Search Results (328)

As variable renewable generation grows, intermittent dispatch of run-of-river hydropower plants may transfer required environmental-flow releases from turbines to spillways, creating conditions that favor total dissolved gas (TDG) supersaturation and may constrain hydropower flexibility. This study presents a reproducible basin-scale screening assessment for 24 selected hydropower plants in the Brazilian Amazon and Tocantins–Araguaia basins. The analysis combines a plant inventory, spillway typology, standardized environmental-flow scenarios, and two configuration-specific linear relationships between unit discharge and the increase in TDG saturation (ΔTDG), derived from digitized Pubugou and Gongzui observations. Two release configurations were examined: flow distributed among all available bays and flow concentrated in a single bay as a theoretical hydraulic bounding case. The Pubugou-based relationship was applied only to broadly comparable ski-jump configurations within 9.1 ≤ UD ≤ 72.3 m³ m⁻¹ s⁻¹, whereas the Gongzui-based relationship was provisionally assigned, as an inventory-level first-order analog, to controlled spillways discharging into stilling basins within 34.6 ≤ UD ≤ 234.6 m³ m⁻¹ s⁻¹. Hydraulically dissimilar cases were classified as NE-H, and cases outside the applicable empirical domain as NE-UD. Digitization sensitivity, regression uncertainty, and model-form selection were explicitly evaluated and documented. None of the distributed-flow scenarios produced a numerical estimate: cases assigned to the Pubugou- or Gongzui-based relationships were classified as NE-UD, whereas hydraulically dissimilar free-surface cases were classified as NE-H. Four single-bay scenarios produced configuration-specific $\Delta \mathrm{T}\mathrm{D}\mathrm{G}$ increments: 22.5–33.4 percentage points for three Gongzui-based cases and 13.6 percentage points for one Pubugou-based case. Upstream TDG was not added, and no plant-specific final concentration or universal ranking was reported. Sinop and Colíder observations were retained as qualitative contextual evidence of limited transferability and the importance of site-specific hydraulics. The outputs support conditional monitoring prioritization under standardized assumptions, not compliance prediction, ecological-risk assessment, or gate-operation recommendations. Synchronized monitoring and plant-specific rating curves are required before TDG-related variables can be incorporated into operational planning. Full article

Small lakes are widespread, yet their biogeochemistry, particularly regarding greenhouse gases, remains insufficiently studied. This article presents the findings from an investigation of six small lakes in the Southern European part of Russia, conducted from September to October 2024. The primary aim was to examine the coupled distribution of methane (CH₄) and sulfide sulfur (a key metabolite of H₂S) in the lake sediments, in relation to geochemical parameters such as pH, Eh, sediment density, moisture, and the contents of sulfate ions (SO₄²⁻), organic matter, and granulometric composition. The studied sediment layers, reaching depths of up to 110 cm, consist primarily of silty clay. The lakes studied represent both freshwater (0.2–0.7 g/L) and brackish (1.3–24.2 g/L) systems. During the study period, the water column exhibited temperatures of 10.4–22.1 °C, pH values of 7.36–8.53, and dissolved O₂ concentrations ranging from 3.16 mg/L (34% saturation) to 11.79 mg/L (125% saturation). Methane concentrations in the water varied widely, from 1.6 µL/L to 37,380 µL/L. The lowest values were found in the highly mineralized Lake Bolshoy Tambukan (1.6–2.0 µL/L), while exceptionally high concentrations were detected in the bottom waters of the thermally stratified freshwater Lake Staroe. In the shallow, productive freshwater lakes, a significant portion of the organic matter undergoes limited mineralization in the water column and settles to the sediments as partially decomposed remains of sand- and coarse-silt-sized organisms. The subsequent degradation of this labile organic matter reduces bottom-water oxygen, triggering intense anaerobic processes in the upper sediment layer. In these freshwater sediments, where sulfate concentrations are relatively low, sulfate reduction is typically suppressed. Combined with an abundance of labile substrates, this condition fosters intensive methanogenesis, resulting in maximum CH₄ concentrations (33–179 µg/g). Under stable thermal stratification, such high CH₄ concentrations can also accumulate in the bottom water (e.g., up to 37. 4 mL/L in Lake Staroe), posing a risk of significant pulse emissions during autumn mixing. Conversely, the brackish Lake Bolshoy Tambukan exemplifies the crucial role of sulfate reduction, which is stimulated by sulfate-dependent anaerobic oxidation of CH₄. This process acts as a powerful natural biogeochemical barrier that curtails the emission of a major greenhouse gas. The sediments of this lake exhibited minimal CH₄ content (0.14–0.57 µg/g) alongside maximal sulfide sulfur concentrations (1.06–8.57 mg/g). Overall, this theoretical and experimental analysis demonstrates that sulfate reduction is a key determinant of redox potential, acid–base conditions, and the vertical distribution of CH₄ in the anaerobic sediments of small lakes in Southern Russia. Given the projected salinization of lakes in steppe and arid landscapes under climate change, a reduction in CH₄ emissions to the atmosphere is likely due to the enhanced sulfate-dependent anaerobic CH₄ oxidation associated with sulfate reduction in the sediments. Full article

