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• HO• and RNS during VUV photolysis of NO3− contributed to TCNM formation. • Solution pH, chloride and bicarbonate cannot effectively dimmish TCNM formation. • TCNM formation showed a linear relationship with the Hammett constant. • Newly formed 1161 nitrogen-containing compounds have higher aromaticity. • Results indicated TCNM formation risk of VUV applying in water treatment. Vacuum ultraviolet (VUV) photolysis is recognized as an environmental-friendly treatment process. Nitrate (NO 3 −) and natural organic matter (NOM) are widely present in water source. We investigated trichloronitromethane (TCNM) formation during chlorination after VUV photolysis, because TCNM is an unregulated highly toxic disinfection byproduct. In this study: (1) we found reactive nitrogen species that is generated under VUV photolysis of NO 3 − react with organic matter to form nitrogen-containing compounds and subsequently form TCNM during chlorination; (2) we found the mere presence of 0.1 mmol/L NO 3 − can result in the formation of up to 63.96 µg/L TCNM; (3) we found the changes in pH (6.0-8.0), chloride (1-4 mmol/L), and bicarbonate (1-4 mmol/L) cannot effectively diminish TCNM formation; and, (4) we established the quantitative structure-activity relationship (QSAR) model, which indicated a linear relationship between TCNM formation and the Hammett constant (σ) of model compounds; and, (5) we characterized TCNM precursors in water matrix after VUV photolysis and found 1161 much more nitrogen-containing compounds with higher aromaticity were generated. Overall, this study indicates more attention should be paid to reducing the formation risk of TCNM when applying VUV photolysis process at scale. [Display omitted]. [ABSTRACT FROM AUTHOR]

The complex of natural organic matter (NOM) and iron minerals in sediment is the main host and source of groundwater iodine. However, the transformation pathways of the complex remain unclear. The groundwater and sediment from the Hetao Basin were collected in this study to analyze multi-isotopes, NOM molecular characteristics, and iron mineral phases. The results showed that high-iodine groundwater was mainly observed in the discharge area, where biodegradation of NOM, sulfate reduction and methanogenesis occurred. Compared to the shallow clayey sediments, the confined sandy sediments had lower iodine content, a lower fraction of crystalline iron oxides, and a higher fraction of carbonate associated Fe(II) minerals, suggesting that the release of sediment iodine in the aquifer is related to the transformation of sediment Fe(III) hydroxides/oxides. Moreover, the molecular features of high-iodine groundwater NOM and sandy sediment NOM were characterized by a higher proportion of refractory compounds, suggesting that the reductive transformation of sediment Fe(III) hydroxides/oxides is fueled by degradable organic compounds. The microbial Fe-reducing and/or sulfate-reducing processes cause the enrichment of groundwater iodine in the form of iodide via the transformation of iodine species. These findings provide new insights into the genesis of high-iodine groundwater. [Display omitted] • High-iodine groundwater was observed under reducing conditions with processes of sulfate reduction and methanogenesis. • Transformation of iron hydroxides/oxides fueled by biodegradable NOM caused the release of sediment iodine. • The DOM of high-iodine groundwater was characterized by larger molecular and recalcitrant organic compounds. [ABSTRACT FROM AUTHOR]

Understanding the mechanisms underlying the assembly of communities has long been the goal of many ecological studies. While several studies have evaluated community wide ecological assembly, fewer have focused on investigating the impacts of individual members within a community or assemblage on ecological assembly. Here, we adapted a previous null model β-nearest taxon index (βNTI) to measure the contribution of individual features within an ecological community to overall assembly. This new metric, called feature-level βNTI (βNTIfeat), enables researchers to determine whether ecological features (e.g., individual microbial taxa) contribute to divergence, convergence, or have insignificant impacts across spatiotemporally resolved metacommunities or meta-assemblages. Using βNTIfeat, we revealed that unclassified microbial lineages often contributed to community divergence while diverse groups (e.g., Crenarchaeota, Alphaproteobacteria, and Gammaproteobacteria) contributed to convergence. We also demonstrate that βNTIfeat can be extended to other ecological assemblages such as organic molecules comprising organic matter (OM) pools. OM had more inconsistent trends compared to the microbial community though CHO-containing molecular formulas often contributed to convergence, while nitrogen and phosphorus-containing formulas contributed to both convergence and divergence. A network analysis was used to relate βNTIfeat values from the putatively active microbial community and the OM assemblage and examine potentially common contributions to ecological assembly across different communities/assemblages. This analysis revealed that P-containing formulas often contributed to convergence/divergence separately from other ecological features and N-containing formulas often contributed to assembly in coordination with microorganisms. Additionally, members of Family Geobacteraceae were often observed to contribute to convergence/divergence in conjunction with both N- and P-containing formulas, suggesting a coordinated ecological role for family members and the nitrogen/phosphorus cycle. Overall, we show that βNTIfeat offers opportunities to investigate the community or assemblage members, which shape the phylogenetic or functional landscape, and demonstrate the potential to evaluate potential points of coordination across various community types. [ABSTRACT FROM AUTHOR]

