Search Results (174)

South Dongting Lake is an essential aquatic ecosystem that receives substantial water inflows from the Xiangjiang and Zishui Rivers. However, it is significantly impacted by human activities, including mining, smelting, and farming. These activities have led to serious contamination of the lake’s sediments with heavy metals (HMs). This study investigated the distribution, mobility, and influencing factors of HMs at the sediment–water interface. To this end, sediment samples were analyzed from three key regions (Xiangjiang River estuary, Zishui River estuary, and northeastern South Dongting Lake) using traditional sampling methods and Diffusive Gradients in Thin Films (DGT) technology. Analysis of fifteen HMs (Pb, Bi, Ni, As, Se, Cd, Sb, Mn, Zn, V, Cr, Cu, Tl, Co, and Fe) revealed significant spatial heterogeneity. The results showed that Cr, Cu, Pb, Bi, Ni, As, Se, Cd, Sb, Mn, Zn, and Fe exhibited high variability (CV > 0.20), whereas V, Tl, and Co demonstrated stable concentrations (CV < 0.20). Concentrations were found to exceed background values of the upper continental crust of eastern China (UCC), Yangtze River sediments (YZ), and Dongting Lake sediments (DT), particularly at the Xiangjiang estuary (XE) and in the northeastern regions. Speciation analysis revealed that V, Cr, Cu, Ni, and As were predominantly found in the residual fraction (F4), while Pb and Co were concentrated in the oxidizable fraction (F3), Mn and Zn appeared primarily in the exchangeable fractions (F1 and F2), and Cd was notably dominant in the exchangeable fraction (F1), suggesting a high potential for mobility. Additionally, DGT results confirmed a significant potential for the release of Pb, Zn, and Cd. Contamination assessment using the Pollution Load Index (PLI) and Geoaccumulation Index (Igeo) identified Pb, Bi, Ni, As, Se, Cd, and Sb as major pollutants. Among these, Bi and Cd were found to pose the highest risks. Furthermore, the Risk Assessment Code (RAC) and the Potential Ecological Risk Index (PERI) highlighted Cd as the primary ecological risk contributor, especially in the XE. The study identified sediment grain size, pH, electrical conductivity, and nutrient levels as the primary influencing factors. The PMF modeling revealed HM sources as mixed smelting/natural inputs, agricultural activities, natural weathering, and mining/smelting operations, suggesting that remediation should prioritize Cd control in the XE with emphasis on external inputs. Full article

The role of on-site wastewater treatment (OSWT) is increasingly important for water reuse and local sustainability, but treatment efficiency is highly dependent on hydraulic behavior and mixing. This study used validated CFD simulations and tracer experiments to analyze flow patterns and mixing performance in a six-zone OSWT unit under different operational scenarios, including inflow, aeration, recirculation, combined mechanisms, and closed-loop operation without inflow. The results show that influent flow is essential for maintaining convective transport and system-wide momentum, while aeration and recirculation enhance local mixing, but cannot fully overcome geometric dead zones. The combined use of inflow, aeration, and recirculation achieved the highest mixing efficiency and minimized the dead volume, whereas scenarios lacking inflow exhibited severe stagnation and expanded dead zones. These findings highlight the need to integrate hydraulic interventions with thoughtful reactor design to ensure effective and resilient small-scale wastewater treatment systems. Full article

In the current configuration of Brazil’s hydro-thermal-wind power system, hydroelectric reservoirs have progressively lost their long-term regulatory role due to inadequate planning, inefficient energy use, and reduced inflows. In the context of the energy transition and the incorporation of low-emission technologies into the generation mix, this study proposes expanding nuclear baseload capacity as a “regulatory thermal buffer” to mitigate hydrological uncertainty and strengthen grid stability. Using the São Francisco River basin as a case study, an equivalence factor is developed to relate nuclear energy output to stored hydropower reservoir volume. Results show that nuclear generation can help restore the multi-annual regulatory capacity of Brazil’s hydropower system and enhance the resilience of the National Interconnected System by contributing substantial inertia to an increasingly variable, renewable-based grid. Full article

