Ecohydrology最新文献

The hydrological drivers triggering overwintering migration of fish in the headwaters of the Yangtze River, characterized by winter bottom-up freezing, remain poorly understood. This study investigated the hydrological dynamics influencing the overwintering migration of Schizopygopsis microcephalus, a key endemic species. Combining ultrasonic telemetry data with continuous, hourly water temperature and depth monitoring at an identified overwintering ground (October 2020–June 2023), we employed statistical analyses (including Mann–Kendall [M-K] test, wavelet transform, generalized linear mixed model, receiver operating characteristic analysis and decision trees) to identify migration triggers. Results revealed significant diurnal thermal fluctuations at the overwintering site. During the overwintering period, the daily temperature difference ranged from 0.2°C to 16.1°C, with a dominant 36-h periodicity in both temperature and depth. Returning periods exhibited temperatures of 0°C–8.7°C and large daily fluctuations (1.1°C–8.4°C), while leaving periods showed 0°C–16.9°C and fluctuations of 2.3°C–13.9°C. Distinct hydrological thresholds governed migration phases: both decreasing temperature (< 0.9°C) and depth (> 0.81 m) triggered autumn returning, while increasing temperature (> 4.6°C) and depth (> 0.81 m) initiated spring departure. The synergy between water temperature and depth is the primary driver of S. microcephalus overwintering migration. This study provides key data for the hydrological demands of the overwintering migration of important fish species in Yangtze headwaters and serves as a basis for overwintering response to climate change.

Globally, the operation of hydraulic engineering projects alters downstream river habitat, thereby affecting aquatic organisms and threatening aquatic ecosystems. Using 30 years of time series data and statistical analyses, including structural equation modelling (SEM) and redundancy analysis (RDA), this study examined the influence of the world's largest reservoir—Three Gorges Reservoir (TGR)—on the habitat and organisms of the downstream Jingjiang River. Among all habitat components, water and sediment are the most fundamental. After reservoir operation, the proportion of flood-season discharge in the annual total decreased by about 5%, while suspended sediment concentration sharply declined from about 0.8 kg/m³ to less than 0.2 kg/m³. Water and sediment discharge determine other components of river habitat: changes in discharge increased water temperature, while reduced sediment supply intensified channel scouring and lowered water levels. They also shape the chemical habitat by controlling nutrient fluxes and composition. Water discharge directly affects fish spawning through changes in flow magnitude and timing, while sediment indirectly affects spawning by modifying water transparency and nutrient availability. Variations in water and sediment together explained approximately one-third of the observed changes in fish spawning. Although reservoirs alter downstream habitats, they also offer opportunities for habitat restoration and organism protection through ecological scheduling, which may even be more effective than managing individual habitat components at local scales.

An understanding of the hydroclimatic environment in river systems is essential for identifying the main extrinsic factors affecting aquatic communities. This study addresses this topic by using an unprecedented historical dataset (from 1975 to 2017) on the ecological aspects of the key invertebrate species of the large Parana River's sandy bed: Narapa bonettoi (Oligochaeta). This large dataset was examined in the context of a large series of environmental variables measured in the section of the river where invertebrate samples were obtained. The statistical analysis of this information, combined with the findings of previous studies, enabled the selection and/or design of 36 crucial hydroclimatic variables. These variables were used to construct, calibrate and validate a generalized linear models (GLM). This model predicts the densities of N. bonettoi under different hydroclimatic scenarios (R² = 0.52). The general results indicate significant ecological changes during the rising and receding limbs of a flood and the hydrological period following its end. These changes occur due to variations in the intensity of hydraulic forces along the riverbed during flood and drought. Therefore, this model can serve as a valuable tool for understanding the ecological consequences of climate change in large rivers.

Rheophilic fish populations are experiencing significant declines, primarily because of human-induced modifications of riverine ecosystems. River damming and associated habitat changes favour generalist fish species, potentially exacerbating the challenges faced by rheophilic species. In this study, we investigated the interaction between two fish species: the rheophilic asp (Leuciscus aspius; Linnaeus, 1758) and the generalist common bream (Abramis brama; Linnaeus, 1758), with a focus on the latter's predation on asp eggs. We hypothesized that habitat modifications—specifically, reduced water flow caused by high water level retention in downstream reservoir—directly influence the accessibility of asp spawning grounds. From 2018 to 2020, we monitored asp egg abundance at a fluvial spawning ground and used passive telemetry arrays to track common bream presence. Gut content analysis was used to confirm predation of asp eggs by common bream at the site. Our findings show that high water levels in 2018 and 2019, which slowed water flow, facilitated common bream access to the spawning ground. In contrast, the significantly lower water levels in 2020 increased water flow rates by two to three times, restricting common bream access. Statistical modelling revealed that river habitat modifications intensify interspecific interactions among fish species that would otherwise have minimal interactions in unaltered environments. These subtle yet significant shifts in trophic dynamics within anthropogenically altered riverine landscapes may contribute to the ongoing decline of rheophilic fish species.