Dissolved gas analysis (DGA) is widely used for power transformer fault diagnosis, but many learning-based studies still treat gas concentrations and derived ratios as flat input features. KGRAT is positioned here as an IEC-informed graph representation with a relation-conditioned graph attention learner, rather than as a universally strong predictor. Gas, symptom, and fault entities are linked by four standards-informed relation types, and relation-conditioned attention is learned over this fixed graph. On a six-class benchmark of 589 samples evaluated with stratified 10-fold cross-validation, KGRAT achieved 0.7233 accuracy and 0.7089 Macro-F1. In this single-seed evaluation, it scored above IEC Three-Ratio, Duval Triangle, raw-feature SVM, raw-feature MLP, and a complete-graph GAT ablation; the dependent-fold Holm diagnostic supported the complete-graph contrast within that run but is not seed-robust inference. Feature-engineered tree ensembles were stronger, with GBDT using ratio/symptom features reaching 0.8283 Macro-F1. A filtered four-label Cliango/DGA evaluation is reported only as a constrained stress test over common labels, not as six-class external validation. The evidence therefore supports KGRAT as a standards-aligned, relation-level inspectable representation for DGA modeling, not as a deployment-ready diagnostic system or a substitute for stronger feature-engineered tree ensembles on this dataset. Full article

Ex situ hydrogen biomethanation represents a promising approach to converting surplus renewable electricity into CH₄-rich gas through the biological reduction in CO₂ with H₂, mediated by hydrogenotrophic methanogens. In this study, an ex situ H₂ biomethanation process was investigated in a lab-scale mesophilic anaerobic reactor operated in fed-batch mode. The system followed a cyclic operational strategy comprising sequential gas feeding, reaction, and discharge phases. Hydrogen was supplied through a pressure-controlled feeding strategy, whereas CO₂ injection maintained dissolved CO₂ concentrations at 25, 17, and 2 mg L⁻¹ during the initial, intermediate, and final stages, respectively. During early operation, volatile fatty acids (VFAs) temporarily accumulated to 3 g L⁻¹, accompanied by a decrease in pH. Progressively lowering the dissolved CO₂ target restored process stability, reduced the VFA concentration to 618 mg L⁻¹, and increased the pH to 7.6. Under stable final-stage conditions, the reactor achieved an average CH₄ concentration of 93.3%, a hydrogen utilization efficiency of 99%, and a methane evolution rate (MER) of 3.95 NL CH₄ L_VR⁻¹ d⁻¹. These results show that combining pressure-controlled hydrogen injection with dissolved CO₂ regulation enhances methane production and maintains stable ex situ biomethanation. Full article

