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Dam removal is increasingly considered as a river restoration tool for impoundments that harm the environment or have exceeded their lifespan. However, few studies report the ecological consequences of large dam removal.We performed a multiple before‐after/control‐impact (mBACI) study to investigate the consequences of the decommissioning of a large dam (42 m high) on instream habitat and invertebrate communities in a temperate, forested catchment of northern Spain.Before decommissioning, lack of fine sediments and high concentrations of manganese and iron occurred below the dam but decreased downstream. Invertebrate taxa richness and diversity were reduced, and pollution‐sensitive taxa were missing just below the dam.The drawdown of the reservoir, the first step towards its decommissioning, mobilized stored sediments causing frequent turbidity peaks downstream, which nevertheless, caused no detrimental effects on macroinvertebrate communities. One year after drawdown, the communities downstream from the dam, as well as those in the newly formed stream in the area formerly impounded by the reservoir, became very similar to those in control reaches, showing a successful restoration project.Synthesis and applications. Dam decommissioning helps restore instream habitats and facilitates the recovery of invertebrate communities in a very short time frame if there are nearby sources of potential colonizers. Slow drawdown reduces the transport of the sediments accumulated in the reservoir and their potential downstream impacts, even more if prior to drawdown the reservoir is kept full for years to promote the deposition of sediments in marginal areas that will later be readily colonized by trees. [ABSTRACT FROM AUTHOR]

Water diversion and pollution are two pervasive stressors for river ecosystems that often co‐occur. The individual effects of both stressors on river communities and energy transfer across the food webs are well described; however, how they interact remains unknown. We hypothesised that low‐to‐moderate nutrient pollution gradient would cause a mild increase in invertebrate driven herbivory and water diversion a strong reduction in detritivory, whereas their joint effect would reduce invertebrate abundance and diversity, as well as total energy fluxes (from basal resources to invertebrates and fish). We also expected a shift in body size spectra slope with increased energy transfer between trophic levels with moderate pollution, but not with water diversion.To test these hypotheses, we selected four rivers across a range of nutrient pollution levels (a proxy of water quality) subject to similar water diversion schemes and compared food webs upstream and downstream of their diversion weirs.Both stressors changed the availability of basal food resources. Nutrient pollution induced changes in the green food web (i.e., biofilm‐based) by enhancing biofilm stocks, whereas water diversion affected the brown food web (i.e., detritus‐based) by decreasing stocks of detritus.The propagation of the effects to higher trophic levels differed with each stressor: pollution increased the homogeneity of community within the reach, whereas water diversion made communities more heterogeneous. Moreover, pollution induced changes within omnivores, increasing herbivory and carnivory, whereas diversion reduced the total energy fluxes through a decrease in detritivory, especially with pollution.Although most of the variables studied seemed to be more sensitive to water diversion, pollution often accentuated the response, being the interaction between both stressors more explanatory than any of the two stressors on its own.The effects of water diversion on diversity and energy flow through food webs are more detrimental to moderately polluted rivers than to systems with high quality water.We show that the use of tools merging knowledge on trophic relationships among species and their metabolic requirements enables disturbances to be detected that would otherwise go unnoticed. [ABSTRACT FROM AUTHOR]

Traditionally, researchers have assessed diet selection by comparing consumed versus available taxa. However, taxonomic assignment is probably irrelevant for predators, who likely base their selection on characteristics including prey size, habitat, or behavior. Here, we use an aquatic insectivore, the threatened Pyrenean Desman (Galemys pyrenaicus), as a model species to assess whether biological traits help unravel the criteria driving food and habitat preferences. We reanalyzed data from a previous taxonomy-based study of prey selection in two contrasting streams, one with excellent conservation status and the other affected by diversion for hydropower and forestry. Available and consumed prey were characterized according to nine biological traits, and diet selection was estimated by comparing availability—measured from Surber net samples, and consumption—analyzed by metabarcoding desman feces. Traits offered a biologically coherent image of diet and almost identical selection patterns in both streams, depicting a highly specialized rheophilic predator. Desmans positively selected prey with a preference for fast flow and boulder substrate, indicating their preferred riffle habitat. On the other hand, they positively selected prey with larger but not the largest potential size, living in the water column or the litter, and not inside sediments. They also chose agile prey, swimmers or prey attached to the substrate, prey with high body flexibility, and prey living exposed and clustered in groups. Overall, our results offer a picture of desman diet preference and point to biological traits as being better than taxonomic identity to describe the diet preference of consumers. [ABSTRACT FROM AUTHOR]

Droughts, or severe reductions of water flow, are expected to become more frequent and intense in rivers in many regions under the ongoing climate change scenario. It is therefore important to understand stream ecosystem functioning under drought conditions. We performed a meta-analysis of studies addressing drought effects on litter decomposition in streams (50 studies contributing 261 effect sizes) to quantify overall drought effects on this key ecosystem process and to identify the main moderators controlling these effects. Drought reduced litter decomposition by 43% overall, which can impact energy and matter fluxes along heterotrophic food webs. The magnitude of drought effects on litter decomposition depended on the type of drought (natural drought > human-induced drought), type of decomposer community (microbes + macroinvertebrates > microbes) under natural drought, climate (warm and humid > temperate and Mediterranean) under human-induced drought, and on litter identity. The magnitude of drought effects on litter decomposition also increased with the severity of the drought. The effects of ongoing climate change will likely be strongest in streams with abundant shredders undergoing natural drought, especially if the streams become temporary. The composition of the riparian vegetation may modulate the magnitude of drought effects on litter decomposition, which may have management applications. [ABSTRACT FROM AUTHOR]

The sea lamprey (Petromyzon marinus L.) can be considered an ecosystem engineer, as it can substantially modify the river beds where it spawns. Sea lampreys dig nests by removing large volumes of cobbles to create a pit, and leaving them in a mound downstream, thus altering local bed morphology. Previous studies showed that sea lamprey nest-building behaviour increases riverbed heterogeneity in depth and water velocity, which in turn promotes macroinvertebrate diversity. Based on that finding, our study aimed at assessing whether these changes promoted ecosystem functioning. We measured multiple ecosystem functions (biofilm accretion, phosphate and ammonium uptake, and litter breakdown) on the pit and the mound of 30 lamprey nests, as well as on 30 unmodified sites. In spite of the physical heterogeneity, all processes measured showed no differences among sites, pointing towards a complex relationship between physical heterogeneity, biodiversity, and ecosystem function. [ABSTRACT FROM AUTHOR]

Population estimation implies considering the biology of the species, but also the constraints of logistic aspects such as cost. While common methods based on individual counts can provide precise estimates, they require an extensive sampling effort. An alternative to these methods is using cues linked to the species abundance. In that case, producing absolute estimates requires assessing the relationship between the individuals and these cues. In this paper, we propose a model based on data on spawning behaviour and Approximate Bayesian Computation to estimate the number of sea lamprey spawners using nest counts data. By counting the daily number of occupied nests and using parameters from a behavioural study, we set up a model simulating a spawning season and returning a population estimate by comparison with field data. Our model gives realistic estimates and we discuss the parameters on which to prioritize data collection with a sensitivity analysis, and show that halving the sample size provides a still satisfactory accuracy. We made an easily parametrizable application to run the model for any people interested in sea lamprey population estimation, and believe this framework to be a good way to increase data collection for both endangered and invasive sea lamprey. [ABSTRACT FROM AUTHOR]

