Anthropogenic Flow Alterations Research Articles

Flow augmentation from off‐channel storage improves salmonid habitat and survival

AbstractObjectiveIn the western United States, juvenile salmon Oncorhynchus spp. and steelhead O. mykiss are especially vulnerable to streamflow depletion in the dry season. Releasing water from off‐channel storage into small streams is a novel restoration strategy to offset impacts from anthropogenic flow alteration on salmonid fishes. To date, no studies have evaluated the ecological effects of small‐scale flow augmentations. Here, we quantify the effects of one such augmentation project on habitat connectivity, water quality, invertebrate drift, and juvenile salmonid movement and survival.MethodsOur study took place in a northern California stream and included an unusually wet summer (2019) and a more typical dry summer (2020). We used categorical and time‐series analyses in a before–after, control–impact (BACI) design, along with capture–mark–recapture methods to evaluate the ecological impacts of a 13.9‐L/s flow augmentation.ResultWe found that differences in ambient streamflows between the two years mediated the physical and ecological effects of the flow augmentation treatment. In the dry year, habitat connectivity and dissolved oxygen markedly increased at sites over 1.5 km downstream from the point of augmentation, whereas during the wet year, the effects on those variables were negligible. In both years, invertebrate drift marginally increased after augmentation. Interpool movement of wild juvenile steelhead and stocked Coho Salmon O. kisutch increased after augmentation during the dry summer but not during the wet summer. Flow augmentation increased the survival probability for salmonids, with a larger effect during the dry summer (24% higher survival for Coho Salmon and 20% higher survival for steelhead) than during the wet summer (no effect was observed for steelhead survival, and Coho Salmon survival increased by 11%).ConclusionThis study indicates that appropriately designed small‐scale flow augmentations can improve conditions for rearing salmonids in small streams, particularly during dry years. More broadly, it provides empirical evidence that efforts to restore summer streamflow in small, salmon‐bearing streams can yield significant ecological benefits.

Going with the flow: Spatio‐temporal drift patterns of larval fish in a large alpine river

Abstract Fish larval drift is an essential step in the life cycle of riverine fish species as it determines dispersal and colonisation. Anthropogenic flow alterations and interruption of longitudinal and lateral connectivity by river damming and straightening can severely affect larval drift patterns. In this study, we characterised spatio‐temporal drift patterns of fish larvae in the heavily regulated large alpine River Inn and within a constructed nature‐like fish bypass. Drift was investigated in the main reproduction period of the fish fauna in this river, ranging from mid‐April to end of June. Diel patterns were assessed by samples taken during day, dusk, night, and dawn each day of sampling. To obtain robust species identification, we used DNA barcoding for genetic verification of phenotypically pre‐sorted groups. From a total of 1,069 fish larvae and 283 fish eggs caught, DNA barcoding revealed 16 species from five families, including several target species of conservation. We found strong evidence that several endangered species, such as Chondrostoma nasus, Thymallus thymallus, Cottus gobio, and Aspius aspius successfully reproduced in the bypass system. Genetic species verification showed a high level of homogeneity in most phenotypically pre‐sorted groups. Distinct seasonal patterns were observed, with the majority of fish species in the drift observed in mid‐June. Thymallus thymallus and Cottus gobio dominated larval drift at the beginning of the observation followed by mainly unimodal abundance peaks of several Cyprinid species. Nocturnal drift prevailed in all species. Our results on the spatial occurrence and abundances of fish larvae highlight the importance of bypass systems in heavily modified waterbodies to provide valuable spawning habitats and drift corridors around dams. Moreover, the distinct species‐specific time patterns of larval drift represent a first basis to direct future discharge and river management plans in large alpine rivers towards a protection of the sensitive larval stages of specific target species of conservation. This includes bypass and turbine operation modes in the period of highest drift activity, as well as the construction of nature‐like bypass systems and creation of spawning grounds therein.

A review and evaluation of the effects of hydrodynamic variables on freshwater mussel communities

