Environmental and Earth Sciences

Abstract: Brackish water aquaculture provides good livelihoods for many coastal regions in the world. However, it also creates nutrient-rich wastewater that poses a risk of eutrophication if untreated. Researching the use of plants to absorb nutrients and harvest biomass is a trend of many recent studies. This study evaluated the efficiency of Sesuvium portulacastrum L. in an integrated system with Litopenaeus vannamei shrimp under a salinity gradient from 5 to 25‰. During the 28-day experiment, plant growth, shrimp performance, and nitrogen/phosphorus mass balances were assessed. Results showed that S. portulacastrum exhibited strong adaptability, with dry biomass increasing by 2.0–3.3 times. Tissue nutrient analysis showed significant accumulation capacity, with total nitrogen ranging from 19,735 to 29,433 mg kg⁻¹ DW and phosphorus from 1,099 to 1,912 mg kg⁻¹ DW. The integrated system performance was optimal at 10‰ salinity, and the system reached the highest total nitrogen removal efficiency of 46.98%. The calculated areal nitrogen removal rate achieved by this model was 383 mg N m⁻² day⁻¹. Although it is a salt-tolerant plant, high salinity (≥20‰) reduced the nutrient absorption efficiency. These findings confirm that integrating S. portulacastrum into recirculating aquaculture systems (RAS) at moderate salinity (5–15‰) is a feasible strategy to harvest plant biomass.

Abstract: Water availability is the primary environmental factor limiting plant settlement in arid and semi-arid ecosystems, and increasing drought stress due to climate change is making forest restoration efforts in the Mediterranean basin increasingly critical. The Eastern Mediterranean region of Turkey, particularly Kahramanmaraş Province, is characterized by increasingly severe drought stress resulting from low natural precipitation and rising temperatures under global warming. This study comparatively evaluates the ecophysiological responses of Ailanthus altissima (Mill.) Swingle and Crataegus orientalis Pall. ex M. Bieb. under adequate irrigation and drought-stress conditions. To determine plant water status, pre-dawn and midday leaf water potentials were measured; water use efficiency (WUE) was calculated using net photosynthesis rate, stomatal conductance, and transpiration parameters. Both species were able to maintain photosynthetic activity under drought conditions and showed higher WUE values compared to control conditions. However, significant differences in physiological adaptation strategies emerged between the species. Ailanthus altissima exhibited a water-spending strategy with rapid physiological adjustment, while Crataegus orientalis adopted a conservative water-saving strategy through pronounced stomatal regulation. Modeling results, supported by spatial drought stress indices, have shown that both species have high adaptation potential in arid and semi-arid rehabilitation areas. The findings reveal that ecophysiological characteristics play a critical role in the selection of drought-tolerant woody species and provide a scientific basis for sustainable forest restoration under climate change.

Abstract: Global climate change impacts snow and ice resources and the frequency and timing of dangerous hydrological phenomena. The article presents the results of a study of snow resource variability in Western Kazakhstan in the context of global warming. The research aims to assess the impact of global climate change on regional snow cover conditions. Statistical analysis methods were used to assess these effects. A database of snow and regional climate was collected. The statistical error of the initial data was 2-4%. It was established that snowmelt runoff from rivers mainly forms in the low-mountain areas of Mugalzhary in the north of the Aktobe region and on the Podural plateau in the north of the West Kazakhstan region. This affects the timing of the spring flood. However, these trends are not statistically significant (the coefficient of determination is 0.02-0.24) and their value is within the statistical errors. The calculated Spearman statistics prove the existence of a statistical relationship between global and regional climate indicators (correlation coefficients 0.23-0.40). Changes, but it is influenced by many local factors. This must be taken into account when planning economic activities in the region.

