Article

Effects of hydro- and thermopeaking on benthic macroinvertebrate drift

Authors:
  • Hessisches Ministerium für Umwelt, Klimaschutz, Landwirtschaft und Verbraucherschutz
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Abstract

The operation of storage hydropower plants is commonly linked to frequent fluctuations in discharge and water level (hydropeaking) of downstream river stretches and is often accompanied by cooling or warming of the water body downstream (cold or warm thermopeaking, respectively). The objective of this study is to assess the single and combined effects of hydropeaking and cold thermopeaking on the drift of selected aquatic macroinvertebrates in experimental flumes. The study specifically aims to (1) investigate the macroinvertebrate drift induced by hydropeaking, (2) identify taxon-specific drift patterns following combined hydropeaking and cold thermopeaking and (3) quantify diurnal drift differences under both impact types. Overall, hydropeaking induced significantly higher drift rates of most macroinvertebrate taxa. Combined hydropeaking and cold thermopeaking, however, revealed reduced total drift rates, however with strong taxon-specific response patterns. Hydropeaking during night led to significantly higher drift rates than during daytime, while in combination with thermopeaking the same trend was observable, although insignificant. Taxon-specific analysis revealed lower drift rates following hydropeaking for rheophilic and interstitial taxa (e.g. . Leuctra sp., . Hydropsyche sp.), whereas many limnophilic taxa adapted to low current showed markedly increased drift (e.g. . Lepidostoma hirtum and Leptoceridae). In line with previous studies, our results confirm a significant loss of limnophilic macroinvertebrate taxa following hydraulic stress. The mitigating effect of cold thermopeaking might be explained by behavioural patterns, but requires further investigation to clarify if macroinvertebrates actively avoid drift and intrude into the interstitial, when cold water is discharged. Our results imply that river restoration projects must address the hydrological regime and, if necessary need to include suitable management schemes for hydropower plants. Besides operative management measures, the construction of reservoirs to buffer hydropeaks or the diversion of hydropeaks into larger water bodies could mitigate hydropeaking effects and foster biological recovery including limnophilic taxa.

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... Se rencontre jusqu'à des vitesses de courant de 0,5 m/s maximum. (Cushman, 1985, Schmutz et al., 2013, Schülting et al., 2016. La question de savoir dans quelle mesure les modifications subites des con di tions d'écoulement affectent l'émergen ce ou perturbent les adultes lors de la ponte n'a pas encore été suffisamment étudiée. ...
... Selon la saison, ces modifications peuvent aller dans le sens d'un réchauffement (warm thermopeaking) ou d'un refroidissement (cold thermopeaking). En se surimposant aux éclusées, ces effets thermiques peuvent, suivant la composition en espèces des communautés et le sens du changement, accroître ou réduire la dérive des larves et accélérer ou freiner le développement des oeufs (Bruno et al., 2013, Elliott, 1972, Schülting et al., 2016. De même, le développement des pupes peut être influencé par la température de l'eau (Hogg et Williams, 1996). ...
... Réactions variables aux éclusées en relation avec le « thermopeaking » : moindre dérive suite au refroidissement subit(Schülting et al., 2016)*, pas de perturbation du développement larvaire suite aux variations de température(Frutiger, 2004)* ...
Article
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En Suisse, l’assainissement des éclusées dans les cours d’eau se base sur des mesures de construction et, éventuellement d’exploitation, visant à atténuer les variations de débit dues à l’exploitation par éclusées des centrales hydroélectriques. Ces mesures d’assainissement peuvent être complétées par des mesures morphologiques ponctuelles comme l’installation d’amas de bois mort, la disposition de blocs brise-lames ou la création d’anses. Dans cet article, nous nous proposons de discuter de leurs effets sur les macroinvertébrés aquatiques qui, de par leur grande diversité spécifique et la complexité de leurs cycles de vie, sont souvent très affectés par les éclusées. Nous traiterons de la façon dont les différents types de mesures peuvent atténuer localement les impacts du régime d’éclusées, que ce soit en réduisant les paramètres hydrauliques, en assurant une surface mouillée permanente ou encore en favorisant la dynamique sédimentaire.
... Flume setups are common approaches to disentangle and quantify effects from multiple variables, since these allow precise control of the setting and a reduction of confounding factors (Bruno, Cashman, Maiolini, Biffi, & Zolezzi, 2016;Carolli, Bruno, Siviglia, & Maiolini, 2011;Imbert & Perry, 2000). To test the short-term reactions of macroinvertebrate assemblages at HP unaffected streams, we therefore used an experimental setup in artificial flumes, with macroinvertebrate drift as response variable (see also Schülting et al., 2018;Schülting, Feld, & Graf, 2016). We hypothesized that HP -induced macroinvertebrate drift will increase with increasing flow-amplitudes and up-ramping rates. ...
... Please also see Schülting et al. (2016Schülting et al. ( , 2018. Since the control unit allows controlling the hydrological setting within the mixing basins but not in the flumes directly, flow velocities, depths, and speed of the water level changes had to be measured for different discharge and ramping setups in each flume to guarantee equal conditions for each flume. ...
... This further emphasizes the importance of a high identification level. Further, the larval stage and individual size may additionally affect drift responses, with a tendency of younger instars showing larger drift responses (Poff et al., 1991;Schülting et al., 2016;Waringer, 1989 ...
Article
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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 up‐ramping 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 up‐ramping 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 discharge‐related 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.
... Accelerated flood recession hampers the establishment of plant seedlings on the riverbanks, as young shoots fail to reach subsiding water levels (Rood et al., 2005). An increase in sub-daily flow fluctuation caused by hydropeaking (FIGURE 4C-D) diminishes fish and macroinvertebrate populations through stranding and drift (Auer et al., , 2014Moog, 1993;Schülting et al., 2019Schülting et al., , 2016, as well as through reduced spawning and rearing success (Casas-Mulet et Figure 1.4 Comparison of natural (blue) and modified (red) river flows: (a) Mean daily flows of runof-river Touvedo dam (start of operation in 1993), Lima River, Portugal (modified after: Rivaes and Aguiar, 2019); (b) median monthly flows in the San Joaquin River in California, USA; the red line shows the alterations caused by an an irrigation supply dam (modified after: Richter and Thomas, 2007); (c) annual and (d) daily short-term flow regime changes in the Ume River, a Swedish hydropeaking river, in comparison to the free-flowing Vindel River (modified after: Bejarano et al., 2017). al., Kennedy et al., 2016;McMichael et al., 2005bMcMichael et al., , 2005a. ...
... Therefore, these anthropogenic induced rapid flow fluctuations may cause different ecological impacts, including periphyton biomass reduction , drift of macroinvertebrates (Schülting et al., 2016), and physical as well as physiological constraints for riparian vegetation (Bejarano et al., 2017a). Regarding fish biota, hydropeaking can reduce and alter spawning and rearing success (Becker et al., 1982;Casas-Mulet et al., 2014;McMichael et al., 2005), lead to downstream displacement and stranding Nagrodski et al., 2012), cause metabolic changes Flodmark et al., 2002;Taylor et al., 2012) and influence fish growth (Kelly et al., 2017;Korman and Campana, 2009;Puffer et al., 2017). ...
... Hydropeaking negatively affects density, biomass and species diversity through the catastrophic drift occurring during peak-flow, particularly when combined with high content of suspended solids, and, for some taxa, through the behavioral drift in the base-flow conditions (Bruno et al., 2010;Moog, 1993). Also, the effects of thermopeaking on the drift of benthic invertebrates have been reported (Carolli et al., 2012;Schülting et al., 2016). In Europe, the assessment metrics and benthic habitats regarded in WFD may not reflect the effects of hydropeaking events , which may require further research for the development of mitigation strategies regarding the benthic communities. ...
Thesis
Full-text available
Free-flowing rivers support diverse, complex and dynamic ecosystems, as well as provide societal and economic services. Globally, however, the water flow of many rivers has been regulated by hydropower or other sources. Flow modification affects crucial ecosystem functions and processes, and organism’s capacity to fulfil its life cycle requirements. In light of these widespread effects, it is urgent to mitigate ecological impacts caused by existing water infrastructures. To achieve environmental objectives, as well as to manage water uses in a sustainable way, a thorough understanding of ecological responses to hydrological alterations on different temporal levels (e.g., environmental flow, hydropeaking) is essential. This work aims to establish holistic approaches for restoring flows in modified rivers, and to develop environmental flows able to sufficiently mitigate the ecological effects of short-term and annual flow modifications in fluvial ecosystems. This thesis disentangles the effects of multiple stressors and shows that flow regulation is a primary predictor of fish populations. Moreover, by assessing flow-ecology relationships on annual, seasonal, and sub-daily levels, this work identifies fundamental principles to implement flow restoration measures in rivers affected by water abstraction and hydropeaking. While more dynamic flows are generally recommended as environmental flows, flow restrictions are needed for hydropeaking mitigation. Regarding the latter, a seasonal framework for hydrological mitigation based on fish life-history stages is established, and thresholds are synthesized. Overall, this thesis advances the establishment of guidelines for successful flow restoration in river systems affected by competing water uses by establishing holistic flow restoration schemes and by subsuming quantitative and qualitative hydropeaking thresholds. Moreover, this thesis sets the topic of flow restoration into the broader context of hydromorphological river rehabilitation. Hence, this work contributes to a more balanced discussion on trade-offs between societal and environmental water uses.
... More recently, research on the ecological impacts of hydropeaking focused not only on the direct impacts of rapid flow changes, but also on the associated short-term fluctuations in water temperature (Carolli et al. 2011;Bruno et al. 2012;Schülting et al. 2016;Choi and Choi 2018;Feng et al. 2018;Auer et al. 2023), a process known as thermopeaking ). Thermopeaking occurs due to water stratification in reservoirs, following a seasonal pattern (McCartney 2009;Toffolon et al. 2010;Hayes et al. 2022a). ...
... While awareness of the impacts of thermopeaking is growing, its ecological impacts on freshwater populations are still poorly understood. Much of the published literature on the ecological effects of thermopeaking focuses on macroinvertebrate drift (e.g., Carolli et al. 2011;Bruno et al. 2012;Schülting et al. 2016). Fewer studies have assessed the impacts of thermopeaking on fishes Casas-Mulet et al. 2016). ...
Article
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Unlabelled: Research on how intermittent water releases from hydropower plants affect the early life stages of fish has advanced in the last years, focusing not only on the direct impacts of rapid flow changes (hydropeaking), but also on the short-term fluctuations in water temperature (thermopeaking). Flow and thermal fluctuations caused by hydropeaking may affect fish movement patterns and migration at critical stages of a species' life cycle, e.g., by inducing passive downstream drift. Using two experimental outdoor channels, we investigated how nase (Chondrostoma nasus, Cypriniformes) larvae respond to a rapid drop in water temperature during hydropeaking (simulating a cold thermopeaking event), reaching on average 5.5 °C under peak flow (maximum discharge) conditions, in comparison with a hydropeaking treatment with a constant water temperature regime. Responses of fish larvae were analyzed during acclimation, up-ramping (increase in discharge), peak flow and down-ramping (decrease in discharge) phases. Fish drift increased during peak flow in the cold thermopeaking treatment compared to hydropeaking. Higher drift rates were also negatively associated with pronounced water temperature drops during peak flow conditions. In addition, the starting temperature of the experiment influenced drift during up-ramping. Overall, the results suggest that cold thermopeaking may increase drift in the early life stages of cypriniform fish compared with hydropeaking with stable water temperature. Hence, monitoring and active water temperature adjustments following hydropower releases should be adopted as strategies to mitigate power plant-related impacts on aquatic organisms. Supplementary information: The online version contains supplementary material available at 10.1007/s00027-023-00955-x.
