Search Results (270)

Permanent surface water is an important component of regional hydrological systems, yet basin-scale area statistics alone may overlook structural changes in highly modified basins. This study investigated long-term permanent surface-water dynamics in the Lower Yangtze River Basin (LYRB), China, during 2000–2020 using a basin-to-pixel remote sensing framework that combined annual water mapping with multi-scale structural diagnostics. Annual permanent surface-water maps were derived from Landsat imagery using adaptive thresholding. The reliability was evaluated through product-level comparison, reference-based accuracy assessment, and representative complex-scene comparisons with machine learning and deep learning baselines in urban-shadow, turbid-water, and algae-affected environments. Basin-scale landscape metrics, centroid migration, and pixel-level Spatial Water Variation (SPAT) indices were constructed to characterize structural change, while generalized additive models were applied to examine changing associations with hydro-climatic, land-surface, and anthropogenic factors. The extracted dataset achieved high overall accuracy (OA = 98.43%) and improved delineation of narrow channels and fragmented littoral boundaries. Permanent surface water in the LYRB followed a decline–recovery–stabilization trajectory, but basin-scale expansion often co-occurred with increased pixel-scale fragmentation and reduced aggregation. Expansion was mainly expressed through scattered small patches, whereas shrinkage was concentrated along the margins of existing water bodies. Driver analysis further showed that NDVI remained the strongest explanatory variable throughout the study period, while land-surface and anthropogenic variables became more prominent in later periods relative to hydro-climatic variables. These results indicate that basin-scale area statistics alone are insufficient to describe the full evolution of permanent surface water and provide a useful multi-scale perspective for understanding permanent surface-water change in highly modified river–lake basins. Full article

Winter imposes severe ecological constraints on Eurasian otters (Lutra lutra), yet the environmental characteristics of their winter marking sites remain poorly understood. We characterized winter sprainting sites along a human disturbance gradient in Changbai Mountain, northeastern China. In January 2025, 55 sites were recorded along three rivers and assigned to urban or wild river-reach contexts based on the broader spatial and management context of each reach. We measured topographic, hydrological, riparian, fish-diversity, and anthropogenic variables. Broad environmental gradients were summarized using Factor Analysis of Mixed Data (FAMD), and five local variables were compared between river-reach contexts using exploratory tests with Holm adjustment. Of the 55 sites, 54 were beside flowing, unfrozen water. Intermediate-to-deep water, natural banks and forested riparian backgrounds were common. The first two FAMD dimensions explained 52.5% of environmental variation, representing a spatially coupled gradient involving anthropogenic remoteness and river-section fish resource background, and a topographic and channel-structure contrast. Urban and wild sites differed in water depth, bank type, and vegetation cover, while sprainting sites occurred in both. These findings show that winter marking activity was concentrated within accessible river sections embedded in contrasting landscape contexts. Full article

Alternanthera philoxeroides, an invasive alien species, spreads rapidly in river systems via vegetative propagation from stem fragments, requiring river-system-scale monitoring to understand its expansion dynamics and habitat preferences. This study used multi-temporal Sentinel-2 data to analyze spatio-temporal variations in fractional vegetation cover (FVC) within a 3.5 km river reach. FVC estimates derived from vegetation indices were validated against high-resolution aerial images, with an EVI-based model achieving the highest accuracy (RMSE = 9.2%), enabling reliable monitoring even in narrow (~24 m) channels. Time-series analysis from 2019 to 2024 revealed downstream expansion beginning in 2022. Annual maximum FVC (C_max) was used to assess relationships with removal records and bank structures, showing that removal effects were temporary and more pronounced in the first year, while steel sheet-pile banks limited vegetation growth compared to concrete revetments. These results demonstrate that Sentinel-2 data can provide an effective and accessible tool for evaluating invasive plant dynamics and management effectiveness in low-flow river systems where A. philoxeroides dominates the floating vegetation community. Full article

