Article

Effects of hydro- and thermopeaking on benthic macroinvertebrate drift

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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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... The papers in this first group are based on detailed investigations of hydropeaking processes and biotic responses from a small (patch) scale (Schülting et al., 2016;Auer et al., in press;Casas-Mulet et al., in press;Leitner et al., 2016) up to local scale and reach scale assessment (Capra et al., in press; Pulg et al., in press). The patch-scale analyses are carried out on studies in an artificial outdoor research facility for macroinvertebrates (Schülting et al., 2016) and fish (Auer et al., in press) as well as on field investigations (Casas-Mulet et al., in press;Leitner et al., 2016). ...
... The papers in this first group are based on detailed investigations of hydropeaking processes and biotic responses from a small (patch) scale (Schülting et al., 2016;Auer et al., in press;Casas-Mulet et al., in press;Leitner et al., 2016) up to local scale and reach scale assessment (Capra et al., in press; Pulg et al., in press). The patch-scale analyses are carried out on studies in an artificial outdoor research facility for macroinvertebrates (Schülting et al., 2016) and fish (Auer et al., in press) as well as on field investigations (Casas-Mulet et al., in press;Leitner et al., 2016). Three papers focus on fish (Auer et al., in press; Capra et al., in press; Casas-Mulet et al., in press), two on macroinvertebrates Schülting et al. (2016); Leitner et al., 2016) and one on a completely new chemical-physical feature of hydropeaking (Pulg et al., in press). ...
... The patch-scale analyses are carried out on studies in an artificial outdoor research facility for macroinvertebrates (Schülting et al., 2016) and fish (Auer et al., in press) as well as on field investigations (Casas-Mulet et al., in press;Leitner et al., 2016). Three papers focus on fish (Auer et al., in press; Capra et al., in press; Casas-Mulet et al., in press), two on macroinvertebrates Schülting et al. (2016); Leitner et al., 2016) and one on a completely new chemical-physical feature of hydropeaking (Pulg et al., in press). ...
... 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.
... An overall decreasing in macroinvertebrate density and an increasing in downstream drift have been reported as usual responses of lotic macroinvertebrates to several types of disturbance including water pollution (Feio et al., 2010;Friberg et al., 2010;Ortiz et al., 2005) and inherent hypoxia (Rueda et al., 2002), and alterations in flow regime (Gibbins et al., 2010;Schülting et al., 2016). Low flow periods often result in an increase in limnophilic taxa to the detriment of rheophilic (Jowett and Duncan, 1990). ...
... As a result, mesocosm systems have been extensively used in stream ecosystem research to improve understanding of multiple stressor effects on freshwater biota (e.g. Branco et al., 2016;Elbrecht et al., 2016;Jones et al., 2015;Matthaei et al., 2010;Piggott et al., 2012;Poff et al., 2003;Schülting et al., 2016). Yet, to our knowledge, macroinvertebrate instantaneous drift patterns still remain poorly understood in the context of interacting effects of reduced flow and increasing oxygen deficit under different seasons. ...
... The downstream transport of benthic invertebrates in the water column (drift) can occur actively or passively (Brittain and Eikeland, 1988), and has been related to a variety of biotic and abiotic factors, including life-cycle stage, current/discharge (Gibbins et al., 2010;Poff and Ward, 1991;Schülting et al., 2016), water chemistry and contamination (Araújo et al., 2016;Beketov and Liess, 2008). Our study revealed an overall significant decrease in macroinvertebrate community drift behaviour with slower flow velocity. ...
Article
In Mediterranean rivers, water scarcity is a key stressor with direct and indirect effects on other stressors, such as water quality decline and inherent oxygen depletion associated with pollutants inputs. Yet, predicting the responses of macroinvertebrates to these stressors combination is quite challenging due to the reduced available information, especially if biotic and abiotic seasonal variations are taken under consideration. This study focused on the response of macroinvertebrates by drift to single and combined effects ofwater scarcity and dissolved oxygen (DO) depletion over two seasons (winter and spring). A factorial design of two flowvelocity levels - regular and low (vL) - with three levels of oxygen depletion - normoxia, medium depletion (dM) and higher depletion (dH) - was carried out in a 5-artificial channels system, in short-term experiments. Results showed that both stressors individually and together had a significant effect on macroinvertebrate drift ratio for both seasons. Single stressor effects showed that macroinvertebrate drift decreased with flow velocity reduction and increased with DO depletion, in both winter and spring experiments. Despite single stressors opposing effects in drift ratio, combined stressors interaction (vL × dM and vL × dH) induced a positive synergistic drift effect for both seasons, but only in winter the drift ratio was different between the levels of DO depletion. Stressors interaction in winter seemed to intensify drift response when reached lower oxygen saturation. Also, drift patterns were different between seasons for all treatments, which may depend on individual's life stage and seasonal behaviour. Water scarcity seems to exacerbate the oxygen depletion conditions resulting into a greater drifting of invertebrates. The potential effects of oxygen depletion should be evaluated when addressing the impacts of water scarcity on river ecosystems, since flow reductions will likely contribute to a higher oxygen deficit, particularly in Mediterranean rivers.