Direct numerical simulations (DNSs) of the T106A low-pressure turbine were conducted for various turbulence intensities and length scales to investigate their effects on flow behaviour and transition. A source-term formulation of the synthetic eddy method (SEM) was implemented in the Nektar++ spectral/hp element framework to introduce anisotropic turbulence into the flow field. A single sponge layer was imposed, which covers the inflow and outflow regions just downstream and upstream of the inflow and outflow boundaries, respectively, to avoid acoustic wave reflections on the boundary conditions. Additionally, in the T106A model, mixed polynomial orders were utilized, as Nektar++ allows different polynomial orders for adjacent elements. A lower polynomial order was employed in the outflow region to further assist the sponge layer by coarsening the mesh and diffusing the turbulence near the outflow boundary. Thus, this study contributes to the development of a more robust and efficient model for high-fidelity simulations of turbine blades by enhancing stability and producing a more accurate flow field. The main findings are compared with experimental and DNS data, showing good agreement and providing new insights into the influence of turbulence length scales on flow separation, transition, wake behaviour, and loss profiles. Full article

With water availability being one of the world’s major challenges, this study aims to propose a Zero Liquid Discharge (ZLD) system for treating saline effluents from an urban wastewater treatment plant (UWWTP), thereby supplementing into the existing water cycle. The system, which employs membrane (nanofiltration and reverse osmosis) and thermal technologies (multi-effect distillation evaporator and vacuum crystallizer), has been installed and operated in Cyprus at Larnaca’s WWTP, for the desalination of the tertiary treated water, producing high-quality reclaimed water. The nanofiltration (NF) unit at the plant operated with an inflow concentration ranging from 2500 to 3000 ppm. The performance of the installed NF90-4040 membranes was evaluated based on permeability and flux. Among two NF operation series, the second—operating at 75–85% recovery and 2500 mg/L TDS—showed improved membrane performance, with stable permeability (7.32 × 10⁻¹⁰ to 7.77 × 10⁻¹⁰ m·s⁻¹·Pa⁻¹) and flux (6.34 × 10⁻⁴ to 6.67 × 10⁻⁴ m/s). The optimal NF operating rate was 75% recovery, which achieved high divalent ion rejection (more than 99.5%). The reverse osmosis (RO) unit operated in a two-pass configuration, achieving water recoveries of 90–94% in the first pass and 76–84% in the second. This setup resulted in high rejection rates of approximately 99.99% for all major ions (Cl⁻, Na⁺, Ca²⁺, and Mg²⁺), reducing the permeate total dissolved solids (TDS) to below 35 mg/L. The installed multi-effect distillation (MED) unit operated under vacuum and under various inflow and steady-state conditions, achieving over 60% water recovery and producing high-quality distillate water (TDS < 12 mg/L). The vacuum crystallizer (VC) further concentrated the MED concentrate stream (MEDC) and the NF concentrate stream (NFC) flows, resulting in distilled water and recovered salts. The MEDC process produced salts with a purity of up to 81% NaCl., while the NFC stream produced mixed salts containing approximately 46% calcium salts (mainly as sulfates and chlorides), 13% magnesium salts (mainly as sulfates and chlorides), and 38% sodium salts. Overall, the ZLD system consumed 12 kWh/m³, with thermal units accounting for around 86% of this usage. The RO unit proved to be the most energy-efficient component, contributing 71% of the total water recovery. Full article

