Search Results (1,693)

This study examined the effects of pollution from the Shituru hydrometallurgic complex on the Upper Lufira Basin, Democratic Republic of the Congo, between September 2015 and September 2017. Physico-chemical water variables and trace metal elements in water and sediment, as well as diversity and infection parameters of monopisthocotylan parasites infesting Clarias ngamensis, were assessed at three sites: the Lufira River, Panda River, and Lake Tshangalele. We hypothesised that low pollution would correlate with greater ectoparasite species richness and higher infection parameters. Results indicated severe ecological degradation in the highly polluted Panda River (with high concentrations of TMEs; e.g., 510.830 ± 0.86; 82.470 ± 0.200 µg/L for Co²⁺ and Cu²⁺ in water; 15,771 ± 7068 and 1585 ± 1450 µg/g for Cu²⁺ and Zn²⁺ in the sediment), where neither fish nor parasites were present. Across the other sites, eight parasite species were identified. Seven species occurred on fish from the slightly polluted Lufira River (mean intensity (MI) of 31.28 ± 28.95 parasites per infested fish), while five were found in Lake Tshangalele (MI: 3.23 ± 2.89 parasites per infested fish), confirming the hypothesis. Three species, Quadriacanthus halajiani, Q. domatanai, and Macrogyrodactylus clarii, demonstrated potential as sensitive bioindicators of aquatic pollution in the region. Full article

Soil erosion in the hilly and gully region of the middle reaches of the Yellow River is severe, threatening regional ecological security and the water–sediment balance of the Yellow River. The area features fragmented topography and significant spatial heterogeneity in soil thickness, forming a unique binary “soil–rock” structural system. The soil in the study area is characterized by silt-based loess, and the underlying bedrock is an interbedded Jurassic-Cretaceous sandstone and sandy shale. It has strong weathering, well-developed fissures, and good permeability, rather than dense impermeable rock layers. However, the spatiotemporal differentiation mechanism of soil moisture in this system remains unclear. This study focuses on the typical hilly and gully region—the Geqiugou watershed. Through field investigations, soil thickness sampling, multi-scale soil moisture monitoring, and analysis of meteorological data, it systematically examines the cascade relationships among microtopography, soil–rock combinations, soil moisture, and meteorological drivers. The results show that: (1) Based on the field survey of 323 sampling points in the study area, it was found that soil samples with a thickness of less than 50 cm accounted for 85%, which constituted the main structure of soil thickness in the region. Macrotopographic units control the spatial differentiation of soil thickness, forming a complete thickness gradient from erosional units (e.g., Gully and Furrow) to depositional units (e.g., Gently sloped terrace). Based on this, five typical soil–rock combination types with soil thicknesses of 10 cm, 30 cm, 50 cm, 70 cm, and 90 cm were identified. (2) Soil–rock combination structures regulate the vertical distribution and seasonal dynamics of soil moisture. In thin-layer combinations, soil moisture is primarily retained within the shallow soil profile with higher dynamics, whereas in thick-layer combinations, under conditions of substantial rainfall, moisture can percolate deeply and become notably stored within the fractured bedrock, sometimes exceeding the moisture content in the overlying soil. (3) The response of soil moisture to precipitation is hierarchical: light rain events only affect the surface layer, whereas heavy rainfall can infiltrate to depths below 70 cm. Under intense rainfall, the soil–rock interface acts as a rapid infiltration pathway. (4) The influence of meteorological drivers on soil moisture exhibits vertical differentiation and is significantly modulated by soil–rock combination types. This study reveals the critical role of microtopography-controlled soil–rock combination structures in the spatiotemporal differentiation of soil moisture, providing a scientific basis for the precise implementation of soil and water conservation measures and ecological restoration in the region. Full article

With accelerating urbanization, rivers have been severely polluted, resulting in widespread black and odorous waterways. The coagulation–sedimentation and contact oxidation bypass treatment process is characterized by low operational cost and simple operation and management. In this study, a coagulation–sedimentation–contact oxidation biofilter process was developed to treat heavily polluted malodorous blackwater. Among the tested biofilm carriers, rigid aramid fiber exhibited the fastest biofilm formation and the best pollutant removal performance. Based on a comprehensive evaluation of effluent quality and treatment capacity, the optimal operating conditions of the proposed process were identified as a PAC dosage of 50 mg/L, an air-to-water ratio of 7:1, and a hydraulic retention time (HRT) of 2 h. Under these conditions, the effluent concentrations of chemical oxygen demand (COD), ammonia nitrogen (NH₄⁺-N), and suspended solids (SSs) were consistently maintained below 30, 5, and 5 mg/L, respectively. Moreover, the optimized system demonstrated strong resistance to shock loading, maintaining stable operation at influent COD and SS concentrations of approximately 150 mg/L and 40 mg/L, respectively, while complying with the Class A Discharge Standard of Pollutants for Municipal Wastewater Treatment Plants. This study provides an efficient treatment strategy for malodorous blackwater remediation. Full article

