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Soil organic matter (SOM) plays a key role in the global carbon and nitrogen cycles. Soil biogeochemistry is regularly studied by extracting the base-soluble fractions of SOM: acidinsoluble humic acid (HA) and acid-soluble fulvic acid (FA). Electrospray ionization−Fourier transform−ion cyclotron resonance−mass spectrometry (ESI-FT-ICR-MS) is commonly utilized for molecularly characterizing these fractions. Different sample preparation techniques exist for the analysis of HA and FA though questions remain regarding data comparability following different preparations. Comparisons of different sample preparation techniques here revealed that the negative-mode ESI-FT-ICRMS analytical window can be skewed to detect different groups of molecules, with primary differences in oxygenation, aromaticity, and molecular weight. It was also observed that HA and FA from soils versus an aquatic matrix behaved very differently. Thus, we conclude that sample preparation techniques determined to be ?most optimal? in our study are in no way universal. We recommend that future studies of HA and FA involve similar comparative studies for determining the most suitable sample preparation technique for their particular type of HA or FA matrices. This will enhance data comparability among different studies and environmental systems and ultimately allow us to better understand the complex composition of environmental matrices. Made available in DSpace on 2022-09-28T18:06:04Z (GMT). No. of bitstreams: 1 P-Comparison-of-Sample-Preparation-Techniques-for-the-8722ESI-FTICR-MS-Analysis-of-Humic-and-Fulvic-Acids.pdf: 4440230 bytes, checksum: b5f1ae1f920e91892bfd9853652654d3 (MD5) Previous issue date: 2022

With the increased occurrence of wildfires around the world, interest in the chemistry of pyrogenic organic matter (pyOM) and its fate in the environment has increased. Upon leaching from soils by rain events, significant amounts of dissolved pyOM (pyDOM) enter the aquatic environment and interact with microbial communities that are essential for cycling organic matter within the different biogeochemical cycles. To evaluate the biodegradability of pyDOM, aqueous extracts of laboratory-produced biochars were incubated with soil microbes, and the molecular changes to the composition of pyDOM were probed using ultrahigh-resolution mass spectrometry (Fourier transform–ion cyclotron resonance–mass spectrometry). Given that solar irradiation significantly affects the composition of pyDOM during terrestrial-to-marine export, the effects of photochemistry were also evaluated in the context of pyDOM biodegradability. Ultrahigh-resolution mass spectrometry revealed that many different (both aromatic and aliphatic) compounds were biodegraded. New labile compounds were produced, 22 %–40 % of which were peptide-like. These results indicated that a portion of pyDOM has been labilized into microbial biomass during the incubations. Fluorescence excitation–emission matrix spectra revealed that some fraction of these new bio-produced molecules is associated with proteinaceous fluorophores. Two-dimensional 1H–1H total correlation nuclear magnetic resonance (NMR) spectroscopy identified a peptidoglycan-like backbone within the microbially produced compounds. These results are consistent with previous observations of peptidoglycans within the soil and ocean nitrogen cycles where remnants of biodegraded pyDOM are expected to be observed. Interestingly, the exact nature of the bio-produced organic matter was found to vary drastically among samples indicating that the microbial consortium used may produce different exudates based on the composition of the initial pyDOM. Another potential explanation for the vast diversity of molecules is that microbes only consume low molecular-weight compounds, but they also produce reactive oxygen species (ROS), which initiate oxidative and recombination reactions that degrade high molecular-weight compounds and produce new molecules. Some of the bio-produced molecules (212–308 molecular formulas) were identified in estuarine and marine (surface and abyssal oceanic), and 81–192 of these formulas were of molecular composition attributed to carboxyl-rich alicyclic molecules (CRAM). These results indicate that some of the pyDOM biodegradation products have an oceanic fate and can be sequestered into the deep ocean. The observed microbially mediated diversification of pyDOM suggests that pyDOM contributes to the observed large complexity of natural organic matter observed in riverine and oceanic systems. More broadly, our research shows that pyDOM can be substrate for microbial growth and be incorporated into environmental food webs within the global carbon and nitrogen cycles.

Sediment samples along a transect extending from the Mississippi River Birdsfoot Delta to the Mississippi Canyon on the Louisiana continental shelf were examined, by advanced analytical techniques, electrospray ionization coupled to a 12T Fourier transform ion cyclotron resonance mass spectrometer (ESI-FTICR-MS) and quantitative solid-state multiple cross polarization magic angle spinning (multi-CPMAS) 13C NMR, in an effort to understand the source and export of terrigenous organic matter to the Gulf of Mexico. Both NMR and mass spectral data indicate that condensed aromatics (CA) and carboxyl-containing aliphatic molecules (CCAM) are present at the mouth of the river, reflective of high contributions from terrigenous soil-like organic matter. Mass spectral peak magnitudes of CA diminish by 15%, with increasing distance offshore, and represent 30% of integrated NMR peak areas. In contrast, mass spectral and NMR CCAM peaks increase by 7 and 13%, respectively. These trends in humic acid extracts, provide novel molecular evidence of terrigenous organic matter deposition in offshore sediments.