Understanding the interactions between vegetation dynamics and surface water availability is essential for assessing the resilience of tropical floodplain ecosystems under increasing hydroclimatic variability. This study analyzes the spatio-temporal dynamics of vegetation cover, surface water, and land use in Zambrano, a floodplain-dominated sector of the lower Magdalena River basin (Colombian Caribbean), over the period 1990–2025. Multi-temporal Landsat imagery was used to derive the Normalized Difference Vegetation Index (NDVI) and the Normalized Difference Water Index (NDWI), enabling the evaluation of seasonal and interannual ecohydrological variability under contrasting dry and rainy conditions. In addition, land-use classification was performed using a CORINE Land Cover methodology adapted for Colombia (CLC-C) to characterize the spatial organization of the landscape and its influence on vegetation–water interactions. Results show that vegetation dynamics are strongly controlled by hydroclimatic seasonality. Dense vegetation consistently expands during rainy periods, while dry seasons promote the expansion of open and sparse vegetation, reflecting seasonal vegetation stress rather than long-term degradation. NDWI patterns indicate that surface water and soil moisture are highly seasonal and spatially constrained, with open water largely confined to the Magdalena River channel and localized floodplain depressions. Extreme hydroclimatic events associated with the El Niño–Southern Oscillation (ENSO) produce abrupt but temporary changes in vegetation structure and surface moisture distribution. A strong inverse correlation between NDVI and NDWI reflects the contrasting spectral responses of vegetation and water surfaces resulting from the shared near-infrared (NIR) band in both indices. This spectral relationship is consistent with the observed seasonal variations in vegetation greenness and surface moisture across the floodplain. Land-use analysis reveals the progressive consolidation of the landscape, where the agropastoral matrix expanded from ~18,000 ha in 1990 to over 22,000 ha by 2025, driving a systematic reduction in natural and semi-natural forest structures. Forest conservation areas serve as critical ecological buffers, exhibiting lower seasonal variability in vegetation greenness. Overall, the results indicate that the Zambrano floodplain functions as a structurally stable yet highly responsive ecohydrological system, where vegetation dynamics and surface water availability are predominantly governed by interannual hydroclimatic pulses rather than long-term directional degradation. These findings demonstrate that while the structural matrix of the floodplain exhibits strong baseline resilience, its ecological functioning remains critically coupled with, and vulnerable to, the extreme phase shifts in ENSO cycles. Full article

Brachymystax lenok tsinlingensis is an endangered salmonid endemic to China. Traditional trapping methods frequently fail to detect this rare fish in low-density mountain streams, hampering evidence-based conservation. Here, we employed environmental DNA quantitative PCR (eDNA-qPCR) with species-specific primers to assess the spatial biomass distribution of this species in the Zhouzhi Heihe River. Concurrently, we surveyed plankton, benthic macroinvertebrates, and physicochemical water parameters. eDNA detected the target species at 12 of 14 sites, with reliable quantification achieved at 9 sites, suggesting that the method may be more effective than conventional trapping for detecting this species under the studied low-density conditions. eDNA-derived relative biomass exhibited pronounced spatial heterogeneity, ranging from 6.0 × 10⁻⁴ to 1.5 × 10⁻² g/cm³. Water depth showed a significant positive association with biomass (r = 0.5347), whereas phytoplankton Shannon diversity (a measure of species richness and evenness) was significantly negatively correlated (r = −0.5447). Flow velocity displayed a negative trend that did not reach statistical significance (r = −0.5009). Plankton and benthic communities indicated overall ecological conditions but did not directly explain the observed spatial variation in fish biomass. These findings indicate that the spatial pattern of B. lenok tsinlingensis is primarily shaped by local physical habitat structure, with deeper, hydraulically more complex channel units serving as key microhabitats. eDNA-qPCR thus represents an effective, low-disturbance monitoring tool for this endangered cold-water fish and provides a scientific basis for targeted habitat protection and restoration. Full article

The Liujiaxia–Heishanxia reach is critical for water and sediment regulation in the upper Yellow River, where changes in runoff–sediment relationships greatly affect downstream channel stability and flood safety. Climate change and intensive human activities have substantially altered local hydrological regimes in recent decades. Using long-term hydrological records from five stations during 1956–2020, this study applied the Mann–Kendall test, moving t-test, wavelet analysis and XGBoost algorithms to analyze the trends, abrupt changes and periodic features of runoff and sediment load, and quantify the contributions of natural and human drivers. The results show that both runoff and sediment load decreased significantly, with a sharper decline in sediment load. Major abrupt changes occurred in 1969, 1986, 1996 and 2008, and both variables presented a dominant 40-year interdecadal cycle. Human-induced landscape changes became the leading factor driving hydrological variations after 1996. Our findings suggest that future watershed management should combine landscape optimization and climate adaptation to maintain stable runoff-sediment conditions. This work provides scientific references for water resource management and the construction of the Heishanxia Water Conservancy Project. Full article

