ABSTRACT We propose an integrated geomorphic framework for floodplain zoning along a 140 km stretch of the Narmada River, India (between Bargi Dam and Barmanghat). This framework utilizes Sentinel‐2 multispectral images (10 m), Copernicus Forest and Building‐Free DEM (FABDEM), and topographic profiles measured in the field using Differential GPS (DGPS). Following Central Water Commission (India) guidelines, we classified the floodplain into three zones. These include the No‐Go Zone (NGZ; 2–5‐year return period), Regulatory Zone (RZ; 25‐year return period), and Warning Zone (WZ; 100‐year return period). We delineated these zones entirely based on geomorphic features, topographic breaks, and riparian vegetation. The NGZ includes hydrologically connected depressions, swamps, and bank‐intact gullies with water‐tolerant riparian vegetation. The RZ comprises flood channels, large depressions, crevasse splays, and wetlands with lush woody vegetation. The WZ encompasses elevated terraces, paleochannels, and ravines with wide‐canopy, trunk‐root trees. We performed field validation through reconnaissance, local surveys, RTK‐DGPS surveys (< 2 cm vertical accuracy), and drone images (1–2 cm resolution). To assess this holistic geomorphological approach, a 1D HEC‐RAS model was set up for comparison along a 70‐km sub‐reach (Bhedaghat–Barmanghat). We merged the channel bathymetry measured using an Acoustic Doppler Current Profiler (ADCP) and FABDEM for the true representation of channel geometry into the model. We calibrated and validated the model using water‐level data recorded from 1977–2023 at a gauge station near Belkhedi. This model yielded an RMSE of 1.25 m and . Comparing the floodplain zonation obtained from geomorphic approach to the model, we found the value of Intersection‐over‐Union (IoU) for NGZ = 0.53, RZ = 0.42, and WZ = 0.31. The NGZ area demonstrates a consistently close agreement between the two approaches. However, flow regulation and anthropogenic modifications significantly decoupled the RZ and WZ in contemporary hydraulic inundation patterns. Hydraulic models underestimated the flood extents of the RZ and WZ due to dynamic terrain changes. Geomorphic analysis and local surveys enabled us to refine these flood zone boundaries by identifying land‐use impacts. These landform alterations lead to rapid flood pattern changes observed in the field survey. The geomorphic component does not rely on discharge data; we believe that the geomorphic framework directly applies to managing flood risk in ungauged or data‐scarce river corridors. The geomorphological zonation provides a scientific foundation of first‐order functional classification of floodplains for long‐term river corridor planning.
Centuries of river modification, particularly straightening and incision, have severely reduced lateral connectivity between rivers and their floodplains. As a result, Stage 0 riverscapes, characterised by high lateral connectivity (e.g., anastomosing or wetland riverscapes), are now rare in anthropogenic landscapes. Restoration to a Stage 0 condition is gaining international momentum but remains relatively untested, particularly in human-modified landscapes with novel constraints and challenges. Here, we provide a perspective on lessons learnt from restoration to Stage 0 in anthropogenically constrained settings. We draw on experience from the design, construction, and monitoring of two UK restoration projects, among the first valley-floor reset rivers in Europe: the River Aller and the River Witham. Through infilling incised channels and regrading the floodplain, valley-floor reset transformed the single-thread, incised channels into multi-thread, river- wetlandscapes and substantially increased river-floodplain connectivity. In response, the water table elevation rose by about 1 m and baseflow wetted width increased by 9- to 20-fold; for example, average baseflow wetted width at the Aller increased from 4 to 81 m (maximum baseflow width increased from 7 to 147 m). We summarise six lessons learnt: (1) Restoring dynamic riverscapes means embracing uncertainty and navigating societal expectations, (2) Stage 0 and valley-floor reset are not appropriate everywhere: informed restoration is required, (3) Space exists for restoring river lateral connectivity, even in anthropogenically-constrained catchments, (4) Interrupting long-profile connectivity with grade-control structures needs careful design, (5) Restoring lateral connectivity creates multi-functional landscapes for water, wildlife and people, and (6) Structured, transdisciplinary research is needed to align restoration of natural processes with societal needs in a changing climate, and unlock the potential of river lateral connectivity to enhance biodiversity, river ecosystem services and climate resilience.