Spring waters (n = 103) from locations surrounding Great Salt Lake (GSL) were mapped, collected, and analyzed to determine their chemical compositions. A ternary Ca-SO₄-alkalinity plot was used to group these waters into compositional types based on the principle of chemical divides. Different spring water types were mixed with Bear, Jordan, and Weber River waters to determine the amount of spring inflow needed to reproduce the chemical composition of GSL. The Pitzer-based computer program EQL/EVP was used to simulate evaporation of spring-river water mixtures. The goal was to find spring-river water mixtures that, when evaporated, reproduced the chemical composition of modern GSL. This approach yielded GSL brine composition from a starting mixture of 12% spring inflow and 88% river water, by volume. The calculated spring inflow–river water mixture contains, on a molar percentage basis, greater than 50% of the B, K, Li, Na, and Cl supplied by springs and greater than 50% of the Ba, Ca, Sr, SO₄, and alkalinity derived from rivers. Understanding GSL spring inflow and brine evolution as lake elevation drops is critical to lake environments, ecosystems, and industrial brine shrimp harvesting and mineral extraction. Full article

Approach sequencing is important for multiple unmanned electric vertical take-off and landing (eVTOL) vehicles landing in vertiport. In this study, the additional intermediate transition ring (AIR) approach procedure in a balanced traffic flow scenario, the single ring movement-allowed (SRMA) approach procedure in an imbalanced traffic flow scenario, and the additional ring and allowing of movement (ARAM) approach procedure in a mixed scenario are proposed and designed to improve the efficiency of approach sequencing. Furthermore, a priority loss classification method is proposed to consider the unmanned eVTOL flight priority difference. Finally, a multi-objective optimization model is constructed with the constraints of inflow, outflow, moment continuity, flow balance, and conflict avoidance. The objectives are minimizing the power consumption, total operation time, and priority loss. Comparison experiments are conducted, and the final results demonstrate that the ARAM approach procedure can reduce the average holding time by 8.4% and 7.6% less than the branch-queuing approach (BQA) and AIR in a balanced traffic flow scenario, respectively. The ARAM approach procedure can reduce the average holding time by 6.5% less than BQA in an imbalanced traffic flow scenario. Full article

Labor markets worldwide are increasingly strained by skill shortages, mismatches, and migration pressures, disrupting workforce stability and economic growth. This study conducts a comparative sectoral analysis in North Macedonia, Türkiye, Ethiopia, and Ukraine, focusing on the manufacturing, information and communication technology, and hospitality sectors, to examine the root causes and economic consequences of these challenges. Using a qualitatively driven mixed-methods approach, the research integrates expert interviews, surveys, and labor market data to assess skill gaps, workforce imbalances, and the role of migration. The findings reveal education–industry misalignment, inadequate vocational training, and low wages as persistent drivers of shortages. Additionally, the war in Ukraine, internal conflicts in Ethiopia, and refugee inflows in Türkiye amplify workforce instability, while North Macedonia faces severe emigration, particularly in the sectors of manufacturing and information and communication technologies. These insights are essential for policymakers, industry leaders, and educators in designing labor market interventions that foster workforce resilience. The study recommends national qualification reforms, industry–education collaboration, and improved wage structures to mitigate talent loss and strengthen labor market sustainability. By offering empirical evidence from diverse socio-economic contexts, this research contributes to global discussions on workforce development, migration economics, and labor policy reforms. Full article

The study examined the influence of foreign aid on foreign direct investment (FDI) in upper-middle-income economies using panel data (2011–2021) analysis methods such as two-stage least squares (2SLS) and system GMM (generalized methods of moments). The study also explored if human capital development enhanced foreign aid’s influence on FDI in upper-middle-income economies during the same timeframe. The conflicting, divergent, and mixed results and views on the relationship between foreign aid, human capital development, and foreign direct investment (FDI) motivated the undertaking of this study to fill in the existing gaps. Apart from FDI enhanced by its own lag, foreign aid significantly improved FDI (under system GMM). FDI was also improved significantly by human capital development across all two panel methods. Under 2SLS and system GMM, foreign aid significantly improved FDI through the human capital development channel. To promote FDI inflows, upper-middle-income economies should develop and implement policies aimed at attracting foreign aid and enhancing the development of human capital. The study suggests that further research on threshold regression analysis on foreign aid–FDI nexus in upper-middle-income economies could better help develop an FDI policy that is beneficial toward economic growth. Full article

