Abstract: Water conservation, a critical ecosystem service, is primarily quantified through water retention (WR), which plays a pivotal role in sustainable socio-economic development and water resources management. However, the absence of multi-temporal modeling of land use and climate change impacts on eco-hydrological processes limits the accurate estimation of WR, particularly in humid regions. This study employed the Soil and Water Assessment Tool (SWAT) model coupled with the water balance principle to estimate WR in the source area of the Xin'an River (SXAR) in China from 2009 to 2017. The multi-temporal variations of WR and its response to climate and land use changes were analyzed through scenario-based hydrological simulations. Results indicated that annual WR ranged from 256.4 mm to 412.7 mm, monthly WR varied between 0 mm and 67.6 mm, and peak daily WR coincided with extreme rainfall events. Precipitation and evapotranspiration were identified as the primary factors influencing WR variability at daily and monthly scales. Spatially, higher WR values were observed in the northeastern SXAR, reflecting the influences of land use patterns and topography. Notably, agricultural land exhibited negative WR during summer months due to crop water storage demands. Overall, climate change exerted more immediate effects on WR at shorter timescales, whereas land use change produced longer-term impacts. This study offers valuable theoretical insights into WR mechanisms of response to environmental changes and provides practical guidance for water resources planning and management in humid and sub-humid regions.
Abstract: Accurate streamflow prediction under climate change is essential for mitigating natural disasters and optimizing water resources management. However, streamflow prediction is subject to considerable uncertainties due to the complexity of hydrological model structures, parameterization, and input forcing data. This study predicted monthly streamflow in the upper Han River Basin in China under three Shared Socioeconomic Pathways (SSP) scenarios, using climate projections from five Coupled Model Intercomparison Project Phase 6 (CMIP6) climate models. Bias correction of climate model outputs was performed prior to streamflow simulation using four deep learning approaches: long short-term memory, gated recurrent unit, temporal convolutional network, and transformer. To reduce uncertainties inherent in individual deep learning models, Bayesian model averaging (BMA) was employed to integrate their predictions. The results showed that the three deep learning models achieved satisfactory performance with Nash-Sutcliffe model efficiency coefficient (NSE) values exceeding 0.8, while BMA exhibited superior robustness and accuracy, with the highest NSE and lowest root mean square error. Projected precipitation, mean air temperature, and potential evapotranspiration generally decreased during 2026-2100 relative to the historical period (1970-2017), suggesting a colder and drier regional climate. Streamflow was projected to decline significantly across all three scenarios, particularly from June to September, highlighting the potential for exacerbated water scarcity in the future.
Abstract: Pesticides are widely used in agriculture and can enter river-lake systems through surface runoff, adversely affecting non-target organisms and threatening ecological security. This study investigated the occurrence and distribution of 52 pesticides in a typical river-lake system in China and evaluated their ecological risks to aquatic organisms. The average total pesticide concentration in surface water was 203.05 ng/L, with carbendazim being the dominant pollutant, contributing 23.66% to the contamination. In sediments, the average pesticide concentration was 6.34 ng/g, with tebuconazole being the primary contributor at 28.57%. Fungicides were the main pesticide type in both river water and sediments, accounting for 76.86% and 85.10%, respectively. Pesticides predominantly accumulated in lake sediments, with the small lake showing high pesticide concentrations near river outflow areas and the large lake accumulating pesticides near lake inlets. Pesticide concentrations in both water and sediments increased downstream along rivers. Ecological risk assessment revealed high mixed risks to algae, daphnia, and fish, with risk levels rising along with trophic levels of aquatic organisms. The correlation between pesticide concentration and mixed ecological risk was weaker for algae than for daphnia and fish, and certain pesticides posed high risks to algae even at low concentrations, indicating more targeted toxicity for lower trophic organisms. These findings provide reference data for ecological risk assessment and pesticide pollution management in river-lake systems in agricultural regions.