Abstract Riverine species are governed by the physical (i.e. hydrodynamic) forces generated by flowing water. Freshwater species are also disproportionately imperilled compared to terrestrial and marine species in large part due to widespread anthropogenic alteration of the natural flow regimes to which organisms are adapted. Sedentary species such as freshwater mussels (Bivalvia: Unionoida) are especially vulnerable because they are unable to move quickly in response to novel flow patterns created by impoundments and water withdrawals. We evaluated the effects of hydrodynamic variables on mussel communities. We reviewed the literature to synthesise the relationships between three categories of hydrodynamic variables (hydrologic, simple hydraulic, and complex hydraulic) and mussel community parameters. We evaluated which variables are most useful in predicting mussel presence, abundance, and species richness, provided recommendations to help standardise their use in characterising mussel habitat and reviewed the reciprocal influence of mussels on hydraulic forces at the sediment–water interface. Hydrologic variables such as stream size and anthropogenic flow alteration were useful in predicting basin‐ and landscape‐scale changes in mussel communities. At finer scales, complex hydraulic variables—mainly shear stress and Reynolds number—were more useful at predicting mussel community responses. Simple hydraulic variables (flow velocity, depth, discharge) had mixed success as predictors of mussel community parameters and are likely to be indirectly correlated to mussel responses because they are used to calculate more complex variables. More emphasis should be placed on species‐ and basin‐specific responses of freshwater mussels when considering the effects of the hydrologic regime on mussels, with an eye towards sustainable water management (e.g. flow restoration, environmental flows). Simple hydraulic variables should be assessed across the range of discharge at a site, in combination with channel and substrate characteristics. This allows the calculation of complex hydraulic variables that may be more directly limiting to mussel communities. Mussels also alter near‐bed hydraulic characteristics, resulting in feedbacks between mussel community parameters and local hydraulic variable s. Researchers should consider that mussel beds have a reciprocal influence on near‐bed flow characteristics and should continue to explore the effects of such ecological engineering for possible interspecific facilitation benefits between mussel species.

Long-term river invertebrate community responses to groundwater and surface water management operations

River flow regimes have been transformed by groundwater and surface water management operations globally, prompting widespread ecological responses. Yet, empirical evidence quantifying the simultaneous effects of groundwater and surface water management operations on freshwater ecosystems remains limited. This study combines a multi-decadal freshwater invertebrate dataset (1995-2016) with groundwater model outputs simulating the effects of different anthropogenic flow alterations (e.g. groundwater abstraction, effluent water returns) and river discharges. A suite of flow alteration- and flow-ecology relationships were modelled that tested different invertebrate community responses (taxonomic, functional, flow response guilds, individual taxa). Most flow alteration-ecology relationships were not statistically significant, highlighting the absence of consistent, detectable ecological responses to long-term water management operations. A small number of significant statistical models provided insights into how flow alterations transformed specific ecological assets; including Ephemeroptera, Plecoptera and Trichoptera taxa which are rheophilic in nature being positively associated with groundwater abstraction effects reducing river discharges by 0-15%. This represents a key finding from a water resource management operation perspective given that such flow alteration conditions were observed on average in over two-thirds of the study sites examined. In a small number of instances, specific invertebrate responses displayed relative declines associated with the most severe groundwater abstraction effects and artificial hydrological inputs (predominantly effluent water returns). The strongest flow-ecology relationships were recorded during spring months, when invertebrate communities were most responsive to antecedent minimum and maximum discharges, and average flow conditions in the preceding summer months. Results from this study provide new evidence indicating how groundwater and surface water resources can be managed to conserve riverine ecological assets. Moreover, the ensemble of flow alteration- and flow-ecology relationships established in this study could be used to guide environmental flow strategies. Such findings are of global importance given that future climatic change and rising societal water demands are likely to further transform river flow regimes and threaten freshwater ecosystems.

Functional responses of aquatic macroinvertebrates to flow regulation are shaped by natural flow intermittence in Mediterranean streams

Abstract Running waters in Mediterranean regions are strongly regulated by dams, which produce significant alterations to natural flow regimes. Climate change will reduce discharge and increase flow intermittence in Mediterranean streams, which will lead to an intensified flow regulation to meet water demands. Very little is known about how the functional features of aquatic communities vary along combined anthropogenic flow alteration and natural intermittence gradients. As intermittent streams are subjected to natural stress (droughts and flash floods), the flow regime alteration effect may differ from that observed in perennial rivers. Consequently, studies that aim to determine the effects of flow regulation on the functioning of aquatic communities in a global change context are crucial. By applying linear mixed‐effect models and null models to the macroinvertebrate communities from 65 stream sites in the Segura River Basin (south‐east Spain), we assessed the separate effects of natural flow intermittence and flow regulation, as well as their interaction, on biological traits and functional diversity indices. Natural flow intermittence and flow regulation were mainly associated with loss of taxa with semivoltine or univoltine cycles and more sensitive aquatic stages (i.e. eggs), and with the replacement by taxa with multivoltine cycles and more resistant aquatic stages (i.e. adults). Flow regulation intensified the impact of natural flow intermittence on some biological traits, producing synergistic effects (i.e. decreasing interstitial taxa and tegument breathers and increasing taxa with aquatic adult stages). At the same time, antagonistic (life cycle) and opposing (shredders) interaction effects were also observed. Functional diversity, functional dispersion, and functional redundancy underwent a non‐random decrease as the flow regime alteration increased, and a significant antagonistic interaction was also found between both stressors for functional redundancy. In general, flow regulation effects were stronger in perennial than in intermittent streams because natural intermittence imposes a previous eco‐evolutionary pressure on aquatic biota by selecting those resistant or recovery traits that confer resilience to anthropogenic flow regime alterations. Thus, the natural flow regime influences the functional sensibility of communities to anthropogenic flow alteration.