Anthropogenic impacts on the thermal regime of rivers include climate change and deforestation. For the latter, developing modelling tools that can account for the impact of varying vegetation cover on river temperatures is essential. This study describes a new addition to the CEQUEAU hydrological and water temperature model: a shading algorithm. This relatively simple tool accounts for vegetation height, stream orientation and the associated shadow length on the river to modulate incoming solar shortwave radiation. The algorithm was tested on seven different sites from five Canadian rivers. The results indicate that the algorithm either maintained or slightly improved model performance. Different deforestation and afforestation scenarios were tested and the model showed sensitivity to changes in riparian vegetation height, as a function of width and initial vegetation cover.
Sediments are avoided in many river and dam managements because of their adverse effects on water usage and flood control. Recently, sedimentation control measures, including sluicing, have been employed to manage sediments in river channels and restore communities in dammed rivers. Sediment sluicing is a technique used to control sedimentation in reservoirs by allowing sediment-laden water to pass through dams during high-flow events by establishing lotic conditions. Although sluicing operations can provide sediment and increase community diversity in river channels below dams, their effects on reservoir fauna remain unclear. Therefore, this study aimed to investigate the effects of sluicing operations on fish and benthic invertebrate communities in two reservoirs using 14-year monitoring data. Our results showed significant increases in total nitrate in water and oxidation-reduction potential at the bottom, decreases in suspended solids in winter, and reductions in taxon richness and total density of summer macroinvertebrate communities after sluicing operations. However, the results suggested that the population of macroinvertebrates and fish recovered over time after each dam operation. In conclusion, although sluicing operations reduced reservoir biota, macroinvertebrate and fish richness were restored within a few months after the operation, suggesting that the impact of dam operations on biota may be minimal.
ABSTRACT Longitudinal connectivity in the Austrian section of the Danube has improved over the last three decades thanks to the progressive installation of fish passage facilities at hydropower plants. However, navigation locks which are present at all barrages remain poorly quantified with respect to their role in fish migration. This study used long‐term PIT tag monitoring to evaluate the impact of navigation locks on the upstream migration of fish at the Aschach hydropower plant in Upper Austria over a 16‐month period (March 2019 to June 2020). Additionally, indirect evidence of ship lock passage was obtained by analysing long‐distance movements across dams lacking fishways. A substantial number of fish, representing a wide range of species and body sizes, were detected passing through ship locks. The repeated detection of individual fish and their passage through multiple consecutive locks indicates a consistent and deliberate pattern of use rather than an incidental occurrence. Lock passage showed pronounced seasonal peaks in spring and autumn, and detections were predominantly diurnal. These temporal patterns were not significantly correlated with the frequency of lock operation. Nevertheless, an effect of lock operations could not be ruled out. Our results demonstrate that navigation locks can serve as supplementary migration routes in large, regulated rivers. They also provide novel insights into species composition and size structure, as well as seasonal and diurnal patterns of lock use.
Restoration measures, such as river widening, aim to reactivate key morphodynamic processes, which are critical drivers of fluvial habitat dynamics. While some evidence supports the important role of sediment supply on river widening's morphology, its link to fish habitat availability and dynamics remains unclear. To quantify this link, we used one-sided river widening morphologies formed under varying sediment supplies (100%, 80%, 60%, and 20% of the channel's transport capacity), upscaled from laboratory. The experiments started from a channelized alternating bar morphology that was subjected to a steady 1.5-year flood until equilibrium, followed by a 30-year flood event. We delineated the habitat for juvenile and adult brown trout (Salmo trutta) and evaluated their spatial dynamics across discharges, using 2-D hydrodynamic modeling and suitability curves. Our results showed that the near-equilibrium sediment supply morphologies (i.e., 100% and 80%) increased habitat at average to high flow conditions, with the 30-year flood further increasing low-flow habitats. In contrast, the widening morphologies formed with the reduced-sediment supply of 60% and 20% did not show an improvement in habitat quantities following both formative events. We found that the correspondence of the spatial habitat dynamics to morphodynamic processes depends on habitat location: juvenile habitats, typically occupying channel margins, corresponded to shoreline length dynamics, whereas adult habitats, typically found within the channels, corresponded to elevation change dynamics, both influenced by sediment supply. Our insights expand the understanding of sediment-habitat dynamics and can further assist holistic, resilient widening restoration strategies across multiple scales.
