Groups Of Organic Matter Research Articles

Molecular insights into the formation of carbon dioxide hydrates on the external surface of sodium montmorillonite in the presence of various types of organic matters

To address the urgent challenge of global climate change due to the greenhouse effect resulting from increasing carbon dioxide (CO2) emissions, viable technologies for geological CO2 storage must be developed. Of such technologies, CO2 hydrates holds significant promise for CO2 storage in seabed sediments, which typically contain clay minerals and organic matter (OM). Thus, investigating the structure of clay mineral interfaces and their interactions with OM is crucial for understanding the nucleation and growth of CO2 hydrate in seabed sediments. In this study, molecular dynamics simulations were used to investigate CO2 hydrate formation on the external surface of sodium montmorillonite (Na-Mnt) in the presence of various types of OM. The results show that the Na-Mnt surface adsorbed certain numbers of sodium ions (Na+) and OM molecules. The hydration of Na + disrupted of the hydrogen bond structure of CO2 hydrates, while hydrogen bonds that formed between OM and H2O molecules hindered CO2 hydrate formation. Consequently, CO2 hydrates predominantly formed in the bulk-like solution away from the Na-Mnt. However, the electrostatic interaction between the carboxyl groups of OM and Na+ mitigated the inhibitory effect of Na+ on CO2 hydrate formation. Over all, these findings can serve as a fundamental theoretical basis for understanding the formation and occurrence characteristics of CO2 hydrates in seabed sediments with a rich Mnt content. Such understanding will help to advance the development of CO2 storage technologies utilizing CO2 hydrates in seabed sediments.

Hydraulic characterization of earthworm macropore surfaces using miniaturized infiltration data

Water repellency related to organic matter (OM) of coatings along the earthworm burrows (EB) walls can facilitate preferential flow due to limiting the water exchange with the soil matrix. The objectives of this work were (i) to characterize the hydraulic behavior of EB wall and the surrounding matrix using a miniaturized infiltrometer; (ii) to compare standard infiltration analyses with BEST-WR algorithm; and (iii) to determine the local spatial distribution of water repellency at the EB wall surface in relation to that of the OM composition. Infiltration experiments were carried out on intact sample surfaces, including the EB wall and the surrounding matrix. Soil samples were collected from Bt and C horizons in a characteristic Haplic Luvisol. Hydraulic conductivity (K) at different water pressure heads (h) and water and ethanol sorptivity (Sw and Se, respectively), water repellency index (RI) and water repellency cessation time (WRCT) were determined from infiltration data. The adapted Beerkan Estimation of Soil Transfer parameters (BEST) algorithm for water-repellent soils (BEST-WR) was used for analysing infiltration data. The potential water repellency index (PWRI), relating C-H with CO functional groups in OM, was determined at the same locations using diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy. Lower values of K and Sw in the coatings as compared to the soil matrix were found related to higher PWI values. Water repellency was also reflected in the shape of the cumulative infiltration curves and in the RI-values. The latter were significantly higher for EB as compared to matrix surfaces. The fittings provided by the BEST-WR algorithm characterizing the hydraulic properties of the macropore surfaces were comparable to those obtained with standard method. The tested methods could help to improve the estimation of parameters for macropore-matrix mass exchange in two-domain models.

The effect of organic matter fractions on micropollutant ozonation in wastewater effluents

