Degree Of Organic Matter Decomposition Research Articles

The hidden depths of forest soil organic carbon chemistry in a pumice soil

Forest ecosystems can store massive amounts of organic carbon (OC) deep in their soils. Soil OC (SOC) is composed of several complex organic compounds of which groupings of these organic compounds can provide an insight into evaluating the formation and fate of SOC. However, there is little information available regarding the chemical composition of deep forest SOC and how they compare to upper soil depths. The objective of this study was to explore the SOC chemistry changes with increasing soil depth on a fine spatial scale in a planted forest soil derived from young volcanic erupted airfall deposits. Soil core samples to 1 m depth were collected from Puruki Experimental Forest (New Zealand) and examined for incremental depth changes in SOC functional groups, or chemical shift regions, using solid-state 13C cross polarisation magic angle spinning nuclear magnetic resonance (13C CPMAS-NMR) spectroscopy. The results showed that soil depth was a driver of change in soil chemical shift regions. The presence of a coarse-textured soil horizon, lapilli layer, at depth was a driver of significant (p < 0.05) differences between SOC functional groups. In the upper soil profile (0–10 cm), the chemical shift distribution was dominated by O-alkyl C (39%) followed by alkyl C (32%), aromatic C (23%), and carboxyl C (6%). In the deep soil layers, we found alkyl C increased below the lapilli layer (varying depth > 50 cm) compared to above the lapilli layer. In the deep soil layers the alkyl C was the dominant functional group (55%), followed by O-alkyl C (28%). Furthermore, there was a decrease at depth in aromatic (12%) and carboxyl C (5%). The A/O-A ratio increased with depth from soil above the lapilli layer compared to soils below the lapilli layer indicating a greater degree of organic matter decomposition and a corresponding decrease in the labile OC fractions. Within the lapilli layer the SOC functional groups and A/O-A ratio were highly variable. These results highlight that changes in SOC chemical composition occur with increasing soil depth, a property of deep soil that is frequently understudied, and are highly influenced by the multi layered nature of soil derived from volcanic airfall deposits.

Mercury mobilization in shrubland after a prescribed fire in NE Portugal: Insight on soil organic matter composition and different aggregate size

Soils constitute the major reservoir of mercury (Hg) in terrestrial ecosystems, whose stability may be threatened by wildfires. This research attempts to look at the effect of prescribed fire on the presence of Hg in a shrubland ecosystem from NE Portugal, delving into its relationship with soil aggregate size and the molecular composition of soil organic matter (SOM). During the prescribed fire, on average 347 mg Hg ha−1 were lost from the burnt aboveground biomass of shrubs and 263 mg Hg ha−1 from the combustion of the soil organic horizon. Overall, Hg concentration and pools in the mineral soil did not show significant changes due to burning, which highlights their role as long-term Hg reservoirs. The higher Hg concentrations found in smaller aggregates (<0.2 mm) compared to coarser ones (0.5–2 mm) are favored by the higher degree of organic matter decomposition (low C/N ratio), rather than by greater total organic C contents. The Hg-enriched finest fraction of soil (<0.2 mm) could be more prone to be mobilized by erosion, whose potential arrival to water bodies increases the environmental concern for the Hg present in fire-affected soils. The SOM quality (molecular composition) and the main organic families, analyzed by Fourier-transform infrared spectroscopy in combination with multivariate statistical analysis, significantly conditioned the retention/emission of Hg in the uppermost soil layers. Thus, before the fire, Hg was strongly linked to lipid and protein fractions, while Hg appeared to be linked to aromatic-like compounds in fire-affected SOM.

Plant‐Soil Relationships Influence Observed Trends Between Manganese and Carbon Across Biomes