Abstract: Frequent saltwater intrusion induced by extreme climate events poses significant challenges to water supply security in coastal cities. This study developed a supply-demand balance model for urban water supply systems based on the system dynamics (SD) method, employing the supply-demand gap and water stress index (WSI) as risk indicators. Dynamic simulations were conducted in Zhongshan City in China across five development and 17 saltwater boundary scenarios, and corresponding emergency water reserve requirements were proposed for emergency durations of 10-60 d. The results showed no supply-demand gaps from 2016 to 2023, although water supply was notably affected by saltwater intrusion. The highest risk occurred in 2021 when saltwater fronts reached the Renyi and Dafeng intakes, resulting in a peak WSI of 0.45. Water demand would peak in 2035 across all development scenarios. The economic development scenario exhibited the highest demand, the conservation development scenario the lowest, and the comprehensive development scenario the second lowest, with the latter balancing economic and social development with resource conservation, enhancing its policy relevance. Across the 17 saltwater boundary scenarios, the conservation development scenario demonstrated the lowest WSI values (0-6.74) and water supply risk level, followed by the comprehensive development scenario (with WSI values of 0-7.11), while the economic development scenario demonstrated the highest WSI values (0-7.84) and water supply risk level. Under worst-case saltwater conditions with 60-d emergency reserves, supply-demand gaps in 2030 would reach 7.938 × 107 m3 and 8.928 × 107 m3 in the conservation and economic development scenarios, respectively, and increase to 10.164 × 107 m3 and 12.354 × 107 m3 by 2035. This methodology offers actionable insights for coastal cities to optimize development strategies and emergency water reserve planning.
Abstract: Understanding the processes and dynamics of tidal wave propagation in estuaries is critical for assessing the impacts of natural processes and human interventions on estuarine systems. However, current knowledge of tidal dynamics in micro-tidal estuaries and their variability across various timescales remains limited. This study used an analytical framework and field observations to investigate the fundamental physical processes and mechanisms governing tidal wave propagation in the Yongjiang Estuary, a micro-tidal estuary on the eastern coast of China. The analytically computed tidal amplitude and wave propagation timing aligned with observed data. Significant wet/dry and spring/neap variations in tidal wave properties were identified, primarily influenced by the interplay between channel convergence and bottom friction. Given the high siltation rates in the Yongjiang Estuary, analytical simulations suggested that human-induced dredging enhances tidal dynamics, while channel bed siltation weakens hydrodynamic processes, potentially exacerbating local sedimentation. The findings of this study provide valuable insights for estuarine management and establish a foundation for future research on sediment dynamics in the Yongjiang Estuary.
Abstract: Inefficient water management can lead to water and nutrient losses in rice cultivation, causing economic and environmental challenges. This study evaluated the effects of irrigation and percolation management on nutrient leaching, rice yield, and water footprint using field lysimeters during the Aman (wet) and Boro (dry) seasons in Mymensingh, Bangladesh. Irrigation treatments included zero ponding (saturated soil), 2-cm ponding, and 5-cm ponding, while percolation management involved uncontrolled percolation, reuse of percolated water, and no percolation. Leachate samples collected every 10 d were analyzed for mineral nitrogen and available phosphorus, with yield and water use measurements. The zero ponding treatment yielded lower water footprints in the Aman and Boro seasons (1 224 L/kg and 1 289 L/kg, respectively) than the 2-cm ponding (1 252 L/kg and 1 662 L/kg, respectively) and 5-cm ponding (1 360 L/kg and 1 953 L/kg, respectively) treatments, with comparable grain yields. The no-percolation treatment increased tiller count in the Aman season but had no significant effect in the Boro season. The uncontrolled percolation treatment resulted in total percolated water depths of 10-13 cm and 20-21 cm in the Aman and Boro seasons, respectively. The no-percolation treatment led to lower water footprints (1 224-1 289 L/kg) than the uncontrolled percolation (1 409-1 706 L/kg) and percolation-reuse (1 448-1 516 L/kg) treatments. Percolation reuse reduced phosphorus leaching in the Aman season, lowered NH+4-N leaching late in the Boro season, and decreased NO-3-N leaching in multiple events compared to uncontrolled percolation. These findings inform improved water and nutrient management strategies in rice ecosystems for enhanced sustainability.