Abstract: The growing problem of municipal solid waste (MSW) generation presents a challenge in the efficient and scalable sorting of urban solid waste. Although deep learning models hold potential for automated waste segregation, their effectiveness is limited by the large Intra-class variance, Inter-class Similarity and Class Imbalance in some real world data. To overcome these limitations, we present a deep learning model with attention mechanisms, ResNet-CBAM, combining a ResNet-50 backbone with a Convolutional Block Attention Module (CBAM) to enhance feature representation through channel and spatial awareness. The approach is tested on the open Waste Segregation Image Dataset, which includes eight classes of biodegradable and non-biodegradable waste. To overcome the class imbalance problem, a combination of data augmentation and undersampling is applied. The findings reveal that our approach can attain an accuracy of 93.09% and an F1 score of 0.9122, surpassing some baseline approaches. The use of attention mechanisms improves the model's discriminative ability, resulting in better classification performance, especially in visually diverse environments. While minor errors still remain among visually similar classes, these results show a stable performance of the proposed model for all classes. In conclusion, the ResNet-CBAM model presents a reliable and transparent solution for waste classification, which can be further integrated into smart waste management and smart cities.

Abstract: Harmful cyanobacterial blooms are increasing in frequency and severity due to fresh-water eutrophication. This study systematically evaluated the feasibility of repurposing electrolytic manganese slag (EMS), an industrial by-product, as a functional material for controlling the bloom-forming cyanobacterium Microcystis aeruginosa. The effects of key operational parameters including EMS dosage, algal density, light, temperature, and pH on chlorophyll-a removal efficiency were systematically investigated. EMS achieved a maximum chlorophyll-a removal efficiency of approximately 83% at 2.0 g·L^⁻1, with enhanced performance under optimal light conditions and moderate temperatures. Physiological analyses revealed that EMS exposure significantly impaired photosynthetic activity by inhibiting the biosynthesis of essential pigments, concomitant with a marked reduction in dissolved oxygen evolution. Moreover, EMS treatment effectively removed total phosphorus and nitrogen from the water and promoted algal sedimentation without significant cell lysis. Notably, the treatment mitigated secondary pollution risks by stabilizing extracellular microcystin-LR levels and reducing intracellular toxin concentrations over time, while limiting the release of extracellular organic matter. Together, these results demonstrate that EMS can effectively remove M. aeruginosa without compromising water quality, validating its potential as a sustainable waste-to-resource strategy for cyanobacterial bloom control.

Abstract: Inner Mongolia is the dominant spring wheat production area in northern China and a core commodity grain supply base. Against the background of global warming, mete-orological disasters, such as drought, dry-hot winds, and frost, are occurring more frequently and with increasing overlap, posing a threat to stable spring wheat produc-tion. This study covers the period 1961–2020 and draws on observational data from 107 meteorological stations alongside agricultural and socioeconomic data. Using the Standardized Precipitation Evapotranspiration Index, dry-hot wind index, and frost index, we constructed a reginal disaster index system encompassing drought, dry-hot winds, and frost. Comprehensive risk assessment and zoning were conducted across four dimensions: hazard, exposure, vulnerability, and disaster prevention and mitiga-tion capacity. The results showed that: (1) Temporally, the study area exhibited a sig-nificant warm and dry trend, with intensifying aridification across all growth periods and an abrupt change concentrated in the 1990s. The occurrence range of dry-hot wind trended upward, while that of frost trended downward. (2) Spatially, the comprehen-sive hazard presented a pattern dominated by drought-dry hot wind in the west, drought-frost in the east, and multiple disasters overlapping in the central part. (3) High exposure occurred in major production areas, such as eastern Hulunbuir, Xing'an League, and Bayannur, while vulnerability followed the pattern central part > eastern > western regions. (4) Comprehensive risk analysis showed that sub-high and high-risk areas were concentrated in central Xilingol League and parts of Hulunbuir, whereas low- and sub-low-risk areas occurred in irrigated agricultural regions west of Baotou. The zoning results were consistent with the spatial distributions of yield reduction rate and vulnerability. This study clarifies the spatiotemporal evolution and risk differen-tiation mechanisms of meteorological disasters affecting spring wheat in Inner Mon-golia, providing a scientific basis for disaster prevention, mitigation, and cli-mate-adaptive spring wheat production.

