Search Results (13)

Introduction: Freshwater ecosystems are among the most threatened worldwide, with river fragmentation, primarily caused by dams and weirs, identified as a major driver of biodiversity loss. This issue is particularly acute in Europe, where more than one million instream barriers disrupt longitudinal connectivity and compromise the movement of migratory fish. Fishways are widely implemented to mitigate these impacts, yet attraction efficiency at fishway entrances remains poorly understood, especially for Iberian potamodromous cyprinids, a group facing severe conservation pressures. Objective: This study aims to investigate how hydraulic conditions and social context influence the attraction and passage behavior of Luciobarbus bocagei, a rheophilic potamodromous cyprinid endemic to the Iberian Peninsula, in an experimental Vertical slot fishway (VSF) entrance. Methodology: Experiments were conducted in a controlled flume equipped with a VSF entrance design. Two hydraulic scenarios were tested, a Low Head Drop (LD) and a High Head Drop (HD), under a constant discharge of 34 L/s. A computational fluid dynamics (CFD) model was used to characterize and compare the flow field hydrodynamics. Fish were tested individually and in groups of three to assess the role of social dynamics. The metrics collected included time to first approach, first attempt, time to first successful passage, attraction efficiency, and passage efficiency. Cox proportional hazards models were applied to evaluate treatment effects. Results: Preliminary results showed that social context influenced fish attraction behavior. In the two hydraulic scenarios, individuals tested alone tend to exhibit lower likelihoods of approaching, attempting, and successfully negotiating the fishway compared to fish in schools. Delays were also evident for attempts and successful passages, with LD_Ind performing the worst. Conclusions: These findings highlight the importance of hydraulic conditions and social behavior in shaping attraction efficiency. They underscore the need to integrate species-specific behavioral ecology into fishway design, operation, and attraction assessment, acknowledging that fish attractivity is influenced by environmental and ecological factors beyond fishway structure, particularly in Mediterranean river systems where fragmentation pressures are high and potamodromous cyprinids are at risk. Full article

This study uses high-frequency monitoring across a river–barrier lake–reservoir continuum in the upper Minjiang River, southwestern China, to quantify the spatiotemporal dynamics and drivers of aquatic CO₂ partial pressure (pCO₂) and to identify the dominant controls under contrasting lotic and lentic conditions. River reaches were CO₂-supersaturated throughout the year, with higher pCO₂ in the wet season (mean 521 ppm) than in the dry season (421 ppm), indicating persistent CO₂ evasion to the atmosphere. In contrast, the downstream canyon-type reservoir showed a pronounced seasonal reversal. During the wet season, surface-water pCO₂ averaged 395 ppm, about 24% lower than that of the river and below atmospheric levels (~419 ppm); more than 55% of observations were undersaturated, with minima as low as 141–185 ppm, indicating temporary CO₂-sink behavior. In the dry season, mean pCO₂ increased to 563 ppm, exceeding both riverine and atmospheric levels and returning the reservoir to a CO₂ source. The reservoir pCO₂ variability was governed by the interaction of hydrology and metabolism: rising water levels and longer residence times likely enhanced CO₂ accumulation from the decomposition of inundated organic matter, while warm temperatures, high light and monsoon-driven nutrient inputs promoted phytoplankton growth that removed dissolved CO₂ and elevated dissolved oxygen, producing temporary sink behavior. In the river, short residence time and strong turbulence limited in-stream biological regulation, and pCO₂ variability was mainly driven by catchment-scale carbon inputs along the elevation gradient. Overall, our results demonstrate that dam construction and impoundment can substantially modify carbon cycling in high-mountain rivers. Under specific conditions (warm water, sufficient nutrients, high algal biomass), lentic environments may strengthen photosynthetic CO₂ uptake and temporarily transform typical riverine CO₂ sources into sinks, with important implications for carbon-budget assessments and reservoir management in mountainous basins. Full article

Various types of tidal barriers are used in estuaries to reduce saltwater intrusion and regulate freshwater discharge, but they often alter the physicochemical environment and faunal composition. With the use of these structures expected to increase due to climate change, there is a need to understand their impacts. A tidal exclusion barrier in the Ramsar-listed Vasse–Wonnerup Estuary (Australia) was found to act as an ecotone, fragmenting the estuarine gradient into two distinct components, a relatively stable marine-like environment downstream and a highly variable oligohaline to hypersaline (~0 to >100 ppt) environment upstream. The downstream regions contained a speciose and functionally rich estuarine fauna, comprising mainly polychaetes and bivalves. The upstream regions were taxonomically and functionally depauperate, containing insects, gastropods, and ostracods typically found in saline wetlands. The fragmentation of the estuary has likely impacted the provision of ecosystem services, with the fauna downstream mainly comprising burrowing species that bioturbate and, thus, aid in nutrient cycling. In contrast, the environmental conditions caused by the barrier and the resultant epifaunal invertebrate assemblages upstream aid little in bioturbation, but provide nutrition for avian fauna. These results may help in understanding the impacts of constructing new barriers in coastal ecosystems in response to climate change. Full article

