Ntegrated geochemical assessment of sediments from Plungė Municipal sewage outfall and sediments from Mažoji Sruoja Stream, Lithuania

Summary We know much about the influence of management on stocks of organic matter in subtropical soils, yet little about the influence on the chemical composition. We therefore studied by CPMAS 13 C NMR spectroscopy the composition of the above‐ground plant tissue, of the organic matter of the whole soil and of silt‐ and clay‐size fractions of the topsoil and subsoil of a subtropical Acrisol under grass and arable crops. Soil samples were collected from three no‐till cropping systems (bare soil; oats−maize; pigeon pea + maize), each receiving 0 and 180 kg N ha −1 year −1 , in a long‐term field experiment. Soil under the original native grass was also sampled. The kind of arable crops and grass affected the composition of the particulate organic matter. There were no differences in the composition of the organic matter in silt‐ and clay‐size fractions, or of the whole soil, among the arable systems. Changes were observed between land use: the soil of the grassland had larger alkyl and smaller aromatic C contents than did the arable soil. The small size fractions contain microbial products, and we think that the compositional difference in silt‐ and clay‐size fractions between grassland and the arable land was induced by changes in the soil's microbial community and therefore in the quality of its biochemical products. The application of N did not affect the composition of the above‐ground plant tissue nor of the particulate organic matter and silt‐size fractions, but it did increase the alkyl C content in the clay‐size fraction. In the subsoil, the silt‐size fraction of all treatments contained large contents of aromatic C. Microscopic investigation confirmed that this derived from particles of charred material. The composition of organic matter in this soil is affected by land use, but not by variations in the arable crops grown.

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.

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

Core Ideas Soil organic matter chemical composition highlighted the inputs of varied vegetation communities in the past. Soil N is an indicator of peat decomposition based on relationship of functional group C and total N. Future surveys of soil organic matter biogeochemical parameters and C chemical composition should be pursued. Climate change in the subarctic region has increased the rate of inundation of peatlands due to increased temperatures, precipitation, and permafrost thaw. Increased inundation may result in vegetation community shifts, as documented in a subarctic mire near Abisko, Sweden. The wet fen communities have established in former sphagnum areas, and sphagnum colonized in degraded palsa hummocks. At Stordalen mire, we studied the influence of vegetation community on chemical composition of peat soil organic matter (SOM). Vegetation and soil samples were obtained along a hydrologic gradient with representative communities: palsa, sphagnum, and fen. Soil organic matter chemical composition indicated shifts in vegetative communities. Total N and N isotope signatures in fen soils showed characteristics of sphagnum and palsa communities at >6‐cm depth, and sphagnum soil profile signatures shifted from sphagnum to palsa properties at a 20‐cm depth. Soil chemical composition measured by Fourier Transform Infrared (FTIR) spectroscopy and 13 C Nuclear Magnetic Resonance (NMR) spectroscopy showed increasing recalcitrant C (alkyl and aromatic) in palsa soil. Sphagnum soil profiles sustained labile organic C (O‐alkyl) until 15 cm then shifted to humified soil, and fen soil profiles showed areas of sphagnum and palsa signatures. Furthermore, the strong relationship between functional group C (O‐alkyl and alkyl) and total N demonstrated that soil N is an effective indicator of peat decomposition. Our results identified change points in soil chemical composition in regards to N content and C functional group which highlights the importance of historic vegetation community on chemical composition of peat soils.

Amount and composition of clay-associated soil organic matter in a range of kaolinitic and smectitic soils

Cycling and composition of organic matter in terrestrial and marine ecosystems

To investigate the effects of short-term nitrogen (N) deposition on organic matter composition of litter and soil in Moso bamboo (Phyllostachys edulis) forests, we established a N-addition treatments (50 kg N·hm-2·a-1) to simulate the ambient and N deposition in a subtropical Moso bamboo forest from July 2020 to January 2022. We analyzed the organic matter composition of Moso bamboo leaf/root litter and soil by using pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) technique. The results showed that short-term N deposition significantly increased the relative content of soil phenols by 50.9%, while significantly decreased fatty acids by 26.3%. The rela-tive content of alkanes & alkenes and lignin in leaf litter was significantly increased by 51.9% and 33.5%, respectively, while that of phenols and polysaccharides significantly decreased by 52.2% and 56.3%. In root litter, eleva-ted N significantly decreased the relative content of polycyclic aromatic hydrocarbons by 16.6%. Moreover, the relative content of fatty acids in soil organic matter was significantly positively correlated with the relative content of poly-saccharides in leaf litter. The relative content of phenols in soil organic matter was significantly positively correlated with the relative content of lignin, and negatively correlated with the relative content of polysaccharides in leaf litter. Our results demonstrated that short-term N deposition did not change the concentration of total organic carbon, total nitrogen, and C/N of the soil, leaf litter, and root litter, but significantly altered the chemical composition of organic matter. In addition, the changes in chemical composition of organic matter in soil under short-term N deposition were affected by the composition of organic matter in leaf litter.

