Search Results (165)

Understanding the dynamics of carbon (C), nitrogen (N), and phosphorus (P) stoichiometry and C stocks along a stand development chronosequence has been extensively studied in forest ecosystems. However, despite the global economic and ecological importance of apple orchards, such knowledge remains limited for these intensively managed perennial agroecosystems. We examined C, N, and P concentrations and stoichiometric ratios in tree tissues (root, stem, branch, foliage) and soils (0–100 cm depth), as well as ecosystem C stocks, across a chronosequence of 4, 8, 12, and 16 yr old Malus pumila orchards in the eastern Yan Mountains, Hebei Province, North China. The results showed that C concentrations exhibited no consistent age-dependent trend in tree tissues. In contrast, N and P concentrations in all tree tissues decreased significantly with stand age, while their C:N and C:P ratios increased. The leaf N:P ratios suggested progressive P limitation as orchards aged. In soil, C, N, and P concentrations first decreased and then increased along the chronosequence, with the highest values observed in the 16 yr stands. This U-shaped trajectory reflected the dynamic interplay between stand development and anthropogenic management. Intercropping and intensive fertilization in the 4 yr orchards initially elevated soil nutrient levels, while the cessation of intercropping and nutrient removal via fruit harvesting in the 8 yr stands led to a decline. Thereafter, accumulation of litter decomposition and root turnover, combined with continued organic matter inputs, progressively replenished soil nutrient pools in the 12 and 16 yr stands. The total ecosystem C stocks ranged from 70.80 to 136.13 Mg ha⁻¹, initially declining from 4 to 8 years and then increasing at 12 and 16 years, with soil contributing 84.7–99.7% of the total. Plant and soil nutrient concentrations showed predominantly negative correlations, indicating weak coupling between tree and soil nutrient pools. Our findings demonstrated that stand age profoundly influenced C:N:P stoichiometry and C stocks in apple orchard ecosystems and that prolonged orchard development enhanced both tree biomass C and soil C stocks. These results provide a scientific basis for nutrient optimization and sustainable management of apple orchards in temperate regions. Full article

As a widely adopted approach for the resource utilization of pig manure, the ability of composting to reduce risk pollutants such as antibiotic resistance genes (ARGs) has gained significant attention. Temperature plays a pivotal role in determining the effectiveness of composting, with the maximum composting temperature and duration of high temperature being key indicators of compost quality. This study investigated the influences of adjusting the thermophilic stage on the dynamics of ARGs during pig manure composting. The results revealed that the adjustment strategies of thermophilic stage controls (i.e., prolonging the duration of the thermophilic stage or raising the maximum temperature) slightly promoted the absolute abundance of total ARGs by 0.72–0.99 logs, whereas their relative abundance was notably reduced by 49.7~64.1%. Some ARGs (i.e., tetW, tetO, tetM, fexA, fexB, ermA, and ermB) could be effectively removed by the composting, whereas sulI, sulII, aadA, and tetL enriched the horizontal gene transfer and diversified the potential bacterial hosts. The variations of ARG profiles and the succession of bacterial communities could be divided into two stages, which coincided with the organic carbon (OC) content (82%). The nutrient factors, especially the OC content, were strongly relative to several ARGs, implying that the organic nutrient could be an important driving force in shaping ARG distribution, potentially by influencing bacterial community succession. Three potential opportunistic pathogens (Mycobacterium, Bordetella and Bacillus) exhibited positive correlations with enriched ARGs, highlighting the potential risks of the dissemination of antibiotic-resistant pathogens though the application of compost products. Full article

Constructed wetlands operated in plateau habitats may experience constrained biological treatment because low temperature, low atmospheric pressure, and low-carbon wastewater can jointly limit microbial metabolism. This 80-day pilot screening study evaluated three nonreplicated modular constructed wetland configurations (MCW1-MCW3) containing different sequences of zeolite, ceramsite, and quartz sand and planted with Veronica anagallis-aquatica. Each configuration consisted of one independent treatment train; therefore, the comparisons were interpreted as configuration-specific and exploratory rather than as statistically generalizable treatment effects. Pollutant-removal performance and microbial community succession were evaluated through repeated water-quality monitoring and 16S rRNA gene sequencing. MCW1 showed the highest observed mean NH₄⁺-N removal efficiency (88.6%), whereas MCW3 showed the highest observed mean TP and COD removal efficiencies (79.56% and 47.40%, respectively) and an NH₄⁺-N removal efficiency of 85.51%. TN removal by MCW3 remained limited at 20.49%, consistent with carbon limitation of denitrification. Under the naturally low-temperature plateau laboratory conditions, the observed COD reduction indicated partial mineralization or retention of organic pollution loads, potentially supported by substrate biofilms and cold-adapted microbial assemblages. Apparent module-contribution analysis suggested that zeolite contributed substantially to NH₄⁺-N reduction, whereas ceramsite contributed to TP and COD removal under the tested sequences. Because plant biomass and tissue nutrient contents were not measured, nitrogen and phosphorus removal could not be attributed quantitatively to hydrophyte uptake. Overall, substrate sequence influenced pollutant-removal patterns and microbial community assembly, providing preliminary evidence for habitat-adapted optimization of modular constructed wetlands for plateau domestic wastewater. Full article