The responses of benthic fauna to channel modifications of mountain rivers by low-head barriers are poorly understood. The study aimed (1) to estimate the impact of two different low-head barrier types: concrete sills and block ramps, on Oligochaeta and Trichoptera communities in two small Carpathian rivers (Porębianka and Mszanka) in southern Poland, and (2) to determine changes in these communities in the mountain Porębianka River after 50 years by comparing current data with historical data. Both types of channel modifications led to a transformation from lotic to more lentic habitats. The research shows that habitat conditions and induced bed siltation greatly influenced the studied communities. In both rivers, the taxa richness and dominant taxa of Oligochaeta and Trichoptera were similar, alongside similar species compositions of Trichoptera. However, the river with the lower bed siltation rate had a higher Trichoptera density and a greater diversity in their density among habitats. After 50 years, the taxonomic richness of Oligochaeta and Trichoptera remained similar, unlike the considerable shift in their species compositions. Many species typical of mountain rivers have been replaced by species more tolerant to siltation, characteristic of lowland rivers. The family Tubificidae (Oli-gochaeta) and the genus Hydropsyche (Trichoptera) became dominant in both rivers in the early 2020s. Additionally, the functional feeding group (FFG) of Trichoptera changed considerably. Oligochaeta and Trichoptera communities serve as valuable indicators for moni-toring the environmental changes in these ecosystems. Full article

Accurate hydrological data with high spatial resolution is important for flood risk and water resource management, particularly under the context of climate change. The cost of monitoring networks, as well as the characteristics of the hydrological environment itself, can be a barrier to meeting these data requirements, however. This study covers the design and testing of a low-cost, “build-it-yourself”, instream water depth sensor providing an assessment of its potential in future hydrological monitoring projects. The low-cost sensor was built using an Arduino microcontroller, a differential pressure sensor and a thermistor, a real-time clock, and an SD card module. The low-cost logger was deployed in tandem with a factory-calibrated Solinst^®LevelLogger^® 5 Junior for 6 months in the River Wissey, UK. We found the mean absolute error of the Arduino-based logger relative to the commercial setup to be ±0.69 cm for water depth and ±0.415 °C for water temperature. Economically, the Arduino-based logger offers an advantage, costing a total of £133.35 (USD 168.26 at time of publication) comparative to the industrial comparison’s cost of £408 (USD 514.83 at time of publication). This study concludes that the low cost of the Arduino-based logger gives a strong advantage to its incorporation in hydrological data collection, if the trade-offs (i.e., time investment and accuracy) are considered acceptable and appropriate for a project. Full article

This study investigated the leap characteristics of rainbow trout (also known as steelhead) (Oncorhynchus mykiss) present in the Laurentian Great Lakes. To aid in the collection and annotation of leaps, a custom web application was developed and through the labeling of key markers, the launch speed, launch angle, and length of the fish were calculated. Data collection took place during migratory runs in the spring of 2022 and 2023 that resulted in 173 total leaps annotated with mean launch angles of 58.73 and 68.2 degrees, in 2022 and 2023, respectively. The mean launch speed normalized by body length was consistent across years at 8.6 body lengths per second. The integration of leaping data with computational fluid dynamics simulations revealed steelhead launch angle aligns closely with the water velocity direction as the velocity magnitude increases. Applications of this study include hazard analyses for unintended escapement and informed design of intelligent migratory barriers such as those to be developed at FishPass, an instream research facility under design for the Boardman (Ottaway) River in Traverse City, MI, USA. Full article

The ability to colonize new habitat is essential for wild populations affected by disturbance or other forms of habitat change. For aquatic insects in small streams, overland flight is an important strategy for dispersal when barriers to in-stream migration exist and when populations are isolated in upland habitats. Two Ozark-endemic water beetles (Heterosternuta sulphuria and Heterosternuta phoebeae) have shown little overlap in distributions, with the former frequently occurring in small upland watersheds and the latter occurring in aquatic habitats farther downstream in larger watersheds. Because H. sulphuria has been associated with perennial aquatic habitats, we hypothesized that H. sulphuria individuals could exhibit low capacity for flight, thereby affecting population distributions over time. Laboratory flight observations showed that zero individuals of H. sulphuria flew (n = 67), whereas 17 of 76 individuals of H. phoebeae were observed to fly. Stream habitat drying experiments provided further evidence of the weak capacity for flight and overland migration of H. sulphuria, with low probabilities of survivorship in microhabitats exposed to drying. Weak flight capacity and apparent intolerance to habitat drying have important implications for the evolutionary history and conservation of H. sulphuria in small Ozark streams exposed to variable flow regimes and stream margins vulnerable to disturbances. Full article