The Arctic warms four times faster than the global average, resulting in widespread permafrost thaw. Organic matter that was stored in permanently frozen soil for up to millennia now becomes available to microbial decomposition. Warming might also alter microbial community composition and physiology and thus change the decomposition potential of soils. Our current knowledge about permafrost soil organic matter (SOM) composition and decomposition is limited, particularly in regard to the heterogeneity of permafrost landscapes, thus hampering our ability to predict possible permafrost soil feedbacks to climate change. The objective of this study was to characterize SOM and microbial community composition of the active layer and the upper permanently frozen soil from permafrost-affected polygonal lowland tundra.We collected more than 80 soil samples from four different soil layers (organic, mineral, cryoturbated, permanently frozen) from three developmental stages of ice-wedge polygons (low-center, flat-center, high-center polygons) in NW Canada, and analyzed organic matter composition by a pyrolysis-GC/MS fingerprinting approach and microbial community composition by amplicon sequencing of the 16S rRNA gene (bacteria, archaea) and the ITS1 region (fungi).Our results suggest that the spatial heterogeneity of permafrost soils is not only reflected in soil physical parameters, but also in the chemical composition of organic matter and the composition of microbial communities. The organic soil layer comprised both the highest microbial diversity and the most diverse SOM composition. The distribution of major compound classes (carbohydrates, lignins, lipids, N-compounds, phenols & aromatics) differed between organic, mineral, cryoturbated and permanently frozen organic matter. This pattern followed a gradient from low to high organic matter degradation with soil depth. Soil organic matter composition also differed among polygon types, indicating different decomposition pathways, likely depending on differences in vegetation and soil water availability. We also found distinct microbial communities for soils from low-center polygons, possibly driven by prevailing anoxic conditions in this landscape unit. Bacterial and archaeal communities differed among all soil layers, while only fungal communities from the organic soils differed from the other layers.The observed differences in SOM and microbial community composition among soil layers and polygon types highlight the importance of considering spatial heterogeneity when studying permafrost soils. Moreover, our results might help to explain observed differences in microbial decomposition patterns on different spatial scales and emphasize the need to include aspects of permafrost soil heterogeneity to finetune current ecosystem and climate models.This study is part of the EU H2020 project “Nunataryuk”.

Effects of sources and diagenesis on the isotopic and chemical composition of carbon and sulfur in Cretaceous shales

We investigated the spatial variability of sediment organic matter content and composition in three areas (A, B and C) of the Northwestern Adriatic Sea, subjected to a putative gradient of trophic state ( i.e. , increasing distance from the Po river outflow) in order to determine the appropriate sample size and replication. The analysis of the mesoscale variability was carried out comparing variability on the scale of meters ( i.e. among different deployments) with the variability observed on a scale of several kilometres ( i.e. among different sampling areas). Sediment samples, collected on April 1999, October 1999, April and October 2000, were analysed for chloropigment content (chlorophyll-a and phaeopygments) and protein, carbohydrate and lipid concentrations. Chloropigment, protein, carbohydrate and lipid concentrations were high, indicating that this system shares trophic conditions typical of highly productive environments. All organic matter components displayed a distribution independent from the increasing distance from the Po river outflow and a clear spatial variability, characterised by significant differences among different areas, but not among deployments. Carbohydrates were the biochemical compound displaying the highest spatial variability among the three areas. Chloropigment, protein, carbohydrate and lipid concentrations displayed also significant temporal changes. When spatial and temporal variability were compared, chlorophyll-a, phaeopigment and protein concentrations displayed a higher temporal than spatial variability. Conversely, for carbohydrates and lipids spatial and temporal variability was of the same order of magnitude. Organic matter composition displayed limited changes among areas, but a strong temporal variability. The results from the Adriatic sea suggest that analyses from sediments collected from a single deployment are sufficient for assessing organic matter concentration and composition over areas of several hundreds of square meters. However, for estimating organic matter composition over larger spatial scales ( i.e. miles) the identification of different sampling areas is needed.

