Despite the growing number of dam removals, very few have been studied to understand their impacts on stream fish communities. An even smaller proportion of dam removal studies focus on the impacts of low-head dam removals, although they are the most common type of dam. Instead, the majority of removal studies focus on the impacts of larger dams. In this study, two previously impounded Illinois rivers were monitored to assess the impacts of low-head dam removal on the functional assemblage of stream fishes. Study sites were sampled each fall from 2012-2015 (pre-dam removal) and 2018-2020 (post-dam removal) in three habitat types: downstream of the dam, impounded areas, and runs of rivers. Fishes were aggregated into habitat and reproductive guilds, relating community changes to habitat, environmental metrics, and stream quality. Prior to removal, the slackwater guild was the most prevalent habitat guild throughout both rivers, while nest builders and benthic spawners were the most abundant reproductive guilds. During the two years following removal, habitat conditions and fish assemblages improved throughout both rivers, with improvements in QHEI, IBI, water temperature, and dissolved oxygen, as well as a shift to more evenly distributed representation of habitat and reproductive guilds. The improvements in environmental metrics and overall stream quality, particularly in the formerly impounded habitats, indicate diminished habitat homogeneity, and a shift towards natural habitat diversity. This habitat diversification likely led to the restoration of a range of potential niches, thereby increasing the array of guild types inhabiting these rivers, while simultaneously preventing single-guild dominance.
Spatial and temporal heterogeneity, or messiness, is a broadly desirable characteristic of river corridors and an indicator of many of the geomorphic processes that sustain fluvial ecosystems. However, quantifying geomorphic heterogeneity is complicated by a lack of consistent metrics, classification schemas for dividing the river corridor into the patches that form the basis for those metrics, and guidance on interpreting metrics. Drawing from both geomorphic and landscape ecology concepts, we offer ideas and guidance intended to help investigators, from researchers to restoration practitioners, more effectively and reliably use heterogeneity to describe river corridor processes and characteristics. We define geomorphic heterogeneity both spatially and temporally. Spatially, heterogeneity can be described by diversity, or the evenness and richness of geomorphic units, and spatial configuration, or the arrangement and shape of geomorphic units. Temporally, heterogeneity can be described by turnover rate, or the rate of change of geomorphic units. Interpretation of heterogeneity metrics depends integrally on the definition of the geomorphic unit schema on which metrics are based. Contextual information, such as measurements of process space (i.e., how much room a river has to move), disturbance frequency, and geomorphic trajectory, can also be key to interpreting measurements of heterogeneity. Geomorphic applications of heterogeneity require carefully defined geomorphic unit schemas that reflect processes and characteristics of interest, robust metrics of heterogeneity whose meaning is appropriate to the question at hand, and interpretation of those metrics based on the context of expected geomorphic processes and the disturbance regime.
Numerical hydrodynamic models enable the simulation of hydraulic conditions under various scenarios and are thus suitable tools for hydropeaking related assessments. However, the choice of the necessary model complexity and the consequences of modelling choices are not trivial and only few guidelines exist. In this study we systematically evaluate numerical one-dimensional (1D) and two-dimensional (2D) hydrodynamic models with varying spatial resolution regarding their suitability as input for hydropeaking-sensitive, ecologically relevant hydraulic parameters (ERHPs), and their computational efficiency. The considered ERHPs include the vertical dewatering velocity, the wetted area variation between base and peak flow and the bed shear stress as a proxy for macroinvertebrate drift. We then also quantified the habitat suitability of brown trout for different life stages. The evaluation is conducted for three channel planforms with morphological characteristics representative for regulated Alpine rivers, ranging from alternating bars to a braiding river morphology. Our results suggest, that while a highly resolved 1D model is sufficient for accurate predictions of the dewatering velocity and wetted area in the less complex alternating bar morphology, a 2D model is recommended for more complex wandering or braiding morphologies. For the prediction of habitat suitability and bed shear stress, a 1D model appears to be always insufficient, and a highly resolved 2D model is suggested. Reducing the spatial resolution of 2D models leads to computational efficiency similar to 1D, while providing more accurate results. This study can serve as guideline for researchers and practitioners in the selection and setup of hydrodynamic models for hydropeaking.