Numerical modeling methods were used to study the combined effects of the autumn thermal bar and river inflow mineralization on deep-water renewal processes in Lake Baikal. A cross-section from the Boldakov River to Maloye More strait characterized by great depths was chosen for the study. Numerical experiments showed that under low levels of river mineralization, downwelling in the thermal bar front played a key role in water mixing. Under high levels of mineralization, the crucial factor was the large-scale near-slope circulation appearing when the stable temperature stratification of deep waters was broken. The haline characteristics of river inflow influenced the time of thermal bar appearance and the speed of propagation in the open lake. Moreover, it was shown that eddy structures can form on both sides of the thermal bar only under minor differences between river and lake mineralization levels. Full article

Nitrate contamination poses a significant global environmental threat, impacting the water quality in surface and groundwater systems. Despite its considerable impact, there remains a lack of comprehensive understanding of nitrate sources and discharge patterns, particularly in the Lake Victoria basin of East Africa. To address this gap, a study was conducted in the Kagera River basin, responsible for 33% of Lake Victoria’s surface inflow. This study utilized δ¹⁵N and δ¹⁸O isotope analysis in nitrate, hydrochemistry, and the Bayesian mixing model (MixSIAR) to identify and quantify nitrate sources. Spatiotemporal data were collected across three seasons: long rains, dry season, and short rains, in areas with diverse land uses. Nitrate isotopic data from water and potential sources were integrated into a Bayesian mixing model to determine the relative contributions of various nitrate sources. Notable spatial variations were observed at sampling sites with concentrations ranging from 0.004 to 3.31 mg L⁻¹. Spatially and temporally, δ¹⁵N-NO₃⁻ values ranged from +6.0% to +10.2‰, whereas δ¹⁸O-NO₃⁻ displayed significant spatial differences with mean ranges from −1% to +7‰. MixSIAR analysis revealed important contributions from manure and sewage sources ranging between 49% and 73%. A boron analysis revealed manure was the main source of nitrates in the manure and sewage. These results show that it is necessary to implement improved manure and sewage management practices, especially through proper waste treatment and disposal systems, to enable informed policy decisions to enhance nitrogen management strategies in riparian East Africa, and to safeguard the region’s water resources and ecosystems. Full article

Oscillations in animate and inanimate systems are ubiquitous phenomena driven by sophisticated chemical reaction networks. Non-autonomous chemical oscillators have been designed to mimic oscillatory behavior using programmable syringe pumps. Here, we investigated the non-autonomous oscillations, pattern formation, and front propagation of amphoteric hydroxide (aluminum (III), zinc (II), tin (II), and lead (II)) precipitates under controlled pH conditions. A continuous stirred-tank reactor with modulated inflows of acidic and alkaline solutions generated pH oscillations, leading to periodic precipitation and dissolution of metal hydroxides in time. The generated turbidity oscillations exhibited ion-specific patterns, enabling their characterization through quantitative parameters such as peak width (W) and asymmetry (As). The study of mixed metal cationic systems showed that turbidity patterns contained signatures of both hydroxides due to the formation of mixed hydroxides and oxyhydroxides. The reaction–diffusion setup in solid hydrogel columns produced spatial precipitation patterns depending on metal cations and their concentrations. Additionally, in the case of tin (II), a propagating precipitation front was observed in a thin precipitation layer. These findings provide new insights into precipitation pattern formation and open avenues for metal ion identification and further exploration of complex reaction–diffusion systems. Full article

This study focused on exploring the influence of infrastructural development on foreign direct investment (FDI) in BRICS countries, including Brazil, Russia, India, China, and South Africa, using a fixed-effects approach. Secondary data ranged from 1991 to 2021. Existing theoretical and empirical literature on the subject (the infrastructural development-led FDI nexus) is quite mixed, which therefore makes it difficult for policy makers to make decisions. Internet penetration and fixed telephone subscriptions had a significant enhancing effect on FDI, whilst renewable energy infrastructure’s effect was found to be minimal and non-significant. In the fixed-effects model, the interaction term produced results showing that financial development enabled infrastructural development and significantly enhanced FDI inflows into BRICS countries. To improve FDI inflows, BRICS nations should implement policies with the aim of enhancing Internet penetration, fixed telephone subscriptions, and financial development. A threshold analysis of the infrastructural development levels that significantly improve FDI inflows is recommended to provide more clarity and specificity for policy making. Full article

