter) but not to high intermittency during summer. In contrast, functional diversity indices at the α and β levels (based on trait abundances) did not differ across intermittency categories. Considering the moderate level of functional redundancy, we interpreted this as an indication that changes in taxonomic diversity may have resulted primarily from stochastic processes.Analysis of community and trait composition indicated that deterministic selection may indeed have occurred with increased intermittency, but this process was likely to be minor in comparison to stochastic extinctions. Notably, community evenness was highest in periodically intermittent streams and lowest in perennial streams, suggesting that frequent drying prevented competitive exclusion.Our results suggested that most macroinvertebrate populations are resilient to intermediate intermittency levels but are filtered at high intermittency, irrespective of their resilience capacities. However, more research is needed to clarify the specific roles of different facets of flow regimes, specifically frequency, duration, and timing of intermittency. Understanding the consequences of responses in diversity and community evenness with increasing intermittency on the functional properties of communities will allow better prediction of the future ecological status of alpine stream networks to ongoing environmental change. [ABSTRACT FROM AUTHOR]

The Macun lakes form a high-alpine (> 2,600 m asl) cirque landscape (3.6 km²) in the Swiss National Park, comprising 26 small lakes together with a number of temporary ponds. Streams interconnect the four largest lakes, forming the drainage network that flows into the Inn River at the town of Lavin. The drainage network of Macun consists of a north and a south basin that overlie an ortho-gneiss, meta-granitoid bedrock. The south basin is influenced by various rock glaciers. The physico-chemistry of surface waters at 10 sites has been monitored annually in mid-summer since 2001. Further, an YSI EXO2 Multiparameter Sonde (Exosonde) with various water quality sensors has been employed since 2016 at the last lake in the network to examine seasonal and diel patterns in physico-chemistry. Results showed clear physico-chemical differences between the two basins, which mostly reflect rock-glacier inputs in the south basin. Nitrogen values were two-fold higher and particulate phosphorus values two-fold lower in the south basin than in the north basin. Over time, the physico-chemistry in the two basins became more homogeneous, with a reduction in rock-glacial inputs in the south basin and an overall decrease in nitrogen in the catchment. Data from 30 springs and tributaries sampled in 2002 and 2017 reflected the basin differences and temporal changes observed at the primary study sites. Continuous temperature records showed north basin streams to be ca. 3°C warmer than south-basin streams, but with high inter-annual variation that reflected annual differences in weather and no evidence of a general change over time (increase or decrease). Exosonde data revealed strong seasonality in measured parameters as well as seasonality in diel patterns (e. g., dissolved oxygen, temperature, chlorophyll-a); diel fluctuations were most pronounced in summer and least in winter. The results highlight the importance of long-term monitoring for understanding ecosystem state changes in alpine freshwaters, especially during periods of rapid environmental change. [ABSTRACT FROM AUTHOR]

In high‐altitude Alpine streams, seasonal cycles of snowmelt, glacial melt, and rainfall drive variation in the availability of algal food resources. Yet, high‐altitude streams also exhibit varying degrees of flow intermittency, ranging from solely winter‐drying streams to others that dry periodically throughout summer and autumn. These environmental drivers may interact in different ways to determine the functional trophic base of macroinvertebrates inhabiting high‐altitude streams. Here, we estimated the proportional contribution of autochthonous resources to the assimilated diets of benthic macroinvertebrates in 26 headwater streams of Val Roseg, a high Alpine glacial catchment, using stable isotope analysis (δ13C and δ15N) of different macroinvertebrate families and their potential food sources. We compared dietary estimates along a gradient of flow intermittency and across three seasons (Alpine spring, summer, and autumn). Assimilation from autochthonous sources was highest for collector‐gatherers and filter feeders in spring, and for grazers in summer. Grazers had higher estimated assimilation from autochthonous sources in intermittent streams than in perennial streams, particularly in summer, while collector‐gatherers showed little effect of flow intermittency on dietary estimates. However, responses were highly taxon‐specific, with different responses to variation in flow intermittency and season across families within functional groups. Our results suggest that frequent summer‐drying events represent tradeoffs between greater access to algal food resources and a higher risk of desiccation, but that differing life history and functional feeding traits across macroinvertebrate taxa drive marked variation in the risks or benefits associated with inhabitants of drying streams. [ABSTRACT FROM AUTHOR]

Flow refugia, locations that maintain substrate stability and low hydraulic stress during periods of high flow, can ensure riverine resilience in the face of increasing hydrological unpredictability. Despite their known importance, they have been overlooked in recent years with work on drought refugia currently seeing greater attention. Moreover, research on the role of flow refugia during artificial flood pulses in regulated rivers, where flood disturbances are no longer part of the hydrograph, is essentially absent. Here, we compared flow refugia for benthic macroinvertebrates among six habitats (main channel, side channel, riffle, margin, lentic including a floodplain pond, and inundated floodplain) within four different sites in response to an artificial flood pulse. We found that the grain‐size distribution and macroinvertebrate community composition changed at each site following the flood. Macroinvertebrate assemblages became longitudinally homogeneous, but within‐site beta diversity and taxa richness remained temporally stable following the flood pulse, suggesting the presence of flow refugia. In this respect, margin, inundated floodplain and lentic (a floodplain pond) habitats provided important flow refugia locations, particularly for the mobile mayfly Rhithrogena sp. In contrast, low substrate stability in riffle and side channels resulted in limited refugia potential for most taxa. Refuge use was however patchy with high levels of intra‐habitat variability being evident for Rhithrogena sp. and the amphipod Gammarus fossarum in margin and side channel habitats. Further work is required to advance our knowledge of flow refugia in rivers with differing flow regimes to enable their integration into management and restoration schemes. [ABSTRACT FROM AUTHOR]

Changing weather patterns and receding glaciers are predicted to increase flow intermittency in alpine streams. If aquatic macroinvertebrate communities largely comprise taxa adapted to perennial flows, an increase in flow intermittency substantially reduces biodiversity and affects functional processes. We conducted a before-after-control-impact field experiment to examine how macroinvertebrate communities in an alpine headwater stream responded to and recovered from a repeated experimental increase in flow intermittency. Flow in one channel was manipulated to simulate increased summer intermittency (June–September) over two consecutive years, whilst an adjacent channel served as a control. We monitored the density of benthic macroinvertebrates, periphyton and organic matter at approximately monthly intervals over three years during the snow-free period. Before manipulation, both channels had similar ecological properties. The flow manipulation reduced the overall macroinvertebrate density, and especially the proportional rheophile density, across both years. Recovery of the macroinvertebrate community following experimental flow intermittency took more than a year, and longer than our study period. This could be due to long aquatic life stages, dispersal limitation and biotic interactions. We conclude that climate-induced changes in alpine stream flow regimes can lead to a fundamental shift in macroinvertebrate assemblages through local extinctions, mostly of rheophilic species. [ABSTRACT FROM AUTHOR]