Abstract: A capacity analysis report (CAR) is an essential document that assists public water system owners in prioritizing water infrastructure and resources for future capital improvements. The United States Environmental Protection Agency states that public water systems should develop a CAR when average daily production approaches or exceeds a certain percentage of the system design capacity. Different states have different CAR requirements; this report is a guide for developing a CAR for drinking water facilities based on State of Florida requirements. This document will also demonstrate how to use a water demand time series predictive model to forecast future demand. An illustration of how to develop two models is provided. Both models use time as the predictor/independent variable and water demand/consumption as the dependent variable. The first model uses full data to determine the linear regression equation, while the second model uses partitioned data to develop the linear regression equation. The model with the lowest Mean Absolute Error (MAE) is selected for future demand predictions. City of Fort Myers Water Treatment Plant data was used to demonstrate how to develop a CAR and demand forecasting models.

Abstract: The Tomarrazón-Camarones River (La Guajira, Colombia) is characterized by frequent, widespread flooding and, anthropogenically, by intense instream sediment mining. Mapping flood hazard is hence essential to develop effective flood management plans; and a knowledge of the water regime (duration curves) is also essential to estimate sediment transport and carry out sediment budgets to inform on the impacts and sus-tainability of the mining activity. However, neither water levels nor discharges are monitored by official gauging stations, and only a few rainfall gauging stations are available in the area, with daily records often affected by data gaps. Therefore, a first challenge is to reconstruct flowrate time series by an affordable effort, scaled to the fi-nancial-labor resources available in that challenging context. This paper presents an integrated approach that combines satellite-derived rainfall data with ground observa-tions. A semi-distributed hydrological model (HEC-HMS) is used to reconstruct the full flow-rate time series once calibrated and validated with data derived from automatic sensors and field measurements. The model is fed with hourly data derived from daily data at ground gauging stations temporally downscaled by adopting the spatially dis-tributed hourly rainfall patterns obtained from satellite records. Before that, observed water levels in three stations equipped with water level sensors are to be traduced into discharge time series using analytical relationships based on field-measured geometric and physical characteristics. Then, these event-based hydrographs are used to calibrate and validate the model. Results show good agreement with observations, supporting a reasonable confidence in the approach. The calibrated model is then applied to long term datasets to retrieve duration curves and return periods of peak discharges.

Abstract: The desert-oasis ecotone is a critical ecological buffer in arid regions, and its evapo-transpiration (ET) process is vital for local water cycling and ecosystem stability. However, due to sparse meteorological stations and the coarse spatial resolution of satellite remote sensing, traditional methods struggle to accurately capture the highly heterogeneous spatial patterns of ET in these transition zones. This study focuses on typical desert-oasis ecotones in the Hexi Corridor and proposes a novel method for high-resolution ET estimation by integrating unmanned aerial vehicle (UAV)-based thermal infrared remote sensing with a Three-Temperature (3T) model. A UAV equipped with a thermal infrared camera was used to acquire land surface tempera-ture (LST) data at meter-scale resolution. Combined with meteorological data and vegetation parameters, the 3T model was constructed and solved to produce high-precision ET maps. The model's performance was validated spatially against the Surface Energy Balance Algorithm for Land (SEBAL) model and at the point scale against a two -source model. The results show that: 1) The 3T model effectively cap-tured the spatial gradient of decreasing ET from cropland, through shelterbelts, to de-sert areas, with ET values ranging from 0.12 to 10.69 mm d⁻¹; 2) The model performed well in validation, with coefficients of determination (R²) of 0.80–0.98, indices of agreement (IOA) of 0.83–0.99 against SEBAL, and a mean absolute error of 0.38 mm d⁻¹ against the two-source model; 3) The model performed best in cropland areas (R²=0.92, RMSE=0.24 mm d⁻¹), while a slight overestimation was observed in structurally com-plex shelterbelts. This study demonstrates the effectiveness of combining UAV thermal infrared data with the 3T model for high-resolution ET simulation in complex ecologi-cal transition zones, providing a reliable technical approach for detailed ecohydrolog-ical monitoring and optimized water resource allocation in arid regions.