Organic matter (OM) is the most important factor influencing the effectivity and efficiency of micropollutant (MP) ozonation in wastewater effluents. The importance of the quantity of OM is known, because of this, total organic carbon (TOC) is generally used to determine the required ozone dose for any water sample. Still, the effect of OM type on MP ozonation is not well understood. In this study, effluents from five wastewater treatment plants were collected and the organic matter in these effluents was fractionated using membranes (F1-4) and resin (HI, HOA, HON and HOB). Fractions were diluted to the same TOC concentration, spiked with MPs and ozonated at three ozone doses. Our results show that all five effluents had comparable OM compositions and similar MP removal, confirming the suitability of OM quantity (TOC) to compare the ozone requirements for wastewater effluents. From the 19 analysed MPs, three groups were identified that showed similar removal behaviour. The strongest differences between the groups were observed around MP ozone reactivities of 102, 104 and 106 M−1 s−1. This indicates the presence of three OM groups in the samples that interfere with the removal of different MPs. MP removal in the resin fraction HON were higher for MPs with high and medium ozone reactivity, indicating a low interference of OM in this fraction with MP ozonation. OM in the resin fractions HOA and HI showed higher interference with MP ozonation. Therefore, removing the HOA and HI fractions prior to ozonation would result in a lower required ozone dose and a more efficient removal of the MPs. MP removal correlated with the OM characteristics A300, SR and fluorescence component comp 2. These characteristics can be used as inline tools to predict the required ozone dose in water treatment plants.

The effect of autogenous tooth bone graft material without organic matter and type I collagen treatment on bone regeneration

ObjectivesThe aim of this study is to examine the effect of particulate autogenous tooth graft removed with organic matter and type I collagen addition on bone regeneration and to validate the possibility of useful allograft material for jaw defects.Material and methodsAutogenous tooth bone maker (Korean Dental Solution® KOREA) made particulate autogenous tooth not including organic matter. We used to the developed tooth grafts for experiment. Cell adhesion test with hemacytometer and energy dispersive X-ray spectroscopy (Supra40 VP®, Carl Zeiss, Germany) analysis about the particulate autogenous tooth and type I collagen were performed. Rabbits were divided into three groups: bone graft with organic matter (OM) removing particulate autogenous tooth group, bone graft with OM removing particulate autogenous tooth and type I collagen group, and a control group. Bone grafting was performed in rabbit’s calvaria. The rabbits were sacrificed at different interval at 1, 2, 4, and 6 weeks after bone grafting for the histopathologic observation and observed the effect of bone regeneration by SEM, H-E & Masson stains, osteocalcin IHC staining.ResultIn vitro cytopathological study showed affinity for cells, cell attachment pattern, and cell proliferation in the order of control group, OM-removed and collagen-treated group, OM-removed particulate autogenous tooth group. The results of the degree of mineralization were opposite to those of the previous cell experimental results, and the OM-removed group, OM-removed group and collagen-treated group were relatively higher than the control group. Histopathologic analysis showed that vascularization and neonatal bone formation were higher in particulate autogenous tooth group with removing OM and with addition of collagen than control group and group of OM removed only. Immunohistochemical analysis showed that osteocalcin (OSC) expression was not observed in the control group, but at 4 weeks groups, OSC expression was observed the OM removed and OM-removed-collagen-treated particulate autogenous tooth, and the degree of expression was somewhat stronger in group of the OM removed and collagen additionally treated particulate autogenous tooth.ConclusionParticles that do not contain organic matter, the saint tooth, was responsible for sufficient bone graft material through the role of space maintenance and bone conduction, and further improved bone formation ability through additional collagen treatment. Therefore, research on various extracellular substrates and autologous bone grafting materials is necessary, and through this, it is possible to lay the foundation for a new type of autologous bone grafting material with excellent academic and technical utility.

Copper transformation, speciation, and detoxification in anoxic and suboxic freshwater sediments

The complex chemistry of copper (Cu) in freshwater sediments at low concentrations is not well understood. We evaluated the transformation processes of Cu added to freshwater sediments under suboxic and anoxic conditions. Freshwater sediments from three sources in Michigan with different characteristics (Spring Creek, River Raisin, and Maple Lake) were spiked with 30 or 60 mg kg−1 Cu and incubated under a nitrogen atmosphere. After 28-d, each treatment subset was amended with organic matter (OM) to promote anoxic conditions and evaluate its effects on Cu speciation. OM addition triggered a shift from suboxic to anoxic conditions, and sequential extractions showed that Cu accordingly shifted from acid-soluble to oxidizable fractions. Extended X-ray absorption fine-structure (EXAFS) spectroscopy revealed that Cu sulfides dominated all anoxic samples except for Spring Creek 30 mg kg−1, where Cu(I) was predominantly complexed to thiol groups of OM. Covellite and chalcopyrite (CuFeS2) were the predominant Cu species in nearly all anoxic samples, as determined by Raman spectroscopy, scanning electron microscopy, and X-ray absorption near-edge structure (XANES) spectroscopy. Copper reduction also occurred under suboxic conditions: for two of three sediments, around 80% had been reduced to Cu(I), while the remaining 20% persisted as Cu(II) complexed to OM. However, in the third coarsest (i.e., Spring Creek), around 50% of the Cu had been reduced, forming Cu(I)-OM complexes, while the remainder was Cu(II)-OM complexes. Toxicity tests showed that survival of H. azteca and D. magna were significantly lower in suboxic treatments. Anoxic sediments triggered a near-complete transformation of Cu to sulfide minerals, reducing its toxicity.

