Original Organic Carbon Research Articles

Response of Organic Carbon Mineralization to Nitrogen Addition in Micro-aerobic and Anaerobic Layers of Paddy Soil

In field conditions, a micro-aerobic layer with 1 cm thickness exists on the surface layer of paddy soil owing to the diffusion of dissolved oxygen via flooding water. However, the particularity of carbon and nitrogen transformation in this specific soil layer is not clear. A typical subtropical paddy soil was collected and incubated with13C-labelled rice straw for 100 days. The responses of exogenous fresh organic carbon(13C-rice straw) and original soil organic carbon mineralization to nitrogen fertilizer addition[(NH4)2SO4]in the micro-aerobic layer(0-1 cm) and anaerobic layer(1-5 cm) of paddy soil and their microbial processes were analyzed based on the analysis of 13C incorporation into phospholipid fatty acid(13C-PLFAs). Nitrogen addition promoted the total CO2 and 13C-CO2 emission from paddy soil by 11.4% and 12.3%, respectively. At the end of incubation, with the addition of nitrogen, the total soil organic carbon (SOC) and13C-recovery rate from rice straw in the anaerobic layer were 2.4% and 9.2% lower than those in the corresponding micro-aerobic layer, respectively. At the early stage(5 days), nitrogen addition increased the total microbial PLFAs in the anaerobic layer with a consistent response of bacterial and fungal PLFAs. However, there was no significant effect from nitrogen on microbial abundance in the micro-aerobic layer. Nitrogen addition had no significant impact on the abundance of total 13C-PLFAs in the micro-aerobic and anaerobic layers, but the abundance of 13C-PLFAs for bacteria and fungi in the micro-aerobic layer was decreased dramatically. At the late stage(100 days), the effect of nitrogen addition on microbial PLFAs was consistent with that at the early stage. The abundances of total, bacterial, and fungal 13C-PLFAs were remarkably increased in the anaerobic layer. However, the abundance of 13C-PLFAs in the micro-aerobic layer showed no significant response to nitrogen addition. During the incubation, the content of NH4+-N in the anaerobic soil layer was higher than that in the micro-aerobic soil layer. This indicates that nitrogen addition increased microbial activity in the anaerobic soil layer caused by the higher NH4+-N concentration, as majority of microorganisms preferred to use NH4+-N. Consequently, the microbial utilization and decomposition of organic carbon in the anaerobic soil layer were accelerated. By contrast, richer available N existed in the form of NO3--N in the micro-aerobic soil layer owing to the ammoxidation process. Thus, the shortage of NO3--N preference microorganisms in the paddy soil environment prohibited the microbial metabolism of organic carbon in the micro-aerobic layer. As a whole, nitrogen fertilization enhanced organic carbon loss via microbial mineralization in paddy soil with a weaker effect in the micro-aerobic layer than that in the anaerobic layer, indicating the limited microbial metabolic activity in the surface micro-aerobic layer could protect the organic carbon stabilization in paddy soil. This study emphasizes the heterogeneity of paddy soil and its significant particularity of carbon and nitrogen transformation in micro-aerobic layers. Consequently, this study has implications for optimizing the forms and method for the application of nitrogen fertilizer in paddy cropping systems.

Restoration of sedimentary environment and geochemical features of deep marine Longmaxi shale and its significance for shale gas: A case study of the Dingshan area in the Sichuan Basin, South China

With the urgent need to increase shale gas production and reserves, deep shale gas has gradually become an important target for further exploration in China. However, there is still a lack in systematic research on the quality of different lithofacies types of shales in deep shale gas reservoirs. The overmature shales have a common problem, that is, the organic matter (OM) quality could not be clearly characterized by using conventional organic geochemical indicators, hindering the process of fine shale gas exploration. In this study, the deep marine Longmaxi (LMX) shale samples in the Dingshan area, southeastern Sichuan Basin were selected as a study case to investigate their lithofacies types, sedimentary environment and organic matter accumulation (OMA) mechanism, and restore the original OM attributes including original organic carbon content (TOCo) and original hydrogen index (HIo) for the different shale types to identify the favorable lithofacies for shale gas enrichment. The results show that the LMX shale can be divided into five different lithofacies, such as the OM-rich siliceous (RS) shale, OM-rich mixed (RM) shale, OM-lean siliceous (LS) shale, OM-lean mixed (LM) shale and OM-lean argillaceous (LA) shale, with a gradually decrease of their TOC contents. The TOC content of the LMX shale has a positive synergy with the indicators of paleoproductivity and redox conditions. However, since the studied area is close to the underwater highland with a high oxygen content in the bottom water and a great input of terrigenous debris, the OMA mainly depends on the level of high paleoproductivity. The analysis of sedimentary environment indicates that the OM amount and quality in various lithofacies shales are different. The RS shale at the lower part of the LMX shale has a better OM quality and a greater TOCo, which result in the greater effective organic carbon (TOCe), gas production potential, and retained gas content. It is followed by the RM, LS, and LM shales. In contrast, the LA shale lacks material base for shale gas enrichment. Combined with the available data from other deep blocks in the southern Sichuan Basin, the original OM attributes of RS and RM shales are always better than those of LM, LS, and LA shales. For deep and ultra-deep Longmaxi shale gas exploration, the RS shale should be the first choice, and then the RM shale.