A maturing body of evidence suggests that anthropogenic impacts on river-wetland corridors may be greater and more widespread than previously recognized. We applied the Geomorphic Grade Line (GGL) method to define pre-Anthropocene valley surfaces within segments of the 42-kilometer Entiat River Valley (ERV) of the North Cascade Mountains, USA. We developed GGL-relative elevation models (GGL-REMs) by subtracting, from high-resolution digital elevation data, a detrending surface based on relic fluvial features of the valley floor. We validated the GGL-REMs using surficial geologic maps, C 14-dated soil profiles, and the identifiable remnants of historic dams. We interpreted these data in the context of settlement land use practices including channelization, large wood removal, and beaver ( Castor canadensis) trapping. Our analysis indicates that since the early 20 th century, the river has incised more than two meters in many areas. This triggered a rapid state and process change, wherein unconfined and partially-confined valleys transitioned from net deposition to erosion and transport environments. The distribution of river types shifted from ecologically rich river-wetland corridors towards simpler, single-threaded channels common in confined valleys. The effects of this state change on salmon productivity were profound. Results from the Entiat and other locales indicate that GGL-REMs can be used to help define the fluvial process-form domains, including the vertical dimension needed to guide valley floor restoration. These tools can be used to envisage pre-degradation riverscapes, especially when used in concert with other datasets. Once the pre-Anthropogenic conditions of rivers like Entiatqua have been recognized, the case for restoring lost river-wetland corridors to unlock their ecological potential becomes compelling.
One of the negative effects of hydropower on river environment includes rapid changes in flow and habitat conditions. Any sudden flow change could force fish to move towards a refuge area in a short period of time, causing serious disturbances in the life cycle of the fish. A probability-based multiscale model was developed to quantify the impact of hydropeaking on habitat suitability for two fish species. The model used habitat preference curves, river flow and depth to develop the suitability maps. The suitability index maps reveal that habitat suitability deteriorates as flow increases in this part of the river. The probability model showed that, on average, suitability indices are higher for adult grayling than juvenile trout in hydropeaking events in the studied area. In addition, the life stages of fish determine their response to the sudden flow change. The method developed shows the potential to be used in river management and the evaluation of hydropeaking impacts in river systems affected by hydropower.
Hydropeaking operation leads to fluctuations in wetted area between base and peak flow and increases discharge-related hydraulic forces (e.g., flow velocity). These processes promote macroinvertebrate drift and stranding, often affecting benthic abundance and biomass. Our field experimental study – conducted in three hydropeaking-regulated Swiss rivers – aimed to quantify (i) the short-term effects of the combined increase in flow amplitude and up-ramping rate based on macroinvertebrate drift and stranding, as well as (ii) long-term effects based on the established community composition. Hydropeaking led to increased macroinvertebrate drift compared to base flow and to unaffected residual flow reaches. Moreover, stranding of macroinvertebrates was positively related to drift, especially during the up-ramping phase. Flow velocity and up-ramping rate were identified as major determinants for macroinvertebrate drift, while flow ratio and down-ramping rate for stranding. Particularly high sensitivity towards HP was found for Limnephilidae, whereas Heptageniidae seemed to be resistant in respect to short and long-term hydropeaking effects. In the long-term, hydropeaking did not considerably reduce benthic density of most taxa, especially of some highly resistant and resilient taxa such as Chironomidae and Baetidae, which dominated the community composition even though they showed comparably high drift and stranding responses. Therefore, we argue that high passive drift and/or stranding, especially of individual-rich taxa, does not necessarily indicate strong hydropeaking sensitivity. Finally, our results demonstrate the necessity to consider the differences in river-specific morphological complexity and hydropeaking intensity, since these factors strongly influence the community composition and short-term drift and stranding response of macroinvertebrates to hydropower pressure.