Aging dams and the rising efforts to restore stream ecosystems are increasing the number of dam decommissioning programs. Although dam decommissioning aims at improving in‐stream habitat, biodiversity, and ecosystem functioning in the long term, it might also cause ecological impacts in the short term due to the mobilization of the sediment accumulated in the reservoir. Benthic biofilm in particular can be impaired by episodes of high turbidity and scouring. We conducted a multiple before‐after/control‐impact experiment to assess the effects of the drawdown of a large dam (42 m tall), a first step to its decommissioning, on biofilm structure (biomass and chlorophyll‐a) and functioning (metabolism, nutrient uptake, and organic matter breakdown). Our results show that the reservoir drawdown reduced the autotrophic biofilm biomass (chlorophyll‐a) downstream from the dam, which in turn lowered metabolism. However, nitrogen and phosphorus uptake by the biofilm was not affected. Organic matter breakdown was slower below the dam than in nearby undammed reaches before and during drawdown. All drawdown effects quickly disappeared and reaches downstream from the dam approached values found in nearby undammed reaches. Thus, our results indicate that the effects of reservoir drawdown on stream biofilms exist but may be small and disappear rapidly. [ABSTRACT FROM AUTHOR]

The habitat heterogeneity hypothesis states that increased habitat heterogeneity promotes species diversity through increased availability of ecological niches. We aimed at describing the local-scale (i.e. nest and adjacent substrate) effects of nests of the sea lamprey (Petromyzon marinus L.) as ecosystem engineer on macroinvertebrate assemblages. We hypothesized that increased streambed physical heterogeneity caused by sea lamprey spawning would modify invertebrate assemblages and specific biologic traits and promote reach-scale diversity. We sampled thirty lamprey nests of the Nive River, a river of the south western France with a length of 79.3 km and tributary of the Adour River, in three zones: the unmodified riverbed (upstream) and zones corresponding to the nest: the area excavated (pit) and the downstream accumulation of pebbles and cobbles (mound). The increased habitat heterogeneity created by lamprey was accompanied by biological heterogeneity with a reduced density of invertebrates (3777 ± 1332 individuals per m2 in upstream, 2649 ± 1386 individuals per m2 in pit and 3833 ± 1052 individuals per m2 in mound) and number of taxa (23.5 ± 3.9 taxa for upstream, 18.6 ± 3.9 taxa in pit and 21.2 ± 4.5 taxa for mound) in the pit compared to other zones. However the overall taxa diversity in nest increased with 82 ± 14 taxa compared to the 69 ± 8 taxa estimated in upstream zone. Diversity indices were consistent with the previous results indicating a loss of α diversity in pit but a higher β diversity between a pit and a mound than between two upstream zones, especially considering Morisita index accounting for taxa abundance. Trait analysis showed high functional diversity within zones with a reduced proportion of collectors, scrapers, shredders, litter/mud preference and small invertebrates in mound, while the proportion of "slabs, blocks, stones and pebbles" preference and largest invertebrates increased. Pit presented the opposite trend, while upstream had globally intermediate trait proportions. Our results highlight important effects on species and functional diversity due to habitat heterogeneity created by a nest-building species, what can ultimately influence food webs and nutrient processes in river ecosystems. [ABSTRACT FROM AUTHOR]

Animals of many species lay their eggs in nests built to provide their offspring a suitable microhabitat during a critical phase of development. Nest characteristics result from two processes: habitat choice and modification that may impact differently nest suitability for eggs. This field-based study aimed to estimate their independent effects and their interaction effects on the capacity of sea lamprey nests to retain eggs. Physical variables linked to both habitat choice and habitat modification affected nest suitability, but higher effect sizes indicated the prevalence of habitat modification. The most retentive nests were built in habitats with slower current (habitat choice) and had steeper slope between the deepest part of the nest (pit) and the downstream mound (habitat modification); the positive effect of the steep slope increasing with flow velocity in the nest. Our results show that habitat choice and habitat modification must be taken into account in evolutionary or conservation studies that analyze nest-building animals. [ABSTRACT FROM AUTHOR]

Water diversion and pollution are two pervasive stressors in river ecosystems that often co‐occur. Individual effects of both stressors on basal resources available to stream communities have been described, with diversion reducing detritus standing stocks and pollution increasing biomass of primary producers. However, interactive effects of both stressors on the structure and trophic basis of food webs remain unknown. We hypothesized that the interaction between both stressors increases the contribution of the green pathway in stream food webs. Given the key role of the high‐quality, but less abundant, primary producers, we also hypothesized an increase in food web complexity with larger trophic diversity in the presence of water diversion and pollution. To test these hypotheses, we selected four rivers in a range of pollution subject to similar water diversion schemes, and we compared food webs upstream and downstream of the diversion. We characterized food webs by means of stable isotope analysis. Both stressors directly changed the availability of basal resources, with water diversion affecting the brown food web by decreasing detritus stocks, and pollution enhancing the green food web by promoting biofilm production. The propagation of the effects at the base of the food web to higher trophic levels differed between stressors. Water diversion had little effect on the structure of food webs, but pollution increased food chain length and trophic diversity, and reduced trophic redundancy. The effects at higher trophic levels were exacerbated when combining both stressors, as the relative contribution of biofilm to the stock of basal resources increased even further. Overall, we conclude that moderate pollution increases food web complexity and that the interaction with water abstraction seems to amplify this effect. Our study shows the importance of assessing the interaction between stressors to create predictive tools for a proper management of ecosystems. [ABSTRACT FROM AUTHOR]

The structure and function of many rivers and streams worldwide are altered by water abstraction. However, this impact is often coupled with changes in flow regimes, water quality, and sediment transport, making it difficult to separate the effects of each of these disturbances. Here, we used a field manipulation to measure the responses of taxonomic and biological trait metrics to a 2-mo experimental water abstraction in an unpolluted mountain stream. We diverted water to reduce discharge by 65% while mimicking the effects of small hydropower plants by maintaining continuous flow in the bypassed impact reach. Water abstraction altered the taxonomic composition of invertebrate assemblages, creating combinations not found before in this stream. Abstraction did not affect total invertebrate density, but by narrowing the wetted channel, it reduced total invertebrate abundance/unit channel length to <½ that of control values. Abstraction also changed the density of some dominant taxa and reduced functional dispersion (computed from 9 biological traits related to movement, diet, and respiration mode). This effect was mainly driven by homogenization of diet. Moreover, abstraction affected the relative abundance of 3 biological traits, indicating additional changes in the way the assemblages use the stream. Our results show that abstraction produced rapid and intense reductions in invertebrate abundance, along with functional modifications, even though flow continuity was maintained. Together, these alterations may impair the capacity of the stream ecosystem to process, transform, and export organic matter. [ABSTRACT FROM AUTHOR]

The Pyrenean desman (Galemys pyrenaicus) is an endangered stream‐dwelling insectivore endemic to the Iberian Peninsula and the north of the Pyrenees. It favours riffles over slow habitats such as runs or pools, yet it is still unclear whether habitat preference is based on prey availability or on other factors, such as mechanical constraints on its hunting habits.Desman diet and prey selection were analysed along the pristine Elama Stream and the slightly modified Leitzaran Stream in the Basque Country, Spain.In each stream the prey consumed were identified by metabarcoding 94 desman faeces, and prey availability characterized from 10 Surber samples taken in each habitat type (riffles, runs and pools). Invertebrates were sorted and identified, the biomass of each taxon was calculated, and their DNA was also extracted, amplified using PCR, and sequenced to build a reference database.Prey availability and diet varied between streams. Desmans positively selected shredders and invertebrates that live on the substrate, and selected against taxa that live in fine sediment, taxa with hard shells or those that are highly mobile. The diet of desmans was more selective in the Elama, the stream with better ecological status. Food availability did not differ among habitats, and therefore does not explain the preference of desmans for riffles; rather, mechanical constraints to deal with buoyancy and physical habitat heterogeneity were hypothesized to be the reason behind the habitat preference.The results suggest that promoting the formation of riffles in streams can improve the situation of some desman populations living in degraded habitats. [ABSTRACT FROM AUTHOR]