... Benthic macroinvertebrates are excellent indicators of the ecological conditions in aquatic systems as a multitude of species have distinct habitat requirements. Moreover, the physical environment and disturbances due to hydropeaking on benthic populations are well-studied (e.g., Schülting, Feld, & Graf, 2016). The alterations include shifts in longitudinal zonation, loss, and abundance reduction of specific taxa (Aldridge, Fayle, & Jackson, 2007;Lagarrigue et al., 2002), as well as impaired larval development (Frutiger, 2004). ...
... Both taxa are typical elements of alpine streams and rivers and well known to inhabit distinct hydraulic habitats: species of the genus Rhithrogena explicitly prefer fast flowing stony areas, while A. auricollis is restricted to slowly flowing or even stagnant riverine habitats (Schülting et al., 2016;Waringer, Graf, & Malicky, 2013). Therefore, these antagonistic taxa were chosen to describe the investigated effects of pulse releases. ...
Article
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The Ziller River, a tributary to the Inn in Tyrol, Austria, is affected by hydropower generation. Macroinvertebrate habitat‐preferences were investigated in the field and corresponding habitat suitability curves were applied successfully to a novel integrative assessment method based on hydrodynamic modelling. Here, a reach of the Ziller River is simulated using a three‐dimensional unsteady hydrodynamic model. The three‐dimensional simulation results are applied to a predictive macroinvertebrate habitat model. Habitat suitably indices (HSI) are calculated based on temporal alterations of bed shear stress values. Model results are free from two‐dimensional flow‐averaging approximations and demonstrate the critical information lost in lower‐order models due to simplification procedures. Shear stress values, three‐dimensional simulated velocity components, and temporal alterations of flow are provided in the current study. Considering the simulation results, the implementation of the provided supplementary simulation details in macroinvertebrate studies and the integration into further habitat investigations is discussed.
... Shear stress and high water velocities are properties of flowing water that affect benthic macroinvertebrate communities by potentially inducing drift. Flow regime variability associated with, for example, hydropeaking can greatly increase drift of benthic macroinvertebrates (Schülting et al., 2016), resulting in reduced benthic biomass (Moog, 1993) and less diverse communities (Valentin et al., 1995). In addition to effects on the communities that are going to be sampled, flow can bias the sampling results. ...
... We found no effect of flow treatment on the number of individuals colonizing the Hester-Dendy samplers. Although previous studies have shown that fluctuating flows rapidly cause increased drift of benthic macroinvertebrates (Schülting et al., 2016), our fluctuating flow treatment did not appear to hinder colonization. The diversity was, however, higher in aquaria with the constant than in those with the fluctuating flow treatment. ...
Article
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Reliable methods for assessing the ecological status of degraded rivers are essential for evaluating restoration efforts in lotic habitats. Several methods are based on biological indicators, such as benthic macroinvertebrates. The Hester–Dendy multi-plate sampler is a commonly used tool for sampling macroinvertebrates, but its performance under different environmental conditions is not well understood. In a laboratory experiment, we assessed if fluctuating and increasing water velocity influences the performance of Hester–Dendy samplers, by studying colonization of the samplers in relation to a pre-determined composition of benthic macroinvertebrates. Biodiversity (Shannon-Wiener index) of colonizing macroinvertebrates was higher in a constant than in a fluctuating flow treatment, but there was no effect on the number of colonizing individuals. The results suggest a potential bias in the interpretation of biodiversity data from sites with sub-daily flow changes, for example, downstream of hydropeaking power plants.
... The composition of drift during our peak was similar to that reported elsewhere (see Bruno et al., 2010), with juvenile instars of Ephemeroptera, Plecoptera, Tricoptera, and Diptera as dominant taxa. Most of our taxa were early larval instars which have been shown by Schülting et al. (2016) to influence drift abundance. More specifically, our peak drift samples had a high abundance of high flow sensitive species: Baetidae (Ephemeroptera), Rhyacophilidae (Tricoptera), Limnephilidae (Tricoptera), and Chironomidae (Diptera) (Kjaerstad et al., 2018). ...
... In their review, Poff and Zimmerman (2010) outlined the importance of incorporating environmental factorsfor example, water temperaturewhen assessing ecological responses to altered flow regimes. A study completed by Schülting et al. (2016) assessing the effects of combined hydropeaking and cold thermopeaking on macroinvertebrate drift in experimental flumes, found that water temperature can have a mitigating impact on drift during thermopeaking (see also Carolli et al., 2012;Bruno et al., 2013). In light of this, it is worth noting that we did not find any relationship between macroinvertebrate drift or benthos and water temperature. ...
Article
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As the demand for hydroelectricity progresses worldwide, small hydropower operators are increasingly examining the feasibility of using existing infrastructure (e.g., settling basins) in run-of-the-river schemes for intermittent power production. Such flexible production causes short-term discharge fluctuations (hydropeaking) in downstream reaches with potential adverse effects for the sensitive fauna and flora in alpine streams. In an experimental field study on a previously unregulated section of the upper Rhone River (Switzerland), we measured density and composition of macroinvertebrate drift in two habitats (riffle, pool) following a 15-minute hydropeaking wave. The experimental hydropeaking was replicated five times over 14 days with decreasing recovery times between peaks (8, 3, 2 days, and 24 h), and drift measurements were compared with kick samples for the benthic community. Results from the kick sampling showed that benthic macroinvertebrate abundance and composition did not significantly change between the experimental peaks. There were habitat specific reactions in macroinvertebrate drift to hydropeaking, with the pool experiencing more pronounced drift abundances than the riffle. Overall, drift abundance was not significantly correlated with recovery time, but results indicate taxa-specific differences. This research advocates for the importance of completing more in-situ field experiments in order to better understand the ecological impact of flexible power production in small hydropower plants.
... Possible mechanisms that explain decreases in the abundance of macroinvertebrates at sites affected by hydropeaking relate to downstream drift, physical habitat and water quality alterations as well as food availability changes (Bunn and Arthington, 2002;Brooks et al., 2018;Wang et al., 2019b). Hydropeaking induced catastrophic drift has been previously documented and is expected to affect macroinvertebrates across all ecological organization levels (Moog, 1993;Céréghino and Lavandier, 1998;Céréghino et al., 2002;Bruno et al., 2013;Schülting et al., 2016;Schülting et al., 2019). A previous study in the Biobío River has shown that hydropeaking related discharge peak caused significant macroinvertebrate drift and the abundance of drifting macroinvertebrates was directly proportional to macroinvertebrate abundance in benthic habitats at corresponding sampling sites (García, 2011). ...
... A previous study in the Biobío River has shown that hydropeaking related discharge peak caused significant macroinvertebrate drift and the abundance of drifting macroinvertebrates was directly proportional to macroinvertebrate abundance in benthic habitats at corresponding sampling sites (García, 2011). Furthermore, catastrophic drift may also be caused by sediment mobilization as shown in other river systems (Gibbins et al., 2007;Schülting et al., 2016Schülting et al., , 2019Vericat et al., 2020). In addition to macroinvertebrate drift caused by the direct effect of higher water velocities and sediment mobilization, abrupt water temperature changes also cause significant increase of downstream drift frequency (Carolli et al., 2012). ...
Article
Hydropeaking leads to major anthropogenic disturbance of river networks worldwide. Flow variation imposed by hydropeaking may significantly affect macroinvertebrate assemblages within the river network. As such, the responses of macroinvertebrate assemblages to hydropeaking are expected to be complex and vary across spatial and temporal scales as well as ecological organization levels. To unpack this complexity, we assessed the interplay of geomorphic and hydrological variables as drivers of the responses of macroinvertebrate assemblages to hydropeaking. Specifically, we studied different levels of ecological organization of macroinvertebrate assemblages in two functional process zones (FPZs; Sub-Andean and Central Valley Gravel Dominated) subjected to different flow management in two Chilean Andean river networks. Hydropeaking caused significant reduction of macroinvertebrate abundances in both FPZs and at all ecological organization levels with the exception of one feeding guild (scrapers). Furthermore, the response of macroinvertebrate assemblage variance was stronger in the Central Valley Gravel Dominated FPZ. Both geomorphic and hydrological variables drove macroinvertebrate assemblage responses. However, the effects of the principal geomorphic variables operated at valley (meso) spatial scale and main hydrological variables operated at sub-daily (micro) temporal scale. Therefore, to minimize the effects of hydropeaking on macroinvertebrate assemblages, flow management should consider reduction of sub-daily variability. Furthermore, placement of new barriers should take into account not only their position within the river network but also their effects downstream that strongly depend on characteristics of river valley.
... The term thermal pollution is applicable only to the second group of sources. Thermal pollution is one type of physical pollution of the natural environment characterized by a periodic or prolonged input of hot or cold waters to the natural water bodies that cause the degradation of water quality by changes in water temperature associated with human activities [43][44][45]. ...
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The inheritance of historic human-induced disruption and the fierceness of its impact change aquatic ecosystems. This work reviews some of the main stressors on freshwater ecosystems, focusing on their effects, threats, risks, protection, conservation, and management elements. An overview is provided on the water protection linked to freshwater stressors: solar ultraviolet radiation, thermal pollution, nanoparticles, radioactive pollution, salinization, nutrients, sedimentation, drought, extreme floods, fragmentation, pesticides, war and terrorism, algal blooms, invasive aquatic plants, riparian vegetation, and invasive aquatic fish. Altogether, these stressors build an exceptionally composite background of stressors that are continuously changing freshwater ecosystems and diminishing or even destroying their capability to create and maintain ongoing natural healthy products and essential services to humans. Environmental and human civilization sustainability cannot exist without the proper management of freshwater ecosystems all over the planet; this specific management is impossible if the widespread studied stressors are not deeply understood structurally and functionally. Without considering each of these stressors and their synergisms, the Earth’s freshwater is doomed in terms of both quantitative and qualitative aspects.
... It is a crucial factor in the life cycle of aquatic macroinvertebrates as it ensures the gene flow between metapopulations (Briers et al., 2004) and the (re-)colonisation of habitats after the species' release from natural and anthropogenic stressors (Brooks & Boulton, 1991;Vos et al., 2023;Winking et al., 2016), and compensates for riverine downstream drift in lotic systems (Hershey et al., 1993). Macroinvertebrate dispersal is driven by a wide range of abiotic and biotic drivers, for example, by stream flow velocity (James et al., 2008;Naman et al., 2017;Schülting et al., 2016), the presence of predators (Hernandez & Peckarsky, 2014;Lancaster, 1990) and the infestation of macroinvertebrates with parasites (Prati et al., 2023;Vance, 1996) that varies by habitat and therefore may affect different life stages. ...
Article
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While macroinvertebrate dispersal operates at the individual level, predictions of their dispersal capabilities often rely on indirect proxies rather than direct measurements. To gain insight into the dispersal of individual specimens, it is crucial to mark (label) and capture individuals. Isotopic enrichment with ¹⁵N is a non‐invasive method with the potential of labelling large quantities of macroinvertebrates. While the analysis of ¹⁵N is widely utilised in food web studies, knowledge on the specific utility of isotopic enrichment with ¹⁵N for mass labelling of macroinvertebrate individuals across different taxa and feeding types is limited. Previous studies have focused on single species and feeding types, leaving gaps in our understanding of the broader applicability of this method. Therefore, this study aimed to test and compare isotopic mass enrichment across several macroinvertebrate taxa and feeding types. We released ¹⁵NH4Cl at five stream reaches in North‐Rhine Westphalia, Germany, and successfully enriched 12 distinct macroinvertebrate taxa (Crustacea and Insecta). Significant enrichment was achieved in active and passive filter feeders, grazers, shredders and predators, and predominantly showed positive correlations with the enrichment of the taxa's main food sources phytobenthos and particulate organic matter. Enrichment levels rose rapidly and peaked at distances between 50 m and 300 m downstream of the isotopic inlet; significant enrichment occurred up to 2000 m downstream of the isotopic inlet in all feeding types. Macroinvertebrate density estimates on the stream bottom averaged to a total of approximately 3.4 million labelled individuals of the 12 investigated taxa, thus showing the high potential of isotopic (¹⁵N) enrichment as a non‐invasive method applicable for mass labelling across different macroinvertebrate feeding types. Hence, isotopic enrichment can greatly assist the analysis of macroinvertebrate dispersal through mark‐and‐recapture experiments, as it allows to measure the movement at the level of individual specimens.
