Development of a river habitat quality index (RHQI) framework for dry-hot valleys: Unraveling driving mechanisms and management implications.

Artificial riffles are increasingly used in river renaturalization to stabilize incised channels and enhance habitat diversity. However, their long-term structural stability remains under-researched, particularly in reservoir-impacted systems. This study evaluates the nine-year persistence of 12 artificial and 4 seminatural riffles in the regulated upland Bóbr River (Poland) using RTK GPS field surveys, hydraulic and grain size measurements, and hydromorphological assessments (River Habitat Survey). The results demonstrate a clear divergence in evolution based on construction quality. Well-executed riffles (n = 6) maintained high morphological and hydraulic stability (p > 0.05) throughout the monitoring period (2015-2023). In contrast, poorly-executed structures (n = 10) underwent significant degradation, characterized by a significant increase in mean channel depth (p = 0.037) and flow velocity (p = 0.014). In these structures, the winnowing of finer fractions led to a coarsening of the substrate, with the median grain size of the riffle runs increasing from 35mm to 78mm, resulting in a fragmented 'dragon's teeth' morphology. While artificial riffles proved to be a durable and nature-friendly alternative to traditional bed-stabilization works, their long-term success is strictly dependent on adherence to design grain size distributions (D50, D84) and proper substrate mixing. These findings provide critical technical benchmarks for the sustainable renaturalization of incised, gravel-bed upland rivers.

The Cheshmeh-Langan River is a semi-arid mountain river in Iran that has been strongly affected by Inter-Basin Water Transfer (IBWT) operations since 2005. This study investigates the combined effects of IBWT and climatic drought on river hydrology, habitat characteristics, and fish habitat integrity. Field surveys conducted in 2022 compared environmental conditions, mesohabitat composition, and fish–habitat associations between two segments (upstream control and downstream impacted). Long-term meteorological and hydrological droughts were assessed using standardized precipitation (SPI) and streamflow drought (SDI) indices. Habitat Suitability Curves (HSCs) were developed for key native fish species across different life stages. Results indicate a significant shift in the hydrological regime following IBWT operation. The coupling between precipitation and discharge weakened, with the correlation between SPI and SDI declining from r = 0.67 before water transfer to r = 0.34 afterward. Mean SDI values shifted from + 0.69 in the pre-transfer period to –0.93 post-transfer, demonstrating the emergence of a persistent, transfer-induced hydrological drought. This altered flow regime substantially changed habitat exploitation, as shown by HSCs. Capoeta pyragyi fingerlings and Oxynoemacheilus frenatus showed different habitat associations between the segments, while C. pyragyi adults used the same habitats but showed lower abundance downstream. Additionally, downstream fish assemblages exhibited clear species turnover and expansion of the non-native species Petroleuciscus esfahani , likely facilitated by IBWT. • IBWT alters flow regimes, causing chronic anthropogenic hydro-drought. • Langan IBWT reduces habitat suitability for two native fish species. • IBWT spreads Petroleuciscus esfahani downstream, raising biotic homogenization. • Habitat-based benchmarks guide adaptive environmental-flow management. • Hydrology–habitat coupling quantifies ecological risk under regulation.

ABSTRACTPlant litter decomposition in rivers is shaped by multiple environmental conditions, which are modified by riparian zone characteristics and human activities, thereby impacting in situ plant litter decomposition rates. However, disentangling the relative importance of these conditions for plant litter decomposition rates is challenging without large‐scale studies encompassing wide environmental and anthropogenic gradients. We carried out a continental‐scale study on plant litter decomposition in 72 river locations across 7 catchments in Europe (Germany, Italy, Portugal, Spain, Sweden), representing wide gradients in climatic conditions, riparian zone characteristics, land‐use intensity, and human population density. We used remote sensing data and field surveys to quantify catchment, riparian, and river habitat characteristics. To assess decomposition rates, we used standardized wood sticks as a model substrate, representing a globally important source of organic matter in river systems. Wood decomposition rate (percent mass loss per day) increased by 4.3% per 1°C rise in mean annual air temperature but decreased by 3.4% per 10 people increase in population density (per 3.14 km2), 2.3% per 100 mm increase in mean annual precipitation, and 0.5% per 1 m increase in channel width. Land‐use intensity and riparian zone characteristics showed no significant effects on wood decomposition rates across the studied gradients. Our results show that wood decomposition rates in the studied rivers are likely to increase linearly with ongoing global warming, reducing the longevity of wood substrates and their reliability as carbon sinks. However, this warming effect might be offset in rivers experiencing concurrent increases in precipitation and human population density. Consequently, the net effect of global change on wood decomposition rates in rivers may be difficult to predict.

