Search Results (534)

Soil organic carbon (SOC) responds rapidly to vegetation changes, and exploring SOC sequestration mechanisms under different vegetation types is critical for optimizing wetland carbon sink functions. This study investigated the abiotic and biotic mechanisms driving SOC stability across four typical vegetation types (reed marsh, woodland, farmland, and wasteland) in the 0–10 cm and 10–20 cm soil layers of Hengshui Lake wetland. Results showed that reed marshes exhibited the highest total organic carbon (TOC) and particulate organic carbon (POC), owing to anaerobic soil conditions and stable macroaggregate physical protection. Woodlands accumulated higher dissolved organic carbon (DOC) and microbial biomass carbon (MBC) via an efficient microbial carbon pump, despite weaker aggregate stability. In contrast, farmlands and wastelands presented intense labile organic carbon (LOC) turnover and enzymatic decomposition, accelerating SOC mineralization and carbon dissipation with poor carbon sequestration capacity. Proteobacteria and Acidobacteriota dominated bacterial communities, while Ascomycota prevailed in fungi. Soil water content (SWC) and bulk density (BD) were the core drivers of microbial community succession, and fungi were more sensitive to vegetation changes. Conclusively, distinct vegetation types shape divergent SOC sequestration pathways. This work provides a theoretical basis for wetland restoration and regional carbon sink enhancement. Full article

This study assessed the performance of three microfiltration (MF) membrane modules: M1 (spiral, polyvinylidene fluoride), M2 (capillary, polypropylene), and M3 (capillary, α-Alumina) in treating backwash water from utility-scale surface water (SW) and infiltration water (IW) plants, each with a capacity of approximately 100,000 m³/day. Considering 168 h (one-week) filtration cycles, the membranes were evaluated for permeate flux, turbidity removal, dissolved organic carbon (DOC) removal, and reduction in total number of microorganisms (TNM). In contrast to most previous studies that have primarily examined surface water sources under laboratory conditions, this research contributes to the literature by evaluating membrane performance using actual backwash water from both SW and IW treatment plants. The comparative assessment of three structurally and materially distinct membrane modules under identical flow-through conditions yields new insights into the trade-offs among hydraulic performance, contaminant removal, and treatment cost. Logarithmic models fitted to permeate flux data yielded determination coefficients (R²) ranging from 0.60 to 0.99, supporting the prediction of early-stage performance. No consistent trend in flux decline was observed, mainly due to fluctuations in the water bacterial load. With a median TNM removal efficiency of 97%, M1 outperformed M2 and M3 (84% and 70%, respectively) in terms of microorganism removal. The effectiveness of DOC removal generally depended on the type of backwash water; the highest efficiency was observed for M2 in the case of backwash from IW treatment and for M1 in the case of backwash from SW treatment. M2 provided the highest permeate flux rates, regardless of water type or operational limitations. The ceramic membrane (M3) exhibited the greatest variability in hydraulic performance and removal efficiency, depending on the type of backwash water. A simplified cost analysis over two filtration cycles found that treatment costs were generally higher for SW backwash, with differences reaching up to 90% between membrane-water type combinations. Although treatment costs are higher than those for raw water treatment, the increasing water scarcity makes it a potential additional source of safe water. Full article

Expanded polystyrene litter in marine environments harbors diverse and distinct microbial communities, referred to as the plastisphere. This study aimed to investigate the monthly dynamics of bacterial and potentially pathogenic bacterial (PPB) communities on expanded polystyrene over one year. Vibrio species dominated the PPB community, cooccurring at consistently higher abundances on expanded polystyrene than in the surrounding seawater, particularly under higher temperatures and low dissolved organic carbon (DOC) levels. At a temperature threshold of 16 °C, the abundance of zoonotic species, such as Vibrio parahaemolyticus and Vibrio alginolyticus, increased significantly. Some psychrotrophic Vibrio spp. were detected under moderately eutrophic conditions, suggesting that expanded polystyrene may also serve as a dispersal vector facilitating their transport to more favorable habitats. Multivariate analyses, including partial least squares path modeling, revealed temperature and DOC as the primary environmental factors influencing PPB community composition. However, environmental responses varied by taxonomic groups, with different preferences observed under varying eutrophic conditions. In conclusion, these findings demonstrate that expanded polystyrene litter supports a selective and environmentally responsive bacterial population, highlighting the potential role of plastic debris in promoting pathogenic bacterial persistence and spread in marine ecosystems, particularly under conditions associated with climate change, including warming and eutrophication. Full article

