Natural River Research Articles

A control system for low-head diversion run-of-river small hydro plants with pressure conduits considering the tailwater level variation

This paper presents a control system for low-head diversion run-of-river small hydro plants with pressure conduits. Since these hydropower plants usually have low or null water storage capacity, the water discharged through the turbines should be adapted to the possible extent to the natural river inflow. For this purpose, a control scheme aimed at maintaining a constant water level in the head pond is normally used in these cases. As an alternative, the option of maintaining a constant water level in the surge tank is studied in this paper. Furthermore, since in low-head hydro plants the tailwater level variation may represent a relatively important contribution to total head losses, it has been explicitly considered in the proposed control system. A small-perturbation stability analysis has been carried out in order to analyze the influence of the plant design and controller parameters in the plant dynamic response. Finally, in order to illustrate the applicability of the proposed control system, several simulations have been carried out using data gathered from a real hydro plant.

The incipient motion safety factor of sediment considers the coupling between the surface and subsurface flows under multi-motion modes

The incipient movement of sediment particles in natural rivers under the action of water scour has remained a key issue in river sediment movement research. In this study, we establish a mathematical coupling model between surface and subsurface flows for investigating the interface velocity. The Navier-Stokes equation and Darcy's law are employed to describe surface and subsurface water flows, respectively. The interface velocity U between surface and subsurface flows is derived by introducing the Beavers–Joseph boundary conditions. Furthermore, based on the force equilibrium of a single particle, combined with three incipient modes, namely, sliding, rolling, and saltation, analytical solutions are derived for the critical instantaneous bottom velocity u0, and mean incoming velocity. The derived analytical solutions exhibit a higher computational accuracy than existing flume test data and classical flow velocity model results, with relative errors less than 12 %. Furthermore, the incipient motion state of sediment particles can be directly assessed by defining the critical incipient safety factor for particle motion (i.e., k = U/u0). Sensitivity analysis of the safety factor for sediment particle motion reveals a nonlinear positive correlation with the slope angle, riverbed permeability, riverbed porosity, and hydraulic gradient, while indicating a linear positive correlation with the water depth. However, a nonlinear negative correlation is observed with the B-J coefficient, relative exposure degree, and sediment particle dry bulk density. The safety factor shows a rapid decrease followed by a stabilizing trend with increasing B-J coefficient. Additionally, the safety factor first increases and then decreases with increasing in sediment particle size.

Incorporating a backward-forward stochastic particle tracking model into a hydraulic modeling framework to identify probable sedimentation sources during typhoons

Study regionShih-men Reservoir, Taiwan Study focusThe primary purpose of this research is to integrate the novel backward-forward stochastic particle tracking model (BF-SPTM) into a three-dimensional sediment transport model for the Shih-men Reservoir. This integration aims to simulate the distribution of sediment during typhoon events and effcientlyidentify probable sedimentation sources . Additionally, a Genetic Algorithm (GA) is developed to optimize the critical parameters of the EFDC hydrodynamic module and sediment transport module. New hydrological insightsIn the proposed BF-SPTM, the influence function is applied for the first time in a three-dimensional hydraulic model to integrate the backward and forward particle tracking processes, thereby providing more precise probable sources. In this study, a 'probable source' is considered a grid cell rather than a point, which substantially reduces the computational time in the BF-SPTM model. A case study using BF-SPTM during Typhoon MEGI demonstrates its capabilityto identify probable sources in natural water using the EFDC model. The output of the BF-SPTM can be effectively used to identify potential sources of sedimentation. Additionally, this study incorporated more realistic boundary and flow conditions from a natural river to enhance the practical application of BF-SPTM. These conditions included flow velocity, diffusivity, water surface, and bed topography.

