Use of 13C and 15N Mass Spectrometry to Study the Decomposition of Calamagrostis epigeios in Soil Column Experiments with and Without Ash Additions

Abstract

The dynamics of C and N in terrestrial ecosystems are not completely understood and the use of stable isotopes may be useful to gain further insight in the pathways of CO₂ emissions and leaching of dissolved organic carbon (DOC) and nitrogen (DON) during decomposition of litter. Objectives were (i) to study the decomposition dynamics of Calamagrostis epigeios, a common grass species in forests, using ¹³C-depleted and ¹⁵N-enriched plants and (ii) to quantify the effect wood ash addition on the decomposition and leaching of DOC and DON. Decomposition was studied for 128 days under aerobic conditions at 8°C and moisture close to field capacity in a spodic dystric Cambisol with mor-moder layer. Variants included control plots and additions of (i) Calamagrostis litter and (ii) Calamagrostis litter plus 4 kg ash m^?2.

• Decomposition of Calamagrostis resulted in a CO₂ production of 76.2 g CO₂–C m^?2 (10% of added C) after 128 days and cumulative DOC production was 14.0 g C m^?2 out of which 0.9g C m^?2 was Calamagrostis-derived (0.1% of added C). The specific CO₂ formation and specific DOC production from Calamagrostis were 6 times higher (CO₂) and 4 times smaller (DOC) than those from the organic layer. The amount of Calamagrostis-derived total N (NH₄ ⁺, NO₃ ^?, DON) leached was 0.7g N m^?2 (4.8% of added N). Cumulative DON production was 0.8g N m^?2 which was slightly higher than for the control. During soil passage, much of the DOC and DON was removed due to sorption or decomposition. DOC and DON releases from the mineral soil (17cm depth) were 6.3g C m^?2 and 0.5g N m^?2.

  Addition of ash resulted in a complete fixing of CO₂ for 40 days due to carbonatisation. Afterwards, the CO₂ production rates were similar to the variant without ash addition. Production of DOC (98.6g C m^?2) and DON (2.5g N m^?2) was marked, mainly owing to humus decay. However, Calamagrostis-derived DOC and Culamagrostis-derived total N were only 3.9g C m^?2 (0.5 YO of added C) and 0.5g N m^?2 (3.4% of added N). The specific DOC production rate from the organic layer was 6 times higher than that from Cularnagrostis. The results suggest that with increasing humification from fresh plant residues to more decomposed material (O_F and O_H layers) the production ratio of DOC/CO₂-C increases. Addition of alkaline substances to the forest floor can lead to a manifold increase in DOC production.

     

Degradation pathways of dissolved carbon in landfill leachate traced with compound-specific (13)C analysis of DOC

The isotopic compositions of carbon compounds in landfill leachate provide insights into the biodegradation pathways that dominate the different stages of waste decomposition. In this study, the carbon geochemistry of different carbon pools, environmental stable isotopes and compound-specific isotope analysis (CSIA) of leachate dissolved organic carbon (DOC) fractions and gases show distinctions in leachate biogeochemistry and methane production between the young area of active waste emplacement and the old area of historical emplacement at the Trail Road Landfill (TRL). The active area leachate has low DOC concentrations (<200 mg l(-1)) dominated by fulvic acid (FA=160 mg l(-1)), and produces CH(4) dominantly by CO(2) reduction (D- excess=20.6 per thousand). Leachate generated in the area of older waste has high DOC (>4770 mg l(-1)) dominated by FA (4482 mg l(-1)) and simple fatty acids (acetic=1008 mg l(-1) and propionic=608 mg l(-1)), and produces CH(4) by the acetate fermentation pathway (D- excess=9.8 per thousand). CSIA shows an advanced degradation and a progressive accumulation of (13)C of fatty acids in leachate from the older area. The enriched (13)C value of FA (-20 and-26 per thousand for the older and active parts, respectively,) and of low molecular weight DOC (-8 and-27 per thousand) as well as of the bulk DOC (-21 and-25 per thousand) shows more advanced degradation in the older part of the landfill, which is consistent with the shift in the humic/FA ratios (0.05 and 0.18). The (13)C enrichment of acetate (-12 per thousand) above the (13)C of DOC (-21 per thousand) and of propionic acid (-19 per thousand), in older leachate, suggests that this acetate has not evolved from the simple degradation of larger organic molecules, but by homoacetogenesis from the enriched dissolved inorganic carbon (DIC) pool (8 per thousand) and H(2,) which produce a more enriched (13)C of acetate. In contrast, the (13)C of the minor acetate in the active area (-17 per thousand) indicates that CO(2)-reducing bacteria must be the primary consumers of H(2), which has resulted in enriched (13)C(DIC) (10 per thousand) and depleted (13)C(CH4) (-58 per thousand).     