To elucidate the geochemical features of produced water in coalbed methane (CBM) wells of the Gujiao Block and their indicative significance for production, systematic testing of ion composition and total dissolved solids (TDS) of produced water from ten CBM wells was conducted through five discrete sampling campaigns over an 18-month period. Combined with production performance data, the spatiotemporal evolution patterns, controlling factors, and the response relationship with productivity were analyzed. The results show that the water chemistry type of produced water in the study area is mainly identified as the Na-HCO₃ type. The TDS averages 1716.62 mg/L. The hydrochemical characteristics are primarily controlled by water/rock interactions, with Na⁺ and K⁺ mainly derived from silicate mineral weathering and dissolution, coupled with cation exchange processes. The Na/Cl ratio suggests that halite dissolution contributes to both Na⁺ and Cl⁻, whereas the excess Na⁺ relative to Cl⁻ likely reflects cation exchange or dissolution of Na-bearing silicate minerals. As drainage proceeded, Na⁺ and K⁺ concentrations increased, Ca²⁺ decreased, Cl⁻ increased, and SO₄²⁻ first increased and then decreased. Spatially, TDS increases from north to south, with the central-southern region representing a stagnant groundwater zone. Productivity response analysis reveals that Na⁺, HCO₃⁻, and TDS all show a trend of initially slow increase followed by rapid increase with increasing gas production. A negative trend is observed between gas production and the concentrations of Cl⁻, Ca²⁺, Mg²⁺, and SO₄²⁻. The productivity response index for the Gujiao Block ranges from 3.75 to 42.43, with an average of 17.78. As the productivity response index increases, gas production initially decreases and then increases. The findings clarify the geochemical evolution mechanisms of produced water in the Gujiao Block, providing a scientific basis for productivity evaluation of CBM wells. Full article

Oil-immersed power transformers and high voltage reactors may experience abnormal mechanical vibration during operation, especially under complex electromagnetic and load conditions. Such vibration can induce periodic pressure fluctuations in narrow oil–paper gaps, promoting bubble formation, collapse, and associated characteristic gas production. Since characteristic gases are important indicators for insulation condition assessment, vibration-induced gas generation may affect the interpretation of dissolved gas analysis and fault diagnosis. However, the gas production behavior and underlying mechanism of oil–paper insulation under combined mechanical vibration and electric field stress remain insufficiently understood. In this work, an equivalent oil–paper gap model was developed to experimentally investigate the effects of vibration parameters and electric field strength on gas generation under vibration–electric field coupling. The bubble collapse dynamics under vibration were further analyzed using a modified Rayleigh–Plesset (R-P) equation. Results indicate that the localized high-temperature region produced during bubble collapse in the positive-pressure phase of vibration initiates pyrolysis of insulating oil and paper, generating characteristic gases including H₂, CO, CO₂, CH₄, C₂H₄, C₂H₆, and C₂H₂, among which CO₂, CO, H₂, C₂H₄, and CH₄ are the dominant components under test conditions. At low electric field strength (before partial discharge inception), the additional pressure contributed by electrostatic forces intensifies bubble collapse, increasing the concentrations of H₂, CO_x, and THC by 15.9%, 7.6%, and 29.8%, respectively. At high electric field strength (after partial discharge inception), discharge-induced decomposition of oil and paper further increases the concentrations of H₂, CO_x, and THC by approximately 47.7%, 30.0%, and 44.9%, respectively. These findings provide theoretical and data support for evaluating insulation conditions and understanding failure mechanisms in oil-immersed power equipment subjected to vibration. Full article