Accumulation of polyethylene microplastics in river biofilms and effect on the uptake, biotransformation and toxicity of the antimicrobial triclosan

The interaction of multiple stressors in freshwater ecosystems may lead to adverse effects on aquatic communities and their ecological functions. Microplastics (MPs) are a class of contaminants of emerging concern that can exert both direct and indirect ecotoxicological effects. A growing number of studies have investigated MPs-attached microbial communities, but the interaction between MPs and substrate-associated biofilm (i.e., on natural river substrates, such as stones and sediments) remains poorly studied. In this work, the combined effects of polyethylene MPs (PE-MPs) with a particle size of 10–45 μm (2 mg/L) and the antimicrobial triclosan (TCS) (20 μg/L) were investigated on river biofilms through a short-term exposure experiment (72 h). To the best of authors’ knowledge, this is the first time that the combined effects of MPs and chemical contaminants in substrate-associated river biofilms were assessed. Different response parameters were evaluated, including (i) exposure assessment and ii) contaminants effects at different levels: bacterial community composition, antibiotic resistance, extracellular polymeric substances (EPS), photosynthetic efficiency (Yeff), and leucine aminopeptidase activity (LAPA). Triclosan was accumulated in river biofilms (1189–1513 ng/g dw) alongside its biotransformation product methyl-triclosan (20−29 ng/g dw). Also, PE-MPs were detected on biofilms (168−292 MP/cm2), but they had no significant influence on the bioaccumulation and biotransformation of TCS. A moderate shift in bacterial community composition was driven by TCS, regardless of PE-MPs co-exposure (e.g., increased relative abundance of Sphingomonadaceae family). Additionally, Yeff and EPS content were significantly disrupted in TCS-exposed biofilms. Therefore, the most remarkable effects on river biofilms were related to the antimicrobial TCS, whereas single PE-MPs exposure did not alter any of the evaluated parameters. These results demonstrate that biofilms might act as environmental sink of MPs. Although no interaction between PE-MPs and TCS was observed, the possible indirect impact of other MPs-adsorbed contaminants on biofilms should be further assessed.

Element Free Galerkin (EFG) Formulation in Solving Kinematic Wave Equation for Hydrological Modelling

Meshfree methods such as Element Free Galerkin Method (EFG) are the cutting edge of numerical methods as it does not require user to perform meshing which often is time consuming and tedious. The method being "meshfree" for the user can theoretically generate more accurate models which follow more complex boundary conditions such as natural rivers etc. The time saving and potential of higher accuracy in modelling makes EFG formulation an interesting research topic. EFG formulation is used to solve kinematic wave equations which is detailed in this paper. Galerkin weighted residual method using EFG’s shape function parameters is used to discretize the partial differential equation (PDE) of kinematic wave equations. To discretize the equations, a forward difference scheme is used for temporal discretization and Picard direct substitution method is employed to solve the nonlinear system at each time step. The formulations are validated by making a comparison between well-established numerical techniques against actual recorded datasets. After which it is found that EFG method agrees with conventional established techniques, thus validating the formulations as useful. To further investigate the usefulness of this formulation, an optimal performance study was also conducted to determine the most optimal shape function parameters. The optimal shape function values improved the performance to where it was found that established methods such as FDM were surpassed and on par with FEM. This shows that EFG is a good alternative for hydrological modelling.

Experimental Evaluation of Estimating Local Bed Shear Stress Using Log Law in a Straight River Channel

Bed shear stress is a critical parameter in riverine environments, directly influencing sediment transport, erosion, deposition, and flow dynamics. However, direct measurement of bed shear stress in natural rivers is nearly impossible, and estimating bed shear stress by extrapolating the Reynolds stress profile, though known for accuracy, faces practical limitations due to the challenges of measuring turbulence in natural rivers. As alternatives, indirect methods, such as global bed shear stress estimation based on bed slope and hydraulic radius (assuming uniform flow) and local bed shear stress estimation through regression of velocity profiles using the log law, have been employed. The estimation of local bed shear stress using the log law has primarily been derived from laboratory flow conditions due to the limitations in observing detailed turbulence in field conditions. Consequently, the applicability of the log-law method under field conditions has not been sufficiently evaluated. This study aims to assess local bed shear stress using the log law through a dedicated field experiment in a specific river condition, comparing it with methods utilizing the Reynolds stress profile. The experiment was conducted in a straight river channel with a width of approximately 6.5 m, a depth of 0.61 m, and a mean flow velocity of 0.56 m/s. A total of 197 points of regularly distributed velocity and turbulence data for the given cross-section were acquired using micro-acoustic Doppler velocimeter measurements with a duration of 90 s. We found that the log-law method overestimated local bed shear stress by an overall factor of 2.3 compared to the method using Reynolds stress profiles. Thus, the experimental results conclusively indicate that local bed shear stress estimated from the log law in natural river conditions could be overestimated. However, additional research is needed under more diverse flow and geometric conditions to develop a correction formula for applying the log law in estimating local bed shear stress.