A serious emerging threat to southern California riparian ecosystems is the invasive shot hole borer ( Euwallacea spp.; SHB), a non-native beetle that cultivates a pathogenic fungus that kills trees of 66 reproductive host species. We examined the response of the bird community at the Tijuana River, California, to a massive SHB infestation in 2015 using data from a Monitoring Avian Productivity and Survivorship (MAPS) station operated during 7 pre-infestation (2009-15) and 7 post-infestation (2017-23) years. Species richness did not change between pre- and immediate (2017-18) post-SHB periods, but average annual adult captures declined by 27%. Among the species making up ≥ 5% of the total individuals caught in any one year (n=15), abundance declined by up to 76% in 10 species, including those most abundant at the station (Bushtit ( Psaltriparus minimus ), Song Sparrow ( Melospiza melodia ), Common Yellowthroat ( Geothlypis trichas ), Orange-crowned Warbler ( Leiothlypis celata ), and Wilson’s Warbler ( Cardellina pusilla )). Mean annual abundance increased slightly for the endangered Least Bell’s Vireo ( Vireo bellii pusillus ) and Northern Yellow Warbler ( Setophaga aestiva ) and doubled for House Finch ( Haemorhous mexicanus ) and Western Warbling-Vireo ( V. swainsoni ). We compared species trends at the Tijuana River to those at a nearby uninfested MAPS station on the Santa Margarita River to isolate the effect of SHB from other factors influencing annual abundance. The contribution of SHB to changes in abundance post-SHB was high (63-80%) for 7 declining species, moderate (22-45%) for 4 species, and weakly to moderately positive (18-40%) for 3 species. By 2019, the SHB infestation at the Tijuana River had abated and canopy cover was recovering through resprouting of mature willows ( Salix spp.) and seedling establishment. Bird abundance tracked this regrowth, with all of the species strongly affected by SHB increasing between 2019-23. The rapid recovery of the Tijuana River habitat and the associated response by the bird community are encouraging signs that the threat of the invasive shot hole borer to regional biodiversity may not be as great as originally anticipated.

The River Habitat Survey (RHS) is a method used to assess the condition of river channels and valleys by considering hydromorphological factors. It evaluates the degree of naturalness or anthropogenic alterations based on physical and landscape data. The study hypothesized that the quality of river habitats, as demonstrated by the RHS, should correlate with the composition of aquatic bugs (Heteroptera) fauna. The research was conducted in the River Krąpiel, a small lowland river in north-western Poland, across 6 sites and 43 sub-sites. Our analyses suggest that the RHS method can predict the composition and quality of aquatic bug fauna. Other indicators, such as the Habitat Quality Assessment (HQA) and the Riverine Habitat Quality Index (RHQI), are associated with different habitat types. Depending on the geographic location and river type, these indicators may reflect differences between habitats associated with the mainstream river and mineral substrates versus those covered by vegetation with relatively slow water flow. Linking the size and character of the river, RHS may be a good method for estimating the water bug fauna.

ABSTRACT 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.

Introduction River herring (alewife, Alosa pseudoharengus , and blueback herring, Alosa aestivalis ) are native along the East Coast of North America. These fish are culturally important and provide critical ecosystem linkages between marine and freshwater habitats. Due to overfishing, and habitat loss (through degradation and damming), river herring populations are at historical lows across their native range. In the last 200 years, dams and other impoundments have reduced access to spawning habitat for these and other anadromous fish. Methods To assess the theoretical coast-wide spawning potential for river herring, we quantified historically accessible spawning habitat (pre-dam) in coastal freshwater rivers using physical river characteristics (width and gradient). To assess the impact of dams on spawning habitat, we used a dams database to segment river reaches. This allowed us to characterize spawning habitat upstream and downstream of dams. River-specific population models were then used to estimate the number of potential spawners for each species, based on habitat estimates and life history parameters. We investigated three scenarios: no dams, favorable dam passage, and no dam passage. We use these simulations to compare the theoretical spawning potential for river herring prior to and after dam construction coastwide. Results We estimated that 52% of alewife and 51% of blueback herring habitat is located upstream of dams throughout the East Coast of North America. This results in a theoretical loss of ~880 million alewife and ~100 million blueback herring potential spawners due to dams, reducing both the ecological connection and fishery potential of these species. Discussion Even with the best-case “current” scenario for fish passage, we observed marginal increases in spawner abundance. These results highlight the relatively small theoretical influence current passage structures may have on restoring river herring to their historical abundances compared to dam removal. Our sensitivity analyses demonstrate that upstream passage to access additional habitat is only advantageous when effective juvenile and adult downstream passage are in place.