Abstract: Wastewater reuse offers a potential solution to global drought and water scarcity but may have environmental impacts, particularly on soil microbial communities and their metabolic activities. This study investigated the effect of selected irrigation water types on soil bacterial enzymatic activities. Three differently treated urban wastewaters (secondary effluent, ultraviolet (UV)-treated effluent, and ultrafiltration (UF)/UV-treated effluent) were compared with river water over a two-year irrigation period. Soil samples were regularly analysed for potential nitrification activity (PNA) and dehydrogenase activity (DHA). The results indicate that treated wastewater significantly increased DHA in surface soil (at depths of 0-25 cm), with the greatest increase observed for the UF/UV-treated effluent (up to a 59% increase relative to the initial value). In contrast, PNA decreased by up to 82% during the first year across all treatments, suggesting a shift in microbial community structure away from nitrifiers. In the second year, microbial activity stabilised across all treatments. Statistically significant correlations were identified between soil temperature, humus content, and enzymatic activity (p < 0.001). These findings imply that wastewater reuse enhances total microbial biomass and potentially alters nitrogen cycling dynamics, underscoring the need for targeted monitoring of soil microbiological health in long-term wastewater reuse scenarios.
Abstract: Industrial effluents pose significant environmental challenges due to the presence of water-soluble organic dyes such as rhodamine B (RhB), necessitating the implementation of effective removal strategies. Although adsorption is recognised as a promising alternative to conventional dye removal methods, developing cost-effective, sustainable, and highly efficient adsorbents remains challenging. This study investigated RhB adsorption using the bacterial cellulose (BC)/graphene oxide (GO) composite. GO was incorporated to enhance adsorption capacity by improving electrostatic interactions and introducing additional functional groups. The methodology involved synthesising GO from Sawahlunto coal, preparing BC/GO composites with varying GO contents, and conducting RhB adsorption experiments across different pH levels. Comprehensive characterisation confirmed successful GO synthesis and integration into the BC matrix. While pristine BC exhibited limited RhB removal efficiency and adsorption capacity (42.04% and 0.093 4 mg/g, respectively), BC/GO demonstrated significantly improved performance. The optimal composite containing 50 mg of GO achieved a removal efficiency of 98.91% and an adsorption capacity of 0.219 mg/g. Further optimisation at a pH value of 3 enhanced adsorption efficiency and capacity to 99.50% and 0.221 mg/g, respectively. Langmuir isotherm analysis with a coefficient of determination of 0.934 revealed a monolayer adsorption mechanism, highlighting the potential of BC/GO for advanced environmental remediation in industrial wastewater treatment.
Abstract: The development of low-cost, efficient, and environmentally friendly adsorbents capable of simultaneously removing both heavy metals and synthetic dyes from wastewater remains a critical challenge in environmental remediation. In this study, a novel chitosan/pumice (CS/PM) composite was synthesized and evaluated for its multifunctional adsorption performance toward four common and toxic pollutants: lead (Pb(II)), cadmium (Cd(II)), methylene blue (MB), and Congo red (CR). Characterization confirmed the successful integration of chitosan with pumice, resulting in reduced crystallinity, enhanced thermal stability, and active functional groups involved in adsorption. Adsorption experiments demonstrated optimal pollutant removal at a pH value of 6, with the composite exhibiting high affinity for all tested contaminants. The adsorption kinetics followed a pseudo-second-order model, indicating that chemical interactions predominantly govern the adsorption process. Furthermore, the adsorption isotherms closely fit the Langmuir model, followed by the Sips model, suggesting monolayer adsorption on a homogeneous surface with potential heterogeneous interactions. The maximum adsorption capacities of CS/PM, calculated from the Langmuir model, were 150.60 mg/g, 123.14 mg/g, 135.20 mg/g, and 120.33 mg/g for Pb(II), Cd(II), MB, and CR, respectively. This study introduces a straightforward approach for designing porous composite materials with high adsorption capacities, offering promising applications in environmental remediation.
Abstract: One of advanced methods for treating textile wastewater is photocatalytic processes that decolorize and degrade organic pollutants. In this study, a photoreactor using TiO2/chitosan/glycerol (TCG) beads under ultraviolet A (UVA) irradiation was employed to degrade acid blue 193 (AB193) and treat secondary textile wastewater (STWW). The photoreactor's dye removal efficiency was evaluated by varying fixed TCG thickness, initial dye concentration, and hydraulic retention time. Optimal dye removal was achieved at 15 min in batch mode with fixed TCG thicknesses of 0.75-1.25 cm. The apparent rate constant (kapp) increased with initial dye concentration, indicating that the degradation process followed pseudo-first-order kinetics. The continuous-flow system exhibited lower removal efficiencies and rate constants (kr) than the batch system, with kr decreasing from 0.841 to 0.781 as the fixed TCG thickness increased from 0.75 cm to 1.75 cm. In contrast, the batch system showed a slight increase in kr from 1.010 to 1.034. The batch system outperformed the continuous-flow photoreactor, particularly at high contaminant concentrations. In continuous-flow experiments, STWW decolorization slightly increased from 76.0% to 77.2%, while COD removal decreased from 83.7% to 78.8% with an increase in fixed TCG thickness from 0.75 cm to 1.25 cm. These findings demonstrate that the TCG beads combined with the continuous-flow photoreactor effectively treat textile wastewater, producing effluent that meets Vietnamese environmental standards.
