Chemical Composition Of Organic Matter Research Articles

Temperature response of litter and soil organic matter decomposition is determined by chemical composition of organic material

The global soil carbon pool is approximately three times larger than the contemporary atmospheric pool, therefore even minor changes to its integrity may have major implications for atmospheric CO2 concentrations. While theory predicts that the chemical composition of organic matter should constitute a master control on the temperature response of its decomposition, this relationship has not yet been fully demonstrated. We used laboratory incubations of forest soil organic matter (SOM) and fresh litter material together with NMR spectroscopy to make this connection between organic chemical composition and temperature sensitivity of decomposition. Temperature response of decomposition in both fresh litter and SOM was directly related to the chemical composition of the constituent organic matter, explaining 90% and 70% of the variance in Q10 in litter and SOM, respectively. The Q10 of litter decreased with increasing proportions of aromatic and O-aromatic compounds, and increased with increased contents of alkyl- and O-alkyl carbons. In contrast, in SOM, decomposition was affected only by carbonyl compounds. To reveal why a certain group of organic chemical compounds affected the temperature sensitivity of organic matter decomposition in litter and SOM, a more detailed characterization of the (13) C aromatic region using Heteronuclear Single Quantum Coherence (HSQC) was conducted. The results revealed considerable differences in the aromatic region between litter and SOM. This suggests that the correlation between chemical composition of organic matter and the temperature response of decomposition differed between litter and SOM. The temperature response of soil decomposition processes can thus be described by the chemical composition of its constituent organic matter, this paves the way for improved ecosystem modeling of biosphere feedbacks under a changing climate.

Characterization of laboratory analogs of interstellar/cometary organic residues using very high resolution mass spectrometry

Studying the chemical composition of organic matter in astrophysical environments is an important means to improve our understanding of its origin and evolution. This organic matter evolves from molecular clouds to protoplanetary disks, and as a final destination, takes part in the formation of many objects of our solar system, such as primitive chondritic material, planetesimals and finally planets. In this contribution, we perform experimental simulations based on the VUV irradiation and warming-up of primitive interstellar ice analogs (CH3OH:NH3:H2O), and characterize, for the first time, the resulting refractory residue, using very high resolution mass spectrometry (VHRMS) with an LTQ-orbitrap-XL instrument. An electrospray source allows ionizing all the molecules having proton donor or acceptor chemical functions, while limiting as much as possible their damages. Thus, this method provides the analysis of the whole ionizable molecules making up the residue. The analysis of the spectra shows that these residues contain a large number of molecules formed of CHNO elements, including macromolecular entities beyond 4000Da. The average elemental composition of the residue is of H/C=1.5, N/C=0.4, O/C=0.4. These first results are tentatively compared to VHRMS analyses of the soluble organic matter (SOM) present in the Murchison’s meteorite, a primitive chondrite of the CM class. The molecular richness observed can be considered as the “first step” of the complex abiotic organic matter in extraterrestrial media. This initial matter, that may be rather universal, could then evolve toward more processed materials in parent bodies, such as comets and asteroids, materials that are then observed and subsequently analyzed in meteorites found on Earth. In addition to providing some insight on the mixture complexity, VHRMS allows for the search of specific molecules. For instance, hexamethylenetetramine (HMT) and some of its derivatives are identified in these residues. With the possibility to characterize the whole residue as well as some specific molecules, we consider that VHRMS is a powerful analytical tool for the understanding of the chemical evolution of organic matter in astrophysical environments.

The Podzol Hydrosequence of Itaguaré (São Paulo, Brazil). 2. Soil Organic Matter Chemistry by Pyrolysis‐Gas Chromatography/Mass Spectrometry