Hydrocarbon generation and expulsion of the Fengcheng Formation in the Mahu sag, Junggar Basin, China: Implications for shale oil resource potential

The Permian source rocks in the Junggar Basin are widely developed, especially the Fengcheng Formation, which is the most significant source rock in the basin. However, due to insufficient research on the hydrocarbon generation (HG) and hydrocarbon expulsion (HE) characteristics of the source rocks, it is unclear whether a significant amount of retained hydrocarbons remain within shales. In general, the original organic matter abundance and kerogen type control hydrocarbon generation potential (HGP) and HE capacity in lacustrine shales. Therefore, the degradation rate method was used to establish the original organic carbon recovery model for different types of kerogen. Combined with the geologic and geochemical characteristics of the source rock, the HG, HE, and shale oil resource potential of the Fengcheng shale have been evaluated. We have found that the Fengcheng shale is mainly carbonate-type mudstone widely distributed with an average thickness greater than 100 m. The Fengcheng shale is composed of type II kerogen and reached the mature to high-mature thermal maturity stage, with the maximum original organic carbon exceeding 4.0 wt%. Meanwhile, the amount of retained hydrocarbons within shales is abundant according to the HGP model. Monte Carlo simulation finds that the shale oil resources of the Fengcheng shale are 23.30 × 108 t. Free oil resources account for 60%, reaching 13.75 × 108 t, indicating tremendous shale oil exploration potential.

Subsurface Microbial Community Composition in Anchialine Environments Is Influenced by Original Organic Carbon Source at Time of Deposition

Prokaryotes constitute the majority of sedimentary biomass, where they cycle organic carbon and regulate organic matter transformation. The microbes inhabiting sediment are diverse and the factors controlling microbial community composition are not fully understood. Here, we characterized the prokaryotic community using 16S rRNA gene sequencing in 24 stratigraphic layers within a 89 cm (dated to ~1900 years old) sediment core from an anchialine sinkhole in the Bahamas with a stratified water column and anoxic bottom water. The microbial community was dominated by members of the Alphaproteobacteria, Dehalococcoidia, Gammaproteobacteria, Bathyarchaeota, and Campylobacter classes. Most interestingly, subsurface microbial community structure could be correlated to previous evidence for timewise changes in the main source of organic matter that was supplied to the sediment accumulating during the last 2000 years, which itself was caused by regional terrestrial vegetation changes. The C:N ratio was correlated to the relative abundance of the microbial classes, and the microbial communities followed three previously determined time periods based on the source of organic matter, which suggests that the carbon source at time of deposition influences the resultant subsurface microbial community composition. These results show that carbon source is a driver of the microbial community composition inhabiting anoxic sediment, which could have implications for improving understanding of carbon cycling in coastal sedimentary basins.

Integrated source rock evaluation along the maturation gradient. Application to the Vaca Muerta Formation, Neuquén Basin of Argentina