Relieving barriers and increasing free flowing rivers is a global imperative to restore habitat connectivity for migratory fish stocks. While reducing river fragmentation will certainly improve biodiversity, the spread of non-native species throughout a river system may be facilitated as an inadvertent outcome. Environmental assessment of river systems tabled for barrier alleviation is thus essential to appraise the risk posed by non-native species on a site-by-site basis. Non-native freshwater crayfish are species of concern globally and are implicated as a stressor to native salmonid populations and multiple invertebrates. Here, we demonstrate and compare the use of trapping, remote underwater video (RUV), baited RUV (BRUV) and eDNA to risk assess the implications of removing in-stream barriers and invasive signal crayfish (Pacifastacus leniusculus) throughout the River Calder catchment, United Kingdom. There was no difference between the detection probability of trapping, remote underwater video (RUV) and baited RUV (BRUV) for signal crayfish. No crayfish were detected by eDNA in any of our sites, suggesting a lack of utility in eDNA for rapid and accurate crayfish species occurrence at our sampling level. Distance from barriers played a key role in determining crayfish presence, with populations of crayfish more likely to be found directly downstream from the nearest upstream barrier. Crayfish abundance was higher at locations with lower Oxidation-Reduction Potential (ORP), although it is unclear whether low ORP is caused by the crayfish. There were 53 barriers encapsulated by our survey; over half (50.9%) of these barriers were found to have invasive crayfish both above and below them, and a further 17% had crayfish directly below them. Both tributaries that had reported presence of native white-clawed crayfish (Austropotamobius pallipes) had several barriers between them and the nearest record of signal crayfish; it is recommended that these barriers remain in place and are potentially reinforced, while those that have been identified as breached be the focus of barrier alleviation. In-stream barriers may be creating micro-habitats and relief from strong flow which support crayfish persistence and therefore removal may facilitate flow regimes which are less conducive for non-native crayfish.
Lived experiences from past environmental events can promote societal learning from ecological systems, known as Socio-Ecological Learning (SEL). SEL occurs when new Knowledge, Attitudes, and Practices (KAP) develop from these experiences. However, research has rarely documented SEL through a historical KAP perspective. This study uses Social Ecological Systems Theory and Social Learning Theory to evaluate SEL in riparian vegetation management, focusing on a historical KAP analysis in the Rwizi catchment. Participatory Rural Appraisal protocols were developed to stimulate discussions among participants about what has been learned from 1992 to 2022. Village transect walks and historical timelines were used to collect data from study participants. The findings reveal complex interactions in the Rwizi catchment, marked by causality, feedback, nonlinearity, heterogeneity, and cross-scale dynamics. The knowledge of participants about riparian vegetation has evolved over time, shaped by various events stemming from unsustainable human activities. Attitudes have shifted from viewing riparian zones as unlimited to viewing them as finite and vulnerable. Although they understand sustainable management practices, they have hardly applied them on a community-wide scale. Lessons show complex, interdependent interactions in socio-ecological systems, as riparian vegetation pressures from community-resource interactions reveal causality, feedbacks, heterogeneity, nonlinearity, and cross-scale dynamics. Over time, SEL in riparian management has been achieved, seen in knowledge sharing, attitude change, and sustainable practices among Rwizi catchment communities.