Soil redox conditions exert substantial influence on biogeochemical processes in terrestrial ecosystems. Humid tropical forest soils are often characterized by fluctuating redox, yet how these dynamics affect patterns of organic matter decomposition and associated CO2 fluxes remains poorly understood. We used a 13C-label incubation experiment in a humid tropical forest soil to follow the decomposition of plant litter and soil organic matter (SOM) in response to four redox regimes—static oxic or anoxic, and two oscillating treatments. We used high-resolution mass spectrometry to characterize the relative composition of organic compound classes in the water extractable OM. CO2 production from litter and SOM showed different responses to redox treatments. While cumulative production of SOM-derived CO2 was positively correlated with the length of oxic exposure (r = 0.89, n = 20), cumulative 13C-litter-derived CO2 production was not linked to oxygen availability. Litter-derived CO2 production was highest under static anoxic conditions in the first half of the experiment, and later dropped to the lowest rate amongst the treatments. In anoxic soils, we observed depletion of more oxidized water-extractable OM (especially amino sugar-, carbohydrate-, and protein-like compounds) over the second half of the experiment, which likely served as substrates for anaerobic CO2 production. Results from two-pool kinetic modeling showed that more frequent anoxic exposure limited decomposition of a slow-cycling C pool, but not a fast-cycling pool. These results suggest that aerobic and anaerobic heterotrophs were equally effective at degrading labile substrates released from fresh plant litter in this humid tropical forest soil, while aerobic decomposers were more effective in breaking down the potentially refractory compounds found in SOM. [ABSTRACT FROM AUTHOR]

Predictive biogeochemical modeling requires data-model integration that enables explicit representation of the sophisticated roles of microbial processes that transform substrates. Data from high-resolution organic matter (OM) characterization are increasingly available and can serve as a critical resource for this purpose, but their incorporation into biogeochemical models is often prohibited due to an over-simplified description of reaction networks. To fill this gap, we proposed a new concept of biogeochemical modeling—termed substrate-explicit modeling —that enables parameterizing OM-specific oxidative degradation pathways and reaction rates based on the thermodynamic properties of OM pools. Based on previous developments in the literature, we characterized the resulting kinetic models by only two parameters regardless of the complexity of OM profiles, which can greatly facilitate the integration with reactive transport models for ecosystem simulations by alleviating the difficulty in parameter identification. The two parameters include maximal growth rate (μmax) and harvest volume (Vh) (i.e., the volume that a microbe can access for harvesting energy). For every detected organic molecule in a given sample, our approach provides a systematic way to formulate reaction kinetics from chemical formula, which enables the evaluation of the impact of OM character on biogeochemical processes across conditions. In a case study of two sites with distinct OM thermodynamics using ultra high-resolution metabolomics datasets derived from Fourier transform ion cyclotron resonance mass spectrometry analyses, our method predicted how oxidative degradation is primarily driven by thermodynamic efficiency of OM consistent with experimental rate measurements (as shown by correlation coefficients of up to 0.61), and how biogeochemical reactions can vary in response to carbon and/or oxygen limitations. Lastly, we showed that incorporation of enzymatic regulations into substrate-explicit models is critical for more reasonable predictions. This result led us to present integrative biogeochemical modeling as a unifying framework that can ideally describe the dynamic interplay among microbes, enzymes, and substrates to address advanced questions and hypotheses in future studies. Altogether, the new modeling concept we propose in this work provides a foundational platform for unprecedented predictions of biogeochemical and ecosystem dynamics through enhanced integration with diverse experimental data and extant modeling approaches. [ABSTRACT FROM AUTHOR]