... In addition to abiotic impacts, hydropeaking can cause drastic aquatic drift (during up ramping) and stranding (during down ramping) of benthic invertebrates and fish (e.g. Auer et al., 2017;Espa et al., 2022;Schülting et al., 2016) and can also affect near shore-riparian habitats (Fette et al., 2007). Hydropeaking events can affect large parts of a river system (Halleraker et al., 2022). ...
Article
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Study region: Eight rivers in Slovenia and Croatia that are tributaries of the Danube River or the Adriatic Sea Study focus: The different types of hydropower plants alter river hydrology at several temporal scales and to a varying degree, respectively, but impacts have hardly been quantified in an integrative way structured by hydropower plant type. Hence, we analysed hydrological data from rivers affected by 13 HPPs belonging to 3 operational types, namely run-of-river (RoR), storage (ST), and diversion storage (DST). Daily discharge data in pre-and post-impact periods were compared by applying the Ecodifference and Indicators of Hydrologic Alteration methods. In addition, sub-daily discharge data were analysed for potential alterations induced by hydropeaking. New hydrological insights for the region: Studied HPP types caused mostly strong but varying alterations of flow regime. To facilitate comparisons, the three existing impact indicators were integrated into a composite Holistic Score of River Hydrology Impact. Holistic Score of River Hydrology Impact showed that DST HPPs caused most severe impacts in residual river reaches, followed by ST HPPs, while RoR HPPs had less severe impact. Environmental flows were not provided to five of six residual river reaches. We detected hydropeaking in 9 HPPs, but probably underestimated their impacts, as sub-daily discharge was only available for 58% of the gauging stations in the study area.
... The term thermal pollution is applicable only to the second group of sources. Thermal pollution is one type of physical pollution of the natural environment characterized by a periodic or prolonged input of hot or cold waters to the natural water bodies that cause the degradation of water quality by changes in water temperature associated with human activities [43][44][45]. ...
Article
Full-text available
The inheritance of historic human-induced disruption and the fierceness of its impact change aquatic ecosystems. This work reviews some of the main stressors on freshwater ecosystems , focusing on their effects, threats, risks, protection, conservation, and management elements. An overview is provided on the water protection linked to freshwater stressors: solar ultraviolet radiation, thermal pollution, nanoparticles, radioactive pollution, salinization, nutrients, sedi-mentation, drought, extreme floods, fragmentation, pesticides, war and terrorism, algal blooms, invasive aquatic plants, riparian vegetation, and invasive aquatic fish. Altogether, these stressors build an exceptionally composite background of stressors that are continuously changing freshwater ecosystems and diminishing or even destroying their capability to create and maintain ongoing natural healthy products and essential services to humans. Environmental and human civilization sustainability cannot exist without the proper management of freshwater ecosystems all over the planet; this specific management is impossible if the widespread studied stressors are not deeply understood structurally and functionally. Without considering each of these stressors and their synergisms, the Earth's freshwater is doomed in terms of both quantitative and qualitative aspects.
... Depending on operation regime, hydropower operations may result in abrupt changes in hydrology, according to power demands. This so-called hydropeaking frequently causes the drift (owing to increased hydraulic forces) and stranding (owing to the reduction of the wetted area) of fish and macroinvertebrates, considerably reducing biodiversity and biomass in the downstream sections of the river (Schülting et al. 2016;Greimel et al. 2018). ...
Article
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Within the upper Neretva catchment in Bosnia several hydropower plants are projected. Between 28.6. and 1.7.2022 a baseline survey was initiated to screen the area regarding the diversity of aquatic insects and its linked conservation value. In total, 59 Trichoptera species, ten Plecoptera species, 19 Ephemeroptera and 16 Diptera (Tipuloidea) species were collected, of which Baeoura sp. is new to science. 35 species are endemics of the Balkans, most species are rheobiontic and need high water current. The most abundant taxa are species of the trichopteran genus Agapetus (A. slavorum and A. ochripes) – surface grazers sensitive to water fluctuations and therefore vulnerable to hydropower-induced water level changes. With estimated 40,000 attracted specimens per night, light traps were extraordinarily successful. The extremely high diversity, as well as the enormous abundance of aquatic insects, underline the importance of the upper Neretva as an unimpacted riverine system embedded in dense natural and near-natural forest.
... The rapid and artificial flow fluctuations associated with hydropeaking operations affect riverine biota (fauna and flora) directly and indirectly. Direct effects include organism displacement, involuntary drift, and stranding, often leading to deterioration and death [104][105][106][107][108][109]. Indirect effects are linked to changes in river hydro-morphology with consequences for habitat quality and availability and include alterations of biochemical processes and biotic interactions [13,110]. ...
Article
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As the share of renewable energy grows worldwide, flexible energy production from peak-operating hydropower and the phenomenon of hydropeaking have received increasing attention. In this study, we collected open research questions from 220 experts in river science, practice, and policy across the globe using an online survey available in six languages related to hydropeaking. We used a systematic method of determining expert consensus (Delphi method) to identify 100 high-priority questions related to the following thematic fields: (a) hydrology, (b) physico-chemical properties of water, (c) river morphology and sediment dynamics, (d) ecology and biology, (e) socioeconomic topics, (f) energy markets, (g) policy and regulation, and (h) management and mitigation measures. The consensus list of high-priority 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. We find that there is already a strong understanding of the ecological impact of hydropeaking and efficient mitigation techniques to support sustainable hydropower. Yet, a disconnect remains in its policy and management implementation.
... As the downstream reach lacks a gauging station, the weekly temperature variation was not monitored. However, the frequent flushing from the Jiufeng reservoir for flood prevention in the wet season, water rafting in the dry season and hydropeaking from the Jiufeng HPP (Schülting et al., 2016) might have led to thermopeaking effects (Tan et al., 2018) with rapid temperature decrease, as the water temperature in the Jiufeng reservoir is much lower than other parts of the Houda stream. The abrupt thermal alterations caused by anthropogenic activities can lead to the significant increase in the downstream drift behaviour of BMs, especially for some sensitive taxa such as Baetidae and Chironomidae (Carolli et al., 2012). ...
Article
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The determination of minimum flow requirements for green small hydropower plants (GSHP) in China primarily relies on hydrological methods such as the Tennant method with no seasonal variation. However, the direct application of hydrological methods without local ecological data for calibration lacks ecological validity, potentially resulting in unsuitable minimum flow recommendations for local aquatic biota. Hydraulic‐habitat modelling (HHM) is assumed to provide more ecologically relevant and reliable environmental flow recommendations (EFRs), but benthic macroinvertebrates (BMs), crucial in the aquatic food web, have rarely been the focus in HHM studies. Moreover, the strong subjectivity in HHM processes hinders the comparison of EFRs across different biota and geographical regions. This study aims to investigate the ecological validity of using the Tennant method to set minimum flow requirements for local BM communities and the impacts of various methods used in HHM on derived EFRs. To achieve this, a pseudo‐2D HHM approach is employed, integrating the 1D hydraulic models HEC‐RAS and CASiMiR with the habitat model HABFUZZ. The EFRs downstream of Jiufeng reservoir, one of China's first GSHPs, are derived for wet (April–June) and dry seasons (July–September). Our findings highlight that setting minimum flow alone is inadequate for preserving BM community integrity downstream of GSHPs. It is crucial to incorporate more diverse environmental flow criteria, including minimum flows and peak flows, into GSHP assessment standards, with recommended flow levels varying across different seasons. Additionally, the development of a standardized HHM methodology is essential to mitigate the inherent subjectivity in HHM and facilitate the comparison of EFRs generated from different studies. This study's innovative modelling framework and findings will enhance the optimization of minimum flow assessment criteria for GSHP in China, deepen understanding of seasonal e‐flow requirements of BM communities, and refine the methodology used in BM HHM for e‐flow recommendation.
... The fulfillment of these socio-metabolic requirements (electricity demand) by establishing and operating hydropower plants plays a substantial role in transforming natural into industrial rivers . These transformations severely alter spatiotemporal hydro-ecological connectivity and affect aquatic organisms (macroinvertebrates, fish, algae, and macrophytes) and their biodiversity by altering the prevailing natural, river-type specific hydromorphological conditions (Dudgeon et al., 2006;Schülting et al., 2016). ...
Article
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The access to an adequate quantity and quality of water is vital to sustain healthy ecosystems and human socioeconomic development. However, the shift from an agrarian, solar energy based to an industrialized, fossil fuel‐based socio‐metabolic regime has put natural water resources under stress and led to dramatic transformations of riverine landscapes in the Anthropocene. Thus, we need interdisciplinary research approaches that integrate the knowledge and methods from ecology, humanities, and engineering. The Doctoral School “Human River Systems in the 21st Century” (HR21) studies riverine landscapes as coupled socio‐ecohydrological systems (SEHS) within four research clusters, that is, connectivity, metabolism, vulnerability, and governance. HR21 analyzes the transformation processes and coevolution of nature and society in rivers and their response to future environmental, social, cultural, and economic drivers of change. HR21 aims to improve the understanding of the coupling of the socioeconomic, ecological, and hydrological systems within industrialized riverine landscapes to support their urgent, more sustainable transformation. To discuss how this agenda can be implemented, five different HR21 PhD projects are presented, clearly routed in one scientific domain, applying a combination of the research clusters and addressing various topics: (i) hydropower effects in high alpine river ecosystems, (ii) wastewater impacts on carbon storage and greenhouse gas fluxes in tropical wetlands, (iii) the nutrient retention and ecosystem service potential of floodplains in large river catchments, and the influence of hydrometeorological variables on (iv) the runoff response and on (v) the transit time distribution of runoff, both impacting water resource management at the basin level. These examples highlight how disciplinary PhD research can be framed within an interdisciplinary research agenda to coupled SEHS.
... Schwall-und Sunkereignisse im Zusammenhang mit Wasserkraftwerken können sich stark negativ auf aquatische Lebensgemeinschaften auswirken (Holzapfel et al., 2017) und die Individuendichten spezifischer Arten reduzieren Schülting et al. 2016; (Dossi et al., 2016;2020). Holzansammlungen im Gewässer können jedoch Verklausungen initieren, die Überschwemmungen verursachen können und die daher beseitigt werden. ...
... Schwall-und Sunkereignisse im Zusammenhang mit Wasserkraftwerken können sich stark negativ auf aquatische Lebensgemeinschaften auswirken (Holzapfel et al. 2017) und die Individuendichten spezifischer Arten reduzieren , Schülting et al. 2016. In Kombination mit morphologischen Degradationen wie Begradigungen wirken sich Effekte von hydraulischen Schwankungen besonders auf bodenlebende Organismen wie Steinfliegenlarven aus. ...
... Schwall-und Sunkereignisse im Zusammenhang mit Wasserkraftwerken können sich stark negativ auf aquatische Lebensgemeinschaften auswirken und die Individuendichten spezifischer Arten reduzieren (Schülting et al. 2016(Schülting et al. , 2018 ...
... In addition, the daily peak-shaving operation of the hydropower station also significantly altered hydrological parameters [22]. The daily operation of the hydropower station affects the survival of aquatic organisms [23][24][25] and even leads to the reduction of fish populations [26]. For example, the daily operation of Itiquira power station resulted in approximately 400 adult fishes being stranded and dying when discharge flow rapidly changed over 18 h [27]. ...
