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Hydropeaking operation leads to fluctuations in wetted area between base and peak flow and increases discharge-related hydraulic forces (e.g., flow velocity). These processes promote macroinvertebrate drift and stranding, often affecting benthic abundance and biomass. Our field experimental study – conducted in three hydropeaking-regulated Swiss rivers – aimed to quantify (i) the short-term effects of the combined increase in flow amplitude and up-ramping rate based on macroinvertebrate drift and stranding, as well as (ii) long-term effects based on the established community composition. Hydropeaking led to increased macroinvertebrate drift compared to base flow and to unaffected residual flow reaches. Moreover, stranding of macroinvertebrates was positively related to drift, especially during the up-ramping phase. Flow velocity and up-ramping rate were identified as major determinants for macroinvertebrate drift, while flow ratio and down-ramping rate for stranding. Particularly high sensitivity towards HP was found for Limnephilidae, whereas Heptageniidae seemed to be resistant in respect to short and long-term hydropeaking effects. In the long-term, hydropeaking did not considerably reduce benthic density of most taxa, especially of some highly resistant and resilient taxa such as Chironomidae and Baetidae, which dominated the community composition even though they showed comparably high drift and stranding responses. Therefore, we argue that high passive drift and/or stranding, especially of individual-rich taxa, does not necessarily indicate strong hydropeaking sensitivity. Finally, our results demonstrate the necessity to consider the differences in river-specific morphological complexity and hydropeaking intensity, since these factors strongly influence the community composition and short-term drift and stranding response of macroinvertebrates to hydropower pressure.

Hydropeaking has received increasing attention in the last years, but many knowledge gaps remain, potentially hampering effective policy and management efforts in rivers under such type of hydropower production. In this study, we collected open hydropeaking research questions from over 200 experts in river science, practice, and policy across the globe using an online survey available in five languages. We used a systematic method of determining expert consensus (Delphi method) to identify 100 core questions related to the following thematic fields: (i) hydrology, (ii) physico-chemical properties of water, (iii) river morphology and sedimentology, (iv) ecology and biology, (v) socio-economics and energy markets, (vi) policy and regulation, as well as (vii) management and mitigation measures. The consensus list of questions shall inform and guide researchers in focusing their efforts to foster a better science-policy interface, thereby improving the sustainability of peak-operating hydropower in a variety of settings.

The hydrological regime of many alpine rivers is heavily altered due hydroelectric power generation. Hydropeaking operation produces frequent and irregular discharge fluctuations. Depending on the operational changes of flow amplitude and/or upramping rate as well as on river morphology, hydropeaking can lead to quick and strong variations in hydraulic stress affecting stream invertebrates and causing increased drift. In the present flume experimental study, we analyzed trait-specific drift reactions to single and combined effects of increased flow amplitude and upramping rate. We analyzed taxa according to their hydraulic habitat preference and flow exposure, as these traits seem to be indicative toward hydropeaking. The results show that the sudden increase in discharge and related flow velocity led to increased macroinvertebrate drift proportions in hydropeaking treatments, which differed significantly to parallel control runs (mean drift proportion in all hydropeaking setups: 13% compared to 5% in controls). Increasing flow amplitudes led to an increase in drift for most taxa and traits. This was particularly significant for taxa associated with lentic areas. The effect of the up-ramping rate on macroinvertebrate drift was nonsignificant but showed strong interactive effects with the flow amplitude, especially for taxa dwelling on the substrate surface. Our results therefore indicate that dischargerelated parameters, such as flow velocity, primarily affect macroinvertebrate drift and the importance of the up-ramping rate increases, if certain discharge-related thresholds are exceeded. Vice versa, a reduction of the up-ramping rate at hydropeaking events with high flow amplitudes may reduce the effect on macroinvertebrate drift. Flow-exposed (surface) and flow-sensitive (lentic) taxa showed distinct drift reactions following hydropeaking treatments, which were significantly higher compared to effects on taxa associated to lotic and interstital habitats. Therefore, we conclude that both traits (hydraulic and vertical habitat preference) have proven as promising for analyzing hydropeaking effects. The trait classifications should be extended to a higher number of taxa and to different life stages as these may show different drift patterns.