Abstract This ethnobiological study examines how local ecological knowledge (LEK) of mangrove aquatic fauna is shaped by gender and age in two Diola villages (Elia and Elalab) in northern Guinea-Bissau. We challenge the common assumption that local ecological knowledge grows linearly with age and mainly belongs to adult men by using ethnographic (participant observation) and ethnobiological (photo-based species identification) methods to explore if girls, boys, women, and men know local species names. Adults showed higher overall accuracy than children, but village- and gender-specific patterns emerged. In Elia, women named more species correctly, and children (especially girls) demonstrated high accuracy from an early age. In Elalab, knowledge was more strongly male-dominated, with boys and men outperforming females. These contrasts reflect local fishing strategies: in Elia, both genders engage in fishing and shellfish collection across river, rice paddies, and intertidal habitats, while in Elalab, fishing is more concentrated among males. The results demonstrate that LEK is not simply a product of age or gender but develops through situated practice. This article underscores the importance of inclusive conservation and resource management that account for intra-cultural and intra-community diversity in ecological knowledge.

Seasonal temperature rise influences nitrous oxide and methane accumulation in freshwater habitats via distinctive microbial processes.

In river ecosystems, unidirectional flow and habitat fragmentation threaten prey persistence, necessitating protection zones. This study explores the dynamics of a generalist predator-prey model with a boundary-upstream protection zone for prey and Holling-II type functional response in open advective environments. Firstly, we establish complete system dynamics driven by the interplay of variable advection rates, protection zone lengths and predator carrying capacity, revealing their coupled effects on population persistence and extinction. We identify a critical protection zone length, beyond which predator take-over is prevented within a prey advection range, regardless of predator strength, thereby promoting species coexistence. Furthermore, through bifurcation analysis, the existence and multiplicity for positive steady states are studied, linking prey attack-evasion ability and predator advection rate to bistable outcomes. The asymptotic behaviors of positive steady states induced by large diffusion rates are characterized, showing that enhanced dispersal counteracts flow-induced washout. This study uniquely integrates Holling-II response with upstream refuge effects, revealing critical thresholds for predator control. The findings guide designing flow-adaptive protection zones to mitigate generalist predator dominance in aquatic ecosystems, offering actionable management strategies.

Cascade dams fragment river habitats, but how seasonal hydrology modulates the biogeography and assembly of fish gut microbiota remains unclear. We surveyed gut bacterial communities of the omnivorous fish Saurogobio punctatus across 10 reaches separated by cascade dams in the Qijiang River during the wet (summer) and dry (winter) seasons using 16S rRNA gene amplicon sequencing. Sampling was synchronized among reaches to minimize temporal variability. Winter exhibited stronger differentiation among reaches and a steeper distance-decay pattern, and reach-scale environmental heterogeneity (especially dissolved inorganic nitrogen) was more stable under weak hydrodynamics. Null model analyses showed that stochastic processes dominated in summer, with dispersal-related processes and drift being prominent under high connectivity, whereas deterministic assembly increased in winter and was mainly associated with homogeneous selection. Compositionality-aware differential abundance analysis (ANCOM-BC2) identified 409 genera with a significant seasonal differential abundance after adjusting for reach (FDR q < 0.05). Random forest classification, used as a complementary prediction-oriented feature-ranking analysis, indicated higher reach discriminability in winter, with Nitrospirota ranking among the top features. PLS-PM indicated that α-diversity had the strongest direct association with β-diversity in the specified model, whereas spatial and environmental effects were linked to β-diversity mainly through indirect, α-diversity-mediated pathways. Biologically, α-diversity may reflect an integrative summary of the within-gut taxon pool shaped by host filtering and environmentally derived inputs (e.g., diet- and habitat-associated sources), which can influence the magnitude of between-reach compositional turnover. Together, these results show that seasonal hydrological regimes tune spatial turnover and assembly of fish gut microbiota in cascade-regulated rivers.