Abstract: Groundwater is a critical freshwater resource in the western Himalaya, where increasing anthropogenic pressure and environmental variability are raising concerns regarding groundwater quality and water security. However, regionally integrated assessments of groundwater-quality variability across the western Himalayan states remain limited. This study evaluates groundwater quality across Jammu & Kashmir, Himachal Pradesh, and Uttarakhand using groundwater-monitoring data obtained from the Central Ground Water Board (CGWB). A total of 338 observation-well samples collected during 2019–2022 were analysed using the weighted arithmetic Water Quality Index (WQI) based on Bureau of Indian Standards (BIS) and World Health Organization (WHO) drinking-water guidelines. Spatial and temporal variability were examined through hydrochemical, correlation, and geospatial analyses. The results reveal substantial regional and district-level variability in groundwater quality across the western Himalaya. Groundwater in Himachal Pradesh and Uttarakhand is predominantly classified as “Excellent” to “Good”, whereas Jammu & Kashmir exhibits greater hydrochemical variability and localized groundwater deterioration. Elevated WQI values are concentrated within foothill and valley-transition districts, while high-altitude recharge zones maintain comparatively lower WQI values. Hydrochemical analyses indicate that groundwater-quality variability is primarily associated with mineralization processes, lithological control, and localized anthropogenic influence. Temporal trends further indicate moderate groundwater-quality improvement between 2019 and 2022, particularly in parts of Jammu & Kashmir. Overall, the findings demonstrate that western Himalayan aquifers retain considerable hydrogeological resilience, although localized deterioration is increasingly evident within densely populated and land-use-intensive environments. Strengthened groundwater monitoring and recharge-zone protection are therefore essential for sustaining long-term water security in this climate-sensitive mountain region.

Abstract: Biochar, a carbon-rich material produced through pyrolysis of biomass under limited oxygen, offers a potentially sustainable and cost-competitive solution (qualitative assessment; quantitative LCA and techno-economic data are beyond the scope of this review) for the removal of heavy metals from wastewater. Its high porosity, surface area, and surface functional groups enable diverse adsorption mechanisms including complexation, ion exchange, and precipitation. Feedstock selection and production parameters critically influence biochar’s physicochemical properties and adsorption performance. Modification techniques such as chemical functionalization, metal impregnation, and composite formation enhance removal efficiency and selectivity for specific contaminants. Applications span industrial, municipal, and agricultural wastewaters, addressing multicontaminant challenges under variable environmental conditions. Factors affecting removal efficiency include pH, temperature, contaminant concentration, and competing ions, while regeneration methods are essential for maintaining long-term functionality and are discussed. Biochar can be reused and regenerated using bases and acids, but environmental risks related to biochar use, including potential contaminant leaching and ecological impacts, require careful management and regulatory compliance. Future research should focus on novel modification strategies, scaling production for industrial use, and optimizing integration within treatment systems to meet stringent discharge standards and promote sustainable water management.

Abstract: Schoenoplectus californicus is a dominant freshwater wetland macrophyte with ecolog-ical, technological, and biocultural importance. This review synthesizes its ecological functioning and environmental applications through a systematized analysis of 44 studies screened by title, abstract, and full text. The literature was classified into seven thematic categories: water treatment and phytoremediation; wetland ecology, biomass, and ecosystem functioning; functional ecology, growth, and landscape connectivity; morphology, anatomy, and functional adaptation; biocultural dimensions, sustainable construction, and technological applications; nutritional and ethnobotanical uses; and cultural heritage and traditional management. Research was concentrated mainly in water treatment and phytoremediation (12 studies, 27.3%) and wetland ecology, biomass, and ecosystem functioning (10 studies, 22.7%). Functional ecology, growth, and landscape connectivity represented 4 studies (9.1%), while morphology, anatomy, and functional adaptation represented 3 studies (6.8%). The remaining three categories each included 5 studies (11.4%). Across these themes, S. californicus was associated with contaminant removal, metal tolerance, bioindication, phytostabilization, biomass production, habitat structure, biodiversity support, carbon-related functions, ecological plasticity, sustainable construction, technological applications, nutritional uses, ethnobotanical relevance, and biocultural value. Overall, S. californicus emerges as a multifunctional wetland species requiring interdisciplinary research.