Introduction: Otoliths have been widely used in recent years as tracers of fish life history, ranging from visual aging to chemical analyses that reconstruct environmental conditions, migration patterns, and metabolic changes. Yet, Iberian endemic or endangered species are understudied. This study focuses on Andalusian barbel (Luciobarbus sclateri), endemic to the southern half of the Iberian Peninsula. Objective: The aim was to evaluate whether otolith chemical profiles can simultaneously support age estimation and reveal the impact of environmental variations, particularly hypoxia. Methodology: Fish were caught in two sites with different environmental properties, including strong hypoxia: the Guadalquivir estuary and the dock of Seville (which is isolated from the main river channel by a ship lock and could, therefore, be used as a control). Otolith chemical composition was analyzed from core-to-edge transects with a laser-inductively coupled plasma mass spectrometer (LA ICP-MS). Results: Patterns of variation in Mg and Mn in relation to hypoxia and environmental conditions are discussed. We visually counted growth rings in the sections, and we found a strong correlation (R² = 0.904) in Mg:Ca peaks with growth rings. Body condition, assessed using Fulton’s condition factor (K), differed between sites, with fish from the estuary exhibiting a lower condition than those from the dock. Conclusions: The strong correlation between counter growth rings and Mg:Ca peaks suggests that chemical analysis could be used as a valid method for supporting aging. The pattern of lower condition in fish from the estuary is consistent with persistent hypoxic events documented in the estuary but not within the dock environment. This whole approach provides a powerful framework to assess habitat quality and support conservation of L. sclateri in the Guadalquivir estuary. Full article

The Tietê River, heavily polluted by the largest Brazilian city (São Paulo), has significant ecological and socioeconomic importance. The effects of water-quality degradation on zooplankton diversity (taxonomic and functional) and limnological variables were evaluated through a comparison of the Tietê River’s main channel, one of its marginal lagoons and a low-impacted tributary. Samplings covered both a rainy and a dry season. Environmental conditions are distinctive, with the main river and lagoon classified as hypereutrophic and the tributary as oligo-mesotrophic. The zooplankton, an essential community for aquatic ecosystem functioning, also exhibited remarkable spatial variation. Richness varied between six (lagoon/dry) and 43 (tributary/rainy). There was a much higher abundance in the lagoon (mean = 6.5 × 10⁵), followed by the Tietê River (mean = 4.0 × 10⁴) and tributary (mean = 2.5 × 10³), and a higher taxonomic diversity (Shannon mean = 2.98) and functional richness (mean = 0.66) in the tributary, contrasting with the intermediate values in the Tietê River (means of 1.7 and 0.31, respectively) and lower in the lagoon (1.49 and 0.01). Zooplankton from the Tietê River and the lagoon positively correlated with pH, total solids, chlorophyll and phosphorus. Negative pollution’s effects on the zooplankton community were intensified by the lagoon’s lentic hydrodynamics. The low-impacted tributary seems to act as a refuge for the regional zooplankton biodiversity, taxonomically and functionally, which is restricted to highly tolerant species in the main river. Full article

Deep stormwater drainage tunnels are increasingly being used to mitigate urban flooding, but in-tunnel sediment deposition reduces their discharge capacity and complicates their maintenance. With direct field observation constrained, numerical simulation is essential, and river-based total sediment load formulas require reassessment for use in deep tunnels. The three-phase (air–water–sediment) CFD solver SedInterFoam is first validated against a benchmark open-channel suspended sediment experiment, and is then applied to a horseshoe tunnel under a fixed design discharge for multiple inlet sediment concentrations spanning urban stormwater conditions. Four classical formulas (Yang, Shen–Hung, Ackers–White, Engelund–Hansen) are evaluated at the CFD-resolved hydraulic state; Toffaleti is omitted because its zone-based formulation is incompatible with the partially filled horseshoe geometry. The CFD consistently shows persistent retention of a substantial fraction of the inlet sediment load, whereas the transport capacity-limited interpretation of the classical formulas predicts near-complete sediment throughput—indicating structural inadequacy for the dilute, supply-limited regime typical of urban stormwater. A Universal Soil Loss Equation (USLE)-style dimensionless deposition formula is therefore proposed, with inlet sediment loading as the explicit independent variable and a tunnel correction factor $K_{tunnel}$ absorbing the geometric, hydraulic, and sediment variations. Its regression yields an almost linear scaling and a nearly constant deposition ratio, while analysis of the internal flow and concentration fields shows that the retained sediment is strongly concentrated near the bed and that near-bed turbulent mixing weakens moderately with a rising inlet concentration. While calibrated for a single non-cohesive settleable sand fraction, the framework provides a transferable basis for inlet-loading-dependent deposition prediction in deep stormwater drainage tunnels, and subsequent extension of $K_{tunnel}$ to broader sediment conditions with field-based validation is expected to enable maintenance planning, dredging volume estimation, and sediment retention risk assessment. Full article