Photochemical production of hydroxyl radical (·OH) from algal organic matter (AOM) collected from Lake Torrens in South Australia was examined using a sunlight simulator. The two AOM isolates featured lower molecular weight, lower chromophoric content, and lower SUVA 254 (0.7 and 0.9, L mgC−1 m−1) than the reference Suwannee River hydrophobic acid (SR-HPO), they had considerably higher apparent quantum yields ( ϕ N O M O H , 3.03 × 10−5 and 2.18 × 10−5) than SR-HPO (0.84 × 10−5). Fluorescence excitation-emission matrix (FEEM) showed that the major components in the AOM were aromatic protein-like and soluble microbial substances. Unique formulas of the two AOM isolates as compared to SR-HPO were revealed using FTICR-MS and classified into four areas, namely protein-like molecules with low O/C (H/C > 1.5, O/C: 0.2–0.4), lignin-derived moieties with low O/C (H/C:1.0–1.5, O/C: 0.1–0.3), protein-like molecules with high O/C (H/C > 1.5, O/C: 0.5–0.7), and carbohydrate derivatives (H/C > 1.5, O/C > 0.7). These unique AOM moieties characterised utilizing FEEM and FTICR-MS were tentatively postulated to contribute to the high ϕ N O M O H . To the best of our knowledge, this is the first study performed to both evaluate natural AOM as an efficient photosensitiser of ·OH and propose AOM moieties responsible for the high ϕ N O M O H . Image 1 • Algal organic matter showed higher quantum yield than Suwannee River organic matter. • Algal organic matter was characterised by FEEM and FTICR-MS. • Possible sources of higher quantum yield were proposed. [ABSTRACT FROM AUTHOR]

Reactive oxygen species (ROS) are thought to play an important, although poorly understood, role in modifying the composition of terrigenous-derived dissolved organic matter (tDOM) upon export to aquatic systems. Of the dominant ROS in natural systems, OH has been shown to substantially modify lignin under laboratory conditions, simulating processes responsible for transformation of DOM in natural waters. Utilizing high performance liquid chromatography (HPLC) in conjunction with ultrahigh resolution mass spectrometry, we examined HPLC fractionated lignin extracts in an effort to establish which fractionated components of the lignin extract were (i) most susceptible to attack by OH and (ii) most likely to be responsible for compounds observed in the DOM. The results indicate that the most polar components of the lignin extract, representing tDOM, could be responsible for a large portion of newly generated formulas observed within DOM in natural waters. This suggests that partially oxidized lignin may be readily altered to compounds observed in DOM which are not typically associated with terrigenous OM, such as alicyclic and condensed aromatic-like compounds. [ABSTRACT FROM AUTHOR]

[Display omitted] • Immobilized enzymes could improve sludge disintegration efficiency. • Enzyme pretreatment increased the abundance of dominant anaerobes. • CLSM and FTICR-MS were employed to analyze the transformation of organic matter. Sludge hydrolysis is a vital step in anaerobic digestion of sludge. This study compared the efficacy of free versus immobilized enzymes at different concentrations in promoting sludge disintegration. Pretreatment with 1,000 mg/L immobilized enzymes was more efficient in promoting sludge disintegration than free enzymes at the same concentration. Under the optimized conditions, volatile fatty acids (VFAs) were produced at 10.6 g/L, accounting for 85 % of total soluble chemical oxygen demand. Improved VFA production was attributed to the release of large amounts of polysaccharides and proteins from the enzymatically pretreated sludge. Released organic matter are the substrates for VFAs generated by the determined microbial community of Firmicutes, Proteobacteria, Bacteroidetes, Actinobacteria, and Chloroflexi. In this study, anaerobic fermentation was used to successfully convert organic matter in sludge into high-value-added VFAs. Therefore, this process can be selected as a strategy to reduce carbon emissions from wastewater treatment plants (WWTPs). [ABSTRACT FROM AUTHOR]

Molecular composition of surface sediments reflects a shift in the nature of organic matter along the land-sea transect in the Pearl River estuary and coastal South China Sea. [Display omitted] • Comprehensive molecular screening of organic matter in surface sediment from land to sea. • Freshwater site is characterized by hydrocarbon and sulfur-containing compound classes. • Marine site shows molecular indicators of phototroph sourced biomass. • FTICR-MS rapidly characterized dynamic changes of organic matter along environmental gradients. The Pearl River drains the second largest watershed in China, funnelling large amounts of freshwater and organic matter into the northern part of the South China Sea through an estuary characterized by pronounced biogeochemical gradients. In this study we used a newly developed single injection Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS) method to analyze organic extracts of surface sediments transitioning from freshwater to marine settings in the Pearl River estuary and coastal South China Sea. Results show a complex mixture of molecular markers, with distinct fingerprints characterizing the freshwater and saline sites. Notable examples include steroidal and thiophenic species at the freshwater site, indicative of possible anthropogenic organic matter inputs from the continent; on the other hand, samples from the coastal site are uniquely characterized by putative tetrapyrrole species, indicative of phaeopigments sourced from marine phytoplankton. This study demonstrates the potential application of single injection FTICR-MS in rapidly probing the dynamic changes of organic matter sources and fates occurring in estuaries influenced by anthropogenic activities. [ABSTRACT FROM AUTHOR]