Gold mining is currently one of the main anthropogenic sources of mercury in the environment. In this study, the total mercury content was measured in bottom sediments, benthic macroinvertebrates (mayfly larvae), and fish (Siberian dace) along the Boroo River in northern Mongolia. There was a gold recovery plant in the middle reaches of the river until the mid-twentieth century; an accident there in the 1950s caused a mercury spill. We found an increased content of mercury in measured ecosystem components near the plant compared to the upper reaches of the river. The mercury content in sediments varied from trace amounts in the upper Boroo to 2200 ng/g dry weight (dw) in the vicinity of the plant ruins. The mercury content in mayfly larvae ranged from 50 to 2940 ng/g dw and had a spatial pattern as sediments, with the highest concentrations near the plant. The mercury content in sediments was lower at the mouth of the Boroo River than near the plant, reflecting the lower boundary of the mercury spill. Maximum values of mercury content in fish muscle were found at the river's mouth and were several times higher than in other rivers of northern Mongolia. Median mercury content in muscles of dace from the lower Boroo in 2016 has doubled since studies in 2010–2012, which may be the result of current mercury releases from gold mining. [ABSTRACT FROM AUTHOR]

An introduction to the journal is presented in which the editor discusses the various topics within the issue, including spatial habitat heterogeneity, hydrologic aspect of habitat, and the effects of hydropeaking in rivers.

More frequent and more severe forest fires mean more severely burned wood in streams. Instream wood provides habitat complexity, alters geomorphology, retains organic and inorganic material, promotes hyporheic flow and acts as substrate for biofilm and invertebrates. However, little is known about instream wood functions in fire‐prone biomes and how they combine with wood burning levels to guide postfire management efforts.Over 3 years, we tracked instream wood following forest fires in central Portugal. We examined for the first time the influence of burning level, season and a large suite of driving factors on the likelihood of four different functions having primary ecological consequences—retention of organic matter, serving as substrate for aquatic biota, being key pieces forming wood jams and deflecting flow including pool habitat formation.One of the main ecological functions of wood in rivers is to provide substrate for vegetation, periphyton, biofilm and oviposition. Our results show that this can be negatively affected when the wood is severely burned.Except for jam formation, the probability of each stream wood function changed markedly with season and the probability of non‐function was nearly twice as high in the Euro‐Mediterranean dry season than in the wet season.More anchored and decayed wood increased the probability of all functions, whereas the effect of submergence depended on the function. Challenging the 'size paradigm' that larger sized pieces provide more function, our data suggest that the effect of size is function‐specific.Synthesis and applications. We show how postfire stream restoration success can be maximized by selecting the most appropriate wood and taking advantage of attribute‐function relationships. We urge managers to refrain from removing wood or to selectively remove the most severely carbonized only, allowing the persistence of great potential to provide substrate for stream biota. The non‐attraction of severely burned wood as substrate can be compensated for by other wood with attributes enhancing this function, such as wood deeper within the bankfull area, and with large diameters. These results will help to inform successful management, as is increasingly asked from restoration ecology. [ABSTRACT FROM AUTHOR]

Drying in alpine streams might decrease aquatic-terrestrial trophic linkages by reducing terrestrial predation on aquatic prey. We tested this hypothesis by investigating whether a common riparian predator (hunting spiders) in alpine environments assimilated a lower proportion of aquatic prey with increasing stream intermittency. We used high temporal-resolution data from electrical resistance sensors to map patterns of naturally-occurring flow intermittency across 30 headwater streams of Val Roseg, a glacierized catchment in the Swiss Alps. We collected riparian hunting spiders, as well as potential terrestrial and aquatic macroinvertebrate prey, from streams and their associated riparian zones across two seasons (Alpine spring and summer). We estimated aquatic contributions to spider diets (pA) using (i) a gradient approach with aquatic invertebrate and spider carbon stable isotope ratio values (δ13C), and (ii) Bayesian carbon and nitrogen (δ15N) isotope mixing models. Spider pA from the gradient method were not statistically different from zero in spring (0.08 ± 0.10) and low in summer (0.16 ± 0.04). Mixing models also estimated low dependence on aquatic prey in both seasons, although with potentially higher contributions in summer. Spider diet did not vary with increasing flow intermittency in either season. Our results suggested that alpine hunting spiders obtain most of their carbon from terrestrial prey. The slight increase in spider pA during summer may correlate with peak emergence periods for aquatic insects, indicating opportunistic feeding by this riparian predator. [ABSTRACT FROM AUTHOR]

Glacial retreat, accompanied by shifts in riparian vegetation and glacier meltwater inputs, alters the energy supply and trophic structure of alpine stream food webs. Our goal in this study was to enhance understanding of dietary niches of macroinvertebrates inhabiting different alpine streams with contrasting glacial and non‐glacial (groundwater, precipitation, snowmelt) water inputs in conjunction with seasonal and habitat‐specific variation in basal resource availability.We measured a range of stream physico‐chemical attributes as well as carbon and nitrogen isotopes (δ13C, δ15N) of macroinvertebrates and primary food sources at seven sites across seasons within a Swiss glaciated catchment (Val Roseg) undergoing rapid glacial retreat (1–2 km between 1997 and 2014). Sampling sites corresponded to streams used in a previous (1997/1998) study within the same alpine catchment.Physico‐chemical attributes showed wide variation in environmental conditions across streams and seasons. Significant correlation among physico‐chemical proxies of glacier meltwater (phosphate‐P, total inorganic carbon, conductivity, turbidity) and macroinvertebrate δ13C, δ15N, and size‐corrected standard ellipse area (a proxy for feeding niche width) values showed that the extent of glacial water input shapes the energy base among alpine streams. Feeding niche differences among common alpine stream insect taxa (Chironomidae, Baetidae, Heptageniidae) were not significant, indicating that these organisms probably are plastic in feeding behaviour, opportunistically relying on food resources available in a particular stream and season.Seasonal trends in macroinvertebrate δ13C largely followed patterns in periphyton δ13C values, indicating that autochthonous resources were the main consumer energy source within the stream network, as shown previously. The overall range in macroinvertebrate δ13C (−33.5 to −18.4‰) and δ15N (−6.9 to 6.7‰) values also corresponded to values measured in the previous study, suggesting that macroinvertebrates altered diets in line with changes in environmental conditions and food resources during a period of rapid glacial retreat. Our results suggest that environmental changes brought on by rapid glacial retreat have not yet caused a profound change in the trophic structure within these fluvial networks. [ABSTRACT FROM AUTHOR]