Composition and origin of organic matter in surface sediments of Lake Sarbsko: A highly eutrophic and shallow coastal lake (northern Poland)

<p>Soil mineral characteristics have been shown to play a dominant role in stabilizing soil organic matter over medium to long term timescales. However, while great strides have been made (Kleber et al, 2021) toward understanding organic matter stabilization processes, there remain uncertainties about the chemistry, time scales, and age of carbon that is stored on soil minerals. We applied modern thermal analysis methods to investigate soil mineral effects on the thermal stability, chemical composition, and age distribution of soil organic matter. We selected subsoil mineral fractions that contained a single dominant stabilizing pathway (e.g. 2:1 clays, iron oxides, short-range order minerals, crystalline minerals) to isolate effects of individual minerals. We paired thermal fractionation with pyrolysis-GC/MS to describe the relationships of SOM age and chemical composition. Early results show that while certain minerals display heterogeneous thermal stabilities, single mineralogies contain generally narrow age ranges. In addition, organic matter chemistry associated with diverse minerals varies widely and indicates that certain minerals provide higher stability to complex, energy-rich molecules. Associated with this work, we also present novel continuous SOM radiocarbon distributions from thermal fractionation.</p>

Bulk Organic Matter and Lipid Biomarker Composition of Chesapeake Bay Surficial Sediments as Indicators of Environmental Processes

Soil organic matter at high latitudes is an important and sensitive indicator of climate change. This article describes the main morphological features, chemical properties, and composition of organic matter in the main types of soils along the altitudinal gradient of the Subpolar Urals. Soils formed in the mountain tundra zone (gleyic humus-illuvial podbur/Skeletiс Stagnic Entic Podzol (Turbic)), in the mountain subalpine zone (gray-humus soil/Skeletiс Umbrisol), in the mountain taiga zone (iron-illuvial podzol/Skeletiс Albic Podzol), and in the mountain tundra zone with permafrost (permafrost-affected gleyic humus-illuvial podbur/Skeletiс Folic Cryosol (Humic)) were studied. The method of densimetric fractionation was applied to study soil organic matter; it enabled us to distinguish its three fractions, differing in carbon participation in the biological turnover: free particulate organic matter (fPOM 1.6). The latter fraction dominated in the upper mineral soil horizons and comprised 89–93% of the total organic carbon. The content of light fractions was significantly lower (0.6–4.7%). However, the content of organic carbon and nitrogen in the studied soils directly correlated with the contents of light fractions fPOM<1.6 (r = 0.40 and r = 0.79, p < 0.05) and oPOM<1.6 (r = 0.68 and r = 0.83, p < 0.05). Aliphatic fragments dominated in the composition of POM; their content varied from 74.5 to 80.5% for fPOM<1.6 and from 77.9 to 84.2% for oPOM<1.6. In addition, it was found that the organic matter of the oPOM<1.6 fraction was characterized by a higher decomposition rate (0.4–2.4) and hydrophobicity (34.7–66.5%).

Environmental context Organic matter (OM) biodegradation plays a key role as it is one of the main processes causing changes in the amount, composition and properties of OM in sediment. However, a complete understanding of its processes and mechanisms is still not reached. In this study, we aim to explore the chemical composition changes during biodegradation and identify underlying processes. Rationale Although the scientific community has widely investigated organic matter biodegradation processes, only a limited number of studies have explored the molecular changes of this material, whereas its structure, composition and origin play a key role in these processes. Methodology We decided to examine the effects of biodegradation on the chemical composition of sedimentary organic matter and to explore the underlying mechanisms. We conceived a laboratory-based degradation experiment utilising organic-rich sediments artificially composed of two contrasting organic matter end-members (i.e. soil and algae) under two oxygen conditions. The sediment samples before and after incubation were then analysed by laser desorption ionisation–Fourier-transform–ion cyclotron resonance–mass spectrometry for molecular characterisation and by thermally assisted hydrolysis and methylation gas chromatography–mass spectrometry in order to offer insights into the mechanisms driving the biodegradation processes. Results Our results from molecular characterisation unveiled distinct pathways of biodegradation contingent upon the source material. Moreover, they hinted at a predilection for altering high molecular weight compounds like lignin &amp; carboxylic-rich alicyclic molecules (CRAM) and condensed aromatic structures (CAS), manifesting as a conversion into lower molecular weight counterparts. Furthermore, the complementary findings from biomarker analyses underscored the influence of environmental factors – specifically oxygen conditions and microbial communities – on organic matter decomposition. Discussion Although this study is a controlled laboratory experiment and more studies are needed, it demonstrates the intricate interplay among chemical, biological and environmental factors that profoundly shape the reactivity of organic matter. This study underscores the critical need for persistent inquiry, aimed at unravelling the factors and conditions governing the diverse pathways of biodegradation.