This review provides a comparative critical synthesis of biochar and enhanced rock weathering (ERW), identifies key trends and gaps in soil carbon research, and outlines pathways for improving carbon sequestration and monitoring in soil systems. From a global perspective, materials and agricultural studies were read to examine the properties of these amendments and their effects in cropland and forest soils. The main research question guiding this literature review was as follows: What are common trends in published biochar and ERW studies? Major themes were derived from the stated question and structure the Discussion. The Web of Science provided access to relevant literature for both biochar and ERW, and a total of 38 articles (biochar: 17; ERW: 21) were read and covered in this paper. The findings conveyed the growing number of Chinese studies on these amendments to resolve climate-related soil quality affecting crop yields and potential for carbon sequestration, namely carbon dioxide removal or CDR—which sequesters CO₂ that is already in the atmosphere. Studies commonly used application rates of <5% for biochar and 5 or 50 t/ha for ERW, with (wood) biochar commonly processed at temperatures of 500–550 °C. Finer powders were known to be more effective due to their increased surface area, although there were emissions trade-offs to consider for climate change mitigation. There were options for using glacial rock flour (GRF) as an alternative. For ERW, the type of minerals matters, with basaltic amendments being most investigated and minerals like zeolite, for example, having quick responses and potential to filter out heavy metals. Depth of analysis was an issue in the studies, especially affecting ERW work—which needs to adopt greater depths (>60 cm) and both soil organic carbon (SOC) and soil inorganic carbon (SIC) or total carbon need address, particularly for ERW since studies only provided selective coverage. Biochar studies tended to focus more on crop yields and were not as concerned as ERW studies in CDR. Many studies agreed that these are promising products that need to be economically compared before being applied at a large scale. More field studies are needed to test biochar, while limitations imposed by soil pH (acidification affecting dissolution and nutrient availability) and climate need consideration for ERW—especially since it works best in warm, humid climates. The application rate and duration are important variables to also consider for ERW, and both SOC and SIC dynamics are subsystem components requiring consideration. Ultimately, studies call for field trials executed in the long term at greater depth and in different climates and representing different soil types. Full article

The engineering, resource, and financial constraints in space and spacecraft so far have not allowed the incorporation of biological components into a closed-loop bioregenerative life support system (BLSS), despite decades of research. The expected increase in deep-space exploration and planetary bases with limited access to Earth-based resources necessitates the development of self-sustaining hybrid BLSS technology. The created physicochemical systems, together with photosynthetic organisms and bacteria, aim to revitalize the air, produce food, and recycle nutrients and water in mutually beneficial mini-ecosystems. While plants are best in the function of food production and bacteria in waste recycling, the incorporation of microalgae would add immense benefits in optimizing the life support system (LSS) and increasing the degree of closure. Microalgal photobioreactors (PBRs) could perform wastewater treatment (WWT), removing the nitrogen (N) and phosphorus (P) in the human-derived wastewater (WW), and couple it with converting carbon dioxide (CO₂) from the cabin to oxygen (O₂) and food production. As microalgal WWT on Earth is an emerging field with engineering hurdles, power, mass, volume, microgravity fluid dynamics, and other constraints have also prevented their operations in space. However, in space vehicles, there is no need for large upscaling of a laboratory prototype system, and the WW effluent is easier to predict, facilitating microalgal extraplanetary use in comparison to Earth treatment plants. These factors, combined with the qualities of microalgae such as surface-to-volume efficiency, fast growth rate, high yield, and tolerability to WW, etc., have led to many preliminary testbeds, prototypes, and ground demonstrations from space agencies, space centers, and academia, which show promising results. Microalgal participation in space WWT is beyond current operational practice; however, PBRs are on the space agenda, and the scientific community is elaborating the technologies that would allow their successful implementation. Full article