As ecosystem engineers, beavers (Castor canadensis) modify river corridor form through dam building. When beavers are removed from a river corridor, their unmaintained dams wash out, altering the stream's hydrologic regime. The assumption that beaver dams increase floodplain connectivity is frequently presumed but has not been directly quantified. To address this gap, we assessed changes in floodplain connectivity caused by the loss of beaver dams at three headwater streams in Colorado, USA. Using a forensic analysis of historical beaver activity, we developed two-dimensional hydraulic models to compare metrics of floodplain connectivity under historical (beaver-active) and present (no beaver activity) scenarios. At three simulated flood discharges, we quantified changes in the volume of water on the floodplain, the fraction of flow through the floodplain, the volumetric flux into the floodplain, and mean site and floodplain residence times. The loss of beaver dams decreased floodplain connectivity across all metrics (up to a 96.5% loss in connectivity) except mean floodplain residence time, which increased in the absence of dams. Sensitivity analysis results show that the flow state and condition of beaver dams can have reach-scale impacts on floodplain connectivity. Notably, while we observed floodplain disconnection due to the loss of beaver dams at each site, the magnitude of change varied depending on both site-specific characteristics and on the flood magnitude. We conclude that, in headwater streams, beaver dams play an important and quantifiable role in facilitating floodplain connectivity, and floodplain disconnection from the loss of dams has major implications for other ecological and geomorphic floodplain processes. These results are especially timely considering the increasing interest in beaver-related restoration.
Flow velocity measurement is fundamental to hydrological and hydraulic studies, providing essential data for streamflow estimation and river dynamics analysis. Traditional in situ methods like propeller gauges and acoustic Doppler current profilers are accurate but intrusive and labour-intensive, while non-intrusive image processing methods like large-scale particle image velocimetry (LSPIV) offer a safer, more efficient alternative for measuring flow in challenging environments. Through a combination of controlled flume experiments and field deployments, the method's accuracy, sensitivity, and operational limitations were assessed in this study. Field experiments demonstrated the influence of environmental factors such as wind, reflections, and tracer distribution on velocity estimation. Laboratory tests provided controlled conditions to evaluate software performance across different flow regimes. Across both controlled flume experiments and multiple field deployments, LSPIV performance was found to be most consistent under medium flow conditions within the tested range. By evaluating identical workflows across scales and environments, the analysis demonstrates how tracer type and distribution, key software parameters (particularly interrogation and search area settings), and post-processing and filtering strategies jointly influence velocity estimation accuracy. Within this multi-scale framework, wood-chip tracers provided more robust surface coverage and visibility than biodegradable cornstarch under both laboratory and field conditions. While the method performed well in both laboratory and natural settings, further research is needed to refine image processing under challenging field conditions and to develop capabilities for fully tracer-free velocity estimation. Overall, the LSPIV method represents a robust and adaptable solution for non-contact flow monitoring, with strong potential for broader application in hydrological research and river management.
Urban growth and development opportunities are needed worldwide, but growth and development must be hazard-aware and should follow smart-growth principles. The $2.89 billion Fargo-Moorhead Area Diversion Project was designed to provide flood protection following damaging floods on the Red River of the North. But the project has quadrupled in cost and shifted from protecting existing infrastructure to promoting sprawl across similar to 200 km(2) of previously connected floodplain. We modeled three scenarios-offering divergent visions of growth-and found that expansion onto the floodplain is not required for continued development. All scenarios allowed for a doubling of the region's population, and both no-Diversion scenarios better served low-income, high-vulnerability portions of the Fargo-Moorhead area. Our scenarios do not reflect all available planning and policy tools, but they test key assertions in project justification and implementation. The Diversion project contrasts sharply with flood protection built upstream in Grand Forks, ND after 1997 flooding, which utilized wholesale buyouts, levee setbacks, and other "Room for the River" principles. Changes in the location, scope, and design of the Fargo-Moorhead project seem to reflect local political and economic self-interest, at the expense of bedrock principles of floodplain management and planning. The Diversion project did not begin this way, and we explore the potential role of "path dependence" in this and other suboptimal outcomes. Another pressing issue raised by this project is cost equity, where financial burdens are borne by all taxpayers, whereas benefits accrue to developers and jurisdictions that enabled that development. The Diversion project illustrates the thorny tradeoffs between opening development of floodplain land and, in the process, violating this "Prime Directive" of floodplain management.