Background: Drilling slurry, a waste material generated during natural gas extraction, requires careful chemical characterization to determine its environmental hazard classification and inform appropriate management strategies. Methods: This study characterizes the drilling fluid used as raw material and the resulting drilling slurry waste, using a case study sample from the Buzău extraction area (Well 1 Florica, S.N.G.N. Romgaz S.A.), including total composition analysis, three-stage leaching tests, linear regression of leaching kinetics, and standardized geoaccumulation indices (Igeo, CF, PLI). Results: Total composition analysis confirmed low heavy metal concentrations (Cd = 0.02, Cr = 0.05, Pb = 0.64, Zn = 2.82 mg/kg dry matter). All leachate parameters remained below non-hazardous waste thresholds (Order No. 95/2005), with safety factors of 20–100× for regulated metals and 1.2–2.7× for chlorides, sulphates, and dissolved organic carbon. Standardized pollution indices confirmed Class 0 (unpolluted) status for all five metals, with a composite Pollution Load Index of 0.0124. Leaching regression analysis revealed dissolution-controlled release for chlorides, sulphates, and zinc (R² > 0.93) versus matrix-retention behavior for copper, nickel, cadmium, and chromium. Comparative analysis showed horizontal drilling generates approximately 146% more waste volume than conventional vertical drilling (170 m³ versus 69 m³ at 2100 m depth). Conclusions: The analyzed drilling slurry meets non-hazardous waste classification with substantial safety margins, corroborated by three independent analytical frameworks. Waste minimization strategies and biodegradable fluid substitution offer practical pathways to reduce the environmental footprint of natural gas drilling operations. Full article

Natural lithium-bearing brines are gaining strategic importance as an alternative to traditional hard-rock deposits. Approximately 78% of the identified global lithium resources are hosted in hydromineral environments, including continental brines, oilfield formation waters, and geothermal fluids. The Shu–Sarysu sedimentary basin in southern Kazakhstan is one of the most extensive, yet poorly studied, brine provinces in Central Asia. This study provides a comprehensive hydrogeochemical characterization of lithium-bearing brines in the Moiynkum structural zone of the Shu–Sarysu basin, based on regional field sampling, multielement analysis, and GIS data integration. Water samples were collected from four deep gas production wells (perforation depths of 2029–2290 m) at the Ayrakty and Amangeldy fields. Analytical data demonstrate highly concentrated chloride–calcium–sodium brines with total dissolved constituent concentrations (TDS, calculated as the sum of analyzed ions) ranging from 140.1 to 272.1 g/L, with lithium content of 24.46–55.11 mg/L, strontium 680.5–1648.2 mg/L, rubidium 4.31–8.42 mg/L and cesium 0.317–0.420 mg/L. Piper and Durov diagrams classify the samples as highly evolved Na–Ca–Cl to Ca–Na–Cl formation brines typical of deep, long-residence sedimentary formation waters. Lithium enrichment is interpreted to reflect the combined influence of several processes: water–rock leaching of Li-bearing lithologies, evaporative concentration of ancestral brines, clay-mineral ion exchange, and possible deep fluid contributions, whose relative roles remain to be constrained by isotopic data. The compiled GIS-integrated database, combining new analytical data with archival hydrogeochemical records, delineates two promising lithium-bearing provinces and identifies priority areas for further exploration. The results indicate that the Shu–Sarysu Basin is a prospective region for further exploration of lithium-bearing formation waters in Kazakhstan. The recorded Li concentrations fall within the lower range of sedimentary-basin brines currently being evaluated for lithium extraction, although their economic and technological feasibility remains to be established. Full article