Abstract: Floods triggered by intense precipitation represent one of the most significant natural hazards affecting Mediterranean regions, where complex terrain, rapid hydrological response and increasing urbanization can amplify flood impacts. This study presents a flood hazard assessment for two representative Eastern Mediterranean catchments: the Koiliaris River Basin in Crete-Greece and the Pediaios River Basin in wider Nicosia region in Cyprus. A composite Flood Hazard Index was developed by integrating three indicators representing key drivers of flood generation: the Topographic Wetness In-dex describing terrain-driven water accumulation, the Curve Number representing runoff potential, and the R20 precipitation frequency index. Spatial datasets including EU-DEM elevation data, CORINE land cover, European soil databases and precipita-tion information from the Copernicus CERRA reanalysis were used to derive the indi-cators. Each indicator was classified using the Natural Breaks method and combined through a weighted multi-criteria approach based on the Analytic Hierarchy Process. The resulting maps identify high-susceptibility areas mainly along river corridors and low-lying zones with high runoff and accumulation potential. Higher hazard levels occur in downstream areas of Koiliaris and urbanized zones of the Pediaios basin, par-ticularly around Nicosia. Historical flood events were also analyzed to validate the index and examine links between rainfall intensity and impact severity.

Abstract: The Aral Sea crisis has severely impacted water resources in the Republic of Karakalpakstan, making groundwater a critical alternative source for drinking and irrigation. This study presents a hydroecological assessment of brackish groundwater in the Karauzyak district based on field investigations conducted in 2025. Results showed that groundwater mineralization ranges from 2.1 to 4.8 g/L (predominantly 2.2–3.8 g/L), classifying the water as brackish to highly brackish. The dominant hydrochemical type is sodium-chloride and mixed sodium-sulfate-chloride. Most samples exhibited pH values of 7.1–8.3, moderate to high hardness (6.5–26.5 mg-eq/L), and elevated sulfate and chloride levels. Concentrations of toxic microelements (Pb, Cd, As, Hg, etc.) remained below maximum permissible limits. However, the overall salinity significantly restricts direct use for drinking water supply and limits agricultural application without additional management. Piper diagram analysis revealed distinct hydrochemical facies, reflecting the influence of natural salinization processes, irrigation seepage, and evaporative concentration under arid conditions. The findings highlight both the potential and limitations of local groundwater resources and underscore the need for desalination technologies, improved drainage, and continuous monitoring to ensure sustainable use in the Aral Sea region.