A Late Pleistocene to Holocene hydrosequence of podzols in the coastal plain of São Paulo (Brazil), of which the macromorphology was described previously, was investigated by pyrolysis‐gas chromatography/mass spectrometry (GC/MS). Differences in chemical composition of organic matter (OM) coincided very well with the morphological interpretation of these profiles with respect to drainage conditions, origin of OM, and decomposition. OM in B‐horizons of poorly‐drained profiles has a signature of dissolved organic matter (DOM), while that of well‐drained profiles indicates root‐derived material. Bands that, according to their morphology, were attributed to DOM have different signature within the profiles, reflecting DOM origin. The EB horizons of poorly‐drained profiles show a selective decay of B‐horizon material, resulting in a relative accumulation of aliphatics in poorly drained profiles. In the EB horizons of the well‐drained profiles, however, significant amounts of microbial products were accumulated and poly‐aromatic compounds were the most stable. This has not been described for temperate podzols. Factor analysis suggests that local differences in vegetation are responsible for about 50% of the total chemical variation in pyrolysates, whereas source, transport, and decomposition in the profile account for the other half. The results underline that OM composition of podzol horizons is strongly dependent on hydrological conditions, resulting in divergent soil organic matter (SOM) properties between soils from different landscape contexts. Nonetheless, there is a comprehensible relation between SOM fingerprints of horizons within one profile. Finally, changes in OM composition at horizon transitions provide insight into the podzolization process.

The effect of earthworms on carbon storage and soil organic matter composition in tropical soil amended with compost and vermicompost

The use of organic matter (OM) amendments is widespread in tropical countries and may be beneficial for soil carbon storage. Interactions between earthworms and OM amendments in tropical soils are largely unknown. The aim of this study was to investigate the effect of bioturbation on the quantity and chemical composition of OM in soil amended with compost and vermicompost. Our approach included comparison of soil samples amended with compost, vermicompost or chemical fertilizers in the presence or absence of earthworms during a one-year greenhouse experiment. The soils were submitted to a regular cultivation cycle. After one year, we analysed bulk samples for soil OM elemental composition and characterised its lignin and non-cellulosic carbohydrate components.Our results showed a decrease of the carbon and nitrogen content in soil amended with chemical fertilizers. Vermicompost amendment led to unchanged OC content, whereas the compost amendment increased the soils OC content compared to initial soil. The addition of earthworms reduced OC and N content in soils with organic amendments. This is in contrast to soil amended with mineral fertilizer only, where the presence of earthworms did not have any effect. Bioturbation influenced the lignin signature of the soils, and to a lesser extent the non-cellulosic carbohydrate signature. In conclusion, compost amendment combined with bioturbation influenced the quality and quantity of SOM and as result carbon storage and its biogeochemical cycling in tropical soils. Implications for soil fertility remain to be elucidated.

Characteristics of bottom sediments of Lake Widryńskie

AbstractThe aim of this study was to determine the chemical composition of Lake Widryńskie bottom sediments (max. depth. 27.0 m, area 123.9 ha). The sampling of bottom sediments was conducted once, on 16 August 2010. Sampling was made in 10 specific areas. Among the 10 samples, 4 samples were taken from the littoral and sublittoral zones, while the rest were taken from the profundal zone. The dominant component of the sediments was silica and calcium carbonates were subdominant. Based on the survey, it was determined that silica occurred in greater numbers in littoral sediments, while in sublittoral sediments there was increased participation in the chemical composition of organic matter. The elements that build a capacity complex were a small percentage of the dry weight of sediment. Sediment from the vicinity of inflows contains higher amounts of silica, which confirmed the impact of the catchment on the chemical composition of sediments.

Effect of Organic Matter on the Color of Sphalerite from the Silesia-Cracow Lead-Zinc Deposits, Poland

Abstract Using gas chromatography-mass spectrometry (GC-MS) sphalerite samples from lead and zinc mines of the Silesian-Cracow region were studied in terms of the effect of organic matter on their coloration. The results indicate no correlation between the abundance and chemical composition of organic matter and sphalerite coloration. TOC values for investigated samples are in the range of 0.5-1.28%. A basic feature characterizing all samples is very similar distribution of n-alkanes, with a predominance of short-chain n-alkanes (from n-C13 to n-C21) over long-chain n-alkanes (from n-C25 to n-C35). Among the isoprenoids pristane dominates over phytane (Pr/Ph ratio in one sample is even 8.95), which does not correspond to previous studies (Karwowski et al. 2001) and may be due to the multi-source nature of organic matter present in sphalerite inclusions from the Silesian-Cracow Zn-Pb deposits. The occurrence of hopanes with 17β,21β(H) stereochemistry indicates a low maturity of test samples.