... 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.
... Primary production was found to decrease due to high turbidity and scouring (Cashman, Harvey, Wharton, & Bruno, 2017;Hall et al., 2015), whereas algal drift showed an increase (Kennedy et al., 2014). Abundance and biomass of macroinvertebrates were frequently found to be reduced, due to increased hydraulic stress and resulting passive drift (Brooker & Hemsworth, 1978;Céréghino, Cugny, & Lavandier, 2002;Kennedy et al., 2014;Lauters et al., 1996;Parasiewicz, Schmutz, & Moog, 1998;Schülting, Feld, & Graf, 2016). ...
... This resulted in six experimental units for each treatment (two "ramping simulations": T1 = 0.5 cm/min, T2 = 1 cm/min) and six experimental units for the simultaneous controls (C1 and C2). Experiments were repeated during day and night in June '14 and March '15, resulting in 48 units per season; see also Schülting et al. (2016). Unfortunately, we had to exclude two experimental units in June (leaky buckets) and one in March (mistake in the laboratory). ...
... In March, drift during experiments of both ramping settings did not show any differences. As mentioned above, the specimens generally showed significantly lower drift in March, possibly due to low water temperatures and reduced activity (Schülting et al., 2016;Shearer et al., 2002). If a high proportion of the specimens already dwells in the substrate before the peak, the up-ramping velocity may be of minor importance. ...
Article
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Intermittent storage hydropower production is the only renewable source offering both, a sufficient storage potential and a high temporal flexibility in production to ensure grid stability. However, hydropeaking (generation of peak discharges by hydro‐electric operation) causes fluctuations in the wetted width, water depth, flow velocity and bottom shear stress downstream of a hydro‐electric facility. River biota are known to be affected by these changes, which leads for example to increased drift. Correspondingly, abundance and biomass of macroinvertebrates are frequently found to be reduced in impacted river stretches. While there is sufficient evidence for increasing drift proportions due to hydropeaking, only few studies have highlighted the role of the rapidity of flow increase before and flow decrease after a peak event (ramping velocity). Here, we present the outcome of experimental hydropeaking in artificial flumes, mimicking two different ramping velocity treatments (T1: 0.5 cm/min, T2: 1 cm/min water table change) in early and late spring (June’14, March ‘15). Macroinvertebrate drift was significantly higher in treatments as compared to control flumes. Drift proportions peaked during the up‐ramping phase and were slightly lower during the peak discharge phase. Drift proportions of T2 treatments were significantly higher than those of T1 in June, but not in March. Our findings suggest that hydropeaking requires thoughtful ramping management, to allow macroinvertebrates to seek for refugia on the stream bottom during the peak event. However, the evidence of daytime‐dependent and seasonal drift patterns also plea for adaptive management, to account for the temporal variability of macroinvertebrate drift.
... 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.
... 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.
... Therefore, these anthropogenic induced rapid flow fluctuations may cause different ecological impacts, including periphyton biomass reduction (Bondar-Kunze et al., 2016), 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 (Auer et al., 2017;Boavida et al., 2017;Nagrodski et al., 2012), cause metabolic changes (Costa et al., 2018;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. ...