Chapter
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Daily operation of a hydropower station is conducted to meet the energy requirement. The hydraulic parameters of the downstream are significantly affected by the dam operation, which has a negative impact on the aquatic system. When the multi energy complementary method is used, such as hydro-photovoltaic (hydro-PV) combined power generation, the problem will worsen. Hydropower station A (HSA) on River X was selected to investigate the impact of daily operation. HSA is a part of hydro-PV complementary power generation. The spawning and breeding period of typical fish, April to July, was selected as the study period. According to various scheduling, the changes of hydrological regime were analyzed. The results show that the maximum flow variation was 334 m ³ /s, and the variations in water surface width and velocity during reservoir operation were between natural conditions. The maximum daily water level variations under the two operating scenarios were 1.6 m and 3.5 m respectively. The remarkable change of water level may have a negative impact on aquatic organisms. Considering the daily variation limit of 1.2 m under natural condition, the relationship between the allowable daily variation of reservoir outflow and the reference base flow was proposed. The results in this paper serve as a technical reference for studying changes in the hydrological regime and lessening their impacts on aquatic organisms in hydro-photovoltaic complementary development.
... Further, traits are often sensitive to changing environmental conditions as a result of environmental filtering, thus trait composition reflects current and past conditions. Moreover, trait composition affects the resilience of an ecological community (Moi et al. 2020;Schülting et al. 2016). For example, heat waves are likely to favor species with higher water temperature preferences and restrict cold-dwelling species. ...
Article
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As a result of ongoing climate change, extreme climatic events (ECEs) are expected to become more frequent and severe. The high biodiversity of riverine ecosystems is susceptible to ECEs, especially to water temperature (extreme heat and extreme cold) and discharge-related (flood and drought) events. Long time series are needed to unravel the effects of ECEs on ecological communities. Here, we used 20 years (1986-2005) of unusually high-resolution data from a pristine first-order stream in Germany. Daily recordings of species-level identified aquatic insect (Ephemeroptera, Plecoptera, Trichoptera: EPT) emergence, water temperature and discharge data were used to examine the effects of four types of ECEs (extreme heat, extreme cold, flood, and drought events) on insect abundance , common taxonomic diversity metrics, and selected traits after five different time lags (2 weeks, 1, 3, 6, and 12 months). Extreme heat events increased from 1.8 ± 1.9 SE events per year before 2000 to 5.3 ± 1.9 SE events per year after 2000. Water temperature-related ECEs restructured the EPT community in abundance, species richness, and traits (community temperature index: CTI, and dispersal capacity metric: DCM). The strongest effects on the EPT community were found when it was exposed to multiple ECEs and 1 and 3 months after an ECE. The changing frequencies and durations of ECEs, especially the increasing frequency of extreme heat events and the negative cumulative effects of ECEs, paint a worrisome picture for the future of EPT communities in headwater streams. High-resolution, long-term data across sites is needed to further disentangle the effects of different ECE stressors.
... The rapid and artificial flow fluctuations associated with hydropeaking operations affect riverine biota (fauna and flora) directly and indirectly. Direct effects include organism displacement, involuntary drift, and stranding, often leading deterioration and death [98][99][100][101][102][103]. Indirect effects are linked to changes in river hydromorphology with consequences for habitat quality and availability and include alterations of biochemical processes and biotic interactions [12,104]. ...
Article
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As the share of renewable energy grows worldwide, flexible energy production from peak-operating hydropower and the phenomenon of hydropeaking have received increasing attention. In this study, we collected open research questions from 220 experts in river science, practice, and policy across the globe using an online survey available in six languages related to hydropeaking. We used a systematic method of determining expert consensus (Delphi method) to identify 100 high-priority questions related to the following thematic fields: (a) hydrology, (b) physico-chemical properties of water, (c) river morphology and sediment dynamics, (d) ecology and biology, (e) socio-economic topics, (f) energy markets, (g) policy and regulation, and (h) management and mitigation measures. The consensus list of high-priority 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. We find that there is already a strong understanding of the ecological impact of hydropeaking and efficient mitigation techniques to support sustainable hydropower. Yet, a disconnect remains in its policy and management implementation.
... We found a small number of Leuctra specimens on artificial substrates since they live in interstitial habitats and the moss-like substrates were not a preferable option for them. 49 In addition to the macrolithal, moss was also a preferred habitat for Protonemura, which explains the higher number of individuals found on artificial substates in comparison to the natural habitat. 50 The spring area of the Jankovac stream had a large abundance of Trichoptera, 38,48 as confirmed with the number of individuals found on the natural substrate, but only a small number on artificial substrates. ...
Article
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Freshwater ecosystems, especially springs, are highly sensitive to environmental changes. They are also excellent natural laboratories because of their stable conditions, reducing the number of variables to be considered in field studies. We examined the composition, dynamics and colonisation patterns of macroinvertebrates with respect to canopy coverage and time of day in which available areas are actively colonised. We used artificial substrates that mimicked the natural habitat structure at an isolated karst spring and recovered exposed substrates every 12 h. Physico-chemical parameters of water did not differ significantly regardless of canopy cover. The most numerous representatives and the pioneering champions were larvae of Baetidae (Ephemeroptera) and Chironomidae (Diptera). Simuliidae were also among the most successful pioneering species. Most observed groups more actively colonised substrates in the closed canopy area. Oligochaeta and Gammarus fossarum were more numerous on substrates in the open canopy area. Individuals of all analysed groups showed day-night migration patterns and were more active at night. Coleoptera (Elmis sp.) were the poorest (re)colonisers among the analysed taxa.
... Hein, 2016;Greimel et al., 2018;Bruno, Siviglia, Carolli, & Maiolini, 2013;Hauer, Unfer, Holzapfel, Haimann, & Habersack, 2014;Schülting, Feld, & Graf, 2016;Young, Cech, & Thompson, 2011). Regarding fish, it has been well documented that hydropeaking entails stranding and downstream displacement of individual fish (Nagrodski, Raby, Hasler, Taylor, & Cooke, 2012;Young et al., 2011;Hunter, 1992;Saltveit et al., 2001;Halleraker et al., 2003;Auer, Zeiringer, Führer, Tonolla, & Schmutz, 2017;Führer et al., 2022), which, in turn, diminishes population vitality (Hayes et al., 2021;Schmutz et al., 2015).Linked to artificial flow alteration, hydropeaking possibly also causes unnatural short-term water temperature fluctuations, referred to as "thermopeaking" Ward & Stanford, 1979;Zolezzi, Siviglia, Toffolon, & Maiolini, 2011). ...
Article
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Intermittent water releases from hydropower plants, called hydropeaking, negatively affect river biota. The impacts mainly depend on hydrological alterations, but changes in physical habitat conditions are suspected to be co‐responsible. For example, hydropeaking accompanied by a sudden change of water temperature in the downstream river—called thermopeaking—is also presumed to impair aquatic ecosystems. Still, knowledge about these thermopeaking impacts on aquatic species and life‐stages is limited. We performed flume experiments under semi‐natural conditions to fill this knowledge gap, simulating single hydropeaking events with a change in water temperature. As response parameters, we quantified the drift and stranding of early life‐stages of European grayling (Thymallus thymallus L.), a key fish species of Alpine hydropeaking rivers. Hydropeaking events with a decrease in water temperature (“cold thermopeaking”) led to significantly higher downstream drift (mean = 51%) than events with increasing water temperature (“warm thermopeaking”, mean = 27%). Moreover, during cold thermopeaking, a comparably high fish drift was recorded up to 45 min after the start of peak flows. In contrast, drift rates quickly decreased after 15 min during warm thermopeaking. Remarkably, the spatial distribution of downstream drift along gravel bars during cold thermopeaking showed the opposite pattern compared to those triggered by warm thermopeaking events indicating different behavioral responses. Furthermore, the stranding rates of the cold thermopeaking trials were twice as high (mean = 31%) as those of the warm thermopeaking experiments (mean = 14%). The outcomes present vital information for improving mitigation measures and adapting environmental guidelines.
... Hydropeaking consists of sudden, artificial water releases by storage hydropower plants into rivers to address peaks of energy demand, thus affecting the subdaily flow regime through rapidly increasing and decreasing flow spates. A growing scientific and public awareness of the adverse effects of hydropeaking on stream ecology has developed in the last decades (e.g., Auer, Zeiringer, Fuhrer, Tonolla, & Schmutz, 2017;Bejarano, Jansson, & Nilsson, 2017;Bejarano, Sordo-Ward, Alonso, Jansson, & Nilsson, 2020;Bondar-Kunze, Maier, Schönauer, Bahl, & Hein, 2016;Boavida, Harby, Clarke, & Heggenes, 2017;Casas-Mulet, Alfredsen, & Killingtveit, 2014;Schülting, Feld, & Graf, 2016), leading to increasing attention to the study, design, and implementation of mitigation strategies, based on operational and structural measures (Barillier, Beche, Malavoi, & Gouraud, 2021;Bruder et al., 2016;Greimel et al., 2018;Hauer, Siviglia, & Zolezzi, 2017;Moreira et al., 2019). Operational measures rely on changes in the energy production schemes resulting, however, in a reduced flexibility of operations for the hydropower companies (Gostner et al., 2011), which may hamper their ability to profitably adapt to rapidly variable energy prices and peak requests from the grid. ...
Article
We assessed the effect of a hydropeaking diversion mitigation measure that allows for additional hydropower production, which markedly reduced hydropeaking on a 10‐km stream reach in the north‐eastern Italian Alps. Hydropeaking, caused by a storage hydropower plant, affected the study reach from the 1920s to 2015, when a cascade of three small run‐of‐the‐river plants was installed to divert the hydropeaks from the plant outlet directly into the intake of the RoRs plants, and hydropeaking was released downstream the confluence with a major free‐flowing tributary. The flow regime in the mitigated reach shifted from a hydropeaking‐dominated to a baseflow‐dominated regime in winter, with flow variability represented only by snowmelt and rainfall in late spring and summer. The application of two recently proposed sets of hydropeaking indicators, the hydraulic analysis of the hydropeaking wave, together with the assessment of biotic changes, allowed quantifying the changes in ecohydraulic processes associated with hydropeaking mitigation. The flow regime in the mitigated reach changed to a residual flow type, with much less frequent residual hydropeaks; although an average two‐fold increase in downramping rates were recorded downstream the junction with the tributary, these changes did not represent an ecological concern. The functional composition of the macrobenthic communities shifted slightly in response to flow mitigation, but the taxonomic composition did not recover to conditions typical of more natural flow regimes. This was likely due to the reduced dilution of pollutants and resulting slight worsening in water quality. Conversely, the hyporheic communities showed an increase in diversity and abundance of interstitial taxa, especially in the sites most affected by hydropeaking. This effect was likely due to changes in the interstitial space availability, brought by a reduction of fine sediments clogging. Besides illustrating a feasible hydropeaking mitigation option for Alpine streams, our work suggests the importance of monitoring both benthic and hyporheic communities, together with the flow and sediment supply regimes, and physico‐chemical water quality parameters.
... Specific to fish and their instream habitat, alterations in river depths, velocity and water temperature are the major sources of negative impacts on hydropeaking Burman et al., 2021;Nagrodski et al., 2012). These alterations influence, for instance, the density of drifting invertebrates, the risk of stranding, spawning conditions, behaviour, growth, reproduction and mortality (Moreira et al., 2019;Schülting et al., 2016;Young et al., 2011), with potential long-term effects on population development and community structure (Enders et al., 2017). ...