AbstractManganese (Mn) is an essential plant micronutrient that plays a critical role in the litter decomposition by oxidizing and degrading complex organic molecules. Previous studies report a negative correlation between Mn concentrations and carbon (C) storage in organic horizons and suggest that high Mn concentrations in leaf litter reduce soil C storage in forest ecosystems, presumably by stimulating the oxidation of lignin by fungal enzymes. Yet, the relationship between Mn and C in the litter layer and organic soil remains poorly understood and restricted to a few biomes, hampering our ability to improve mechanistic understanding of soil C accumulation. To examine plant‐soil interactions that underlie observed relationships between Mn and C across a wide range of biomes, we extracted biogeochemical data reported for plants and soils from the National Ecological Observatory Network (NEON) database. We found that increased C and nitrogen (N) storage in organic horizons were associated with declines in Mn concentrations across diverse ecosystems at the continental scale, and this relationship was associated with the degree of organic matter decomposition (i.e., Oi, Oe, and Oa). Carbon and N stocks were more strongly correlated with Mn than with climatic variables (i.e., temperature and precipitation). Foliar Mn was strongly correlated with foliar lignin, and both these parameters increased with a decrease in soil pH, indicating links between soil pH, foliar chemistry, and litter decomposability. Our observations suggest that increased Mn bioavailability and accumulation in foliage under moderately acidic soil conditions support fungal decomposition of lignin‐rich litter and contributes to lower soil C stocks.

Brightness Values-Based Discriminant Functions for Classification of Degrees of Organic Matter Decomposition in Soil Thin Sections

The decomposition of organic matter represents a fundamental pedogenetic process, since it impacts the carbon cycle and the release of nutrients to the soil. However, quantitative research aimed at micro-scale in situ analysis is scarce, despite its relevance in the decomposition process. Therefore, the objectives of this research were to generate discriminating functions of the degrees of organic matter decomposition, based on the brightness values associated with each morphological stage, and from this step, to generate thematic maps. Soil thin sections of forest and compost soils were selected, and petrographic microscope images with three light sources were taken: plane polarized light (PPL), crossed-polarized light (XPL), and crossed polarizers and a retardation plate (gypsum compensator) inserted (XPLλ). Subsequently, the RGB (red, green, blue) image was broken down into three bands, resulting in nine bands for each image. Two thousand sampling points were generated for each band, obtaining brightness values for each decomposed organic matter stage. The points were classified into four categories based on their degree of decomposition: no (A), light (B), moderate (C), and strong (D), in addition to porosity (P). Linear discriminant analysis was performed to obtain classification models for each level of decomposition. The results show that each degree of organic matter decomposition can be highlighted through specific light sources and a set of bands, with an overall accuracy of &amp;gt;94% and kappa coefficients of &amp;gt;0.75 for all classes. In addition, the resulting functions were validated in training images and high-resolution mosaics to create final thematic maps. The use of linear models automated the production and quality of thematic maps at the microscopic level, which can be useful in monitoring the organic matter decomposition process.

Rate of Fen-Peat Soil Subsidence Near Drainage Ditches (Central Poland)

This study analyzed design depths (to), post-subsidence depths (t), shallowing magnitudes (d = to − t) and ratio values (d/t) of 12 drainage ditches in a fragment of the drained Solec fen-peat (central Poland) over a period of 47 years between 1967 and 2014. A significant decrease of the designed depth of the ditches to was shown, from the average designed value of 0.97 m to their average depth after subsidence, t = 0.71 m. The ratio (d/t) of 0.41, which is associated with the degree of organic matter decomposition, indicated medium degree of peat decomposition. The average values of bank and bottom subsidence of the ditches during the analyzed period, 1967–2014, were 0.43 m and 0.17 m, respectively. The values of the average annual rate of land surface subsidence in the vicinity of the ditches were varied and within the range of 0.09 cm year−1 to 1.70 cm year−1, with an average of 0.92 cm year−1. Two linear empirical equations were proposed to calculate the amount of subsidence and the average annual rate of subsidence of peat soil surface near the drainage ditch route, based on the knowledge of the initial thickness of the peat deposit. The results of calculations using the equations proposed by the authors were compared with calculations of the same parameters using 10 equations published in the literature. The results obtained using the proposed equations were mostly larger than those calculated with literature-published equations.

Influence of various degradation conditions on the properties of gas-generating soils in the process of their decontamination

The properties of gas-generating soils (GGS) in the process of biofermentation under anaerobic and aerobic conditions are studied. The degradation of organic matter (OM) in a soil under natural occurrence conditions (without free access of air oxygen) at temperatures from 10 to 12°C is demonstrated to proceed at a specific reaction rate of k = 0.096 year−1. The main phase of gas generation (biogas formation) is shown to take 15 years, with the content of methane in the biogas being 60−80 vol %. It has been established that, under the conditions of forced aeration of the GGS array, the specific reaction rate of OM degradation increases 10-fold, to 0.9673 year−1, with a nearly complete decomposition of OM taking 1.5−2.0 years. A prerequisite for achieving of the predicted result is the maintenance of the environment humidity at a level not lower than 50%. Application of an alternative method, a thermal treatment of GGS increases the degree of OM decomposition to 59% within 4 h at 200°C and to 75% within 2 h at 300°C. In this case, residual organic substances are carbonized in the course of thermal treatment, transforming into a material resistant to microbiological decomposition. In fact, after heating at 200−300°C, GGS becomes inert from the gas-geochemical point of view.