To investigate how steam-explosion pretreatment affects humification during sawdust composting, an aerobic composting experiment was conducted using sawdust, chicken manure, and spent mushroom substrate as feedstocks. Two treatments were established—a steam-explosion-pretreated sawdust group (SEW) and an untreated sawdust control (CK)—each with three replicate reactors. Samples were collected dynamically at five key composting stages (initial, heating, thermophilic, cooling, and maturation) for physicochemical, enzymatic, and microbial community analyses. Linear mixed-effects model analysis revealed that enzyme activities were significantly affected by treatment, composting time, and their interaction. SEW significantly enhanced cellulase and polyphenol oxidase activities, and increased laccase and peroxidase activities at specific stages. Compared with CK (humic substances, 75.30 g/kg), SEW promoted higher humic substance accumulation (120.80 g/kg) and altered the dynamics of dissolved organic carbon. Microbial co-occurrence networks in SEW (50 nodes, 602 edges) were more complex than CK (49 nodes, 464 edges), indicating tighter microbial interactions. Path analysis revealed that HS in CK was mainly influenced by DOC and temperature, while HS in SEW was associated with enzyme activities, microbial diversity, and Pseudogracilibacillus. These results suggest that steam-explosion pretreatment enhances substrate transformation and humic substance formation during composting. Full article

Soil health is critical for the sustainability of tropical plantation ecosystems, However, the ecological factors driving productivity gradients remain inadequately understood. This study investigated rubber plantations on Hainan Island with varying yield levels to assess soil health and its underlying ecological mechanisms using a minimum data set (MDS) approach. Twenty-seven soil physical, chemical, and biological indicators were analyzed at two depths (0–20 cm and 20–40 cm). Principal component analysis identified seven key indicators for the MDS: soil organic matter (OM), alkaline-hydrolyzable nitrogen (AN), cation exchange capacity (CEC), dissolved organic carbon (DOC), microbial biomass phosphorus (MBP), acid phosphatase activity (ACP), and microbial diversity (Shannon-Wiener index, SHDI). The soil health indices derived from the MDS showed strong correlations with those generated from the total data set (TDS) (p < 0.001), confirming the reliability of the MDS framework. Overall, soil health levels were rated low to moderate with no significant differences across low-yield plantations (≤900 kg·ha⁻¹), medium-yield plantations (900–1200 kg·ha⁻¹), and high-yield plantations (≥1200 kg·ha⁻¹)., suggesting a decoupling of soil health and rubber productivity under uniform management practices. Random forest analysis identified microbial-driven phosphorus cycling, particularly MBP and ACP, as the primary determinant of soil health across soil layers, with DOC and SHDI also contributing significantly. These findings highlight the critical role of microbial-mediated nutrient cycling in maintaining soil health in rubber plantations and suggest that current management practices prioritize short-term yields over long-term soil ecological stability. Enhancing microbial activity and increasing organic matter inputs may be essential for improving soil health and ensuring the sustainability of rubber production in tropical agroecosystems. Full article