River reaches downstream of dams with constant residual discharge often lack sediment supply and periodic high flows due to dam sediment retention and flow regulation, respectively. To test a novel multi‐deposit methodology for defining environmental flows for activating the dynamics of the river morphology downstream of dams, a flood was released from Rossens Dam in Switzerland. This event was combined for the first time with a multi‐deposit configuration of sediment replenishment consisting of four artificial deposits allocated as alternate bars along the riverbanks as a restoration measure. To validate the sediment transport behaviour observed in laboratory tests, stones were equipped with radiofrequency identification (RFID) passive integrated transponder (PIT) tags, a fixed antenna was installed at the river bed and a mobile antenna was used to enable the investigation of the erosion, transport and deposition of replenished sediments. The duration of the erosion period was determined for the tracked stones, and average transport velocities were found to be on the order of 10–3 m/s. To estimate the erosion efficiency of the flood, defined as the eroded tagged stones compared with the released water volume, the hydrograph was divided into different periods: rising limb, constant peak discharge, decreasing limb. During the rising limb of the flood, which lasted for 20% of the total flood duration, more than 40% of the PIT tags were transported. The defined erosion efficiency is a measure to support the hydrographic design of artificial flood releases from dams. The deposition of tagged stones resulted in a repeating cluster formation, as expected from previous laboratory experiments, creating an increase in hydraulic habitat diversity. Comparison of the results obtained in the field and from laboratory experiments confirmed the robustness of the multi‐deposit sediment replenishment method. Combined with the knowledge gained on the erosion efficiency, these results could motivate further applications and research into multi‐deposit sediment replenishment techniques as a habitat‐oriented river restoration measure. © 2020 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Flow intermittency occurs naturally in alpine streams. However, changing rainfall patterns and glacier retreat are predicted to increase the occurrence of flow intermittency in alpine catchments, with largely unknown effects on ecosystem structure and function. We conducted a flow manipulation experiment within a headwater stream of Val Roseg, a glacierized alpine catchment, to determine the effects of increased flow intermittency on aquatic macroinvertebrates, periphyton, benthic organic matter, and trophic structure. Compared to an adjacent reference channel, an increase in flow intermittency reduced macroinvertebrate density, taxa richness, and the proportion of rheophilic taxa. Density and richness remained low in the manipulated channel after resumption of natural flow. Flow intermittency did not affect organic matter standing stocks, but increased assimilation of periphyton by aquatic macroinvertebrates. Predation on aquatic invertebrates by riparian spiders also increased. We attribute many of these patterns to the timing of drying, which likely excluded summer-growing cohorts of rheophilic, aerial dispersers. This study suggests that reductions in summer glacial melt and rainfall events might increase flow intermittency and lead to fundamental changes in diversity and function of alpine fluvial networks. [ABSTRACT FROM AUTHOR]

More than one‐third of the world's rivers cease to flow and go dry on a periodic basis—so‐called intermittent rivers. The frequency and duration of flow intermittency in running waters are increasing due to climate change and water demands for human use. Intermittency effects on stream biodiversity and ecosystem functioning are dramatic and are expected to become increasingly prevalent in alpine landscapes in the near future. This project used modified field sensors to measure flow intermittency, temperature, and water origin (groundwater, precipitation, glacier) at high spatio‐temporal resolution throughout an alpine fluvial network (Val Roseg, Switzerland). We continuously recorded water presence in 30 tributary streams and validated sensor performance with field‐collected measures. Three different flow regimes were observed in the network, including periodically intermittent, seasonally intermittent, and permanently flowing streams. Twenty‐four streams (80% of recorded streams) dried at least once during the sampling period. Principal components analysis along with generalized additive models showed alpine streams with low average temperature and high conductivity (groundwater‐fed) were prone to permanent flow, whereas streams with higher average temperature and low conductivity (glacier‐fed) typically had intermittent flow. The field sensors proved precise for simultaneously measuring flow intermittency, temperature, and water origin at high resolution throughout the river network. Overall, this approach provides an effective way to develop eco‐hydrological models that examine the effects of flow intermittency on biodiversity and ecosystem functioning in riverine networks. [ABSTRACT FROM AUTHOR]

Characterising food‐web responses to environmental factors could greatly improve our understanding of environment‐biota relationships, and especially in floodplains where trophic interactions can be particularly important during phases of hydrological disconnection. The effects of floodplain hydrology and environmental attributes on structural aspects of biotic assemblages have been extensively studied, but responses at the functional level remain largely unknown.Here, we characterised a central aspect of food‐web architecture, the food chain length, as the maximum trophic position within 24 macroinvertebrate communities of parafluvial habitats in the Maggia river floodplain, in Switzerland. We investigated how the food chain length changed with different levels of habitat size, primary productivity and disturbance, the three factors potentially affecting food chain length in both theoretical and empirical studies.We found that food chain length was lower in frequently flooded habitats and immediately after a flood. We also showed that trophic omnivory, where predators fed at lower trophic levels after flooding, and in more frequently flooded habitats, may explain these changes.These findings show that trophic omnivory may explain how predators resist disturbance and are maintained in highly dynamic landscapes. More importantly, given that trophic omnivory may overall weaken trophic linkages and thus increase food‐web stability, this suggests that it could be a key mechanism in sustaining biodiversity in river floodplains. [ABSTRACT FROM AUTHOR]

Alpine streams can exhibit naturally high levels of flow intermittency. However, how flow intermittency in alpine streams affects ecosystem functions such as food web trophic structure is virtually unknown. Here, we characterized the trophic diversity of aquatic food webs in 28 headwater streams of the Val Roseg, a glacierized alpine catchment. We compared stable isotope (δ13C and δ15N) trophic indices to high temporal resolution data on flow intermittency. Overall trophic diversity, food chain length and diversity of basal resource use did not differ to a large extent across streams. In contrast, gradient and mixing model analysis indicated that primary consumers assimilated proportionally more periphyton and less allochthonous organic matter in more intermittent streams. Higher coarse particulate organic matter (CPOM) C:N ratios were an additional driver of changes in macroinvertebrate diets. These results indicate that the trophic base of stream food webs shifts away from terrestrial organic matter to autochthonous organic matter as flow intermittency increases, most likely due to reduced CPOM conditioning in dry streams. This study highlights the significant, yet gradual shifts in ecosystem function that occur as streamflow becomes more intermittent in alpine streams. As alpine streams become more intermittent, identifying which functional changes occur via gradual as opposed to threshold responses is likely to be vitally important to their management and conservation. [ABSTRACT FROM AUTHOR]

