Search Results (91)

Iron oxide-mediated abiotic humification is critical for long-term soil organic carbon (SOC) stabilization. Goethite (α-FeOOH), the most thermodynamically stable iron oxyhydroxide in terrestrial ecosystems, is proposed to catalyze coupled Maillard reaction and polyphenol oxidation via surface hydroxyl and Fe(III) active sites. Nevertheless, the divergent interfacial regulatory mechanisms of glycine (Gly, N source) and glucose (Glu, C source) concentration gradients in goethite-catalyzed polyphenol-Maillard systems remain poorly understood. Two independent 360-h gradient incubation experiments were performed using synthetic goethite as a catalyst and catechol as a model polyphenol precursor to probe their concentration-dependent effects on short-term interfacial transformation kinetics and humic-like product properties. Kinetics, product properties, and underlying pathways were characterized via Gaussian and first-order asymptotic modeling, humic-like acid (HLA)/fulvic-like acid (FLA) fractionation, elemental analysis, Fourier-transform infrared (FTIR) spectroscopy, and partial least squares structural equation modeling (PLS-SEM). Results showed that 0.12 mol/L was the optimal concentration for both precursors to accelerate intermediate transformation. Gly elevated the baseline aromaticity parameter y₀ by 108.87% (vs. 20.38% for Glu), while Glu increased the asymptotic maximum dissolved organic carbon (DOC) by 322.66% (vs. 78.02% for Gly). Moderate Gly (0.03 mol/L) yielded the highest C_HLA. Excessive precursors reduced the C_HLA/C_FLA ratio via interfacial competitive adsorption and site occupation. The two precursors exerted opposing effects on the hydroxyl stretching peak of humic products, but both induced goethite surface reconstruction and activated iron-bearing surface functional groups. PLS-SEM confirmed precursor concentration as the dominant driver of humification kinetics. This study clarifies the distinct roles of Gly in aromatic cyclization and Glu as an aliphatic C donor during short-term mineral–organic interfacial processes, providing quantitative benchmarks for optimizing artificial humus production. Full article

Urban drainage overflows can release a large fraction of event-scale pollutants during the early stage, yet current control remains largely driven by hydraulic signals rather than pollutant-release dynamics. This study created a dissolved organic matter (DOM)-based fluorescence fingerprint method to precisely identify the shift from pollutant flushing to dilution or ongoing input, helping determine the timing of first-flush transitions and potential interception. Fourteen wet-weather overflow events from seven drainage systems in Shanghai and Changzhou were investigated using excitation–emission matrix fluorescence spectroscopy, combined with non-negative matrix factorization, random forest feature screening, principal component analysis, mass–volume (M(V)) curve analysis, and Pettitt change-point detection. Five macro-scale fluorescence fingerprints were resolved, representing protein-like, fulvic-like, and humic-like components. Protein-like fingerprints dominated rapid event-scale variations, while fulvic-like and humic-like fingerprints reflected continuous surface-derived input and stable background contribution, respectively. Peak-shift trajectories revealed three fluorescence-evolution modes: directional red-shift migration, peak-position stability, and weak, non-directional variability, reflecting different source-release dynamics and DOM compositional adjustments during overflow. Random forest screening identified 20 high-importance fine-scale fluorescence fingerprints, with 90% concentrated in protein-like regions linked to sewage-derived and labile DOM. Compared with macro-scale fingerprints and conventional water quality indicators, fine-scale fluorescence fingerprints showed clearer stage separation, stronger consistency with M(V)-based cumulative response patterns, and more distinct first-flush interception timing. This timing marked the transition from early concentrated pollutant release to dilution or sustained input, whereas macro-scale fingerprints indicated broader transition intervals and conventional indicators showed delayed responses. These findings highlight the potential of fine-scale fluorescence fingerprints to support future fluorescence-assisted overflow control by improving transition identification and targeted interception decisions. Full article