Soil organic carbon (SOC) responses to straw return are strongly influenced by active carbon dynamics and extracellular enzyme responses, yet how these processes vary with initial SOC status and long-term straw-return history remains unclear. To address this question, we conducted a controlled incubation experiment using soils from long-term straw removal (CK) and straw return (SR) plots at two sites with contrasting SOC levels: a carbon-poor fluvo-aquic soil in Quzhou (QZ) and a carbon-rich black soil in Gongzhuling (GZL). Three fresh-straw input levels were imposed, and CO₂ release, SOC, labile C and N pools, extracellular enzyme activities, and ecoenzymatic stoichiometry were determined. Fresh-straw input markedly stimulated carbon mineralization in both soils, but SOC responses differed substantially. In QZ, SOC increased 12.1–15.7% at day 7 (vs. T0) and remained 6.7–12.1% above the control at day 90 under the long-term straw-return background. In contrast, GZL showed only minor early SOC responses, and doubled straw input reduced SOC 4.9–9.5% at day 90 despite a stronger dissolved organic carbon (DOC) pulse and greater cumulative CO₂ release. Enzyme responses also differed between soils: higher straw input in QZ enhanced β-cellobiohydrolase (CBH), β-xylosidase (BX), and especially L-leucine aminopeptidase (LAP), accompanied by lower ecoenzymatic C:P and higher vector angle, whereas GZL showed later activation of CBH, BX, and NAG with only slight changes in vector angle. Overall, our results indicate that initial SOC status and long-term straw-return history jointly regulate whether fresh-straw input promotes net SOC accumulation or enhanced mineralization. Full article

Enhancing soil nutrient content is fundamental to the ecological restoration of degraded soils. The application of microalgae represents a sustainable approach for soil remediation, as it contributes to environmental CO₂ sequestration while recycling nutrients into degraded ecosystems. Through a 105-day laboratory incubation experiment, this study investigated the impact of applying a mixed microalgal suspension containing active/inactive Chlorella ZJ and Anabaena azotica on the C and N fractions of an alkaline, degraded purple soil. The results showed that both active and inactive microalgae treatments (AM and IM) significantly decreased soil pH and increased soil moisture content (SMC). The AM treatment notably increased the proportion of large soil aggregates and enhanced soil structure. Both treatments significantly enhanced soil C and N fractions: dissolved organic carbon/nitrogen (DOC/DON) increased by 6.41/5.81 times (AM) and 4.22/4.76 times (IM) that of the control (without microalgae application); total organic carbon (TOC) rose by 147.07% (AM) and 138.73% (IM); and the contents of coarse particulate and mineral-associated organic C and N were also significantly elevated. Total nitrogen (TN) significantly increased only under the AM treatment. Soil C and N mineralization capacities were enhanced by 1.01–1.34 times and 7.56–8.43 times that of the control, respectively, indicating a more pronounced stimulation of N mineralization. Fluorescence analysis revealed that both AM and IM treatments increased the complexity and humification of dissolved organic matter. The application of microalgae significantly improved the soil structure and chemical characteristics of the degraded soil and enhanced the C/N pools, thereby creating favorable conditions for soil restoration. Full article

Successive cropping frequently causes a decline in Chinese Fir (Cunninghamia lanceolata) biomass, a problem intricately tied to soil nutrient shifts and microbial processes. This research investigates the mechanisms governing biomass carbon partitioning and soil nutrient shifts in these plantations. This study investigated five Chinese Fir clones (‘ck’, ‘b44’, ‘K13’, ‘F13’, and ‘kt13’) across two cultivation regimes: continuous cropping (second-generation plantation, G2) and first-generation plantation (G1). The focus was on their biomass and soil nutrient status. The results showed that: (1) The biomass of different Chinese Fir clones at 25 years of age decreased significantly with increasing generations of continuous cultivation. Tree height showed no significant differences among clones within the same generation; however, the G2 cultivation significantly inhibited diameter at breast height (DBH). (2) The changes in soil nutrients and microbial activity under different successive generations (G1, G2) was closely linked to the decline in Chinese Fir biomass carbon. Analysis revealed that the decreases in dissolved organic carbon (DOC), dissolved organic nitrogen (DON), and Catalase (CAT) activity were significantly positively correlated with the reduction in biomass carbon. Concurrently, the decrease in soil pH showed a significant negative correlation with microbial biomass carbon (MBC) and Sucrase (SUC) activity. (3) Regarding growth traits, although tree height showed no significant differences among clones within the same generation, DBH was generally and significantly inhibited under G2 cultivation. An exception was the ‘K13’ clone, which remained largely unaffected. In terms of carbon accumulation, G2 cultivation led to a universal decline in biomass carbon across clones; however, the magnitude of reduction in different components (leaf, branch, stem, root) and total biomass carbon varied clone-specifically. Notably, ‘K13’ exhibited the strongest tolerance, with a significantly smaller decrease in tree biomass carbon compared to the other four clones, which showed substantially lower tree carbon stocks across all components relative to G1 plantations. This indicates that successive cropping of Chinese Fir likely constrains the carbon sequestration capacity of plantations by altering soil nutrient properties, thereby suppressing tree DBH growth and biomass carbon accumulation, likely through reduced net primary productivity. Among the five clones, ‘K13’ was the least affected, demonstrating its high potential for adaptation to continuous cultivation. These findings provide implications for sustainable forest management by guiding clone selection to mitigate productivity decline under successive cropping. Full article