Manuring effects on visual soil quality indicators and soil organic matter content in different pedoclimatic zones in Europe and China

A study was carried out to assess if the visual soil assessment method (VSA) would allow recognizing differences between soils receiving organic matter (OM) amendments and similar control soils, by the observation of visual soil quality indicators’ score. 36 practices were identified across 8 pedoclimatic zones. These fields/plots were paired with nearby control fields/plots, without OM amendments, sharing similar farming features. A survey, comprising a VSA of the soil structure status, surface ponding, signs of erosion, earthworm counts and soil stability (slake test), complemented by measurements of soil organic matter (SOM) and permanganate oxidizable organic carbon (LOC) content, soil pH, penetration resistance and texture, on soils of both management system groups (OM addition and Control), was performed in 2016. Correlations of the visual soil quality indicators’ score with SOM, LOC, other soil properties and climate variables and indices were calculated within each group; the correlations between soil properties, and between soil properties (SOM and LOC) and climate variables were also calculated. A statistically significantly higher proportion of soils of the OM group had a good score for “soil structure and consistency” and “soil porosity”. These differences are not directly explained by non-inherent soil properties. No statistically significant Spearman’s correlation coefficients were observed between “soil structure and consistency” and either soil properties or climate variables; concerning “soil porosity”, distinct statistically significant correlations were observed between the two groups with different climate variables and indices. Correlations between the scores of the visual soil quality indicators and climate variables were found to follow the same directions of correlations of LOC content with the same climate variables, although the latter correlations were weak. Mean SOM and LOC content, were slightly higher in the OM group, although differences were not statistically significant. A high linear correlation between LOC (mg/g) and SOM (%) (r = 0.65, n = 26) exists within the Control group, but not within the OM group (r = 0.20 and n = 26). When the relationship of SOM and LOC content with visual soil quality indicators’ score was studied, statistically significant correlations were only observed between SOM and “earthworm count” within the Control group (rs = 0.44), and between LOC and “soil colour” within the OM group (rs=-0.52). Both LOC content and LOC status (ranked as a function of LOC content and soil texture), had only negative statistically significant correlations with visual soil quality indicators’ score, questioning their worth as stand-alone soil quality indicators.

Quantifying organic matter and functional groups in particulate matter filter samples from the southeastern United States – Part 1: Methods

Abstract. Comprehensive techniques to describe the organic composition of atmospheric aerosol are needed to elucidate pollution sources, gain insights into atmospheric chemistry, and evaluate changes in air quality. Fourier transform infrared absorption (FT-IR) spectrometry can be used to characterize atmospheric organic matter (OM) and its composition via functional groups of aerosol filter samples in air monitoring networks and research campaigns. We have built FT-IR spectrometry functional group calibration models that improve upon previous work, as demonstrated by the comparison of current model results with those of previous models and other OM analysis methods. Laboratory standards that simulated the breadth of the absorbing functional groups in atmospheric OM were made: particles of relevant chemicals were first generated, collected, and analyzed. Challenges of collecting atmospherically relevant particles and spectra were addressed by including interferences of particle water and other inorganic aerosol constituents and exploring the spectral effects of intermolecular interactions. Calibration models of functional groups were then constructed using partial least-squares (PLS) regression and the collected laboratory standard data. These models were used to quantify concentrations of five organic functional groups and OM in 8 years of ambient aerosol samples from the southeastern aerosol research and characterization (SEARCH) network. The results agreed with values estimated using other methods, including thermal optical reflectance (TOR) organic carbon (OC; R2=0.74) and OM calculated as a difference between total aerosol mass and inorganic species concentrations (R2=0.82). Comparisons with previous calibration models of the same type demonstrate that this new, more complete suite of chemicals has improved our ability to estimate oxygenated functional group and overall OM concentrations. Calculated characteristic and elemental ratios including OM∕OC, O∕C, and H∕C agree with those from previous work in the southeastern US, substantiating the aerosol composition described by FT-IR calibration. The median OM∕OC ratio over all sites and years was 2.1±0.2. Further results discussing temporal and spatial trends of functional group composition within the SEARCH network will be published in a forthcoming article.