Abstract: The cross-border Lima River Basin, shared between Portugal and Spain, is prone to recurrent meteorological droughts, which are projected to intensify under climate change. This trend underscores the need for robust early-warning systems to support proactive water management. Under the EU-funded RISC_PLUS project—aimed at strengthening resilience to hydro-climatic risks in the cross-border Minho–Lima River Basins—this study develops a regionalised forecasting framework to evaluate meteorological drought forecast skill using precipitation forecasts from the European Centre for Medium-Range Weather Forecasts (ECMWF) Seasonal Forecasting System 5 (SEAS5) for the Portuguese section of the Lima River Basin. The 12-month Standardized Precipitation Index (SPI12) is employed as a long-term drought indicator, computed from hybrid 12-month accumulations that combine observed monthly precipitation (October 1979 to February 2025) and SEAS5 forecasts (October 2018 to February 2025). These data are integrated into four hybrid configurations (1 to 6 months lead time) to maximise forecast skill while preserving observed drought memory: 11 months of observations plus 1 month of forecast (11 obs + 1 fcst), 10 obs + 2 fcsts, 9 obs + 3 fcsts, and 6 obs + 6 fcsts. Forecast performance is assessed over the period October 2018 to February 2025. Deterministic SPI12 forecasts and categorical drought classifications are evaluated using a suite of regression-based metrics (e.g., Pearson correlation, root mean square error (RMSE), and skill scores) and contingency-table-based metrics (e.g., false alarm rate (FAR) and F1-score), across SEAS5 ensemble members, percentiles, and spread-based indicators. The 11 obs + 1 fcst configuration, particularly when using the Dry Spread (SpD; defined as the Q10 + Q25 percentiles) and the Q75 percentile, exhibits the highest skill, achieving a Pearson correlation coefficient of r=0.97, an RMSE of approximately 0.17, and near-perfect categorical performance (probability of detection (POD) = 1.00; FAR = 0.00). Conversely, longer lead-time configurations (9 obs + 3 fcsts and 6 obs + 6 fcsts) exhibit degraded performance, with the 6 + 6 configuration providing limited added value relative to climatology. These results demonstrate that SEAS5 precipitation forecasts can provide skilful drought predictions at lead times of up to six months in the Lima River Basin when integrated within the SPI12 framework. The proposed blending methodology therefore provides a robust technical basis for the operational early-warning system being developed under the RISC_PLUS project to support transboundary drought risk management in the Minho–Lima region.

Abstract: One of the most common dynamic phenomena occurring in surface waters is the transport of soluble and insoluble contaminants from various sources (e.g., industry, agriculture). A key concern associated with this transport is the rate at which contaminants migrate downstream to a point of interest, as well as their overall impact. To characterize contaminant transport in a surface water body (in this case, a river), this study applied a one-dimensional advection-dispersion model incorporating transient storage effects. This allowed for the characterization of nutrient transport, considering varying flow velocities along the river’s course. This work adopts a more comprehensive, or systemic, approach to enable a more holistic environmental application, facilitating parameterization of a considerably larger river than previous case studies. The novelty of the model lies in the use of conventional pollutants as potential tracers that allow characterizing the mixing conditions and pollutant transport in surface water streams, as well as in its dynamic nature, which provides a reasonable approximation of the real system’s behavior over time. Finally, for management purposes, the proposed model is replicable without the need for extensive changes, which may be required in its fundamental structure.

Abstract: Tropical mid-size cities on alluvial floodplains face compounded flood challenges com-bining pluvial accumulation from intense convective storms, regulated river overflow, and aging drainage networks. This study presents an integrated framework for Mon-teria, Colombia (~450,000 inhabitants; Sinu River, Caribbean lowlands), within Colom-bian Decree 1807/2014 and structured in four phases. (1) Hazard: a Rain-on-Grid 2D HEC-RAS 6.6 model covering 4,090 ha, calibrated against four gauged events, identifies three dominant pluvial mechanisms (poor hydraulic connectivity, limited evacuation capacity, downstream channel overflow), plus 17 critical fluvial erosion points affecting ~289 properties at 100-year return period. (2) Vulnerability: depth-damage functions from 1,465 household surveys yield 36.36% of 3,015 assets in high risk, 57.77% in medium risk. (3) Measures: scenario M2 (channel widening plus dikes, land-raising, retention lagoons) removes 80 ha of flooding while displacing 28 ha at COP 845 million pre-design cost. Non-structural measures include a Sustainable Urban Drainage Master Plan, IoT-based Early Warning System, minimum construction-elevation map, and land-management instruments. A Monte Carlo residual-risk model reduces baseline risk to 19.9% under full implementation. (4) Emergency: a February 2026 cold-front event was addressed with a 4,300 m perimeter dike and six pump stations deployed jointly by the Regional Environmental Authority (CVS) and Municipal Administration.