Habitat‐specific invertebrate responses to hydrological variability, anthropogenic flow alterations, and hydraulic conditions

Abstract Quantifying ecological responses to river flow regimes is a key scientific approach underpinning many environmental flow (e‐flow) strategies. Incorporating habitat‐scale influences (e.g. substrate composition and organic matter cover) within e‐flow frameworks has the potential to provide a broader understanding of the causal mechanisms shaping instream communities, which may be used to guide river management strategies. In this study, we examined invertebrate communities inhabiting three distinct habitat groups (HGs—defined by coarse substrates, fine sediments, and the fine‐leaved macrophyte Ranunculus sp.) across four rivers (each comprising two study sites) within a single catchment. We tested the structural and functional responses of communities inhabiting different HGs to three sets of flow‐related characteristics: (1) antecedent hydrological (discharge—m3/s) variability; (2) antecedent anthropogenic flow alterations (percentage of discharge added to or removed from the river by human activity); and (3) proximal hydraulic conditions (characterised by the Froude number). The former two were derived from groundwater model daily time series in the year prior to the collection of each invertebrate sample, while the latter was collected at the point of sampling. While significant effects of hydrological and anthropogenic flow alteration indices were detected, Froude number exerted the greatest statistical influence on invertebrate communities. This highlights that habitat‐scale hydraulic conditions to which biota are exposed at the time of sampling are a key influence on the structure and function of invertebrate communities. Mixed‐effect models testing invertebrate community responses to flow‐related characteristics, most notably Froude number, improved when a HG interaction term was incorporated. This highlights that different mineralogical and organic habitat patches mediate ecological responses to hydraulic conditions. This can be attributed to HGs supporting distinct taxonomic and functional compositions and/or providing unique ecological functions (e.g. flow refuges), which alter how instream communities respond to hydraulic conditions. While the individual importance of both flow and small‐scale habitat effects on instream biota has been widely reported, this study provides rare evidence on how their interactive effects have a significant influence on riverine ecosystems. These findings suggest that river management strategies and e‐flow frameworks should not only aim to create a mosaic of riverine habitats that support ecosystem functioning, but also consider the management of local hydraulic conditions within habitat patches to support specific taxonomic and functional compositions.

Flow velocity–ecology thresholds in Canadian rivers: A comparison of trait and taxonomy‐based approaches

Abstract Understanding the physical and biological mechanisms contributing to flow velocity–ecology relationships is crucial for successful river management. The application of an ecological traits‐based approach offers the potential to explore mechanistic linkages between aquatic communities and a hydrological gradient. To date, however, studies focused on identifying these relationships have been limited by a lack of large‐scale, long‐term biological data. To address this gap at a scale relevant for water policy management, we employed data from a large‐scale standardised benthic monitoring program—the Canadian Aquatic Biomonitoring Network—obtained from wadeable river sites across Canada. We applied the Threshold Indicator Taxa ANalysis method to quantify the response of the macroinvertebrate community, expressed as traditional taxonomic information and also as ecological traits, along a flow velocity gradient in reference and potential reference sites. Five key findings emerged: (1) using taxa and trait modalities revealed different flow velocity thresholds, (2) trait flow velocity indicators were less variable than taxon indicators, especially for positively responding trait modalities, (3) labile and non‐labile trait modalities demonstrated highly similar patterns along the flow velocity gradient, (4) taxa from 12 different orders responded negatively to flow velocity, while only EPT taxa and some dipterans responded positively to flow velocity, and (5) traits related to mobility and ecology (e.g. climber and swimmer habits, preference of cold‐cool eurythermal water and ability to survive desiccation) tended to respond positively to flow velocity, while traits related to morphology, life history and ecology (e.g. sprawler and burrower habits, preference for warm eurythermal water and inability to survive desiccation) tended to respond negatively to flow velocity. Providing ecologically based flow management targets can improve management plans, anticipate ecosystem consequences of anthropogenic change and support the development of policies to mitigate anthropogenic flow alteration. While our taxon and trait modality flow indicators were developed for Canadian watersheds, our methods to develop flow indicators and thresholds are transferrable to other systems where long‐term biomonitoring programs are being developed, underscoring the need for long‐term biomonitoring programs to support better ecosystem management.