Pyrogenic organic matter (pyOM) is the solid residue left after pyrolysis of organic matter, a process occurring in nature during forest fires. Upon rain events, pyrogenic dissolved organic matter (pyDOM) leaches into the rain water and is transferred to the aquatic environment where it has been identified as an important component of the global carbon cycle. Overall, pyDOM consists of highly condensed aromatic compounds (ConAC) and poorly characterized aliphatic molecules. While the ConAC are thought to be persistent in the environment, a large ConAC accumulation that would match the calculated fluxes of pyDOM formation and export has not been observed. Photo-degradation has been identified as a major pyDOM sink, and it can potentially account for the discrepancy in the global mass balance of pyDOM. Photochemistry of pyDOM has been studied to a certain extent, but neither the structural transformation pathways of pyDOM nor how they relate to pyrolysis temperature and parent feedstocks are well understood. In response to this need, we have examined the products after photo-irradiation of pyDOM derived from a temperature series (250, 400, 525, 650 °C) of oak biochars made under controlled laboratory conditions, which can be considered model pyrogenic substances. Ultrahigh resolution mass spectrometry (FT-ICR-MS), one-dimensional 1H NMR, and two-dimensional 1H-1H total correlation spectroscopy (TOCSY) NMR were used to evaluate the compositional changes that occurred with photo-irradiation. In agreement with previous studies, pyDOM aryl groups were the most photo-labile, and alkyl and O-alkyl groups were photo-produced. A new finding is that polysubstituted olefinic moieties of pyDOM were also photo-degraded. Using TOCSY we identified several small molecular weight compounds whose abundances changed non-linearly across the combustion continuum which suggests that different radical processes occur in the different char leachates. Using mass spectrometric data we observed that pyDOM from oak chars made at lower temperatures (250 and 400 °C), as well as pyDOM from a grass char prepared at 650 °C, photo-transformed to a more hydrogenated and oxygenated composition. In contrast, pyDOM from higher temperature char leachates (525 and 650 °C) transformed predominantly into smaller aliphatic compounds. To explain these differences, we propose a photo-transformation mechanism for ConAC which includes oxygenation of ConAC, ring-opening reactions, and sequential decarboxylation yielding small aliphatic N-rich molecules (marine-like composition). These structures could be further polymerized by reactive oxygen species to form straight-chain alkanes if not consumed by microorganisms. Results from these controlled experiments reveal that the extent of photo-transformation appears to be a function of production temperature and parent feedstock. This study enhances our understanding of ConAC and pyDOM, their terrestrial-to-marine transfers, geochemical stability, and eventual fate in sunlit environments. Here we also show the value of structural characterization of pyDOM, and reveal the many unknowns left to be answered for this complex and analytically challenging type of organic matter.

Microbes (bacteria, phytoplankton) in the ocean are responsible for the copious production of exopolymeric substances (EPS) that include transparent exopolymeric particles. These materials act as a matrix to form marine snow. After the Deepwater Horizon oil spill, marine oil snow (MOS) formed in massive quantities and influenced the fate and transport of oil in the ocean. The processes and pathways of MOS formation require further elucidation to be better understood, in particular we need to better understand how dispersants affect aggregation and degradation of oil. Toward that end, recent work has characterized EPS as a function of microbial community and environmental conditions. We present a conceptual model that incorporates recent findings in our understanding of the driving forces of MOS sedimentation and flocculent accumulation (MOSSFA) including factors that influence the scavenging of oil into MOS and the routes that promote decomposition of the oil post MOS formation. In particular, the model incorporates advances in our understanding of processes that control interactions between oil, dispersant, and EPS in producing either MOS that can sink or dispersed gels promoting microbial degradation of oil compounds. A critical element is the role of protein to carbohydrate ratios (P/C ratios) of EPS in the aggregation process of colloid and particle formation. The P/C ratio of EPS provides a chemical basis for the “stickiness” factor that is used in analytical or numerical simulations of the aggregation process. This factor also provides a relative measure for the strength of attachment of EPS to particle surfaces. Results from recent laboratory experiments demonstrate (i) the rapid formation of microbial assemblages, including their EPS, on oil droplets that is enhanced in the presence of Corexit-dispersed oil, and (ii) the subsequent rapid oil oxidation and microbial degradation in water. These findings, combined with the conceptual model, further improve our understanding of the fate of the sinking MOS (e.g., subsequent sedimentation and preservation/degradation) and expand our ability to predict the behavior and transport of spilled oil in the ocean, and the potential effects of Corexit application, specifically with respect to MOS processes (i.e., formation, fate, and half-lives) and Marine Oil Snow Sedimentation and Flocculent Accumulation.

With the increased occurrence of forest fires around the world, interest in the chemistry of pyrogenic organic matter (pyOM) and its fate in the environment has increased. Upon leaching from soils by rain events, significant amounts of dissolved pyOM (pyDOM) enter the aquatic environment and interact with microbial communities that are essential for cycling organic matter within the different biogeochemical cycles. To evaluate the bio-reactivity of pyDOM, aqueous extracts of laboratory-produced chars were incubated with soil microbes and the molecular changes to the composition of pyDOM were probed using ultrahigh resolution mass spectrometry (Fourier transform – ion cyclotron resonance – mass spectrometry). Given that photo-degradation also affects the composition and reactivity of pyDOM during terrigenous-to-marine export, the effects of photochemistry were also evaluated in the context of the bio-reactivity of pyDOM. Ultrahigh resolution mass spectrometry revealed that, after incubation, many different (both aromatic and aliphatic) compounds were degraded, and new labile compounds, 22–40 % of which were peptide-like, were produced. This indicated that a portion of pyDOM has been labilized into microbial biomass during the incubations. Fluorescence excitation-emission matrix spectra revealed that some fraction of these new molecules is associated with fluorophores from proteinaceous and/or autochthonous/microbial biomass origin. Two-dimensional 1H-1H total correlation NMR spectroscopy identified a peptidoglycan-like backbone within the microbially produced compounds. These results are consistent with previous observations of nitrogen from peptidoglycans within the soil and ocean nitrogen cycles. Interestingly, the exact nature of the bio-produced organic matter was found to vary drastically among samples indicating that the used microbial consortium may produce different exudates based on the composition of the initial pyDOM. Another potential explanation for the vast diversity of molecules is that microbes only consume low molecular weight compounds, but they also produce reactive oxygen species (ROS), which initiate oxidative and recombination reactions that produce new molecules. The observed microbially-mediated diversification of pyDOM suggests that pyDOM contributes to the observed large complexity of natural organic matter. More broadly, pyDOM can be substrate for microbial growth and be incorporated in environmental food webs.