Article
Hydroelectric power plants managed in response to sub-daily changes of the electricity market undergo rapid variations of turbine discharge, entailing quickly fluctuating water levels downstream. This operation regime, called hydropeaking, causes numerous adverse impacts on river ecosystems. The hydrological alterations which affect hydropeaking rivers can be described by five parameters that change over space and time (magnitude, rate of change, frequency, duration, and timing), where each parameter may be correlated with distinct environmental impacts and therefore may be used to define flow thresholds and set targets for operational mitigation strategies. Thus, this study aims to present an extensive review on the so far established hydropeaking targets and thresholds regarding the outputs from the scientific community as well as from national regulations. We found that only few European countries (Switzerland and Austria) have legal regulations regarding hydropeaking flow thresholds. Other countries, such as Canada and the USA, present environmental legislation that can force hydropeaking mitigation measures. Most mitigation thresholds and management recommendations in literature deal with the effect of downramping on the stranding of salmonids, as well as with minimum flows between peak-flows to avoid spawning ground desiccation. Regarding other fish species and parameters, information on mitigation targets or thresholds is scarcer or non-existent, as well as on hydropeaking mitigation case-studies, resulting in a lack of knowledge and guidelines for its implementation or regulation. Nevertheless, the available literature indicates that multiple aspects must be considered when assessing such values. Thus, to aid in that process, we propose that mitigation targets and thresholds must be based on key species, including particular features regarding season, life-stage and time of day, which must be combined with site-specific morphological characteristics. The presented approach may benefit impacted organism groups in hydropeaking reaches through the establishment of ecologically-based relevant mitigation thresholds and/or targets.
... 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
Full-text available
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.
... 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.
... Additionally, the timing of a peak event is a critical parameter, since the activity of aquatic organisms changes throughout the day. Several studies showed that drift of macroinvertebrates increases during the night when they are more active feeding, i.e., there is a negative correlation between light intensity and the feeding activity of the animals due to predatory pressure during day (Allan 1987;Elliott 1967Elliott , 2005Poff et al. 1991;Schülting et al. 2016). Experiments on larval and juvenile grayling and juvenile brown trout during summer as well as on larval brown trout during winter showed increased stranding during nocturnal experiments (Auer et al. 2014). ...
... Following hydropeaking, Carolli et al. (2012) and Bruno et al. (2013) observed in experiments increased macroinvertebrate drift associated with warm and cold thermopeaking. By contrast, results of an experimental study by Schülting et al. (2016) suggest that hydropeaking and cold thermopeaking together have an antagonistic effect on drift for aquatic macroinvertebrates. The findings suggest that macroinvertebrate responses to cold thermopeaking are taxa-specific, but in general lead to reduced drift for most taxa. ...
Chapter
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Flow is a major driver of processes shaping physical habitat in streams and a major determinant of biotic composition. Flow fluctuations play an important role in the survival and reproductive potential of aquatic organisms as they have evolved life history strategies primarily in direct response to natural flow regimes (Poff et al. 1997; Bunn and Arthington 2002). However, although the organisms are generally adapted to natural dynamics in discharge, naturally caused flow fluctuations may entail negative consequences (e.g., stranding, drift, low productivity), especially if the intensity is exceptionally high or the event timing is unusual (Unfer et al. 2011; Nagrodski et al. 2012). Aside from natural dynamics in discharge, artificial flow fluctuations with harmful impacts on aquatic ecology can be induced by human activities. Hydropeaking—the discontinuous release of turbined water due to peaks of energy demand—causes artificial flow fluctuations downstream of reservoirs. High-head storage power plants usually induce flow fluctuations with very high frequencies and intensities compared to other sources of artificial flow fluctuations (Fig. 5.1). However, run-of-the-river power plants and other human activities may also create artificial hydrographs due to turbine regulation, gate manipulations, and pumping stations.
... 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.
... When we consider the influence of dams in the context of extreme climatic events, like heat waves and droughts, we expect that an ever-growing portion of biodiversity in running waters will be exposed to altered thermal environments (Ledger & Milner, 2015). Dams and diversions will substantially alter water temperature through prolonged hypolimnetic releases that markedly decrease summer water temperatures (Lugg, 1999;Todd, Ryan, Nicol, & Bearlin, 2005), pulsed releases that accentuate diurnal variability (Sch€ ulting, Feld, & Graf, 2016;Zolezzi, Siviglia, Toffolon, & Maiolini, 2011) and low baseflows that allow rapid heat exchange with air and raise temperatures (Arora, Tockner, & Venohr, 2016;Van Vliet et al., 2011). ...