Chemistry and spectroscopic properties of surface horizons of Arctic soils under different types of tundra vegetation – A case study from the Fuglebergsletta coastal plain (SW Spitsbergen)

Detailed studies of soil organic matter (SOM) are currently very important, especially in the permafrost-affected soils of the High Arctic, as many of these soils contain quite a large amount of SOM, which may be very susceptible to decomposition due to climate change. The main objective of this study was to determine the chemistry and spectroscopic properties of surface horizons (O, A, AC) of High Arctic soils under different types of tundra vegetation in the eastern part of the Fuglebergsletta coastal plain (Hornsund area, SW Spitsbergen) in the context of SOM susceptibility to decomposition due to climate change. The obtained results indicate that soils covered with wet moss and ornithocoprophilous tundra vegetation exhibits significantly higher carbon and nitrogen content in comparison with soils covered with lichen-heath, polygonal, and geophytic initial tundra vegetation. Despite differences in the elemental composition of all the soil surface horizons, the mean C/N ratio for the studied horizons is low and similar (i.e. from 9 to 14). This indicates that C/N ratio is not a good indicator of degree of organic matter decomposition for the High Arctic soils occurring in areas affected by seabirds. A high E4/E6 ratio (i.e. ratio of UV–Vis absorbance measured at 472nm and 664nm and often called humification index) for NaOH-soluble humic substances indicates that the humic substances present in the studied surface horizons of soils covered with wet moss, ornithocoprophilous, and lichen-heath tundra vegetation are characterized by a low degree of humification. The Fourier transform infrared (FTIR) spectroscopy data indicate a prevalence of aromatic rings over aliphatic chains in the surface horizons of Cryosols under polygonal, geophytic initial, and lichen-heath tundra vegetation. Surface horizons of soils covered with wet moss and ornithocoprophilous tundra vegetation types exhibit a prevalence of aliphatic chains over aromatic rings. Such soils, which occupy about one third of the studied area, may act as carbon sources in the context of the emission of greenhouse gases into the atmosphere if the global air temperature will still rise. On the other hand, SOM from the surface horizons of soils covered with polygonal and geophytic initial tundra vegetation and occupying about 40% of the studied area, exhibits low potential susceptibility to decomposition.

Carbon and Nitrogen Stocks and Humic Fractions in Brazilian Organosols

Despite limited geographic expression of Organosols in Brazil, their high carbon storage capacity and natural environmental vulnerability justifies further studies on C and N stocks in these soils and their relationship to the nature of organic matter. Evaluation of physical and chemical properties of organic soils and their ability to store C is important so as to develop sustainable management practices for their preservation. The objectives of the study were to measure the total organic carbon stock (OCst), total nitrogen stock (Nst), and humic fractions in Organosols from different environments and regions of Brazil, and to correlate the data with soil chemical (pH, P, K, Ca2+, Mg2+, Al3+, H+Al, CEC, V) and physical properties (soil bulk density, Bd; organic matter density, OMd; total pore space, TPS; minimum residue, MinR; and proportion of mineral matter, MM), and degree of organic matter decomposition (rubbed fiber content; pyrophosphate index, PyI; and von Post index). For that purpose, 18 Organosol profiles, in a total of 49 horizons, were sampled under different land usage and plant coverage conditions. The profiles were located in the following Brazilian states - Alagoas, Bahia, Distrito Federal, Espirito Santo, Mato Grosso do Sul, Minas Gerais, Parana, Rio de Janeiro, Rio Grande do Sul, Santa Catarina, and Sao Paulo. The OCst and Nst varied significantly among horizons and profiles. The Organosols exhibited, on average, 203.59 Mg ha-1 OCst and 8.30 Mg ha-1 Nst, and the highest values were found in profiles with pasture usage. The content of the humic fraction (humin, HUM; fulvic acid, FAF; and humic acid, HAF) and C storage varied in the soil horizons and profiles according to the degree of decomposition and other factors of soil formation. The OCst, Nst, OMd and the C stocks in the humic fractions were positively correlated. The values of acidity were lower in the soils with higher contents of mineral material, and low pH values were related to a high C/N ratio. The OCst and Nst were correlated with different soil properties, the most important being the degree of soil organic matter decomposition, which was inversely correlated.