Tropical water lilies are a group of aquatic plants with high ornamental value and are widely favored in home gardening. However, most tropical water lily cultivars feature a large plant stature and vigorous spreading growth layout, making them unsuitable for cultivation in small containers. Therefore, developing miniaturization cultivation techniques for tropical water lilies in small containers is required. Plant growth retardants are effective in inducing plant dwarfing and overall miniaturization. In this study, the tropical water lily cultivar ‘Black Beauty’ was used as the experimental material to explore the effects of two plant growth retardants, chlormequat chloride (CCC) and paclobutrazol (PP₃₃₃), on its growth and development, with the objective of screening optimal retardant types, application concentrations and treatment methods. The results showed that the growth rate of ‘Black Beauty’ slowed down under either CCC or PP₃₃₃ treatment, and remained stable from day 21 to day 51. Compared with the control group, treated plants presented reduced crown spread, decreased leaf area and thickened leaves; the number of flowers and leaves declined slightly, and the key ornamental morphological traits (compact plant form, moderate leaf size, normal flowering) were maintained. PP₃₃₃ exhibited a stronger dwarfing effect than CCC. When the plant growth retardants were dissolved in water for application, a 6-day treatment interval delivered better dwarfing efficacy than a 9-day interval. Among all treatments, 30 mg·L⁻¹ PP₃₃₃ applied at 6-day intervals achieved the optimal miniaturization effect. Following this treatment, the endogenous accumulation of chlorophyll, soluble protein and total sugar, together with the activity levels of antioxidant enzymes (SOD, POD, CAT), were markedly higher than those measured in the control and all other treatment groups, whereas the endogenous accumulation of malondialdehyde (MDA) decreased substantially. The contents of endogenous hormones IAA, GA₃ and ZR in all treatment groups decreased with the increase in retardant concentration, whereas the ABA content showed an upward trend. The 30 mg·L⁻¹ PP₃₃₃ treatment applied every six days induced the minimal endogenous accumulation of IAA, GA₃ and ZR, alongside the maximum endogenous ABA accumulation within plant tissues. For potted cultivation of ‘Black Beauty’ water lily, it is recommended to apply 30 mg·L⁻¹ PP₃₃₃ at 6-day intervals and use containers with an outer diameter of 30–35 cm. Full article

When predicting cavitation erosion risk in practical engineering bearings, traditional vapor cavitation models neglect the effect of dissolved air in the lubricant and fail to account for its precipitation and dynamic evolution in local low-pressure regions, leading to deviations in the prediction of cavitation extent, intensity, and distribution. Taking the main bearing of a certain type of diesel engine as the research object, a coupled cavitation model combining the Schnerr–Sauer vapor cavitation model and a Henry’s law-based gas dissolution model is established. Together with large eddy simulation (LES), the accuracy of the numerical model is verified by constructing a visualization experimental platform. Numerical analysis is then carried out to investigate the effect of dissolved air in the lubricant on the cavitating flow field of the bearing oil film under initial conditions ranging from undersaturated to saturated states (air mass concentration of 0–0.4 g/L). The results show that as the mass concentration increases, the amount of air precipitation in the near-wall region gradually increases and extends downstream. When the mass concentration reaches 0.1 g/L, the precipitated air mass reaches 50% of the vapor cavitation mass, significantly expanding the cavitation range. In the critical mass concentration range of 0.24–0.28 g/L, intense air precipitation occurs inside the oil hole and covers the entire region. Through the synergistic effects of inhibiting high-speed jets, altering the local pressure field, and competing for cavitation nuclei, the precipitated air significantly suppresses the development of near-wall vapor cavitation, and the vapor cavitation mass decreases by 83.1% at saturation. In summary, within the practical mass concentration range, the presence of dissolved air significantly enhances the gas phase intensity near the bearing bush surface and expands the cavitation range, thereby exacerbating the risk of cavitation erosion damage in this region, while having little effect on the oil supply performance of the oil hole. Full article

