Classification of natural flow regimes of non-perennial rivers and streams (NPRS) is an incipient field of research. NPRS represent approximately 70% of the total Mediterranean rivers and are expected to increase in the next decades as a result of climate change. Due to the ecological importance of NPRS and the need to improve national ecological assessment methods within the scope of the Water Framework Directive (WFD), this paper aims to classify the hydrological regime of 69 non-regulated streams, testing several hydrological indices related to the frequency, duration, timing, and rate of change in periods of flow cessation. Using daily flow records, a total of 315 indices were calculated and their relationships were examined with Principal Component Analysis (PCA) for different thresholds used to define zero-flow condition set at 0, 1, 2, and 5 l/s. Redundancy analysis identified five indices that better describe the patterns of hydrological variability in Mediterranean NPRS: number of days per year without flow, annual percentage of months without flow, mean daily of annual flows, coefficient of variation of Julian date of the annual start of zero flow and annual rise rate. Using these indices, a self-organizing map (SOM) was trained in order to categorize the NPRS into three groups with similar hydrological features. The results of this study provide a statistically-based hydrological classification of NPRS in Mediterranean environments. We expect that this classification will provide useful insights to water authorities to improve the assessments of the ecological status in this set of water bodies.
Hydrological drought has wide-ranging impacts on water quality, nutrient and carbon metrics that are critical to investigate with the increased drought frequency predicted with climate change. This study compared physicochemical parameters (temperature, conductivity, pH and DO), nutrients (TN, NO X, NH 3, TP) and carbon (TOC and DOC) between hydrological drought conditions (2006–2009) and hydrological normal conditions (2016–2019) at five sites along the lower Savannah River (Georgia, USA). We unexpectedly found temperature (F 1,220=4.27, p=0.04) was significantly lower during drought conditions. Levels of pH (F 1,220=11.99, p<0.01) and DO (% saturation; F 1,220=9.17, p=0.01; and mg L –1; F 1,220=4.04, p<0.01) were significantly higher during drought. We found TN (F 1,220=5.23, p=0.02), TOC (F 1,220=30.22, p<0.01) and DOC concentrations (F 1,220=30.22, p<0.01) were significantly lower during drought, but NO X concentrations (F 1,219=4.04, p=0.05) were significantly higher during drought. Conductivity only varied at the lower river sites, being significantly higher during drought at Sites 3 (F 1,47=12.56, p<0.01), 4 (F 1,47=12.96, p<0.01) and 5 (F 1,34=17.60, p<0.01). These complex changes could be attributed to volume reductions coupled with an increase in the percentage of total flow originating from groundwater and limnetic reservoir inputs, persistent point source pollution, reduced natural catchment inputs and/or reduced floodplain interactions. The changes that occurred during drought may be disruptive to aquatic life, not only from reduced water quantity but also due to a scarcity of some biologically essential materials and lower food resources, combined with artificially high levels of some other potentially stressful materials.
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.
The hydrological regime is the main factor governing the functioning of floodplain rivers. A full comprehension of its dynamic leads to a better understanding of the system’s behaviour and of the proper methods that must be used. We analysed the daily water level of the Paraná River during the last century at three gauge stations using linear and non-linear tools to characterise the hydrological dynamic and to analyse to what extent chaotic behaviour prevails. The three water level time series were characterised as non-linear and non-stationary by power spectrum, autocorrelation function, and surrogate test analyses. A strange attractor was developed when the phase space was reconstructed, having a low dimensional chaos supported by correlation dimension, positive maximum Lyapunov exponents, and recurrence quantification analysis. In line with this, the system resulted unpredictable with a threshold by sample entropy, and with an intermediate hydrological complexity, while Hurst exponent characterised the system as persistent and with sensitive dependence on initial conditions. In a general overview, all the evidence obtained indicates that the Paraná River’s behaviour is at the edge of chaos. A latitudinal gradient of decreasing chaoticity was observed as the floodplain extent increased, whereas complexity was highest at the intermediate river station due to the inflow of tributaries with different hydrology. This paper attempts to offer some additional insights for understanding the hydrological behaviour of floodplain rivers and the proper methods to understand their complexity.
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.