AbstractThe Vaca Muerta Formation (Tithonian–early Valanginian) is the main source rock in the Neuquén Basin and the most important unconventional shale resource in South America. In the present study, organic geochemistry, electron microscopy and basin and petroleum system modelling (BPSM) were combined to evaluate source rock properties and related processes along a transect from the early oil (east) to the dry gas (west) window. The unit is characterized by high present‐day (1%–8% average) and original (2%–16% average) total organic carbon contents, which increase towards the base of the unit and basinal (west) settings. Scanning electron microscopy shows that organic pores derived from the transformation of type II kerogen. Isolated bubble pores are typical of the oil window, whereas bubble and densely distributed spongy pores occur in the gas stage, indicating that the maturity gradient exerts strong control on organic porosity. Organic geochemistry, pressure and porosity data were incorporated into a 2D basin petroleum system model that includes the sequential restoration of tectonic events and calculation of compaction trends, kerogen transformation, hydrocarbon generation and estimation of pore pressure through geologic time. The W–E regional model extends from the Agrio Fold and Thrust Belts to the basin border and allows us to evaluate the relationship between thermal maturity and timing of hydrocarbon generation from highly deformed (west) to undeformed (east) regions. Modelling results show a clear decrease in maturity and organic matter (OM) transformation towards the eastern basin margin. Maximum hydrocarbon generation occurred in the inner sectors of the belt, at ca. 120 Ma; long before the first Andean compression phase, which started during the Late Cretaceous (ca. 70 Ma). Miocene compression (15–7 Ma) promoted tectonic uplift of the inner and outer sectors of the belt associated with a reduction in thermal stress and kerogen cracking, as well as massive loss of retained fluids and a decrease in pore pressure. The OM transformation impacted (a) the magnitude of effective porosity associated with organic porosity development, and (b) the magnitude and distribution of pore pressure within the unit controlled by hydrocarbon generation and compaction disequilibrium. BPSM shows a progressive increase in effective porosity from the top to the base and towards the west region related to the original organic carbon content and maturity increasing along the same trend. Overpressure intervals with high organic carbon contents are the most prone to develop organic pores. The latter represent favourable sites for the storage of hydrocarbons in the Vaca Muerta Formation.

The effect of oil-based drilling mud (OBM) on the assessment of hydrocarbon charge potential

Foundational to source rock assessment in exploration is an understanding of organic enrichment and hydrocarbon generation potential. With an increased use of oil-based drilling mud, particularly in deep water drilling, problems associated with contamination have complicated source rock assessment. Drilling fluid contamination is assumed to increase the apparent values of the basic screening source rock parameters such as total organic carbon (TOC) and total hydrocarbon generation (S1 + S2).It has been commonly assumed that the effect of contamination can be reduced or eliminated by pre-treating samples with organic solvents (i.e., extraction of the sample) prior to analysis. In this study, an attempt is made to characterize this extraction process on a suite of simulated cuttings samples that were contaminated and extracted prior to analysis to validate the assumptions presented in the literature.Results from these experiments show significant differences between values measured on the original and oil-based drilling fluid contaminated samples before and after extraction. After contamination and before extraction, measured TOC and Rock-Eval parameters indicate that the oil-based drilling fluids appear to be acting as an aggressive solvent, altering the apparent source rock potential. Contamination by oil-based drilling fluid appears to reduce the total organic carbon content and the residual generation (S2) potential, while increasing the free hydrocarbon content. This may be a result of the presence of solid bitumen or bituminite in the original sample, which are acted on by the oil-based drilling fluid. Following extraction of the contaminated samples, the TOC and residual generation potential undergo further reduction and the free hydrocarbons were nearly eliminated. It was also observed that uncontaminated samples, when extracted, experienced an increase in TOC and the S3 (CO2) peak. These increases may have resulted from the retention of small amounts of solvent.Unlike the common assumption in the existing literature, these data indicate that once oil-based drilling fluids contaminate a sample, pre-treatment extraction does not provide an accurate measure of either the original organic carbon or residual generation potential. The data indicate that the use of Rock-Eval pyrolysis results from extracted samples that have been contaminated by oil-based drilling fluid can result in a significant underestimation of the system's hydrocarbon source rock potential.

Dynamics of new- and old- soil organic carbon and nitrogen following afforestation of abandoned cropland along soil clay gradient

Disentangling the changes of newly input and original organic carbon (OC) and nitrogen (N) after agricultural land-use transition is crucial for understanding the mechanisms behind soil OC and N dynamics in terrestrial ecosystems. However, these dynamics have received little attention so far due to the lack of an approach separating them. In this study, we determined the natural abundance of 13C and 15N in soils from afforested forestlands and adjacent croplands, the forestlands were established at different times (10, 20 and 30 years) at four sites with different soil textures across the Loess Plateau of China. The objective was to explore the changes of new- and old- OC and N along with soil clay gradient, and to examine the proportions of these changes in total OC and N along with the clay content. We showed that the conversion of cropland to forestland increased total- and new- OC and N stocks by 0.69 kg m−2 and 0.10 kg m−2, but decreased old OC and N stocks by −0.20 kg m−2 and −0.04 kg m−2, respectively. When averaged across afforestation age, the proportions of new OC and N increased, but the proportions of old OC and N decreased with the clay content. In the soils that have a higher clay content, the accumulation of N rates were greater than that of OC in the new stock, and the loss rates of N were higher than that of OC in the old stock after afforestation. In contrast, in the soils that have a lower clay content, the accumulation rates of N were lower than that of OC in the new stock, and the loss rates of N were smaller than the loss of OC in the old stock. These findings indicated that soil texture regulates the changes of OC and N in new and old soil organic matter pools following cropland afforestation.