Isotopic ((13)C) fractionation during plant residue decomposition and its implications for soil organic matter studies

Carbon isotopic fractionations in plant materials and those occurring during decomposition have direct implications in studies of short-and longer-term soil organic matter dynamics. Thus the products of decomposition, the evolved CO(2) and the newly formed soil organic matter, may vary in their (13)C signature from that of the original plant material. To evaluate the importance of such fractionation processes, the variations in (13)C signatures between and within plant parts of a tropical grass (Brachiaria humidicola) and tropical legume (Desmodium ovalifolium) were measured and the changes in (13)C content (signatures) during decomposition were monitored over a period of four months. As expected the grass materials were less depleted in (13)C (-11.4 to -11.9 per thousand) than those of the legume (-27.3 to -25.8 per thousand). Root materials of the legume were less (1.5 per thousand) depleted in (13)C compared with the leaves. Plant lignin-C was strongly depleted in (13)C compared with the bulk material by up to 2.5 per thousand in the legume and up to 4.7 per thousand in the grass. Plant materials were subsequently incubated in a sand/nutrient-solution/microbial inoculum mixture. The respiration product CO(2) was trapped in NaOH and precipitated as CaCO(3), suitable for analysis using an automated C/N analyser coupled to an isotope ratio mass spectrometer. Significant depletion in (13)C of the evolved CO(2) was observed during the initial stages of decomposition probably as a result of microbial fractionation as it was not associated with the (13)C signatures of the measured more decomposable fractions (non-acid detergent fibre and cellulose). While the cumulative CO(2)-(13)C signatures of legume materials became slightly enriched with ongoing decomposition, the CO(2)-C of the grass materials remained depleted in (13)C. Associated isotopic fractionation correction factors for source identification of CO(2-)C varied with time and suggested errors of 2-19% in the estimation of the plant-derived C at 119 days of incubation in a soil of an intermediate (-20.0 per thousand) (13)C signature. Analysis of the residual material after 119 days of incubation showed little or no change in the (13)C signature partly due to the incomplete decomposition at the time of harvesting. Copyright 1999 John Wiley & Sons, Ltd.     

Isotopic discrimination during litter decomposition and delta13C and delta15N soil profiles in a young artificial stand and in an old floodplain forest

In the present study, rates of litter decomposition and microbial biomass nitrogen were monitored over an 8-month period in a young broadleaf plantation (18 y) and in an old floodplain forest. Moreover, delta13C and delta15N temporal variations within soil profiles were evaluated at both sites. Rates of litter decomposition were higher in spring and autumn than in summer, in both forests. At the end of the observation period the percentage of original litter remaining was not statistically different between the young and the old forest and accounted for 60-70% of the original amount. Microbial biomass nitrogen in the remaining litter and the percentage of litter mass lost during decomposition were positively correlated. The difference in litter quality affected the decomposition rate and also the changes in carbon isotopic composition during the decomposition process. In contrast, 15N isotopic signatures showed a similar trend in the litter of the two forests irrespective of the litter quality. Although delta13Csoil and delta15Nsoil showed considerable temporal variation they increased with depth in the soils of both sites but their seasonal changes did not reflect those of the decomposing litter. Within the same soil horizon, both delta13C and delta15N showed similar seasonal trends in the soils of the two forests, suggesting the involvement of environmental factors acting at regional level, such as soil temperature and rainfall variations, in regulating seasonal delta13C and delta15N soil variations.     