Ethylene glycol monoethyl ether (EGME) adsorption by organic matter (OM)-clay complexes: Dependence on the OM Type

The ethylene glycol monoethyl ether (EGME) adsorption method has been used as an available technique for measuring the total specific surface area (TSSA) of soils and clay-rich rocks. However, the existence of organic matters (OM) has recently been proposed to affect the accurate measurement of the TSSA. To explore the effects of OM on the TSSA evaluation of clay-rich samples, EGME adsorption experiments were performed on OM and the OM-clay minerals (OM-clay) complexes that widely exist in soil and clay-rich rocks. Two types of OM, 12-aminolauric acid (ALA) and lauric acid (LA) were used, and montmorillonite (Mt) was selected as the representative clay mineral. OM-clay complexes with OM in interlayer space or OM-clay mixture with OM on the external surface of an expanding clay mineral were prepared to investigate the influence of occurrence sites of OM on the EGME adsorption. The combined methods of X-ray diffraction (XRD) and diffuse reflectance infrared Fourier transform spectroscopy (DRIFT) were used to study the structural characteristics of the OM-clay complexes before and after EGME adsorption for revealing the EGME adsorption mechanisms. The results showed both the occurrence sites and the functional groups of OM significantly influence the EGME adsorption behaviour and TSSA for OM-clay complexes. As ALA intercalated into interlayer space of Mt, it can occupy parts of adsorption sites of EGME leading to a lower TSSA than that of Mt. While as LA located on the external surface of Mt, it affects access to the interlayer surface by the EGME and occupies parts of EGME adsorption sites of the external surface of Mt, resulting in lower adsorption capability and the slight smaller TSSA than Mt. In addition, EGME reacted strongly with LA producing excess TSSA, which brings about a great difference between LA-Mt and ALA-Mt on EGME adsorption behaviour. These fundamental results demonstrated that OM could strongly affect the EGME adsorption on the OM-Mt complexes and further influence detection of TSSA. The occurrence sites and the functional groups of OM in OM-clay complex must be considered when the EGME adsorption method is used for TSSA evaluation of such clay-rich rocks and soil samples.

The Characteristics of the Organic Matter of the Upper Devonian Domanik-Type Deposits in the Northern and Central Regions of the Volga-Ural Basin According to Saturated Biomarkers Composition

The composition of saturated biomarkers (alkanes, steranes, and triterpanes) in the Upper Devonian sediments (the Sargaev, Semiluk, and Mendym horizons, the Famennian stage) that belong to the Domanik formation, which is widespread on the territory of the Volga-Ural basin, was studied. The section elongated from N to S that covers the northern and central regions of the Volga-Ural basin was observed. A set of 21 parameters was used to characterize saturated hydrocarbons, including those rarely used in geochemical studies. For each parameter a set of mean values for the considered region as a whole and its individual parts was calculated and distribution-density plots were built. It was established that the most representative parameter for characterizing the Domanik-type deposits as a whole is a highly specific parameter, that is, the ratio of 29,30-bisnorhopane C28 to hopane C29. Most of the characteristics of the genetic composition demonstrate the difference between the organic matter (OM) of the vault part of the region and the Mukhanov- Erokhovsky trough. There are large differences in the parameters that characterize the maturity of OM. The characteristic values of the parameters for both the vault and the depression zone are given; two to three genetic groups of OM were determined for the majority of the parameters in both regions. A method for constructing the distribution-density graphs of the parameters is proposed that makes it possible to take their features fully into account.