Article
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• Rivers around the world are undergoing shifts in thermal regime due to climate change and human appropriation of water resources. The local impacts of thermal regime change are challenging to predict because water temperature can influence aquatic organisms and communities at multiple levels simultaneously. For example, thermal change can influence the phenology of periphyton blooms, primary consumer physiology and behaviour, and interspecific interactions with predators. • Using tadpoles of the threatened river‐breeding foothill yellow‐legged frog (Rana boylii, Ranidae), their algal foods and their invertebrate predators, we mimicked dam‐induced changes in temperature and observed the outcome of consumer–resource interactions. In stream enclosures, we reared tadpoles across a gradient of cold to warm conditions, quantified the ash content of diet, digestive efficiency and growth rate, and assessed their vulnerability to hemipteran and odonate predators. • Tadpoles reared in a cool stream (15.5°C daily mean) digested epilithic periphyton poorly (6.6 ± 0.4% assimilation efficiency). In contrast, average assimilation efficiency of tadpoles reared at 19°C was 11.6 ± 0.1%. Access to nutritious diatoms (i.e. dinitrogen‐fixing Epithemia spp., Rhopalodiaceae) increased assimilation efficiency to 10.1 ± 0.1% and 13.8 ± 0.1% in the cool and warm treatments, respectively. Assimilation efficiency correlated positively with tadpole growth rate (R = 0.66, p < .001). • The effect of temperature on mortality due to predation was mediated by low tadpole growth rates at cool temperatures and not by the temperature of predator exposure. Non‐lethal effects of predators on tadpole growth and tail injury, however, depended on both rearing temperature and exposure temperature. Contrary to the expectation that the cost of predator avoidance behaviours may be greater at warmer exposure temperatures because basal metabolic rates are higher, our results indicated that the energetic cost of foraging less was amplified at cool temperatures. • Our results show that when thermal conditions impair digestion in a species’ early life stages, recruitment bottlenecks are likely to arise due to the combined negative effects of cool temperatures on assimilation efficiency and growth, and increased predation by invertebrates.
... 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.
... It is the most affordable renewable energy source, and run-of-river hydroelectric power plants have the highest energy payback ratio (267 versus 39 for wind and nine for solar photovoltaic) [4]. However, they contribute greatly to the degradation of river ecosystems and biodiversity [5,6]: Retention structures are obstacles to the longitudinal connectivity of river habitats [7], reduce hydrodynamics, and foster exotic species invasion [8]; hydropeaking causes dewatering, fish stranding and modifies fish assemblage [9,10]; flow modifications have severe consequences for river ecosystems [8], and particularly for the fish population [11][12][13][14][15]. ...
Article
Full-text available
The increase in minimum flows has rarely been considered to mitigate the ecological impact of hydroelectric power plants because it requires a site-specific design and expensive long-term monitoring procedure to identify the most beneficial scenario. This study presents a model-based method to estimate, within the model constraints, the most sustainable scenario of water resource sharing between nature and human needs. We studied physical habitat suitability of the Isar River in Munich (Germany) for three protected fish species: Thymallus thymallus L., Hucho hucho L., and Chondostroma nasus L. The analysis combined a high-resolution two-dimensional (2D) hydromorphological model with expert-based procedures using Computer Aided Simulation Model for Instream Flow Requirements (CASiMIR). We simulated a range of minimum discharges from 5 to 68.5 m 3 /s and four scenarios: (A) maximum use of the resource for humans; (B) slight increase in the minimum water flow; (C) medium increase in the minimum water flow; and, (D) without diversion for hydroelectric production. Under the current hydromorphological conditions, model outputs showed that different life stages of the fish species showed preferences for different scenarios, and that none of the four scenarios provided permanently suitable habitat conditions for the three species. We suggest that discharge management should be combined with hydromorphological restoration actions to re-establish parts of the modified channel slope and/or parts of the previously lost floodplain habitat in order to implement a solution that favors all species at the same time. The modeling procedure that is presented may be helpful to identify the discharge scenario that is most efficient for maintaining target fish species under realistic usage conditions.
... Much research has already been undertaken on the effect of stressors on surface waters (e.g. Feld and Hering, 2007;Stendera et al., 2012;Nõges et al., 2015;Piggott et al., 2015;Baattrup-Pedersen et al., 2016;Schülting et al., 2016). And although a significant body of research has been developed over the last 50 years or so related to a wide range of aspects of GW-SW interactionsin particular the implications for ecological functioning of the riparian zone (Fleckenstein et al., 2010), Sophocleous (2002) identified the following, still unresolved, research challenge: how to better understand the environmental impacts of multiple processes that affect both groundwater and surface water across multiple spatio-temporal scales. ...