Discharge reduction, as caused by water diversion for hydropower, and fine sediments deposition, are prevalent stressors that may affect multiple ecosystem functions in streams. Periphytic biofilms play a key role in stream ecosystem functioning and are potentially affected by these stressors and their interaction. We experimentally assessed the interactive effects of discharge and fine sediments on biofilm metabolism in artificial indoor channels using a factorial split-plot design with two explanatory variables: water discharge (20, 39, 62, 141 and 174 cm3 s-1) and fine sediments (no sediment or 1100 mg L-1 of sediments). We incubated artificial tiles for 25 days in an unpolluted stream to allow biofilm colonization, and then placed them into the indoor channels for acclimation for 18 days. Subsequently, we manipulated water discharge and fine sediments and, after 17 days, we measured biofilm chlorophyll-a concentration and metabolism. Water velocity (range, 0.5 to 3.0 cm s-1) and sediment deposition (range, 6.1 to 16.6 mg cm-2) increased with discharge, the latter showing that the effect of increased inputs prevailed over sloughing. In the no-sediment treatments, discharge did not affect biofilm metabolism, but reduced chlorophyll-a. Sediments, probably as a consequence of nutrients released, promoted metabolism of biofilm and chlorophyll-a, which became independent of water discharge. Our results indicate that pulses of fine sediments can promote biofilm algal biomass and metabolism, but show interactive effects with discharge. Although discharge reduction can affect the abundance of basal resources for food webs, its complex interactions with fine sediments make it difficult to forecast the extent and direction of the changes. [ABSTRACT FROM AUTHOR]

Temporary Mediterranean streams dry out in summer due to low precipitation and high temperatures, thus affecting biota and ecosystem functioning. The consequences of exposing leaf litter to an extreme summer drought, that is, high solar radiation, low humidity, and high temperatures, were evaluated. It was hypothesised that litter exposure to summer drought conditions in a dry streambed would change litter chemical composition, affecting decomposition and associated benthic communities after autumnal flow resumption. Recently fallen black poplar leaves were enclosed in litterbags and separated into two sets: (1) control leaves, kept air-dry in the dark, and (2) drought leaves, exposed to harsh summer conditions in a simulated dry streambed. Both sets were then immersed in a temporary Mediterranean stream in autumn, and leaf litter decomposition monitored. As expected, summer drought exposure increased nitrogen, total fibre, lignin, and cellulose content in drought leaves. After litterbag immersion, higher cellulose-degrading enzyme activity was observed in drought leaves while lignin-degrading enzyme activity was greater in the control leaves. Fungal and bacterial assemblages clearly differed between treatments. Inter-replicate variability was lower in drought leaves for most of the measured variables, suggesting that drought homogenised decomposer and detritivore communities. Despite these drought-related effects, decomposition rates did not vary, apparently due to counterbalancing effects (that is, drought treatment enhanced recalcitrant compounds and nutrient content in leaf litter) probably related to terrestrial microbial colonisation and photodegradation. Our study demonstrates that summer drought has bottom-up critical legacy effects in temporary Mediterranean streams, affecting the structure and function of decomposer communities. [ABSTRACT FROM AUTHOR]

Human activities have altered the environmental controls on river metabolism, i.e., gross primary production (GPP) and ecosystem respiration (ER). These coupled processes affect water quality, CO2 emissions, and biodiversity. Efforts to mitigate these impacts often lack long‐term, high‐resolution data needed to assess their success. Here, we estimated a 20‐yr time series of daily metabolism from dissolved oxygen (DO) data following pollution abatement (sewage treatment) in the Oria River, Spain. Ammonium concentration declined immediately after sewage abatement, whereas dissolved organic matter absorbance (proxy for concentration) declined slowly. Summer GPP declined with ammonium concentration. ER declined more strongly but more gradually than GPP and was driven by lower rates of autotrophic respiration (AR) and heterotrophic respiration following sewage treatment. Reduced AR reflected a decrease in the fraction of daily GPP being respired by algae themselves. Decline in ER caused net ecosystem production to increase from highly negative to approximately zero. Diel DO swings also declined and episodes of hypoxia nearly disappeared following reduced metabolic rates, and were paralleled by lower benthic chlorophyll a, increased macroinvertebrate indices, and a recovery of fish assemblages. Overall, wastewater treatment plants installation constrained river metabolism, greatly improved water quality, and enabled invertebrates and fish to recolonize the river. However, most variables responded gradually and these changes would not have been evident with short‐term DO data. These gradual responses revealed the need of long‐term, high‐resolution data to gain insight into long‐temporal scale responses superimposed on short‐temporal scale metabolic variation, especially in the current context of climate and land‐use change. [ABSTRACT FROM AUTHOR]

Microcosms try to mimic the behaviour of natural ecosystems; however, differences in experimental conditions reduce comparability among studies. A standard incubation duration may increase comparability between experiments without losing realism in the response. Some response variables can respond fast, acting as early warning signals of other, more important oncoming changes. In this experiment, we test the effects of resource quality and incubation duration on the performance of the amphipod Echinogammarus berilloni. Individuals were fed on five leaf species of contrasting quality and we measured their consumption rate, death rate, RNA:body mass (RNA:BM), growth rate, mass body condition and lipid body condition over time. We predicted that (i) resource quality would affect the response variables, (ii) consumption rate and RNA:BM ratio would act as early warning signals of oncoming changes in growth or death rates, and (iii) the inter-individual variation would gradually decrease with time. Resource quality was positively related to consumption rates, although it did not correlate to nutrient concentration and toughness of the materials. Amphipod body mass condition changed with diet, animals feeding on oak and beech showing the lowest values. Death rate, growth rate, RNA:BM, and lipid mass condition did not change with food resources. Consumption, growth rate and mass body condition changed with time. Moreover, consumption, mass body condition and RNA:BM significantly interacted with incubation duration. Variability among individuals in consumption and growth rate decreased with time, as predicted. Our results pointed that special care should be taken when comparing microcosm experiments with different incubation duration. We test the effects of leaf quality and incubation duration on E. berilloni. Resource quality was positively related to consumption. Body mass condition changed with diet. Consumption, mass body condition and RNA:BM significantly interacted with incubation duration. Special care should be taken when comparing experiments with different duration. [ABSTRACT FROM AUTHOR]