The degradation of soil structure and organic carbon in the black soil region of Northeast China threatens sustainable crop production, and straw return combined with appropriate tillage may offer an effective strategy for soil restoration. However, the depth-dependent mechanisms by which straw management–tillage systems regulate aggregate stability, labile carbon distribution, and soil quality under long-term straw return remain unclear. Based on a seven-year field experiment established in 2018 in eastern Inner Mongolia, this study compared conventional tillage with straw removal (CT) and four straw-return practices: deep tillage with straw return (DTS), deep harrowing with straw return (DHS), rotary tillage with straw return (RTS), and no-tillage with straw mulching and direct seeding (NTS). Soil aggregate stability, soil organic carbon (SOC), SOC stock, labile organic carbon fractions, microbial biomass carbon, carbon-acquiring enzyme activity, available nutrients, and soil quality index (SQI) were evaluated across the 0–60 cm soil profile. Straw return combined with tillage improved soil structure, carbon accumulation, nutrient availability, and SQI, with stronger responses observed under NTS and DTS. NTS mainly increased macroaggregate formation and the accumulation of SOC, light fraction organic carbon (LFOC), and particulate organic carbon (POC) in the 0–20 cm layer and was associated with the highest SOC stock in the whole profile. In contrast, DTS showed greater increases in SOC stock, dissolved organic carbon (DOC), readily oxidizable organic carbon (ROC), available nutrients, and SQI in the 20–40 cm layer, likely related to deeper straw incorporation. Partial least squares (PLS) path modeling indicated that labile carbon pools were closely associated with the relationship between aggregate stability and soil quality improvement. These results suggest that NTS appears promising for surface soil conservation, whereas DTS may be beneficial for improving subsoil fertility and carbon sequestration in black soil farmland. Full article

De novo granulation of autochthonous microorganisms of water and wastewater reduces the start-up periods for cultivating aerobic granular sludge (AGS) and enrichment of degrading strains. However, it has not been demonstrated using refractory carbon compounds. This work investigated the formation of AGS from the seawater microbiome and establishment of pollutant removal pathways by feeding acetonitrile as the sole carbon and nitrogen source. Use of acetonitrile at an organic loading rate of 0.124 kg/m³/day enabled rapid emergence of aggregates and then stable granules (size: 1.3 mm; SVI5: 68 mL/g) within two weeks. TOC removal accompanied by ammonium nitrogen release was consistent and stable at 93% during the 50 days of bioreactor operation. Formation of acetamide and ammonium indicated involvement of nitrile hydratase and amidase enzymes in acetonitrile biodegradation. Ammonium released during acetonitrile biodegradation was removed by partial nitrification and the nitrite denitrification pathway. However, incomplete ammonium removal led to accumulation of up to 120 mg/L NH₄⁺-N by day 50. Phosphate was removed via the enhanced biological phosphate removal pathway. This study shows that de novo granulation permits cultivation of AGS via the de novo granulation approach for simultaneous biodegradation of refractory acetonitrile and biological nutrient removal under saline conditions. Full article

Three biodegradable organic acids, citric acid (CA), malic acid (MA), and oxalic acid (OA), were evaluated for their ability to remove cadmium (Cd), lead (Pb), and copper (Cu) from contaminated soils. The effects of organic acid concentration, solution pH, and treatment time on metal removal were systematically investigated. Response surface methodology (RSM) was used to optimize these parameters. Sequential extraction was performed to track changes in heavy metal speciation. Under single-factor conditions (75 mmol/L CA, pH 5.0, 60 min), the removal efficiencies were 12.81% for Cd, 10.36% for Pb, and 14.94% for Cu, respectively. Under the optimized conditions (70 mmol/L, pH 5.0, 100 min), the removal efficiencies were further enhanced. The organic acids preferentially targeted bioavailable fractions (water-soluble, exchangeable, and carbonate-bound), which lowered ecological risk. Although CA was less efficient than chemical chelators such as EDTA, it caused much less nutrient loss. Organic acids, especially CA, provide an environmentally friendly alternative for heavy metal extraction with minimal side effects on soil fertility. They represent a promising low-impact option under the tested laboratory conditions. Nevertheless, the absolute removal values in a single washing step remained below 20% for all three metals, indicating that while the method is sustainable and eco-friendly, it is not suited for heavily contaminated soils as a standalone treatment. Full article