Pyrogenic dissolved organic matter (pyDOM) is known to be an important biogeochemical constituent of aquatic ecosystems and the carbon cycle. While our knowledge of pyDOM’s production, compos...

The Deepwater Horizon oil spill is the largest in US history in terms of oil released and the amount of dispersants applied. It is also the first spill in which the incorporation of oil and/or dispersant into marine snow was directly observable. Marine snow formation, incorporation of oil (MOS – marine oil snow) and subsequent settling to the seafloor, has been termed MOSSFA: Marine Oil Snow Sedimentation and Flocculent Accumulation. This pathway accounts for a significant fraction of the total oil returning back to the sea floor. GOMRI funded studies have determined that important drivers of MOSSFA include, but are not limited to, an elevated and extended Mississippi River discharge, which enhanced phytoplankton production and suspended particle concentrations, zooplankton grazing, and enhanced mucus formation (operationally defined as EPS, TEP, marine snow). Efforts thus far to understand the mechanisms driving these processes are being used to aid in the development of response strategies. These include modeling efforts towards predicting plume dynamics. Although much has been learned during the GOMRI program (reviewed herein and elsewhere), there are still important unknowns that need to be addressed. Understanding of the conditions under which significant MOSSFA events occur, the consequences to the biology, the sinking velocity and distribution of the MOSSFA as well as its ultimate fate are amongst the most important consideration for future studies. Also important is the modification of the oil and dispersant within the MOS and its transport as part of MOSSFA. Ongoing studies are needed to further develop our understanding of these complex and interrelated phenomena.

NMR spectroscopy is widely used in the field of aquatic biogeochemistry to examine the chemical structure of dissolved organic matter (DOM). Most aquatic DOM analyzed by proton NMR (1 H NMR) is concentrated mainly by freeze-drying prior to analysis to combat low concentrations, frequently

Forecasting the long-term fate of plutonium (Pu) is becoming increasingly important as more worldwide military and nuclear-power waste is being generated. Nagasaki sediments containing bomb-derived Pu that was deposited in 1945 provided a unique opportunity to explore the long-term geochemical behavior of Pu. Through a combination of selective extractions and molecular characterization via electrospray ionization Fourier-transform ion cyclotron resonance mass spectrometry (ESI-FTICRMS), we determined that 55 ± 3% of the bomb-derived 239,240Pu was preferentially associated with more persistent organic matter compounds in Nagasaki sediments, particularly those natural organic matter (NOM) stabilized by Fe oxides (NOMFe-oxide). Other organic matter compounds served as a secondary sink of these bomb-derived 239,240Pu (31 ± 2% on average), and

Soluble extractives in wood function to protect living trees from destructive agents and also contribute to wood color and fragrance. Some extractive components have biological activities with medical applications. They also play important roles in wood processing and related applications. To increase the knowledge of wood chemistry, maple and oak were extracted by water. Ultraviolet/visible (UV/vis) spectroscopy indicated the presence of a phenolic compound, resorcinol, in maple extractives having higher molecular mass and more aromatic components than oak extractives. Negative and positive electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI FT-ICR-MS) identified thousands of formulas in the two samples in the m/z range of 200 to 800. They mainly fall into the lignin-like, carbohydrate-like, and tannin-like compound categories. The top 25 peaks (ie, formulas) with the highest relative magnitude in negative ESI represented nearly 50% of the summed total spectral magnitude of all formulas assigned in the maple and oak extractives. Furthermore, the base peak (ie, most abundant peak) accounted for about 14% of the total abundance in each wood sample. Literature comparisons identified 17 of 20 formulas in the top five peaks of the four spectra as specific bioactive compounds in trees and other plants, implying the potential to explore utilization of maple and oak extractives for functional and medicinal applications. The various profiling of the top 25 peaks from the two samples also suggested the possible application of FT-ICR-MS for detecting chemical markers useful in profiling and identification of wood types and sources.

Acid mine drainage (AMD) formed from pyrite (iron disulfide) weathering contributes to ecosystem degradation in impacted waters. Solar irradiation has been shown to be an important factor in the biogeochemical cycling of iron in AMD-impacted waters, but its impact on dissolved organic matter (DOM) is unknown. With a typical AMD-impacted water (pH 2.7-3) collected from the Perry State Forest watershed in Ohio, we observed highly efficient (>80%) photochemical mineralization of DOM within hours in a solar simulator resembling twice summer sunlight at 40°N. We confirmed that the mineralization was initially induced by •OH formed from FeOH2+ photodissociation and was inhibited 2-fold by dissolved oxygen removal, suggesting the importance of both the photochemical reaction and oxygen involvement. Size exclusion chromatography and Fourier transform ion cyclotron resonance mass spectrometry elucidated that any remaining organic matter was comprised of smaller and highly aliphatic compounds. The quantitative and qualitative changes in DOM are likely to constitute an important component in regional carbon cycling and nutrient release and to influence downstream aquatic ecosystems in AMD-affected watersheds.