What determines forest litter decomposition? Global trends and local variance

Global patterns in forest leaf litter decomposition has been studied for decades. The result has been the formulation of a range of models relating organic matter decay rate to climatic and litter-specific factors. It is now commonly accepted that the prime factor determining the litter decomposition rate on a global scale, is actual evapotranspiration (AET). However, this main effect can be seriously modified by the chemical composition of organic matter itself, resulting in large variance at local scales. Among leaf litter components, the lignin concentration, content of water-soluble compounds, concentration of nitrogen and some other nutrients have been indicated by different authors as the major determinants of litter decomposition rate. Unfortunately, our understanding of the factors regulating the decomposition is still far from satisfactory as indicated by the failure of existing models to predict properly litter decay rate in many cases. These include especially ecosystems from outside the temperate climate, such as boreal and wet tropical forests. The existing models still cannot explain the large differences in litter decomposition rates between species, even within reasonably wellstudied temperate forests. My article presents several reasons for the problem of finding satisfactory litter decomposition models. The most important reason is the bias in studies towards temperate ecosystems, high inter-correlations between chemical characteristics of litter and soil, and the lack of properly designed studies on very broad geographic scales.

Concurrent evolution of organic and mineral components during initial soil development after retreat of the Damma glacier, Switzerland

The foreland of the Damma glacier (Switzerland) was investigated to assess the build-up of organic carbon (OC) stocks in mineral soils and organic surface layers with increasing ice-free period (ca. 15, 60–70, 71–80 and 110–140 years). Mature soils outside the proglacial area (soil ages > 700 years) served as reference for advanced soil development. All soils were sampled in triplicate per surface age to estimate the variability of soil formation. Different selective dissolution methods were applied to quantify Fe and Al pools with respect to their role for soil organic carbon (SOC) stabilization during initial pedogenesis. The chemical composition of organic matter was characterized by using solid-state CPMAS 13 C NMR spectroscopy. Leptosols and Regosols were found in the glacier foreland which showed a high variability of development ranging from morphologically undeveloped to soils forming Ah horizons within 70 years. These different stages of soil development were present at a small scale within the same surface age according to past glacier movements. Particle-size distribution varied between soils of similar age and without chronological trend. These results point to the strong impact of different glacial deposition and subsequent glaciofluvial erosion, which was indicated by buried organic surface layers, on soil formation. In general, we found a rapid accumulation of OC in the mineral soils (7.1 g m −2 year −1) and organic surface layers with increasing soil age. Similarly, the amount of poorly crystalline Fe oxides and Al phases increased reflecting the growing potential for SOC stabilization. This was indicated by the strong relationship between SOC stocks and stocks of oxalate soluble Fe and Al. In contrast to strongly increasing quantities, only small changes in the composition of organic matter as well as Fe and Al pools were detected during initial pedogenesis. Fe oxides and inorganic Al phases mainly remained poorly crystalline. Our results point to the concurrent evolution of SOC and poorly crystalline Fe oxides and Al phases with positive feedback mechanisms during initial soil formation. In the Swiss Alpine environment, soil development on silica rich parent material proceeds to Cambisols within at least 700 years as evidenced by the reference soils found outside the proglacial area. They showed indications of weak podzolization as some Fe and Al were translocated downwards. The comparison between the foreland soils and the Cambisols showed decreasing accumulation rates of SOC and pedogenic Fe and Al. This indicates that soil formation processes slow down already after some hundred years or accumulation of Fe and Al increasingly occurs at greater soil depth.

Hypoxia off the Changjiang (Yangtze River) Estuary: Oxygen depletion and organic matter decomposition

In an especially dry year (2006) in the Changjiang Estuary, three cruises were conducted between June and October, to study the process of oxygen depletion. Data for the hypoxic zone pooled for 1959 through 2006 suggest that a dramatic increase in the area of hypoxia has occurred in recent years, and that the center of hypoxia moved northwards in 2006. In August, the hypoxic area (dissolved oxygen, or DO, < 62.5 μM) in the northern region was 15,400 km 2, which is comparable to that in the Gulf of Mexico. A large area of low DO (62.5 μM < DO < 94 μM) also was found in the southern region. In near-bottom waters, particulate organic carbon (POC), dissolved inorganic phosphorus (DIP), dissolved inorganic nitrogen (DIN) and apparent oxygen utilization (AOU) showed coupled variation. For example, relationships can be found between AOU and POC/nutrients (POC/DIP: r = −0.47, POC/DIN: r = −0.50; p < 0.001, n = 86), and between AOU and Δσ of the water column (r = 0.66, p < 0.001, n = 86; Δσ = density near-bottom waters − density surface waters). It is interesting that oxygen depletion in the northern and southern regions developed separately, and they showed distinct differences. Oxygen depletion in the southern region is milder and relatively long lived, whereas in the northern region it is more pronounced and short lived. The different relationships between AOU and inorganic nutrients, indicates different mechanisms for the occurrence of oxygen depletion between the southern and northern regions, respectively. This can be due to 1) the influence of dissolved organic nutrients as another decomposition product besides inorganic forms, 2) and/or different chemical composition of organic matter that decomposed in the near-bottom waters.