Abstract: Electrochemical reactors play a vital role in scaling up wastewater treatment processes, with efficiency influenced by electrode material, reactor geometry, flow dynamics, power supply, and operational mode. This study investigated the continuous electrocoagulation treatment of paper mill wastewater using a reactor equipped with four aluminum electrodes. The effects of flow rate (0.1-0.6 L/min) and retention time on pollutant removal efficiency were examined. Effluent was continuously fed into the reactor via a peristaltic pump, ensuring controlled inflow and uniform distribution for optimal treatment conditions. Experimental results demonstrated that 80% removal of total dissolved solids, total organic carbon, chemical oxygen demand, and color was achieved under optimal conditions: a pH value of 5.0, a conductivity of 7.59 mS/cm, an electrode gap of 1.38 cm, a current density of 10.72 mA/cm2, a retention time of 120 min, and a flow rate of 0.1 L/min. The sludge generated during treatment was characterized using scanning electron microscopy, energy dispersive X-ray spectroscopy, X-ray diffraction, and Fourier transform infrared spectroscopy to assess its composition and potential for reuse or safe disposal. Additionally, the pollutant removal mechanism using aluminum electrodes was elucidated. This study provides a novel contribution by exploring a continuous-flow electrocoagulation system for pulp and paper mill wastewater treatment, an area with limited prior research, and by integrating detailed sludge characterization to evaluate treatment performance and resource recovery potential. These results underscore the effectiveness of continuous electrocoagulation for treating paper mill effluents, advancing sustainable wastewater management practices.
Abstract: The growing prevalence of emerging pollutants has spurred increasing research interest in developing novel materials for treatment. In this study, a Z-scheme Bi2MoO6/g-C3N4 (BMCN) photocatalyst was facilely synthesized via a solvothermal technique and employed to activate peroxydisulfate (PDS) under visible light irradiation. The system of the BMCN photocatalyst with 20% g-C3N4 (BMCN-20) combined with PDS under visible light irradiation (BMCN-20/PDS-Vis) achieved 89.04% ciprofloxacin (CFX) degradation within 90 min. PDS acted as an electron scavenger, suppressing recombination of photo-generated electron-hole pairs and enhancing CFX degradation via additional SO·-4 formation. The CFX degradation rate constant of the BMCN-20/PDS/Vis system was 1.33 and 2.31 times greater than those of Bi2MoO6/PDS and g-C3N4/PDS, respectively, attributed to efficient electron transfer with the Z-scheme BMCN-20. Scavenging experiments identified 1O2, O·-2, and h+ as the primary reactive species driving CFX degradation. Mass spectrometry and density functional theory analyses confirmed the degradation pathways and revealed degradation intermediates. These findings demonstrate the potential of the BMCN-20/PDS/Vis system as an effective and environmentally friendly approach for antibiotic removal from wastewater.
Abstract: Accurately estimating equilibrium scour depths at spur dikes remains challenging due to the complexity of scour around these structures. Scour critically threatens spur dikes built in river estuaries for enhancing navigability and preventing bank erosion. This study conducted 41 experiments to determine the approach flow velocity corresponding to scour initiation at a non-submerged spur dike, which enables prediction of equilibrium scour depth. The results showed that scour incipient velocity depended on spur geometry, approach flow characteristics, and sediment properties, rather than being a fixed value. A new formula for equilibrium scour depth prediction was proposed, based on the scour incipient velocity and the excess abutment Froude number, yielding a determination coefficient of 0.93. The formula demonstrated broader applicability and greater accuracy than previously reported formulas, with 98% of data within a ±25% error margin. The dimensionless sediment size was introduced to capture the effects of sediment size on scour, providing an alternative to the sediment coarseness ratio, which is challenging to replicate in laboratory settings. These findings offer valuable guidance for engineering design and protection of spur dikes under unidirectional flow.
