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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]

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.

Experimental manipulations of streamflow have been used globally in recent decades to mitigate the impacts of dam operations on river systems. Rivers are challenging subjects for experimentation, because they are open systems that cannot be isolated from their social context. We identify principles to address the challenges of conducting effective large-scale flow experiments. Flow experiments have both scientific and social value when they help to resolve specific questions about the ecological action of flow with a clear nexus to water policies and decisions. Water managers must integrate new information into operating policies for large-scale experiments to be effective. Modeling and monitoring can be integrated with experiments to analyze long-term ecological responses. Experimental design should include spatially extensive observations and well-defined, repeated treatments. Large-scale flow manipulations are only a part of dam operations that affect river systems. Scientists can ensure that experimental manipulations continue to be a valuable approach for the scientifically based management of river systems. [ABSTRACT FROM AUTHOR]

Abstract: Polymer nanocomposites offer a basis for the design and manufacture composite materials with greatly enhanced properties at relatively low volume fractions of the included phase. One underlying mechanism, thought to contribute to these properties is the presence of an interfacial region, ∼15nm thick, between the polymer matrix and included particles. The size of the interface makes relatively little contribution to the effective properties of composites with micro-sized particles but, because its thickness is comparable to the size of the nanoscaled included phase, its potential impact within nanocomposites is much greater. In particular, percolated nano-microstructures may result at volume fractions below theoretical thresholds, due to connectivity achieved through rod-interface-rod, or ‘pseudo-percolation’, contact. In this work the influence of the interface layer is incorporated into estimates of critical volume fraction through an excluded volume model. Results show a significant reduction in the range of critical volume fractions. These values are incorporated into a mean-field micromechanics model to illustrate mechanical percolation through changes in predicted effective elastic composite properties. [Copyright &y& Elsevier]

In mountains, environmental gradients are steep in both terrestrial and aquatic systems, and climate change is causing upward shifts of physical and biological features of these gradients. Glacial streams are an interesting system to evaluate such shifts both because streams have a linear nature (for simplicity of analysis), and because the stream habitat will at least temporarily lengthen as it follows receding glaciers upward. The Tschierva Glacier, Swiss Alps, receded 482 m upstream from 1997 to 2008. We tested the null hypothesis that the physical and biological stream gradient below this glacier maintained the same structure between these time periods, but simply shifted upward following the glacial source. We compared longitudinal patterns of water temperature and zoobenthic community structure in 1997 and 2007-2008 during three seasons (spring, summer, fall) along the uppermost ca. 5 stream km. Upward shifts were evident, including colonization of the newly exposed stream reaches by cold-adapted taxa, and the appearance in 2007/2008 of four lower-altitude species that were previously absent. Overall, however, results rejected the null hypothesis, instead revealing significant changes in gradient structures. These included a more steeply increasing temperature profile downstream of the glacier and increased amplitude of seasonal community turnover in 2007/2008 vs. 1997. Long-term (1955-2007) flow records revealed increasing short-term and seasonal hydrologic variability, which might have influenced the increased intra-annual community variability. The steepening of the temperature gradient was likely caused by a warming lake-outlet tributary upon which glacial influence was diminished between 1997 and 2007/2008. These results suggest that upward-shifting gradients in glacial streams can involve complex interactions with other landscape elements and that local-scale climate response can progress even more rapidly than the rate of glacial recession. [ABSTRACT FROM AUTHOR]

The article presents a study which evaluates the long-term effects of floods on a regulated river. With this, the authors hypothesized that sequential floods over time would cause a regime shift in the ecosystem. The floods resulted in little change in the physicochemistry of the river, although particulate organic carbon and particulate phosphorus were lower after the floods. They eliminated moss cover on bed sediments within the first year of flooding and maintained low periphyton biomass and benthic organic matter after the third year of flooding. Experimental floods are being implemented on regulated rivers throughout the world to improve their ecological integrity to simulate the natural flow regime.