Occurrence and partitioning of p-phenylenediamine antioxidants and their quinone derivatives in water and sediment

p-Phenylenediamine antioxidants (PPDs) and PPDs-derived quinones (PPDQs) may pose a threat to the river ecosystem. However, the knowledge on the occurrence and environmental behaviors of PPDs and PPDQs in the natural river environment remains unknown. In this study, we collected paired water (n = 30) and sediment samples (n = 30) from Jiaojiang River, China and analyzed them for nine PPDs and seven PPDQs. Our results showed that target PPDs and PPDQs are frequently detected in water samples, with the dominance of N-(1,3-dimethylbutyl)-N′-phenyl-p-phenylenediamine (6PPD; mean 12 ng/L, range 4.0–72 ng/L) and 6PPD-derived quinone (6PPDQ; 7.0 ng/L, <LOD–21 ng/L), respectively. In sediment samples, detected PPDs and PPDQs were also dominated by 6PPD (mean 31 ng/g, range 1.6–172 ng/g) and 6PPDQ (14 ng/g, <LOD–46 ng/g), respectively. This study first reports the field-based log-transformed sediment-water coefficients (log Koc) for PPDs and PPDQs. Among PPDs, N, N′-diphenyl-p-phenylenediamine (4.0 ± 0.55) had the highest mean log Koc value, followed by N-isopropyl-N′-phenyl-p-phenylenediamine (3.6 ± 0.26). The mean log Koc values of detected PPDQs ranged from 2.0 ± 0.49 to 3.3 ± 0.44. To our knowledge, this is the first study comprehensively investigating the occurrence of PPDs and PPDQs in paired freshwater and sediment. Results of this study provide new insights into their occurrence, spatial distribution, and behaviors in the freshwater environment.

Characteristics and multi-factor mechanisms of dam construction on food web structure in cold-region rivers

Most previous studies have focused on the detrimental effects of dam construction on river ecosystems. However, because of the unique traits of cold-regions, the impact characteristics and multi-factor mechanisms of dam construction on ecological systems remain unclear. In this study, food web structure models were constructed for different river sections based on field data to calculate topological indicators, trophic levels, and diet compositions to characterize the impact of dam construction on the food web structure in cold-region rivers and identify spatial differences. The findings suggest that dam construction can improve the ecological systems of rivers in cold-regions to a certain extent. Specifically, the pre-reservoir sections exhibit a more diverse and complex food web structure than a natural river section, while the food web structure downstream of the reservoir shows a trend of “simplification”, accompanied by a continuous decrease in trophic levels and a shift towards herbivorous feeding. Moreover, redundancy analysis and partial least squares structural equation modeling were used to investigate the mechanisms of the synergistic effects of multiple factors, including flow assurance, water quality, and aquatic organisms, on food web structure. The key influential factor was identified as the “flow assurance degree” (path coefficient 0.716), which needs to be appropriately increased the flow during the ice-covered period (0.849) while meeting the environmental flow targets (0.897) in order to enhance the diversity and complexity of the food web structure. This study provides technical support for the protection and restoration of the ecosystem of rivers in the cold-region.