Earthworms accelerate rice straw decomposition and maintenance of soil organic carbon dynamics in rice agroecosystems.

BackgroundTo promote straw degradation, we inoculated returned farmland straw with earthworms (Pheretima guillelmi). Increasing the number of earthworms may generally alter soil organic carbon (SOC) dynamics and the biological activity of agricultural soils.MethodsWe performed soil mesocosm experiments with and without earthworms to assess the decomposition and microbial mineralization of returned straw and soil enzyme activity across different time periods.ResultsWhen earthworms were present in soil, the surface residues were completely consumed during the first four weeks, but when earthworms were absent, most of the residues remained on the soil surface after 18 weeks. On day 28, the SOC content was significantly higher in the treatment where both earthworms and residue had been added. The SOC content was lower in the treatment where earthworms but no residue had been added. The organic carbon content in water-stable macroaggregates showed the same trend. During the first 14 weeks, the soil basal respiration was highest in the treatments with both residues and earthworms. From weeks 14 to 18, basal respiration was highest in the treatments with residues but without earthworms. We found a significant positive correlation between soil basal respiration and soil dissolved organic carbon content. Earthworms increased the activity of protease, invertase, urease and alkaline phosphatase enzymes, but decreased β-cellobiohydrolase, β-glucosidase and xylosidase activity, as well as significantly reducing ergosterol content.ConclusionThe primary decomposition of exogenous rice residues was mainly performed by earthworms. Over a short period of time, they converted plant carbon into soil carbon and increased SOC. The earthworms played a key role in carbon conversion and stabilization. In the absence of exogenous residues, earthworm activity accelerated the decomposition of original organic carbon in the soil, reduced SOC, and promoted carbon mineralization.

Soil Organic Carbon Storage and Greenhouse Gas Emissions in a Grazed Perennial Forage–Crop Rotation System

Core Ideas Perennial forage–crop rotation did not increase soil greenhouse gases emissions compared to annual peanut‐cotton rotation. Carbon storage was greater for perennial forage–crop rotation compared to continuous peanut–cotton rotation. Grazing resulted in increased uptake of soil CH4 in some instances. Soils in southeastern United States have lost much of their original soil organic carbon (SOC) as a result of intensive row‐cropping systems. One example is an annual rotation of cotton (Gossypium hirsutum L.) and peanut (Arachis hypogaea L.) under conventional tillage (CT). Incorporation of perennial grasses such as bahiagrass (Paspalum notatum Flueggé) into the peanut–cotton crop rotation (also called a forage–crop rotation or FCR) can increase SOC storage. Cattle (Bos sp.) grazing on bahiagrass and winter cover crops can improve productivity of the FCR system, but may result in increased greenhouse gas (GHG) emissions. This study evaluates the impact of a grazed FCR on SOC storage and GHG emissions to assess its environmental impact of Coastal Plain soils. A closed chamber method was used to examine emissions of CO2, CH4, and N2O in the FCR. Results indicated that the FCR has potential to increase SOC storage when conservation tillage is used. Grazing of bahiagrass reduced SOC in the 5‐ to 10‐cm depth, but this effect was not observed in the subsequent peanut crop in the rotation following grazing. A moderate stocking rate of 2.5 cattle ha−1 resulted in fewer emissions of CO2 and N2O during seasonal measurements compared with ungrazed management, dependent on location, season, and crop. Flux of CH4 was often negligible; however, grazing increased soil uptake of CH4 in some instances. For the cattle stocking rates used in this study, grazing did not negatively affect SOC storage or soil GHG emissions in FCR systems.