Understanding how land management influences soil carbon (C) and nitrogen (N) dynamics is critical for improving ecosystem resilience and carbon sequestration potential in semiarid rangelands. This study used classical field- and laboratory-based methods to assess soil organic carbon (SOC), organic matter (OM), and N content at 13 sites across four ecological provinces in eastern Oregon, USA. Treated sites—where traditional rangeland restoration and management practices had been applied to them (i.e., juniper removal, sagebrush removal, post-fire grass seeding, and land conversion to pasture)—were paired with adjacent untreated control sites. Soil samples were collected at two depths, 0 to 10 cm and 15 to 25 cm and analyzed for C, N, OM, bulk density (BD), soil volumetric water content (SVWC), porosity, and texture. Soil C and N stocks were calculated on an area basis (t ha⁻¹), and statistical analyses were conducted using one-way ANOVA and correlation tests. Treated sites generally exhibited higher soil C, N, and OM content compared to untreated sites, particularly in the upper 10 cm of soil. Data obtained from the two soil depths (0 to 10 cm and 15 to 25 cm) were averaged and assumed to represent the top 30 cm of the soil profile, corresponding to the effective rooting zone at each field. The site where sagebrush removal was followed by grass seeding exhibited the highest soil C and N stocks (115.8 t C ha⁻¹ and 9.2 t N ha⁻¹, respectively). This site also had the highest OM content (9.53%), which was observed in the topsoil layer (0 to 10 cm) across all sites and depths. Strong positive correlations between C and N were detected across all sites (mean r = 0.92), while negative correlations were observed between soil C and bulk density at several locations. Results suggest that vegetation management practices such as woody plant removal and grass establishment can enhance soil C storage and nutrient retention in semiarid rangeland ecosystems. These findings provide baseline data to inform land management strategies aimed at improving soil health and carbon sequestration potential in the Pacific Northwest region in the USA. Full article

Municipal wastewater represents an underutilized secondary biomass resource rich in organic carbon and nutrients that can be valorized through biotechnological conversion. In this study, we developed an integrated multi-microbial biorefinery platform to transform municipal wastewater into value-added biofuel via sequential bacterial treatment, microalgal biomass generation, and fungal-assisted harvesting. Wastewater was first pretreated with Bacillus subtilis to enzymatically hydrolyze complex organic substrates and enrich the medium with bioactive metabolites, including auxins and gibberellins. The conditioned wastewater was subsequently used to cultivate Chlorella vulgaris, followed by biomass recovery using Trichoderma viride pellets as a sustainable bioflocculant. The integrated consortium significantly enhanced nutrient removal efficiency and promoted algal biomass accumulation, lipid enrichment, and biodiesel productivity compared to monoculture controls. Elevated hydrolytic enzyme activities (cellulase, protease, and amylases) facilitated organic matter conversion into bioavailable substrates, while increased phytohormone levels stimulated algal growth and lipid biosynthesis. Additionally, fungal bioflocculation substantially improved biomass recovery efficiency, reducing the need for energy-intensive harvesting technologies. This work highlights the potential of a biotechnology-driven approach for integrating wastewater remediation with biofuel production. By integrating microbial metabolism, enzymatic transformation, and sustainable separation processes, the proposed biorefinery system suggests a potentially low-carbon approach for simultaneous environmental remediation and biomass valorization, although further life cycle and energy balance analyses are required to validate this aspect. Full article

The integration of appropriate tillage practices with straw returning can effectively mitigate soil degradation in Northeast China. However, limited research has explored the impacts of different tillage practices combined with varying straw incorporation depths on the structure and diversity of soil microbial communities. In 2016, a field experiment was initiated using a two-factor split-plot design, featuring six treatments: two tillage depths of 10 cm (D10) and 30 cm (D30) combined with three straw management practices—straw mixing incorporation (SM), straw deep burial (SB), and straw removal (SR). Soil samples collected in 2019 were analyzed for multiple soil properties and microbial indices. Results indicated that both straw returning and tillage depth significantly influenced soil organic carbon (SOC), soil total nitrogen (STN), total phosphorus (TP), and total potassium (TK), with the D30 treatment combined with straw returning optimizing soil nutrient contents most effectively. Under straw returning, D10 significantly increased urease activity in the 0–10 cm soil layer, whereas D30 enhanced this enzyme activity in the 10–30 cm soil layer, while β-glucosidase activity was less responsive to tillage depth. For the D10 treatment with straw returning, acid phosphatase activity was markedly higher than that in the straw removal treatment, whereas N-acetyl-β-D-glucosaminidase activity exhibited the opposite trend. Straw-returning methods had no significant effects on the bacterial and fungal Chao1 indices, while the Shannon index was positively correlated with key soil properties. Redundancy analysis (RDA) of microbial community composition at the phylum level and soil environmental factors revealed that soil nutrients in the 0–10 cm soil layer were positively correlated with Actinobacteriota, Ascomycota, and Basidiomycota, whereas the explanatory power of soil nutrients for microbial community variation decreased in the 10–30 cm soil layer. Our results highlight that tillage depth and straw returning can regulate soil microbial community composition and enhance soil nutrient cycling, thereby providing a theoretical basis for optimizing the combined application mode of tillage and straw-returning practices in Northeast China. Full article