Daily hydropower regulation and mainstem backwater generate complex hydrodynamic conditions in the Min River estuary, posing significant challenges to navigation safety. To analyze the impact of mainstem backwater on tributary navigation safety, this study focuses on the lower Min River reach affected by backwater from the Jinsha River. A depth-averaged 2D hydrodynamic model is established, and a water level difference parameter is used to construct the stage–discharge relationship at the estuary based on long-term measured water level and discharge data. Indicators including backwater distance, water surface slope, hydrodynamic axis migration, flow velocity, and cross-flow are used to delineate navigation risk zones. The results indicate the following: (1) The backwater intensity and extent are primarily governed by the mainstem and tributary discharges and by the distance from the estuary. High discharge and water levels produce significant backwater effects and reduced flow velocity. Empirical formulas for backwater length under various discharge conditions are established to support navigation decision-making, with RMSE values ranging from 0.42 km to 0.92 km. (2) Variations in estuarine water level induce oscillations in the hydrodynamic axis. When the upstream discharge is 900 m³/s and the estuarine water level is 258.4 m, the maximum oscillation amplitude reaches 20.33 m. (3) During periods of medium and low water, the reach exhibits significant navigation-obstructing behavior, with high-risk zones concentrated in Tongluowan, Yangjiaoshi, and other shoals 5–8 km being found from the estuary. (4) Under the design discharge condition, the minimum estuarine water level required to ensure adequate channel depth, appropriate flow velocity, and manageable ship resistance for safe navigation is 267.96 m. This study provides a scientific basis for navigation safety and channel regulation in the Min River estuary and similar reaches affected by mainstem backwater, thereby supporting sustainable waterborne transport. Full article

The range of food resources consumed by opportunistic carnivores is shaped by habitat-specific availability and productivity. However, baseline data on the diet of the Japanese weasel (Mustela itatsi) in managed wetland habitats remain scarce. Firstly, we conducted a diet study examining Japanese weasel scats from the Watarase-yusuichi wetland (WYW) (September 2024–August 2025). Based on 103 fecal samples, we calculated seasonal frequency of occurrence (FO) for 16 food categories and estimated their relative volume (RV) using the point-frame method. Surprisingly, plant material and fruit seeds were eaten frequently across seasons, and fruit seeds constituted a major component of scat volume, particularly in summer. Secondly, we compared baseline WYW data with published datasets from two contrasting aquatic habitats (a suburban river area and a rice paddy landscape) using harmonized categories and multivariate analyses. Diet composition differed markedly among study sites, and the PERMANOVA analysis indicated a significant effect of sampling site (R² = 0.643, p = 0.001) with a weaker seasonal effect (R² = 0.208, p = 0.038), with no significant pairwise differences between seasons (all p ≥ 0.300). Although cross-site comparisons should be interpreted cautiously because datasets were collected in different decades (1998, 2018, and 2024–2025), these findings support habitat-associated trophic plasticity in the Japanese weasel, with dietary shifts across habitats and seasons apparently reflecting variation in available food resources. In managed floodplain wetlands such as WYW, maintaining a mosaic of reed beds, ponds, and channels may help sustain dietary flexibility and population persistence in this species. Full article

Reclaimed water-receiving rivers face increased hypoxic and malodorous risks after stormwater runoff. To investigate how initial runoff drives the co-variation of pollutants and microbial communities at the sediment–water interface (SWI), this study constructed a four-channel simulated river system based on the Froude similarity criterion, including two low-intensity rainfall (R-L) treatments and two high-intensity rainfall (R-H) treatments. Each experiment consisted of a 48 h runoff disturbance stage followed by a 48 h recovery stage. The dynamics of carbon (C), nitrogen (N), and phosphorus (P) in both water and sediments were systematically analyzed, together with variations in dissolved organic matter (DOM) composition, microbial communities based on 16S rRNA, and predicted N-cycling functional potential. Results showed that R-H exerted a pronounced dilution effect on pollutants in water but significantly enhanced SWI disturbance, facilitating nutrient accumulation within the system. DOM profiles indicated active microbial metabolism, consistent with long-term reclaimed water inputs. Microbial analyses revealed that TN was a key environmental factor influencing community differences. Nitrification and denitrification potentials were higher under R-H, whereas ammonia assimilation was higher under R-L. These findings highlight the importance of managing N accumulation and transformation following rainfall events in reclaimed water-receiving rivers. Full article