The effects of channelization with low in-stream barriers in mountain rivers on macroinvertebrate communities are still weakly recognised. We aimed to assess the differences in structure and density of benthic macroinvertebrates between two north Carpathian mountain rivers: one channelized with a cascade of concrete sills and the other one with block ramps. Water was collected five times for physicochemical analysis. Macroinvertebrate fauna and fine bottom sediments were collected three times (spring, summer, autumn) from different habitat types: glides, runs, pools and riffles of the estimated channel surface. The in-stream barriers altered the channel gradient and flow velocity, reducing the area of pools and riffles as well as extending the area of glides with slow current velocities, associated with the highest rate of fine sediment deposition. Channel modifications induced a general shift of investigated fluvial systems toward lentic habitat conditions. Macroinvertebrate communities characteristic of slow-flowing rivers and pools became dominant, while those characteristic for the riffles of mountain rivers were confined to only small areas. The studied section of the Porębianka River channelized with block ramps exhibited greater diversity in the macroinvertebrate community between habitats and significantly higher macroinvertebrate density than the Mszanka River which was channelized with concrete sills. Full article

Rivers have always been linked to society development, as such they are amongst the most impacted ecosystems in the world. One of the most impairing impacts is the one promoted by instream barriers that fragment river network connectivity and impede fish movements. Barriers are especially deleterious to freshwater dependent fish species that see their dispersion ability severely affected with possible consequences for population and species maintenance, altering genetic flow and community balance. With this in mind, the European Biodiversity Strategy has the specific goal of rehabilitating 25,000 km of free-flowing rivers. Additionally, the European Water Framework Directive (WFD) also determines that longitudinal connectivity re-establishment is vital to achieve the goal of good ecological status. To implement adequate measures for river network connectivity enhancement, connectivity has to be quantified at the basin scale accounting for the cumulative impacts of all the dams present in a given system. Dammed Fish is a Europe-wide research project aiming to evaluate and propose solutions and tools to inform river network connectivity management, to improve fish biodiversity and enhance the biotic quality of European rivers. The project is structured into five interconnected tasks to evaluate how dams, by themselves and combined with other pressures, affect river network connectivity, biodiversity loss, species range contraction and species turnover in (riverine) fish. Results will contribute to further research and improved management of river network connectivity by developing three free tools: RivFish—to link fish data and river networks; RivConnect—to calculate basin-wide network connectivity; and RivOpt—to optimize basin-wide connectivity management solutions considering conflicting management goals. Thus, Dammed Fish proposes an overall and integrative approach to connectivity management over large spatial extents. Full article

Longitudinal connectivity of freshwater systems allows upstream/downstream movements of aquatic migratory species and can be disrupted by natural or artificial barriers. Multiple obstacles, partially or totally blocking upstream movements, along the river promote cumulative non-additive impacts on freshwater fish. In addition to limiting fish migration, barriers can also affect habitat quality downstream by creating changes in flow regime, sediment and nutrient transport, and water temperature. Practically all European river corridors were already substantially modified by the building of dams and other barriers, resulting in at least 1.2 million instream barriers in 36 European countries. The impact of river network fragmentation is progressively intensifying, with the construction of additional barriers, and by the interaction of exiting barriers with other human-induced pressures such as water abstraction. Hence, it is important to assess the impacts of barriers on the structural and functional longitudinal connectivity of riverine systems and the consequences for fish species, assemblages, and diversity, to improve conservation measures and ecosystem management to halt biodiversity loss. The goal of this thesis project is to understand the impacts of riverine longitudinal connectivity loss, regarding potamodromous and diadromous fish species across Europe. For that, the research will be focused on: (i) determining connectivity loss caused by large dams in Europe, using graph theory analysis; (ii) understanding if we are over or underestimating the effects of artificial barriers by comparing the effects of natural to artificial fragmentation—regarding waterfalls, dams and smaller barriers, and the upstream water reservoir; (iii) distinguishing the effects of different types of barriers; and (iv) determining if functional resilience of fish communities can be improved by restoring connectivity. We expect that the fragmentation of freshwater systems will greatly reduce structural and functional longitudinal connectivity within river basins, which will ultimately have effects on fish species and communities, leading to a decrease of functional resilience. Full article