Molecular techniques allow non-invasive dietary studies from faeces, providing an invaluable tool to unveil ecological requirements of endangered or elusive species. They contribute to progress on important issues such as genomics, population genetics, dietary studies or reproductive analyses, essential knowledge for conservation biology. Nevertheless, these techniques require general methods to be tailored to the specific research objectives, as well as to substrate- and species-specific constraints. In this pilot study we test a range of available primers to optimise diet analysis from metabarcoding of faeces of a generalist aquatic insectivore, the endangered Pyrenean desman (Galemys pyrenaicus, É. Geoffroy Saint-Hilaire, 1811, Talpidae), as a step to improve the knowledge of the conservation biology of this species. Twenty-four faeces were collected in the field, DNA was extracted from them, and fragments of the standard barcode region (COI) were PCR amplified by using five primer sets (Brandon-Mong, Gillet, Leray, Meusnier and Zeale). PCR outputs were sequenced on the Illumina MiSeq platform, sequences were processed, clustered into OTUs (Operational Taxonomic Units) using UPARSE algorithm and BLASTed against the NCBI database. Although all primer sets successfully amplified their target fragments, they differed considerably in the amounts of sequence reads, rough OTUs, and taxonomically assigned OTUs. Primer sets consistently identified a few abundant prey taxa, probably representing the staple food of the Pyrenean desman. However, they differed in the less common prey groups. Overall, the combination of Gillet and Zeale primer sets were most cost-effective to identify the widest taxonomic range of prey as well as the desman itself, which could be further improved stepwise by adding sequentially the outputs of Leray, Brandon-Mong and Meusnier primers. These results are relevant for the conservation biology of this endangered species as they allow a better characterization of its food and habitat requirements. [ABSTRACT FROM AUTHOR]

Allochthonous detritus of terrestrial origin is one of the main energy sources in forested headwater streams, but its poor nutritional quality makes it difficult to use by heterotrophs. It has been suggested that algae growing on this detritus can enhance its nutritional quality and promote decomposition. So far, most evidence of this "priming effect” is derived from laboratory or mesocosm experiments, and its importance under natural conditions is unclear. We measured accrual of algae, phosphorus uptake capacity, and decomposition of poplar leaves in autumn in open- and closed-canopy reaches in 3 forest and 3 agricultural streams. Chlorophyll a abundance did not change significantly with stream type or with canopy cover, although in some agricultural streams it was higher in open than in closed canopy reaches. Canopy cover did not affect either phosphate uptake capacity or microbial decomposition. On the other hand, although there was no effect of canopy cover on invertebrate fragmentation rate, a significant interaction between canopy cover and stream suggests priming occurs at least in some streams. Overall, the results point to a weak or no priming effect of algae on litter decomposition in natural streams during autumn. [ABSTRACT FROM AUTHOR]

Water abstraction modifies the environmental conditions of stream ecosystems, which can affect invertebrate assemblages by altering drift. We examined this issue with a before-after-control-impact design experiment in which we diverted 90% of the natural flow from a headwater stream. We measured flow-reduction effects on drift densities (animals/m3), total drift rates (animals leaving the reach per hour) and net balance of invertebrates entering or leaving the Impact reach. We also identified the specific taxa and traits that drove these responses. The sudden decrease in flow promoted a 12-fold increase in overall drift density at the Impact reach, which was primarily driven by filterers, shredders and taxa associated with fast velocities, such as simulids. By contrast, drift densities of other abundant taxa, such as Baetis, Esolus and chironomids, increased less than what could be expected from the magnitude of flow reduction. While drift rates remained unchanged after water abstraction, the Impact reach became a net invertebrate exporter indicating that many taxa drifted actively as a response to stressful conditions rather than passively, which would be reduced by water abstraction. Therefore, our results suggest that water abstraction influences drift, with potentially important consequences for the invertebrate assemblages and ecosystem processes further downstream. [ABSTRACT FROM AUTHOR]

Abstract: The Pyrenean desman (Galemys pyrenaicus) is an endangered, semi‐aquatic, insectivore mammal, endemic to the northern Iberian Peninsula and the Pyrenees. Owing to its small populations, evasive behaviour, and nocturnal activity, knowledge of its ecological requirements is still limited. Continuing population decline over most of its distribution range – even in regions where water quality has clearly improved – points to other factors as the main conservation threat. Nevertheless, at present there is a lack of information on its habitat preferences within its area of occupancy (e.g. stream microhabitat characteristics), a key point for assessing or improving its habitat. This study used radio‐telemetry data to determine the use of space at microhabitat level by the desman, and how this changed depending upon environmental conditions. Desmans were studied in two contrasting rivers in the Basque Country (northern Iberian Peninsula): Elama, a nearly pristine stream, and the Leitzaran, a clean‐water stream affected by hydropower diversions. Fifteen desmans were captured and radio‐tracked in Elama and 16 were captured and radio‐tracked in the Leitzaran, and nocturnal activity points were assigned to one of three habitat types: riffles, runs, or pools. Habitat use was compared against availability to measure habitat selection in each stream and between streams. Desmans selected riffles positively and pools negatively, with this selection being stronger in the Leitzaran. The results highlight the ecological relevance of riffles as foraging habitats of desmans, and therefore as key features for their conservation. It suggests that channel modifications that reduce the areal cover of riffles impair habitat quality for this species. In addition, water diversion for hydropower is likely to be detrimental for desmans, as it reduces discharge and flow velocity in the bypassed river sections. [ABSTRACT FROM AUTHOR]

Turbulence and aeration are reduced in many streams during low-flow periods as a consequence of drought or water abstraction, thus affecting invertebrate interactions and pivotal ecosystem processes such as the breakdown of organic matter (OM). These effects can be larger in the hyporheic zone (HZ), the ecotone connecting the surface stream and groundwater, especially when fine sediments reduce hydraulic conductivity. In addition, OM breakdown in the HZ could depend on the availability of OM in the benthic zone (BZ), because the latter would not only be a more accessible, and thus preferred, food resource, but also more easily scoured downstream. In a laboratory microcosm experiment of 28 days duration, we manipulated aeration, sediment size and location of OM (either all buried or half buried with half on the surface, simulating the HZ and BZ respectively). Six mayfly (Habroleptoides) individuals and four stonefly (Capnioneura) individuals were enclosed in each microcosm and the consumption of OM was measured. Lack of aeration reduced oxygen saturation from 94 to 66%, reducing OM consumption particularly on the surface, in contrast with our expectations. As hypothesised, the availability of surface OM significantly reduced invertebrate consumption of buried OM. Habroleptoides performed better than Capnioneura, especially in fine sediments. The results suggest that reduced turbulence can affect invertebrate trophic interactions as well as the decomposition of OM, depending on sediment grain size and the location of OM. [ABSTRACT FROM AUTHOR]

Toxic cyanobacterial proliferations in water bodies can cause serious environmental and public health issues, as well as having economic effects. Increased inputs of nutrients and fine sediment caused by forestry have been hypothesised as possible causes of increased Phormidium-dominated proliferations in New Zealand rivers. Little is known about the effect of these proliferations on river ecosystem functioning. In the present study, we evaluated five sites along the Maitai River (New Zealand) differing in pine plantation cover of their catchments. We hypothesised that Phormidium biofilms would trap more sediments and recycle more phosphorus than diatoms, that Phormidium proliferations would increase with forestry cover in the catchment and that the varying abundance of Phormidium would affect river ecosystem functioning. Phormidium did not trap more sediment or recycle more phosphorus (measured as alkaline phosphate activity) than diatom biofilms. However, the cover of Phormidium did increase with the proportion of forestry in the catchment. Organic matter decomposition rates (measured as loss of tensile strength of standard cotton strips) varied very little among sites, whereas river ecosystem metabolism increased with the abundance of Phormidium, especially in the lower part of the river. The results of the present study suggest that pine forestry does promote Phormidium biofilm abundance and affect ecosystem functioning in the Maitai River. [ABSTRACT FROM AUTHOR]