An increase in the demand for renewable energy is driving hydropower development and its integration with variable renewable energy sources. When hydropower is produced flexibly from hydropower plants, it causes rapid and frequent artificial flow fluctuations in rivers, a phenomenon known as hydropeaking. Hydropeaking and associated hydrological alterations cause multiple impacts on riverine habitats with cascading effects on ecosystem functioning and structure. Given the significance of its ecological and socio-economic implications, mitigation of hydropeaking requires an inter- and transdisciplinary approach. An interdisciplinary network called HyPeak has been conceived to enrich international research initiatives and support hydropower planning and policy. HyPeak has been founded based on exchange and networking activities linking scientists from several countries where hydropeaking has been widespread for decades and numerous studies dedicated to the topic have been carried out. HyPeak aims to integrate members from other countries and continents in which hydropower production plays a relevant role, and grow to be a reference group that provides expert advice on the topic to policy-makers, as well as researchers, stakeholders, and practitioners in the field of hydropeaking.

The present chapter provides a comprehensive overview about the biogeographic setting and environmental state of 166 European rivers, stretching from the Atlantic coast to Turkey and the Ural mountains, and identifies future research and management challenges for these rivers. European rivers exhibit a long history of human modification, with very few free-flowing rivers remaining. Hence, the conservation of the last wild rivers is of utmost priority. Moreover, the UN Decade on Ecosystem Restoration offers major opportunities to restore regulated rivers across the entire continent.

Storage hydropower plants, which are an important component of energy production in Switzerland, can lead to hydro- and thermopeaking, affecting river habitats and organisms. In this study, we developed an approach for integrating water temperature simulations into a habitat model to assess the impact of both hydro- and thermopeaking on the availability of suitable fish habitats. We focused on the habitat requirements of juvenile brown trout (Salmo trutta) in a semi-natural braided floodplain along the Moesa River (Southern Switzerland) in early summer. First, we defined different scenarios (with and without hydropeaking) based on the local hydrological and meteorological conditions. Second, we used a two-dimensional depth-averaged hydro- and thermodynamic model to simulate the spatial distributions of water depth, flow velocity, and water temperature. Third, we applied generalized preference curves for juvenile brown trout to identify hydraulically suitable habitats, and developed a new index to assess the availability of thermally suitable habitats. Finally, we quantified the extent to which hydraulically and thermally suitable habitats overlap in space and time. During both base and peak flow phases, most of the hydraulically and thermally suitable habitats are located in the side channels. High flow conditions combined with strong cold-thermopeaking lead to a higher thermal heterogeneity. However, disconnected habitats originate in the dewatering zone, increasing the risk of stranding as well as thermal stress. By helping to better understand the effects of thermopeaking on the availability of fish habitats, our approach could contribute to the design and evaluation of ecological restoration in hydropeaking rivers., River Research and Applications, 39 (3), ISSN:1535-1459, ISSN:1535-1467

Landscape perspectives in riverine ecology have been undertaken increasingly in the last 30 years, leading aquatic ecologists to develop a diverse set of approaches for conceptualizing, mapping and understanding ‘riverscapes’. Spatiotemporally explicit perspectives of rivers and their biota nested within the socio-ecological landscape now provide guiding principles and approaches in inland fisheries and watershed management. During the last two decades, scientific literature on riverscapes has increased rapidly, indicating that the term and associated approaches are serving an important purpose in freshwater science and management. We trace the origins and theoretical foundations of riverscape perspectives and approaches and examine trends in the published literature to assess the state of the science and demonstrate how they are being applied to address recent challenges in the management of riverine ecosystems. We focus on approaches for studying and visualizing rivers and streams with remote sensing, modelling and sampling designs that enable pattern detection as seen from above (e.g. river channel, floodplain, and riparian areas) but also into the water itself (e.g. aquatic organisms and the aqueous environment). Key concepts from landscape ecology that are central to riverscape approaches are heterogeneity, scale (resolution, extent and scope) and connectivity (structural and functional), which underpin spatial and temporal aspects of study design, data collection and analysis. Mapping of physical and biological characteristics of rivers and floodplains with high-resolution, spatially intensive techniques improves understanding of the causes and ecological consequences of spatial patterns at multiple scales. This information is crucial for managing river ecosystems, especially for the successful implementation of conservation, restoration and monitoring programs. Recent advances in remote sensing, field-sampling approaches and geospatial technology are making it increasingly feasible to collect high-resolution data over larger scales in space and time. We highlight challenges and opportunities and discuss future avenues of research with emerging tools that can potentially help to overcome obstacles to collecting, analysing and displaying these data. This synthesis is intended to help researchers and resource managers understand and apply these concepts and approaches to address real-world problems in freshwater management.