Riparian vegetation provides many noteworthy functions in river and floodplain systems including its influence on hydrodynamic processes. Traditional methods for predicting hydrodynamic characteristics in the presence of vegetation involve the application of static roughness ( ns) values, which neglect changes in roughness due to local flow characteristics. The objectives of this study were to: (1) implement numerical routines for simulating dynamic hydraulic roughness ( nd) in a two-dimensional (2D) hydrodynamic model; (2) evaluate the performance of two dynamic roughness approaches; and (3) compare vegetation parameters and hydrodynamic model results based on field-based and remote sensing acquisition methods. A coupled vegetation-hydraulic solver was developed for a 2D hydraulics model using two dynamic approaches, which required vegetation parameters to calculate spatially distributed, dynamic roughness coefficients. Vegetation parameters were determined by field survey and using airborne LiDAR data. Water surface elevations modeled using conventional and the proposed dynamic approaches produced similar profiles. The method demonstrates the suitability in modeling the system where there is no calibration data. Substantial spatial variations in both n and hydraulic parameters were observed when comparing the static and dynamic approaches. Thus, the method proposed here is beneficial for describing the hydraulic conditions for the area having huge variation of vegetation. The proposed methods have the potential to improve our ability to simulate the spatial and temporal heterogeneity of vegetated floodplain surfaces with an approach that is more physically-based and reproducible than conventional “look up” approaches. However, additional research is needed to quantify model performance with respect to spatially distributed flow properties and parameterization of vegetation characteristics.
Riparian zones represent an important ecosystem providing a range of functions and services important to humans—e.g., biodiversity support, a reduction in erosion risk, or the transport of pollutants from the surrounding landscape to watercourses. At the same time, it is, unfortunately, an environment that has been often subjected to significant pressure during the agricultural cultivation of the landscape or the development of industrial and residential activities of human society. Thus, a large number of riparian ecosystems have disappeared or degraded. The assessment of the overall ecological status of riparian habitats constitutes an important source of information for the needs of watercourse management and landscape planning in the riparian landscape, the aim of which should be to maintain good status or to improve the current unsatisfactory state of these habitats. However, in order to reliably evaluate the current ecological status of the landscape, it is necessary to have information on the reference status, i.e., a potentially natural status that would prevail without human influence. For this purpose, a methodology that can determine the potential natural status of riparian zones in Central European conditions was developed. In this study, it was found that approximately a quarter (26 %) of all river basins in the Czech Republic reach very low environmental values of the potential natural status of riparian zones and, conversely, approximately 29 % of river basins are expected to develop significantly above average riparian zone quality if we neglect human impact.
A novel aerial tracer particle distribution system has been developed. This system is mounted on an Unmanned Aerial Vehicle (UAV) and flown upstream from where surface velocimetry measurements are conducted. This enables surface velocimetry techniques to be applied in rivers and channels lacking sufficient natural tracer particles or surface features. Lack of tracers is a common problem during low flows, in lowland rivers, or in artificial channels. This is particularly problematic for analysis conducted using Particle Image Velocimetry (PIV) techniques where dense tracer particles are required. Techniques for colouring tracer particles with biodegradable dye have also been developed, along with methods for extracting them from Red Green Blue (RGB) imagery in the Hue Saturation Value (HSV) colour space. The use of coloured tracer particles enables flow measurements in situations where sunglint, surface waves, moving shadows, or dappled lighting on riverbeds can interfere with and corrupt results using surface velocimetry techniques. These developments further expand the situations where surface velocimetry can be applied, as well as improving the accuracy of the results.
The dilution effect was originally proposed to describe the negative effect of increased host diversity on parasite abundance; with greater host diversity, parasite levels per host are predicted to be lower due to a higher probability of dispersing parasites encountering non-competent hosts. Dilution effects could also occur in many mutualisms if dispersing symbionts encounter hosts that vary in their competency. The introduction of non-native hosts can change community competency of a local group of host species. Crayfish introductions are occurring world-wide and these introductions are likely disrupting native crayfish-symbiont systems. Branchiobdellidan symbionts declined on native Cambarus crayfish occurring in the presence and absence of non-native Faxonius crayfish in the New River, USA. We performed an experiment investigating the effect of host density (1 vs 2 native hosts) and host diversity (1 native host and 1 introduced host) on branchiobdellidan abundance. The introduced F. cristavarius is a non-competent host for these worms. Six C. ingens were stocked on a C. chasmodactylus in each treatment and worm numbers were followed over 34 days. Worm numbers decreased over time on C. chasmodactylus alone and in the treatment in which a C. chasmodactylus was paired with an F. cristavarius. Worm numbers remained highest in the 2 C. chasmodactylus treatment . There was no significant effect of host diversity on worm reproduction. Crayfish invasions may have negative effects on mutualistic symbionts depending on the competence of introduced hosts. Loss of native symbionts is one of the potential hidden, negative effects of invasions on native freshwater diversity.