Morphology, chemical properties, and radiocarbon dating of eutrophic peat in Turkey

Abstract Morphologies, classifications, chemical properties and radiocarbon dates of Akgol–Sakarya peatland located in the northwestern part of Turkey, which has never been studied up to now, were investigated. Three representative profiles were excavated in the study area and soil samples were taken based on soil horizons. Additionally, soil samples were taken at the different depths in each profile for radiocarbon dating. Accretion rates changed between 1.40 and 1.69 mm year − 1 according to 14 C measurements. Radiocarbon ages ranged between 365 ± 90 and 195 ± 50 years depending on sampling depth. Profile I was Sapric Haplohemist, profile II was Hydric Haplohemist and profile III was Typic Haplosaprist. Soil properties varied widely depending on the profiles. Fibre contents were between 9.4% and 34.7% due to degree of organic matter decomposition. pH and ECe values varied between 4.20–6.62 and 0.51–2.50 dS m −1 , respectively. The cation exchange capacity (CEC) ranged from 100 to 140 cmol kg −1 . Total nitrogen and phosphorus ranged from 0.78% to 1.82% and from 0.45% to1.03%, respectively. Total calcium contents were between 1.44% to 3.25%, and magnesium contents varied from 0.22 to 0.71%. Both nutrients were higher in the surface horizons of profiles I and II. Total Fe, Mn, Zn, Cu and B contents varied considerably among profiles. It was found that total amounts of Fe, Zn, Cu and B in samples were between 4660–16220 mg kg − 1 , 89–451 mg kg − 1 , 16–57 mg kg − 1 , 3–11 mg kg − 1 and 12–37 mg kg − 1 , respectively. Cr, Ni and Pb contents in peat samples were 22–55 mg kg − 1 , 24–58 mg kg − 1 , and 3–93 mg kg − 1 , respectively. However, there was no Cd and Hg detected. It was observed that seasonal ground water fluctuations, eutrophic formation and differences in decomposition degrees have a substantial effect on changing of morphological and chemical properties of organic soils in the study area.

Production of well-matured compost from night-soil sludge by an extremely short period of thermophilic composting

The effect of various operational conditions on the decomposition of organic material during the composting of night-soil treatment sludge was quantitatively examined. The optimum composting conditions were found to be a temperature of ca. 60 °C and an initial pH value of 8. Rapid decomposition of organic matter ceased by the sixth day of composting under these optimum conditions, and the final value of the cumulative emission of carbon ( E C), which represents the degree of organic matter decomposition, was less than 40%, indicating that the sludge contained only a small amount of easily degradable organic material. A plant growth assay using Komatsuna ( Brassica campestris L. var. rapiferafroug) in a 1/5000a standard cultivation pot was then conducted for the compost at various degrees of organic matter decomposition: the raw composting material, the final compost obtained on day 6, and the 2 intermediate compost products (i.e., E C = 10% and 20%). It was found that the larger the E C, the greater the yield of Komatsuna growth. It was also found that 6 days of composting is sufficient to promote Komatsuna growth at the standard loading level, which is equivalent to a 1.5 g N/pot, since the promotion effect was as high as that obtained using chemical fertilizer. It can therefore be concluded that well-matured compost could be obtained in a short period of time (i.e., as early as 6 days), when night-soil sludge is composted under optimum conditions.

The effect of high pH alkaline solutions on the mineral stability of the Boom Clay – Batch experiments at 60°C

Boom Clay is currently viewed as a reference host formation for studies on deep geological disposal of radioactive waste in Belgium. The interactions between bulk rock Boom Clay and 0.1 M KOH, 0.1 M NaOH, 0.1 M Ca(OH)2, young cement water and evolved cement water solutions, ranging in pH from 12.5 to 13.2, were examined as static batch experiments at 60 °C to simulate alkaline plume perturbations, which are expected to occur in the repository due to the presence of concrete. Both liquids and solids were investigated at specific times between 90 and 510 days in order to control the elemental budget and to search for potential mineralogical alterations. Also, the clay fraction was separated from the whole-rock Boom Clay at the end of each run and characterized for its mineralogical composition. Thereby, the importance of the mineral matrix to buffer the alkaline attack and the role of organic matter to protect clay minerals were also addressed. The results indicate that the degree of geochemical perturbation in Boom Clay is dependent on the initial pH of the applied solution together with the nature of the major cation in the reactant fluids. The higher the initial pH of the media, the stronger its interaction with Boom Clay. No major non-clay mineralogical alteration of the Boom Clay was detected, but dissolution of kaolinite, smectite and illite occurred within the studied experimental conditions. The dissolution of clays is accompanied by the decrease in the layer charge, followed by a decrease in the cation-exchange capacity. The highest TOC values coincide with the highest total elemental concentrations in the leachates, and correspondingly, the highest dissolution degree. However, no quantitative link could be established between the degree of organic matter decomposition and clay dissolution.