The rapid mobilization of sediment stored behind dams, in amounts that are large relative to mean annual sediment loads, can jumpstart river restoration but can also adversely impact habitat, infrastructure, land, and water use upstream of, within, and downstream of the former impoundment. A wide range of geomorphic and engineering assessment tools were applied to help manage sediment-related risks associated with the removal of two dams from the Elwha River in Washington State and the release of roughly 21 million m³ of sediment. Each of these tools had its strengths and weaknesses, which are explored here. The processes of sediment erosion, transport and deposition were complex. No one model was able to fully simulate all these with the accuracy necessary for predicting the magnitude and timing of coarse and fine sediment release from the reservoir. Collectively, however, the model outputs provided enough information to guide the adaptive sediment management process during dam removal. When the complexity of the morphodynamic responses to dam removal and the associated risks exceeded the capacity of any one tool to adequately assess, synoptic forecasting proved useful. The lessons learned on the Elwha have provided insights into how to use a variety of modeling techniques to address sediment management issues as dam removal scale, complexity and risk increase. Full article

This study focuses on the calibration and verification of a large-scale coupled numerical model to simulate the complex hydrodynamic–wave–sediment transport processes in the coastal and estuarine regions of the Mekong River Delta (MRD), Vietnam. Using the MIKE 21/3 modeling system, the research integrates Hydrodynamics (HD), Spectral Wave (SW), and Mud Transport (MT) modules across a computational domain of 270 × 300 km. The models were rigorously tested using field measurement data from three distinct periods: May 2004 (dry season calibration), September 2017 (first verification), and June 2024 (second verification). The results from the hydrodynamic model demonstrated high accuracy in predicting water levels, with the average Root Mean Square Error (RMSE) values ranging between 4.4% and 5.8%. The wave spectral model showed reliable performance, with the average RMSE values for wave height ranging from 15.1% to 18.0%. Furthermore, the Mud Transport module successfully captured suspended sediment concentrations (SSC), yielding average RMSE values between 26.0% and 32.1% after the fine-tuning of site-specific parameters such as critical shear stress for erosion and deposition. The study highlights the critical importance of utilizing site-specific sedimentological parameters to accurately predict morphological changes in highly dynamic estuarine environments. This validated model provides a robust tool for assessing coastal erosion and developing protection measures in regions that are increasingly vulnerable to climate change and human activities. Full article

The floodplain landscape of the lower Yellow River is jointly shaped by natural water-sediment processes and human activities. With intensified regulation by large reservoirs and increasing human development intensity, the landscape pattern of the floodplain has undergone significant changes. Clarifying the relative contributions of natural and anthropogenic factors, as well as their interactive mechanisms, is crucial for ecological management of the floodplain. Based on 40-year long-term land-use data and hydrological and meteorological observations, this study integrates landscape metrics, the human interference index (HI), grey relational analysis, and partial least squares regression to quantify the spatiotemporal dynamics of landscape pattern in the floodplain of the lower Yellow River and to elucidate the driving mechanisms underlying landscape-pattern evolution. The results indicate that (1) during the study period, the areas of cultivated land and built-up land in the floodplain continuously increased, whereas natural wetlands and grassland decreased accordingly. Taking 2000 as a breakpoint, the rate and direction of landscape change exhibited stage-dependent differences. (2) Landscape pattern metrics changed nonlinearly: the number of patches decreased first and then increased; the patch cohesion index increased first and then declined; and Shannon’s diversity index showed an overall downward trend. These changes suggest a process of landscape consolidation induced by agricultural cultivation, followed by re-fragmentation driven by the expansion of built-up land. (3) Driving-mechanism analysis shows that the HI is the primary driver of the current changes in floodplain landscape pattern. After the operation of the Xiaolangdi Dam, water-sediment conditions tended to stabilize and flood risk in the floodplain decreased, thereby creating favourable conditions for human activities. This study highlights the stage-dependent influences of natural and anthropogenic factors on floodplain landscape evolution under dam regulation and suggests that management strategies should be adapted to the current re-fragmentation phase, prioritizing the strict control of agricultural expansion and the restoration of ecological corridors to mitigate anthropogenic interference under stable dam regulation. Full article