Effect of soil pH on the chemical composition of organic matter in physically separated soil fractions in two broadleaf woodland sites at Rothamsted, UK

Although acid soils are common in forest ecosystems, and there is documented evidence of pH influencing transformations of organic matter in soil, there are surprisingly few studies on the influence of soil pH on the chemical structure of physically fractionated soil organic matter (SOM). The aim of this study was to characterize the influence of pH on the chemical and physical processes involved in SOM stabilization. Forest soils of different pH (4.4 and 7.8) sampled from two long‐term experiments at Rothamsted Research (UK) were physically fractionated. The free light fraction (FLF), the intra‐aggregate light fraction and the fine silt and clay (S + C, &lt;25 µm) were characterized using elemental, isotopic (δ13C), thermogravimetric, differential thermal, diffuse reflectance infrared Fourier transform spectroscopy and high‐resolution magic angle spinning 1H nuclear magnetic resonance analyses. The quantitative distribution of carbon (C) between SOM fractions differed between the two soils. Carbon contents in the light fractions from the acid soil were significantly greater than in those of the alkaline soil. In contrast, in S + C fractions, C content was greater in the alkaline soil. FLF from the acid soil was characterized by a greater C:N ratio, smaller δ13C and greater content of thermo‐labile compounds compared with FLF from the alkaline soil. In contrast, there was only a weak effect of soil pH on the chemical composition of the organic matter in S + C fractions. Irrespective of soil pH, these latter fractions contained mainly aliphatic compounds such as carbohydrates, carboxylic acid, amide and peptide derivates. This suggested that physical mechanisms, involving the interactions between SOM and mineral surfaces, are of greater importance than the presence of chemically recalcitrant species in protecting SOM associated with the finest soil fractions.

Altered microbial community structure and organic matter composition under elevated CO2 and N fertilization in the duke forest

AbstractThe dynamics and fate of terrestrial organic matter (OM) under elevated atmospheric CO2 and nitrogen (N) fertilization are important aspects of long‐term carbon sequestration. Despite numerous studies, questions still remain as to whether the chemical composition of OM may alter with these environmental changes. In this study, we employed molecular‐level methods to investigate the composition and degradation of various OM components in the forest floor (O horizon) and mineral soil (0–15 cm) from the Duke forest free air CO2 enrichment (FACE) experiment. We measured microbial responses to elevated CO2 and N fertilization in the mineral soil using phospholipid fatty acid (PLFA) profiles. Increased fresh carbon inputs into the forest floor under elevated CO2 were observed at the molecular‐level by two degradation parameters of plant‐derived steroids and cutin‐derived compounds. The ratios of fungal to bacterial PLFAs and Gram‐negative to Gram‐positive bacterial PLFAs decreased in the mineral soil with N fertilization, indicating an altered soil microbial community composition. Moreover, the acid to aldehyde ratios of lignin‐derived phenols increased with N fertilization, suggesting enhanced lignin degradation in the mineral soil. 1H nuclear magnetic resonance (NMR) spectra of soil humic substances revealed an enrichment of leaf‐derived alkyl structures with both elevated CO2 and N fertilization. We suggest that microbial decomposition of SOM constituents such as lignin and hydrolysable lipids was promoted under both elevated CO2 and N fertilization, which led to the enrichment of plant‐derived recalcitrant structures (such as alkyl carbon) in the soil.