Article
Abstract Groundwater and surface water are often closely coupled and are both under the influence of multiple stressors. Stressed groundwater systems may lead to a poor ecological status of surface waters but to date no conceptual framework to analyse linked multi-stressed groundwater – surface water systems has been developed. In this paper, a framework is proposed showing the effect of groundwater on surface waters in multiple stressed systems. This framework will be illustrated by applying it to four European catchments, the Odense, Denmark, the Regge and Dinkel, Netherlands, and the Thames, UK, and by assessing its utility in analysing the propagation or buffering of multi-stressors through groundwater to surface waters in these catchments. It is shown that groundwater affects surface water flow, nutrients and temperature, and can both propagate stressors towards surface waters and buffer the effect of stressors in space and time. The effect of groundwater on drivers and states depends on catchment characteristics, stressor combinations, scale and management practises. The proposed framework shows how groundwater in lowland catchments acts as a bridge between stressors and their effects within surface waters. It shows water managers how their management areas might be influenced by groundwater, and helps them to include this important, but often overlooked part of the water cycle in their basin management plans. The analysis of the study catchments also revealed a lack of data on the temperature of both groundwater and surface water, while it is an important parameter considering future climate warming.
... A sediment layer (gravel) was situated at the bottom of each flume. For further details please see (Schülting, Feld & Graf 2016). ...
Conference Paper
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There is evidence that, besides shear stress and flow velocity, the rapidity of flow changes (up-and down-ramping) during a hydropeaking event may be a decisive factor regarding the harmfulness for riverine biota. Quantification of this assumption is still lacking, therefore we present an experimental approach, addressing macroinvertebrate drift response following hydropeaking events with five different ramping velocities at three different peak discharges. Our results indicate that drift responses of macroinvertebrates strongly relate to peak discharge and corresponding flow velocities. Further, our observations indicate that low ramping velocities reduce the drift-rates when discharge-related thresholds at peak flow are exceeded. Measures addressing these key parameters, such as the construction of compensation basins are therefore expected to have strong mitigating effects.
... These projects have been initiated without considering its impacts on local wildlife fauna, although the negative impacts of the effluents/ discharge and thermal/hydro-peaking are as evident as bright daylight (Shi et al. 2015;Bai et al. 2017;Hesthagen et al. 2017;Negi and Punetha 2017;Wang et al. 2018). As revealed by recent studies regarding the ill effects of the hydropower projects on wildlife fauna and more specifically on aquatic animals, these projects will compensate electricity shortage at the cost of environmental degradation, biodiversity loss, and habitat loss of different aquatic animals including fish and macro-invertebrates (Schülting et al. 2016). The indigenous aquatic fauna of the area is therefore under severe threat of extinction and needs to be conserved on a priority basis. ...
... The cost is, however, vulnerability to downstream displacement and 'washout' during high flows (Heggenes & Traaen 1988;Crisp & Hurley 1991;Fausch et al. 2001;Pavlov et al. 2008;Wolter & Sukhodolov 2008) and washed out larvae may be moribound (Elliott 1994). The ability to swim and maintain position by seeking out lowvelocity micro-niches (Heggenes, Bagliniere & Cunjak 1999;Heggenes 2002;Armstrong et al. 2003) improves rapidly with increasing temperature (above) and body size (Heggenes 1988 (Bruno et al. 2013;Bruno et al. 2016;Schulting, Feld & Graf 2016), but this may not be sustained (Miller & Judson 2014), maintenance of habitat for spawning and rearing, and biological cues to trigger spawning, hatching and migration (Young, Cech & Thompson 2011). However, more likely adverse effects are increased mortality due to stranding, downstream displacement of fish, and reduced spawning and rearing success due to untimely/obstructed migration and red dewatering (e.g. ...