Substance transport dynamics in floodplain lakes are fundamental to ecosystem stability, yet their spatiotemporal variability under changing hydrological regimes remains insufficiently understood. The construction of a water control project further complicates these dynamics and poses new challenges to ecosystem integrity. This study integrated a hydrodynamic model with a particle-tracking approach to quantify the substance transport timescales and pathways in Poyang Lake, China. Employing e-folding flushing time as a diagnostic metric, we simulated the transport dynamics under both natural and regulated conditions. Results suggest that (1) the coupled modelling framework reliably captures the transport dynamics of floodplain lakes, effectively representing the spatial and temporal variability of flushing time and transport trajectories; (2) Poyang Lake exhibits pronounced seasonal and spatial heterogeneity in flushing time, ranging from approximately 10 days in spring and winter to over 20 days in summer and autumn, with longer retention in embayment areas than in the main channel and floodplain and (3) while the Poyang Lake Water Control Project alleviates seasonal water shortages, it markedly prolongs flushing times during autumn and winter and reduces spatial heterogeneity, increasing the potential for substance accumulation in low-exchange zones. These findings provide mechanistic insights into the hydrodynamic processes governing substance transport in floodplain lakes and offer a scientific foundation for optimising water resource management and mitigating pollutant accumulation under anthropogenic interventions.

Developing a robust framework for assessing stream ecological status (ES) and establishing defensible nutrient criteria remains a key challenge in aquatic ecosystem management. We applied a fuzzy logic-based approach to evaluate the biological condition gradient (BCG) of 17 streams in the Aras River Basin using biological (Trophic Index of Turkey [TIT], Trophic Index [TI]) and chemical (total phosphorus [TP], electrical conductivity [EC]) metrics during summer, fall and spring seasons. Diatom community and integrated metrics were used to assess ES of aquatic ecosystems. Biological condition gradient scores ranged from 0.23 (Sarısu Stream, fall) to 0.81 (Akçakale Stream, spring), reflecting conditions from degradation to high integrity. Strong correlations were found between BCG and TIT (r = −0.93, p < 0.01), TI (r = −0.90, p < 0.01), TP (r = −0.75, p < 0.01) and EC (r = −0.84, p < 0.01), highlighting BCG's sensitivity. The results indicate diverse ecological statuses across spatiotemporal scales, emphasizing the need for integrated biological and chemical assessments. This approach enhances ecological evaluation precision and offers a scalable methodology for watershed management. Given increasing anthropogenic and climatic pressures, further refinement of BCG could provide critical insights for adaptive management and policy in Türkiye and beyond. Aligning ecological assessments with predictive modelling underscores BCG's potential as a key tool for monitoring, conserving and restoring freshwater ecosystems. We recommend using BCG due to its superior accuracy and flexibility.

Although physical barriers are being commonly used for fish protection and guidance of larger migratory species in hydropower plants, there is a lack of information on how they perform for small-bodied fish species. Here, we tested a small-bodied species (Alburnus escherichii) based on 30 individuals across 16 hydraulic treatments. These included screen angles of 22°, 30°, 38° and 45°, as well as bed slopes of 0% and 1% without a weir. Additionally, the efficacy of crump vs. streamlined bypass weirs was examined at a bed slope of 1%. All trials were video-recorded for analysis of bypass efficiency. For all tested conditions, we found a fish protection efficiency of 100%. Results showed that 38° and 45° screen angles produced the most favourable velocity distribution—reducing approach velocities from ~0.5 m/s (30°) to ~0.4 m/s—and increased passage efficiency. Raising the bed slope from 0% to 1% elevated approach velocities and reduced efficiencies by 10%–23% across all angles. The incorporation of a weir generated a beneficial backwater effect, yielding a 9%–15% improvement over the no-weir condition, with the streamlined profile outperforming the crump weir. Moreover, 38° screen angle has the shortest fish passage time for all tested configurations. These findings provide clear design guidelines—namely, a 38° fine-screen rack, minimal inlet slope and a streamlined bypass weir—to optimize downstream fish guidance and mitigate injury and mortality in run-of-river hydropower installations.