Water abstraction is rapidly increasing worldwide in order to respond to escalating demands for water, food and energy. Abstraction can alter the hydrological regime of streams and rivers, reduce in-stream habitats, change water quality and affect fluvial communities. It can also impair ecosystem functioning, although this aspect has been seldom assessed., We experimentally tested the effect of water abstraction on stream functioning in a headwater mountain stream using a before and after control-impact (BACI) design. We quantified changes in water physicochemical properties, biofilm biomass and activity (exo-enzymes and metabolism), and ecosystem processes (nutrient cycling, organic matter retention and breakdown)., Water abstraction did not affect water physicochemical properties, but reduced the biomass and the alkaline phosphatase activity of biofilm per surface unit, the areal uptake of nutrients, and the travel distance of organic matter. It did not affect the biofilm metabolism and breakdown of submerged leaf litter, but decreased the total breakdown., The impacts were larger when analysed per unit of channel length. All variables, except benthic chlorophyll- a, were significantly reduced by abstraction, due to the contraction of the wetted channel., The decrease in the biomass and activity of biofilm, as well as in nutrient uptake and total organic matter breakdown observed in this study could increase nutrient concentration in downstream reaches and reduce the energy transfer to higher trophic levels. Ecosystem services of permanent headwater streams are likely to be compromised with the reduction of wetted-channel width. [ABSTRACT FROM AUTHOR]

Salmonid females invest heavily in reproduction, through gamete production, habitat selection and maternal care. Habitat selection and maternal care are expected to provide shelter for eggs against scouring and predators. However, females also tend to produce variable egg sizes, and this trait may interact with habitat quality to influence the survival of offspring. In this study, we aimed at evaluating the role of female habitat selection on egg survival conditional on individual egg size and female body size. We monitored female reproductive activity in two natural rivers for 3 years, in order to relate nest characteristics to female body size. Bigger females dug deeper nests at lower shear stress force. Right after the end of nest construction, we sampled a part of the eggs laid by each female, measured them individually, and placed them back using capsules within their original position in the nest. At time of hatching, the capsules within the nest were collected and individual egg mortality was assessed. Our results indicate that scouring was the main driver for mortality (75%) and that nest burial depth and shear stress force above the nest both influenced scouring. However, subsequent survival was influenced by neither nest characteristics, individual egg size, nor the interaction between both. It is therefore expected that traits or tactics that reduce nest scouring probability should be under strong selection. [ABSTRACT FROM AUTHOR]

The analysis of sexual selection classically relies on the regression of individual phenotypes against the marginal sums of a males x females matrix of pairwise reproductive success, assessed by genetic parentage analysis. When the matrix is binarized, the marginal sums give the individual mating success. Because such analysis treats male and female mating/reproductive success independently, it ignores that the success of a male x female sexual interaction can be attributable to the phenotype of both individuals. Also, because it is based on genetic data only, it is oblivious to unproductive matings, which may be documented by behavioral observations. To solve these problems, we propose a statistical approach which combines matrices of offspring numbers and behavioral observations. It models reproduction on each mating occasion of a mating season as three stochastic and interdependent pairwise processes, each potentially affected by the phenotype of both individuals and by random individual effect: visit of a female by a male, concomitant gamete emission, and offspring production. Applied to data from a mating experiment on brown trout, the model yielded different results from the classical regression analysis, with only a negative effect of female body size on the probability of visit and gamete release, while the classical approach based on regression found a positive effect of male size on the number of both visits and offspring, and no effect of female size. Because the general structure of the model can be adapted to other partitioning schemes of the reproductive process, it can be used for a variety of biological systems where behavioral and genetic data are available. [ABSTRACT FROM AUTHOR]

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Discharge fluctuations modify water depth and velocity in streams and this can affect leaf litter breakdown, which is an important ecosystem function. Both during droughts, when parts of the surface dry out, and during floods, which scour the benthic surface, macroinvertebrates can seek refuge in the subsurface. Therefore, as an important part of them depend on organic matter, the effects of discharge fluctuations on leaf breakdown might be greater on the surface than in the subsurface of lotic ecosystems. To test this hypothesis, we measured microbial and total breakdown rates of alder (Alnus glutinosa (L.) Gaertner) both on the surface and in the subsurface in two areas of a stream, namely, the permanently wet channel and the parafluvial areas. Reduced discharge dried out only the surface of the parafluvial areas, and thus, breakdown rates were reduced only in this habitat. In contrast, breakdown rates were similar in both habitats of the permanently wet channel, but also in the subsurface of the parafluvial area. The subsurface can mitigate the effects of discharge alterations on the breakdown of organic matter in streams, which might be critical for the productivity of these ecosystems under increased drought frequencies. [ABSTRACT FROM AUTHOR]

Habitat complexity can influence predation rates (e.g. by providing refuge) but other ecosystem processes and species interactions might also be modulated by the properties of habitat structure. Here, we focussed on how complexity of artificial habitat (plastic plants), in microcosms, influenced short-term processes driven by three aquatic detritivores. The effects of habitat complexity on leaf decomposition, production of fine organic matter and pH levels were explored by measuring complexity in three ways: 1. as the presence vs. absence of habitat structure; 2. as the amount of structure (3 or 4.5 g of plastic plants); and 3. as the spatial configuration of structures (measured as fractal dimension). The experiment also addressed potential interactions among the consumers by running all possible species combinations. In the experimental microcosms, habitat complexity influenced how species performed, especially when comparing structure present vs. structure absent. Treatments with structure showed higher fine particulate matter production and lower pH compared to treatments without structures and this was probably due to higher digestion and respiration when structures were present. When we explored the effects of the different complexity levels, we found that the amount of structure added explained more than the fractal dimension of the structures. We give a detailed overview of the experimental design, statistical models and R codes, because our statistical analysis can be applied to other study systems (and disciplines such as restoration ecology). We further make suggestions of how to optimise statistical power when artificially assembling, and analysing, ‘habitat complexity’ by not confounding complexity with the amount of structure added. In summary, this study highlights the importance of habitat complexity for energy flow and the maintenance of ecosystem processes in aquatic ecosystems. [ABSTRACT FROM AUTHOR]

Dead wood is an important component of natural stream ecosystems, but its abundance has been reduced by human actions. Therefore, in many stream restoration projects dead wood is introduced into stream channels to improve physical habitat, biological communities, and ecosystem functioning. We added dead wood to 4 northern Iberian headwater streams, ranging in mean discharge from 0.026 to 2.5 m3/s, to enhance retention of nutrients, sediments, and organic matter. We placed logs and branches in the stream channels to simulate the amount and orientation found in natural streams and assessed the effects of restoration following a Before-After-Control-Impact design. We measured water and nutrient retention by experimental additions of PO43- and NH4+, with NaCl as a hydrological tracer, and leaf retention by releasing Ginkgo biloba leaves. Introduction of large wood significantly reduced water velocity, especially during high-flow periods, but the overall effects on average nutrient travel distance were not significant. When analyzed individually by stream, effects were significant only for PO43- in 1 stream. Wood addition increased average leaf-litter travel distance overall, but when analyzed individually by stream had no effect in the 2 smaller streams despite the fact that previously reported measures of benthic organic matter increased many fold. This discrepancy between ginkgo measurements and benthic storage raises concerns about the relevance of short-term release measurements and suggests that the effects of wood introduction on nutrient retention might also be stronger than reported here. Overall, wood addition decreased water velocity at all sites, but effects on retention of nutrients and organic matter were variable among sites. Nevertheless, the fact that all statistically significant differences found showed enhanced retention, which can be the basis of important ecosystem services, suggests that wood restoration produces functional benefits beyond the improvement of stream habitat. [ABSTRACT FROM AUTHOR]