Understanding how different food resources sustain stream food webs is fundamental towards increasing our knowledge on trophic structure and energy flow pathways in fluvial ecosystems.Food webs in small mountain streams are sustained by autochthonous (instream primary production) and allochthonous (inputs from the terrestrial ecosystem) organic resources, with their relative importance highly dependent on catchment land cover.This study aimed to understand how catchment land cover determines food resource type (autochthonous, allochthonous) and quantity in mountain streams, and how this affects energy flow pathways and food web structure. We hypothesised that food resource type and quantity would reflect catchment land cover. Thus, changes in food resources would lead to shifts in macroinvertebrate assimilation of autochthonous and allochthonous food resources and consequently in dominant energy flow pathways. We further hypothesised that changes in food resources will have strong effects on dominant feeding groups and community biomass distribution among taxa in food webs.Energy flow pathways were quantified by combining macroinvertebrate biomass measures and assimilation of food resources estimated from δ2H and δ15N in 10 streams along a forest cover gradient, located in the Cantabrian Mountains (northern Spain).Results showed that grassland/shrub dominated streams had a higher proportion autochthonous food resources and a lower proportion of allochthonous food resources, whereas forested streams showed the opposite pattern. Changes in food resources with forest cover resulted in shifts in food resource assimilation and dominant energy flow pathways. Forested streams were mainly sustained by allochthonous resources, while streams flowing through grassland/shrub landscapes were mostly sustained by autochthonous resources.Food resource assimilation differed between feeding groups. Detritivores showed a fixed assimilation of allochthonous resources independent of resource quantity, while omnivore assimilation was determined by the dominant food resource. This was reflected in food‐web structure. There was an increase in detritivore biomass and conservation of omnivore biomass with increasing forest cover, leading to a more equal distribution of community biomass among macroinvertebrates comprising individual food webs.The dependence of stream food webs on dominant food resources highlights the importance of catchment land cover in determining energy flow pathways and food web structure in low order mountain streams. These findings will improve our predictions on the effects of land cover change on the functioning of mountain stream ecosystems. [ABSTRACT FROM AUTHOR]

The geometry and hydrodynamics of river reaches are key ecohydraulic descriptors. Statistics of water depth and velocity measurements are usually taken as proxies for habitat suitability in rivers. However, little is known about the sufficiency of data to produce effective and representative results. In this research, 19 reaches with differences in terms of discharge, river width, substrate, reach length, cross-section spacing and geomorphology are investigated. Measurements of flow depth and velocity were taken at multiple, equally spaced cross-sections along each reach. Data were sub-sampled using different methodologies and analysed each time. The sets of sub-sampled data were then compared with those calculated with the full data set from a reach. The focus was put towards the hydro-morphological index of diversity (HMID), a combination of the classical ecohydraulic variables flow depth and velocity. It represents the spatial variability of hydraulic habitats in a reach. The results point out that, with a well-defined sampling strategy, 100 measurement points lead to a good estimation of the HMID value in a reach, if more than eight measurement points are taken per cross-section. For geomorphologies with small complexity or when the analysis only includes the estimation of mean flow depth or mean flow velocity, this number can be decreased according to the results presented here. These findings help both, aquatic ecologists and engineers to estimate their data reliability for hydraulic field measurements in a river reach and are herein discussed taking into account the different studied morphologies. [ABSTRACT FROM AUTHOR]

The river Spöl flows from Livigno reservoir on the Swiss-Italian border in the central Alps. Flow regulation since 1970 has decreased and stabilized the mean annual discharge of 8.6 to 1.0 m3/s (winter: 0.55 m3/s, summer: 2.5 m3/s). Thirty experimental floods were released between 2000 and 2016 to improve the ecology of the river. A 100-m reach ~2.3 km downstream of the dam was used to monitor changes in water physicochemistry, periphyton, transported and benthic organic matter, and macroinvertebrates. Fish redds (native Brown Trout) were counted each autumn along the same stretch (~2.6 km) of river. Most physicochemical variables displayed strong seasonal cycles unrelated to the flow program, but N, P, and water temperature increased significantly over the 18-y study. Seston decreased after each high flow, but was seasonal and increased over the study. Periphyton biomass decreased after each high flow to low levels and increased between high flows. Benthic organic matter decreased 2× over the study but increased between floods. Macroinvertebrate densities decreased over the study. High flows reduced macroinvertebrate densities to <10,000 individuals (ind)/m2, with densities usually increasing to ~10,000 to 20,000 ind/m2 between floods. Floods reduced taxonomic richness with increases between floods. Ordination showed temporal shifts in macroinvertebrate assemblages over the study. Mayflies and stoneflies responded positively and chironomids and gammarids negatively to the floods over the study. Fish redds increased from 58 in 1999 to >200 by 2003. Redd counts decreased to <30 after an accidental sediment spill in 2013 but rebounded to 153 redds in 2016. Macroinvertebrate assemblages recovered within months after the spill. Long-term monitoring was essential for elucidating ecosystem dynamics and evaluating biological responses to pulse disturbances, such as the sediment spill, during the study. [ABSTRACT FROM AUTHOR]

Construction of small hydropower plants (<10 megawatts) is booming worldwide, exacerbating ongoing habitat fragmentation and degradation, and further fueling biodiversity loss. A systematic approach for selecting hydropower sites within river networks may help to minimize the detrimental effects of small hydropower on biodiversity. In addition, a better understanding of reach‐ and basin‐scale impacts is key for designing planning tools. We synthesize the available information about (1) reach‐scale and (2) basin‐scale impacts of small hydropower plants on biodiversity and ecosystem function, and (3) interactions with other anthropogenic stressors. We then discuss state‐of‐the‐art, spatially explicit planning tools and suggest how improved knowledge of the ecological and evolutionary impacts of hydropower can be incorporated into project development. Such tools can be used to balance the benefits of hydropower production with the maintenance of ecosystem services and biodiversity conservation. Adequate planning tools that consider basin‐scale effects and interactions with other stressors, such as climate change, can maximize long‐term conservation. [ABSTRACT FROM AUTHOR]

Abstract: Aim: Theory and experiments strongly support the importance of interactive effects of multiple factors shaping biodiversity, although their importance rarely has been investigated at biogeographically relevant scales. In particular, the importance of higher order interactions among environmental factors at such scales is largely unknown. We investigated higher order interactions of environmental factors to explain diversity patterns in a metacommunity of aquatic invertebrates at a biogeographically relevant scale and discuss the findings in an environmental management context. Location: All major drainage basins in Switzerland (Rhine, Rhone, Ticino and Inn; 41,285 km2). Methods: Riverine α‐diversity patterns at two taxonomic levels (family richness of all benthic macroinvertebrates and species richness of Ephemeroptera, Plecoptera and Trichoptera) were examined at 518 sites across the basins. We applied a novel machine learning technique to detect key three‐way interactions of explanatory variables by comparing the relative importance of 1,140 three‐way combinations for family richness and 680 three‐way combinations for species richness. Results: Relatively few but important three‐way interactions were meaningful for predicting biodiversity patterns among the numerous possible combinations. Specifically, we found that interactions among elevational gradient, prevalence of forest coverage in the upstream basin and biogeoclimatic regional classification were distinctly important. Main conclusion: Our results indicated that a high prevalence of terrestrial forest generally sustains riverine benthic macroinvertebrate diversity, but this relationship varies considerably with biogeoclimatic and elevational conditions likely due to community composition of forests and macroinvertebrates changing along climatic and geographical gradients. An adequate management of riverine ecosystems at relevant biogeographical scales requires the identification of such interactions and a context‐dependent implementation. [ABSTRACT FROM AUTHOR]