As in many other countries, Peru has the Water Quality Standard (WQS) as the primary tool for managing and diagnosing water resources. An analysis variable by variable to define water quality as poor or good was applied by setting concentration limits. A second group of tools commonly used are Biotic Indexes based on tolerance of benthic macroinvertebrates to pollution, that reflect the impacts caused by a group of variables, even though they cannot identify which variables determine the viability of the ecosystem. This research proposes to include the Stable States approach to evaluate the ecological integrity in central Andes rivers to explore an alternative approach with the capacity to represent a broader number of factors through multivariate analysis. A ten-year database of biological and physical-chemical variables measured in five Andean rivers were evaluated. Our results suggest these rivers fluctuate into two seasonal stable states (wet and dry season), accounting for approximately 31% of the system variability. In the wet season, the equilibrium of the state was dominated by the highest levels of suspended solids, turbidity, coliform, phosphorus, and some metals. During the dry season, the key variables were dissolved oxygen, flow, physical habitat, and biotic and diversity indexes. Likewise, there seems to be a third alternative state influenced by human pressures because of variables that exceed the WQS. Regarding water quality, the concentrations of coliforms, phosphorus, and lead usually exceeded the limits in two stations, but not every year. The ecological condition was better represented by ABI index than EPT.
In our writing, we voice stories of two Australian rivers to convey Indigenous ways of knowing and being. Interweaving academic literature, nature writing and creativity, we craft a story of reconnection that is transformative, action-oriented and potentially political. An open mind, place-intuition and the process of attending can deepen our river relationships, creating a sense of love and communicative connectedness. Paying deep attention, we notice meanings embedded in plain sight, within hearing range of rivers and watery places. Our relationships may be ‘in our faces’ such as the wind, or the air, water or bushes nearby. We communicate across binaries to experience the dissolution of imagined barriers. Feeling, hearing, writing and storytelling can support verbalising of experience, helping to bring to mind place-wisdom. It offers an everyday possibility for people now estranged from their riverine kin. The process uses a post human-centred, common worlds frame to consider the Anthropocene in regenerative ways. It is creative and liberating, and rivers are dying for people to take action by speaking out for and with our greater selves. In this learning journey, we synthesise learnings, hoping to inspire people everywhere to hear the call of rivers, to respond, take action and learn to love their rivers again.
Despite significant investments in watershed-scale restoration projects, evaluation and documentation of their impacts is often limited by inadequate experimental design. This project aimed to strengthen study designs by quantifying and elucidating sources of error in paired-watershed experiments and evaluating the statistical tools that detect and quantify population-level changes from watershed-scale restoration. Meta-analysis of 32 BACI experiments revealed that synchrony between paired-populations was both weak ( ρ ̵̅ = 0.18) and unrelated to the primary experimental error (r = 0.01), the degree to which paired-populations vary independently in time ( independent variance). Instead, it was found that the sum of the paired-population temporal variances ( total variance), accounted for 91% of the variability that controls statistical power. These findings demonstrate that 1) synchrony in paired-populations does not influence the primary error in BACI field experiments and 2) the magnitude of temporal fluctuations is primarily responsible for this error. The second study component, hypothetical BACI simulations, mathematically relates spatial, temporal and sampling errors to the independent variance and power. Design guidance based on these findings are provided to ensure that future restoration experiments have maximum probability of detecting a present restoration impact. We recommend planners quantify error sources directly from pilot studies and apply the tools provided by this research to estimate statistical power in their monitoring designs. Lastly, we propose a paired-reach design which provides a powerful platform to conduct replicated local-scale restoration experiments, which can build understanding of restoration-ecological mechanisms.