Conventional ridge tillage has triggered severe soil organic carbon depletion and soil erosion in sloping maize fields of humid northeast China, posing a persistent threat to black soil health and regional grain security. As representative conservation tillage systems integrated with full straw residue retention, no tillage and strip tillage exhibit prominent potential in soil protection, and their soil-improving benefits are inseparable from continuous straw carbon input; however, their regulatory effects on humus fractions and humic acid molecular properties in erosion-prone sloping farmlands remain largely unclarified. This study aimed to screen the optimal integrated tillage–cultivation mode for sloping farmlands in the northeast China black soil region and to reveal how tillage systems coupled with incremental agronomic practices affect maize yield, humus composition, and humic acid molecular characteristics in Albic soil, a representative degraded soil type of the regional black soil system. A 2-year field experiment was conducted in a typical sloping farmland of Jilin Province, with conventional ridge tillage set as the control. Five incremental integrated management practices (from baseline practice to fertilizer reduction, straw decomposition promotion, and 5–10% higher planting density) were arranged under both under no-tillage and strip-tillage systems. We analyzed dissolved organic matter fluorescence properties, carbon content of humus fractions, and humic acid molecular structural features, and performed principal component analysis for comprehensive performance evaluation of all treatments. This study demonstrates that optimized strip tillage, supported by full straw C input as an indispensable prerequisite, combined with straw decomposition promotion and a 10% planting density increase can synchronously boost soil fertility and maize yield, providing a scientific and practical tillage strategy for sustainable black soil conservation of sloping Albic farmlands in humid northeast China. Strip tillage achieved a 6.78% higher average maize yield than NT, and the maximum yield was recorded with ST5 (strip tillage combined with straw decomposition promotion and 10% planting density increase). Both no tillage and strip tillage significantly increased C_DOM content, humification index and autochthonous contribution, optimized humus component distribution with elevated humic acid carbon content, humic acid carbon-to-fulvic acid carbon ratio and humic acid carbon-to-total organic carbon ratio, and enhanced humic acid aromaticity, thermal stability, and hydrophobicity. The principal component analysis results indicated that ST5 ranked first in comprehensive performance, while conventional ridge tillage ranked the lowest among all treatments. Strip tillage integrated with straw decomposition promotion and 10% increased planting density effectively modulated humus fractions, improved humic acid molecular stability, and synchronously increased maize yield. This integrated management regime provides a scientific and practical tillage strategy for sustainable black soil conservation and high-efficiency maize production in sloping Albic farmlands of humid northeast China. Full article

The oxidative potential (OP) of atmospheric particulate matter serves as an effective indicator for assessing the health risks posed by reactive oxygen species (ROS). Existing studies have mainly focused on conventional particulate matter including PM_2.5, whereas systematic investigations into the OP of road dust in coal–resource–based cities are still limited. Taking Huainan City, China as the study area, this paper explored the characteristics and influencing factors of OP in water–soluble fractions of road dust from different functional zones. The results indicated that the OP of water-soluble fractions in road dust from Huainan City was 0.162 ± 0.079 pmol/min/μg, with the value in the coal mining zone being significantly lower than that in the commercial and industrial zones. The average concentration of water–soluble organic carbon (WSOC) was 67.3 ± 59.4 mg/kg, with lower levels observed in the coal mining and power plant zones. WSOC was primarily dominated by fulvic acid–like (C1) and tryptophan–like (C2) components. C1 prevailed in coal mining, power plant, and other functional zones, whereas C2 was dominant in commercial, park and residential zones. Overall, the WSOC showed a mixed-source signature dominated by endogenous sources and characterized by a low degree of humification. The total concentration of water–soluble heavy metals in road dust was 43.46 mg/kg, dominated by Fe, Sr, Cu, Ba, and Mn, with relatively lower concentrations observed in the industrial and coal mining zones. The influencing factors of OP exhibited differentiation among functional zones: in industrial zones, it was regulated by As, Mn, TC (total carbon), WSOC and its fluorescent components, while in non-industrial zones, it was closely associated with Co, TC, and WSOC. These findings indicate that road dust toxicity and its key chemical drivers in coal mining and power plant zones of coal resource–based cities exhibit distinctive characteristics. This study provides a scientific basis for the precise management of road dust pollution and the prevention of associated health risks. Full article