Following the Deepwater Horizon oil spill in the Gulf of Mexico, natural marine snow interacted with oil and dispersants forming marine oil snow (MOS) that sank from the water column to sediments. Mesocosm simulations demonstrate that Macondo surrogate oil incorporates into MOS and can be isolated, extracted, and analyzed via Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS). Up to 47% of the FTICR-MS signal from MOS extracts can be attributed to formulas also found in Macondo surrogate oil demonstrating extensive oil incorporation. Additionally, oxygenation patterns for MOS extracts provide evidence for degraded oil compounds. Formulas having similar double bond equivalents but higher oxygen content (MOS CHO: CHO2-9, DBE2-16, MOS CHON: CHO0-7N1, DBE9-18; Macondo CHO: CHO1-4, DBE2-15, CHON: CHO0-3N1, DBE9-21) were found in MOS extracts generating isoabundance distributions similar to those of environmentally aged oil. Such shifts in molecular composition are consistent with the transformation of high DBE oil components, unobservable by FTICR-MS until oxygenation in the mesocosms. Low light conditions and the rapid proliferation of hydrocarbon-degraders observed in parallel studies suggest biological activity as the primary cause of oil degradation. MOS may thus represent an important microenvironment for oil degradation especially during its long transit below the euphotic zone to sediments.

9 páginas.- 5 figuras.- referencias., Soil water repellency (SWR) is a physical property due to a complex interaction of factors (e.g., fire, soil organic matter, soil texture) that reduces the soil water infiltration capacity. Traditionally, SWR is attributed to the accumulation and redistribution of hydrophobic compounds within soil profile. To obtain further insight into chemical compounds, which could be associated with SWR, a study was done on coarse (1–2 mm) and fine (< 0.05 mm) granulometric fractions of burned and unburned sandy soils under two Mediterranean vegetation biomes from Doñana National Park (Spain). The water drop penetration time (WDPT) test was used to assess the SWR. The molecular composition of extracted humic substances from the soil organic matter (SOM) was determined by Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR/MS). Partial least squares (PLS) regressions showed that the SWR can be predicted (P = 0.006) solely based on the abundances of approximately 1200 common compounds determined by FT-ICR/MS. This model confirmed the significant correlation between a specific SOM molecular composition and the SWR. The comparative analysis revealed that the SWR in the burned samples was significantly (P < 0.05) related to the abundance of aromatic and condensed compounds, while in the unburned samples there was a significant influence of aromatic hydrocarbons and lignin compounds. In the fine fraction, lipid compounds were significantly associated with the SWR. Contrastingly, the coarse fraction did not show any correlation. Alternatively, soils with a high SWR were significantly related to the presence of lipids and lignin. This analysis showed that combining FT-ICR/MS molecular characterizations with statistical treatments is a powerful approach for exploratory analysis suggesting that the structural features associated with SWR in the studied soils are different depending on the types of vegetation or the soil physical fractions with different particle size., We would like to thank the three anonymous reviewers for their helpful comments on the first version of this paper. Following their suggestions,we included several improvements in the manuscript. We are also grateful to projects MarkFire (PAIDI2020, PY20_01073), co-funded by Junta de Andalucía and EU FEDER funds, and EROFIRE (PCIF/RPG/0079/2018) funded by Fundação para a Ciência e a Tecnologia (FCT, Portugal). The Spanish Ministry of Science and Innovation is acknowledged for funding the project PID2019-108672RJ-I00 and the “Ramón y Cajal” postdoctoral contract of Ana Z. Miller [grant number RYC2019-026885-I]. Espacio Natural de Doñana and Estación Biológica de Doñana are acknowledged for technical and logistic support through Project INTERCARBON (2017/19).

Defatted cottonseed meal is a N-rich biomass that deserves valorized recycling. In this work, slow pyrolysis was applied to produce pyrolytic bio-oil from this biomass. Both the upper oily and lower aqueous fractions were characterized by elemental analysis, Fourier transform infrared (FT-IR) spectroscopy, and ultrahigh resolution Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) with both negative and positive electrospray ionization modes. The contents of C and S were much higher in the oily fraction than in the aqueous fraction. Furthermore, the composition and molecular formulas of the organic compounds in the oily fraction were much more complex and diverse. From the mass spectral analysis, 9 and 14 different oxygen heteroatom classes were detected in the aqueous and oily fractions, respectively. While CHON compounds were found in both fractions, CHONS compounds were detected only in the oily fraction. The van Krevelen diagrams from the FT-ICR-MS data showed the presence of lipid-, peptide-, and lignin-like components in both fractions. However, carbohydrate-like components were found only in the oily fraction. Furthermore, the diagrams revealed more N species in the oily fraction that mostly clustered with O/C

Large amounts of mucous-rich oil-containing marine snow formed in surface waters adjacent to the Deepwater Horizon spill. This marine oil snow (MOS) was implicated in oil delivery to the seafloor. Whether the use of chemical dispersants increased or decreased MOS sedimentation remains controversial. We conducted mesocosm experiments testing the effects of oil and oil plus a dispersant on MOS formation and sedimentation, in coastal seawater . The four treatments used were a surrogate Macondo oil water accommodated fraction (“WAF”), two concentrations of chemically-enhanced WAF (“CEWAF” and diluted CEWAF, “DCEWAF”) containing a dispersant and oil, and Controls (no additions). Based on radiocarbon and 13 C NMR results, the presence of dispersants enhanced the amounts of petro-carbon being incorporated into the sinking oil-carrying aggregates (aka MOS). However, most of the chemically-dispersed oil preferentially partitioned into the colloidal and suspended particulate fractions rather than into the rapidly forming MOS. Thus the oil and non-petro-carbon sedimentation efficiency in treatments with a dispersant was much lower, compared to those in the Control and WAF treatments, during the four-day mesocosm experiment. Formation of MOS and its subsequent sinking sequestered the oil in two stages: first via terrestrial-derived detritus containing humic compounds, and subsequently via freshly produced material, such as exopolymeric substances produced by phytoplankton and bacteria.