Decomposition of benzene using wire-tube AC/DC discharge reactors

Decomposition of benzene was investigated using single and two-stage stainless steel reactors with application of high-voltage AC and DC currents. Benzene removal, CO, and CO₂ were measured as a function of reactor diameter, applied voltage, and stage of reactor configuration. The results showed that, benzene removal and CO₂ selectivity improved in two-stage configuration and reached up to 59% and 97.8% respectively, where the gap size was 8.5 mm. Formation of OH, N-H and N=O function groups were seen in the exhaust gas. Subsequently, organic acids, phenols, and alcohols were identified as the main byproduct of benzene decomposition considering GC-MS analysis.     

含灰湿空气外掠翅片管束积灰和阻力特性实验研究

本文针对以褐煤预干燥乏气为代表的含灰含湿气体余热回收问题,采用含灰湿空气模拟真实干燥乏气/烟气,搭建了混合气体外掠圆形翅片管束对流冷凝实验系统,获得了灰分浓度、水蒸气质量分数、主流气体入口温度等因素对其积灰和阻力特性的影响规律。实验结果表明,阻力系数随着灰分浓度和气体入口温度的增加而增加,随水蒸气质量分数的增加而减小,其中灰分浓度影响重大,当其从1.5g·m3增加到12.8g·m-3时,平均阻力系数从0.07增长到0.46,增长幅度约为536%.积灰程度表现出与阻力系数相同的趋势,当灰分浓度大于7.7g·m3时即积灰严重,甚至会产生堵塞流道的现象,需要及时清理。     

Mössbauer and EXAFS studies of amorphous iron produced by thermal decomposition of carbonyl iron in liquid phase

Decomposition of iron carbonyl Fe(CO)₅ and Fe₂(CO)₉ in liquid phase gave amorphous and crystalline iron powders in the absence and presence of catalyst, respectively. The hyperfine fields were large in amorphous phases prepared from Fe(CO)₅ than from Fe₂(CO)₉. Crystalline iron, iron carbide and a trace amount of Fe₃O₄ were detected in the decomposition products of the amorphous phase prepared from Fe(CO)₅, and iron carbide was mainly included in the decomposition products of the amorphous phase prepared from Fe₂(CO)₉.     

Millipedes and earthworms increase the decomposition rate of 15N-labelled winter rape litter in an arable field

Effects of millipedes and earthworms on the decomposition of 15N-labelled litter of winter oilseed rape were investigated in a microcosm field experiment over a period of 264 days on an oat field near G?ttingen managed by integrated farming. A total of 32 microcosms were filled with defaunated soil. 15N-labelled rape litter was placed either on top of the soil or buried into the soil simulating mulching and ploughing, respectively. To the microcosms nine adult individuals of Blaniulus guttulatus (Diplopoda) and two of Aporrectodea caliginosa (Lumbricidae) were added separately or in combination. In general, the presence of the animals accelerated the decomposition rate of the litter material. The effects were most pronounced in the presence of Aporrectodea caliginosa. The total amount of nitrate, ammonium and the amount of 35N leached from the microcosms was increased in the presence of earthworms or of both earthworms and millipedes. Both species proved to be important members of the detritus food web of the agricultural system studied.     