Article
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Sub‐daily fluctuations in streamflow may have adverse effects on the biota downstream of dams in hydropeaking‐regulated rivers. Although the stranding of salmonid fry is one documented effect of hydropeaking, little is known about the species‐specific behavioural and subsequent growth effects of sub‐daily flow fluctuations. We investigated the effects of sub‐daily flow fluctuation on growth, mortality and behaviour of sympatric Atlantic salmon (Salmo salar) and brown trout (S. trutta) fry (29–34 mm) in a laboratory experiment. The fluctuating flow treatment negatively affected growth and increased mortality for trout but not for salmon. The level of aggressive behaviour was similar in the fluctuating‐ and stable‐flow treatments. Within the fluctuating flow treatment, there was a trend that more fishes were visibly active above the substrate during low than high flow. These findings suggest that hydropeaking‐induced flow fluctuations may affect fry of different salmonid species in different ways and that brown trout fry may be more vulnerable to hydropeaking effects than Atlantic salmon fry. It can therefore be important to consider the possibility of divergent reactions by different fish species under hydropeaking situations and to incorporate species‐specific strategies to conserve culturally and economically relevant riverine fish species.
... immediately downstream from tributaries), and/or (iii) during other periods or conditions (e.g. after flood events supplying fine materials from upstream) is significant in determining the frequency and extent of benthic disturbance (e.g. Gibbins et al., 2007;Wilcock et al., 2009;Schülting et al., 2016). Hence, it should not be neglected when assessing the effects of such flow pulses on the overall ecosystem behaviour. ...
Article
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Hydropeaking, by artificially generated flow peaks, influences hydro-sedimentary dynamics on rivers and, consequently, affects bed material entrainment and transport. This study examines the onset of motion of sediment particles in four sections of a Pyrenean gravel-to-cobble bed river exposed to frequent hydropeaking (once per day, on average). Five criteria of particle entrainment have been used to assess the prediction of the initiation of grain motion at-a-section scale. Theoretical entrainment conditions were validated using real observations of mobility by means of tracers. It was found that the maximum flow discharged by the hydropower plant mostly affects the furthest downstream section, located almost 17 km downstream, in which the finer fractions of the bed are entrained. The mobile grain sizes include up to coarse gravels (≈ 30 mm). Differences in sediment supply (imposed by tributaries), the value of the bed slope and the structure of the coarse surface layer decisively control the downstream variability of incipient particle motion between sections. Results from a 17 km study segment indicated that hydropeaking generate partial transport, that is, a partially size-selective transport that occurs downstream from the hydropower plant and winnows the sand and small gravel further downstream, increasing armouring and depleting fine sediments.
... This ecological process has been studied with a focus on the association of drift with abiotic and biotic factors (Naman et al., 2016). Those factors include diel periodicity (Mendoza et al., 2018), seasonal variations (Ramírez and Pringle, 2001;Castro et al., 2013b), current velocity (Castro et al., 2013a;Schülting et al., 2016), physical habitat structure (Enefalk and Bergman, 2016), resource availability (Siler et al., 2001), intra-and inter-specific competition, and predation (Leung et al., 2008). ...
Article
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Despite long-standing interest, the mechanisms driving aquatic macroinvertebrate drift in tropical streams remain poorly understood. Therefore, the objective of this study was to evaluate which environmental metrics drive macroinvertebrate drift in neotropical sky island streams. It evaluated whether altitude, the abundance of food resources, and variations in water quality influenced macroinvertebrate drift density, diversity, richness, and functional feeding groups. An hypothesis was developed to test whether increased altitude, lower food availability (particulate organic matter), and discharge would increase the density, taxonomic richness, and diversity of drifting invertebrates. Nine headwater stream sites were sampled in the rainy and dry seasons in the Espinhaço Meridional Mountain Range (EMMR) of southeast Brazil. Samples were collected using drift nets deployed from 5:00 p.m. to 8:00 p.m. The abundance of food resources was assessed through estimates of coarse (CPOM) and fine (FPOM) particulate organic matter, and primary producers. CPOM availability was an important explanatory variable for Gathering-Collectors and Scrapers, Altitude was important for Shredders and Predators, and Filtering-Collectors were linked to water discharge, suggesting that functional group drift masses were linked to different ecosystem components. Water temperature, conductivity, dissolved oxygen, current velocity, FPOM biomass and microbasin elevation range exerted little influence on macroinvertebrate drift. Regarding taxa composition, this study also found that Baetidae and Leptohyphidae (Ephemeroptera) and Chironomidae and Simuliidae (Diptera) were the most abundant groups drifting.
... Indeed, this choice may affect the output of the study in a twofold way: 1) we could not consider intraspecific variability, which is increasingly recognized as a factor conditioning overall trait variation (Albert et al., 2010;Siefert et al., 2015); 2) the very local scale of our study could not cope well with trait data collected at much larger scales (Cordlandwehr et al., 2013;de Bello et al., 2021). However, especially for this last issue, we used trait datasets applied in studies of aquatic ecology in Europe at different spatial scales (e.g., Schülting et al., 2016;Scotti et al., 2020). Moreover, when different databases were available for the same trait, we chose the ones more targeted to the environmental and habitat conditions of the Saldur stream (e.g., for microhabitat/substrate preference and feeding type). ...
Article
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Currently, across the entire European river network, there are an estimated 0.74 barriers per kilometer of river length, with hydropower production being the main cause of riverine habitat fragmentation. On the one hand, policy actions have been proposed by different institutions to limit this impact. On the other hand, the compelling need to produce energy from renewable/sustainable resources is further boosting the impoundment of rivers, since, globally, small hydropower plants are expected to contribute greatly to future energy needs. While a few studies have already analyzed the environmental impact of small hydropower plants by researching the structural communities of benthic macroinvertebrates, none have thus far assessed the potential impacts related to the functional diversity of these communities. Here, following a “Before-After-Control-Impact (BACI)” scheme, we implemented different methodologies to study the functional diversity of benthic communities sampled across 4 sites in a fish-free, glacier-fed stream of the Italian Central-Eastern Alps for 5 consecutive years. More specifically, the sampling sites were chosen in an area near the weir of a small “run-of-river” hydropower plant, which constituted the structure from which water was diverted to the turbine. Specific goals were to assess the potential variation in the functional traits of benthic macroinvertebrates in relation to the weir’s presence, investigate whether a variation in trait distribution was caused by alterations in the abundances of common and rare taxa, and quantify functional diversity in space and time through the application of specific indices. Our initial hypothesis of finding significant differences among the sampling sites after the start-up of the hydropower plant was not confirmed by our results, since the benthic communities at all sites continued to exhibit a largely similar set of traits and, consequently, functional diversity. Our results highlighted the need for a better understanding of the relationships between effect traits and ecological processes to establish thresholds from which a shift in these processes may occur. Hence, a better understanding of the assets and liabilities of already established small hydropower plants may be a guide for more conscious decisions concerning the establishment of new ones and/or changes in the management of already existing ones.
... Moreover, sudden variations in water temperature (i.e. thermopeaking) may induce behavioral MIV drift (Bruno et al., 2013;Schülting et al., 2016), and re-suspension of fine sediments increases turbidity and clogging risk (Hauer et al., 2019) further affecting MIV (Bo et al., 2007;Crosa et al., 2010;Jones et al., 2012). In addition to drift, stranding is a possible consequence of HP operations. ...
Article
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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 hydropeakingregulated Swiss rivers—aimed to quantify (a) the short-term effects of the combined increase in flow amplitude and up-ramping rate based on macroinvertebrate drift and stranding, as well as (b) 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 hydropeaking was found for Limnephilidae, whereas Heptageniidae seemed to be resistant in respect to short- and long-term hydropeaking effects. In the longterm, 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 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.
... Nevertheless, an increase in flow-related parameters, such as water depth and flow velocity, leads to increased physical stress acting on the animals and hampers vital processes, such as feeding. Further, the exceedance of hydraulic thresholds leads to detachment of organisms from substrates and downstream transport, which, if exceeding natural drift rates, depletes the populations (Schülting et al., 2016;Auer et al., 2017). Thus, tolerant species (which own morphological or behavioral adaptations like claws or the ability to quickly crawl into the interstices) often dominate over sensitive ones (e.g., surface-dwelling taxa that are exposed to flow changes) in hydropeaked rivers, which feature altered biotic community structures as well as reduced biomass (Moog, 1993;Hayes et al., 2021). ...
Chapter
This chapter provides a holistic overview of the science and management of rapid artificial flow fluctuations caused by peak-operating hydropower. Using a process-based framework, this chapter illustrates the links between hydropeaking drivers and associated pressures on river ecosystem structure, function and integrity, and summarizes the role and effects of mitigation measures. In detail, this chapter highlights how hydropeaking causes abiotic (physical) alterations, which facilitate direct and indirect adverse ecological processes and ecosystem changes. As a response to these effects, different hydrological, morphological and emerging or complementary measures are presented and discussed from a river- and energy-grid-specific perspective and exemplified by case studies. Overall, this chapter provides a concise insight into this controversial topic, and presents possible solutions towards a more sustainable management of hydropeaked rivers.
... The latter response observed might indicate that active drift was initiated by receding water as a mechanism to recolonize instream habitats after disturbance. Changes in water temperature following deep-water releases (so-called thermopeaking; Zolezzi et al., 2011), as during 2018 flood, could add up to flow effects and influence taxon-specific drift responses (Schülting et al., 2016). ...
Article
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Rivers regulated by dams display several ecosystem alterations due to modified flow and sediment regimes. Downstream from a dam, ecosystem degradation occurs because of reduced disturbance, mostly derived from limitations on flow variability and sediment supply. In the last decade, most flow restoration/dam impact mitigation was oriented towards the development of environmental flows. Flow variability (and consequent disturbance) can be reintroduced by releasing artificial high flows (experimental floods). Flow-sediment interactions during experimental floods represent strong ecosystem drivers, influencing nutrient dynamics, and metabolic and functional properties. In river networks, sediment and water inputs from tributaries generate points of discontinuity that can drive major changes in environmental conditions, affecting habitat structure and determining functional differences between upstream and downstream. However, despite the relevance for management, flow/sediment relations during environmental flows − and more importantly during experimental floods − remain poorly understood, mostly due to the lack of empirical evidence. In this study, we examined how a major tributary (source of water and sediments) modified the physical habitat template of a regulated river, thereby influencing ecological and geomorphological responses to experimental floods. Methods combined high-resolution drone mapping techniques with a wide range of biological samples collected in field surveys before, during, and after experimental floods in an alpine river. Data were used to quantify changes in relevant functional and structural ecosystem properties, relating ecological responses to geomorphological dynamics. Results highlight the importance of tributaries in restoring ecosystem properties lost after damming, enhancing the resilience of the system. In addition, we observed that disturbance legacy played a fundamental role in determining ecological conditions of a river prior to experimental floods, thus confirming that considering flow variability and sediment availability is crucial in adaptive dam management and environmental flows design.
... Even though stranding may affect only a small portion of the fish population at a time, and may occur naturally, repeated flow fluctuations (frequency) can cause cumulative mortalities that can result in a significant fish loss (Young et al. 2011). Meanwhile, the ramping range (amplitude) of hydropeaking flow can partially explain the downstream displacement of both fish and macroinvertebrates (Thompson et al. 2010, Schülting et al. 2016. Riparian plants face both physiological and physical constraints because of the shifts between submergence and drainage, and erosion of substrates (Bejarano et al. 2018). ...