Litter breakdown is a pivotal ecosystem function in headwater streams, where it fuels food webs and controls C flux. Breakdown rates depend on environmental characteristics and can display strong seasonal variation, particularly in intermittent streams. To identify the environmental factors driving seasonality of litter breakdown, we ran 5 breakdown experiments with poplar leaves during the wet phase (November-August) in a 3rd-order intermittent Mediterranean stream. We assessed the contribution of decomposers and detritivores to total breakdown seasonality by measuring total (coarse-bag) and microbial (fine-bag) breakdown and estimating invertebrate-mediated breakdown rates (difference between coarse and fine mesh). Breakdown rates (k) increased from autumn to early summer when expressed as k/d and decreased during the drying phase. However, when expressed k/degree-day (dd), rates peaked in early spring and subsequently decreased. The high fine-mesh/coarsemesh ratio (0.70) indicated that microbes drove total breakdown. Hierarchical partitioning (HP) analyses in k/d showed that temperature was the most important environmental factor for microbial breakdown and affected invertebrate breakdown. Temperature presented strong synergistic effects with other variables. Following removal of the temperature effect, total breakdown was related mainly to current and conductivity, microbial breakdown was related to water quality (conductivity, pH, and O2), and invertebrate-mediated breakdown was related only to current. The relation of invertebrate breakdown with current variation might be explained by strong seasonality in total invertebrate and shredder densities, which seemed to be linked to seasonality in discharge. Climate change can profoundly affect stream ecosystems, but the responses of invertebrates and microbes in terms of litter processing and C fluxes can be difficult to predict in intermittent Mediterranean streams. [ABSTRACT FROM AUTHOR]

The effluents of wastewater treatment plants ( WWTPs) include a complex mixture of nutrients and pollutants. Nutrients can subsidise autotrophic and heterotrophic organisms, while toxic pollutants can act as stressors, depending, for instance, on their concentration and interactions in the environment. Hence, it is difficult to predict the overall effect of WWTP effluents on river ecosystem functioning., We assessed the effects of WWTP effluents on river biofilms and ecosystem metabolism in one river segment upstream from a WWTP and three segments downstream from the WWTP and following a pollution gradient., The photosynthetic capacity and enzymatic activity of biofilms showed no change, with the exception of leucine aminopeptidase, which followed the pollution gradient most likely driven by changes in organic matter availability. The effluent produced mixed effects on ecosystem-scale metabolism. It promoted respiration (subsidy effect), probably as a consequence of enhanced availability of organic matter. On the other hand, and despite enhanced nutrient concentrations, photosynthesis-irradiance relationships showed that the effluent partly decoupled primary production from light availability, thus suggesting a stress effect., Overall, WWTP effluents can alter the balance between autotrophic and heterotrophic processes and produce spatial discontinuities in ecosystem functioning along rivers as a consequence of the mixed contribution of stressors and subsidisers. [ABSTRACT FROM AUTHOR]

Eucalypt leaves are an organic matter source of poor quality, and therefore, extensive eucalypt plantations can affect stream ecology. Nevertheless, it is difficult to discern the effects of altered inputs from other impacts of plantations, such as increased erosion from periodic clearcuttings. To assess the effects of eucalypt inputs on organic matter decomposition in streams, we manipulated litter inputs in two headwater streams in the north of the Iberian Peninsula. Three contiguous 50-m long reaches were selected per stream: the upstream reference reach was left unaltered, while the others were covered and separated by mesh to prevent inputs from the surrounding vegetation, and via downstream transport. Regularly, we provided the covered sites with either native deciduous (middle reach) or eucalypt (lower reach) leaf litter, mimicking the amount and seasonality of inputs from the respective forest types. Two decomposition experiments with alder and eucalypt leaves were performed half a year and 1 year after the beginning of the exclusion of natural inputs. Decomposition for both species was lower in sites receiving eucalypt leaf litter, corresponding with the lower density of shredders in these sites. Moreover, higher alder:eucalypt macroinvertebrate density and biomass ratios in sites receiving eucalypt inputs suggest that invertebrates concentrated on the higher quality alder leaves in those sites. Our study shows that eucalypt inputs can impair stream ecosystem processes in a short time span and suggests that maintaining native leaf litter inputs into streams by intact riparian corridors could help to mitigate the effect of eucalypt plantations on streams. [ABSTRACT FROM AUTHOR]

Large dams regulate river hydrology and influence water chemistry, sediment dynamics, channel form and biotic communities. These effects may translate into important changes in river ecosystem processes, especially in rivers naturally subject to strong seasonality, such as those under Mediterranean climate., The effects of flow regulation on ecosystem metabolism [ i.e. gross primary production (GPP) and ecosystem respiration (ER)] were analysed by means of open-stream measurements. Organic matter accrual and metabolism were measured in reaches upstream and downstream from large reservoirs in three tributaries of the Ebro River ( NE Iberian Peninsula) during three sampling campaigns., Dams reduced downstream hydrological variability, dampened floods and increased the duration of interflood periods. Benthic organic matter increased twofold and chlorophyll- a eightfold. GPP increased by 59% on average, whereas ER increased by 75%., In general, flow regulation intensified the capacity of downstream river reaches to store and process materials and energy, therefore increasing the amount of organic carbon processed and altering the whole flux of materials and energy along the river continuum. [ABSTRACT FROM AUTHOR]

Availability and quality of food resources limit consumer performance and modulate food webs, which in turn, can affect ecosystem functioning. Availability and quality of food resources can be especially important in streams, where consumers depend on allochthonous organic matter whose availability and quality can differ markedly both spatially and throughout the year. Most studies of the relationships between food quality and detritivore performance have been based on standardized food types and have not been designed to allow consideration of interactions between resource quantity and quality. Our goal was to evaluate the effects of quality and quantity of resource on shredder performance. We raised larvae of the caddisfly Sericostoma vitattum in the laboratory with food taken from a stream reach. We controlled food type (conditioned Alnus glutinosa leaves, natural leaf packs from riffles, and deposits within thick debris jams) and quantity (low: 2 mg individual-1 d-1; high: 10 mg individual-1 d-1). Consumption rate tended to be higher for lower- than for higher-quality materials, and the differences were more marked at high resource quantity. However, this compensatory mechanism was not enough to compensate growth in the case of lowest-quality food. In addition, food quality and quantity interacted to determine the energy allocation to body condition or growth. Our results show that the interaction between resource quality and quantity can influence invertebrate condition and life cycles. Stored organic matter in large jams, despite their poor quality, could enable consumers to survive until the next high-input season. [ABSTRACT FROM AUTHOR]