Iron speciation in peats: Chemical and spectroscopic evidence for the co-occurrence of ferric and ferrous iron in organic complexes and mineral precipitates

The speciation of iron (Fe) in organic matter (OM)-rich environments under in situ variable redox conditions is largely unresolved. Peatlands provide a natural setting to study Fe–OM interactions. Utilizing chemical, spectroscopic and theoretical modeling approaches, we report the chemical forms, oxidation states and local coordination environment of naturally occurring Fe in the vertically redox-stratified Manning peatlands of western New York. In addition, we report dominant carbon, sulfur and nitrogen species that can potentially stabilize the various Fe species present in these peatlands. Our results provide clear direct and indirect evidence for the co-occurrence of ferrous (Fe2+) and ferric (Fe3+) iron species in peats under both oxic and anoxic conditions. Iron is mostly present within the operationally defined organic and amorphous (i.e., short range ordered, SRO) fractions; ferric iron primarily as magnetically isolated paramagnetic Fe3+ in Fe(III)-organic complexes, but also in mineral forms such as ferrihydrite; ferrous iron in tetrahedral coordination in Fe(II)-organic complexes with minor contribution from pyrite. All of the Fe species identified stabilize Fe(III) and/or Fe(II) in anoxic and oxic peats. Fundamental differences are also observed in the relative proportion of C, S and N functionalities of OM in oxic and anoxic peats. Aromatic CC, ester, phenol and anomeric C (ROCOR), as well as thiol, sulfide and heterocyclic N functionalities are more prevalent in anoxic peats. Collectively, our experimental evidence suggests iron forms coordination complexes with O-, S- and N-containing functional groups of OM. We posit the co-occurrence of organic and mineral forms of Fe(II) and Fe(III) in both oxic and anoxic peat layers results from dynamic complexation and hydrolysis-precipitation reactions that occur under variable redox conditions. Our findings aid in understanding the crucial role OM plays in determining Fe species in soils and sediments.

The upper thermal maturity limit of primary gas generated from marine organic matters

Elemental composition and chemical structure of 16 kerogen samples concentrated from marine source rocks with maturity levels ranging from 0.65 %Ro to 3.3 %Ro were determined. Pyrolysis experiments of seven samples selected from the 16 kerogen samples were conducted in a gold tube system to clarify the process and determine the upper thermal maturity limit for primary gas generation from marine organic matter (OM). The variation of the H/C atomic ratio of the marine OM appears to evolve through three phases with increasing maturity, including a drastic decreasing phase before 1.3 %Ro, a moderate decreasing phase from 1.3 to 2.0 %Ro and a gradual decreasing phase above 2.0 %Ro. The evolution of the chemical structure measured by FTIR indicates that most oxygen containing functional groups in marine OM appear to be released prior to 0.8 %Ro. Aliphatic groups were still detected in the sample with a maturity of 3.0%Ro, but disappeared in the sample with a maturity of 3.3 %Ro. The variation of aliphatic groups VS aromatic rings (I1) displays a similar three stage pattern as the variation of H/C atomic ratio with increasing maturity. A step-by-step heating method in kerogen pyrolysis experiments was adopted to preclude secondary gas generation. The pyrolysis experimental results for samples with different maturities proved that generally the maximum yield of primary gas generated by the marine OM was not more than 140 ml per gram of total organic carbon (TOC). Only 1.16 ml/g TOC of hydrocarbon gas was generated by the sample with the maturity of 3.3 %Ro. Thus, it can be rationally inferred that the upper thermal maturity limit for gas generation from the marine OM may be around 3.5 %Ro. Nevertheless, the main maturity range for the primary gas generation is suggested to be below 2.0 %Ro. The yield of primary gas generated at the maturity range above 2.0%Ro takes up 10% of maximum yield of the primary gas generated by the marine OM.