Abstract: The species concept is the cornerstone of biodiversity science, and any paradigm shift in the delimitation of species affects many research fields. Many biologists now are embracing a new “species” paradigm as separately evolving populations using different delimitation criteria. Individual criteria can emerge during different periods of speciation; some may never evolve. As such, a paradigm shift in the species concept relates to this inherent heterogeneity in the speciation process and species category—which is fundamentally overlooked in biodiversity research. Cryptic species fall within this paradigm shift: they are continuously being reported from diverse animal phyla but are poorly considered in current tests of ecological and evolutionary theory. The aim of this review is to integrate cryptic species in biodiversity science. In the first section, we address that the absence of morphological diversification is an evolutionary phenomenon, a “process” counterpart to the long‐studied mechanisms of morphological diversification. In the next section regarding taxonomy, we show that molecular delimitation of cryptic species is heavily biased towards distance‐based methods. We also stress the importance of formally naming of cryptic species for better integration into research fields that use species as units of analysis. Finally, we show that incorporating cryptic species leads to novel insights regarding biodiversity patterns and processes, including large‐scale biodiversity assessments, geographic variation in species distribution and species coexistence. It is time for incorporating multicriteria species approaches aiming to understand speciation across space and taxa, thus allowing integration into biodiversity conservation while accommodating for species uncertainty. [ABSTRACT FROM AUTHOR]

Glaciers cover ~10% of the Earth's land surface, but they are shrinking rapidly across most parts of the world, leading to cascading impacts on downstream systems. Glaciers impart unique footprints on river flow at times when other water sources are low. Changes in river hydrology and morphology caused by climate-induced glacier loss are projected to be the greatest of any hydrological system, with major implications for riverine and near-shore marine environments. Here, we synthesize current evidence of how glacier shrinkage will alter hydrological regimes, sediment transport, and biogeochemical and contaminant fluxes from rivers to oceans. This will profoundly influence the natural environment, including many facets of biodiversity, and the ecosystem services that glacier-fed rivers provide to humans, particularly provision of water for agriculture, hydropower, and consumption. We conclude that human society must plan adaptation and mitigation measures for the full breadth of impacts in all affected regions caused by glacier shrinkage. [ABSTRACT FROM AUTHOR]

Floodplains are vital components of river ecosystems and play an important role in carbon cycling and storage at catchment and global scales. For efficient river management and conservation, it is critical to understand the functional role of spatiotemporally complex and dynamic habitat mosaics of river floodplains. Unfortunately, the fundamental understanding of mineralization and carbon flux patterns across complex floodplains is still fragmentary. In this study, respiratory potential (i.e., electron transport system activity [ETSA]) was quantified seasonally across different aquatic and terrestrial habitats (wetted channels, gravel bars, islands, riparian forests, and grasslands) of 2 Alpine floodplains differing in climate, altitude, discharge, flow alteration intensity, and land use (Soča [natural flow regime, 12% grassland area] and Urbach [mean annual discharge reduction by 30% due to water abstraction, 69% grassland area]). In situ respiration (R) was measured, and ETSA-R ratios were calculated to examine differences in exploitation intensity of the overall respiratory capacity among floodplain habitats and seasons. ETSA and R provided potential and actual estimates, respectively, of organic matter mineralization in the different floodplain habitats. Hierarchical linear regression across habitat types showed that organic matter, grain sizes <0.063 mm, and water content were the most important predictors of ETSA in both floodplains, and grain sizes 2-0.063 and >8mm were also highly important for the Soča floodplain. The combination of ETSA and R measurements conducted in contrasting floodplains increased our understanding of the relationships between floodplain habitat heterogeneity, organic matter mineralization and human impacts, that is, structural-functional linkages in floodplains. These data are integral towards predicting changes in floodplain function in response to environmental alterations from increasing human pressures and environmental change. [ABSTRACT FROM AUTHOR]

Understanding ecological divergence of morphologically similar but genetically distinct species - previously considered as a single morphospecies - is of key importance in evolutionary ecology and conservation biology. Despite their morphological similarity, cryptic species may have evolved distinct adaptations. If such ecological divergence is unaccounted for, any predictions about their responses to environmental change and biodiversity loss may be biased. We used spatio-temporally replicated field surveys of larval cohort structure and population genetic analyses (using nuclear microsatellite markers) to test for life-history divergence between two cryptic lineages of the alpine mayfly Baetis alpinus in the Swiss Alps. We found that the more widespread and abundant cryptic lineage represents a 'generalist' with at least two cohorts per year, whereas the less abundant lineage is restricted to higher elevations and represents a 'specialist' with a single cohort per year. Importantly, our results indicate partial temporal segregation in reproductive periods between these lineages, potentially facilitating local coexistence and reproductive isolation. Taken together, our findings emphasize the need for a taxonomic revision: widespread and apparently generalist morphospecies can hide cryptic lineages with much narrower ecological niches and distribution ranges. [ABSTRACT FROM AUTHOR]

Temperature models that directly predict ecologically important thermal attributes across spatio-temporal scales are still poorly developed. This study developed an analytical method to estimate seasonal and diel periodicities as well as irregularities in stream temperature at data-poor sites based on Fourier analysis. We first quantified the thermal attributes of a glacier-fed stream in the Swiss Alps using 2-years of hourly-recorded temperature. Stream temperature was accurately decomposed to an average 3.8 °C, diel periodicity spanning 4.9 °C, seasonal periodicity spanning 7.5 °C, and an irregularity having an average of 0.0 °C but spanning 9.7 °C. These thermal attributes then were used to estimate thermal attributes at spot-measured sites along the river, resulting in a different relative contribution (weighting) of attributes among sites. The results confirm that the developed method can infer stochastic behaviors in stream thermal attributes at spot-measured sites. Additional ways to further improve the methodological approach are discussed. [ABSTRACT FROM AUTHOR]