This is the peer reviewed version which has been published in final form at https://doi.org/10.1002/esp.5017 . This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Use of Self-Archived Versions. Hydropower alteration of the natural flow and sediment regime can severely degrade hydromorphology, thereby threatening biodiversity and overall ecosystem processes of rivers and their floodplains. Using sequences of aerial images, we quantified seven decades (1938/1942–2013) of spatiotemporal changes in channel and floodplain morphology, as well as changes in the physical habitats, of three floodplain river reaches of the Swiss pre‐Alps, two hydropower‐regulated and one near‐natural. In the Sarine River floodplain, within the first decades of hydropower impairment, the magnitude and frequency of flood events (Q2, Q10, Q30) decreased substantially. As a result, the area of pioneer floodplain habitats that depend on flood activity and sediment dynamic, such as bare sediments, decreased dramatically by approximately 95%. However, by 2013 vegetated areas had generally increased in comparison to the pre‐regulation period in 1943, indicating general vegetative colonization. Between 1943 and 2013, the active channel underwent essential narrowing (up to 62% width reduction in the residual flow reach) and habitat turnover rates were very low (5% of the total floodplain area changed habitat type five to six times). In contrast, from the 1950s onwards, the near‐natural floodplain of the Sense River experienced recurrent narrowing and widening, and frequent changes between bare and vegetated areas, reflecting the shifting habitat mosaic concept typical for natural floodplains. In the three reaches investigated, we found that the active floodplain width and erosion of vegetated areas were primarily controlled by medium to large floods (Q10, Q30), which combined with reduced time intervals between ordinary floods ≥ Q2 most likely mobilized streambed sediments and limited the ability of vegetation to establish itself on bare gravel bars within the parafluvial zone. These findings can contribute to restoration action plans such as controlled flooding and sediment replenishments in the Sarine and other floodplain rivers of the Alps.

Floodplain areas belong to the most diverse, dynamic and complex ecological habitats of the terrestrial portion of the Earth. Spatial and temporal quantification of floodplain dynamics is needed for assessing the impacts of hydromorphological controls on river ecosystems. However, estimation of land cover dynamics in a post-classification setting is hindered by a high contribution of classification errors. A possible solution relies on the selection of specific information of the change map, instead of increasing the overall classification accuracy. In this study, we analyze the capabilities of Unmanned Aerial Systems (UAS), the associated classification processes and their respective accuracies to extract a robust estimate of floodplain dynamics. We show that an estimation of dynamics should be built on specific land cover interfaces to be robust against classification errors and should include specific features depending on the season-sensor coupling. We use five different sets of features and determine the optimal combination to use information largely based on blue and infrared bands with the support of texture and point cloud metrics at leaf-off conditions. In this post-classification setting, the best observation of dynamics can be achieved by focusing on the gravel-water interface. The semi-supervised approach generated error of 10% of observed changes along highly dynamic reaches using these two land cover classes. The results show that a robust quantification of floodplain land cover dynamics can be achieved by high-resolution remote sensing.