Large-scale exopolymeric substances (EPS) formation was observed in contaminated surface waters of the Gulf of Mexico , after the Deepwater Horizon oil spill. The conditions under which EPS are produced can cause variations in their physico-chemical properties , affecting the fate of the oil through either emulsification or coagulation with particles, followed by aggregation and marine oil snow (MOS) sedimentation . Here, we report results from a four-day mesocosm experiment that examined EPS production, the change in the bulk chemical composition (mainly polysaccharides and proteins), as well as the partitioning into different size fractions (suspended particulate matter (SPM), colloidal fraction, and sinking MOS). The treatments included 1) natural coastal seawater (Control), 2) a water accommodated fraction of oil (WAF), 3) a chemically-enhanced WAF with addition of oil dispersant Corexit (CEWAF), and 4) a diluted CEWAF (DCEWAF). Generally, the presence of WAF stimulated more extracellular polysaccharide production, whereas the addition of Corexit promoted more protein production. Moreover, marine aggregates changed from a terrestrial signature (higher aromaticity, lower EPS content and more uniform monosaccharide distribution) in the early stages of the experiment, to a fresher autochthonous signature (less aromatic, higher EPS content and glucose-dominated monosaccharide distribution) in the later stage of the mesocosm experiment. Corexit promoted the association between oil and proteins, assisting to emulsify the oil in colloids and SPM and delay the settling of EPS and oil (MOS) for the duration of the mesocosm. Furthermore, when oil, especially Corexit-dispersed oil, was present, extracellular polysaccharides were preferentially incorporated into sinking MOS relative to proteins, as evidenced from a lower protein-C/carbohydrate-C ratio of the sinking MOS than those of SPM and colloidal fraction in WAF, CEWAF and DCEWAF, respectively. This is in contrast to a higher protein-C/carbohydrate-C ratio in the sinking marine snow than those of SPM and colloidal fraction in the control. Likely, microbially-mediated extracellular polysaccharides are the key component that anchors the mineral ballast until the aggregates become dense enough and overcome the buoyancy added to the aggregates as a result of their association with oil/Corexit. We conclude that interactions between Corexit and EPS components regulate petroleum hydrocarbon distribution between the water column and sinking MOS.

Summary Examination of wood decking that has been subjected to environmental change for about a decade in contact with Fe nails in the absence of sunlight shows significant modification due to active Fenton chemistry. The wood is blackened and the analysis of benzenepolycarboxylic acids shows that polycondensed aromatic molecules, commonly associated with black carbon from pyrogenic sources, are formed from the lignin abiotically and without pyrolysis. Because this transformation process occurs globally in soils, these results indicate that black carbon found globally in soils and other natural environments may not be exclusively from pyrogenic sources and that Fenton oxidation of wood is capable of producing black carbon. Such a finding will have an impact on the validity of global estimates of pyrogenic black carbon inputs to the environment.

Marine sinking particulate organic matter (POM), acting as a link between surface primary production and burial of organic matter in marine sediments, undergoes a variety of physical and biochemical alterations on its way to the deep ocean, resulting in an increase in its un-characterizable proportion with diagenesis. Further, the binding ligands in POM for iron, an essential nutrient to marine life and tightly coupled with organic matter, has rarely been studied. In the current study, we employed an approach combining sequential extraction with ultrahigh resolution mass spectrometry (ESI-FTICRMS), in order to explore and unravel the chemical characteristics of organic matter compounds relevant to marine particle flux within the mesopelagic and deep ocean, with a focus on the potential iron-carrying molecules. With increasing depth, POM increases in aliphaticity, and decreases in intensity-normalized O/C ratios, aromatics, and carboxylic-rich alicyclic molecules (CRAM)-like compounds. The potential iron-carrying molecules account for ∼14% of total identified molecules, and appear to have been incorporated into the marine particles via ion complexation, hydrophobic interaction, and/or interlayered “occlusion.” The relative abundance of iron-binding organic molecules in these three operationally-defined categories changes with depth: “surficially-complexed” fraction decreases with depth, the “interlayered-occluded” fraction increases to a comparable extent and “hydrophobic interaction” fraction occurs at all depths. Collectively, the potential iron-carrying organic molecules exhibit a set of unique molecular characteristics: a relatively lower average H/C ratio and a higher O/C ratio compared to bulk POM, a dominance of aromatics, black carbon-like compounds and CRAM-like compounds, and minor amounts of aliphatics. These molecules exhibit partial similar molecular features as precursors formed from photochemical reactions in the surface ocean, but they have been greatly modified by flux processes. Noticeably, a minor fraction of these iron-carrying molecules (