Background: Many species contain evolutionarily distinct groups that are genetically highly differentiated but morphologically difficult to distinguish (i.e., cryptic species). The presence of cryptic species poses significant challenges for the accurate assessment of biodiversity and, if unrecognized, may lead to erroneous inferences in many fields of biological research and conservation. Results: We tested for cryptic genetic variation within the broadly distributed alpine mayfly Baetis alpinus across several major European drainages in the central Alps. Bayesian clustering and multivariate analyses of nuclear microsatellite loci, combined with phylogenetic analyses of mitochondrial DNA, were used to assess population genetic structure and diversity. We identified two genetically highly differentiated lineages (A and B) that had no obvious differences in regional distribution patterns, and occurred in local sympatry. Furthermore, the two lineages differed in relative abundance, overall levels of genetic diversity as well as patterns of population structure: lineage A was abundant, widely distributed and had a higher level of genetic variation, whereas lineage B was less abundant, more prevalent in spring-fed tributaries than glacier-fed streams and restricted to high elevations. Subsequent morphological analyses revealed that traits previously acknowledged as intraspecific variation of B. alpinus in fact segregated these two lineages. Conclusions: Taken together, our findings indicate that even common and apparently ecologically well-studied species may consist of reproductively isolated units, with distinct evolutionary histories and likely different ecology and evolutionary potential. These findings emphasize the need to investigate hidden diversity even in well-known species to allow for appropriate assessment of biological diversity and conservation measures. [ABSTRACT FROM AUTHOR]

The respiratory potential [i.e. electron transport system activity (ETSA)] of soils and sediments from five floodplain habitats (channel, gravel, islands, riparian forest and grassland) of the Urbach River, Switzerland, and actual respiration rate (R) of the same samples exposed to experimental inundation were measured. Measurements were carried out at three incubation temperatures (4°C, 12°C and 20°C), and ETSA/R ratios (i.e. exploitation of the overall metabolic capacity) were investigated to better understand the effects of temperature and inundation on floodplain functional heterogeneity. Furthermore, ETSA/R ratios obtained during experimental inundation were compared with ETSA/R ratios from field measurements to investigate the exploitation in total metabolic potential at different conditions. Lowest ETSA and R were measured in samples from channel and gravel habitats, followed by those from islands. Substantially higher values were measured in soils from riparian forest and grassland. Both ETSA and R increased with increasing temperature in samples from all habitats, while the ETSA/R ratio decreased because of a rapid response in microbial community respiration to higher temperatures. The metabolic capacity exploitation (i.e. ETSA/R) during experimental inundation was lowest in predominantly terrestrial samples (riparian forest and grassland), indicating the weakest response to wetted conditions. Comparison of experimentally inundated and field conditions revealed that in rarely flooded soils, the metabolic capacity was less exploited during inundation than during non-flooded conditions. The results suggest high sensitivity in floodplain respiration to changes in temperature and hydrological regime. ETSA/R ratios are considered good indicators of changes in metabolic activity of floodplain soils and sediments, and thus useful to estimate the impact of changes in hydrological regime or to evaluate success of floodplain restoration actions. [ABSTRACT FROM AUTHOR]

Wood is a key structural element in aquatic ecosystems. Wood provides habitat complexity, alters geomorphology, retains organic and inorganic material, promotes hyporheic flow, and acts as substrate for biofilms and invertebrates. Fire is an important disturbance promoting wood recruitment into inland waters, but most studies have focused on streams in western North America. Less is known about fire-derived wood dynamics on other continents or in lake environments. Here, we review fire effects on the recruitment, distribution, and function of in-stream wood, with emphasis on a series of studies from the Euro-Mediterranean. The amount of large wood in these streams was low and is expected to decline in the future because of wildfire. Wildfire engendered inputs of wood with low structural complexity, probably reducing habitat heterogeneity for aquatic organisms. Fire also provided wood with greater diameter than wood recruited by other means, but its longevity may be shorter because burned wood was more decayed and less anchored in the channel than unburned wood. Wood delivery processes are important because macroinvertebrate colonization differed between fire-derived wood that fell directly into the river and wood conditioned first on the forest floor. We present a case study describing wood dynamics in a lake after a wildfire in northern Minnesota, USA. In this study, wildfire created an area of lake shoreline with disproportionately more wood than areas unaffected by wildfire. In contrast to streams, burned wood was more complex than unburned wood in the lake system. One of the explanations may be greater scouring, abrasive action by stream flows, which breaks down burned wood faster than in lakes. Given the expected increase in the probability and severity of fire around the world, information in our review can be used to help manage riparian zones of streams and lakes. [ABSTRACT FROM AUTHOR]

Microbial community assembly and microbial functions are affected by a number of different but coupled drivers such as local habitat characteristics, dispersal rates, and species interactions. In groundwater systems, hydrological flow can introduce spatial structure and directional dependencies among these drivers. We examined the importance of hydrology in structuring bacterial communities and their function within two alpine floodplains during different hydrological states. Piezometers were installed in stream sediments and surrounding riparian zones to assess hydrological flows and also were used as incubation chambers to examine bacterial community structures and enzymatic functions along hydrological flow paths. Spatial eigenvector models in conjunction with models based on physico-chemical groundwater characteristics were used to evaluate the importance of hydrologically-driven processes influencing bacterial assemblages and their enzymatic activities. Our results suggest a strong influence (up to 40% explained variation) of hydrological connectivity on enzymatic activities. The effect of hydrology on bacterial community structure was considerably less strong, suggesting that assemblages demonstrate large functional plasticity/redundancy. Effect size varied between hydrological periods but flow-related mechanisms always had the most power in explaining both bacterial structure and functioning. Changes in hydrology should be considered in models predicting ecosystem functioning and integrated into ecosystem management strategies for floodplains. [ABSTRACT FROM AUTHOR]

The historical reduction in habitat heterogeneity and water quality of running waters is an ongoing challenge being addressed by resource managers worldwide. The persistent legacy of past land use, reflected in part by depauperate macroinvertebrate assemblages, is likely to affect the responses of macroinvertebrate assemblages to novel anthropogenic stressors and amendments (e.g. river restoration)., The response of macroinvertebrate assemblages differing in the abundance of sensitive taxa to stressors was investigated using a mesocosm experiment conducted at five sites within two sub-basins that differed in historic land-use impacts. The sub-basins were similar in morphology and water quality, but a higher dissolved organic carbon ( DOC) level in the sub-basin with a less sensitive assemblage reflected a greater agricultural influence., Macroinvertebrate assemblages were assessed monthly over an annual cycle in replicated in situ mesocosms manipulated with respect to substratum heterogeneity (fine, coarse) and water quality (nutrient amendments) following a full-factorial design. Due to relatively high background nutrient levels, there was no effect of nutrient amendment on macroinvertebrate colonisation of mesocosms., In the sub-basin harbouring a more sensitive macroinvertebrate assemblage, higher total and EPT taxa richness was found in coarse (heterogeneous) substratum than that in fine (homogeneous) substratum mesocosms, whereas this response was not observed in the sub-basin with a less sensitive assemblage. In the former sub-basin, coarse substratum mesocosms were more favourable for sensitive taxa, as they had more diverse flow patterns, less clogging of interstitial spaces and more benthic organic matter than fine substratum mesocosms., These results suggest that past land-use legacies influencing current macroinvertebrate assemblages can underlie differential response patterns of macroinvertebrates to habitat mitigation measures in human-dominated catchments. [ABSTRACT FROM AUTHOR]