The organic complexation of Cu²⁺ in aquatic systems dominates its chemical speciation, affecting its reactivity and bioavailability. Using voltammetry, we investigated Cu²⁺ organic complexing capacity (CuCC) in atmospheric samples, including water-soluble aerosol fraction, rainwater (wet-only deposition), and bulk deposition (wet and dry deposition), collected in a coastal marine area (National Park Brijuni, Adriatic Sea). The focus was on minimizing analytical interferences from surface-active substances (SAS) that accounted for up to 56% of dissolved organic carbon. Method optimization was performed using model SAS (humic-like substances, fulvic acid, and pollen-derived organic material), resulting in an optimal desorption potential of −1.4 V and the addition of 1 mg/L Triton X-100. Under these conditions, CuCC parameters of average ligand concentration and conditional stability constant of (209.8 ± 6.7) nM and log K = (10.2 ± 0.6) in water-soluble aerosol fraction, (117.1 ± 5.0) nM and log K = (9.6 ± 0.2) in rainwater, and (142.9 ± 4.1) nM and log K = (10.2 ± 0.2) in bulk deposition were determined. Atmospheric inputs represented a source of weak Cu-binding ligands for marine areas. In conclusion, short-term monitoring provided insight into the variability of different atmospheric inputs and offered a methodological basis for future long-term, more comprehensive studies. Full article

This study investigates the impacts of algogenic organic matter (AOM) distribution characteristics, specifically molecular weight (MW) and hydrophobicity, on the formation of disinfection byproducts (DBPs) derived from Microcystis aeruginosa. This study focuses on both extracellular organic matter (EOM) and intracellular organic matter (IOM) and their contributions to DBP formation. AOM was divided into 12 fractions based on MW and hydrophobicity (transphilic, hydrophilic, and hydrophobic fractions). The results reveal that the hydrophobic fraction (HPO) contributes the most to IOM, while low-MW (<1 kDa) and high-MW (>100 kDa) organic matter are the main components of AOM. An analysis of fluorescent species indicates that humic acid-like and fulvic acid-like compounds derived from the hydrophilic fraction (HPI) of EOM and the hydrophobic fraction (HPO) of IOM are the dominant low-MW (<1 kDa) species. Additionally, aromatic proteins derived from HPO in both EOM and IOM are the dominant high-MW (>100 kDa) fluorescent species. This suggests that proteins or polysaccharides are the primary adsorbents on the membrane during ultrafiltration (UF), while the humic acid component is not significantly deposited. Furthermore, this study identifies that the >100 kDa HPO in IOM serves as the main precursor for trichloromethane (TCM), trichloroacetic acid (TCAA), and dichloroacetic acid (DCAA). In EOM, the precursor for the highest TCMFP (63.6 µg/mg-C) is the >100 kDa HPI, while the highest contribution to TCM (21%) is from the >100 kDa HPO. These findings provide crucial information for controlling DBPs derived from AOM through membrane filtration, particularly in eutrophic water environments. Full article

To enhance the benefits and ecological safety of tomato residue retention, this study evaluated the regulatory effects of conventional ambient temperature retention (CR) and solar high-temperature retention (TR) on the initial soil environment and rhizosphere microecology of subsequent crops (continuous tomato and rotational cucumber). The results showed that CR promoted the accumulation of humic acid and increased the contents of phenolic acids and small-molecule organic acids in the soil. TR also increased small-molecule organic acids but primarily enriched fulvic acid, accompanied by higher concentrations of phenolic acids. Regarding microecological responses, CR enriched potential plant-growth-promoting bacteria (Pseudomonas, Sphingomonas, Lysobacter) in the rhizosphere, but it also increased the relative abundance of the potential pathogen Fusarium. In contrast, TR promoted the colonization of heat-tolerant beneficial biocontrol microbes (Bacillus, Chaetomium, Mycothermus), with no Fusarium enrichment observed. Redundancy analysis and Mantel tests revealed that the changes in soil nutrients and organic acid fractions induced by residue retention were correlated with the succession of the rhizosphere microbial community and the reconstruction of the metabolic profile. This study demonstrates that TR can effectively mitigate the risk of pathogen enrichment associated with ambient temperature retention, constructing a potentially disease-suppressive initial microecological environment for subsequent crops. Full article