Understanding how changes in catchment conditions affect ecohydrology in response to rainfall-runoff events is crucial when developing informed strategies to enhance flow resilience, restore natural habitats, interpret water quality data or reduce flood risk. This can be undertaken through evaluation of impacts on peak flows or flow attenuation within headwater to meso-scale catchments, extracting rainfall-runoff events from sub-hourly flow and rain timeseries data. Where sub-hourly insight is needed due to the scale of headwater catchments and their rapid flow response. Detailed documentation of a standardised event extraction methodology for sub-hourly flow time series and its applications is limited, and existing common methods have the potential to introduce bias. To address these needs, we present a methodology for event extraction alongside case studies detailing how it has been used to evidence change in hydrological function in relation to several restoration strategies and catchment intervention measures. A workflow is outlined for the delineation and extraction of rainfall-runoff event periods linking key hydrograph metrics, such as antecedent conditions and lag-times, using sub-hourly rainfall and flow observations. Across the case studies, noticeable impact was seen, with peatland restoration reducing peak flows by 49%, leaky dams and beaver dams reducing peak flows by 23% and importantly for water quality, showing that catchment measures which attenuate flows and reduce stormflow peaks can be very beneficial. The outputs of this work have had real world impact, informing catchment management strategies, demonstrating the value of a systematic approach that could be widely adopted across catchments of different typologies.
Fine sediment infiltration (FSI) can lead to riverbed clogging, thereby degrading important habitats for aquatic biota in the hyporheic interstitial zone of gravel-bed rivers (e.g., by reducing oxygen availability). This stress on rivers may increase from anthropogenic influences and can be counteracted by artificial gravel augmentation to improve bed morphology like sediment transport dynamics. For optimal functionality of artificial gravel deposits, knowledge about the infiltration capacity of fine sediments is necessary. For this purpose, 1:1 scale experiments were conducted in an outdoor experimental channel with a very high suspended sediment concentration (up to 48 gL-1). Three different sediment (gravel) mixtures, all without fines and suitable for salmonid spawning, were studied as gravel filters in the horizontal flow direction during three different exposure times to identify the mass of accumulated fine sediment. Although a very high suspended sediment concentration (SSC) was given, the rate of FSI occurred in highly different magnitudes. Narrowly graded gravel mixtures without fine fractions and thus larger voids show the highest, broadly graded gravel mixtures the lowest rates of fine sediment infiltration. The results show that grain-size distribution properties are crucial for FSI and can be used for adapted spawning habitat restoration concepts by for example, artificial gravel augmentation.
The presumptive standards approach to environmental flows offers a method to develop interim guidelines for ecological and social-cultural flow needs. The approach is based on deriving acceptable percent-of-flow limits based on naturalised flows (the absence of depletion or alteration of flow), and it can be an effective precursor to a full assessment of environmental flows, particularly when used to highlight seasonal differences. In this study, we analysed naturalised flows modelled for the period 1979-2010 using the MESH community-based modelling approach for 31 gauges in the Saskatchewan River basin in western Canada differentially affected by hydropower dams or irrigation withdrawals. We assessed deviations of measured runoff from naturalised runoff and estimated presumptive standards for social-ecological protection. Downstream of irrigation withdrawals, measured runoff was lower than naturalised during the open water season, reflecting water use for agriculture. Downstream of hydropower dams, runoff hydrographs were flatter, with lower runoff than naturalised during open water and higher runoff than naturalised during ice-on; deviations during ice-on were most predominant. Presumptive standards were established to allow for a 20% or 30% deviation from median naturalised runoff, representing high and moderate social-ecological protection, respectively. Half the gauges were within or bordered on the 20% or 30% sustainable flow boundary during the open water season, but only five gauges fell within those boundaries during the ice-on season. The deviations from naturalised runoff have implications for habitat quality, environmental cues, and social-cultural flow needs. As climate change continues to impact water availability in these systems, the impacts of flow alteration on ecological and social-cultural flow needs may be magnified.