The uncoordinated water–sediment relationship, fragile eco-environment and unbalanced economic development in the Wei River Basin (WRB) pose serious challenges to its high-quality development. Most existing studies focus on static structures or single elements, making it difficult to systematically reveal the complex interrelationships among ecosystem services (ESs) supply, transmission and demand. To address this issue, this paper innovatively combines the “system perspective” with the “flow network model”. From the perspective of flood-sediment transport, eco-environmental and socio-economic (FES) subsystems, we take the WRB as its research object and systematically analyzes the supply–demand relationship of ESs, the pathways of the ESs flows and ecological compensation (EC) strategies at multiple scales. By constructing a supply–demand assessment model for six types of ESs combined with the water-related flows model, the enhanced two-step floating catchment area method and the gravity model, this paper simulates the ESs flows driven by different transmission media (water, road and atmosphere). The results showed the following: (1) a significant spatial mismatch was observed between the high-supply areas at the northern foothills of the Qinling Mountains and the high-demand areas in the Guanzhong Plains. Furthermore, the degree of this mismatch increased with decreasing scale. (2) The pathways of different ESs flows were influenced by their respective transmission media. The water-related flows passed through areas along the Wei River and the Jing River. The carbon sequestration flows were identified in the upper reaches of the Luo River and between the core urban agglomerations of the Guanzhong Plains. The crop production flows were significantly influenced by the scale of urban crop demand, radiating outward from Xi’an City. (3) At the county and watershed scales, The EC fund pools of 7.5 billion yuan and 2.6 billion yuan were formed, respectively. These EC funds covered over 90% of the areas. These findings verify the applicability of the “FES subsystems” framework for multi-scale EC and provide a theoretical basis for developing an integrated EC mechanism across the entire basin. Full article

Lake Kotokel is one of the largest lakes along the eastern shore of Lake Baikal. Increasing anthropogenic pressure combined with climate variability led to a sharp decline in its ecological condition, culminating in an outbreak of Gaff disease in 2009. Moreover, Lake Kotokel may serve as a source of pollutants to Lake Baikal due to its hydrological connection via a system of rivers. In light of these factors, ongoing research seeks to identify the drivers of ecological degradation in the lake ecosystem and provide a comprehensive assessment of its current environmental status and potential adverse processes. In this study, we report, for the first time, the occurrence of microplastic particles in the surface water and sediments of Lake Kotokel. Mean microplastic concentrations were 0.59 ± 0.25 items/m³ in water and 280 ± 162 items/kg dry weight in sediments, with corresponding average microplastic masses of 2.6 ± 1.4 μg/m³ in water and 1.33 ± 1.21 mg/kg dry weight in sediments. In surface waters, microplastic were predominantly 1–3 mm in size, whereas sediments were dominated by 0.1–1 mm particles. Fibers were the most abundant morphological form, comprising 79.5% and 82.8% of particles in water and sediments, respectively. Five polymer types were identified, with polyethylene terephthalate being the most prevalent. Based on particle abundance and polymer composition, the ecological risk of microplastic in Lake Kotokel was assessed as low to moderate. Full article

Based on the numerical simulation software Delft3D v4.01.00, this study established a three-dimensional water and sediment transport model for the Yellow River subaqueous delta, and simulated the water and sediment diffusion as well as erosion/deposition processes in the study area in 2019. By comparing the water discharge, sediment discharge, and deposition volume of 2019 (a year with water and sediment regulation) and 2017 (a year without water and sediment regulation), the influence of water and sediment regulation on the Yellow River subaqueous delta was explored. The results showed that water and sediment regulation projects change the distribution and diffusion of suspended sediment. Suspended sediment concentration in nearshore areas showed a significant correlation with deposition depth, particularly in the estuary area. When the water and sediment regulation was interrupted in 2017, the overall performance of the study area showed erosion, while when the water and sediment regulation was implemented in 2019, the study area exhibited sedimentation. The implementation of the water and sediment regulation project can promote the sedimentation of the subaqueous delta of the Yellow River. Full article