Food waste is commonly valorized through aerobic composting, yet the responses of water-soluble organic carbon (WSOC) across molecular-weight (MW) fractions remain insufficiently resolved. This study aimed to quantify how distinct composting strategies regulate WSOC MW distribution and compositional evolution and identify the key physicochemical drivers. Food waste was treated by 30-day conventional composting (CK), 15-day phased inoculation (JJ; 2% (w/w) antioxidative consortium dominated by Bacillus/Pseudomonas followed by 2% (w/w) thermophilic cellulolytic consortium enriched in Geobacillus/Paenibacillus when the temperature reached 50 °C), and 24-h rapid thermophilic composting (RC; 2% (w/w) inoculation with a 24-h moist-heat pretreatment). RC yielded a small molecular weight organic carbon (SMOC)-rich product with low aromaticity, with MW < 5 kDa accounting for 68.21% (MW < 500 Da: 28.50%). JJ preferentially enriched more oxidized, fulvic-like/carboxyl-rich organics, increasing the fulvic-like contribution from 15.97% to 35.40% and raising the HMOC/SMOC to 2.72:1. CK showed the strongest humification, with MW > 5 kDa reaching 65.56% and humic-like Region V increasing from 26.25% to 66.36%. pH was the primary predictor of MW (day 6: CK 3.9; JJ 4.9; final ~8.8), while temperature jointly governed humic-like formation in RC. Full article

The pathways governing the transformation of crop residues into humic acid (HA) remain incompletely understood because multiple biochemical routes may operate simultaneously during composting-like humification. In this study, a 30-day solid-state humification experiment was conducted by integrating physicochemical pretreatments, including steam explosion (SE) and ammonification coupled with steam explosion (SE-N), with a multi-fungal inoculation strategy involving Aspergillus niger, Candida spp., and Phanerochaete chrysosporium. Across three representative substrate–pretreatment systems and 81 experimental groups, the contents of lignocellulosic fractions, reducing sugars (RS), a UV-280-based soluble nitrogen-containing precursor index (operationally denoted as SNP), fulvic acid (FA), and HA were compared. The results showed that neither physicochemical pretreatment alone nor single-strain inoculation was sufficient to achieve substantial HA formation. SE mainly improved substrate accessibility and promoted carbon release, whereas ammonification provided essential nitrogen preloading for subsequent precursor coupling. In the saccharification-dominant treatment, RS reached 27.5%, but HA remained negligible. In the Candida-only treatment, the soluble nitrogen-containing precursor index increased markedly, yet HA formation was still minimal. By contrast, the highest HA yield (13.7%) was obtained under multi-fungal co-inoculation, particularly when nitrogen preloading by ammonification was combined with concurrent accumulation of carbon and aromatic precursors. The data suggest that lignin-targeting activity by P. chrysosporium was associated with the likely generation of phenolic and quinone-like intermediates that bridged the condensation of sugar- and nitrogen-derived compounds. Overall, the findings support a synergistic humification framework in which polysaccharide depolymerization, microbial nitrogen transformation, and lignin-derived aromatic precursor formation jointly contribute to HA accumulation, rather than a single linear pathway dominating the process. Full article

Compost-derived humic acids (HAs) and fulvic acids (FAs) play an essential role in enhancing soil microbial diversity and activity by facilitating metabolic processes through electron transfer. Herein, the effect of bioleaching dewatered sludge (BDS) in comparison with filter press dewatered sludge (FDS) on the electron transfer capacity (ETC) of humic substances during composting was investigated as a novel attempt. A variety of characterization methods including UV-Vis, FTIR, 3D-EEM, and electrochemical measurements, were used to explore the change in humic substances during composting. The results indicated that bioleaching treatment significantly influenced the organic matter composition and hindered the accumulation of redox-active functional groups during composting. Notably, the ETC of HA increased by 24.07% in the FDS group but declined by 40.62% in the BDS group. This divergence stemmed from the organic matter loss during bioleaching, leading to reduced quinone-like and tryptophan-like substances associated with electron transfer in HA during composting. Furthermore, BDS showed lower pH, water content, and organic matter, but higher concentrations of ammonium nitrogen (${\mathrm{NH}}_4^{+}\text{-}\mathrm{N}$) and ammonia nitrogen ${\mathrm{NH}}_3^{-}\text{-}\mathrm{N}$, all of which potentially influenced humification efficiency. These findings not only clarify the electron-transfer dynamics of humic fractions but also highlight the importance of optimizing sludge pretreatment for improved composting performance and resource recovery. Full article