Temperate forests managed to maximize sustainable yield of wood products can reduce the availability of dead wood on the forest floor and in adjacent streams, which in turn can impair ecological processes such as retention and transformation of organic matter. Lack of tools to link ecological processes with their effects on human well-being leads forest managers to ignore the cost on other services from terrestrial and aquatic ecosystems., We examine how adding dead wood to restore stream channel complexity affects the provision and value of selected ecosystem services, mainly related to the retention and transformation of matter and cycling of nutrients, as well as to the effects on aquatic biota. Specifically, we evaluated the cost-effectiveness of stream restoration through a comparative analysis of four reach-scale projects in streams flowing through temperate forest and into a drinking water reservoir and two scenarios of active and passive restoration at the basin scale., Results indicate that the lack of dead wood in streams has an important economic cost because of the effects on fish provisioning, opportunities for recreation and tourism, water purification and erosion control. Active reach-scale restoration resulted in a 10- to 100-fold increase in the monetary benefits provided by streams, accounting as much as 1·8 € per metre of restored river length each year. Results of the reach-scale cost-benefit analyses estimated that the time required to recover the active restoration investment ranged from 15 to 20 years in low- to middle-order streams., Synthesis and applications. Our study showed that restoration of natural wood loading in streams greatly increases the ecosystem services they provide. The benefits in terms of the analysed services surpass the costs of active restoration over realistic timeframes, whereas this was not the case for passive restoration. Inclusion of other ecosystem services such as conservation of biodiversity might make restoration more economically profitable. Overall, our study provides a decision framework for managing temperate riparian forests in the context of ecological services. [ABSTRACT FROM AUTHOR]

Because of the serious effects of pollution on water supply much closer attention has been paid to water quality than to other aspects of river integrity. However, channel form and water flow are relevant components of river health, and recent evidences show that their impairment threatens the services derived from them. In this article, we review the literature on the effects of common hydromorphological impacts (channel modification and flow modification) on the functioning of river ecosystems. There are evidences that even light hydromorphological impacts can have deep effects on ecosystem functioning, and that different functional variables differ in their responses. Three criteria (relevance, scale and sensitivity) in the selection of functional variables are suggested as a guide for the river scientists and managers to assess the ecological impacts of hydromorphological modifications. [ABSTRACT FROM AUTHOR]

A preface to the book "Hydrobiologia" is presented.

Small hydropower plants divert part of the water from wide and physically complex stream channels with active hyporheic areas to narrow and hydraulically simple concrete canals, and thus, might affect nutrient dynamics. We compared nutrient uptake in diversion canals and in stream channels in the Leitzaran Stream (Basque Country, northern Spain). We predicted that simple morphology in diversion canals will result in lower nutrient uptake in canals than in stream channels. Periphytic chlorophyll and biomass did not differ significantly between reach types. Water was significantly deeper and faster in canals than in stream channels, but the transient storage zone did not differ significantly between reach types. There were no significant differences between uptake length for neither phosphate nor ammonium between reach types. Uptake length in both stream channels and diversion canals decreased with discharge, in a pattern similar to that previously described for pristine rivers across the world. Uptake velocity and uptake rate for phosphate did not differ significantly between reach types, but in the case of ammonium both retention metrics were significantly larger in the diversion canals. Results suggest that although hydropower schemes have minor effects on nutrient retention, these depend on the proportion of flow diverted. [ABSTRACT FROM AUTHOR]

Organic matter inputs to streams can be retained in contrasting sites, from small leaf packs on top of cobbles to thick organic deposits trapped by wood jams. Differences in environmental conditions and in stability among sites can affect the biological communities, the quality of organic matter and its use by consumers., We measured the accumulation and composition of coarse organic matter and the breakdown of alder leaves on the surface of the streambed, inside gravel bars and in thick litter deposits trapped by log jams. We also monitored fungal sporulation rates and macroinvertebrate diversity and density in these retention sites., The amount of organic matter in these locations differed significantly among sites and ranged from 118 g m−2 in gravel to 11 562 g m−2 in jams. The biomass of shredders also differed significantly among retention sites, being highest in jams (1440 mg m−2) and lowest in gravel (86 mg m−2)., Breakdown of alder leaves in fine-mesh bags did not differ among retention sites. In coarse-mesh bags, leaf breakdown rate was significantly lower in gravel bars than in surface sites or jams. Despite large differences in amount and quality of organic matter between surface sites and jams, alder leaves broke down at the same rate., Density of invertebrates in bags and fungal sporulation rates tended to be highest in surface sites and lowest in gravel bars. The contribution of microbes to breakdown was 67% in gravel, 52% in surface and only 28% in jams. Overall, the differences among sites in leaf breakdown were correlated with invertebrate density., Our results showed large differences in the amount and quality of organic matter accumulated, in biological communities and in the use of organic matter among retention sites of a single stream reach. This spatial variability should be taken into account in studies of ecosystem functioning related to organic matter. [ABSTRACT FROM AUTHOR]

Introduction: The Consolider-Ingenio 2010 project SCARCE, with the full title 'Assessing and predicting effects on water quantity and quality in Iberian Rivers caused by global change' aims to examine and predict the relevance of global change on water availability, water quality, and ecosystem services in Mediterranean river basins of the Iberian Peninsula, as well as their socio-economic impacts. Starting in December 2009, it brought together a multidisciplinary team of 11 partner Spanish institutions, as well as the active involvement of water authorities, river basin managers, and other relevant agents as stakeholders. Methods: The study areas are the Llobregat, Ebro, Jucar, and Guadalquivir river basins. These basins have been included in previous studies and projects, the majority of whom considered some of the aspects included in SCARCE but individually. Historical data will be used as a starting point of the project but also to obtain longer time series. The main added value of SCARCE project is the inclusion of scientific disciplines ranging from hydrology, geomorphology, ecology, chemistry, and ecotoxicology, to engineering, modeling, and economy, in an unprecedented effort in the Mediterranean area. The project performs data mining, field, and lab research as well as modeling and upscaling of the findings to apply them to the entire river basin. Results: Scales ranging from the laboratory to river basins are addressed with the potential to help improve river basin management. The project emphasizes, thus, linking basic research and management practices in a single framework. In fact, one of the main objectives of SCARCE is to act as a bridge between the scientific and the management and to transform research results on management keys and tools for improving the River Basin Management Plans. Here, we outline the general structure of the project and the activities conducted within the ten Work Packages of SCARCE. [ABSTRACT FROM AUTHOR]

Summary 1. Channel complexity affects the physical structure, biotic communities and functioning of stream ecosystems. Large wood (LW) is a key element in the creation and maintenance of physically complex stream channels in forested areas. 2. In an attempt to enhance stream habitat quality and ecosystem functioning and to reduce inputs of organic matter to a downstream reservoir, LW was experimentally introduced into four mountain streams in the Basque Country (northern Spain), ranging in channel width from 3 to 13 m. Following a before-after/control-impact (BACI) design, streams were monitored during 1 year prior to wood addition and during 2 years after addition in one control and one experimental reach per stream. 3. Areal cover of benthic organic matter in the entire channel was measured from regular transects and the mass of stored organic matter from random Surber samples. Breakdown of organic matter was assessed in litter bag experiments performed with black alder leaves. When 50% of the initial mass in the bags remained, invertebrates associated with leaf bags were collected. 4. Wood placement produced a 2- to 70-fold increase in the storage of organic matter, especially in thick deposits upstream from wood jams, with values in excess of 2 kg AFDM per m2 in the small streams. The accumulation of organic matter produced by wood introduction decreased with increasing stream size. 5. Despite the large increase in the availability of organic matter, litter breakdown rates were unaffected by the experimental reaches, suggesting large increases in the total amount of organic matter consumed at the reach scale. 6. Numbers of invertebrates and shredders per gram of leaf litter did not respond to wood addition. Average body mass of invertebrates associated with leaf litter showed a non-significant decreasing trend, which might reflect increased recruitment. 7. Although the effects of wood addition can depend on wood stability and stream size, adding LW to restore channel complexity can improve environmental conditions for invertebrate communities and affect stream ecosystem functioning, enhancing the efficiency to use organic matter inputs on a reach scale. [ABSTRACT FROM AUTHOR]