Rationale Soil fulvic acids (FAs) are considered to be a highly reactive pool of soil organic matter. The functions of FAs are related to their chemical structures, the details of which are largely unidentified. To better understand them, Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS) must be a useful but generally unused tool. Methods The structural properties of the components of five FA samples from a variety of soils were determined using FTICR-MS with negative-mode electrospray ionization. The peaks were assigned to molecular formulae, which were categorized into seven compound groups based on the H/C-O/C van Krevelen diagram. Ramp 13 C cross polarization/magic angle spinning nuclear magnetic resonance (NMR) spectra with phase-adjusted spinning side bands were also recorded to estimate the C composition. Results From FTICR-MS, molecular formulae were assigned to 1746-2605 peaks across the m/z range of 200-700. Those aligned in the lignin-like, tannin-like, and condensed aromatic regions of the van Krevelen diagram accounted for 49-58%, 4-20%, and 18-39% of the total peak magnitude, respectively. The proportion of the summed peak magnitudes that were detected in the lignin-like and condensed aromatic regions correlated positively to the aromatic C% as estimated by 13 C NMR. From Kendrick mass defect analysis using a carboxyl group, 94 molecular formulae were assigned to condensed aromatic acids, of which the maximum ring number was 4-7, as potential structures. Conclusions A high proportion of lignin-like formulae and condensed aromatics, including those probably condensed aromatic acids with small ring numbers, as well as the existence of tannin-like formulae, which were generally lacking in soil humic acids, was suggested as a common feature of soil FAs.

Pyrogenic carbon (pyC) or fire-derived organic C (e.g., charcoal and soot), while generally considered stable in soils and sediments, can leach into pore waters forming dissolved pyrogenic organic carbon (pyDOC). This pyDOC may be exported to the ocean (about 10% riverine DOC may be pyrogenic). Yet, the processes which control this export and how pyrogenic dissolved organic matter (pyDOM) lability is related to its chemical composition are poorly understood. Thus, pyDOM was leached from a thermal series of oak and grass chars (250-650 °C) and photoirradiated in a solar simulator. About 10-20% of oak char leachate pyDOC was mineralized over five days, with greater proportions lost from leachates of higher temperature parent chars. Proton NMR revealed decreased relative amounts of aryl-C and increased low molecular weight C1 and alkyl-C components during the photo-incubation. Quantification of benzenepolycarboxylic acid (BPCA), molecular markers for condensed aromatic carbon (ConAC), indicated that 75-94% of ConAC was lost during the first five days of photoincubation, the majority of which occurred within the first 2 days, with a preference toward loss of ConAC of larger cluster sizes. Over 96-day microbial incubations, 37 to 48% of pyDOC was lost with modelled half-lives of about 13 days. Much of this was low molecular weight C1 compounds, while only 1 to 2% of ConAC was lost, with a preference for losses of smaller cluster size ConAC. Slightly greater proportions of both total pyC and ConAC was lost from pre-photodegraded pyDOM leachates. These results highlight the large portion of pyDOM that is potentially remineralized or transformed in aquatic systems at short timescales, and the need to examine both condensed and non-condensed portions of pyDOM to understand the effects of fires on aquatic biogeochemistry.

Methane (CH4 ), a potent greenhouse gas, is the second most important greenhouse gas contributor to climate change after carbon dioxide (CO2 ). The biological emissions of CH4 from wetlands are a major uncertainty in CH4 budgets. Microbial methanogenesis by Archaea is an anaerobic process accounting for most biological CH4 production in nature, yet recent observations indicate that large emissions can originate from oxygenated or frequently oxygenated wetland soil layers. To determine how oxygen (O2 ) can stimulate CH4 emissions, we used incubations of Sphagnum peat to demonstrate that the temporary exposure of peat to O2 can increase CH4 yields up to 2000-fold during subsequent anoxic conditions relative to peat without O2 exposure. Geochemical (including ion cyclotron resonance mass spectrometry, X-ray absorbance spectroscopy) and microbiome (16S rDNA amplicons, metagenomics) analyses of peat showed that higher CH4 yields of redox-oscillated peat were due to functional shifts in the peat microbiome arising during redox oscillation that enhanced peat carbon (C) degradation. Novosphingobium species with O2 -dependent aromatic oxygenase genes increased greatly in relative abundance during the oxygenation period in redox-oscillated peat compared to anoxic controls. Acidobacteria species were particularly important for anaerobic processing of peat C, including in the production of methanogenic substrates H2 and CO2 . Higher CO2 production during the anoxic phase of redox-oscillated peat stimulated hydrogenotrophic CH4 production by Methanobacterium species. The persistence of reduced iron (Fe(II)) during prolonged oxygenation in redox-oscillated peat may further enhance C degradation through abiotic mechanisms (e.g., Fenton reactions). The results indicate that specific functional shifts in the peat microbiome underlie O2 enhancement of CH4 production in acidic, Sphagnum-rich wetland soils. They also imply that understanding microbial dynamics spanning temporal and spatial redox transitions in peatlands is critical for constraining CH4 budgets; predicting feedbacks between climate change, hydrologic variability, and wetland CH4 emissions; and guiding wetland C management strategies.

Plant biomass is the primary source material for the formation of soil organic matter, which comprises the largest terrestrial pool of the global C cycle. Adsorption of water-extractable organic matter (WEOM) to soil mineral surfaces is a critical step in the process of organic matter accumulation. In this study, we examined the molecular fractionation of WEOM derived from field-grown corn, wheat, and soybean crop residues upon adsorption to iron (oxy)hydroxide (FeOOH) mineral using ultrahigh resolution mass spectrometry. The results show that aromatic, N-containing aliphatic as well as lignin-like molecules with higher O/C atomic ratios have preferential affinity for FeOOH surfaces. Lignin-like molecules with low and high numbers of O atoms were adsorbed, while those with intermediate O numbers were not adsorbed. This pattern is likely due to two different mechanisms of adsorption that is dependent on molecular size: smaller molecules with low O numbers bond through an inner-sphere ligand exchange mechanism, and the larger molecules with high O numbers bond through the formation of multiple H-bonds between the WEOM and FeOOH surface functional groups. Adsorption of WEOM to soil mineral surfaces has wide ecosystem implications, since adsorbed organic matter molecules are now believed to be more protected from microbial decomposition reactions. This study shows that WEOM chemical composition is an important factor controlling its adsorption to mineral surfaces. Understanding these soil and crop chemical interactions at the molecular level will be increasingly important for developing production systems that maintain high SOM levels and soil health in the decades ahead.