Effects of mineral characteristics on content, composition, and stability of organic matter fractions separated from seven forest topsoils of different pedogenesis

Mineral topsoils possess large organic carbon (OC) contents but there is only limited knowledge on the mechanisms controlling the preservation of organic matter (OM) against microbial decay. Samples were taken from the uppermost mineral topsoil horizon (0 to 5cm) of seven sites under mature deciduous forest showing OC contents between 69 and 164gkg−1 and a wide range in mineral characteristics. At first, organic particles and the water-extractable OM were removed from the soil samples. Thereafter, Na-pyrophosphate extractable organic matter (OM(PY)), assumed to be indicative for OM bound via cation mediated interactions, and the OM remaining in the extraction residue (OM(ER)), supposed to be indicative for OM occluded in mechanically highly stable micro-aggregates, were sequentially separated and quantified. The composition of OM(PY) and OM(ER) was analyzed by FTIR and their stability by 14C measurements. The OC remaining in the extraction residues accounted for 38 to 59% of the bulk soil OC (SOC) suggesting a much larger relevance of OM(ER) for the OM dynamic in the analyzed soils as compared with OM(PY) that accounted for 1.6 to 7.5% of the SOC. The FTIR analyses revealed a lower relative proportion of CO groups in OM(ER) compared to OM(PY) indicating differences in the degree of microbial processing between these fractions. Correlation analyses suggest an increase in the stability of OM(PY) with the soil pH and contents of Na-pyrophosphate soluble Fe, Al, and Mg and an increase in the stability of OM(ER) with the soil pH and the contents of clay and oxalate-soluble Fe and Al. Despite the detected influence of soil mineral characteristics on the turnover of OM(PY) and OM(ER), the Δ14C signatures indicated mean residence times less than 100years. The presence of less stabilized OM in these fractions can be derived from methodological uncertainties and/or the fast cycling compartment of mineral-associated OM.

Droplet infiltration and organic matter composition of intact crack and biopore surfaces from clay‐illuvial horizons

AbstractThe organic matter (OM) in biopore walls and aggregate coatings may be important for sorption of reactive solutes and water as well as for solute mass exchange between the soil matrix and the preferential flow (PF) domains in structured soil. Structural surfaces are coated by illuvial clay‐organic material and by OM of different origin, e.g., earthworm casts and root residues. The objectives were to verify the effect of OM on wettability and infiltration of intact structural surfaces in clay‐illuvial horizons (Bt) of Luvisols and to investigate the relevance of the mm‐scale distribution of OM composition on the water and solute transfer. Intact aggregate surfaces and biopore walls were prepared from Bt horizons of Luvisols developed from Loess and glacial till. The mm‐scale spatial distribution of OM composition was scanned using diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy. The ratio between alkyl and carboxyl functional groups in OM was used as potential wettability index (PWI) of the OM. The infiltration dynamics of water and ethanol droplets were determined measuring contact angles (CA) and water drop penetration times (WDPT). At intact surfaces of earthworm burrows and coated cracks of the Loess‐Bt, the potential wettability of the OM was significantly reduced compared to the uncoated matrix. These data corresponded to increased WDPT, indicating a mm‐scaled sub‐critical water repellency. The relation was highly linear for earthworm burrows and crack coatings from the Loess‐Bt with WDPT > 2.5 s. Other surfaces of the Loess‐Bt and most surfaces of the till‐derived Bt were not found to be repellent. At these surfaces, no relations between the potential wettability of the OM and the actual wettability of the surface were found. The results suggest that water absorption at intact surface structures, i.e., mass exchange between PF paths and soil matrix, can be locally affected by a mm‐scale OM distribution if OM is of increased content and is enriched in alkyl functional groups. For such surfaces, the relation between potential and actual wettability provides the possibility to evaluate the mm‐scale spatial distribution of wettability and sorption and mass exchange from DRIFT spectroscopic scanning.