Technical Report
In the seasonal climates of northern Europe and North America, water temperature variations are ecologically challenging for aquatic organisms in natural streams. In winter, low water temperature and ice conditions becall biological responses by aquatic species, whereas in summer water temperatures rise and may, in particular during daytime low flows, approach lethal levels. In ectothermic animals, like the cold-water fish Atlantic salmon and brown trout, and the benthic fauna, biochemical reactions and behaviors depend on water temperature. As many northern rivers are impacted by hydropower regulation, natural water temperature regimes are potentially altered. Typically, low head (run-of-the-river) regulation has limited impacts on water temperatures, but depending on the, usually limited, water storage capacity. In contrast, high head hydropower regulation systems have considerable water storage capacity in reservoirs. This alters downstream water temperatures, typically with an increase in winter (tapped from warm bottom water (below thermocline) in reservoir), and a decrease in summer (bottom water being colder than natural surface water). Thus, the naturally stable, ice-covered mid-winter periods may be replaced by repeated unstable transition periods and changing (or no) ice and flood conditions, whereas in summer, (downstream) water temperatures may be lowered when the hydropower plant is in operation. Conversely, by-pass reaches and reaches with reduced residual or environmental minimum flows during water storage, are more prone to fluctuate with environmental temperatures. In summer, this may lead to higher day-night and seasonal water temperatures and amplitudes, and lower and more frequent sub-zero temperatures in winter. However, the effects of alternative regulation regimes and reservoir intakes/outlets on downstream ambient temperatures are not well publicized. Hydro-peaked systems may aggravate high-low temperature effects, depending on flow regime (ramping rate and amplitude, frequency of flow fluctuations, prior flow conditions, timing of pulse). Atlantic salmon and brown trout feeding and growth performance in summer (and transient periods) depend primarily on water temperatures (above ≈ 3-4°C, optimum ≈ 13-16°C). At high temperatures, and approaching tolerance limits (≈ 22-24°C), trout and salmon reduce and cease feeding, and may move into cooler water in the substrate or groundwater inflow. Larger fish may move more and aggregate in restricted suitable deep-slow or cool refuge habitats, both in summer and winter. In winter, feeding and growth in typically absent, and energy storage is the basic fish low temperature survival strategy. Additional strategies may be risk reduction effected by behavioral changes, and ___ I Stay cool: Temperature in hydropower regulated systems reduced metabolism, tolerance and starvation effected by quiescence. Amount of energy stored may depend on local conditions, but otherwise there is hitherto little indication of adaptation to local thermal climates. However, phenotypic plasticity is important and substantial. The main behavioral strategy at low water temperatures (less than 6-8°C) is risk-reducing daytime sheltering in the substrate and primarily nocturnal activity. In winter, mechanical ice breakups may still reduce survival. Moreover, sudden drops in water flow due to hydropeaking may result in fish stranding, in particular at low temperatures in the daytime when fish are less mobile and seek shelter. Local movements between daytime refuges and nighttime activity areas occur both at low and high temperatures. Water temperature and/or flow may control more local spawning/smolt migrations, particularly in smaller streams. Fish egg development is also closely linked to water temperature. Emerging alevins and young fry are sensitive and vulnerable, often incurring high mortalities. Survival may depend on a delicate balance between temperature, suitable low flows and available drifting food during and after the ‘swim-up’ stage. Benthic macroinvertebrates display various strategies for dealing with high summer temperatures and low winter temperatures coupled with ice formation. Growth temperatures tend to be species specific, and as a group benthic macroinvertebrates exhibit growth across a wide temperature range. Some species are adapted to high summer temperatures, while others undergo quiescence or diapause, most commonly in the egg stage, in order to avoid such unfavorable periods. Likewise, other species avoid unfavorable periods during winter by quiescence or diapause. Another strategy, which can be coupled with diapause/quiescence, is to move down into the substrate, even into the hyporheic, especially in groundwater-fed areas. A further strategy is to undertake seasonal movements, either into tributaries or into deeper ice-free river waters. However, certain species, notably Diptera, but also other orders, have been shown to tolerate freezing – a stay-put strategy. Modified water temperatures may have major effects on life cycles, and even lead to extinction of specialist species, as many facets of growth and emergence are affected by or cued by temperature. Benthic species that have a rigid synchronous one year or univoltine life cycles are most at risk, while species with flexible and asynchronous life cycles will be favored. A reduction in the temperature range between winter and summer will lead to a reduction in species richness, again favoring the widespread, ubiquitous species. Nevertheless, most benthic organisms have high fecundity which may be offset high mortality during the different life cycle stages. ___ II Stay cool: Temperature in hydropower regulated systems Knowledge about thermal changes caused by hydropower regulation, and associated biological impacts on aquatic species, is a prerequisite for sustainable management of regulated rivers. In ongoing revisions of environmental guidelines and terms for hydropower regulated river systems, thermal changes and impacts have gained central focus. Thermal considerations will continue to be a key for setting future environmental flows and mitigation strategies. However, quantitative and observational knowledge is rather limited, whereas theoretical assumptions and modelling are more developed. Therefore, in situ target-oriented investigations in combination with more general research programs on water temperature changes, is essential, both from an operators (reduce costs and production losses) and managers perspective (fact-based knowledge and environmental guidelines). Based on this review, we recommend some main topics for further knowledge development: i) general quantitative knowledge on thermal changes due to hydropower regulation; ii) longitudinal water temperature changes from power outlet and in minimum flow reaches; iii) biological effects of reduced winter snow and ice cover, and increased frazil ice production, iv) invertebrate production in winter-warm rivers, and v) thermal adaptations to changed thermal regimes. With respect to mitigating measures, more knowledge is needed on i) effects of restored/increased minimum flows on invertebrate and fish composition, survival and production, ii) effects of changed/restored thermal regime, e. g. by installing multiple intakes in reservoirs, iii) empirical studies to test and validate the predictions of the at present quite well-developed hydro- hydraulic models. Because of the substantial background variation in river systems, long-term studies are of particular importance.