The spatiotemporal succession of microbial community structure influences sediment nitrogen (N) release. To compare the N release and microbial response between a large-scale wetland and its connecting rivers, sediment samples were collected across three seasons (October 2024, March 2025, and July 2025) and analyzed using sorption isotherms and sequencing to elucidate source–sink dynamics and microbial mechanisms. The results showed that the maximum sorption capacity (Q_max, 9.931 mg/g) exhibited significant seasonal variation (March > July > October) and a vertical decreasing pattern (surface > middle > bottom). The Q_max of wetland sediments (SS) was generally higher than that of river sediments (SH). The N source–sink analysis indicated that SS consistently served as a stable N sink, while SH primarily served as a N source. Among them, the internal N release pressure in the rivers was highest in July, and a relatively high diffusion flux was still maintained in October. Microbial diversity was significantly higher in the warm seasons (July and October) than in spring, and spatially, diversity was higher in SS than in SH. Proteobacteria were the dominant phylum, with a relative abundance ranging from 8.11% to 35.59%. Gammaproteobacteria was the dominant class, with a maximum relative abundance of 28.36%. Anaerolineae in SH were significantly enriched in summer and autumn. The driving factors shifted from the physical particle size (D50) in spring to the organic load and nutrients (total nitrogen or total phosphorus) in summer, and then to the synergistic effect of pH and physical structure in autumn. Functional prediction indicated that the microbial functions in river channels evolved from reserve-type heterotrophic metabolism to high-activity energy metabolism, with the highest predicted potential observed in July. In contrast, the wetland consistently maintained steady-state regulatory functions centered on signal transduction and membrane transport. Full article

Insect assemblages associated with declining riparian black alder (Alnus glutinosa) stands were compared at the community level between two lowland river valleys in Poland that differ in anthropogenic transformation: the near-natural Łutownia River valley within the Białowieża Forest and the urbanised Utrata River valley in the Warsaw metropolitan area. Insects were sampled using active hand sampling and Barber pitfall trapping along a short-distance gradient from the channel during repeated monthly field campaigns in summer and early autumn. The near-natural valley supported a richer assemblage, with a stronger representation of forest-associated, saproxylic and aquatic taxa, whereas assemblages in Utrata contained a higher proportion of widespread disturbance-tolerant taxa. In both valleys, diversity was highest at an intermediate distance from the channel margin, and the between-valley contrast was more pronounced than the within-season shifts visible in the campaign summaries. The results identify a clear assemblage contrast between the two valleys, a consistent intermediate-distance diversity maximum, and only modest within-season variation in pooled campaign totals. These findings indicate that structurally complex riparian alder forests with retained dead wood are associated with richer and more taxonomically varied insect assemblages; microhabitat-related interpretations are retained as cautious sampling-point-scale associations because tree-level attributes and individual microhabitat categories were not quantified separately. Full article

Reptiles with diving capabilities have evolved physiological adaptations as well as conformational changes to temporarily sustain life underwater. Despite the importance of both respiratory and cardiovascular systems during diving, most studies have focused on respiratory adaptations. Thus, characterisation of previously undescribed cardiovascular anatomical variations in diving vertebrates is of broad interest. Thirteen clinically healthy, free-ranging adult female Murray River turtles (Chelidae: Emydura macquarii) were collected for research purposes, euthanised and autopsied. Prominent, valve-like structures, comprised exclusively of smooth muscle myocytes, were identified in medium- and large-calibre muscular arteries of all individuals. Additionally, multiple intramural vascular channels, mimicking post-thrombotic recanalization, were observed within medium-calibre muscular arteries. Further, we confirmed the presence of alpha-smooth-muscle actin-positive cells lining the cardiac atria in E. macquarii. Quantitative morphometric analyses demonstrated that the valve-like structures frequently occupied a substantial proportion of the vascular lumen, in some cases exceeding 90% luminal narrowing. Their consistent presence across multiple individuals and organ systems supports the interpretation that these are physiological vascular structures rather than artefacts. This study examines the potential physiological and evolutionary roles of these vascular structures, providing a basis for further research into cardiovascular adaptations in vertebrates subjected to postural changes and diving-related haemodynamic challenges. Full article