The removal of nitrogen and phosphorus from wastewater with low organic carbon content requires the addition of an external carbon source. The objective of this study was to assess the influence of hydraulic retention time (HRT) on the efficiency of external carbon source utilization and on nitrogen and phosphorus removal in a Rotating Electro-Biological Disc Contactor (REBDC). The energy demand was evaluated based on energy consumption (E) and current efficiency (CE). Hydroponic tomato wastewater was treated in the REBDC at a constant current density of 2.5 A/m². Sodium acetate was used as the carbon source. Two C/N ratios were tested, 2.0 and 3.0, under HRT conditions of 24 h and 48 h. For both C/N ratios, extending the HRT resulted in decreased nitrogen removal efficiency. At HRT = 48 h and C/N = 3.0, the nitrogen concentration in the effluent was more than three times lower compared with C/N = 2.0. The highest phosphorus removal efficiency was achieved at C/N = 3.0 and HRT = 48 h (98.8%). Increasing the HRT led to reduced TOC utilization for both C/N ratios. As a consequence of extended HRT, lower CE values and higher E values were observed, indicating increased energy demand for nutrient removal. 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

Biological wastewater treatment relies primarily on activated sludge and anaerobic digestion for the removal of organic matter. In urban wastewater treatment plants discharging into eutrophication-sensitive environments, the simultaneous removal of carbon, nitrogen, and phosphorus is required to meet increasingly stringent discharge limits. Under these conditions, the transformation of complex organic matter into volatile fatty acids (VFAs) represents a more efficient strategy than complete mineralization, as biodegradable carbon is essential to sustain biological nitrogen and phosphorus removal processes. In this study, an anaerobic sequencing batch reactor was operated under acidogenic conditions to promote the conversion of organic matter into VFAs. For the first time, this study demonstrates how temperature-controlled acidogenic pretreatment can reliably supply biodegradable carbon to support efficient downstream nitrogen and phosphorus removal in municipal wastewater treatment. A kinetic model was developed to describe the temporal evolution of the different carbon fractions involved in anaerobic digestion, including biodegradable and non-biodegradable organic matter, intermediate compounds, short-chain volatile fatty acids, and biogas. The model assumes first-order kinetics and constant biomass concentration and was successfully validated against experimental data, with deviations below 10%. Estimated kinetic constants exhibited a strong temperature dependence, particularly for hydrolysis and acidogenic pathways, whereas methanogenic steps showed lower sensitivity. Overall, the results demonstrate that temperature is a key operational parameter governing acidogenic performance and carbon transformation pathway. The simple and novel proposed kinetic model provides a useful tool for predicting VFA production and optimizing anaerobic pretreatment strategies aimed at enhancing downstream nutrient removal processes. Optimizing SBR operation for nutrient removal also offers sustainability benefits by improving resource efficiency and reducing energy and chemical inputs. Full article

Our work develops the financial engineering module of the REGENerative Agriculture (REGENA) Production Function, with Soil Organic Carbon (SOC) as ecosystem service and contract underlying index, contributing to the global literature and business practices. Specifically, we design and engineer a 30-year Net Present Value (NPV) intergenerational ecological bond instrument tailored for carbon farming (CF) as a part of regenerative practices. With SOC constituting a fundamental soil health indicator for the European Union Soil Observatory (EUSO), we model the flow of value from atmospheric CO₂ removal and its metabolism into SOC within a stochastic SOC Value at Risk (VaR) framework. We assess the SOC VaR in five experimental plots in five Mediterranean countries in South Europe and North Africa for three different treatments in each plot. In turn, the SOC VaR is incorporated into an adjusted Shannon entropy index (H(X)_ADJ) to estimate the coefficient of a positive, net-zero, or negative carbon balance and further assess the risk-adjusted discount rate. The monetary value per gram of carbon per kilogram of soil (g C/kg Soil) signifies a clear advantage of combined regenerative treatments. Finally, three selected extensions of our work are discussed, such as the application of the framework to other nutrients, the establishment full cost–benefit accounting methods for monetizing the environmental benefits of CF to upscale investments and the lifecycle accounting of ecosystem services. Full article