... Current knowledge on multiple stressors and related response of fish assemblages is limited in most parts of the world, especially in terms of quantifiable understanding on multiple hydromorphological stress effectssuch as morphological alterations, residual flow and connectivity disruption, hydropeaking and impoundmentspaired with water quality stress. Several studies on local/experimental spatial scale found responses of aquatic organisms (including fish) to multistressor situations, including stressors combined with impoundments (Alonso et al., 2015;Marzin et al., 2012;Van Looy et al., 2014), connectivity disruption and thereby evoked habitat fragmentations by dams and barriers (Alonso et al., 2015;Falke et al., 2013;Van Looy et al., 2014;Branco et al., 2016), water abstractions and residual flow conditions (Lange et al., 2014), morphological alterations (Alonso et al., 2015;Marzin et al., 2012;Milly et al., 2008;Rolls et al., 2013;Van Looy et al., 2014) and hydropeaking (Schülting et al., 2016;Auer et al., 2017;Wright et al., 2016). In contrast, on a very general, pan-European scale, Schinegger et al. (2016) investigated the impact of multiple stressors on fish ecological status in European rivers, including hydromorphological-, connectivity-and water quality stressors, with specific fish metrics responding to certain river types. ...
Article
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This work addresses multiple human stressors and their impacts on fish assemblages of the Drava and Mura rivers in southern Austria. The impacts of single and multiple human stressors on riverine fish assemblages in these basins were disentangled, based on an extensive dataset. Stressor configuration, i.e. various metrics of multiple stressors belonging to stressor groups hydrology, morphology, connectivity and water quality were investigated for the first time at river basin scale in Austria. As biological response variables, the Fish Index Austria (FIA) and its related single as well as the WFD biological- and total state were investigated. Stressor-response analysis shows divergent results, but a general trend of decreasing ecological integrity with increasing number of stressors and maximum stressor is observed. Fish metrics based on age structure, fish region index and biological status responded best to single stressors and/or their combinations. The knowledge gained in this work provides a basis for advanced investigations in Alpine river basins and beyond, supports WFD implementation and helps prioritizing further actions towards multi-stressor restoration- and management.
... The experiment durations were aligned to the receptor metrics in the study. For instance the trails on fish behavior and invertebrate drift rates only took between 30min and 5 h (Branco et al., 2016;Bruno et al., 2013;Sch€ ulting et al., 2016;Calapez et al., 2017). The experiment on invertebrate community response in natural stream reaches lasted for 334 days (Baumgartner and Robinson, 2015). ...
Chapter
Freshwater ecosystems are among the most imperiled on earth, with rivers being particularly susceptible to anthropogenic stress. Environmental monitoring across Europe reveals that 45% of rivers are affected by more than one human-driven pressure. Detecting and quantifying the impact of multiple stressors exerted from these pressures thus represent important scientific tasks in support of aquatic ecosystem management. This chapter reviews the scientific literature on experimental and field-based observational studies investigating into multistressor effects. Forty experimental and 48 field-based observational studies were covered, dealing with 72 and 151 paired stressor combinations, respectively. Morphological stress paired with either nutrient or hydrological stress was most frequently addressed in both study types. While experiments focused on a broad range of receptor organisms including phytobenthos, benthic invertebrates, fish, microorganisms (e.g., bacteria and fungi) and related processes (e.g., leaf decomposition), field studies mainly investigated the effects on benthic invertebrates and fish. Stressor interactions were more relevant in the experimental studies, with almost 50% of phytobenthos receptor metrics featuring interactions, as compared to the field studies, where stressor interactions were often not specified. Unknown stressor interactions challenge aquatic ecosystem management by posing risks of unwanted “ecological surprises.” Future scientific efforts need to concentrate on classifying the relevance and strength of interactive effects across types of stressors, receptors, and existing ecosystems, considering the specific local conditions of the water bodies to be managed. River basin management will benefit from ecosystem modeling to diagnose the causes of detrimental ecological effects, or to predict the benefits and trade-offs of management strategies in multistressor contexts.