Article
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Hydropeaking, a hydroelectricity generation strategy involving rapid changes to flow releases from dams in response to fluctuations in hourly-adjusted electricity markets has been widely applied due to its economic efficiency. However, these operational practices produce sub-daily flow fluctuations that pose substantial hazards to riverine ecosystems and human activities. To ascertain the downstream impacts of hydropeaking, features of hydropeaking have been analyzed with respect to ecologically relevant hydrologic variables. However, since studies aiming to characterize hydropeaking regime often require manual feature extraction, they are commonly limited to small temporal and spatial scales. Additionally, riverine ecologists have commonly treated hydropeaking as a broadly similar flow-alteration pattern regardless of the complexities of the electricity market and differences in the natural settings where it is applied. Therefore, this study sought to determine whether significantly different hydropeaking patterns exist on a regional scale, as revealed by temporal variations in hydropeaking over a long temporal scale (> five years). To fulfill this goal, a new algorithm, the Hydropeaking Event Detection Algorithm (HEDA), was developed in R to automate the characterization of hydropeaking flow regimes. Clustering analyses were conducted to explore the similarities and differences of hydropeaking regimes among 33 sites in numerous hydrologic regions of California. Four distinct classes of hydropeaking flow regimes were identified and distinguished by the duration and frequency of hydropeaking. Meanwhile, rate of change, amplitude and timing of hdyropeaking played less important roles in the classification.
... HPP operations lead to variable and short-term changes in hydrology, according to power demand. This so-called hydropeaking frequently causes the drift (owing to increased hydraulic forces) and stranding (owing to the reduction of the wetted area) of fish and macroinvertebrates, considerably reducing biodiversity and biomass in the downstream sections of the river (Greimel et al. 2018;Schülting et al. 2016). ...
Technical Report
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This report summarizes the value of the river Vjosa system as one of the few remaining reference sites for dynamic floodplains in Europe. The morphological floodplain of the Vjosa is characterized by an exceptionally high near-nature status, hence representing an extreme rare reference site for medium sized rivers in Europe. The high values of habitats listed in the EU Habitat Directive underscore its value on an international scale. These protected habitats provide the basis for a highly endangered fauna and flora. More than 1100 documented species, including high numbers and vital populations of protected and endangered species listed in national and international laws and conventions highlight the significance of this natural environment on an international scale. The investigations carried out so far were timely limited and reveal a snapshot only. More intense inter- and multidisciplinary studies would be a prerequisite for the in-depth evaluation of potential impacts caused by hydropower plants. Anyhow, the present study represents a sound baseline survey listing the presently documented fauna and flora, their status, future developments under the prospected stressor of a Hydropower Plant (HPP) and includes national and international Guidelines and Directives. In summary three main arguments are raised against the proposal of a hydropower plant, such as HPP Kalivaç, at the river Vjosa. The project will degrade the extremely high ecological value of the entire River Vjosa from the Delta to the upstream areas of the planned dam significantly. The planned project contradicts clearly the concept of a sustainable development also in an economical perspective. Within the planned project violations of international and national laws are clearly identified.
... Hydropower infrastructure may disconnect sediment flux from upstream to downstream (notably in the case of dams) or modify it substantially where water is abstracted [56,57]. The result can be substantially negative, with direct and indirect impacts on stream ecosystems downstream of hydropower infrastructure (e.g., [25,[58][59][60][61][62][63][64][65][66][67]). Although the need to set e-flows that guarantee a baseflow for downstream ecosystems is well established, it is now recognized that, downstream of dams, there can be, (a) loss of higher flows which may have an important biological function [4], (b) reduced supply of habitat-important gravel and coarser sediment [68,69], and (c) development of stream-bed colmation due to the accumulation of finer material [70] and reduced perturbation of the stream bed [71]. ...
Article
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Setting environmental flows downstream of hydropower dams is widely recognized as important, particularly in Alpine regions. However, the required flows are strongly influenced by the effects of the physical environment of the downstream river. Here, we show how unmanned aerial vehicle (UAV)-based structure-from-motion multiview stereo (SfM-MVS) photogrammetry allows for incorporation of such effects through determination of spatially distributed patterns of key physical parameters (e.g., bed shear stress, bed grain size) and how they condition available stream habitat. This is illustrated for a dam-impacted Alpine stream, testing whether modification of the dam’s annual flushing flow could achieve the desired downstream environmental improvement. In detail, we found that (1) flood peaks in the pilot study were larger than needed, (2) only a single flood peak was necessary, (3) sediment coarsening was likely being impacted by supply from nonregulated tributaries, often overlooked, and (4) a lower-magnitude but longer-duration rinsing flow after flushing is valuable for the system. These findings were enabled by the spatially rich geospatial datasets produced by UAV-based SfM-MVS photogrammetry. Both modeling of river erosion and deposition and river habitat may be revolutionized by these developments in remote sensing. However, it is combination with more traditional and temporarily rich monitoring that allows their full potential to be realized.
... immediately downstream from tributaries), and/or (iii) during other periods or conditions (e.g. after flood events supplying fine materials from upstream), is relevant for defining the frequency and extent of benthic disturbance (e.g. Wilcock et al., 2009;Gibbins et al., 2006;Schülting et al., 2016), and therefore need not be neglected when assessing the effects of such flow pulses on the overall ecosystem functioning. ...
Article
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Hydropower is considered a renewable form of energy production, but generating electricity from rivers is not always environmentally benign. The global demand for renewables is increasing rapidly as fossil fuels are gradually phased out, so rivers will continue to be subjected to the pressures imposed by hydropower for decades to come. Finding ways of operating hydropower plants that limit impacts on downstream river ecosystems is therefore a pressing global concern. Usually, these plants cause marked and rapid fluctuations in flow in downstream river reaches, termed ‘hydropeaking’. Hydropeaks result in a variety of ecological changes in the dynamic mountain rivers they typically affect; declines in fish and insect populations are evident, especially in reaches immediately downstream from the plant. While these changes are often acute and readily apparent, the underlying causal mechanisms remain unclear. We argue here that riverbed sediments are a critical but neglected causal link between hydropeaking flow regimes and ecological changes. We outline how a variety of tools from different branches of river science can now be brought together to understand precisely why hydropeaking alters sediment dynamics; these tools provide a mechanistic explanation for changes in bed sedimentary conditions and channel form across multiple scales and, consequently, a better understanding of ecological changes. By allowing us to simulate the effects of flow fluctuations on sediment dynamics and channel form, these tools also allow us to develop ways of releasing water from hydropeaking dams that limit impacts on aquatic habitat and species.
... immediately downstream from tributaries), and/or (iii) during other periods or conditions (e.g. after flood events supplying fine materials from upstream), is relevant for defining the frequency and extent of benthic disturbance (e.g. Wilcock et al., 2009;Gibbins et al., 2006;Schülting et al., 2016), and therefore need not be neglected when assessing the effects of such flow pulses on the overall ecosystem functioning. ...
Article
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Hydropeaking, through artificially generated flow peaks, affects hydro-sedimentary dynamics on rivers. The frequency and magnitude of such artificial flow pulses impact sedimentary process and, inevitably, affects bed-material entrainment. This study analyses the entrainment of particles in six sections of a Pyrenean river under frequent hydropeaking. Three equations of particle entrainment with contrasting behaviours, validated for particle mobility from tracer data, have been used to predict the initiation of motion in each section. Results show that the peak discharge generated by the hydropower station mostly affects the section immediately downstream from the hydropower plant, where the finer fractions of the bed are mobilised. The mobile grain sizes include fine to medium gravels (< 20 mm). Channel geometry and higher slopes also have an effect on particle entrainment. Entrainment of the finer size fractions of the bed is termed partial transport, i.e. a partially size-selective transport that occurs downstream from the hydropower station and winnows the sand and small gravel further downstream.
... Downstream of electricity generation stations, water may be returned to the river, leading to multiple daily flow peaks ("hydropeaks"; Bratrich et al., 2004) that follow consumer demand for electricity rather than natural flow variability. The stress created by hydropower-induced low flows and hydropeaking has been shown to have major impacts upon stream ecosystems (e.g., Brooker & Hemsworth, 1978;Céréghino & Lavandier, 1998;Cushman, 1985;Lauters et al., 1996;Moog, 1993;Schmutz et al., 2015;Schülting et al., 2016Schülting et al., , 2019Smokorowski et al., 2011). ...
Article
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Alpine hydroelectric power exploitation often aims to increase the volume of water stored behind impoundments which may be achieved through flow abstraction and lateral transfer to storage. Intakes are designed to separate water from sediment which accumulates in settling basins and may be flushed sometimes at sub‐daily frequencies in glaciated basins. In some countries (e.g. Switzerland) intakes drain a greater basin area than impoundments yet legislation designed to improve instream ecosystems impacted by hydropower has almost entirely ignored them. Some research suggests that such streams have exceptionally low abundance and diversity of macroinvertebrates for some kilometres downstream of the intake flushing at high frequency in summer, but that populations can recover rapidly as soon as flushing frequency decreases in early autumn. However, such patterns could also result from natural flow variability, sediment transport and morphological change in glacier‐fed streams. We combine field measurements with habitat modelling to assess the impacts of sediment flushing on macrozoobenthos as compared to what might be expected in a natural, hydromorphologically dynamic Alpine stream. We show that water abstraction in itself could improve habitat conditions because it increases the relative contribution of less turbid and groundwater/unregulated sources. However, intake flushing leads to short duration, sediment‐laden flows that can destabilise substantial areas of the stream bed and cause rates of lateral displacement of habitat much greater than the possible response by macroinvertebrates. Our results challenge current emphasis on minimum flows in such streams and argue that much more emphasis needs to be placed on sediment management.
... Sava, Drava, Dobra) [33,100]. Furthermore, storage HPPs that operate in hydropeaking mode cause ecological effects such as stranding and catastrophic drift of fish and macroinvertebrates downstream of the water releases from HPPs [101][102][103]. The structure and functions of biological communities in river sections affected by hydropeaking becomes highly altered, causing serious environmental concerns [101]. ...
Article
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Currently, Southeast Europe (SEE) is witnessing a boom in hydropower plant (HPP) construction, which has not even spared protected areas. As SEE includes global hotspots of aquatic biodiversity, it is expected that this boom will result in a more severe impact on biodiversity than that of other regions. A more detailed assessment of the environmental risks resulting from HPP construction would have to rely on the existence of nearby hydrological and biological monitoring stations. For this reason, we review the distribution and trends of HPPs in the area, as well as the availability of hydrological and biological monitoring data from national institutions useable for environmental impact assessment. Our analysis samples tributary rivers of the Danube in Slovenia, Croatia, Bosnia and Herzegovina, Serbia, and Montenegro, referred to hereafter as TRD rivers. Currently, 636 HPPs are operating along the course of TRD rivers, most of which are small (<1 MW). An additional 1315 HPPs are currently planned to be built, mostly in Serbia and in Bosnia and Herzegovina. As official monitoring stations near HPPs are rare, the impact of those HPPs on river flow, fish and macro-invertebrates is difficult to assess. This manuscript represents the first regional review of hydropower use and of available data sources on its environmental impact for an area outside of the Alps. We conclude that current hydrological and biological monitoring in TRD rivers is insufficient for an assessment of the ecological impacts of HPPs. This data gap also prevents an adequate assessment of the ecological impacts of planned HP projects, as well as the identification of appropriate measures to mitigate the environmental effects of existing HPPs.
... sessile, attached, crawling or swimming) and the shape (i.e. streamlined, cylindrical, dorsoventrally-flattened or spherical) of invertebrates also influence their probability to be washed by the flow as the drag force exerted by the water on individuals depends on their length, width and height Schülting et al. 2016). However, the critical factor remains the abundance of the taxon in the system. ...