化学氮肥有机替代条件下黑土DOC荧光光谱特征

有机无机肥配施是实现土壤培肥、减少无机肥施用的有效措施。为探讨黑土区有机肥替代无机肥(氮肥)对土壤溶解性有机碳（DOC）含量及结构的影响,本研究采用有机肥不同比例替代化学氮肥,分析土壤DOC的含量及荧光光谱特征。结果表明,M(100%有机替代化学氮肥)处理土壤DOC显著高于其他处理,其含量为325.97 mg·kg-1。与CK(不施肥)处理相比,各施肥处理荧光峰各波长均有不同程度蓝移,各处理土壤DOC的荧光指数(FI)分布在1.54~1.59范围内,腐殖化指数(HIX)均小于0.85,表明DOC来源受自生源和陆生源共同作用的影响,土壤腐质化程度均较低。平行因子分析法分析识别出3个荧光组分,分别为2个腐殖质类组分（富里酸类物质和腐殖酸类物质) 及1个类蛋白组分(类酪氨酸蛋白质物质)。各施肥处理3个组分荧光强度均高于CK处理,其中M和M₂N₂(25%有机替代化学氮肥)处理下土壤DOC总荧光强度较高,C3组分荧光强度以M₂N₂处理最高,土壤DOC中3个有机组分的相对比重以荧光组分C1最高,接近50%,表明该地区土壤中小分子物质占有较大比例,施肥能够提高土壤腐质化程度,有利于土壤DOC固定,合理的有机肥配施化学氮肥能增加DOC的有效性,提升土壤供肥能力。     

不同水文情形下巢湖有色可溶性有机物来源及分布特征

于2018年1月(枯水)、4月(平水)、7月(丰水)对巢湖开展野外观测,探讨不同水文条件下有色可溶性有机物(CDOM)的光谱组成结构及分布特征。结果表明丰水期巢湖溶解性有机碳(DOC)均值(3.90±0.40) mg·L-1与枯水期均值(3.89±0.19) mg·L-1无显著差异(t-test, p>0.05),丰水期S_275～295均值(21.48±1.56) μm-1显著大于枯水期均值(19.24±0.98) μm-1(t-test, p<0.001)。平行因子分析得到了4个荧光组分,分别为短波类腐殖质组分C1、类色氨酸组分C2、类酪氨酸组分C3和长波类腐殖质组分C4。TP,TN,Chl-a和DOC浓度与短波类腐殖质组分C1、长波类腐殖质组分C4都呈显著正相关(p<0.01);DOC与类色氨酸组分C2也存在一定正相关(p<0.05)。此外巢湖CDOM的组成与来源有明显的季节差异性,丰水期陆源类腐殖酸输入是巢湖西部湖区CDOM库主要贡献源;平水期湖泊藻类生物降解为重要贡献源。为有效保护巢湖水质,应对十五里河及南淝河流域实施一定的管控措施。     

Characteristics of suspended matter in the River Sava watershed,Slovenia

A combination of C/N ratios, δ¹³C and δ¹⁵N values in suspended matter was used to examine the seasonal (late summer 2004 and spring 2005) relationship with hydrological characteristics of the River Sava watershed in Slovenia. The values of C/N ratios range from 1.2 to 19.1, δ¹³C values range from?29.2 to?23.0 ‰ and δ¹⁵N values from 0.5 to 16.7 ‰ and indicate that the samples are a mixture of two end members: modern soils and plant litter. A simple mixing model was used to indicate that soil organic carbon prevails over plant litter and contributes more than 50% of suspended material. The calculated annual particulate organic carbon flux is estimated as 5.2×10¹⁰ g C/year, the annual particulate nitrogen flux 8.5×10⁹ g N/year and the total suspended solid flux is estimated to be 1.3×10¹² g/year. Anthropogenic impact was detected only in a tributary stream of the River Sava, which is located in an agriculture–industrial area and is reflected in higher δ¹⁵N values in suspended matter and high nitrate concentrations in the late summer season.     

Carbon isotope analysis of dissolved organic carbon in fresh and saline (NaCl) water via continuous flow cavity ring-down spectroscopy following wet chemical oxidation

This work examines the performance and limitations of a wet chemical oxidation carbon analyser interfaced with a cavity ring-down spectrometer (WCO-CRDS) in a continuous flow (CF) configuration for measuring δ¹³C of dissolved organic carbon (δ¹³C-DOC) in natural water samples. Low-chloride matrix (<5?g Cl/L) DOC solutions were analysed with as little as 2.5?mg C/L in a 9?mL aliquot with a precision of 0.5?‰. In high-chloride matrix (10–100?g Cl/L) DOC solutions, bias towards lighter δ¹³C-DOC was observed because of incomplete oxidation despite using high-concentration oxidant, extended reaction time, or post-wet chemical oxidation gas-phase combustion. However, through a combination of dilution, chloride removal, and increasing the oxidant:sample ratio, high-salinity samples with sufficient DOC (>22.5?µg C/aliquot) may be analysed. The WCO-CRDS approach requires more total carbon (µg C/aliquot) than conventional CF-isotope ratio mass spectrometer, but is nonetheless applicable to a wide range of DOC concentration and water types, including brackish water, produced water, and basinal brines.     