... Much research has already been undertaken on the effect of stressors on surface waters (e.g. Feld and Hering, 2007;Stendera et al., 2012;Piggott et al., 2015;Baattrup-Pedersen et al., 2016;Schülting et al., 2016). However, the inclusion of groundwater in this research is still limited, despite the fact that it has been known for several decades that groundwater and surface water are essentially one resource (Brunke and Gonser, 1997;Winter et al., 1998). ...
Technical Report
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In the previous report (D4.1, September 2016) we have developed predictive linkages between indicators of environmental quality and ecosystem services, and different types of pressures, single or multiple, across river basins from all over Europe, in a latitudinal and a west-east gradient, and having very different conditions of climate and land use drivers. Using such predictive linkages resulting both from empirical data treatment and process based modelling, and following a common approach for climatic scenario changes, downscaled to region level, we have studied the future evolution of indicators and services. Furthermore, we have looked into the programs of measures that are being implemented in each country and we attempted to understand how will be the responses of the indicators of quality and services, according to such implementation. The studies performed in these 16 basins have a great potential for common applications and studies, and these are being developed in the moment. Although the hydrological and nutrient process-based models that were used and calibrated at each basin scale mostly contain liaisons between the different water compartments, these studies were mostly focused in surface waters and in the indicators of quality that were developed for the Water Framework Directive, as also the information from monitoring taking pace for the last decade, or in previous times. Many issues remain to be studied, related with interfaces between water compartments and also with the biotic aspects of the pressures, also important for some communities and in some cases. This Deliverable (D4.2) is composed of five reports, dealing with stressor effects at the river basin level. These reports cover special aspects of the linkage between ecosystem compartments, multiple pressures and the responses of particular elements, notably the interface between terrestrial and aquatic environments represented by the riparian transitional ecosystems (D4.2-1), stressor propagation between surface waters and groundwaters (D4.2-2) and estuarine waters (D4.2-3), or deal with particular biological stressor effects when such are added to the more common chemical and physical stressors (D4.2-4 and D4.2-5). Most of these reports use different case studies (D4.2-1, D4.2-2 and D4.2-4) from MARS to pool data and experiences for a common target. The other two focus on the stressor propagation in transitional waters in the example of the estuary of Nervion (D4.2-3) and finally two other are related with biotic pressures, i.e. fisheries management and pathogens (D4.2-4 and D4.2-5). All of these studies will be adapted/are being prepared for publication submission. MARS Deliverable 4.2: Manuscripts on stressor effects at the river basin level The Deliverable 4.2. is therefore composed of five reports, with the non-technical summaries following this introduction: D4.2-1: Riparian-to-catchment management options for stressor reduction and service enhancement D4.2-2: Stressor propagation through surface-groundwater linkages and its effect on aquatic systems D4.2-3: Stressor propagation through inland-transitional linkages and management consequences D4.2-4: Fisheries as a source and target of multiple stressors D4.2-5: Multiple-stressor risks for pathogens Summary of D4.2-1 Riparian management is considered a key management option to improve lotic ecosystem status, functioning and services. Vegetated riparian buffer strips can retain nitrogen from sub-surface runoff, and phosphorous and fine sediments from surface runoff. Thus, they can reduce and mitigate the effects of diffuse pollution by agricultural and other land uses. However, the effectiveness of riparian buffers, to a large extent, depends on the location within the stream continuum, as well as on the land use conditions further upstream of the buffered stream sections. Catchment-scale effects can counteract riparian management effects. In the manuscript, we synthesise the evidence of riparian management options in light of catchment-scale pressures. We reviewed 53 management studies addressing both scales and developed a conceptual model to highlight management options with and without conflicts among management scales. Summary of D4.2-2 The good ecological status of Europe's freshwaters is still lacking. This paper reviews the role of groundwater in these systems and demonstrates that it is an important factor to include in surface water management. Groundwater influences streamflow, water chemistry and water temperature and connects rivers and streams with their catchment and thus functions as a pathway for stressors to reach the surface water. A new 'Groundwater DPS' framework is proposed which shows how groundwater fits in the system of a stressed aquatic ecosystem. The functioning of this framework is demonstrated using examples from four different European lowland catchments: the Thames, Odense, Regge and Dinkel catchments. The importance of groundwater varies between scales, between catchments and within catchments.
... 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
Full-text available
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.
... 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
Full-text available
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.
... 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
Full-text available
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.
... 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.
... 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.
... 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.
... 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
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.
... 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.
... 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.
... 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
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.
... 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.
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.
Article
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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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