Negative priming effect of three kinds of biochar on the mineralization of native soil organic carbon

AbstractThis study was conducted to improve our understanding of the effect of biochar on the degradation of original soil organic carbon (SOC) and the resulting net C sequestration. A 120‐day incubation experiment was conducted to detect the CO2 evolution from soil amended with three kinds of biochar, namely, rice husk biochar (RH), pecan shell biochar (PS), and bamboo biochar (BB), at biochar to soil ratios of 0% (as control), 1%, 2%, and 5%, as well as 100% pure biochar, and to evaluate their priming effect on SOC mineralization. Results showed that the cumulative mineralized amounts of SOC decreased by 7.95–10.7% with 5% RH, PS, and BB treatments, whereas there were no significant differences in 1% or 2% biochar treatments after 120 days of incubation compared with the control. Biochar had a suppressing influence on native SOC decomposition, and the effect increased with the amount of applied biochar increasing. The negative priming effect of biochar on the mineralization of SOC was mainly observed after 15 days of incubation and increased with incubation time. The negative effects of BB and RH were significantly stronger than that of PS at the 5% application ratio. This was mainly due to the less pores and smaller specific surface area of PS, which resulted in the weaker encapsulation and adsorption protection effect of PS than RH and BB, and inhibited the degradation of the adsorbed native SOC. Therefore, BB and RH have great potential for C sequestration and mitigation, especially in soils with low organic C.

Assessment of unconventional shale gas potential of organic-rich Mississippian and Lower Pennsylvanian sediments in western Germany

The assessment of unconventional shale gas potential for the Mississippian Alum shales, the Kulm-Plattenkalk and the Lower Pennsylvanian Ziegelschiefer Formation in western Germany provides insight on how fluctuation in depositional environments has a significant role on lithofacies and shale gas potential. This paper uses a standard evaluation workflow for unconventional shale gas potential taking into account thickness, TOC content, mineral composition and brittleness, porosity and permeability data as well as thermal maturity. The average organic carbon content of the Lower and Upper Alum Shales reaches 2.4 wt% and 2.6 wt%, respectively and deposition took place in an oxygen-depleted marine environment, where hydrogen-rich type II kerogen was preserved in the sediments. In this study, the Kulm-Plattenkalk is investigated for the first time with regard to unconventional shale gas potential. The TOC content ranges between 0.22% and 6.85% (average: 2.45%) and carbonate content is 21% on average. In contrast, the Lower Pennsylvanian Ziegelschiefer Fm was deposited in a shallow marine suboxic to oxic environment with stronger terrestrial influence. TOC is 1.2% on average and the kerogen rich in terrestrial material has only a moderate original hydrocarbon generation potential. It should be noted that all samples are in the gas generation window and may hence have already lost about half of their original organic carbon content. A simple control of mineralogy on porosity and permeability was not evident, but a weak correlation was found between permeability and the average effective pore radii or slit widths. The Mississippian black shales have great similarity in terms of organic richness, thickness and quartz content with known gas shales of similar stratigraphic age from the US. However, differences with respect to burial and uplift history might have important influence on gas in place.

Biochemical stabilization of soil organic matter in straw-amended, anaerobic and aerobic soils

Crop straw incorporation is a useful approach for increasing the quantity and changing the chemical composition of soil organic matter (SOM). This process is influenced by soil aeration. The present study investigated the stability of whole SOM, particulate organic matter (POM) and mineral-associated organic matter (MinOM) fractions with wheat straw amendment under aerobic and anaerobic conditions over a 12-month incubation period. Solid-state nuclear magnetic resonance and Fourier transform infrared spectroscopy were used to analyze the chemical composition of whole SOM, POM and MinOM fractions. The decomposition rate of wheat straw was lower under anaerobic than under aerobic conditions (0.014 vs. 0.020day−1). Wheat straw incorporation increased the original soil organic carbon content (7.4g kg−1) under both aerobic (up to 10.2g·kg−1) and anaerobic (up to 10.3g·kg−1) conditions, but the content of mineral-associated organic carbon (MinOC) under aerobic condition (7.0g·kg−1) was significantly larger than that under anaerobic condition (4.9g·kg−1). The proportion of alkyl carbon (C) in SOM, POM and MinOM fractions was greater under anaerobic than under aerobic conditions, while the opposite was true for the proportion of O-alkyl C of SOM and POM and MinOM fractions. A/O-A indices (i.e., the ratio of alkyl C to O-alkyl C) of whole SOM, POM and MinOM were higher under anaerobic than under aerobic conditions. We conclude that wheat straw incorporation resulted in the enrichment of alkyl C in the POM and MinOM fractions under anaerobic conditions, and thus improved the stability of SOM. In this way, the decomposition of crop residue influenced SOM structural chemistry at the molecular level.