Early mechanical performance of glass fibre-reinforced manufactured sand concrete

The use of manufactured sand as fine aggregate in concrete has been widely adopted in engineering to alleviate the shortage of natural river sand supply. However, there are many factors that affect the properties of manufactured sand concrete (such as the early shrinkage cracking phenomenon is more common than that in natural-sand concrete). In this study, glass fibre was added to manufactured sand concrete to improve its mechanical properties and determine the optimum content of manufactured sand and glass fibre. This study investigated the effects of the replacement rate of manufactured sand and glass fibre dosage on the compressive strength, flexural strength, and shrinkage of concrete. The results show that the optimal replacement ratio of the manufactured sand and ideal glass fibre dosage ranged 60%–80 % and 0.2%–0.3 %, respectively. Concrete exhibited significant improvements in various properties, including 22.97 %, 42.6 %, 7.1 %, and 34.7 % increase in the maximum compressive strength, peak strain, elastic modulus, and flexural strength, respectively. Concrete shrinkage was reduced by 16.1 %. Moreover, a reliable compressive constitutive model for concrete was established, demonstrating high accuracy in predicting the stress-strain relationship of glass-fibre concrete with manufactured sand. The combined utilization of manufactured sand and glass fibres proved to be effective in enhancing the mechanical strength and crack resistance of concrete.

Incorporation of edge-N into La-doped hierarchical carbon framework enables high-efficiency phosphate electrosorption: Boosting accessible active centers and bridging charge transfer paths

Achieving high-efficiency removal of phosphate has been an urgent issue to combat eutrophication and meet ever-stricter emission standards. Electro-assisted adsorption, a mild electrochemical technology, demonstrated great potential for wastewater treatment owing to the merits of considerable removal performance, facile operation, and energy efficiency. Exploring and boosting the properties of electrode materials is exceedingly vital for technological advancement. In this study, the novel edge-N decorated La-doped hierarchical carbon composites (LNPCs) were developed via in-situ nucleation and one-pot pyrolysis strategy as phosphate capture electrodes. The LNPC900 electrode exhibited an ultrahigh phosphate removal capability of 533.06 mg PO43- g−1 at 1.2 V, surpassing most of the reported electrode materials. Furthermore, this electrochemical system also performed well in the purification of natural river water with low phosphate concentration, where the treated concentration was below the first-class emission standard in China (0.5 mg P L−1). Comprehensive analysis and theoretical calculations indicate that the synergistic property of edge-N and small graphitic carbon nanodomains ensured more accessible active centers and conductive efficiency. The superb phosphate removal capability mainly originated from the coupling contribution of the electrical double layer capacitance, ligand exchange, and electrostatic attraction. This study possesses insight into the theoretical basis for the practical application of phosphate electrosorption and provides a new level of the technology.

A novel preparation of trace iron-doped 3D urchin-like TiO2 for efficient degradation and mineralization of trimethoprim under simulated sunlight

In this study, trace iron-doped 3D urchin-like titanium dioxide (Fe–TiO2) were prepared via a straightforward water bath process. The successful incorporation of trace iron into the TiO2 structure was confirmed through detailed EDX, EPR, and XPS analyses. Moreover, the Fe–TiO2 photocatalyst exhibited remarkable efficacy in degrading the targeted compound, trimethoprim (TMP), achieving an impressive degradation rate of 95.6 % within a concise 60-min timeframe and a captivating mineralization rate of 32.1 % within 120 min. These performance metrics outshone those of pristine TiO2 by substantial factors of 1.9 and 1.2, respectively. Photoelectric characterization results also confirmed that Fe doping significantly enhanced the efficiency of charge carrier separation of TiO2. Furthermore, the catalytic performance of Fe–TiO2 remains essentially unchanged after a tenfold expansion in equal proportion using the water bath doping system. This confirms the practicality of the batch preparation approach for Fe-doped TiO2. The Fe–TiO2 catalyst consistently demonstrated efficient degradation capabilities across various water sources, ranging from natural river water to treated secondary effluents from sewage plants and tap water, further emphasizing its significant potential for practical applications. This comprehensive study provides fresh insights into the batch preparation of doped catalysts and their utility in mitigating water pollution.