In Situ DRIFT Characterization of Organic Matter Composition on Soil Structural Surfaces

The properties of preferential flow path surfaces may affect transport processes in structured soil. Wetting and sorption depends on the organic matter (OM) at the effective outermost surface of flow paths, which is largely unknown locally with respect to OM composition and distribution. The objectives are to adapt Diffuse Reflectance infrared Fourier Transform (DRIFT) spectral analysis for the in situ characterization of coated crack surfaces and linings of earthworm burrow walls. The Kubelka‐Munk (KM) transformed DRIFT spectra are used to analyze OM composition in terms of the ratio between CH‐ (Band A) and C=O groups (Band B). The A/B ratio indicates a relation between hydrophobic and hydrophilic groups in OM. Disturbed soil samples are arranged (i) in standard cup (CUP) and (ii) larger box (BOX) devices; intact aggregate and burrow surfaces are prepared from clods with cracks and earthworm burrows. The disturbed samples with relatively homogeneous surfaces are used to compare data obtained from CUP with those from the BOX device. The A/B ratios are determined in a stepwise mapping‐type procedure and compared with pictures of the surfaces for inferring a spatial distribution of OM composition along transects. The DRIFT mapping results indicate negligibly small texture effects for the finer‐textural subsoil samples for which the applicability of KM is not restricted. For intact surfaces like soil aggregates, cracks, and earthworm burrow walls, the A/B ratios are relatively higher near a root residue and relatively lower near a quartz grain. The millimeter‐scale variability of OM composition obtained here by an in situ analysis of A/B ratios at structural surfaces seems promising for determination of locally distributed OM properties. The DRIFT mapping may improve understanding the development of soil structural properties, from which descriptions of preferential flow and transport may benefit.

Cation Exchange Capacity and Composition of Soluble Soil Organic Matter Fractions

The cation exchange capacity (CEC) of soils depends on the amount and composition not only of clay minerals but also of soil organic matter (SOM). While the CEC of soil clay minerals has been intensively studied, little is known about the CEC of organic matter (OM) fractions, in particular those obtained with newly developed SOM extraction techniques. The objective of this study was to develop and test a method to quantitatively determine the CEC of extracted OM fractions and to relate CEC(OM) to OM functional groups possibly responsible for sorption of cations. Water‐ and pyrophosphate‐soluble OM fractions were sequentially extracted from differently managed arable soils of two well‐known long‐term field experiments. The CEC of a freeze‐dried pyrophosphate‐soluble OM fraction [OM(PY)] (0.03 g) mixed with quartz sand (4.97 g) was determined by applying the standard percolation method. The chemical composition of OM(PY) was analyzed by Fourier‐transform infrared (FTIR) spectroscopy. For all plots except those fertilized with farmyard manure, the sorption properties of the OM(PY) fraction were found to be site specific and to reflect soil and crop rotation effects. The relative contribution of the CEC of OM(PY) to the CEC of the soil (0.8–11.6%) is dependent on soil C content and extractability. For all plots, however, the relative contents of carboxylic functional groups in OM(PY) determined with FTIR spectroscopy was found to be linearly related to the CEC of the OM(PY), similar to pure organic substances. This relationship indicates the usefulness of CEC determination on OM(PY) fractions. The results suggest that the relative contents of carboxylic functional groups in OM(PY) reflect long‐term effects of fertilization and crop rotation on the sorption properties of the SOM.

Long‐term effects of crop rotation and fertilization on soil organic matter composition

SummaryLong‐term effects of crop rotation and fertilization are mostly observed with respect to the amount of soil organic matter (SOM) and measured in terms of soil organic carbon (SOC). In this paper, we analyze the SOM composition of samples from long‐term agricultural field experiments at sandy and clayey sites that include complex crop rotations and farm‐yard manure applications. The organic matter (OM) composition of the soil samples, OM(Soil), and that of sequentially extracted water, OM(W), and sodium pyrophosphate, OM(PY), soluble fractions was analyzed using Fourier Transform Infrared Spectroscopy (FTIR). The fraction OM(PY) represented between 13 and 34% of SOC, about 10 times that of OM(W). Site specific differences in OM(Soil) composition were larger than those between crop rotations and fertilizer applications. The smaller C=O group content in FTIR spectra of OM(W) compared with OM(PY) suggests that analysis of the more stable OM(PY) fraction is preferable over OM(W) or OM(Soil) for identifying long‐term effects, the OM(Soil) and OM(W) fractions and the content of CH groups being less indicative. Farm‐yard manure application leads to a more similar content of C=O groups in OM(PY) between crop rotations and fertilizer plots at both sites. Short‐term effects from soil tillage or potato harvesting on composition of OM require further studies.