Microscopic investigation of soot and ash particulate matter derived from biofuel and diesel: implications for the reactivity of soot

Investigation of soot and ash particulate matter deposited in diesel particulate filters (DPFs) operating with biofuel (B100) and diesel (pure diesel: B0 and diesel₈₀/biofuel₂₀ blend: B20) by means of optical microscopy, scanning electron microscopy, and high resolution transmission electron microscopy (HRTEM) reveals the following: the rapeseed methyl ester biofuel used for this study contributes to ash production, mainly of Ca?CS?C and P-bearing compounds ranging in size between 50 and 300?nm. Smaller ash particles are less common and build aggregates. Ash is deposited on the inlet DPF surface, the inlet channel walls, and in B100-DPF at the plugged ends of inlet channels. The presence of Fe?CCr?CNi fragments, down to tens of nanometers in size within the ash is attributed to engine wear. Pt particles (50?C400?nm large) within the ash indicate that the diesel oxidation catalyst (DOC) upstream of the DPF shows aging effects. Radial cracks on the coating layer of the DOC confirm this assumption. The B100-DPF contains significantly less soot than B20 and B0. Based on the generally accepted view that soot reactivity correlates with the nanostructure of its primary particles, the length and curvature of graphene sheets from biofuel- and diesel-derived soot were measured and computed on the basis of HRTEM images. The results show that biofuel-derived soot can be more easily oxidized than diesel soot, not only during early formation but also during and after considerable particle growth. Differences in the graphene sheet separation distance, degree of crystalline order and size of primary soot particles between the two fuel types are in line with this inference.     

缺氧及富氧条件下CuFe2O4催化热解酸性红B的原位FTIR反射光谱研究

用原位红外漫反射光谱法研究了在缺氧及富氧条件下CuFe2O4催化热解酸性红B(ARB)的反应过程。结果表明，两种反应气氛对染料分子中磺酸基团的热分解没有影响，但对偶氮基团及芳环的氧化分解影响显。在空气中，ARB的热解更迅速，300℃时可完全氧化为CO2及硝酸盐。而在N2气氛中，加热至300℃时ARB难以完全氧化热解，此时即使再通空气也不易将其完全氧化，而要在更高温度下(500℃)才能快速、彻底氧化成CO2及硝酸盐。     

Crude glycerol combustion: Particulate,acrolein, and other volatile organic emissions

Crude glycerol is an abundant by-product of biodiesel production. As volumes of this potential waste grow, there is increasing interest in developing new value added uses. One possible use, as a boiler fuel for process heating, offers added advantages of energy integration and fossil fuel substitution. However, challenges to the use of crude glycerol as a boiler fuel include its low energy density, high viscosity, and high autoignition temperature. We have previously shown that a refractory-lined, high swirl burner can overcome challenges related to flame ignition and stability. However, critical issues related to ash behavior and the possible formation of acrolein remained. The work presented here indicates that the presence of dissolved catalysts used during the esterification and transesterification processes results in extremely large amounts of inorganic species in the crude glycerol. For the fuels examined here, the result is a submicron fly ash comprised primarily of sodium carbonates, phosphates, and sulfates. These particles report to a well-developed accumulation mode (0.3–0.7 μm diameter), indicating extensive ash vaporization and particle formation via nucleation, condensation, and coagulation. Particle mass emissions were between 2 and 4 g/m³. These results indicate that glycerol containing soluble catalyst is not suitable as a boiler fuel. Fortunately, process improvements are currently addressing this issue. Additionally, acrolein is of concern due to its toxicity, and is known to be formed from the low temperature thermal decomposition of glycerol. Currently, there is no known reliable method for measuring acrolein in sources. Acrolein and emissions of other volatile organic compounds were characterized through the use of a SUMMA canister-based sampling method followed by GC–MS analysis designed for ambient measurements. Results indicate crude glycerol combustion produces relatively small amounts of acrolein (～15 ppbv) and other volatile organic compounds, with emissions comparable to those from natural gas combustion.     