Rice cultivation is widely used for the reclamation of saline–sodic soils. However, the mechanisms by which prolonged flooding alters soil chemical conditions and regulates carbon redistribution and stabilization across the soil profile remain unclear. This study compared soils reclaimed for 6 years (R6) and 17 years (R17) with unreclaimed saline–sodic soil (CK) in the Songnen Plain, Northeast China, and evaluated changes across three depths (0–20, 20–40, and 40–60 cm). Reclamation significantly improved aggregate stability, with corresponding increases in mean weight diameter and water-stable aggregates. R17 and R6 promoted greater soil organic carbon (SOC) retention within macroaggregates and increased humic substance concentrations, indicating improved structural protection of carbon. The fulvic/humic acid (FA/HA) ratio increased with depth under flooded conditions, suggesting greater fulvic acid mobility. Although HA and humin (HM) decreased with depth, their concentrations, particularly the HM/SOC ratio, remained higher and more stable in R17. Reductions in salinity acted as a key mediating pathway, regulating carbon redistribution across the soil profile, with mobile carbon fractions destabilizing surface aggregates but promoting organo-mineral bonding and aggregate formation at subsurface depths (20–40 cm). Overall, these findings indicate that rice-based reclamation stabilizes carbon via interconnected processes of salinity reduction, vertical carbon redistribution, and aggregation driven by carbon quality, highlighting subsurface layers as essential for long-term carbon stabilization in saline–sodic soils. Full article

The distribution of water-soluble organic matter (or dissolved organic matter DOM) in narrow (nano-and micrometer) fractions of chernozem was studied by sequential filtration on track-etched membranes. Multimodal (IR and fluorescence) two-dimensional correlation (2D-COS) spectroscopy was used. Protocols for attenuated total reflectance (ATR) FTIR of DOM were proposed. ATR-FTIR 2D-COS provides a larger volume of information on characteristic bands compared to traditional FTIR, especially in C–H ranges (3000–2800 and 1450–1300 cm⁻¹). The fluorescence excitation–emission matrix 2D-COS showed that the indexes and ratios of humic- to protein-like compounds are reproducible, and exhibit significant variation among size fractions, with maximum amounts of saturated humic-like compounds in the largest (2–10 μm) and finest fractions (0.01–0.03 μm), while medium fractions (0.05–1 μm) are dominated by fulvic acids and fresh organic matter. Heterospectral fluorescence–IR 2D-COS enhanced the accuracy of identification and assessment of DOM group composition and showed that C–H IR band intensities correlate with tyrosine-like EEM bands and biogenic fluorescence indexes, while carboxylic components have humate-like bands and humification fluorescence indexes. Element profiles in DOM fractions correlate with fluorescence indexes; humification indexes with P, S, Cr, Mg, Ca, Cu, and Zn; biogenic with Mg, P, Cr, Cd, K, S, and Ca. Full article

Biodiverse composts obtained through composting are widely used in regenerative agriculture due to their ability to improve soil quality, crop growth, and productivity, primarily by promoting beneficial microorganisms. These composts result from the decomposition of mixtures containing nitrogenous and plant biomass. During plant biomass preparation, litter serves as a source of beneficial microorganisms, which transition from endophytes to decomposers. This study tested the hypothesis that the type of litter influences the composition of bacterial and fungal communities in biodiverse composts, thereby affecting species abundance and diversity. To this end, litter from the tree species Handroanthus impetiginosus (Angiosperm—AC) and Pinus elliottii (Gymnosperm—GC) was evaluated in compost preparation, also investigating the impact of litter type on the concentration of macronutrients, chemical parameters (such as organic carbon, cation exchange capacity—CEC; carbon/nitrogen ratio—C/N; organic matter—OM; pH, and humic substances fractions, including humic and fulvic acids), and microbiological quality (assessed by Microbial Biomass Carbon—MBC). The microbial composition of composts prepared with both AC and GC litter was more influenced by the composting method than by plant origin, with bacterial genera such as Thermobacillus (representing 1.27% and 1.23% of the genera present in AC and GC, respectively) and thermotolerant species, adapted to the high temperatures of the thermophilic phase, being notably present. GC litter favored a higher abundance of bacterial (pi = 0.027) and fungal species (pi = 0.042), despite the antimicrobial properties of P. elliottii. In contrast, AC compost accumulated higher levels of macronutrients and OM (39.5%), reflecting the efficacy of specific fungi in decomposition, particularly species from the phyla Chytridiomycota and Zoopagomycota, identified exclusively in this compost. MBC analysis indicated that composts reach optimal efficiency and nutritional quality between 60 and 90 days of maturation, suggesting that this period is the most suitable for leveraging the resident microbiota and producing high-quality composts for agricultural use. Full article