Thesis
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Global Climate Change will increase precipitations in the temperate and Northern coast of Europe during winter and spring. In riverine ecosystems, precipitations affect strongly the discharge of running waters and, thus, it is predicted that streams will face more severe floods. Additionally, air and water temperature will increase all over the world. These new environmental conditions can alter the phenology of species and predator/prey interactions. Newborns of brown trout (Salmo trutta L.) start their exogenous feeding in March/April. This stage is a critical step as individuals undergo huge physiological and behavioral changes. To allow a good development and a high survival rate, preys have to be abundant, particularly during early ontogenesis when fish are most vulnerable to food scarcity and predation. In this thesis, experiments in controlled-environment were conducted to estimate the effect of water velocity on the drift of preferred prey taxa for salmonids and to understand the effect of temperature on the metabolism of alevins facing starvation. Experiments in semi-natural conditions were set up to better understand the effects of floods on invertebrate communities and on survival, behavior and growth of first-feeding alevins. Our data support that floods affect trout differently depending on when they start feeding (early or late spring) and the availability of prey in their environment.
... Research has shown that both hydropeaking and thermopeaking can influence macroinvertebrate communities [86]. Although we did not integrate macroinvertebrates into our conceptual mitigation framework, this group should be included in more holistic approaches in the future, not only because benthic communities are an essential food source for fish, but also because they are an indispensable aspect of functioning river systems [87]. ...
Article
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Peak-operating hydropower plants are usually the energy grid’s backbone by providing flexible energy production. At the same time, hydropeaking operations are considered one of the most adverse impacts on rivers, whereby aquatic organisms and their life-history stages can be affected in many ways. Therefore, we propose specific seasonal regulations to protect ecologically sensitive life cycle stages. By reviewing hydropeaking literature, we establish a framework for hydrological mitigation based on life-history stages of salmonid fish and their relationship with key parameters of the hydrograph. During migration and spawning, flows should be kept relatively stable, and a flow cap should be implemented to prevent the dewatering of spawning grounds during intragravel life stages. While eggs may be comparably tolerant to dewatering, post-hatch stages are very vulnerable, which calls for minimizing or eliminating the duration of drawdown situations and providing adequate minimum flows. Especially emerging fry are extremely sensitive to flow fluctuations. As fish then grow in size, they become less vulnerable. Therefore, an ‘emergence window’, where stringent thresholds on ramping rates are enforced, is proposed. Furthermore, time of day, morphology, and temperature changes must be considered as they may interact with hydropeaking. We conclude that the presented mitigation framework can aid the environmental enhancement of hydropeaking rivers while maintaining flexible energy production.
... Consequently, changes in stream temperature can act as a stressor on aquatic species (e.g. Piggott et al., 2015;Poole and Berman, 2001;Schülting et al., 2016). It is therefore not surprising that much research has been done on the effect of climate warming on stream temperature and aquatic species (e.g. ...
Article
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Groundwater seepage influences the temperature of streams and rivers by providing a relatively cool input in summer and warm input in winter. Because of this, groundwater seepage can be a determining factor in the provision of suitable water temperatures for aquatic biota. Climate warming affects stream and groundwater temperatures, and changes the thermal characteristics of streams leading to the potential disappearance of habitats. In this study the importance of groundwater for the temperature of two Dutch lowland streams and its possible role in mitigating the effects of climate change was determined by combining field measurements and a modelling experiment. Stream temperature measurements using fibre optic cables (FO-DTS) and sampling of ²²² Rn were done to map localized groundwater inflow. Several springs and seepage ‘hot-spots’ were located which buffered the water temperature in summer and winter. A stream temperature model was constructed and calibrated using the FO-DTS-measurements to quantify the energy fluxes acting on stream water. This way, the contribution to the stream thermal budget of direct solar radiation, air temperature and seepage were separated. The model was then used to simulate the effects of changes in shading, groundwater seepage and climate. Shading was shown to be an important control on summer temperature maxima. Groundwater seepage seemed to buffer the effect of climate warming, potentially making groundwater dominated streams more climate robust. Protecting groundwater resources in a changing climate is important for the survival of aquatic species in groundwater-fed systems, as groundwater seepage both sustains flow and buffers temperature extremes.
Article
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Hydropower is commonly considered a renewable energy source. Nevertheless, this does not imply an absence of impacts on the riverine ecosystem, the extent of which is expected to increase in the coming years due to the energy transition from fossil fuels to renewable sources and for the climate change. A common consequence of hydroelectric power generation is hydropeaking, which causes rapid and frequent fluctuations in the water flow downstream of hydropower plants. The review incorporates 155 relevant studies published up until November 2023 and follows a systematic review method, Preferred Reporting Items for Systematic Reviews and Meta- Analyses (PRISMA), which is a multi-stage systematic procedure for the identification and selection of research documents. The selected studies highlighted several prominent impacts of hydropeaking on aquatic environments. The primary effects include alterations in flow patterns, modification of water temperature, changes in sediment dynamics and fluctuations in dissolved gas levels. These alterations have been found to affect various aspects of aquatic ecosystems, including fish growth, behavior, reproductive success, habitat, and migration patterns, and benthic macroinvertebrate communities. Furthermore, hydropeaking can also lead to habitat fragmentation, erosion, and loss of riparian vegetation, thereby impacting terrestrial ecosystems that depend on the aquatic environment. Despite the body of literature reviewed, several knowledge gaps were identified, underscoring the need for further research. There is limited understanding of the long-term ecological consequences of hydropeaking and its cumulative effects on aquatic ecosystems. Additionally, there is lack of consensus regarding the quantification of ecosystem services, economic impact, soil moisture content, and weighted usable area due to flow fluctuation and global evolution of energy production from renewable energy sources. Addressing the identified research gaps is crucial for achieving a balance between energy production and the conservation of freshwater ecosystems in the context of a rapidly changing global climate.
Chapter
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Structural applications of composite materials are used in various structures of the oil and gas industry, water supply and sewage systems and a wide range of industries, such as marine, aerospace, and military industries. This paper aims to numerically investigate the influence of local dent caused by an indenter on the buck-ling behaviour of glass fabric-reinforced polymer cylindrical shells when subjected to external pressure. For this purpose, 24 finite element numerical models with five layers and a stacking sequence [30/-30/30/-30/30] were simulated in ABAQUS. The effect of dent depth (2, 4, 6 and 8 mm) and orientation (0 and 90 degrees) that was created at the mid-height, the 1/3rd and the 2/3rd of the shell height on the buckling behaviour of the composite cylindrical shells were evaluated. The results underscored that whilst the location of the local dent and the depth affected the shells’ buckling capacity, the dent’s orientation had minimal effect on the buckling capacity of the cylindrical shells.
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Water temperature is one of the main abiotic factors affecting the structure and functioning of aquatic ecosystems and its alteration can have important effects on biological communities. Macroinvertebrates are excellent bio‐indicators and have been used for decades to assess the status of aquatic ecosystems as a result of environmental stresses; however, their responses to temperature are poorly documented and have not been systematically evaluated. The aims of this review are: (i) to collate and summarize responses of freshwater macroinvertebrates to different temperature conditions, comparing the results of experimental and theoretical studies; (ii) to understand how the focus of research on the effects of temperature on macroinvertebrates has changed during the last 51 years; and (iii) to identify research gaps regarding temperature responses, ecosystem types, organism groups, spatiotemporal scales, and geographical regions to suggest possible research directions. We performed a comparative assessment of 223 publications that specifically consider freshwater macroinvertebrates and address the effects of temperature. Short‐term studies performed in the laboratory and focusing on insects exposed to a range of temperatures dominated. Field studies were carried out mainly in Europe, at catchment scale and almost exclusively in rivers; they mainly investigated responses to water thermal regime at the community scale. The most frequent biological responses tested were growth rate, fecundity and the time and length of emergence, whereas ecological responses mainly involved composition, richness, and distribution. Thermal research on freshwater macroinvertebrates has undergone a shift since the 2000s when studies involving extended spatiotemporal scales and investigating the effects of global warming first appeared. In addition, recent studies have considered the effects of temperature at genetic and evolutionary scales. Our review revealed that the effects of temperature on macroinvertebrates are manifold with implications at different levels, from genes to communities. However, community‐level physiological, phenological and fitness responses tested on individuals or populations should be studied in more detail given their macroecological effects are likely to be enhanced by climate warming. In addition, most field studies at regional scales have used air temperature as a proxy for water temperature; obtaining accurate water temperature data in future studies will be important to allow proper consideration of the spatial thermal heterogeneity of water bodies and any effects on macroinvertebrate distribution patterns. Finally, we found an uneven number of studies across different ecosystems and geographic areas, with lentic bodies and regions outside the West underrepresented. It will also be crucial to include macroinvertebrates of high‐altitude and tropical areas in future work because these groups are most vulnerable to climate warming for multiple reasons. Further studies on temperature–macroinvertebrate relationships are needed to fill the current gaps and facilitate appropriate conservation strategies for freshwater ecosystems in an anthropogenic‐driven era.
Article
There is well-established evidence that dams disconnect upstream to downstream sediment flux in rivers and that this may have negative impact on downstream ecosystems. For this reason, the development of environmental flows now includes sediment supply and transport whether through reconnecting upstream supplied sediment to a river downstream of a dam, eco-morphogenic flows to rework the stream bed, or artificial sediment supply. However, especially in Alpine systems, there may be unregulated tributaries that are able to deliver gravel and coarser sediment naturally to compensate for the effects of dam-related sediment disconnection. To represent these effects we propose a geomorphic form of the serial discontinuity concept and apply it to two hydropower dam-impacted Alpine streams in the Swiss Pennine Alps. Conceptually, the relative position of a dam influences the degree of coarse sediment disconnection as well as the rate of coarse sediment recovery, especially as many Alpine valleys have strong down-valley gradients in tributary sediment delivery. In both case-studies, there was rapid recovery in likely coarse sediment delivery downstream of the dams. By following geomorphic response of the rivers to eco-morphogenic flow trials, proposed as a solution to dam-driven coarse-sediment disconnection, we confirmed that both rivers are likely to have more than sufficient natural coarse sediment supply and unregulated floods. Natural coarse sediment supply is rarely considered in the management of Alpine streams impacted by hydropower but it needs to be evaluated through a geomorphological assessment, considering both the geomorphic context of the river reaches downstream of the dam and the geomorphic attributes of the basin in which the dam is found.
Article
Sudden instream releases of water from hydropower plants (hydropeaking [HP]) can cause abrupt temperature variations (thermopeaking [TP]), typically on a daily/sub-daily basis. In alpine rivers, hydropeaking and thermopeaking waves usually overlap, which leads to a multiple stressor of flow velocity pulses and temperature alteration. Periphytic communities could give important insights into the effects of combined thermo- and hydropeaking (THP) in stream ecosystems. Thus, the study's first aim was to assess the combined effects of thermo-hydropeaking on structural (composition, biomass) and functional (photosynthesis, enzyme activity) properties of periphyton. The second aim was to assess the interaction between periphytic algae and the heterotrophic communities (bacteria) and determine how biotic and abiotic factors explain the variability of bacterial enzymatic activities in the periphyton. We assessed the effects of repeated cold and warm thermo-hydropeaking for 24 days on periphyton, by manipulating discharge and temperature in six experimental flumes directly fed by an Alpine stream. Our study revealed that THP had structural and functional effects on periphyton in oligotrophic streams, where the effects depending on the direction of the temperature change (cold/warm) and on the morphological setting (pool/riffle). The results showed that even a short-term increase in flow velocity and temperature decrease could induce better growth conditions for diatoms. Additionally, an increase in the interaction between periphytic algae and bacteria during thermo-hydropeaking was also shown, this coupling being more pronounced in pool than in riffle sections. Our results clearly showed that riffle sections develop less periphytic algal biomass and activity and therefore, THP can reduce biomass availability for primary consumers in large areas of impacted streams. These findings highlight the importance of mitigation measures, focusing on establishing heterogeneous stream bed areas, with frequent pool and riffle sequences.