Plant biomass is the primary source material for soil organic matter formation. Soil organic matter comprises the largest terrestrial pool of the global C cycle and provides critical ecosystem services. The objective of this study was to document microbially-driven molecular-level changes to the water-soluble organic matter (WSOM) fraction extracted from crop residues as it undergoes biodegradation in laboratory microcosms using ultrahigh resolution mass spectrometry. Crop residues from corn and soybean fields after harvest and a leguminous, hairy vetch green manure were the sources of the WSOM studied. The results show that, at the individual molecule-level, the biodegradation process does not follow the expected trends, i.e. that higher N and lower lignin concentrations in plant biomass should favor its decomposition compared to material with lower N and higher lignin. We also show that S- and P-containing molecules are consistently more biodegradable, as compared to N-containing molecules. In addition, the results suggest that carbohydrate molecules may be less biodegradable, and that aromatic compounds may be more biodegradable, than conventionally understood. Future studies are suggested to increase our knowledge of microbially-driven biodegradation of plant biomass. Understanding plant biomass decomposition at the molecular level is fundamental to understanding how soil organic matter forms and is stabilized. This knowledge is necessary to design management practices to preserve soil organic matter and the ecosystem services it provides.

Microplastic particles (

The Deepwater Horizon oil spill stimulated the release of marine snow made up of dead/living plankton/bacteria and their exopolymeric polysaccharide substances (EPS), termed marine oil snow (MOS), promoting rapid removal of oil from the water column into sediments near the well site. Mesocosm simulations showed that Macondo surrogate oil readily associates with the marine snow. Quantitative solid-state 13C NMR readily distinguishes this oil from naturally formed marine snow and reveals that adding the dispersant Corexit enhances the amount of oil associated with the MOS, thus contributing to rapid removal from the water column. Solvent extraction of MOS removes the oil-derived compounds for analysis by one and two-dimensional GC/MS and evaluation of potential transformations they undergo when associated with the EPS. The results reveal that the oil associated with EPS is subjected to rapid transformation, in a matter of days, presumably by bacteria and fungi associated with EPS.

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.

It has been well accepted that humic acids in soils comprise both aromatic and aliphatic structural units that harbor mainly oxygenated functional groups such as carboxylic acids, aldehydes, ketones, and hydroxyl groups. Recent mass spectral data obtained from electrospray ionization-Fourier transform ion cyclotron resonance mass spectrometry (ESI-FTICRMS) suggest that the main functional groups in humic acids are carboxylic acids bound to both alicyclic and condensed aromatic molecules. It was suggested that these structural entities originate from oxidation of lignin. To provide additional support, detailed structural characteristics were obtained here using several multi-dimensional nuclear magnetic resonance (NMR) techniques to observe the molecular connectivity of humic acid components, with a focus on carboxylic acids in particular. The humic acid sample examined had been shown to exhibit structural characteristics similar to a larger set of soil humic acids. In this study, many carboxylic acid resonances were found to correlate with protons that could be assigned to aliphatic and alicyclic chemical shift regions. Functional groups with heteroatoms such as alcohols, some olefins and an assortment of methyl groups were found to correlate within 2–3 bonds of carboxylic acid groups. The collection of structural components and their proximity to a variety of carboxylic groups supports the occurrence of carboxylated alicyclic molecules as important elements of the aliphatic portion of soil humic acids and a pathway from lignin is consistent with recent findings.

Evidence suggests that reactive oxygen species (ROS) are important in transforming the chemical composition of the large pool of terrestrially-derived dissolved organic matter (DOM) exported from land to water annually. However, due to the challenges inherent in isolating the effects of individual ROS on DOM composition, the role of ROS in the photochemical alteration of DOM remains poorly characterized. In this work, terrestrial DOM was independently exposed to singlet oxygen (1O2), and superoxide ( O 2 - under controlled laboratory conditions). Using ultra-high resolution mass spectrometry to track molecular level alterations of DOM by ROS, these findings suggest exposure to 1O2 (generated using Rose Bengal and visible light) removed formulas with an O/C > 0.3, and primarily resulted in DOM comprised of formulas with higher oxygen content, while O 2 - exposure (from KO2 in DMSO) removed formulas with O/C 1.5). Comparison of DOM altered by ROS in this study to riverine and coastal DOM showed that (20–80%) overlap in formulas, providing evidence for the role of ROS in shaping the composition of DOM exported from rivers to oceans.

A novel method to rapidly methylate glycerol and generate products having greater value has been demonstrated using tetramethylammonium hydroxide (TMAH) thermochemolysis. Through analysis with GC–MS, it is shown that the reaction between TMAH and glycerol at elevated temperatures produces a series of mono, di and tri-methoxylated glycerols with potential applications as organic solvents. While other methylation reactions can only be carried out in batch reactions, thermally assisted methylation using TMAH can be performed in a continuous flow process.