The comprehensive analysis of stable carbon isotopes in dissolved organic carbon (δ¹³C-DOC) and dissolved inorganic carbon (δ¹³C-DIC) is essential for understanding carbon cycling in groundwater systems. This study evaluated the performance, stability, and accuracy of a Total Organic Carbon analyzer coupled with Cavity Ring-Down Spectroscopy (TOC-CRDS) for the determination of δ¹³C-DOC and δ¹³C-DIC. Long-term stability tests using solid standards (acetanilide) demonstrated an average precision of 0.21‰ over five days, though initial instrument stabilization was found to be critical. Systematic sensitivity experiments revealed a strong dependence of isotopic accuracy on carbon mass. For liquid samples, a minimum carbon threshold of 50 μg C (equivalent to 6.25 mg/L DOC in an 8 mL injection) was established; above this threshold, analytical precision consistently remained better than 0.3‰. Validation using synthetic samples showed excellent agreement between measured and calculated values for both DOC and DIC. Furthermore, comparative analysis of natural groundwater samples revealed that TOC-CRDS results were highly consistent with those obtained by GasBench–Isotope Ratio Mass Spectrometry, with relative deviations within 5% for DOC and 6% for DIC. The study confirms that TOC-CRDS provides a robust, high-precision (<0.3‰), and cost-effective alternative to mass spectrometry for analyzing groundwater carbon isotopes, provided that sample carbon content exceeds the determined thresholds and appropriate calibration strategies are employed. Full article

Soil organic carbon (SOC) and total nitrogen (TN) are key indicators of soil fertility; however, the dynamics of carbon (C) and nitrogen (N) fractions during winter wheat growth under different tillage systems remain poorly understood. This study examined the effects of three tillage practices: no tillage (NT), subsoiling tillage (SS), and deep tillage (DT) on four soil organic carbon fractions (SOC, soil organic carbon; EOC, easily oxidized organic carbon; DOC, dissolved organic carbon; POC, particulate organic carbon) and four nitrogen fractions (TN, total nitrogen; NO₃⁻-N, nitrate nitrogen; NH₄⁺-N, ammonium nitrogen; DON, dissolved organic nitrogen) across five winter wheat growth stages (sowing, overwintering, jointing, filling and harvest) in the 0–50 cm soil profile. The results showed that SOC, its labile fractions, and TN all decreased with increasing soil depth, with tillage effects mainly confined to the 0–20 cm layer. SS achieved the highest SOC and TN contents in the topsoil, while NT and SS significantly enhanced the surface enrichment of C and N. In contrast, DT promoted more uniform nutrient distribution into the 30–50 cm subsoil. DON continuously accumulated throughout the growing season with faster accumulation rates under SS and NT; DOC peaked at the jointing stage, while EOC and NH₄⁺-N followed a consistent “decline–recovery–decline” seasonal pattern. SS yielded the highest total SOC stock (166.20 t ha⁻¹) in the 0–50 cm profile, particularly in the 0–30 cm layer. Correlation analysis showed that the coupling relationships among C and N indicators varied with soil depth, with the strongest positive correlation between SOC and EOC in the topsoil. Both SS and DT maintained higher soil water content (SWC) than NT in the 20–50 cm layers throughout the experimental period. In conclusion, SS emerges as the optimal balanced tillage strategy for dryland wheat fields on the Loess Plateau, simultaneously improving topsoil fertility, water retention, and C sequestration; meanwhile, DT is more effective for enhancing subsoil water and nutrient conditions. These findings provide a scientific basis for targeted tillage management to sustain soil fertility and productivity in rainfed dryland farming systems. Full article