Nature and dynamics of phosphorus-containing components of marine dissolved and particulate organic matter

The molecular sources, dynamics and analytical characterizations of the phosphorus (P) containing components of marine dissolved and particulate organic matter (OM) are reviewed. Using a combination of 13C and 31P nuclear magnetic resonance spectroscopy on samples collected from a depth profile (20–4000 m) at Station Aloha in the North Pacific subtropical gyre, the biomolecular associations of P functional groups in marine OM are identified. Compositional differences between ultrafiltered dissolved organic matter (UDOM; 1–100 nm size fraction) and ultrafiltered particulate organic matter (UPOM; 0.1–60 μm size fraction) as reflected by NMR and elemental analyses indicate that UDOM does not originate from simple solubilization of UPOM, and the aggregation of UDOM is not the primary source of UPOM. Regression analyses indicated a large fraction of the P in UDOM is associated with carbohydrates and amino acids, but not with lipids. Similar analyses for UPOM indicated that P is associated with carbohydrates, amino acids and lipids. The P functional groups also appear to be balanced in their distribution among molecular classes, because they remain in relatively constant proportion throughout the ocean.

Preservation of Sedimentary Organic Matter Through Natural Sulphurisation: An Overview

Preservation of organic matter (OM) in sediments has been and still is a major topic of research in earth sciences because it significantly affects the global biogeochemical cycles and because it is of prime importance for the formation of fossil fuels. Both the influence of oxygen on OM preservation as well as the actual mechanisms of preservation (e.g. condensation, selective preservation, sorptive preservation, natural sulphurisation) have been studied and debated in the last decade. The reaction of reduced inorganic sulphur species with OM during the early stages of diagenesis is an important mechanisms to transform labile low-molecular-weight OM into an insoluble form (i.e. kerogen), especially in the marine realm. The developments in this area over the last decade will be discussed. Studies of immature kerogens over the last years have demonstrated that they can contain high levels of organic sulphur, which may reach almost 20 wt.% and occur much more widespread than previously assumed. Kerogens with an atomic Sorg./C ratio of >0.04 have been designated as special kerogen types (Orr, 1986) and occur as Type I-S, Type II-S as well as Type III-S, depending on their atomic H/C and O/ C ratios. Recognition of these kerogen types is very important from a petroleum geochemistry point of view since they will generate petroleum at a significantly lower thermal stress than corresponding sulphur-poor kerogen types, due to the presence of relatively weak S-S and C-S bonds. The relatively early loss of sulphur from these kerogens during maturation may have caused the underestimation of the occurrence of sulphur-rich kerogens. How are sulphur-rich kerogens formed? It has been well established that the sulphur in sulphur-rich kerogens is predominantly of diagenetic and not of biogenic origin. In anoxic sediments reduced inorganic sulphur species are formed by sulphate reducing bacteria and, depending on the availability of iron species, this sulphur is capable of reaction with functionalised groups in OM. This reaction may occur in an intramolecular fashion, leading to formation of low-molecular-we ight sulphur compounds, or in an intermolecular fashion, generating sulphur-rich macromolecular aggregates including kerogen. The timing of this reaction has been studied mainly by the formation of lowmolecular-weight sulphur compounds, which are relatively easy to analyse. This reaction is almost completed within the upper 10 m of the sediment. A recent study of the sediments of the Cariaco Basin, where it was possible to monitor this reaction by both the increase in concentration of a tricyclic triterpenoid sulphide and the decrease in the concentration of its precursor indicated that the reaction was completed within 10 ka (Werne and Sinninghe