The field of microbial ecology has grown tremendously with the advent of novel molecular techniques, allowing the study of uncultured microbes in the environment, and producing a paradigm shift: now, rather than using bacteria cultures for evaluating cell-specific questions, researchers use RNA and DNA techniques to examine more broad-based ecological and evolutionary constructs such as biogeography and the long-debated biological species concept. Recent work has begun to relate bacteria functional genes to ecosystem processes and functioning, thereby enabling a better understanding of the interactive role of bacteria in different and often-changing environments. The field continues to mature and will most likely make substantial contributions in the future with additional efforts that include metagenomics and genomics. Here we review progress in the application of molecular techniques to study microbial communities in freshwater environments. [ABSTRACT FROM AUTHOR]

Examine the effect of nutrient regime on periphyton community development in large rivers. Accounts on the structure of benthic algal assemblages; Physical and chemical characteristics of the study sites; Decrease of the concentration of nutrient treatments.

This study assessed the effect of nutrient enrichment on organic matter breakdown in an alpine springbrook, using alder leaf packs to which phosphorus and nitrogen were added in the form of slow-release fertilizer briquettes. The breakdown of leaf packs with nutrients added (k=0.0284 day–1) was significantly faster than that of unfertilized packs (k=0.0137 day–1), resulting in a 30% higher mass loss after 42 days. Unfertilized leaves enclosed in fine-mesh bags broke down at an even slower rate (k=0.0062 day–1). Phosphorus and nitrogen concentrations were initially higher in leaf packs with nutrients added, but this difference disappeared within 3 weeks. Fungal biomass developing in decomposing leaves was substantial (c. 55 mg dry mass per 1 g leaf dry mass) although similar between fertilized and unfertilized packs, as was the sporulation activity of aquatic hyphomycetes. There was a significantly greater number and higher biomass of macroinvertebrates (shredding nemourid stoneflies in particular) on the fertilized packs, suggesting that the increased leaf mass loss was brought about by shredder feeding. [ABSTRACT FROM AUTHOR]

Exploitation of hydropower potential in alpine areas undermines the ecological integrity of rivers. Damming and water abstraction substantially alter the physical habitat template of rivers, with strong repercussions on aquatic communities and their resources. Tools are needed to predict and manage the consequences of these alterations on the structure and functioning of macroinvertebrate communities and resource availability in alpine streams. We developed habitat preference models for taxa, functional feeding guilds, and organic resources to quantify the effects of discharge alteration on macroinvertebrate communities in two alpine streams. Our physical habitat model related an indirect measure of bottom hydraulic forces (FST hemispheres) to the distribution of macroinvertebrate taxa and their resources. We observed that flow-dependent habitat availability for macroinvertebrate communities generally decreased with increasing water abstraction. We were able to relate these changes to near-bed hydraulic conditions. Our results suggest, however, the existence of upper discharge thresholds delimiting optimal habitat conditions for taxa. In contrast, we found weak effects of near-bed hydraulic conditions on resource distribution. Overall, our findings contribute towards predicting the impacts of water abstraction on macroinvertebrate communities in small alpine streams and the benefits of baseflow restoration. [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]

River reaches downstream dams where a constant residual flow discharge is imposed, often lack sediment supply and periodic inundation due to the absence of natural flood events. In this study, a two-year return flood was released from an upstream reservoir and combined with sediment replenishment to enhance instream habitat conditions downstream of Rossens hydropower dam on the Sarine River in western Switzerland. Sediment replenishment consisted of four sediment deposits distributed as alternate bars along the river banks, a solution which was previously tested in laboratory. The morphological evolution of the replenishment and of the downstream riverbed were surveyed including pre- and post-flood topography. A hydro-morphological index to evaluate the quality of riverine habitats, based on the variability of flow depth and flow velocity in the analyzed reach, was investigated. The combination of the artificial flood with sediment replenishment proved to be a robust measure to supply a river with sediment and to enhance hydraulic habitat suitability. [ABSTRACT FROM AUTHOR]