Fish age and size distributions and species composition in a large, hydropeaking Prairie River

AbstractFluctuations in river flows result from diverse natural and/or anthropogenic causes. Hydropeaking, an important anthropogenic flow alteration, results from the rapid increase or decrease of water releases from reservoirs at hydroelectric power stations to meet variable demand for electrical power, thereby altering the flow regime of the river downstream of the hydroelectric power station. Hydropeaking causes short‐term, artificial fluctuations in flow on an hourly, daily, and/or weekly basis. The frequent and regular occurrences of these high and low flow events are fundamentally different from natural flood and drought events and may affect fish fauna. We compared the fish species composition and fish age and size distributions in the Saskatchewan River (Saskatchewan, Canada) downstream of a hydropeaking facility with results from an unaffected Reference Site situated upstream of the reservoir. Lower fish diversity was observed in the 2 downstream sites (Sites 1 and 2, number of species = 11 and 9, respectively) closest to Generating Station in comparison to Site 3 (n = 15) situated further downstream and the upstream reference site (n = 13). There was no difference in the age–length relationship of any of the fish species above and below the Generating Station suggesting that fish grew at the same rates. However, lower numbers of small‐bodied and juvenile fish were caught downstream of the Generating Station suggesting the possibility of increased mortality, decreased habitat suitability, or altered behaviour of small fish downstream of the dam. These data illustrate potential impacts of hydropeaking power stations and has management implications.

Long‐term changes in flow regime and fish assemblage composition in the guadalupe and san marcos rivers of texas

AbstractRiverine flow regimes are naturally dynamic, but become increasingly homogenized following anthropogenic flow alteration. Loss of dynamism disrupts naturally occurring structuring mechanisms within the associated biotic communities, at times causing shifts in composition. Here we considered how stream fish assemblages in two Central Texas rivers changed after alteration of flow regime by either construction of a mainstem, deep storage reservoir or flood‐retaining structures. Following impoundment, number of large and small floods increased from 0.81 to 1.07 floods per year (FPY) in the upper Guadalupe River, decreased from 0.84 to 0.42 FPY in the lower Guadalupe River and decreased from 0.87 to 0.7 FPY in the San Marcos River. Historical ichthyofauna data ranging from 1938 to 2006 were used to assess changes in assemblage composition and species abundance. Assemblages did not differ in the upper Guadalupe River (Bray–Curtis index = 37.4%; ANOSIM global R = 0.079, p = 0.08), but did differ in the lower Guadalupe River (25%; global R = 0.409, p < 0.01) and San Marcos River (27%; global R = 0.19, p < 0.01). In general, habitat generalist species dominated assemblages during periods of reduced flood frequencies (i.e. drought of record; following impoundment), whereas regionally endemic species (N = 3) and substrate and broadcast spawning species (N = 5) declined (b1 < 0; α = 0.05). Based on the results from this study, managing flows in the lower Guadalupe River to mimic historical timing of flood pulses might attenuate contemporary disruption of natural assemblage composition. Copyright © 2010 John Wiley & Sons, Ltd.

Impact of climate change on freshwater ecosystems: a global-scale analysis of ecologically relevant river flow alterations