Copyright by the Ecological Society of America Passive acoustic monitoring is gaining popularity in ecology as a practical and non-invasive approach to surveying ecosystems. This technique is increasingly being used to monitor terrestrial systems, particularly bird populations, given that it can help to track temporal dynamics of populations and ecosystem health without the need for expensive resampling. We suggest that underwater acoustic monitoring presents a viable, non-invasive, and largely unexplored approach to monitoring freshwater ecosystems, yielding information about three key ecological elements of aquatic environments – (1) fishes, (2) macroinvertebrates, and (3) physicochemical processes – as well as providing data on anthropogenic noise levels. We survey the literature on this approach, which is substantial but scattered across disciplines, and call for more cross-disciplinary work on recording and analysis techniques. We also discuss technical issues and knowledge gaps, including background noise, spatiotemporal variation, and the need for centralized reference collection repositories. These challenges need to be overcome before the full potential of passive acoustics in dynamic detection of biophysical processes can be realized and used to inform conservation practitioners and managers.

High-head storage hydropower is deemed to be the ideal renewable energy source in Alpine regions to meet the increasing demand for daily peak electrical energy. However, this mode of operation - called hydropeaking - can imply severe hydrological and hydromorphological consequences for river ecosystems, affecting fish populations by e.g. drift and stranding of young life stages. Several fish-stranding experiments using physical models have been performed in the past, but until now very little is known about influences of time of day or gravel bank heterogeneity. We performed experiments during late summer 2013 with juvenile European grayling ( Thymallus thymallus ) (mean length: 53 mm) in a nature-like experimental channel enabling hydropeaking simulations. In the first experiments (n = 21) we observed relative drift and stranding rates for a single hydropeaking event focusing on the effect of time of day on a homogenous gravel bank. The second test series (n = 15) focused on two dewatering potholes installed as potential traps. Additional experiments (n = 6) were done with a reduced downramping rate to gain information about potential mitigation effects on stranding risk. During daytime and decreasing water level, we observed low drift rates of 15% and stranding rates below 5% in dewatering potholes and on homogenous gravel banks. However, in the presence of dewatering potholes, nighttime drift rates were about three times and stranding rates about ten times higher than on the homogenous gravel bank. A lowered downramping rate reduced drift to about a quarter and almost eliminated nocturnal stranding risk. These results might be used to effectively regulate water releases from high-head storage hydropower plants in a more suitable way for sensitive life stages of fish. Reducing the downramping rate or shifting peaks to daytime can reduce negative effects of hydropeaking in consideration of the morphological character of affected rivers.

Im Zuge der Umsetzung der Ziele der WRRL sind in den nächsten Jahren Massnahmen zur Reduktion des Schwall-Sunk-Einflusses gefordert. Diese werden hydrologische, morphologische, aber mitunter auch sedimentologische Komponenten beinhalten müssen. Aufbauend auf Schwalluntersuchungen am Alpenrhein und unterschiedlichen Fließgewässern in Österreich wird im vorliegenden Beitrag eine Diskussion bestimmter abiotischer Kriterien durchgeführt. Mit dem Ziel, eine zielgerichtete Implementierung von Sanierungsmassnahmen zu ermöglichen.

The overpresence of fine sediment and fine sediment infiltration (FSI) in the aquatic environment of rivers are of increasing importance due to their limiting effects on habitat quality and use. The habitats of both macroinvertebrates and fish, especially spawning sites, can be negatively affected. More recently, hydropeaking has been mentioned as a driving factor in fine sediment dynamics and FSI in gravel-bed rivers. The primary aim of the present study was to quantify FSI in the vertical stratigraphy of alpine rivers with hydropeaking flow regimes in order to identify possible differences in FSI between the permanently wetted area (during base and peak flows) and the so-called dewatering areas, which are only inundated during peak flows. Moreover, we assessed whether the discharge ratio between base and peak flow is able to explain the magnitude of FSI. To address these aims, freeze-core samples were taken in eight different alpine river catchments. The results showed significant differences in the vertical stratification of FSI between the permanently wetted area during base flow and the dewatering sites. Surface clogging occurred only in the dewatering areas, with decreasing percentages of fine sediments associated with increasing core depths. In contrast, permanently wetted areas contained little or no fine sediment concentrations on the surface of the river bed. Furthermore, no statistical relationship was observed between the magnitude of hydropeaking and the sampled FSI rate. A repeated survey of FSI in the gravel matrix revealed the importance of de-clogging caused by flooding and the importance of FSI in the aquatic environment, especially in the initial stages of riparian vegetation establishment.