In this paper a collaborative writing group explores how we, two rivers, express ourselves over time, place and space, our energies long interpreted as veins and arteries carrying the Country’s life affirming blood. Voiced as River: I, River, this position reflects a worldview in which interrelationship with living river is normal, and River Spirit is ever-present. It is a position underpinned by Indigenous narratives as riverine expressions of place-based love. At times the paper is also voiced as writing group or individuals, with voices being interchanged where required for smooth reading. We see this as part of the decolonising process, which feels liberating and healing amongst the writers. Each writer is equally valued as co-creator, contributor, narrator and story teller. The two Rivers, being Martuwarra Fitzroy River (Kimberley, Western Australia), and Unamen Shipu Romaine River (North Shore, Québec, Canada) illustrate a common condition of being, through heritage, life, change and possibility. Through stories and voices, the socio-scientific implications of colonisation and lost connections become clear, considering the interaction, the dialogue and the cultural synthesis of living water systems that have always incorporated all life forms into rivers of life. As a way of navigating towards wholeness, Aboriginal knowledge systems and narratives for healing are used to bring together findings of this intercultural river learning journey.
Biological invasions are regarded as one of the largest threats to native biodiversity. The eradication of non-native parasites by culling of hosts are a controversial conservation strategy, particularly when using indiscriminate methods involving whole ecosystem collateral damage. While short-term effects are abundantly documented, long-term surveys are needed to detect potential wider ecosystem effects. Here, we report a six-year study on effects of the piscicide rotenone on invertebrate communities from a Norwegian water course using a Before-After-Control-Impact design. Kick-net samples of benthic invertebrates were collected from three lentic sampling stations and two lotic stations two to four times per year in both a control and a treated watershed. In general, only relatively minor short-term effects immediately after the treatment on species turnover, measured as temporal beta-diversity, of benthic invertebrates were observed both in lentic and lotic locations. However, the lotic fauna was temporarily severely negatively affected following a period of rotenone exposure from an upstream lake. Species turnover co-varied markedly between control and treatment locations, indicating that natural environmental variation override effects of rotenone treatment. Likewise, the abundance of invertebrate taxa varied considerably both over time and between control and treatment locations. Our study indicates minor short-term (i.e. < one month) or long-term (i.e. four years) effects of rotenone treatment on benthic invertebrates, but severe effects on the lotic fauna eight months after treatment. However, long-term effects are likely to be taxa-specific and vary depending on habitat connectivity and thus potential for re-colonization and will differ among locations and among taxa.
This study provides a comprehensive review of the existing river measurement data of South Korea. The specific sediment yield in the country is 5–1,500 tons/km 2·year. The watershed area decisively affects the shapes of the curves for flow duration, sediment rating, and cumulative distribution of water and sediment discharge, and it can determine the effects of topographic and anthropogenic characteristics on erosion and sedimentation processes. Regarding flow regime, small watersheds have flashy hydrographs and high sediment concentrations at a given flow discharge. The coefficient of the sediment rating curves for various rivers decreases from 1 to 0.02 as the watershed area increases from 100 to 20,000 km 2, with the exponent of the curves ranging from 1.5 to 2.0. Moreover, sediment transport in small watersheds depends on large floods. The half-yield discharge typically ranges from 5 to 40 times the mean discharge, and it decreases with increasing watershed area. This study proposes equations to calculate the annual discharges, flow duration curves, sediment yield, and cumulative distribution curves of the flow and sediment, as well as the sediment yield at reservoirs in South Korea. Additionally, the sediment regimes in the country are compared to those in other continental regions.
Numerical modeling of braided channels showed no significant differences in the number of cross-sectional branches between different water periods in the middle reaches of the Yarlung Tsangpo River. During most of the year (wet, normal and dry periods), flow velocities in the higher-branching (HB) channels were significantly lower than in the other two branching categories, while the overall distribution of depth in the higher-branching channels maintained a high degree of consistency with the moderate-branching channels (MB), which partly explains why the HB channels are important habitats for fish spawning, nursery and baiting (lower flow velocity distribution with a wider range of depth). Based on the examination of the water surface width, the water surface width may not be a limiting factor for fish habitat within braided rivers. Simulation of the hydrodynamic parameters of the fish-spawning grounds revealed that the average cross-sectional flow velocity and water depth fluctuated the least at different flows during the fish-spawning period for the HB channels. By counting the hydraulic parameters of the spawning grounds during the spawning period, it can be seen that the most preferred flow velocity for fish in the braided river in the study section was 0.1-0.4 m/s, and the water depth was 0-1.2 m. This article analyses the characteristics of the hydraulic parameters of the braided river and provides theoretical support for the restoration of fish habitats in braided rivers.