Spatial Extent, Age, and Carbon Stocks in Drained Thaw Lake Basins on the Barrow Peninsula, Alaska

Thaw lakes and drained thaw lake basins are ubiquitous on the Arctic Coastal Plain of Alaska. Basins are wet depositional environments, ideally suited for the accumulation and preservation of organic material. Much of this soil organic carbon (SOC) is currently sequestered in the near-surface permafrost but, under a warming scenario, could become mobilized. The relative age of 77 basins on the Barrow Peninsula was estimated using the degree of plant community succession and verified by radiocarbon-dating material collected from the base of the organic layer in 21 basins. Using Landsat-7+ imagery of the region, a neural network classifying algorithm was developed from basin age-dependent spectra and texture. About 22% of the region is covered by 592 lakes (>1 ha), and at least 50% of the land surface is covered by 558 drained lake basins. Analysis of cores collected from basins indicates that (1) organic layer thickness and the degree of organic matter decomposition generally increases with basin age, and (2) SOC in the surface organic layer tends to increase with basin age, but the relation for the upper 100 cm of soil becomes obscured due to cryoturbation, organic matter decomposition, and processes leading to ice enrichment in the upper permafrost.

Relationship between Organic Matter Decomposition and Odorous Compounds' Emission during Thermophilic Composting

We investigated the effect of inoculant on the emission of odorous compounds during isothermal thermophilic composting processes at 60°C. Of these compounds, ammonia and odorous sulfur compounds, hydrogen sulfide (H 2 S), methylmercaptane (MMC), dimethylsulfide (DMS), and dimethyldisulfide (DMDS) were measured. We used three different inoculants, and found that composting with two of them, where vigorous organic matter decomposition occurred, generated a very high concentration of NH 3 , as high as 4000 ppm, and also generated high concentrations of sulfur compounds, especially of MMC and DMDS. In contrast, very few odorous compounds were emitted during composting with the third inoculant; however, there was an extremely small degree of organic matter decomposition in this composting. These results indicate that it is not sufficient to merely compare odor emission when assessing the best operational conditions for composting with a small amount of odor emission. In other words, in assessing composting operations with regards to the effective reduction of odor emissions, it is important to simultaneously quantify the degree of organic matter decomposition that occurs.

Some genetic implications of silica and aluminosilicates in peat and coal

The inorganic content of Okefenokee peat, in the absence of a significant detrital contribution, is a function of sponge spicule, phytolith, and diatom abundance in addition to the degree of organic matter decomposition and the frequency of fires. The detrital component (quartz) dominates ash composition where it is present. No clear correlation has been observed between the inorganic content of coals examined in this study and their maceral composition. Vitrinite-rich coals have a wide range of ash yield. These observations suggest that the minerals have been introduced detritally rather than accumulated as a result of peat degradation. Quartz in the coals appears to be detrital, and the presence of 2m 1 mica indicates that there is also a detrital contribution to the clay minerals present.

Physical and Chemical Properties of the Forest Floor in Birch and Aspen Stands in Interior Alaska

AbstractThis study was conducted to establish the mass and nutrient status of the forest floor in quaking aspen (Populus tremuloides Michx.) and paper birch (Betula papyrifera Marsh.) forests in interior Alaska. Results of this investigation show that aspen forests have a greater mass of organic matter and nutrient elements in the forest floor than birch forests. The more favorable base status in aspen forest floors is reflected in higher pH and lower exchangeable hydrogen than encountered in birch forest floors. Increasing degree of organic matter decomposition in the forest floor of both vegetation types (L layer &gt; F layer &gt; H layer) is associated with increased N content and cation exchange capacity of the organic matter in the respective layers.