10.1007/s11476-008-2005-7

The chemical composition of organic matter (Corg, Norg, δ13C, δ15N, and n-alkanes) was studied in the top layer of bottom sediments of the East Siberian Sea. Possible ways were proposed to estimate the amount of the terrigenous component in their organic matter (OM). The fraction of terrigenous OM estimated by the combined use of genetic indicators varied from 15% in the eastern part of the sea, near the Long Strait, to 95% in the estuaries of the Indigirka and Kolyma rivers, averaging 62% over the sea area.

Biogeochemistry of mineral–organic associations across a long-term mineralogical soil gradient (0.3–4100 kyr), Hawaiian Islands

Organic matter (OM) in mineral–organic associations (MOAs) represents a large fraction of carbon in terrestrial ecosystems which is considered stable against biodegradation. To assess the role of MOAs in carbon cycling, there is a need to better understand (i) the time-dependent biogeochemical evolution of MOAs in soil, (ii) the effect of the mineral composition on the physico-chemical properties of attached OM, and (iii) the resulting consequences for the stabilization of OM. We studied the development of MOAs across a mineralogical soil gradient (0.3–4100 kyr) at the Hawaiian Islands that derived from basaltic tephra under comparable climatic and hydrological regimes. Mineral–organic associations were characterized using biomarker analyses of OM with chemolytic methods (lignin phenols, non-cellulosic carbohydrates) and wet chemical extractions, surface area/porosity measurements (N 2 at 77 K and CO 2 at 273 K), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), and differential scanning calorimetry (DSC). The results show that in the initial weathering stage (0.3 kyr), MOAs are mainly composed of primary, low-surface area minerals (olivine, pyroxene, feldspar) with small amounts of attached OM and lignin phenols but a large contribution of microbial-derived carbohydrates. As high-surface area, poorly crystalline (PC) minerals increase in abundance during the second weathering stage (20–400 kyr), the content of mineral-associated OM increased sharply, up to 290 mg C/g MOA, with lignin phenols being favored over carbohydrates in the association with minerals. In the third and final weathering stage (1400–4100 kyr), metastable PC phases transformed into well crystalline secondary Fe and Al (hydr)oxides and kaolin minerals that were associated with less OM overall, and depleted in both lignin and carbohydrate as a fraction of total OM. XPS, the N 2 pore volume data and OM–mineral volumetric ratios suggest that, in contrast to the endmember sites where OM accumulated at the surfaces of larger mineral grains, topsoil MOAs of the 20–400-kyr sites are composed of a homogeneous admixture of small-sized PC minerals and OM, which originated from both adsorption and precipitation processes. The chemical composition of OM in surface-horizon MOAs, however, was largely controlled by the uniform source vegetation irrespective of the substrate age whereas in subsoil horizons, aromatic and carboxylic C correlated positively with oxalate-extractable Al and Si and CuCl 2-extractable Al concentrations representing PC aluminosilicates and Al-organic complexes ( r 2 > 0.85). Additionally, XPS depth profiles suggest a zonal structure of sorbed OM with aromatic carbons being enriched in the proximity of mineral surfaces and amide carbons (peptides/proteins) being located in outer regions of MOAs. Albeit the mineralogical and compositional changes of OM, the rigidity of mineral-associated OM as analyzed by DSC changed little over time. A significantly reduced side chain mobility of sorbed OM was, however, observed in subsoil MOAs, which likely arose from stronger mineral–organic bindings. In conclusion, our study shows that the properties of soil MOAs change substantially over time with different mineral assemblages favoring the association of different types of OM, which is further accentuated by a vertical gradient of OM composition on mineral surfaces. Factors supporting the stabilization of sorbed OM were (i) the surface area and reactivity of minerals (primary or secondary crystalline minerals versus PC secondary minerals), (ii) the association of OM with micropores of PC minerals (via ‘sterically’ enhanced adsorption), (iii) the effective embedding of OM in ‘well mixed’ arrays with PC minerals and monomeric/polymeric metal species, (iv) the inherent stability of acidic aromatic OM components, and (iv) an impaired segmental mobility of sorbed OM, which might increase its stability against desorption and microbial utilization.

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.