River damming alters hydrology, light availability and nutrient dynamics, thereby reshaping both pelagic and benthic primary producers. In double-dam systems, it remains unclear whether the two structures function as a single unit (“double-dam effect”) or whether the downstream dam adds cumulative impacts (“cascade effect”). Over two hydrological years, we investigated the responses of phytoplankton and periphyton to cascading dams, along the Sélune River (France), focusing on photosynthetic activity, biomass and assemblage. Using multivariate analyses, we quantified the relative influence of local environmental and climatic conditions (light, temperature, turbidity, nutrient concentrations and stoichiometry, conductivity, pH, dissolved oxygen, rainfall), spatial position along the river continuum, habitat type (lotic vs. lentic), and season on both communities. Local environmental factors explained most of variance in phytoplankton and periphyton, with light availability, temperature, and nutrient stoichiometry (TDN:TDP) as the dominant drivers. By explicitly testing cascade versus double-dam effects through comparisons of biological variables (activity, biomass and species abundances) between dams and with the downstream lotic station, we found evidence for a single-dam effect for both phytoplankton and periphyton. This pattern likely reflects short water residence times, which constrain the development of cumulative impacts along the dam cascade.

Evaluating the ecological effects of daily hydropeaking on lithophilous fish spawning habitat in a large mountainous river.

ABSTRACT Dams and deforestation are key drivers of freshwater biodiversity loss in the Amazon, as they alter river connectivity, water quality and habitat structure. This study investigates how connectivity (Reach Connectivity Index—RCI), elevation and natural land cover influence the diversity and composition of fish assemblages in a highly fragmented Amazonian river network. Based on their distinct life‐history traits, we analysed migratory and non‐migratory species separately, hypothesizing differential responses to these environmental gradients. Generalized linear models (GLMs) were used to evaluate the effects of RCI, elevation and land cover on species richness (alpha diversity) and the Local Contribution to Beta Diversity (LCBD, a measure of community uniqueness). Additionally, we examined the influence of these variables on community composition using distance‐based RDA and hierarchical partitioning. We found that species richness for both groups was higher at lower elevations. However, only non‐migratory species richness increased with greater connectivity (RCI), whereas migratory species richness was unaffected by RCI. For community uniqueness (LCBD), values for migratory species were higher in areas with more conserved land cover. In contrast, non‐migratory species had higher LCBD at less connected sites. Community composition analysis revealed that non‐migratory species were strongly influenced by elevation, while migratory species composition showed no significant relationship with the environmental variables analysed. Our results confirm distinct ecological responses between migratory and non‐migratory species to fragmentation, supporting our initial hypothesis. These findings underscore the critical importance of considering species' life‐history traits when planning conservation strategies and river connectivity restoration in the Amazon.

In the past decade, non-native suckermouth armored catfish, Pterygoplichthys spp., have spread throughout the highland rivers of Lam Dong province, Vietnam. We examined spatial and temporal variation in endocrine and biochemical profiles across different river reaches, river systems, and between two sampling years (2020 and 2022). Seven blood parameters related to metabolism and energy balance were measured: total and free triiodothyronine, cholesterol, triglycerides, total protein, creatinine, and direct bilirubin. Concentrations of thyroid hormones and cholesterol did not differ significantly across sites or years. Multivariate analyses indicated that thyroid-related pathways were only weakly influenced by the environmental variation, suggesting preserved thyroid homeostasis. In contrast, triglycerides, total protein, creatinine, and direct bilirubin varied among rivers and between years at the same site, likely reflecting differences in food availability and energy balance. These results suggest that biochemical variation in non-native armored catfish is primarily expressed through lipid metabolism and protein turnover, while thyroid function remains comparatively conserved across invaded river habitats.

Microbiome of soil waste dumpsite and adjacent river habitat harbors dynamic plastic degrading bacterial diversity and abundant functional enzymes.