Soil respiration (Rs) plays an important role in the carbon (C) dynamics of terrestrial ecosystems and is strongly regulated by nitrogen (N) inputs. While the impact of N fertilization on Rs has been widely documented in conventional farmland ecosystems, its patterns and influencing factors in perennial tea plantation systems are still poorly understood. In the study, we conducted a 15-year field experiment in a representative tea plantation to investigate the effects of different N rates (0, 112.5, 225, and 450 kg N ha⁻¹ yr⁻¹) on Rs. Compared to the control (N0), soil pH decreased significantly (p < 0.05) by 6.07%, 11.82%, and 16.12% under N112.5, N225, and N450, respectively. Concurrently, cation exchange capacity (CEC), ammonium (NH₄⁺-N), nitrate (NO₃⁻-N), and available phosphorus (AP) increased with increasing N rates, whereas available potassium (AK) decreased. Soil microbial biomass carbon (MBC) initially increased and then decreased with increasing N rates, while dissolved organic carbon (DOC) content increased consistently. The Rs rate exhibited a distinct seasonal pattern with a single peak in August. The annual mean Rs rates were 2.79, 3.15, 4.06, and 3.85 μmol·m⁻²·s⁻¹ for the N0, N112.5, N225, and N450 treatments, respectively. Soil temperature explained 55.41% to 61.08% of the variation in Rs rates across N treatments, and a composite model incorporating both soil temperature and moisture further improved the prediction of Rs dynamics. Cumulative soil CO₂ emissions (CCEs) over the study period ranged from 10,427 to 14,221 kg CO₂-C ha⁻¹ across treatments and were significantly negatively correlated with soil pH, and positively correlated with DOC, MBC, and NO₃⁻-N content. A non-linear relationship between N application rate and CCEs was observed, highlighting the complexity of optimizing N management for balancing productivity and climate mitigation in tea plantation systems. These findings provide a theoretical basis for developing rational N fertilization strategies and improving the predictive capacity of C cycle models in agroecosystems. Full article

Phytoremediation is a prevalent approach for addressing remediation and production goals in polluted agricultural land. In this study, we examined the impact of four distinct planting ratios on crop growth, accumulation of arsenic (As), and rhizosphere soil dynamics of peanut and maize. The results revealed that intercropping significantly reduced grain As accumulation (42.11–63.16% in maize; 62.28% in peanut under the 1:2 ratio, T2), achieving compliance with Chinese food safety standards (GB 2762-2017, 0.05 mg kg⁻¹). Meanwhile, the T2 treatment exhibited a significantly higher As bioconcentration factor (BCF) and the lowest translocation factor (TF). The metal removal equivalent ratio (MRER) under different planting systems was 1.09, 2.41, 1.07, and 1.46. Additionally, while intercropping did not increase grain biomass per plant, the LER values > 1 for T1 (1.88) and T2 (1.25) demonstrated that complementary resource use enhanced total productivity. Intercropping treatments significantly affected soil properties in both maize and peanut rhizospheres. For maize, intercropping lowered soil pH and available As content but increased dissolved organic carbon (DOC). Notably, only the T1 treatment significantly reduced the cation exchange capacity (CEC) of maize soil. Peanut’s rhizosphere experienced increases in both pH and CEC due to intercropping, with only the T2 treatment yielding a slight rise in DOC. The findings suggest that the maize–peanut intercropping system, especially the T2 system, effectively alters the soil–plant interface to limit As uptake while maintaining productivity, demonstrating its promise for safe utilization of As-contaminated land. Full article