Geomorphological alterations, hydrological disconnectivity and water pollution are among the dominant pressures affecting ecological integrity in urban streams. River restoration approaches often involve utilising in-stream structures to encourage flow heterogeneity and promote habitat diversity. However, few studies examine the success of such projects. In this study, fish density, biomass and community structure at paired restored and unrestored reaches across five tributaries of the River Thames were examined. Fish density varied among rivers and reaches but was generally higher at restored sites. Restored sites also exhibited higher overall fish biomass, attributed mainly to the presence of brown trout (Salmo trutta L.) at the River Wandle. Despite higher density and biomass values at restored sites, the community structure analysis did not identify strong links between either river or restoration status using either species-specific density or biomass. Our results highlight that although reach-scale restoration can lead to localised increases in species density and biomass, this may chiefly be due to aggregation owing to preferential habitats created through restoration activities at these sites. Over larger spatial scales, significant improvements to species richness and diversity are likely to be limited due to the poor water quality and disconnected nature of these urban streams. Whilst reach-scale restoration clearly has the potential to provide preferential habitats for fish species, future efforts should focus on improving connectivity for fish across the wider Thames basin network by removing barriers to passage, improving water quality, restoring watershed processes and creating well-connected, diverse habitats which can facilitate the survival of a wide array of fish species throughout their life cycle. Full article

In-streamstructurescontributegreatlytothebiodiversityinstreamsandplayanimportant role in restoring and protecting rivers. They usually have complex geometries. To evaluate their impact and effectiveness, computational models are increasingly used. However, how to faithfully represent them in computer models remains a challenge. Often, simplifications have to be made. This work evaluated the effects of geometric simplification of an example in-stream structure, an engineered log jam (ELJ), in computational models. Three different representations were considered, namely full resolution, the porous media model and the solid barrier model. The turbulent flow was resolved with large eddy simulation (LES). First, the simulations were validated with a physical experiment in a flume. Then, the results from the three models were comparedandanalyzedonvariousaspectsrelatedtothestabilityandfunctionalitiesofthestructures. Unsurprisingly, it is found that the porous media model and the solid barrier model, which are computationally economic, can describe the flow dynamics only to some extent. From the calibration ofdragforceandwakelength,wefoundthattheequivalentgrainsized50 intheporositymodelshould scale as the key element diameter for the simulated ELJ. A wake length scale analysis was performed for the semi-bounded flow around this in-stream structure near the bank. The length estimator in the literature for unbounded vegetation patches can be used with modifications. The results also show that the flow passing through the porous in-stream structure has a significant impact on mean velocity, turbulence kinetic energy, sediment transport capacity and integral wake length. Since geometrically-fully-resolved simulations are not currently feasible for engineering practices, the following suggestions are made based on this study. If the near-field and wake are important for the purpose of the structure, the well-calibrated porosity model seems to perform better than the solid barrier model. However, care needs to be taken when interpreting the results because this work also identified substantial loss of physical information with the porosity model. When the emphasis is the far field away from the structure, both the porosity model and the solid barrier model give comparable results Full article

The main objective of this study was to quantify the impacts of the run of river (ROR) scheme on the instream habitat and macroinvertebrate community. We sampled the macroinvertebrate assemblages and collected the habitat variables above and below an ROR hydropower plant: Aotou plant in the Hailang River, China. The effects of the ROR scheme on habitat conditions were examined using regulation-related variables, most of which, particularly the hydrological variables and substrate composition, presented spatial variations along the downstream direction, contributing to heterogeneous conditions between reaches. The macroinvertebrate richness, the density and the diversity metrics showed significant decreases in the “depleted” reach compared with the upper and lower reaches. Approximately 75% of reach-averaged densities and 50% of taxa richness suffered decreases in the “depleted” reach compared with the upper reach. Furthermore, functional feeding groups also showed distinct site differences along the channel. The relative abundance of both collector-gatherers and the scrapers reduced considerably at the “depleted” sites, particularly at the site immediately downstream of the weir. The total variance in the the functional feeding group (FFG) data explained by Canonical correlation analysis (CCA) was more than 81.4% and the high-loadings factors were depth, flow velocity, DO and substrate composition. We demonstrated that flow diversion at the 75% level and an in-channel barrier, due to the ROR scheme, are likely to lead to poor habitat conditions and decrease both the abundance and the diversity of macroinvertebrates in reaches influenced by water diversion. Full article