Small-scale metapopulation structure of a limnophilic fish species in a natural river system investigated using microsatellite genotyping by amplicon sequencing (SSR-GBAS)

Habitat niches of fish species can exert a strong influence on population structure, even on a small geographical scale. In this scope, Pelasgus thesproticus is a great model species to study connectivity in riverine environments owing to its naturally patchy habitat distribution. Furthermore, it is important to conduct such studies in near-natural systems to avoid the impact of human disturbances on the river, such as fragmentation, morphological changes and habitat degradation. In this sense, the Vjosa in Albania is an excellent study area. A total of 204 individuals were sampled from five locations in the lower Vjosa and two tributaries and genotyped with 33 newly designed microsatellites loci using high throughput sequencing. The application of microsatellite genotyping by sequencing revealed genetic structure and some differentiation, even at a small spatial scale (< 65 river km). A total of 500 alleles were found with an average of 0.93 private alleles among sites with rather low FST values (< 0.04). The extent of admixture observed in some populations indicate that the genetic structure is mainly influenced by upstream populations, either from the main river itself or from tributaries. In addition, the connection between a tributary and the other sites is disrupted by the flow regime, which is reflected in a high degree of divergence from the other populations. Our results indicate that hydrological conditions of the flowing river present strong barriers to gene flow, particularly in the upstream direction, but at the same time act as dispersal corridors in the downstream direction and exhibit source-sink dynamics in which upstream populations contribute disproportionately to downstream populations for this habitat specialist along the river. It is suggested that processes of colonization and reinforcement may play an important role in shaping the genetic structure of patchily distributed fish species in natural river systems. Future studies should increase the knowledge of dispersal factors, habitat heterogeneity, consequence of source-sink dynamics, and gene flow within the system, which will help to understand and maintain important processes related to metapopulation theory and the potential evolutionary consequences of habitat loss and fragmentation.

Investigation of a large-scale waste dump failure at the Mae Moh mine in Thailand

This research investigates the potential mechanisms and possible causes of a large-scale waste dump failure in the Mae Moh Lignite Mine, which is Thailand's largest open-pit coal mine. The large-scale failure of the waste dumpsite covered an area of approximately 1.56 km2 when the dump materials reached a height of 135 m from the original ground. The failure event involved the mobilization of a 70-Mm3 mass of the dump material with 1.2 km in length and 1.3 km in width. The causes of this failure were investigated in this research based on a scientific investigation approach for the remedial action. The geophysical and geotechnical investigation was first performed to characterize the waste dump materials and the perched water condition. The electrical resistivity tomography analysis was also performed within the failure zone and its results were calibrated with the boreholes and interpreted to depict the overview of the geotechnical conditions of waste dump materials. Finally, the stability of the waste dumpsite was investigated using the finite element method (Plaxis 2D program). Based on the critical analysis of the studied data, the causes of waste dump slope failure could be attributed to two main factors, which are the presence of a perched water table associated with the high porewater pressure and the presence of a weak basal layer at the interface between the hard foundation and the waste dump materials. This weak basal layer was the claystone deposited in the swamp area above the hard foundation and deteriorated over time with the increasing amount of waste dumped. The dumping of waste materials over the natural river and pond and the rainwater infiltration over time caused the presence of a perched zone in the waste dumpsite. Failure of the dump slope can be classified as due to a wedge mode of failure, which causes the kinematics with the horizontal translation of a passive wedge and vertical subsidence of an active wedge.