We examined for a glacial fingerprint on the ecology of two postglacial streams within the Swiss National Park over a 14 yr period (1999-2013). One stream (Aqua) emerges from a small rock glacier (0.2% of the catchment area), whereas the other stream (Fuorn) flows from a remnant ice field (0.02% of the catchment area). In general, abiotic and biotic properties of each stream showed a typical glacial-nival seasonality and strong between-year synchrony. Benthic organic matter and periphyton biomass peaked during so-called 'windows of opportunity' in early spring and late autumn as in other glacial streams. Importantly, the streams contrasted regarding the glacial signature in which Fuorn had highest average turbidity, total inorganic carbon (TIC), particulate organic carbon and phosphorus levels, whereas Aqua had highest average nitrogen levels and lowest temperature and electrical conductivity. The difference in glacial signature also was evident in macroinvertebrate density (fourfold higher in Aqua) and diversity (lower in Aqua) differences between streams. In contrast to most proglacial streams, macroinvertebrate assemblages were relatively diverse and dominated by typical alpine stream species, stoneflies in particular. Both streams experienced increases in phosphorus and TIC following 2006 in response to external climate drivers with concomitant increases in simuliids and Leuctra stoneflies and decreases in heptageniid mayflies in Fuorn and Protonemura stoneflies in Aqua. Our results suggest that a glacial legacy is an inherent feature of most postglacial alpine streams, this being especially important as glacial streams transform to postglacial status in response to ongoing transformation of alpine glacial landscapes globally. [ABSTRACT FROM AUTHOR]

Glacial alpine landscapes are undergoing rapid transformation due to changes in climate. The loss of glacial ice mass has directly influenced hydrologic characteristics of alpine floodplains. Consequently, hyporheic sediment conditions are likely to change in the future as surface waters fed by glacial water (kryal) become groundwater dominated (krenal). Such environmental shifts may subsequently change bacterial community structure and thus potential ecosystem functioning. We quantitatively investigated the structure of major bacterial groups in glacial and groundwater-fed streams in three alpine floodplains during different hydrologic periods. Our results show the importance of several physico-chemical variables that reflect local geological characteristics as well as water source in structuring bacterial groups. For instance, Alpha-, Betaproteobacteria and Cytophaga-Flavobacteria were influenced by pH, conductivity and temperature as well as by inorganic and organic carbon compounds, whereas phosphorous compounds and nitrate showed specific influence on single bacterial groups. These results can be used to predict future bacterial group shifts, and potential ecosystem functioning, in alpine landscapes under environmental transformation. [ABSTRACT FROM AUTHOR]

The combination of changing climate and anthropogenic activities is increasing the probability of wildfire around the world. When fires occur in riparian zones, associated tree mortality can add wood directly to streams or wood may fall to the forest floor and remain there for some time before being transported into stream channels. Wood provides critical structure for aquatic macroinvertebrates, so our objectives were to assess the effects of wood burn status, conditioning, and their interaction on macroinvertebrate community composition, taxon and functional diversity, and trait affinities. We conducted a field experiment with pieces of freshly cut wood (length = 10 cm, diameter ≈ 7.5 cm) for which we first manipulated burn status (burned, unburned) and then, conditioned by placing burned and unburned wood directly into streams (no conditioning) or by leaving pieces in streams (water conditioning) or on the forest floor (soil conditioning) for a year before submergence. We used distance-based redundancy analysis to assess community structure by wood treatments and linear mixed-effects modeling to assess effects of wood treatments on taxon and functional diversity and trait affinity. Changes in wood quality resulting from fire may not alter macroinvertebrate community structure. Taxonomic and functional patterns of stream invertebrate colonization did not differ between burned and unburned wood, even after a year of incubation in the stream or on the forest floor. Conditioning status affected taxonomic composition, taxon and functional diversity, and trait affinities of wood invertebrate communities. The terrestrial legacy of soil conditioning was clearly important in structuring macroinvertebrate assemblages. Our results suggest that macroinvertebrate communities may be more sensitive to fire effects on the dynamics of wood input than to effects of fires on the wood itself. [ABSTRACT FROM AUTHOR]

Greater scientific knowledge, changing societal values, and legislative mandates have emphasized the impor-tance of implementing large-scale flow experiments (FEs) downstream of dams. We provide the first global assess-ment of FEs to evaluate their success in advancing science and informing management decisions. Systematic review of 113 FEs across 20 countries revealed that clear articulation of experimental objectives, while not uni-versally practiced, was crucial for achieving management outcomes and changing dam-operating policies. Furthermore, changes to dam operations were three times less likely when FEs were conducted primarily for sci-entific purposes. Despite the recognized importance of riverine flow regimes, four-fifths of FEs involved only dis-crete flow events. Over three-quarters of FEs documented both abiotic and biotic outcomes, but only one-third examined multiple taxonomic responses, thus limiting how FE results can inform holistic dam management. Future FEs will present new opportunities to advance scientifically credible water policies. [ABSTRACT FROM AUTHOR]

Glaciated alpine floodplains are responding quickly to climate change through shrinking ice masses. Given the expected future changes in their physicochemical environment, we anticipated variable shifts in structure and ecosystem functioning of hyporheic microbial communities in proglacial alpine streams, depending on present community characteristics and landscape structures. We examined microbial structure and functioning during different hydrologic periods in glacial (kryal) streams and, as contrasting systems, groundwater-fed (krenal) streams. Three catchments were chosen to cover an array of landscape features, including interconnected lakes, differences in local geology and degree of deglaciation. Community structure was assessed by automated ribosomal intergenic spacer analysis and microbial function by potential enzyme activities. We found each catchment to contain a distinct bacterial community structure and different degrees of separation in structure and functioning that were linked to the physicochemical properties of the waters within each catchment. Bacterial communities showed high functional plasticity, although achieved by different strategies in each system. Typical kryal communities showed a strong linkage of structure and function that indicated a major prevalence of specialists, whereas krenal sediments were dominated by generalists. With the rapid retreat of glaciers and therefore altered ecohydrological characteristics, lotic microbial structure and functioning are likely to change substantially in proglacial floodplains in the future. The trajectory of these changes will vary depending on contemporary bacterial community characteristics and landscape structures that ultimately determine the sustainability of ecosystem functioning. [ABSTRACT FROM AUTHOR]