Chemical coagulation is a highly important step of the conventional treatment processes, determination of the optimum coagulant dose to meet the demand of particulate materials and natural organic matters (NOMs) in raw water is crucial for good drinking water quality. WTC-Coag is a universal non-site-specific coagulant prediction model using three raw water quality parameters, UV₂₅₄, colour, and turbidity, as model inputs. The empirical model can determine the dose for maximum dissolved organic carbon (DOC) removal to achieve the conditions of enhanced coagulation; it also features an operator-selectable input—% setpoint (as % DOC removal)—to establish a dose for the desirable treated water quality. This hybrid modelling and control approach in practice is extremely useful for operators to be able to optimise the process by balancing between water quality and use of resources (chemical and sludge disposal costs) for sustainable operation. This paper discusses the practicality of this hybrid modelling approach via a long-term evaluation by comparing the plant dose against predicted dose using five years historical operations and water quality data. The assessment covered raw water quality change against treatment performance, predictability, usability and operator behaviour in response to the dose change situation. During the study period, five “black water” events were captured, and the performance of the predictability due to operational changes and operator’s response in these extreme events have been analysed. The comparison between the predicted enhanced dose and the plant dose indicated enhanced coagulation would not be always required. Furthermore, the selection of 50% setpoint from the targeted dose option matched well with the plant dose during which the lower-dose situation would be sufficient, with 90% of the predicted doses within ±10 mg/L of the plant dose and 95% of the predicted doses within ±15 mg/L of the plant dose during the normal period. The use of a correction factor to compensate for the particulate demand due to powdered activated carbon (PAC) dose during “black water” events has shown to be effective. The 50% setpoint matches with the plant alum dose over the entire period after accounting for the PAC dose, with 70% of the predicted doses within ±10 mg/L and 80% within ±15 mg/L of the plant dose. All the coagulation-related prediction functions have been evaluated and confirmed their non-site-specific nature. This study is unique in terms of using real operations data for an extended period to evaluate this novel hybrid modelling concept towards the sustainability goal. Full article

Elevated tropospheric ozone (O₃) and global warming can affect nitrous oxide (N₂O) and nitric oxide (NO) emissions from rice paddies, but their interactive effect is poorly understood. Two-year field observations of soil properties were implemented to quantify the impact of elevated O₃ and warming on N₂O and NO fluxes and identify dominant regulatory factors. Results indicated that elevated O₃ reduced N₂O and NO fluxes, whereas warming increased N₂O and NO fluxes, relative to respective ambient conditions. The combined O₃ elevation and warming treatment resulted in reductions in N₂O and NO fluxes compared to the warming treatment. The N₂O and NO emissions under elevated O₃ and warming were primarily associated with significant changes in soil dissolved organic carbon (DOC) and NH₄⁺. Furthermore, under warming treatment, N₂O and NO emissions were also linked to significant variations in soil NO₃⁻, but were independent of soil microbial biomass carbon (MBC), microbial biomass nitrogen (MBN), and pH. This study found that high O₃ concentrations significantly suppress nitrogen oxide emissions from paddy fields under warming. This suppression necessitates the explicit integration of O₃ into agroecosystem emission prediction frameworks for accurate estimation of nitrogen oxide fluxes. Full article

Stormwater runoff represents a significant vector for the transport of organic pollutants and pathogens into aquatic ecosystems, posing serious environmental and public health risks. Although extensively employed for bank stabilization, traditional gabion structures demonstrate constrained efficacy in pollutant removal. In this study, an enhanced ecological gabion (EG) system was developed by integrating a stratified configuration of functional fillers (ceramsite, maifanite, and biochar) with vegetation (Iris germanica). This design leverages synergistic effects to enhance the concurrent removal of dissolved organic matter (DOM), particulate organic matter (POM), and fecal indicator bacteria (FIB) from simulated stormwater. The system was evaluated in continuous flow experiments through comparison with a traditional gravel gabion (TG). Results showed that, compared with the TG, the EG exhibited markedly enhanced removal performance, with chemical oxygen demand (COD), NH₄⁺–N, and TN removal efficiencies being approximately 2.48, 3.68, and 3.56 times those of the TG, respectively. In addition, the EG exhibited significantly higher removal efficiencies for both particulate organic carbon (POC) and dissolved organic carbon (DOC) than the TG, with increases of 329% and 137%, respectively. Fluorescence spectroscopy and particle size distribution analyses revealed that the EG effectively transformed and removed diverse DOM components and fine particulates. The stratified filler media synergistically enhanced pollutant retention, with biochar serving as the primary agent for nutrient and pathogen adsorption. These findings demonstrate the viability of the EG as an integrated, eco-friendly solution for enhanced stormwater purification in riparian zones, providing a compact and multifunctional alternative to conventional end-of-pipe systems. Full article