Reliable state assessment of railway traction power transformers is challenged by heterogeneous operating environments, measurement disturbances, coupled gas-generation mechanisms, and uneven fault-sample distributions. Conventional dissolved gas analysis (DGA) ratio rules and single-model classifiers often show insufficient generalization when rare faults and boundary-ambiguous operating states are encountered. To address this issue, this paper proposes a feature-guided stacking framework for state assessment of oil-immersed railway power transformers. First, a DGA-oriented fusion-feature representation is established by combining raw gas concentrations, gas-ratio descriptors, and an aggregated dissolved-gas analysis factor. Second, DBSCAN-assisted sample structuring is introduced to identify density patterns, sparse rare fault regions, and boundary samples, thereby improving the organization of imbalanced monitoring records. Third, a monitoring-feature-embedded stacking model is developed in which heterogeneous base learners are adaptively weighted according to feature-reliability information and integrated through a cross-validated meta-learner. This synthetic-data-based validation provides a controlled and reproducible proof-of-concept. Therefore, the reported results should be interpreted as evidence of methodological feasibility. Under the default synthetic setting, the proposed feature-guided stacking (FE-stacking) method achieves an accuracy of 99.70% and a macro-F1 of 99.55%. Under the severe minority-retention setting in which only 25% of low-energy discharge (LD) and low-temperature overheating (LT) training samples are preserved, it obtains an accuracy of 99.62%, a macro-F1 of 99.40%, and an LT recall of 96.61%, slightly surpassing random forest (RF) and outperforming Original Stacking in rare fault robustness. These results indicate that feature-guided ensemble learning can improve the generalization stability of DGA-based transformer state assessment under imbalanced and boundary-ambiguous conditions. From a practical perspective, the proposed framework can serve as a decision-support module for transformer condition screening, maintenance prioritization, and alarm verification in railway traction power-supply systems. Full article

Hydraulic fracturing creates long-lasting contact between aqueous fracturing fluids and gas-bearing ultra-low permeability matrix rock, making fluid retention and dissolved-species penetration important for interpreting matrix–fracture mass exchange and post-fracturing flowback behavior. These processes are controlled by the coupled effects of capillary imbibition, fracture–matrix pressure assistance, and species diffusion, but their relative importance is difficult to distinguish through a concentration profile. This study develops a regime-adaptive pressure-assisted imbibition and species-transport framework for interpreting fracturing-fluid species movement from a hydraulic fracture into a gas-bearing porous matrix. The framework couples a pressure-assisted imbibition (PAI) model with a one-dimensional advection–diffusion equation (ADE), where the PAI-derived velocity provides the transient advective input for species transport. The same formulation continuously represents capillary-dominated, mixed pressure–capillary, and pressure-dominated behavior without switching governing equations. Three diagnostic limiting cases, Capillary-driven Advection, Pressure-driven Advection, and Diffusion-only, are introduced to compare reduced mechanism-specific responses with the Full PAI-ADE response without interpreting them as additive components of the full solution. At 100 days, the Full PAI-ADE concentration front in the Ultra-Low Matrix reached 31.9 cm at $C=0.10$, compared with 18.0 cm for Capillary-driven Advection, 9.2 cm for Pressure-driven Advection, and 21.7 cm for Diffusion-only, indicating a mixed diffusion–capillary response. For the High-Perm Matrix at 0.20 day, the Full PAI-ADE and Pressure-driven Advection fronts reached 211.6 and 210.9 cm, respectively, with a normalized profile error of 0.003, identifying a pressure-advection-dominated limiting behavior. A dimensionless mechanism-weight analysis based on the pressure–capillary ratio (${\mathsf{\Pi }}_{\mathrm{p}\mathrm{c}}$) and front-scale Péclet number (Pe) further summarizes these behaviors. The results demonstrate that the proposed framework provides a compact diagnostic tool for linking pressure–capillary driving, advective–diffusive tendency, and observable species-transport profiles in ultra-low permeability gas-reservoir applications. Full article

Ozonation is widely used in wastewater treatment, but its efficiency is often limited by the low solubility of ozone and insufficient gas–liquid mass transfer. High-gravity technology offers an effective intensification strategy by enhancing liquid-film renewal, interfacial contact, and micromixing under centrifugal fields. This review summarizes recent advances in high-gravity ozonation for wastewater treatment. The fundamental oxidation pathways of ozonation, the characteristics of typical high-gravity reactors, and recent applications in both homogeneous and heterogeneous systems are discussed. Current studies show that high-gravity ozonation can significantly improve ozone utilization, pollutant degradation, and mineralization efficiency. It was reported that the equilibrium dissolved ozone concentration and ozone decomposition rate constant in heterogeneous catalytic high-gravity systems were 2.5 and 2.6 times higher than those in conventional bubbling reactors, respectively, leading to markedly enhanced pollutant and TOC removal. These findings highlight the potential of high-gravity ozonation for intensified wastewater treatment. Despite these advances, its practical application still faces challenges related to real wastewater adaptability, byproduct and toxicity control, reactor scale-up, catalyst stability, economic feasibility, and energy demand. This review provides a useful reference for the further development and engineering application of high-gravity ozonation technology. Full article