Background:Understanding mosquito larval ecology is essential for planning and implementations of vector control strategies. The biotic and abiotic factors affect larval occurrence , density, survival and morphogenesis of mosquitoes. Artificial containers are very suitable larval habitats for some species of Anopheles and Aedes mosquitoes in urban and peri-urban settings. Therefore, this study we identified, mapped and characterized larval habitats, estimated larval density and indices larval habitats. In addition, we determined the species composition of Anopheles mosquitoes and species evenness in urban, peri-urban and rural areas of Dire Dawa city adminstrationMethods:Larval habitats were surveyed and identified monthly for a period of 16 months from February 2023 to December 2024 in urban, peri-urban and rural areas of Dire Dawa. Mosquito larvae and pupae were collected and those larvae identified as Anopheles were fed on fish-food. Emerged adults were provided with 10% sucrose solution and kept under standard conditions in field insectary. Females Anopheles was identified morphologically and further species-specific PCR assay was employed to identify members of An.gambiae s.l. In addition, real time PCRassay was performed to identify An.stephensi and An.arabiensis. Water samples were taken from the larval habitats and the physico-chemical parameters were measured using HANNA Multi-parameter (H198194). Larval habitat diversity, larval abundance and distribution were assessed across the three ecological settings (urban, peri-urban and rural).Results:A total of 23, 526 larvae and 1,808 pupae of Anopheles mosquitoes were collected from 909 man-made(uncovered cemented cisterns (Brick), plastic sheets, steel drums, Tire tracks, Canal ditch, plastic tanker/Barrel) and natural habitats (River edges, ponds, animal hoof prints and swaps) in urban, peri-urban areas of Dire Dawa. The highest mean larval density (51 larvae per dip) of Anopheles mosquitoes was recorded from peri-urban sites in uncovered water tanker (brick) followed by urban site in brick (46 larvae per dip). Anopheles larvae were not found in steel drum and plastic barrels in rural sites.A total of 2,934 adult Anopheles mosquitoes were emerged from immatures collected from all sites, of which 75% (2194/2934) were An. stephensi, and 22 % (636 / 2934) were An.arabiensis. The remaining 3.0% were An. pharoensis, An. coustani, An .amharicus, and An. pretoriensis. Anopheles stephensi, An. arabiensis and An. amharicus shared the same habitats across the three ecologies. Larval density was positively correlated with availability of brick making, proximity to houses, urban setting, presence of competitors /predators, vegetation cover, shade cover and substrate type. But larval presence was not correlated with presence/absence of intervention. Larva/pupa presence were positively correlated with pH (r=0.264, p=0.01) and water pressure (r=0.21, p<0.05).There was positive correlation among temperature, electrical conductivity (EC), total dissolved solids (TDS), salinity and dissolved oxygen (DO) and negative correlation among temperature with resistivity, pH with mvPH. Larval presence was positively correlated with water salinity and pH.Conclusion:Anopheles stephensi was the predominant species found in the study area, followed by An.arabiensis, An.amharicu, An.pharoensis, An.coustani and An.pretoriensis. Uncovered water tankers (Bricks) were the most prolific artificial habitats in urban and peri-urban sites followed by plastic sheets while natural habitats such as hoof prints and river basins were the most efficient habitat types in rural and urban settings, respectively. Anopheles stephensi was found in natural habitats of Butuji and legehare rivers from urban site, and in rural sites from man-made habitat of plastic sheet.Anopheles amharicus larvae was found in plastic sheet, an artificial habitat common in urban, peri-urban and rural areas.We report here the occurrence of An.stephensi in rural areas, breeding in natural habitats, and co-existing with An. gambiae s.l complex.Availability of brick making, shorter distance from living houses being in urban ecology were directly correlated with larval density. Habitat abundance and positivity of uncovered water tankers (cemented cisterns or bricks) in urban and pre-urban sites could indicate for feasibility and proper implementation of larval source management.

Abstract Lateral connectivity between the floodplain and river channel is hypothesised to expand fish community isotopic trophic niches and increase overlap of river–floodplain food webs. To evaluate how flood magnitude influences trophic dynamics in a large tropical free-flowing river (Roper River, Australia), we measured community isotopic niches in low- and high-magnitude flood years in wetland and river habitats. Contrary to our hypothesis, isotopic niche area of the river fish community contracted following the high-magnitude flood year, when compared to a low-magnitude flood year. Wetland fishes maintained more similar niche space regardless of flood conditions, but showed the same pattern of contracting niche area following a large magnitude flood. Niche overlap was lowest for river low-magnitude flood and wetland high-magnitude flood and highest for river and wetland high-magnitude flood. Our results suggest that river–floodplain fish communities exploit a wider isotopic range of food sources during low-flood years, including enriched sources of potentially marine origin, while sharing abundant less diverse resources in high-magnitude flood years. As water resources in tropical rivers are developed, our findings highlight the importance of conserving multiple dimensions of connectivity in riverine landscapes to maintain intact river–floodplain food webs.

Amphibian diversity and distribution patterns in Chaohu Lake basin based on environmental DNA and traditional line transect method