Abstract: Microplastics, plastic particles smaller than 5 mm in size, have become a contaminant of priority concern in the environment. Microplastic pollution is a significant environmental challenge, highlighting the need for improved water treatment methods. This study investigates the removal of two fractions of polyurethane microplastics ranging in size from smaller than 100 µm, D1, and in range 200 µm - 500 µm, D2, from aqueous synthetic solutions having a concentration of 0.2 g/L, around 175 NTU. In the first stage of the study, tests were performed to identify the optimal doses of efficient reactive agents for microplastic removal, using the classical method: the Jar test. At this stage, attention was directed towards analyzing the variation of turbidity and their removal efficiency in the presence of classical coagulants such as aluminum sulfate, SA, ferrous sulfate, SF, aluminum polychloride, PA; aloe vera flocculant; and activated carbon, CA of the Norit GAC 830 W type. The classical coagulants such as aluminum sulphate, ferrous sulphate have a good efficiency on microplastic removal, which can provide a residual turbidity in range of 6-10 NTU after a retention time of 50 - 60 minutes. In the second stage of the study, the efficiency of smart decantation-filtration system, DFS, was determined. The efficiency of decanter was studied using Response Surface Methodology (RSM) for identification of the mathematical models necessary to evaluate the effects of key process variables: Flow rate (A), Microplastic size (B), and Aluminum sulphate concentration (C) on microplastic removal efficiency. The sedimentation can raise the optimal value of 98.98 % at the outlet of the decanter. Microplastics in D1 and D2 sized synthetic solutions can be removed from contaminated water by decantation and filtration, the efficiency is around maximum permissible limit, MPL, values of 1 NTU.

Abstract: This study presents a sodium alginate/chitosan/activated carbon (SA/CS/AC) gel microspheres loaded with citrus peel allelochemicals for continuous inhibition of Microcystis aeruginosa by controlled release. Preparation parameters were optimized via response surface methodology (RSM) for improved algal inhibition, yielding an optimal formulation: 1.97% SA, 0.76% CS, 0.31% AC. The optimized gel microspheres showed a 7-day inhibition rate of 85.17 ± 2.49%, consistent with the predicted 85.29%. Characterization revealed that AC enriched the gel’s porous structure and surface functionality, increasing allelochemical adsorption sites, enhancing loading efficiency, and sustaining long-term release with a 25-day cumulative release of 70%. Algal inhibition declined slightly from day 7 to 30 due to allelochemical depletion but remained 76.27%, versus 30.58% for the blank SA/CS/AC carrier and 52.81% for the allelochemical-loaded SA/CS gel microspheres. AC thus synergistically strengthens algal inhibition by elevating allelochemical loading and prolonging activity, providing a feasible strategy for sustainable cyanobacterial bloom control.

Abstract: Constructed wetlands offer sustainable, decentralized solution for wastewater treatment and reuse in Morocco. This study evaluates and compares four advanced vertical flow constructed wetlands (AVFCWs) incorporating locally sourced reactive media, to evaluate phosphate mining residues as a novel substrate. AVFCWs were designed with different substrate combinations, of pozzolan, phosphate mining residues (CW-B), clay (CW-C), and biochar (CW-D), alongside a control system (CW-A). The systems were operated under hydraulic retention times (HRTs) of 24, 48, and 72 hours corresponding to phase I, II and III respectively. Key water quality parameters in domestic wastewater were monitored, and evapotranspiration driven water losses were quantified. The results revealed that the use of reactive media significantly improved treatment efficiency, with CW-D achieving high removal efficiencies across most parameters. COD and TSS removal reached 80% and 88% respectively at 48h HRT, while nitrogen removal exceeded 82% in optimal configurations. CW-B achieved 76% phosphorus removal at 24h HRT, reaching 88% for CW-C at 72h. All AVFCWs exceeded 85% removal for heavy metals (Cu and Cd), with phosphate residues facilitating metal removal. On the other hand, faecal coliforms reached 3 Log reduction at an HRT of 24 h and decreased in subsequent phases, nevertheless exceeding Moroccan reuse limits. Extending hydraulic retention time improved the AVFCWs performance, but increased water loss (up to 28% at 72h) due to pronounced evapotranspiration in semi-arid to arid regions. Although all substrates demonstrated high performance, phosphate mining residues emerge as promising substrate pending further optimization, supporting circular economy objectives.