Im vorliegenden Artikel wird versucht, den aktuellen Wissensstand zu den Auswirkungen von Schwall und Sunk auf die aquatische Gemeinschaft zusammenzufassen. Künstliche Pegelschwankungen verursachen kurz- und langfristige Auswirkungen auf die Fließgewässerökologie. Auf Basis von Indikatoren lassen sich diese Auswirkungen bis zu einem gewissen Grad abschätzen und daraus möglichst effiziente Sanierungsmassnahmen ableiten. Abschließend wird der Stand der Schwallsanierung in der Schweiz kurz beschrieben.

Im Rahmen der Entleerung des Stausees Raterichsboden (Berner Oberland, Schweiz) wurden verschiedene gewasserokologische Schutzmasnahmen realisiert. Fur den Erhalt des Seeforellenjahrgangs 2014/15 entwickelte die Fachstelle Okologie der Kraftwerke Oberhasli AG ein mobiles fischschonendes Leitsystem fur aufsteigendeWandersalmoniden, um die laichbereiten Seeforellen in ein Nebengewasser umzuleiten. Im Praxistest konnte sowohl die okologische Funktionsfahigkeit als auch die Hochwassersicherheit nachgewiesen werden. Das Leitsystem konnte auch fur andere fischokologische Fragestellungen adaptiert werden.

New Swiss legislation obligates hydropower plant owners to reduce detrimental impacts on rivers ecosystems caused by hydropeaking. We used a case study in the Swiss Alps (hydropower company Kraftwerke Oberhasli AG) to develop an efficient and successful procedure for the ecological evaluation of such impacts, and to predict the effects of possible mitigation measures. We evaluated the following scenarios using 12 biotic and abiotic indicators: the pre-mitigation scenario (i.e. current state), the future scenario with increased turbine capacity but without mitigation measures, and future scenarios with increased turbine capacity and four alternative mitigation measures. The evaluation was based on representative hydrographs and quantitative or qualitative prediction of the indicators. Despite uncertainties in the ecological responses and the future operation mode of the hydropower plant, the procedure allowed the most appropriate mitigation measure to be identified. This measure combines a basin and a cavern at a total retention volume of 80,000 m3, allowing for substantial dampening in the flow falling and ramping rates and in turn considerable reduction in stranding risk for juvenile trout and in macroinvertebrate drift. In general, this retention volume had the greatest predicted ecological benefit and can also, to some extent, compensate for possible modifications in the hydropower operation regime in the future, e.g. due to climate change, changes in the energy market, and changes in river morphology. Furthermore, it also allows for more specific seasonal regulations of retention volume during ecologically sensitive periods (e.g. fish spawning seasons). Overall experience gained from our case study is expected to support other hydropeaking mitigation projects.

With 7 figures Abstract: Turbulent flow in rivers and the associated movement of sediment creates unique underwater sound- scapes that can be measured passively with hydrophones while Acoustic Doppler Profilers (ADP) are an active form of hydroacoustic sampling that can be used to provide a surrogate measurement of Apparent Bedload Veloc- ity (ABV). In our study, longitudinal profiles of ADP and sound were simultaneously measured, while floating the river in a raft on the Nyack Floodplain of the Middle Fork of the Flathead River, USA during flood events exceeding bankfull conditions. In addition, similar measurements were carried out on the Kootenai River during a prescribed flood release aimed at mobilizing gravel bed sediment to positively impact White Sturgeon spawn- ing. Both data sets revealed spatially explicit zones of coherent ABV and bedload intensity (sound) over the two 12 km river segments. The ability to remotely and in real-time assess bedload transport for large gravel-bed rivers, on the floodplain scale, is a missing piece of information important for basic ecological understanding and applied science, specifically management decisions regarding regulated rivers worldwide. With these data sets we dem- onstrate a new methodology for rapid real-time spatial surveying of bedload transport in large gravel-bed rivers.