To elucidate the driving factors and regulatory mechanisms of epilithic algal communities in subtropical rural rivers, we investigated the water physicochemical parameters, sediment characteristics, phytoplankton, macroinvertebrates, and epilithic algal communities in the Shilipu and Xiabu Rivers during the summer period (June and August 2023). A total of 131 epilithic algal species belonging to five phyla were identified, with Cyanobacteria, Chlorophyta, and Bacillariophyta constituting the dominant groups. Core dominant species included Lyngbya sp. C. Agardh, 1824, Oscillatoria sp. Vauch., 1803, and Gomphonema sp. Agardh, 1824. Epilithic algal communities exhibited significant monthly differences, with both biomass and abundance being significantly higher (p < 0.05) in August than in June. Environmental factors, encompassing both abiotic and biotic parameters, collectively explained 56.76% and 56.99% of the variation in epilithic algal abundance and biomass, respectively. Water physicochemical parameters and phytoplankton biomass emerged as the core driving factors. Both showed highly significant positive correlations with epilithic algal abundance (R = 0.26, p < 0.001; R = 0.27, p < 0.001) and biomass (R = 0.21, p < 0.001; R = 0.27, p < 0.001). Sediment factors exerted a mild regulatory effect (abundance: R = 0.13, p < 0.05; biomass: R = 0.17, p < 0.01) by releasing nutrients to supplement the water column. The impact of macroinvertebrates was weak and biomass-dependent, showing only a weakly significant positive correlation with epilithic algal biomass (R = 0.12, p < 0.05). This study reveals the synergistic regulatory effects of abiotic and biotic factors on epilithic algal communities in subtropical rural rivers, where elevated external nutrient input attenuates the competitive effects of phytoplankton and the grazing pressure of macroinvertebrates. This provides a scientific basis for the ecological monitoring and restoration of similar river systems. Full article

Under the dual pressures of global climate change and anthropogenic activities, enhancing the ecological functions of hydraulic structures has become a critical direction for sustainable watershed management. While traditional spur dike designs primarily focus on bank protection and flood control, current demands require additional consideration of river ecosystem restoration. Numerical simulations were performed using the RNG k-ε turbulence model to solve the three-dimensional Reynolds-averaged Navier–Stokes equations, a formulation that enhances prediction accuracy for complex flows in curved channels, including separation and reattachment. Following a grid independence study and the application of standard wall functions for near-wall treatment, a comparative analysis was conducted to examine the flow characteristics and ecological effects within a 180° channel bend under three configurations: no spur dikes, a single-side arrangement, and a staggered arrangement of non-submerged, flow-aligned, rectangular thin-walled spur dikes. The results demonstrate that staggered spur dikes significantly reduce the lateral water surface gradient by concentrating the main flow, thereby balancing water levels along the concave and convex banks and suppressing lateral channel migration. Their synergistic flow-contracting effect enhances the kinetic energy of the main flow and generates multi-scale turbulent vortices, which not only increase sediment transport capacity in the main channel but also create diverse habitat conditions. Specifically, the bed shear stress in the central channel region reached 2.3 times the natural level. Flow separation near the dike heads generated a high-velocity zone, elevating velocity and turbulent kinetic energy by factors of 2.3 and 6.8, respectively. This shift promoted bed sediment coarsening and consequently increased scour resistance. In contrast, the low-shear wake zones behind the dikes, with weakened hydrodynamic forces, facilitated fine-sediment deposition and the growth of point bars. Furthermore, this study identifies a critical interface (observed at approximately 60% of the water depth) that serves as a key interface for vertical energy conversion. Below this height, turbulence intensity intermittently increases, whereas above it, energy dissipates markedly. This critical elevation, controlled by both the spur dike configuration and flow conditions, embodies the transition mechanism of kinetic energy from the mean flow to turbulent motions. These findings provide a theoretical basis and engineering reference for optimizing eco-friendly spur dike designs in meandering rivers. Full article

The Yangtze-to-Huaihe Water Diversion (YHWD) project has raised concerns about balancing economic benefits and ecological impacts in Lake Caizi, a nationally protected wetland recognized by the World Wildlife Fund. To assess post-diversion contamination and ecological risks, seasonal variation in polycyclic aromatic hydrocarbons (PAHs) was investigated in surface sediments from Lake Caizi. Total PAH concentrations were 103–565 ng/g dw in the wet season, marginally exceeding the 97.1–526 ng/g dw observed in the dry season. The lowest levels occurred in the western sub-lake (Lake Xizi), showing marked declines relative to a decade ago, attributable to enhanced wastewater treatment, farmland-to-lake restoration, and a 10-year fishing ban. Conversely, PAH concentrations in the main lake, particularly the southeastern and northern sectors of the Caizi route, have increased, reflecting pollutant inflows from Zongyang County via the Yangtze River and accumulation driven by the diversion flows. The diagnostic ratio and positive matrix factorization model indicated biomass burning as the dominant PAH source in Lake Xizi across seasons. In contrast, PAH in the main lake were primarily derived from petroleum combustion and leakage, with coal combustion during the wet season shifting to coal combustion dominance in the dry season due to the seasonal halt of shipping activity. Although overall ecological risk remains low in Lake Caizi, localized hotspots near the Caizi routes and industrial zones pose moderate-to-high risks, necessitating continuous monitoring in the future. Full article