Comparison of the chemical alteration trajectory of Liriodendron tulipifera L. leaf litter among forests with different earthworm abundance

To investigate the control of earthworm populations on leaf litter biopolymer decay dynamics, we analyzed the residues of Liriodendron tulipifera L. (tulip poplar) leaves after six months of decay, comparing open surface litter and litter bag experiments among forests with different native and invasive earthworm abundances. Six plots were established in successional tulip poplar forests where sites varied in earthworm density and biomass, roughly 4–10 fold, of nonnative lumbricid species. Analysis of residues by diffuse reflectance Fourier transform infrared spectroscopy and alkaline CuO extraction indicated that open decay in sites with abundant earthworms resulted in residues depleted in cuticular aliphatic and polysaccharide components and enriched in ether‐linked lignin relative to open decay in low earthworm abundance plots. Decay within earthworm‐excluding litter bags resulted in an increase in aliphatic components relative to initial amendment and similar chemical trajectory to low earthworm open decay experiments. All litter exhibited a decline in cinnamyl‐based lignin and an increase in nitrogen content. The influence of earthworm density on the chemical trajectory of litter decay was primarily a manifestation of the physical separation and concentration of lignin‐rich and cutin‐poor petioles with additional changes promoted by either microorganisms and/or mesofauna resulting in nitrogen addition and polysaccharide loss. These results illustrate how projected increases in invasive earthworm activity in northern North American forests could alter the chemical composition of organic matter in litter residues and potentially organic matter reaching the soil which may result in shifts in the aromatic and aliphatic composition of soils in different systems.

Composition and genesis of the organic matter in the bottom sediments of the East Siberian Sea

The chemical composition of organic matter (C org , N org , δ 13 C , δ 15 N, and n -alkanes) was studied in the top layer of bottom sediments of the East Siberian Sea. Possible ways were proposed to estimate the amount of the terrigenous component in their organic matter (OM). The fraction of terrigenous OM estimated by the combined use of genetic indicators varied from 15% in the eastern part of the sea, near the Long Strait, to 95% in the estuaries of the Indigirka and Kolyma rivers, averaging 62% over the sea area.

Physical carbon‐sequestration mechanisms under special consideration of soil wettability

AbstractThe protective impact of aggregation on microbial degradation through separation has been described frequently, especially for biotically formed aggregates. However, to date little information exists on the effects of organic‐matter (OM) quantity and OM quality on physical protection, i.e., reduced degradability by microorganisms caused by physical factors. In the present paper, we hypothesize that soil wettability, which is significantly influenced by OM, may act as a key factor for OM stabilization as it controls the microbial accessibility for water, nutrients, and oxygen in three‐phase systems like soil. Based on this hypothesis, the first objective is to evaluate new findings on the organization of organo‐mineral complexes at the nanoscale as one of the processes creating water‐repellent coatings on mineral surfaces. The second objective is to quantify the degree of alteration of coated surfaces with regard to water repellence. We introduce a recently developed trial that combines FTIR spectra with contact‐angle data as the link between chemical composition of OM and the physical wetting behavior of soil particles. In addition to characterizing the wetting properties of OM coatings, we discuss the implications of water‐repellent surfaces for different physical protection mechanisms of OM. For typical minerals, the OM loading on mineral surfaces is patchy, whereas OM forms nanoscaled micro‐aggregates together with metal oxides and hydroxides and with layered clay minerals. Such small aggregates may efficiently stabilize OM against microbial decomposition. However, despite the patchy structure of OM coating, we observed a relation between the chemical composition of OM and wettability. A higher hydrophobicity of the OM appears to stabilize the organic C in soil, either caused by a specific reduced biodegradability of OM or indirectly caused by increased aggregate stability. In partly saturated nonaggregated soil, the specific distribution of the pore water appears to further affect the mineralization of OM as a function of wettability. We conclude that the wettability of OM, quantified by the contact angle, links the chemical structure of OM with a bundle of physical soil properties and that reduced wettability results in the stabilization of OM in soils.