In achieving sustainable development goals, soils play a key role in environmental protection, natural resources, and food security. Peatlands are particularly important here, as they function at the interface between terrestrial and aquatic ecosystems and store large amounts of organic matter. However, organic soils are highly susceptible to transformation and degradation; therefore, their degradation caused by, among others, drainage properties is a high risk to both the environment and agriculture—it disrupts the ecosystems, causes greenhouse gas emissions, and eutrophicates the hydrosphere. Soil degradation in drained peatlands is associated with the transformation of soil organic matter (SOM), which in organic soils is the dominant component of the solid phase of the soil. The aim of our study was to assess the properties and degree of organic matter transformation in drained temperate peatland soils, with particular emphasis on sequential fractionation of SOM and humic acid properties. Due to the fact that in Poland, as many as 90% of non-forest peat bogs have been drained, we compare the mursh horizons that formed after peat bog drainage with the peat horizons that constitute the parent rock (where anaerobiosis occurs and morphological changes in the soil material are absent due to peat bog drainage). Studies were conducted on 11 soil profiles located in central-eastern Poland. Basic physicochemical soil properties were determined: pH, bulk density, contents of ash, SOM, total carbon (TC), and total nitrogen (TN). Sequential carbon fractionation was used to qualitatively analyze organic matter, which allowed for the identification of labile fractions, lipid fractions, humic substances (fulvic and humic acids), and residual fractions. Humic acids (HAs) were extracted using the Schnitzer method and analyzed for their elemental composition and spectrometric parameters in the VIS range. It was demonstrated that SOM transformation in drained temperate peatland soils was correlated with comprehensive changes in the soil’s physical and chemical properties. Compared to peat horizons, topsoil horizons were characterized by higher ash content and density, lower SOM content, and a lower TC/TN ratio. Qualitative SOM transformation during aerobic SOM transformation after draining the studied peatlands consisted of an increase in the amount of labile fractions and humic substances and a decrease in the lipid and residual fractions. The research results have shown that the HAs properties depended on the depth. HAs from topsoil horizons, compared to peat horizons, were characterized by a lower “degree of maturity,” as reflected by the values of atomic ratios (H/C, O/C) and absorbance coefficients (A_4/6 and ΔlogK). It was found that the share of the distinguished SOM fractions and HAs properties were closely correlated with the physical and chemical properties of the soils. The study demonstrated the usefulness of the sequential carbon fractionation method for assessing the effects of dewatered peat transformation. The obtained results could contribute to the development of good practices ensuring high quality of organic matter and stability of ecosystems, as well as to the development of methods for limiting the mineralization of organic matter (SOM), greenhouse gas emissions, and the loss of organic soils in agricultural areas. Full article

Soil organic matter (SOM) governs critical soil functions, including carbon storage, nutrient cycling, and microbial activity; yet the specific fractions responsible for its spectral predictability remain poorly understood. This study addresses a fundamental research gap by comparing visible–near-infrared (vis–NIR), mid-infrared (MIR), and fused spectroscopy for predicting SOM and its components: humic acid (HA), fulvic acid (FA), and Humin. Using 93 soil samples from subtropical croplands in southeastern China, we employed partial least squares regression with full spectra and LASSO-selected wavelengths to build predictive models. Results demonstrated that both vis–NIR and MIR individually provided moderately strong predictive performance for SOM and Humin (R² = 0.79–0.90, CCC = 0.85–0.93), while FA remained unpredictable (R² < 0.24) due to weak, overlapping spectral features. The strong predictability of SOM was primarily attributed to the Humin fraction, which comprises approximately 50 percent of total SOM and exhibits abundant spectrally active functional groups. Contrary to expectations, spectral fusion did not improve predictions because both spectral regions already contained complementary information, and fusion introduced redundancy and scale imbalance rather than increasing effective dimensionality. This study establishes that accurate SOM estimation depends fundamentally on the predictability and abundance of the Humin fraction, providing new mechanistic insights for spectroscopic soil carbon monitoring and highlighting the need for component-specific modeling approaches in soil organic matter research. Full article