Abstract. River flow regimes, including long-term average flows, seasonality, low flows, high flows and other types of flow variability, play an important role for freshwater ecosystems. Thus, climate change affects freshwater ecosystems not only by increased temperatures but also by altered river flow regimes. However, with one exception, transferable quantitative relations between flow alterations and ecological responses have not yet been derived. While discharge decreases are generally considered to be detrimental for ecosystems, the effect of future discharge increases is unclear. As a first step towards a global-scale analysis of climate change impacts on freshwater ecosystems, we quantified the impact of climate change on five ecologically relevant river flow indicators, using the global water model WaterGAP 2.1g to simulate monthly time series of river discharge with a spatial resolution of 0.5 degrees. Four climate change scenarios based on two global climate models and two greenhouse gas emissions scenarios were evaluated. We compared the impact of climate change by the 2050s to the impact of water withdrawals and dams on natural flow regimes that had occurred by 2002. Climate change was computed to alter seasonal flow regimes significantly (i.e. by more than 10%) on 90% of the global land area (excluding Greenland and Antarctica), as compared to only one quarter of the land area that had suffered from significant seasonal flow regime alterations due to dams and water withdrawals. Due to climate change, the timing of the maximum mean monthly river discharge will be shifted by at least one month on one third on the global land area, more often towards earlier months (mainly due to earlier snowmelt). Dams and withdrawals had caused comparable shifts on less than 5% of the land area only. Long-term average annual river discharge is predicted to significantly increase on one half of the land area, and to significantly decrease on one quarter. Dams and withdrawals had led to significant decreases on one sixth of the land area, and nowhere to increases. Thus, by the 2050s, climate change may have impacted ecologically relevant river flow characteristics more strongly than dams and water withdrawals have up to now. The only exception refers to the decrease of the statistical low flow Q90, with significant decreases both by past water withdrawals and future climate change on one quarter of the land area. However, dam impacts are likely underestimated by our study. Considering long-term average river discharge, only a few regions, including Spain, Italy, Iraq, Southern India, Western China, the Australian Murray Darling Basin and the High Plains Aquifer in the USA, all of them with extensive irrigation, are expected to be less affected by climate change than by past anthropogenic flow alterations. In some of these regions, climate change will exacerbate the discharge reductions, while in others climate change provides opportunities for reducing past reductions. Emissions scenario B2 leads to only slightly reduced alterations of river flow regimes as compared to scenario A2 even though emissions are much smaller. The differences in alterations resulting from the two applied climate models are larger than those resulting from the two emissions scenarios. Based on general knowledge about ecosystem responses to flow alterations and data related to flow alterations by dams and water withdrawals, we expect that the computed climate change induced river flow alterations will impact freshwater ecosystems more strongly than past anthropogenic alterations.

Potential impacts to freshwater ecosystems caused by flow regime alteration under changing climate conditions in Taiwan

Observed increases in the Earth’s surface temperature bring with them associated changes in precipitation and atmospheric moisture that consequentially alter river flow regimes. Climate-induced flow regime changes are examined using the Indicators of Hydrologic Alteration. This article uses observed daily streamflow data to examine the flow regime alteration and how these changes might potentially affect freshwater ecosystems. Flow data from 23 gauging stations throughout Taiwan show that the annual extreme water conditions (1-, 3-, 7-, 30-, 90-day annual minima or maxima) have increased alteration compared to baseline periods (1961–1990). Specifically, more severe flood and drought events occur in the period after 1991 than the period from 1961 to 1990. The frequency and duration of flood and drought events also show increased fluctuation. Flow regimes are currently being altered by stressors that will continue into the foreseeable future and it is also happing elsewhere in the world. Aquatic organisms not only need to defend themselves from anthropogenic damage to the river system, but also face the on-going threat from climate change-induced thermal and flow regime alteration. This article raises this issue so that water resources managers may identify precautionary measures that reduce the cumulative effects of both anthropogenic flow alteration and changing climate conditions.

A Database and Meta-Analysis of Ecological Responses to Stream Flow in the South Atlantic Region

Generalized and quantitative relationships between flow and ecology are pivotal to developing environmental flow standards based on socially acceptable ecological conditions. Informing management at regional scales requires compiling sufficient hydrologic and ecological sources of information, identifying information gaps, and creating a framework for hypothesis development and testing. We compiled studies of empirical and theoretical relationships between flow and ecology in the South Atlantic region (SAR) of the United States to evaluate their utility for the development of environmental flow standards. Using database searches, internet searches, and agency contacts, we gathered 186 sources of information that provided a qualitative or quantitative relationship between flow and ecology within states encompassing the SAR. A total of 109 of the 186 sources had sufficient information to support quantitative analyses. Ecological responses to natural changes in flow magnitude, frequency, and duration were highly variable regardless of the direction and magnitude of changes in flow. In contrast, the majority of ecological responses to anthropogenic-induced flow alterations were negative. Fish abundance, diversity, reproduction, and habitat consistently showed negative responses to anthropogenic flow alterations, whereas other ecological categories (e.g., macroinvertebrates and riparian vegetation) showed somewhat variable responses and even positive responses (e.g., algal abundance). Fish and organic matter had sufficient sample sizes to stratify natural flow-ecology relationships by specific flow categories (e.g., high flow, baseflows) or by physiographic province (e.g., Coastal Plain, Piedmont). After stratifying relationships, we found that significant correlations existed between changes in natural flow and fish responses. In addition, a regression tree explained 57% of the variation in fish responses to anthropogenic and natural changes in flow. Altogether, our results suggested that the source of flow change and the ecological category of interest played primary roles in determining the direction and magnitude of ecological responses. Furthermore, our results suggest that developing broadly generalized relationships between ecology and changes in flow at a regional scale is unlikely unless relationships are placed within meaningful contexts, such as environmental flow components or geomorphic settings.