Hydropower plants are an important source of renewable energy. In the near future, high-head storage hydropower plants will gain further importance as a key element of large-scale electricity production systems. However, these power plants can cause hydropeaking which is characterized by intense unnatural discharge fluctuations in downstream river reaches. Consequences on environmental conditions in these sections are diverse and include changes to the hydrology, hydraulics and sediment regime on very short time scales. These altered conditions affect river ecosystems and biota, for instance due to drift and stranding of fishes and invertebrates. Several structural and operational measures exist to mitigate hydropeaking and the adverse effects on ecosystems, but estimating and predicting their ecological benefit remains challenging. We developed a conceptual framework to support the ecological evaluation of hydropeaking mitigation measures based on current mitigation projects in Switzerland and the scientific literature. We refined this framework with an international panel of hydropeaking experts. The framework is based on a set of indicators, which covers all hydrological phases of hydropeaking and the most important affected abiotic and biotic processes. Effects of mitigation measures on these indicators can be predicted quantitatively using prediction tools such as discharge scenarios and numerical habitat models. Our framework allows a comparison of hydropeaking effects among alternative mitigation measures, to the pre-mitigation situation, and to reference river sections. We further identified key issues that should be addressed to increase the efficiency of current and future projects. They include the spatial and temporal context of mitigation projects, the interactions of river morphology with hydropeaking effects, and the role of appropriate monitoring to evaluate the success of mitigation projects.

Schwall und Sunk wurde als eine der wesentlichen anthropogenen Beeinträchtigungen alpiner Fliessgewässer ausgewiesen und vielfach als prioritär für eine Sanierung definiert. Mitunter sind aber Mehrfachbelastungen in den alpinen Fliessgewässern vorhanden, deren negative Auswirkungen sich auf das Gewässerökosystem überlagern können. Ziel des vorliegenden Beitrags ist es, anhand von Untersuchungen am Alpenrhein und an einigen ausgewählten Fallbeispielen aus Österreich wesentliche Komponenten für eine zielgerichtete Massnahmenplanung zur Sanierung von Schwallstrecken aufzuzeigen.

Im Rahmen eines Ausbauprojekts wird die heute maximal mögliche Wasserrückgabe in die Hasliaare von 70 m³/s auf künftig 95 m³/s erhöht. Damit werden die Effekte der künstlichen Pegelschwankungen verschärft. Im Vorfeld wurde daher die gewässerökologische Situation eingehend untersucht und eine ökologische Beurteilung des heutigen Zustands und für künftige Zustände (Ausbau mit verschiedenen Schwalldämpfungsmaßnahmen) durchgeführt. Seit 2013 wird zwischen Kraftwerk und Wasserrückgabe ein Zwischenspeicher (Beruhigungsbecken und Stollen) mit 80 000 m³ Volumen realisiert.

River floodplains are heterogeneous landscapes composed of a mosaic of aquatic and terrestrial habitats. While flow has frequently been considered as a master variable that controls aquatic biodiversity and species behavior in river floodplains, little is known about thermal heterogeneity and its effect on aquatic biota in complex landscapes. However, quantifying thermal patch dynamics at the river floodplain scale remains a challenging task. In this study, we applied airborne thermal infrared (TIR) imagery to characterize spatial thermal heterogeneity under high (March 2010) and mean (July 2010) flow conditions in a 347.5 ha lowland river floodplain (Oder River, Germany). Concurrently, we electro-fished all major floodplain water bodies (main channel, side channel, and permanently connected ponds) to identify the composition of associated fish assemblages. In addition, we deployed temperature loggers from March to July across the entire range of floodplain water bodies to assess seasonal temperature patterns at 20 min intervals. Under both flow conditions, the TIR imagery revealed a complex mosaic of thermal patches across the floodplain. Cumulative degree-days and average and maximum temperatures were the main variables that thermally differentiated individual water bodies. The water body types delineated based on spatial and seasonal thermal signatures also contained distinct fish assemblages. Distinct temperature gradients at the floodplain scale and both within and across distinct water body types were resolved with airborne thermal data, providing a fully spatial and concurrently available temperature mosaic. A delay in response of fish distribution to a strong thermal gradient recorded in spring, that has never been predicted or observed elsewhere, could be assessed by the use of TIR imagery. This study demonstrates the potential of airborne remotely sensed TIR imagery as a non-invasive method for detecting and quantifying spatial heterogeneity and ecologically relevant temperature gradients in complex landscapes, thereby facilitating the “up-scaling” of ecosystem processes to the landscape scale and expanding current understanding of fish behavior.