Many streams today have modified channels, substratum composition, flows and temperature regimes. Understanding how these potential stressors affect key processes governing populations is crucial towards counteracting species decline and loss. For aquatic organisms with complex life cycles that include a terrestrial adult stage, successful reproduction involving a transition from the terrestrial to aquatic environment for oviposition can be an important constraint., Our main goal was to test for the effects of local stream degradation on egg mass densities of macroinvertebrates with different requirements for oviposition habitat. We experimentally manipulated oviposition substrate availability in two Swiss gravel-bed rivers by adding bricks to stream beds of channelised, restored and near natural reaches differing in their depth profile and availability of large rocks. We followed oviposition on bricks and natural rocks between May and October 2008 and quantified egg mass densities of two aquatic insects with a terrestrial stage ( Baetis spp. and Hydropsyche spp.) and an entirely aquatic leech Erpobdella octoculata. Individual and interactive effects of mean water depth fluctuations, depth variability, frequency of large rocks and temperature on egg mass densities were evaluated using a model selection approach., Response to our manipulation in terms of relative use of bricks for oviposition was strongest in the two insect taxa, whose egg mass densities responded to the presence of large substrata in study reaches. We also found evidence for a weak water level effect on egg mass densities of Baetis, a mayfly that uses protruding rocks for oviposition, in contrast to Hydropsyche, which apparently is capable of diving. While no clear response to our manipulation was found in Erpobdella octoculata, its overall cocoon densities were influenced by the variability of depth profile and increased in reaches with lower streambed heterogeneity., Our results suggest that stream degradation has high potential to constrain reproduction of many species, in particular those with complex life cycles such as aquatic insects. Investigation in modified riverscapes of the specific effects of different constraints to recruitment processes is a prerequisite for successful management and conservation. [ABSTRACT FROM AUTHOR]

Factors driving bacterial community composition (BCC) and linkages to ecosystem function (EF) are a fundamental interest in microbial ecology. Climate warming is expected to cause a shift from glacial- to groundwater-dominated water sources in alpine catchments due to receding glaciers, which is likely accompanied by a shift in BCC and EF. In this context, we performed a reciprocal transplant experiment of hyporheic sediments within a Swiss alpine floodplain. We assessed the influence of water source (groundwater = krenal, glacial water = kryal) and nutritional state (C, N, and P) on BCC and EF. Experimental response was tested using automated ribosomal intergenic spacer amplification and potential activities of eight different enzymes. BCC from both kryal and krenal systems was highly resistant to changes in water source, yet exhibited pronounced EF flexibility. Major factors determining BCC and EF response were sediment origin followed by seasonal variation in BCC. The gradient in seasonal change in BCC showed different strengths in the two water systems. Krenal BCC was more seasonally stable compared with kryal BCC, although functional plasticity showed the same extent in both. This difference in connectivity between BCC and EF suggests that krenal BCC was dominated by generalists, whereas kryal BCC was dominated by specialists. The weak effect of altered nutritional state on BCC and EF indicates a complex but hierarchically structured relationship among these factors. We conclude that microbial communities in alpine catchments are able to rapidly buffer the effect of shifts in water source on ecosystem functioning. [ABSTRACT FROM AUTHOR]

Downed wood pieces are key links between terrestrial and aquatic ecosystems. They promote organic matter retention, create habitat, and potentially increase stream productivity. The stock of downed wood in a river system is a product of the interaction between wood supply, transport, in situ losses, and retention characteristics of the system. Fire and forest management are important disturbances that influence the amount and organization of stream wood with boom-and-bust periods of recruitment and fluvial transport processes. We examined 1st - through 3rd-order Portuguese streams flowing through 3 common silvicultural systems in southern Europe: forests of cork oak, eucalyptus, and maritime pine. Our data set included 1483 pieces of wood in 27 streams, all of which had experienced extensive wildfires within the previous 6 y. We used binned neighbor-k analysis to assess wood organization (segregated, random, or aggregated). We then used linear mixed-effects modeling to evaluate the effects of stream order, forest type, and their interaction on wood volume and organization. The best predictor of wood volume and organization was the interaction between forest type and stream order. Most wood pieces were burned and organization was low, suggesting that arrangement of wood was largely a product of input dynamics rather than transport processes at this time. Potential drivers of across-system variability included vegetation obstructions, wood length:channel width ratios, management actions, and effects of fire. Climate models predict more droughts in the Euro-Mediterranean region in the future, with implications for wood volume, transport, and function as terrestrial vegetation invades intermittent stream channels and plant communities shift from managed forests to shrublands with few trees. [ABSTRACT FROM AUTHOR]

The article presents information about long-term changes in community assembly, resistance, and resilience of macro invertebrates in a flow regulated river. It mentions that floods reduced the density and taxon richness of macro invertebrates, and a nonmetric dimensional scaling (NMDS) analysis distinguished temporal shifts in community assembly. It also states that long-term perspective is required for management actions targeted towards regulated and fragmented rivers.

Long-term research on freshwater ecosystems provides insights that can be difficult to obtain from other approaches. Widespread monitoring of ecologically relevant water-quality parameters spanning decades can facilitate important tests of ecological principles. Unique long-term data sets and analytical tools are increasingly available, allowing for powerful and synthetic analyses across sites. Long-term measurements or experiments in aquatic systems can catch rare events, changes in highly variable systems, time-lagged responses, cumulative effects of stressors, and biotic responses that encompass multiple generations. Data are available from formal networks, local to international agencies, private organizations, various institutions, and paleontological and historic records; brief literature surveys suggest much existing data are not synthesized. Ecological sciences will benefit from careful maintenance and analyses of existing long-term programs, and subsequent insights can aid in the design of effective future long-term experimental and observational efforts. Long-term research on freshwaters is particularly important because of their value to humanity. INSET: What is long term with respect to ecological data?. [ABSTRACT FROM AUTHOR]

Summary 1. Determined by landscape structure as well as dispersal-related traits of species, connectivity influences various key aspects of population biology, ranging from population persistence to genetic structure and diversity. Here, we investigated differences in small-scale connectivity in terms of gene flow between populations of two ecologically important invertebrates with contrasting dispersal-related traits: an amphipod ( Gammarus fossarum) with a purely aquatic life cycle and a mayfly ( Baetis rhodani) with a terrestrial adult stage. 2. We used highly polymorphic markers to estimate genetic differentiation between populations of both species within a Swiss pre-alpine catchment and compared these results to the broader-scale genetic structure within the Rhine drainage. Landscape genetic approaches were used to test for correlations of genetic and geographical structures and in-stream barrier effects. 3. We found overall very weak genetic structure in populations of B. rhodani. In contrast, G. fossarum showed strong genetic differentiation, even at spatial scales of a few kilometres, and a clear pattern of isolation by distance. Genetic diversity decreased from downstream towards upstream populations of G. fossarum, suggesting asymmetric gene flow. Correlation of genetic structure with landscape topography was more pronounced in the amphipod. Our study also indicates that G. fossarum might be capable of dispersing overland in headwater regions and of crossing small in-stream barriers. 4. We speculate that differences in dispersal capacity but also habitat specialisation and potentially the extent of local adaptation could be responsible for the differences in genetic differentiation found between the two species. These results highlight the importance of taking into account dispersal-related traits when planning management and conservation strategies. [ABSTRACT FROM AUTHOR]