Advanced Hydrodynamic Modelling of Flow at a River Bridge: Insights from 3D Computational Fluid Dynamics

Failure of river bridges is often due to hydraulic reasons, such as the development of severe scouring around piers and abutments. In many cases, the presence of bridge structures produces complex flow fields, which are difficult to predict using standard hydraulic models. This entails difficulties in estimating the hydrodynamic actions on the structure and the potential scour on the riverbed. A three-dimensional Computational Fluid Dynamics (3D CFD) model is used to analyze the flow field and the bed shear stresses at an existing bridge. The Volume of Fluid (VoF) method allows resolving the deformable free-surface, and the Detached Eddy Simulation (DES) approach allows resolving the dynamics of the energetically important turbulent eddies in the flow. The analysis deals with modeling the flow around a realistic, full-scale, multi-pier bridge in the Po River. Simulations considered different hydrodynamic regimes, i.e., the free-surface flow regime and the hypothetical pressure-flow regime which would occur when water levels are higher than the low chord of the bridge deck. The numerical application highlights the potential of the DES technique for analyzing the hydrodynamics of flow at bridges in natural river channels. Besides the turbulent flow fields and the description of the vortical structures, relevant results include the time-varying spatial distribution of the hydrodynamic forces acting on the different parts of the bridge and the time-varying distribution of the shear stress on the bed. This aspect is of particular interest because i) the estimation of drag forces on the structure components may be oversimplified using canonical, averaged formulas, and ii) the fluctuations in time of the bed shear stresses play a key role in determining the removal of sediments from the bed and the scour hole close to the bridge piers.

An experimental study on strength of concrete having calcium carbonate as a partial replacement material to cement and natural river sand

Limestone is a sedimentary rock mainly composed of calcium carbonate mineral. Limestone is quarried abundantly in and around Piduguralla region, Andhra Pradesh, India. Good quality limestone is used to manufacture cement. Calcium oxide is used as white wash which is obtained by heating calcium carbonate. Limestone, as fine powder or as coarse grains is also used as base for paint. In this research, the calcium carbonate mineral in the form of limestone procured from Piduguralla region is used in concrete in two different forms i.e as powder form and as sand form. The cement was partially replaced with the calcium carbonate powder when the calcium carbonate is used as fine powder. The natural river sand was partially/fully replaced with calcium carbonate sand when the calcium carbonate is used as sand (coarser) form. Experiments on cube, cylinder and beam specimens are conducted using Universal Testing Machine to establish compression strength, split tensile strength and flexural strength of concrete having calcium carbonate. The test results support the usage of calcium carbonate in concrete to enhance the strength of concrete. Up to thirty percent cement can be replaced with calcium carbonate powder without adversely affecting the strength of concrete. Natural river sand can be partially/fully replaced with calcium carbonate sand which in turn increases the strength of concrete, but the optimum percentage of replacement is fifty percent of natural sand

Toward a New Flood Assessment Paradigm: From Exceedance Probabilities to the Expected Maximum Floods and Damages

AbstractTo assess flood risks, we seek to estimate the probability distribution of the worst possible single‐event over a contiguous period of N years rather than the cumulative losses expected over a planning horizon. For this we use the probability distribution FN of extreme flood events over a multi‐year period, which is different from using the conventional single‐valued exceedance probability of 1/N years. FN can be used to estimate the hazard and then proceed to the estimation of risk, which we define as the “largest expected damage” over the set period. It also allows for a more coherent determination of design values, which descend from fully acknowledging the aleatoric uncertainty of the underlying natural river flow process. The epistemic uncertainty is removed by marginalizing the aleatoric‐epistemic uncertainty joint distribution over the parameter space. The advantage of the proposed Bayesian approach, which can be summarized in 12 steps, is demonstrated for the 2021 River Ahr flood in Germany, which caused casualties and huge material damage. Adopting the multi‐year maxima extreme value distribution can potentially lead to the reclassification of vulnerability levels for flood‐prone areas and reconsideration of current policy‐making and flood risk communication.

To study the mechanical and durability characteristics of concrete utilizing waste foundry sand

Currently, the availability of high-quality natural river sand is scarce, requiring transportation over long distances, and its rapid depletion is a significant concern. In this project, the focus lies on assessing the behavior of concrete by partially replacing natural sand with waste foundry sand. The experimental investigation primarily examines the mechanical and durability, split tensile strength, Ultrasonic Pulse Velocity Test, flexural strength, and permeability of concrete. This evaluation involves replacing natural river sand with varying percentages (0%, 10%, 20%, 30%, 40%) of waste foundry sand by weight. Tests are conducted on cubes and beams to analyze the mechanical properties and durability characteristics of concrete with waste foundry sand compared to concrete with natural sand as fine aggregate. The study includes assessments of splitting tensile strength and flexural strength at different ages (7, 28, 56, and 90 days). Results indicate a decrease in workability as the percentage of waste foundry sand in the mix increases.