Studying sedimentary distribution in water reservoirs is essential to understand the depositional processes and develop sustainable environmental management strategies. Characterization of deposited sediments provides information about the sources of particulate matter, transport patterns and predominant deposition mechanisms in different compartments of the reservoir. This study aimed to evaluate active deposition processes and to improve the understanding of sedimentation in water reservoirs. In this case, the Espora hydroelectric power plant, located on the Corrente River, southwestern Goiás, Brazil, was employed as a model environment. Sediment cores were collected at 29 points along the reservoir, covering different aquatic compartments. Particle-size analysis of the sediments was performed based on established methodologies using textural classification to identify sedimentary facies. The results indicated the predominance of stream deposits (sandy material) in areas where water flow velocity was higher, and bed deposits, composed predominantly of clays and silts, in regions of lower water flow velocity and greater depth. Full article

Headwater streams comprise almost 90% of global river networks, and their microorganisms play critical roles in organic matter decomposition and nutrient cycling. These functions, however, are affected by recurrent drying and rewetting. This study examined spatial variation in microbial enzyme activity tied to organic carbon degradation (β-glucosidase, phenol oxidase, and peroxidase) and nitrogen (N-acetylglucosaminidase) and phosphorus (phosphatase) mineralization in water, epilithic biofilm, leaf litter, and sediment in two intermittent streams: Gibson Jack Creek (Idaho, USA) and Pendergrass Creek (Alabama, USA), representing different climactic and physiographic settings. Microbial activity was greater in Gibson Jack Creek, where the activity of leaf litter enzymes varied along the stream network, and there were strong correlations in microbial activity between different stream habitats. Microbial activity in Pendergrass Creek showed primarily within-habitat associations. Activity in water, sediment, and biofilm showed broader spatial heterogeneity in both stream networks. Ratios of microbial activity (enzyme stoichiometry) suggested that microbial communities in both systems were primarily limited by carbon and phosphorus, although there was more spatial variation in nitrogen limitation, particularly in water and sediment at Pendergrass Creek and in biofilm at Gibson Jack Creek. These findings underscore the spatial heterogeneity and environmental sensitivity of microbial processes in intermittent streams. Full article

Geothermal water from different orogenic belts, surrounding rock weathering, and salt-forming elements sourced from surface basins jointly shape the hydrochemical characteristics, evaporation evolution sequences, and prospects for subsequent development and utilization of terminal salt lakes. In view of the lack of research on the metallogenic model of a single salt lake in the Qinghai–Tibet Plateau, this paper selects the Nie’er Co Salt Lake, a terminal lake in Northern Tibet, and systematically samples the water, river sediments, and surrounding rocks of the upper reaches of the recharge river, the Xiangqu. The Piper, Gibbs, and Durov, combined with ion ratio analysis, correlation analysis, PHREEQC, quantitative calculations of surrounding rock weathering and tributary contributions to salt-forming elements, were applied to comprehensively characterize groundwater hydrochemistry and surface water system runoff, and clarify the evolution of salt-forming elements in the terminal lake. The driving mechanism of surface runoff and surrounding rock weathering on ion enrichment in the terminal lake was revealed. The Nie’er Co Salt Lake in Tibet evolves from Ca/Na-HCO₃ springs to Na-SO₄²⁻ via dilution, rock leaching, and evaporation. Tributaries contribute 39.6%, 8.2%, and 52.3% of the major ions. Silicate weathering dominates (75%–80%), shifting to evaporite–carbonate inputs. The overall performance is dominated by silicate weathering. The contribution rate of silicate weathering decreases, and the trend of evaporite–carbonate weathering increases. The evolution of surface runoff can be divided into a tributary ion concentration growth section, a mixed ring section (evaporation concentration–TDS increase), and a terminal lake sedimentary section (enrichment evaporation to form the salt lake), revealing that multi-branch superposition and surrounding rock weathering synergistically affect the formation of salt lake hydro-chemical types. Full article