[Display omitted] • Soil fractions had distinct SOC profiles, especially silt and clay and coarse POM. • Physical protection of SOC was altered by temperature and moisture. • Simple C was altered by both temperature and moisture. • Complex C was altered by moisture. Understanding the complex interplay of biotic and abiotic controls on soil organic carbon (SOC) stabilization and aggregate formation is a vital and evolving research field, with implications for C and climate change modeling. Here, we delve into the effects of temperature and moisture treatments on aggregate SOC composition. Aggregate fractions representing different levels of physical protection for SOC were isolated three times during a 6-month incubation with 2x2 factorial temperature and moisture treatments (22 or 30 °C, 45% or 65% water-filled pore space). The chemical composition within each fraction was analyzed using high-resolution Fourier-transform ion cyclotron resonance mass spectrometry (FTICR-MS) to evaluate the prevalence of different classes of C compounds by fraction and temperature and moisture treatments. In addition, a partial least square regression (PLSR) was used to explore potential correlations between relative abundance of C compound classes and C content within aggregate fractions. We found that organic matter in the macro- (>250 µm) and micro-aggregates (53 to 250 µm) was relatively enriched in lipid-, carbohydrates-, and protein--like compounds compared to silt and clay fractions (<53 µm). Organic matter in silt and clay was, on the other hand, relatively enriched in compounds with no specific classification, with overall high aromaticity. Broadly, simpler, low-molecular-weight C storage was altered by both temperature and moisture, while complex C storage was especially altered by moisture, within aggregates. Univariate effects of temperature and moisture on specific compound classes varied by soil fraction, but across fractions temperature increased the relative abundance of condensed- and unsaturated hydrocarbon-, tannin-, and amino sugar-like compounds and decreased the relative abundance of protein-like compounds. Moisture increased tannin-, condensed hydrocarbon-like compounds, and the overall aromaticity, and had the most pronounced effect in fractions occluded within macroaggregates, suggesting that substrate diffusion and pore connectivity within the aggregate environment drive the composition of C protected within aggregates. The PLSR indicated that treatments promoted different compounds to contribute to C accrual. Under dry conditions, condensed hydrocarbon-like compounds were associated with microaggregates, while amino sugar-like compounds were associated with macroaggregates and coarse particulate organic matter (POM), and lipid-like and aliphatic compounds were associated with silt and clay. Temperature effects on PLSR results were most visible in silt and clay fractions, where carbohydrate- and tannin-like compounds were associated with C content. This suggests that warmer conditions under climate change may more substantially alter mineral-associated C content, while changing water regimes will alter C content in physically protected environments, with the most significant changes under cool and moist conditions. Overall, our data reveal distinct resource pools in different climate and aggregate environments, a baseline for our understanding of SOC accrual and soil structure under different conditions. More research into how microbes process physically protected SOC under altered environments may fine-tune our ability to predict soil functions including water behavior and nutrient release. [ABSTRACT FROM AUTHOR]

Size-exclusion chromatography was coupled to electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (SEC–FTICR–MS) to separate a fulvic acid isolate into three size fractions and to determine the elemental composition of fulvic acids in these fractions. Molecular formulas of about 3000 ions in the mass range of 200–700Da were derived, many of which occur in all three fractions and follow the same system of elemental composition. Product ion spectra generated by SEC coupled to quadrupol-time-of-flight-MS (Q-TOF-MS) confirmed that the ions of all three fractions are basically polycarboxylates with hardly any other functional moiety. However, SEC–FTICR–MS revealed that the ions generated from the high molecular weight (HMW) fraction are enriched in carboxyl groups and are more aromatic as compared with the low molecular weight (LMW) fraction. These findings support the idea that the HMW fulvic acids are formed from LMW fulvic acids. The shift in the relative frequency of ions from the LMW to the HMW fraction is in line with different interaction mechanisms: HMW fulvic acids may be aggregates held together by electrostatic interaction of the carboxylate groups via hydrogen bonds or with polyvalent cations or by hydrophobic interaction of their carbon backbone, or consist of LMW fulvic acids covalently bound to each other or to (aliphatic) alcohols. [Copyright &y& Elsevier]

The gas-phase reactions of the lanthanide series cations Ln+ (Ln=La–Lu, except Pm) with methanol, ethanol, and 2-propanol were studied by Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS). The majority of the lanthanide cations react exothermically with the alcohols, with formation of LnO+ and LnOH+ ions as main primary products. These ions participate in subsequent reactions with the alcohols that lead to Ln(OR)x(HOR)y+ species, where x=1–2 and y=0–3. The study of the reaction sequences and of the corresponding kinetics showed the existence of important differences in the relative reactivity of the lanthanide series cations, in agreement with the known data on the reactivity of these metal cations with other organic molecules. The results obtained also evidenced the similarities between the reactivity of the lanthanide series cations and of group 3 metal cations. [Copyright &y& Elsevier]