Tropical rivers play a key role in regional carbon budgets, yet greenhouse gas (GHG) dynamics in regulated systems remain poorly understood. This study investigates the seasonal variability of carbon dioxide (CO2) and methane (CH4) concentrations, isotopic composition (delta 13C), and river-atmosphere fluxes in the lower Tocantins River, a clearwater system affected by flow regulation and land-use change. Over a three-year period (2014-2016), monthly biogeochemical measurements were conducted along with hydrological monitoring. CO2 concentrations and fluxes peaked during the high-water season and were positively correlated with discharge, dissolved oxygen, pH, suspended sediments, and dissolved organic carbon. In contrast, CH4 fluxes were significantly higher during the low-water season and associated with reduced river discharge, wind speed, and fine suspended sediments. Isotopic analysis of delta 13CO2 suggested shifts in carbon sources across seasons, with respired terrestrial inputs dominating contributions to river pCO2 during high-water. These findings highlight the influence of seasonal hydrology on GHG emissions, even though discharge regulation by upstream dams dampens flood pulse dynamics and reduces lateral connectivity with floodplains. Given the increasing regulation and land conversion in Amazonian basins, understanding these processes is essential to guide sustainable river management and improve regional GHG inventories.
Exploiting the sensory physiology of migratory fishes to guide them away from hazards like hydroelectric turbines is of interest to regulatory agencies and hydropower operators to achieve conservation and management goals. Here we describe a river-scale experiment where out-migrating adult American eel (Anguilla rostrata) were tracked downstream via acoustic telemetry as they encountered a 216 m long floating LED light array on the St. Lawrence River. Eel (N = 51) spatial responses to light were compared to eels detected on control (no light) nights with the expectation that light would cause eels to deflect laterally along the light array toward the river-right shore. Eels generally swam near the surface at night, and 39.5% of eels that encountered the light altered their downstream trajectories consistent with lateral deflection, although those responses were relatively modest. However, 76.7% of eels demonstrated diving responses of >= 4 m, consistent with seeking darker passage under the light field. Although we observed some degree of light avoidance, additional research is needed to optimize use of light for effective behavioral guidance in large rivers.
Post-flood riparian vegetation recovery demands significant attention; however, the complexity of traditional remote sensing methods often hinders environmental managers from implementing rapid vegetation monitoring. This paper developed a model using a Deep Learning Model within ArcGIS to classify and detect recovery of vegetation with high resolution aerial imagery following the 2022 major flood of the Brisbane River at 4 sites: Colleges Crossing, Corinda, Kholo and Priors Pocket. The model was 91% accurate across all sites and was most accurate in post-flood imagery and in the water and low vegetation classes at 100% for both. Low vegetation was found to recover at all sites except Priors Pocket whilst tall vegetation and bare ground did not. By leveraging this streamlined and efficient solution for monitoring post-flood riparian vegetation recovery, damaged vegetation can be more effectively identified, allowing more precise and cost-effective rehabilitation efforts. Future studies should further develop the model to increase accuracy and applicability to other catchments.