A new method of reconstruction of original total organic carbon for sediments in salt water lakes-A case study on modern sediments in Buha River estuary, Lake Qinghai

烃源岩中原始有机碳（TOC）总量的恢复是烃源岩评价的重点和难点，以青海湖西北部的布哈河口区沉积物为研究对象，探讨一种全新的利用沉积物中硼元素含量对原始TOC含量进行恢复的方法.布哈河口区沉积物主要为泥、粉砂、细砂及其过渡类型，黏土矿物含量总体较低，沉积物中干酪根类型主要为Ⅱ₁和Ⅱ₂型，有机质大部分来自陆源生物，少量来自水生生物.布哈河口区沉积物中TOC含量介于0.02%~4.29%之间，其中半深湖及前三角洲环境TOC含量总体较高.有机质对部分微量元素有明显的富集作用，沉积物中TOC含量与硼、钪、钴、镍、锌、镓、铷、铯、铅及铀等微量元素存在明显相关性.有机质对微量元素的富集能力和强度受沉积物和水体接触时间控制，因此微量元素与TOC含量的相关性在不同沉积环境存在明显差异：在河流、三角洲平原、前三角洲、浅湖及半深湖沉积区较高，而在滨湖区较低.硼元素对TOC含量变化的反映最灵敏，即便是在间歇暴露的滨湖沉积中硼含量与TOC含量呈明显的正相关性，因此硼可以作为反映烃源岩原始TOC含量的有效指标.根据布哈河口区沉积物中硼含量与TOC含量之间极好的线性相关性，建立了利用烃源岩中的硼含量对原始TOC含量进行定量计算的公式，该公式主要适用于陆相微咸水、半咸水及咸水环境泥质岩类原始TOC总量的恢复.;Reconstruction of original total organic carbon (TOC) in source rocks is the key and difficult point of hydrocarbon source rock evaluation. The paper focuses on the sediments of Buha River estuary in the northwest of Lake Qinghai, and a new method of original TOC reconstruction via born element in sediments was discussed. The sediments of Buha River estuary sediments are mainly made of mud, silt, fine sand and transitional type composition. The sediments are generally have low clay mineral content. The main types of kerogen in the sediments were Ⅱ₁ and Ⅱ₂, and most of organic matter come from terrigenous organisms while a small quantity of organic matter come from aquatic organisms. TOC in Buha River estuary sediments is in the range of 0.02% to 4.29%. TOC in the sediments of semi-deep lake and prodelta is usually higher than that in other environmental sediments. Organic matter has a significant effect on the enrichment of some trace elements. There is a significant positive correlation between the trace element concentration and TOC content in the sediments, the trace elements include boron, cobalt, nickel, zinc, gallium, rubidium, cesium, lead and uranium. The enrichment ability and intensity of organic matter to trace elements are controlled by the contact time of sediment and water, and so the correlation between trace element and TOC has obvious difference in different sedimentary environment. TOC is higher in sediments of fluvial, delta plain, prodelta, shallow lake and semi-deep lake environment, while it is lower in sediments of lakeshore environment. Boron was the most sensitive to the variation of organic carbon content, and the content of boron in the sediments of intermittent exposure environment like lakeshore is also showed a significant positive correlation with TOC. Boron is an effective index that can reflect original organic carbon content of the hydrocarbon source rocks. According to the excellent linear relationship between the boron concentration and TOC in the sediments of Buha River estuary, a formula for the quantitative calculation of the original organic carbon content via the content of boron in the source rock was established. The formula is suitable for the reconstruction of the original total organic carbon in the terrestrial brackish water and salt water of environment.

Organic petrology and micro-spectroscopy of Tasmanites microfossils: Applications to kerogen transformations in the early oil window