- Streams in the Aiako Harria Natural Park (Basque Country, Spain) have excellent water quality, but are physically impoverished after centuries of snagging. In an attempt to restore channel complexity and ecosystem functioning, especially in-channel retention of sediments and organic matter, large woody debris (LWD) was introduced into four mountain streams (channel width 3-13 m) following a before/after, control/impact (BACI) design. Logs were introduced by means of hand-held machinery and located uncabled, mimicking the natural amount and disposition of LWD in streams. Floods disrupted most of the structures at the large stream, but caused little damage to those in the small ones. Only minnow and brown trout inhabit in the area. Before wood addition, trout densities were fairly high in the small streams, low in the large one, where recruitment seemed very poor. In the small tributaries, trout populations showed a strong imbalance towards young fish, adults being only found in the spawning season. Wood addition produced some interesting trends in trout, although statistical significance was low as a result of large environmental variability. Fish densities showed small changes, but biomass increased, especially in the spawning season. Also, there was a trend towards more aged 2+ or larger, thus suggesting wood addition improved adult habitat. Although restoring LWD is extremely unusual in Spain, the changes in physical habitat and the trends in fish populations detected in the present project suggest it is worth making more experiments, at least in safe settings where there is no risk of flooding or damaging properties. [ABSTRACT FROM AUTHOR]

River channels tend to a dynamic equilibrium driven by the dynamics of water and sediment discharge. The resulting fluctuating pattern of channel form is affected by the slope, the substrate erodibility, and the vegetation in the river corridor and in the catchment. Geomorphology is basic to river biodiversity and ecosystem functioning since the channel pattern provides habitat for the biota and physical framework for ecosystem processes. Human activities increasingly change the natural drivers of channel morphology on a global scale (e.g. urbanization increases hydrological extremes, and clearing of forests for agriculture increases sediment yield). In addition, human actions common along world rivers impact channel dynamics directly, e.g. river regulation simplifies and fossilizes channel form. River conservation and restoration must incorporate mechanisms of channel formation and ecological consequences of channel form and dynamics. This article (1) summarizes the role of channel form on biodiversity and functioning of river ecosystems, (2) describes spatial complexity, connectivity and dynamism as three key hydromorphological attributes, (3) identifies prevalent human activities that impact these key components and (4) analyzes gaps in current knowledge and identifies future research topics. [ABSTRACT FROM AUTHOR]

Metabolism is an integrative measurement of stream and river ecosystem functioning, and thus, could be used to assess impairment. Stream metabolism is measured by different methods which often yield contrasting results. Furthermore, open-channel measurements of metabolism, which offer the best potential for continuous monitoring of stream functioning, rely on calculations of gas exchange with the atmosphere, for which a plethora of methods exists. Therefore, to incorporate metabolism in stream monitoring programs, it is necessary to determine which methods yield comparable results under a given set of environmental conditions. We studied 21 streams in the Basque Country (northern Spain), ranging widely in physical characteristics and water quality. We calculated reaeration during summer baseflows using three different approaches: the night-time drop in oxygen, the lag between noon and peak oxygen concentration, and ten empirical equations relating depth and velocity with reaeration coefficients obtained from the literature. Differences among methods were very large, especially at the shallower sites. The results obtained with most empirical equations were highly correlated, but showed little agreement with the night-time and peak lag methods. We then analyzed the response of reaeration rate to river stage: reaeration calculated by the night-time method during 1 year of continuous monitoring was regressed against discharge at each site, and the resulting model was compared to the results of empirical equations, using software HecRas 2.2 to model hydraulic conditions at different river stages. The shape of reaeration-discharge plots differed greatly and in a site-dependent manner, and there was little agreement between methods. Finally, we investigated the effects of reaeration rate on estimates of metabolism. The choice of method greatly affected the estimates of both primary production and respiration. The empirical equations, except E7 and E10, yielded the most unrealistic estimations of stream metabolism. Overall, the night-time method, especially when regressed against discharge, seems to be the most robust and reliable among those tested, with the energy dissipation method (E10) appearing to be a viable alternative when the night-time method does not work. [ABSTRACT FROM AUTHOR]

Human perception of riverscapes with and without large wood (LW) has been investigated with a photo-questionnaire submitted to 2250 students in ten countries, capturing reactions to 20 pictures in terms of naturalness, danger, aesthetics and need for improvement. Principal component analysis performed on average scores per country per item showed that the primary discriminating factors are human modification, turbulence and extent of water shown in the scenes. Wood discriminated the perception of student groups, but other factors are also critical. Features associated with human activity (channel deepening and straightening, rip-rapping) were perceived to be less aesthetically pleasing than wood. Perception of the most dangerous riverscapes is not specifically affected by wood, but by turbulent flows and wide rivers. The presence of wood clearly discriminated the need for human intervention. Perceptions differed among countries, reflecting different cultural contexts. Students from Germany, Sweden and Oregon perceived LW more positively as a natural and wild component of watercourses. These perceptions are linked to positive attitudes towards natural riverscapes. Other students, such as those from China, Russia or India, perceived rivers with wood as needing regulation and maintenance. Whatever the socio-cultural context, large wood elicits an emotional influence on how one perceives riverscapes. [ABSTRACT FROM AUTHOR]

Dead wood has been identified as an important structural component of stream ecosystems, and researchers have stressed its role in retaining sediments and organic matter, increasing habitat diversity and providing refugia for aquatic organisms. Because it is a highly refractory compound, known to take very long periods to break down underwater, it has been considered a slow source of dissolved or fine particulate organic matter. We evaluated the contribution of dead wood to the total carbon flux in two headwater forested streams in northern Spain, one running under mature deciduous forest, the other under eucalyptus plantations. Breakdown rates were measured from branches (10 cm long, 3 cm in diameter) of alder, oak and eucalyptus, the main species present at the streams, applied to the standing crop of fine dead wood following four different models and compared with the breakdown loss of leaf litter calculated in a previous work for the same reaches. Calculations showed breakdown losses of fine wood (FW, diameter 1-5 cm) to range from 6.0 to 123 g ash-free dry mass (AFDM) m-2 y-1 at the deciduous stream and from 4.6 to 7.1 g AFDM m-2 y-1 at the eucalyptus stream. Conservative assumptions show that fine wood breakdown losses amount to 21% of the mass lost by leaf breakdown at the deciduous stream and to 9% of leaf breakdown at the eucalyptus stream. So, fine dead wood contributes to a significant fraction of the total breakdown of allochthonous organic matter in the studied streams; other sizes of dead wood (twigs, coarse wood) increase the breakdown by an order of magnitude, and thus can result in a large part of the carbon flux being derived from wood. [ABSTRACT FROM AUTHOR]

Reintroduction of wood in rivers for restoration purposes is now recognized in a positive way by scientists. Nevertheless, the perception of wood in riverscapes is strongly affected by the socio-cultural environment. This cultural influence might explain why wood reintroduction is accepted and promoted in some regions of the world but not in others, despite the demonstrated ecological benefits. From an extensive student perception survey, we show that most of the groups from nine countries in the world considered riverscapes with wood to be less aesthetic, more dangerous, and needing more improvement than riverscapes without wood. By contrast, this way of thinking was not observed in Germany, Sweden, and Oregon (USA), where the first instances of wood reintroduction occurred. [ABSTRACT FROM AUTHOR]