Chemical analysis of atmospheric aerosols

An aerosol is an assembly of liquid or solid particles which are suspended in a gaseous medium long enough to enable observation and measurement. The atmospheric aerosol thus describes the system of particles suspended in our atmosphere. Generally, the sizes of aerosol particles are in the range 0.001–100 μm. Sampled aerosol particles are also called particulate matter (PM). According to the cutoff used during sampling, a suffix is often used, thus, PM10 denotes all aerosol particles with an aerodynamic particle diameter d≤10 μm. Most legal standards are related to PM10. Atmospheric aerosols are of interest mainly because of their effects on health and climate. Concerning health, many epidemiological studies have shown a link between increased mortality/morbidity and increased PM10 or PM2.5 (see [1] and references therein). Concerning climate, aerosol particles scatter and absorb light (known as the direct effect on climate), and modify cloud properties (with a variety of effects known as indirect effects) [2]. These effects are influenced by the chemical and physical properties of the aerosol particles, which makes these properties important to be measured. In addition, the chemical composition reveals information about the sources of the atmospheric aerosols. Thus, for optimal mitigation processes the chemical composition needs to be known. Figure 1 presents the average chemical composition of PM10 from Zurich (data from [3]). Elemental carbon (EC), trace elements and mineral dust are so-called primary aerosol constituents, i.e., they are directly emitted into the atmosphere in particulate form. On the other hand, nitrate and sulfate are only formed in the atmosphere through the oxidation of the gaseous species NOx (i.e., sum of NO and NO2) and SO2 to nitric and sulfuric acid and subsequent neutralization of ammonia. These components are thus called secondary. Organic matter (OM) is composed of organic carbon (OC), which includes a variety of heteroatoms such as oxygen, hydrogen, or nitrogen. A conversion factor is therefore used to calculate OM from the measured OC concentration. OM can be of primary or secondary origin. The sum of OM and EC is also called carbonaceous aerosol. The unknown fraction consists of a considerable amount of water [3]. While the sources of the inorganic constituents are quite well known, very little is still known about the chemical composition of OM. This paper therefore focuses on the chemical analysis of OM, and includes a discussion of primary versus secondary and anthropogenic versus biogenic carbon.

Stable carbon isotope signature and chemical composition of organic matter in lignite-containing mine soils and sediments are closely linked

We studied the chemical and stable carbon isotope composition of soil organic matter at a mine site, rehabilitated for soil development 40 years ago. The site contains two types of organic matter: fresh plant material and lignite inherent to the parent substrate. A transect was sampled, consisting of mine soil rehabilitated with forest, partially submerged sediment and submerged sediment. Our objective was to assess whether the stable carbon isotope signature is related to the chemical composition of the organic matter. We analysed the chemical composition using 13C cross polarization, magic angle spinning (CPMAS) nuclear magnetic resonance (NMR) spectroscopy and lignin parameters determined after CuO oxidation. The organic matter was most enriched in 13C in the bulk soil of the forest plot and partially submerged plot. The stable isotopic signature (δ 13C) was related to the chemical composition of the sample as seen with 13C CPMAS NMR spectroscopy. The ratio (alkyl + aromatic)/(O-alky + carbonyl C) was strongly correlated with the δ 13C value regardless of the site conditions (aerobic soil or submerged sediment). Such a correlation was also observed between δ 13C and lignin content (V + S + C, where V = vanillyl, S = syringyl, C = cinnamyl oxidation products), as well as parameters indicating lignin diagenetic state [(Ac/Al)V, S/V and C/V, where Ac = acids, Al = aldehydes]. Taking δ 13C as an indicator for lignite contribution, we explain the relationships by an increasing influence of lignite contribution not only on bulk chemical composition but also on lignin parameters when the organic matter shows 13C enrichment.

CHEMICAL COMPOSITION OF CARBON DISULFIDE-EXTRACTABLE FRACTION FROM OIL SHALES OF THREE CHINESE DEPOSITS

Understanding chemical composition of organic matter in oil shales in detail is of importance to both organic geochemistry and efficient utilization of oil shales. Because of low boiling point and good penetrability, carbon disulfide was used for extraction of organic matter from solid fossils. In the present study, oil shale samples from Fushun, Longkou and Huadian deposits of China were extracted with carbon disulfide, and extraction solutions were analyzed with gas chromatography and gas chromatography/mass spectrometry. The results show that alkanes, including a series of normal alkanes, isoprenoids and cyclanes, are predominant in extraction solutions. Other compounds detected in the extraction solutions are alkenes, alkylated arenes and organo-oxygen compounds. Normal alkanes are predominant in the carbon disulfide-extractable fraction (CDEF) from Huadian oil shale. CDEF from Longkou oil shale contains much more alkanes than those from other two oil shales, whereas CDEF from Fu shun oil shale contains more cyclanes than those from other two oil shale deposits.