The transformation of kerogen to hydrocarbons in the early stages of oil generation is critical for understanding the resource potential of liquid-rich shale plays. Organic petrology commonly is used for visual evaluation of type, quality, and thermal maturity of organic matter, but the relationship of visual petrographic changes to chemical transformations is not well characterized. To improve understanding of these processes, organic-walled microfossils of the unicellular green alga Tasmanites (composed of algaenan) in Upper Devonian Ohio Shale (Huron Member, Appalachian Basin) were analyzed by micro-spectroscopy techniques including micro-Fourier transform infrared (micro-FTIR), X-ray photoelectron (XPS), electron probe microanalysis (EPMA), and fluorescence. Immature to mid-oil window maturation sequences of core and outcrop samples with solid bitumen reflectance (BR) and vitrinite reflectance (VR) values ranging from 0.45 to 0.80%Ro were used. Hydrous pyrolysis was applied to low-maturity (BR: 0.25–0.39%Ro) Huron and time-correlative New Albany shale samples to create similar artificial maturation sequences for comparison. Micro-FTIR spectroscopy revealed a decrease in the CH2/CH3 ratio with increasing maturity, indicating Tasmanites aliphatic chains become shorter and more branched. Oxygenated functional groups decreased relative to aliphatic stretching bands and increased aromaticity was noted at the highest maturities. In samples that were pyrolyzed for 72h at temperatures of 300–320°C (BR: 0.56–0.68%Ro), Tasmanites showed similar trends, whereas at pyrolysis temperatures of 340°C and higher (BR>1.0%Ro), Tasmanites was pseudomorphed by accumulations of solid bitumen, carbonate and sulfide. Replacement of Tasmanites by these phases in hydrous pyrolysis experiments ≥340°C and its absence at higher maturities (peak oil, VR and BR≥0.9%Ro) in naturally matured samples, as documented in a previous study, implies that a large fraction of the algaenan component of original organic carbon is converted to petroleum during thermal maturation. XPS analysis indicated the molar proportion of aliphatic carbon increases with increasing thermal maturity, accompanied by decreases in oxygenated functional groups and olefinic carbon. EPMA of Tasmanites showed highest concentrations of S, with concentrations of redox-sensitive trace elements U, Mo, Ni and V generally at or below detection limits. Decrease in organic S with increasing thermal maturity may be related to cleavage of Tasmanites at CS linkages; however, this relationship was inconsistent and presence of adjacent or entrained nanoscale silicate or sulfide phases may impact measured trace element concentrations. Fluorescence microscopy and spectroscopy showed a red shift in spectral maxima and decreased emission intensities with increasing maturity, interpreted as due to non-radiative energy loss possibly because of increased aromaticity. Collectively, these results provide new insights into the in situ chemical transformations that accompany petrographic changes as oil-prone kerogen converts to petroleum with thermal advance from immature conditions into the mid-oil window.

Investigating the relative contribution of colloidal and soluble fractions of secondary effluent organic matter to the irreversible fouling of MF and UF hollow fibre membranes

Abstract Effluent organic matter (EfOM) matrices were modified by applying physical chemical treatments on biologically treated wastewater effluents in order to identify the EfOM fraction(s) responsible for irreversible fouling of low-pressure membranes. Anion exchange resin (AER) adsorption preferentially removed humic-like structures, while oxidation processes, such as ozonation and H2O2/UV resulted in the breakdown of high molecular weight (MW) structures into lower MW compounds. After re-concentration to the original organic carbon content, the fouling potential of the modified EfOM matrix was investigated using multi-cycle filtration tests performed with commercially available microfiltration (MF) and ultrafiltration (UF) membranes. The pre-oxidized effluents showed low fouling potential regardless of the membrane used. The results confirmed the major role of high MW biopolymers on MF and UF total fouling. Results from MF experiments highlighted that AER treated effluents exhibited similar fouling properties as the untreated effluent indicating that humic-like substances do not significantly affect MF fouling and confirm again that biopolymers is the fraction responsible for fouling. The same tests performed with UF membrane showed a lower irreversible fouling with AER treated effluent suggesting the strong contribution of humic fractions to irreversible fouling. These findings were supported by the results obtained with two different secondary effluent matrices, a conventional activated sludge treated effluent and a membrane bioreactor supernatant.

Organic porosity evaluation of Lower Cambrian Niutitang Shale in Qiannan Depression, China

ABSTRACTQiannan Depression was selected as a study case to confirm the contribution of organic pores (microscale and nanoscale pores within organic grains in shale) formed by hydrocarbon generation to shale gas reservoir space. Using the material balance principle combined with chemical kinetics methods, an evaluation model of organic porosity for shale gas reservoirs was established. The results indicate that there are four important model parameters to consider when evaluating organic porosity in shale: the original organic carbon (w(TOC0)), the original hydrogen index (IH0), the transformation ratio of generated hydrocarbon (F(Ro)) and the organic pore compression coefficient (C). The organic porosity of carbonaceous shale in the middle and lower part of the Niutitang Formation in the Cy1 well is from 0.68 to 5.24%, and the average value is 3.01%.

Impacts of Biochar and Straw Application on Soil Organic Carbon Transformation

To explore the effects of biochar and straw application on soil carbon constitution and transformation, an incubation experiment was conducted to study the characteristics of the release of carbon dioxide,as well as the changes in microbial biomass carbon and organic carbon in soil after applying biochar or straw only, or biochar plus straw. The results showed that the straw mineralization rate of organic carbon in soil was 21.50% at 2% application level, which was much higher than that of biochar (8.09%). With the same addition amount of biochar and straw at 4% level for 200 days incubation, the soil organic carbon content was 24.40 and 17.40 g·kg^-1,respectively. It suggested that the positive impact of biochar application on improving soil organic carbon was greater than that of straw. The application of biochar had protective function on soil original organic carbon. Biochar promoted the straw mineralization and resulted in positive interaction effect between biochar and straw on mineralization of soil organic carbon. The application of straw increased soil microbial biomass carbon (MBC) greatly, while biochar had less impact on MBC. The application of straw and biochar also increased soil microbial biomass carbon, but the interaction effect could be positive or negative, which was dependent on the incubation time or application rate.