Deep placement of nitrogen fertilizer (DPN) is an effective fertilization strategy for improving nitrogen use efficiency in rice systems, but its effects on methane (CH₄) emissions and the associated microbial mechanisms remain insufficiently understood. This study aimed to determine whether DPN mitigates CH₄ emissions in a rice–wheat rotation system and to clarify how it regulates methanogenic and methanotrophic communities. A two-year field experiment was conducted in East China with two nitrogen management practices, i.e., conventional surface application and DPN. Compared with surface application, DPN significantly reduced cumulative CH₄ emissions by 22.9% in 2023 and 17.0% in 2024, while tending to increase rice grain yield. During the tillering stage, DPN decreased soil dissolved organic carbon by 19.0% and increased NH₄⁺-N and NO₃⁻-N concentrations by 35.8% and 44.1%, respectively. These changes were accompanied by a 24.7% reduction in methanogen abundance and a 26.9% decrease in methanogenic activity. Although total methanotroph abundance was not significantly affected, DPN increased methanotrophic activity by 24.6%. Amplicon sequencing further showed that DPN shifted the methanogenic community from acetoclastic taxa toward hydrogenotrophic taxa, as indicated by the decline in Methanosarcina and Methanothrix and the enrichment of Methanobacterium and Methanoregula. In parallel, DPN promoted Type I methanotrophs, especially Methylomonas, while suppressing the Type II methanotroph Methylocystis. These results demonstrate that DPN mitigates CH₄ emissions by reducing labile carbon availability, suppressing methanogenic abundance and activity, and enhancing the functional potential of methane oxidation through methanotrophic community restructuring. Overall, this study indicates that DPN mitigates CH₄ emissions through coordinated regulation of carbon substrate availability and functional microbial community restructuring, suggesting that DPN is a promising strategy for sustainable rice production and greenhouse gas mitigation. Full article

The dynamics of methane (CH₄), nitrous oxide (N₂O) and carbon dioxide (CO₂) in groundwater have rarely been investigated. As dissolved gases they may be transported to distant sites and, hence, to the atmosphere. Crumps Cave (CC) is located on a perched aquifer in south-central Kentucky. Water was sampled at a waterfall within the cave located 15 m below the surface, at two adjacent surface wells 15 m and 50 m deep, providing samples from the epikarst and regional aquifer, respectively. Dissolved gases and geochemistry parameters were analyzed for seasonal changes across three years of weekly monitoring (2015–2017) using Kruskal–Wallis H tests and Bonferroni-corrected pairwise comparisons. Dissolved CO₂ concentrations are mainly controlled by percolation through the epikarst, influenced by soil respiration, and vary with rainfall and seasonal temperature fluctuations. CH₄ showed a site-dependent pattern: concentrations were significantly elevated in warm seasons at the shallow and deep wells, where anaerobic conditions and agriculturally derived organic matter promote methanogenesis; no seasonal variation was detected at the cave site, where oxic conditions limit CH₄ year-round. N₂O was significantly elevated in cold seasons at all three sites, driven by cold-season denitrification of agriculturally derived nitrates. N₂O did not differ between sites, indicating seasonal temperature-driven denitrification as the primary control rather than site hydrology, with cold-season denitrification of agriculturally derived nitrates from fertilizer application. Indirect gas emissions are characteristic of karst systems and may be transported or stored in aquifers through complex interactions of groundwater recharge, microbial activity, and seasonal land-use variability. Full article