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Hydropeaking refers to the mode of hydropower dam operation where sub-daily changes in flow are used to vary the generation of electricity in accordance with demand. A typical pattern produces maximum power during the day (i.e., the peak), and minimal power at night. Hydropeaking is considered necessary to stabilize the energy grid since it is the only reliably flexible method of producing electricity besides fossil fuels. With the planned phase-out of traditional coal-fired electricity production across Canada by 2030, and the increased reliance on intermittent wind and solar generation, the flexibility of hydropeaking will assume an increased importance. However, hydropower generation comes with costs; hydropeaking in particular is considered one of the most ecologically harmful modes of operation since downstream biota are subjected to flows that deviate greatly from typical natural flow regime patterns. The ecological effects of hydropeaking have been examined in a growing body of literature, but mitigation options do exist that include dam operational and/or structural modifications. This paper will explore the importance of hydropeaking in the Canadian electricity system, the ecological consequences of flexible hydropower, and mitigation options that could potentially strike a balance between meeting Canadian energy needs and minimizing ecosystem impacts.
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Human population growth, economic development, climate change, and the need to close the electricity access gap have stimulated the search for new sources of renewable energy. In response to this need, major new initiatives in hydropower development are now under way. At least 3,700 major dams, each with a capacity of more than 1 MW, are either planned or under construction, primarily in countries with emerging economies. These dams are predicted to increase the present global hydroelectricity capacity by 73 % to about 1,700 GW. Even such a dramatic expansion in hydropower capacity will be insufficient to compensate for the increasing electricity demand. Furthermore, it will only partially close the electricity gap, may not substantially reduce greenhouse gas emission (carbon dioxide and methane), and may not erase interdependencies and social conflicts. At the same time, it is certain to reduce the number of our planet’s remaining free-flowing large rivers by about 21 %. Clearly, there is an urgent need to evaluate and to mitigate the social, economic, and ecological ramifications of the current boom in global dam construction.
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Aquatic and terrestrial ecosystems are linked through lateral interactions that support and maintain biodiversity in both regions. However, in many places, river regulation and channelization have isolated rivers from surrounding riparian areas. We evaluated the effects of channelization on the linkages between aquatic and terrestrial invertebrate assemblages in the Rio Grande, New Mexico via comparison of quantitative macroinvertebrate survey data and analyses of carbon and nitrogen isotopes to test for changes in nutrient flow between channelized and non-channelized reaches of this highly regulated system. Aquatic and terrestrial macroinvertebrates were surveyed in summer 2008 at channelized and non-channelized reaches. Average densities of aquatic macroinvertebrates were 50% lower in the channelized reaches. Taxonomic richness and densities of macroinvertebrates in the transition zone between the river and forested floodplain were also lower in channelized reaches and this effect was especially pronounced for predatory macroinvertebrate species. Carbon isotope ratios in consumers indicated that instream (i.e., benthic algae) production served as the major source of carbon for predaceous arthropods in the transition zone. Our results indicate that river regulation that leads to channelization can reduce diversity and macroinvertebrate densities at the landscape scale by severing linkages between the aquatic and riparian communities. These effects appear especially acute for predaceous macroinvertebrates, perhaps because preferred prey density is lowered. Restoration of natural flow regimes is vitally important to reduce channelization and maintain connectivity between the aquatic and terrestrial environments to conserve the unique assemblage of macroinvertebrates in the transition zone.
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The stream orders of the Austrian running waters Stream orders represent an ideal system for classifying major aspects of running waters, taking into account a number of abiotic factors changing from source to mouth. Dimensions such as of length, width, depth, water temperature, catchment area, water discharge and other factors can be assessed rather accurately. All these parameters being closely interlinked, even biotic factors can be projected precisely with regard to their relation to the stream orders. These aspects are discussed in the first part of this study. Especially in North America, stream orders play an outstanding role within river classification. But they are getting more and more important in Middle Europe, too. Among the various stream order systems presented in the study at hand, the one developed by Strahler is the most common applied all over the world. Part II concentrates on classifying all Austrian river segments according to the Strahler system. Thus the catalogue presents the first country-wide evaluations of this key element of river classification and will have a positive effect on water management and protection activities and on the efforts concerning standardization and harmonization of national and international studies.
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We conducted two experiments to assess drift and benthic invertebrate responses to stepwise and abrupt changes in non-scouring flow in gravel-bed experimental streams. Intuitively, a stepwise flow increase should allow aquatic invertebrates more time to seek refuges than would an abrupt increase. We hypothesized that abrupt flow increases would result in larger increases in taxon richness and in the number of invertebrates in the drift, and a larger decrease in benthic density than would stepwise flow increases. Two kinds of drift response to flow increases were observed in the stepwise experiment: (1) no response (e.g. Caenissp. [Ephemeroptera] and Sphaeriidae [Pelecypoda]); (2) threshold response of some aquatic (e.g. Crangonyx pseudogracilis[Amphipoda]) and semiaquatic (e.g. Ormosiasp. [Diptera]) taxa. Drift richness and drift density in both experiments declined after reaching a peak. The peak was reached almost immediately in the abrupt treatment and later in the stepwise treatment. Maximum richness of taxa and taxon composition in the drift were similar in both experiments. Despite significant increases in drift, stepwise and abrupt increases in flow did not have a significant effect on benthic density. However, relative to reference streams, the percentage of total benthic invertebrates in the drift increased 10× in the stepwise experiment and 33× in the abrupt experiment. These non-scouring increases in flow were non-trivial. Our results suggest that several high flow events of the same magnitude (i.e. 2.5–3.0 fold increases) may cause considerable losses of benthic populations to the drift. The rate of increases in flow appears to be important: abrupt increases in flow had a stronger effect on invertebrate drift than did stepwise increases.
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Although spatial scale, upstream-downstream gradients, environmental variability, and floodplain connectivity and complexity have been recognized as integral components of our understanding of riverine pattern and process, aquatic invertebrate community structure across lateral gradients from headwaters to the lowland of a river has received little empirical documentation. Aquatic invertebrate density, distribution, and richness were investigated at 29 study sites distributed laterally (main channel-floodplain) among 6 geomorphologically distinct river reaches from the headwaters to near the mouth of one of the last seminatural river corridors draining the European Alps, the Tagliamento River in northeastern Italy. Community relationships were examined using multivariate and diversity analyses to investigate patterns of taxonomic richness. Diversity parameters were scaled at the site, reach, and catchment levels to better understand local and regional patterns. Mean invertebrate density increased from 7484 ± 2480 (±1 SE) individuals/m2 in the headwaters to 98,811 ± 18,037 individuals/m2 on the lowland floodplain. Crustacea, Coleoptera, and Ephemeroptera richness increased and nonchironomid Diptera and Plecoptera richness declined along the corridor. Richness (α diversity) and turnover (β diversity) showed no consistent increase or decrease along connectivity gradients within geomorphic reaches along the river corridor, possibly because each reach had unique characteristics. α diversity was similar among geomorphic reaches along the corridor, whereas β diversity between reaches increased as a function of distance between them. Direct gradient analysis indicated high taxa-to-environment concordance along lateral (i.e., floodplain water bodies) and longitudinal (upstream-downstream) dimensions and indicated distinct floodplain communities. These results demonstrate how lateral gradients (floodplain dimension) structure zoobenthic communities and how this structure can change along the longitudinal dimension (upstream-downstream). Our results highlight the importance of off-channel environments to macroinvertebrate community structure and diversity. Conservation, restoration, and preservation measures must consider the lateral dimension along river corridors as integral to maintaining diversity and community structure.
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The bottom fauna and drift in the Kakanui River, New Zealand, were studied for a period of one year. The fauna was dominated by Ephemeroptera and Chironomidae. A diurnal drift rate was found with maximum rates just after sunset. A mechanism is postulated to account for the observed correlation of decrease in light intensity at sunset and increase in drift rate. There was a quantative change in the drift at night with the occurrence of comparatively large numbers of mayfly nymphs and Rhyacophilidae larvae. Lowest drift rates were recorded during the winter. There is a close interrelationship between drift and bottom fauna: proportional occurrence in the bottom fauna is similar to that in drift but is modified by differences in behaviour of the animals, and the occurrence of pieces of algae, containing animals. During the study a flood occurred which halved the density of the bottom fauna but within three weeks the denslty returned to near its pre-flood value. Some species had higher densities after the flood than before it. Recolonization of the substrate by the animals could be followed by interdependent changes in bottom fauna and drift samples. A large increase in drift rate was recorded at sunset immediately after the flood had occurred.
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This paper reviews the literature on invertebrate drift in running waters, emphasising papers published during the last 10–15 years. The terms constant drift, catastrophic drift, behavioural drift, active drift and distributional drift are defined, but their use should be limited as much confusion has arisen. Sampling methods are briefly reviewed. The composition of drift in streams and rivers is assessed, especially with respect to temporal variation, drift densities and drift distances. This body of descriptive literature is subsequently analysed in relation to both abiotic and biotic variables, such as current/discharge, photoperiod, temperature, benthic densities, predators and life cycle stage. The ecosystem significance of drift in terms of colonization and distribution, population dynamics and its importance as a food resource are then reviewed and discussed. Drift enables organisms to escape unfavourable conditions and gives them the potential to colonize new habitats. However, mortality poses a constant threat. The drift community is composed of components whose presence in the drift may be due to widely differing reasons. This renders unsuccessful most attempts to explain drift in terms of one or even a few factors, except in extreme cases, such as floods or pollution. The question whether drifting organisms are alive, dead, or “ecologically dead” is seldom addressed, as is variation at the level of the individual. The drift literature is dominated by large numbers of discriptive papers and there is a need for laboratory and field studies aimed at testing specific hypotheses.
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Rapid changes in flow below hydroelectric facilities result from peaking operations, where water is typically stored in a reservoir at night and released through turbines to satisfy increased electrical demand during the day. Potential impacts of these short-term, recurring disturbances of aquatic systems below dams are important considerations in hydropower development. Reduced biotic productivity in tailwaters may be due directly to flow variations or indirectly to a variety of factors related to flow variations, such as changes in water depth or temperature, or scouring of sediments. Many riverine fish and invertebrate species have a limited range of conditions to which they are adapted. The relatively recent pattern of daily fluctuations in flow is not one to which most species are adapted; thus, such conditions can reduce the abundance, diversity, and productivity of these riverine organisms. Information needs for site-specific evaluations of potential impacts at hydroelectric peaking projects are outlined, along with management and mitigation options to reduce anticipated adverse effects.
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Relative importance of different dispersal modes (drift and crawling) on macroinvertebrate colonization within seasons under differing disturbance regimes was tested by field experiment. Forty individual substrata (tiles) were placed in a series of riffles in Mink Creek, Idaho, a third-order, Rocky Mountain stream. Twenty tiles were mounted on steel bars to elevate them above the streambed and 20 were placed directly on the streambed to distinguish invertebrates colonizing by drift from those colonizing by crawling. After an initial colonization period of 32 days, all invertebrates were removed from tiles every 2, 4 or 8 days or left undisturbed during the 16 day experimental period. Experiments were conducted in the spring, summer and autumn of 1992. In the spring experiment, invertebrate abundance was greater (524%) but diversity (D) was lower (-42%) on elevated tiles as compared to unelevated tiles. No significant differences were found between elevated and unelevated tiles or disturbance frequencies in terms of abundance and diversity in summer. Abundance decreased with increasing levels of disturbance in autumn (-58%) (2-day disturbance to 8-day disturbance treatments). No significant differences in diversity were found between disturbance treatments or between tile elevations in the autumn. Relative importance of drift and crawling as modes of colonization varied with season. Colonization through drift was important in spring, when water temperature was low, discharge was high, and algal resources were low. In summer and autumn, when water temperature was high, discharge was low, and algal resources were abundant, drifting and crawling taxa colonized equally rapidly.