Dissolved organic matter (DOM) composition is influenced by and modulates biogeochemical processes, yet DOM characterization techniques are challenged by its heterogeneous properties and structures. In this paper, ultrahigh electrospray ionization Fourier transform ion cyclotron resonance (ESI-FTICR) mass spectrometry is used to characterize previously isolated and well-characterized four DOM fractions from a water reservoir in the southwestern part of the USA. About 50–60 L water samples were collected from Lake Pleasant (a water reservoir of Colorado River) and isolated and fractionated using a sequential isolation and fractionation procedure. DOM was firstly fractionated to the colloids and soluble permeate, then hydrophobic acids (HPO-A) and neutrals (HPO-N) plus amphiphilic acids (AMP-A) and neutrals (AMP-N) were fractionated using the resin-in-tandem procedure. Approximately 0.7 mg sample was dissolved in 250 μL methanol/water mixture (1:1, v/v) and diluted twice with 0.1 % (by volume) NH4OH (in 1:1 methanol/water, v/v) and measured by ESI-FTICR in negative ion mode. In the m/z range of

NMR spectroscopy is widely used in the field of aquatic biogeochemistry to examine the chemical structure of dissolved organic matter (DOM). Most aquatic DOM analyzed by proton NMR (

During the past decade, Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS) has been established as a technique of choice for the comprehensive chemical assessment of some of the most complex organic mixtures, such as petroleum, or dissolved organic matter. In the aftermath of the Deepwater Horizon (DWH) blowout, FTICR-MS demonstrated its applicability for the characterization of oil spill residues produced by abiotic weathering, such as photooxidation, and/or microbial processes and interactions, for example, marine oil snow aggregation. Such residues are abundant in high molecular weight, polar, and heteroatom-bearing chemical species, which cannot be analyzed by the typical oil spill forensics tools such as gas chromatography. Therefore, the expansion of the analytical window afforded by FTICR-MS is crucial for the monitoring and understanding of long-term oil spill fate. Furthermore, capability of FTICR-MS to characterize non-hydrocarbon petroleum fractions will be very important in the case of potential future spills of heavy, unconventional oils, such as bitumen.

Large amounts of oil containing mucous-like marine snow formed in surface waters adjacent to the Deepwater Horizon spill that was implicated in oil delivery to the seafloor. However, whether chemical dispersants that were used increased or decreased the oil incorporation and sedimentation efficiency, and how exopolymeric substances (EPS) are involved in this process remains unresolved. To investigate the microbial responses to oil and dispersants in different oceanic settings, indicated by EPS production, petro- and non-petro carbon sedimentation, four mesocosm (M) experiments were conducted: 1) nearshore seawater with a natural microbial consortia (M2); 2) offshore seawater with f/20 nutrients (M3); 3) coastal seawater with f/20 nutrients (M4); 4) nearshore seawater with a natural microbial consortia for a longer duration (M5). Four treatments were conducted in M2, M3 and M4 whereas only three in M5: 1) a water accommodated fraction of oil (WAF), 2) a chemically-enhanced WAF prepared with Corexit (CEWAF, not in M5), 3) a 10-fold diluted CEWAF (DCEWAF); and 4) controls. Overall, oil and dispersants input, nutrient and microbial biomass addition enhanced EPS production. Dispersant addition tended to induce the production of EPS with higher protein/carbohydrate (P/C) ratios, irrespective of oceanic regions. EPS produced in M4 was generally more hydrophobic than that produced in M3. The P/C ratio of EPS in both the aggregate and the colloidal fraction was a key factor that regulated oil contribution to sinking aggregates, based on the close correlation with %petro-carbon in these fractions. In the short term (4–5 days), both the petro and non-petro carbon sedimentation efficiencies showed decreasing trends when oil/dispersants were present. In comparison, in the longer-term (16 days), petro-carbon sedimentation efficiency was less influenced by dispersants, possibly due to biological and physicochemical changes of the components of the oil-EPS-mineral phase system, which cooperatively controlled the sinking velocities of the aggregates.

Extracellular polymeric substances (EPS), produced by microorganisms , are implicated for greatly influencing the fate of environmental contaminants , including oil. Transparent exopolymeric particles (TEP) are gel-like acidic polysaccharide particles that can be stained with Alcian blue, whereas Coomassie stainable particles (CSP) contain proteins and are stained with Coomassie brilliant blue. Marine microgels are reversibly formed from EPS. These terms are often used interchangeably, but they have rarely been measured simultaneously. Mesocosm and bottle experiments provided an opportunity to compare EPS, TEP, CSP and microgels in a water-accommodated fraction (WAF) of oil and seawater (control). Our results reveal that the biopolymers making up EPS, TEP and CSP consisted primarily of polysaccharides and proteins, mostly likely as proteoglycans and glycoproteins . Significant correlations were found between concentrations of TEP-C vs particulate organic carbon (POC), TEP-C vs particulate organic nitrogen (PON), TEP vs EPS, TEP vs CSP, TEP vs carbohydrates, proteins, CSP and carbohydrates, CSP vs proteins, and carbohydrates vs proteins. Chemical analysis of whole particles and colloids yielded both protein and polysaccharides concentrations higher than those in EDTA extraction, thus providing an upper limit of actual EPS contents in the particulate phase. The EPS that was electrostatically held onto particle surfaces (extractable by 1% EDTA) accounted for a minor (~4%) yet relatively constant proportion of TEP. Overall, the concentrations of the three terms ranked in the order of [gels] > [TEP] > [particulate EPS] in the water. Lastly, spectrophotometric methods have limitations in identifying complex or refractory polysaccharides, as evidenced by the comparison between NMR-quantified EPS and the total EPS determined by spectrophotometric methods. This study is the first time these terms were compared in the same sample. They provide useful information when reviewing historical TEP, CSP, EPS data collected field- and laboratory-studies, and provide linkages between them. In addition, they also demonstrate that they could provide complementary information relevant to ecosystem and flux studies.