The Yellow River (~5464 km) and the Yangtze River (~6300 km) are large rivers that originate from the Tibetan Plateau and flow into the western Pacific Ocean. The shelf seas of the western Pacific Ocean (e.g., Bohai, Yellow, and East China seas) serve as critical sites for investigating the evolution of these rivers. Distinguishing the material signals of the Yellow River from those of the Yangtze River is an essential step in this research. Therefore, we analyzed published zircon U-Pb ages (n = 1568 for the Yellow River and n = 1216 for the Yangtze River) and K-feldspar Pb isotopes (n = 380 for the Yellow River and n = 158 for the Yangtze River) from the middle and lower reaches of both rivers. The results indicate that the detrital material in the lower reaches of the Yellow River is primarily influenced by the western North China Craton and the Qinling Mountains, whereas the detrital material in the lower reaches of the Yangtze River mainly derives from the South China Block. The Qinling Mountains influence the material composition of the lower Yellow River, primarily due to the formation of overhanging rivers along the river’s course. These geological features inhibit the inflow of materials from the eastern North China Craton, thereby preventing the mixing from the Qinling Mountains. In contrast, the influence of the Qinling Mountains on the material composition of the lower Yangtze River is minimal. This limited impact is attributed to the influx of materials from the South China Block, which dilutes the contributions from the Qinling Mountains. Notably, substantial discrepancies exist in the U-Pb ages and Pb isotopic compositions of detrital zircons and K-feldspar from the lower Yellow River compared to those from the lower Yangtze River and the surrounding geological units. These disparities provide a robust foundation for investigating large river provenance tracing in the western Pacific Ocean shelf sea through the integration of these two analytical methods. However, the U-Pb age distributions of detrital zircons in the lower Yellow River have changed significantly over geological time. The U-Pb age data for detrital zircons collected from the eastern Sanmen Gorge of the middle Yellow River should be utilized to examine river evolution prior to the Quaternary period. Conversely, the U-Pb data from detrital zircons in the lower Yellow and the Yiluo rivers should be considered when discussing Quaternary river evolution. The zircon U-Pb age characteristics of the lower Yangtze River can be directly employed to analyze the evolution of large rivers in the western Pacific Ocean shelf sea during the Neogene. Full article

The inflow of saline water reduces water quality and limits its use as drinking water. The risk of seawater intrusion into groundwater along the Polish coastline was assessed using two methods. The vulnerability method (GALDIT) considered six aquifer parameters. The second method focused exclusively on the chemical parameters of groundwater: EC, seawater mixing index (SMI), rHCO₃/rCl, rNa/rCl, and the concentrations of Cl⁻ and Br. The analysis focused on monitoring results collected from points located within 5 km of the Baltic Sea coastline. Both risk assessment methods used a division into three risk classes (low, moderate, and high), but the results differed between the two approaches. A comparison of the results from both classification methods was conducted, followed by a comprehensive risk assessment integrating the outcomes of both approaches. No straightforward relationship was observed between individual threat assessment parameters and distance from the sea. However, when the overall assessment, incorporating multiple parameters, was considered, such a relationship emerged. The classes of seawater intrusion risk differ in terms of the medians and ranges of individual parameters. Ratios such as rHCO₃/rCl, rCa/rMg, and Cl/Br play a significant role in risk assessment, whereas the rNa/rCl ratio has a relatively smaller impact. Seawater intrusion risk should be assessed based on multiple parameters. The highest risk of seawater intrusion occurs within approximately 800 m of the coastline. Full article