The Marias River flows from Glacier National Park through northcentral Montana, and into the Missouri River. Annual flows gradually declined from 1902 to 2024 (similar to 3.2%/decade) and the 1952 Tiber Dam and Lake Elwell reservoir were operated to attenuate peak flows and stabilize downstream flows year-round. We had assessed riparian woodlands along the Upstream versus Downstream Reaches in 1991-1994, and for this study we reassessed the riparian conditions three decades later, in 2025. Following the flow stabilization, the downstream river channel was stabilized, and dense herbaceous vegetation encroached into the Colonization Band between the river and the mature riparian woodland. Consequently, there was sparse seedling colonization of plains and narrowleaf cottonwoods (Populus deltoides and P. angustifolia) along the Downstream Reach, in contrast to prolific colonization along the relatively free flowing Upstream Reach (lineal extent with colonizing cottonwoods: Upstream 82%, Downstream 35%). Conversely, colonization by the native shrub, silver buffaloberry (Shepherdia argentea), and related, non-native Russian olive (Elaeagnus angustifolia), was more extensive along the Downstream Reach (lineal extent: Upstream 1.4%, Downstream 52%). Additionally, the mature cottonwoods appeared healthier Upstream, with less branch and crown dieback. Extending from these post-dam patterns, the riparian cottonwood forest downstream from Tiber Dam will probably decline further without a more naturalized river flow regime, with regular seasonal variation and occasional higher flows to provide geomorphic disturbance, disfavor encroaching vegetation, and enable cottonwood replenishment. Similar to other regulated rivers, any prospective environmental flow regime below Tiber Dam must also consider the other social and environmental outcomes.
Poyang Lake, the largest river-connected freshwater lake in China, plays a vital role in maintaining regional ecological security and water resource balance; however, its flood-to-drought transition process has become increasingly pronounced, posing severe threats to wetland habitats and socioeconomic development. Existing studies fail to clarify the nonlinear interactive mechanisms between upstream inflows and the Yangtze River during the transition. This study used a Long Short-Term Memory (LSTM) model and SHapley Additive exPlanations (SHAP) to explore the drivers of this transition from 1988 to 2018. Results showed that the LSTM model achieved high-precision water level simulation, with Nash-Sutcliffe Efficiency and Root Mean Square Error reaching 0.97 and 0.42 m for Xingzi Station (northern lake zone), 0.96 and 0.45 m for Tangyin Station (central lake zone), and 0.95 and 0.48 m for Kangshan Station (southern lake zone), respectively. SHAP analysis revealed that before the TGD, the Yangtze River dominated the flood-to-drought transition, and its influence was 385% that of the upstream rivers (Gan, Fu, Xin, Rao, and Xiu Rivers). After the TGD, the Yangtze's influence declined acceleratedly, while the upstream rivers' influence increased-even exceeding the Yangtze in central and southern zones. Furthermore, under the Yangtze River's modulation, the upstream inflow presented a clear critical discharge threshold for its marginal contribution to lake water level, with the effect shifting from no effective promotion of water level rise to significant lifting as discharge increased. This threshold decreased markedly after the TGD operation, indicating a significantly enhanced sensitivity of upstream inflow impacts on the lake's hydrological regime. This study quantifies altered interactive mechanisms of transition drivers, supporting the lake's water resource management amid flood and drought risks.
Large free-flowing rivers are rare but important ecosystems. Environmental conditions in these systems vary through space and time, resulting in dynamic patterns of habitat quality for aquatic species. Such variability could influence invasive species success by altering habitat quality, thereby supporting native species adapted to these conditions. Our study examined spatial and temporal trends in energetic habitat quality between native gizzard shad (Dorosoma cepedianum) and invasive silver carp (Hypophthalmichthys molitrix) in the free-flowing Wabash River, USA. Environmental conditions (water temperature, velocity, prey type and density) were sampled throughout the river and used as input data to a spatially explicit bioenergetics model to predict fish growth rate potential as an index of habitat quality. Seasonal energetic habitat quality varied considerably for both species. Spring habitat quality was poor for both species throughout the river, and only small portions of the river were suitable during summer, mainly in off-channel habitats. More of the river was suitable for gizzard shad, especially during autumn. During all seasons, spatial overlap in high-quality habitat was high between species, especially in the highly suitable off-channel and main-channel border habitats. Promoting habitats in unregulated rivers that provide combinations of flow, food availability, and temperature unique to native species may be important for supporting native species and deterring invasive species. Dam removals that allow access to diverse off-channel habitats may promote biodiversity and protect against invasions in riverscapes.