Experimental Study on Influence of Different Patterns of an Emergent Vegetation Patch on the Flow Field and Scour/Deposition Processes in the Wake Region

AbstractFlume experiments were conducted to comprehend the impact of different patterns of an emergent vegetation patch on the flow field and the scour process in natural rivers. Velocity measurements, flow visualization, and scour tests were undertaken around different vegetation patch patterns, which were simulated inspired by the expansion process of a typical instream vegetation. The patch expansion process was idealized with an initially circular patch of rigid emergent stems becoming elongated due to positive and negative feedbacks. The expansion of the vegetation patch was considered to occur in three stages, in which the density of the patch from the previous stage was increased while the patch was also elongated by connecting at its downstream side with another sparser vegetation patch. These stages were replicated succesively by increasing the density and elongating the patch. In this way, two processes (i.e., elongation and decrease in permeability), which usually have hydrodynamically opposite effects on flow fields, were simulated at the same obstruction. Despite generally elongated obstacles being streamlined bodies, the morphometric analysis obtained by laser scanner revealed that streamlined elongation of permeable patches amplifies global scour and enhances localization of the local scour hole. This situation implies that as the patch expands, in the wake region, the steady‐wake region becomes shorter, turbulence diminishes, lateral shear stress enhances, and deposition cannot occur far from the patch. Consequently, as the patch expands, the hydrodynamic consequences may restrict further patch expansion after a certain length/density.

Kelp Nanofiber‐Based Composite Membranes for Highly Efficient Osmotic Energy Conversion

AbstractThe blue osmotic energy harvesting based on the nanofiber‐based layered membranes has received tremendous attention. However, the most nanofiber‐based ion‐selective membranes are suffering from uneconomical, environmentally unfriendly characteristics and a long growth cycle, as well as insufficient power density. In this work, kelp cellulose nanofibers (KCNFs) from green and inexpensive kelp with short growth cycle are compounded with hydrophilic MXene nanosheets to prepare KCNF/MXene nanofluidic membranes. Notably, the KCNF/MXene‐40 (40 is the mass fraction of KCNF) membrane with an aligned nacre‐like nanostructure achieves 3.03‐fold increase in mechanical strength compared to the pure MXene membrane. The ingenious combination of the surface charge of the MXene nanosheets and the space charge formed by negatively charged KCNFs endows the KCNF/MXene‐40 membrane with enhanced cation selectivity (≈0.85), high energy conversion efficiency of 24.04% and high power density of 66.23 W m−2 in a 500‐fold concentration gradient, which has exceeded most reported state‐of‐the‐art 2D nanofluidic membranes. More importantly, the membrane exhibits the exceptional long‐term stability with relatively unchanged power density within 6000 s. Under the conditions of the natural seawater and simulated river water, the KCNF/MXene‐based generator deliveries an output power density of ≈10.56 W m−2.

On Care, Opposition, and River World Dynamics: The Nu River Anti-dam Campaign (2003−2016) in China

ABSTRACT Crisis and care have been paired as complementary terms. The dialectical relationship invests itself within and across planetary biomes that struggle to thrive. China is a land of ancient heritage and abundant rivers, as well as a drive to modernize through hydropower and electricity. This essay focuses on the important case of the Nu River controversy to add to the corpus of care and crisis discourse in environmental communication. This example requires a move outside the over-determination of spaces that involve episodes of immediate stories of protracted engagement. In a study of how Chinese ENGOs and environmentalists fought hard in a 13-year-long battle to save China’s last natural river, I illustrate China’s ways of working through assertions of crisis, opposition to care, and an outcome opened by new care strategies for creating consensus.