The patterns of underwater acoustic signals, called soundscapes, were characterized at the river segment scale. A hydrophone was mounted onto the frame of an inflatable multihull raft and held just below the water's surface while floating for 5–24 km to continuously record acoustic signals along the longitudinal axis of the main channel (thalweg) of five hydro-geomorphologically different river segments in Italy, Switzerland, and the United States of America. The river segments could be clearly distinguished based on sound pressure level (SPL), sound variability, and the spatial organization of the acoustic signal (10 octave bands: 0.0315–16 kHz). The spatial soundscape diversity between river segments was most likely related to the organization of turbulence along the segment length (distance between rapids) and to sound source (hydraulic turbulence or local sediment transport). Hydraulically and morphologically heterogeneous segments revealed more complex soundscapes than more homogeneous ones. Higher flow levels resulted in higher SPLs over most frequency bands. The acoustic variability of single octave bands increased from base to intermediate flow, while it decreased from intermediate to bankfull flow. The pulsating sound produced by breaking and reforming turbulent waves on flow obstacles was associated with SPL peaks and high acoustic variability in midrange frequency bands (0.063–0.5 kHz), whereas high-frequency SPLs (1–16 kHz) were related to particle collisions during streambed sediment transport. Underwater soundscapes provide an independent measure to quantify habitat heterogeneity and spatial habitat organization that can be applied to river corridors at the segment scale.

River floodplains are composed of a shifting mosaic of aquatic and terrestrial habitats. Each habitat type exhibits distinct environmental and ecological properties. Temperature is a key property driving ecological processes and controlling the composition and distribution of biota. However, given the size and complexity of floodplains, ground surveys based on point measurements are spatially limited. In this study, we applied thermal infrared (IR) imagery to quantify surface temperature patterns at 12–15 min intervals over 24 h cycles in two near-natural Alpine river floodplains (Roseg, Tagliamento). Furthermore, vertical temperature distribution was measured at 3–5 min intervals in unsaturated gravel sediment deposits (at 1 cm distances; 0–29 cm depth). Each habitat type exhibited a distinct thermal signature creating a complex thermal mosaic. The diel temperature pulse and maximum daily temperature were the main thermal components that differentiated habitat types. In both floodplains, exposed gravel sediments exhibited the highest diel pulse (up to 23°C), whereas in aquatic habitats the pulse was as low as 11°C (main channel in the Roseg floodplain). In the unsaturated gravel sediment deposits, the maximum diel kinetic temperature pulse ranged from 40.4°C (sediment surface) to 2.7°C (29 cm sediment depth). Vertically, the spatiotemporal variation of temperature was about as high as horizontally across the entire floodplain surface. This study emphasized that remotely sensed thermal IR imagery provides a powerful non-invasive method to quantitatively assess thermal heterogeneity of complex aquatic and terrestrial ecosystems at a resolution required to understand ecosystem processes and the distribution of biota.

Aquatic river habitat types have been characterized and classified for over five decades based on hydrogeomorphic and ecological variables. However, few studies considered the generation of underwater sound as a unique property of aquatic habitats, and therefore as a potential information source for freshwater organisms. In this study, five common habitat types along 12 rivers in Switzerland (six replicates per habitat type) were acoustically compared. Acoustic signals were recorded by submerging two parallel hydrophones and were analysed by calculating the energetic mean as well as the temporal variance of ten octave bands (31·5 Hz–16 kHz). Concurrently, each habitat type was characterized by hydraulic and geomorphic variables, respectively. The average relative roughness, velocity-to-depth ratio, and Froude number explained most of the variance of the acoustic signals created in different habitat types. The average relative roughness predominantly affected middle frequencies (63 Hz–1 kHz), while streambed sediment transport increased high-frequency sound pressure levels (2–16 kHz) as well as the temporal variability of the recorded signal. Each aquatic habitat type exhibited a distinct acoustic signature or soundscape. These soundscapes may be a crucial information source for many freshwater organisms about their riverine environment. Copyright © 2010 John Wiley & Sons, Ltd.