Effect of the Soil Organic Content on Slurries Involved in Mudflows

The effect of the soil organic content on the stability of a soil involved in a rapid mud flow is here experimentally investigated. The soil is collected form a site where a catastrophic landslide took place (Cervinara – AV) and it is chemically treated to selectively remove different aliquots of its original organic carbon. In particular, The Dissolved Organic Carbon (i.e. the carbon soluble in water)results the 6% of the soil organic carbon and it is removed with a mild chemical treatment to obtain the DOC 6 sample, the 77% and 89% of the Total Organic Carbon (i.e.the pool of oxidizable soil organic carbon)is removed with a strong chemical treatment to obtain the TOC 77 and TOC 89 sample, respectively. The stabilizing effect of the organic carbon is investigated by following the evolution of the particle size distribution of soils induced by a mild mixing of diluted slurries and we showed that the particle size distribution of the original soil sample is unaffected by the slurry mixing, while those of DOC 6,TOC 77 and TOC 89 evolve during time, revealing the breakup of soil aggregates. Our findings highlight the stabilizing effect of SOC in the investigated liquid slurries and, furthermore, they suggest that the organic carbon quality, more than its quantity, plays a crucial role in the soil stability. Indeed, it is enough to remove the Dissolved Organic Carbon to register a soil disaggregation process comparable to that observed for TOC 77 and TOC 89 samples. This suggests that Dissolved Organic Carbon is the fundamental organic fraction stabilizing the slurry microstructure.

Organoporosity evaluation of shale: a case study of the Lower Silurian Longmaxi Shale in southeast Chongqing, China.

The organopores play an important role in determining total volume of hydrocarbons in shale gas reservoir. The Lower Silurian Longmaxi Shale in southeast Chongqing was selected as a case to confirm the contribution of organopores (microscale and nanoscale pores within organic matters in shale) formed by hydrocarbon generation to total volume of hydrocarbons in shale gas reservoir. Using the material balance principle combined with chemical kinetics methods, an evaluation model of organoporosity for shale gas reservoirs was established. The results indicate that there are four important model parameters to consider when evaluating organoporosity in shale: the original organic carbon (w(TOC0)), the original hydrogen index (I H0), the transformation ratio of generated hydrocarbon (F(R o)), and the organopore correction coefficient (C). The organoporosity of the Lower Silurian Longmaxi Shale in the Py1 well is from 0.20 to 2.76%, and the average value is 1.25%. The organoporosity variation trends and the residual organic carbon of Longmaxi Shale are consistent in section. The residual organic carbon is indicative of the relative levels of organoporosity, while the samples are in the same shale reservoirs with similar buried depths.

Identification of effluent organic matter fractions responsible for low-pressure membrane fouling

Anion exchange resin (AER), powder activated carbon (PAC) adsorption and ozonation treatments were applied on biologically treated wastewater effluent with the objective to modify the effluent organic matter (EfOM) matrix. Both AER and PAC led to significant total organic carbon (TOC) removal, while the TOC remained nearly constant after ozonation. Liquid Chromatography–Organic Carbon Detection (LC-OCD) analysis showed that the AER treatment preferentially removed high and intermediate molecular weight (MW) humic-like structures while PAC removed low MW compounds. Only a small reduction of the high MW colloids (i.e. biopolymers) was observed for AER and PAC treatments. Ozonation induced a large reduction of the biopolymers and an important increase of the low MW humic substances (i.e. building blocks).Single-cycle microfiltration (MF) and ultrafiltration (UF) tests were conducted using commercially available hollow fibres at a constant flux. After reconcentration to their original organic carbon content, the EfOM matrix modified by AER and PAC treatments exhibited higher UF membrane fouling compared to untreated effluent; result that correlated with the higher concentration of biopolymers. On the contrary, ozonation which induced a significant degradation of the biopolymers led to a minor flux reduction for both UF and MF filtration tests. Based on a single filtration, results indicate that biopolymers play a major role in low pressure membrane fouling and that intermediate and low MW compounds have minor impact. Thus, this approach has shown to be a valid methodology to identify the foulant fractions of EfOM.