The hydrogeomorphology and ecology of rivers and streams has been subject of intensive research for many decades. However, hydraulically-generated acoustics have been mostly neglected, even though this physical attribute is a robust signal in fluvial ecosystems. Physical generated underwater sound can be used to quantify hydro-geomorphic processes, to differentiate among aquatic habitat types, and it has implications on the behavior of organisms. In this study, acoustic signals were quantified in a flume by varying hydro-geomorphic drivers and the related turbulence and bubble formation. The acoustic signals were recorded using two hydrophones and analyzed using a signal processing software, over 31 third-octave bands (20 Hz–20 kHz), and then combined in 10 octave bands. The analytical method allowed for a major improvement of the signal-to-noise ratio, therefore greatly reducing the uncertainty in our analyses. Water velocity, relative submergence, and flow obstructions were manipulated in the flume and the resultant acoustic signals recorded. Increasing relative submergence ratio and water velocity were important for reaching a turbulence threshold above which distinct sound levels were generated. Increases in water velocity resulted in increased sound levels over a wide range of frequencies. The increases in sound levels due to relative submergence of obstacles were most pronounced in midrange frequencies (125 Hz–2 kHz). Flow obstructions in running waters created turbulence and air bubble formation, which again produced specific sound signatures.

Erworben im Rahmen der Schweizer Nationallizenzen (http://www.nationallizenzen.ch), Relatively little is known regarding the extent of intermittent streams or the general ecology of headwaters in alpine catchments with glacial influence. This study quantified the contribution of intermittent streams to the total length of the stream network along with an ecological assessment during spring-summer of headwater streams (higher than 1,900 m above sea level) in the Val Roseg, a high Alpine glacial catchment. Stream network mapping revealed that ca. 90 % (76.8 km) of the drainage network consisted of intermittent streams. Glacier-fed headwaters experienced diel surface flows in late spring and summer, most going dry during the night due to reduced glacial inputs. In contrast, groundwater-fed streams often went dry in summer with the contraction of groundwater and other subsurface inputs. A principal components analysis of physico-chemical characteristics revealed headwaters to be primarily glacial-fed (kryal), groundwater-fed (krenal), or having a mixed water source. Although quite variable, periphyton biomass reached high levels (ca. 40 mg m-2 chla, 10 g m-2 AFDM) by late spring in most headwaters. Organic matter in transport (seston) ranged from 0.03 to 0.09 mg L-1 mostly consisting of fine particulate organic matter (FPOM: 33–76 %). Hyporheic sediment respiration rates varied considerably, ranging from 0.005 to 0.126 mg O2 h-1 kg-1 sediment and primarily related to the amount of loosely attached organic matter. These results indicate that intermittent streams are predominant in alpine landscapes, comprising mostly 1st to 2nd order systems, and that ecosystem properties vary substantially among headwater streams likely in relation to annual/daily changes in flow and water source. Such headwaters may contribute strongly to the production, processing and transport of organic matter to downstream waters, especially in light of the expected increase in intermittent streams in alpine catchments experiencing rapid glacial recession.

Publisher Summary Rivers recognize no political boundaries. This is particularly true for Europe, which has over 150 transboundary rivers. For example, the Danube is the 29th longest river globally and it drains parts of 19 countries and 10 ecoregions. Further, 8 of the 10 largest catchments in Europe are in the eastern plains of Russia and the Ukraine and information on their present status is highly limited. Europe also has a long history in river training with most rivers being severely fragmented, channelized, and polluted. The European Union launched an ambitious program called the Water Framework Directive (WFD), which requires a catchment management plan for all major European rivers for achieving “good ecological status” by 2015. This chapter provides a comprehensive overview of all major European catchments included in the book, starting with the bio-geographic setting, with an emphasis on physiography, hydrology, ecology/biodiversity, and human impacts.