Surface Acidity of H-Birnessite: Infrared Spectroscopic Study of Formic Acid Decomposition

This paper presents the adsorption and thermal decomposition mechanism of formic acid on an H-birnessite sample. Changes in the surface and structure were characterized using infrared spectroscopy, N₂ gas adsorption–desorption, and thermal analysis techniques. The acid sites of H-birnessite were investigated by infrared and thermal analysis using pyridine as a molecular probe. Decomposition of formic acid started on H-birnessite at 120°C and was complete at 400°C. Infrared spectra revealed that the molecularly adsorbed formic acid species were transformed to a formate species, and the formate species were transformed to CO. The most stable adsorption structure for formic acid was found as a molecular monodentate configuration.     

Chemical and carbon isotopic composition of dissolved organic carbon in a regional confined methanogenic aquifer

This study demonstrates the advantage of a combined use of chemical and isotopic tools to understand the dissolved organic carbon (DOC) cycle in a regional confined methanogenic aquifer. DOC concentration and carbon isotopic data demonstrate that the soil zone is a primary carbon source of groundwater DOC in areas close to recharge zones. An in-situ DOC source linked to organic rich sediments present in the aquifer matrix is controlling the DOC pool in the central part of the groundwater flow system. DOC fractions, 13C-NMR on fulvic acids and 14C data on DOC and CH4 support the hypothesis that the in-situ DOC source is a terrestrial organic matter and discard the Ordovician bedrock as a source of DOC.     

Characteristics of suspended matter in the River Sava watershed, Slovenia

A combination of C/N ratios, delta(13)C and delta(15)N values in suspended matter was used to examine the seasonal (late summer 2004 and spring 2005) relationship with hydrological characteristics of the River Sava watershed in Slovenia. The values of C/N ratios range from 1.2 to 19.1, delta(13)C values range from-29.2 to-23.0 per thousand and delta(15)N values from 0.5 to 16.7 per thousand and indicate that the samples are a mixture of two end members: modern soils and plant litter. A simple mixing model was used to indicate that soil organic carbon prevails over plant litter and contributes more than 50% of suspended material. The calculated annual particulate organic carbon flux is estimated as 5.2x10(10) g C/year, the annual particulate nitrogen flux 8.5x10(9) g N/year and the total suspended solid flux is estimated to be 1.3x10(12) g/year. Anthropogenic impact was detected only in a tributary stream of the River Sava, which is located in an agriculture-industrial area and is reflected in higher delta(15)N values in suspended matter and high nitrate concentrations in the late summer season.     

13C and 15N distributions in three spodic dystric cambisols under beech and spruce

The study of natural isotopic abundance signatures is useful to gain further insights in the processes resulting in depthwise changes in the composition of soil organic matter (SOM). Objectives were to describe the delta 13C and delta 15N abundances of SOM with depth in soils from a 153-year old beech (B1), a 119-year old spruce (F1) and a 61-year old spruce (F2) stand at Solling, north-west Germany, and to study, how podzolisation affects the isotopic abundances of 13C and 15N in the SOM. The degree of podzolisation decreased in the order F1 > B1 > F2. At the surface of the humus layer of all three sites, delta 13C values are approximately 1 to 4/1000 higher than in the leaves and needles, probably mainly due to the discrimination of 13C by microbial decomposition. 13C abundances in the organic layers of B1 and F2 increased only slightly from -27.6/1000 PDB (B1, L) to -27.2/1000 PDB (B1, Oh) and from -26.3/1000 PDB (F2, L) to -25.9/1000 PDB (F2, Oh), suggesting that biotic activity resulted in mixing of organic matter. At F1, however, 13C abundance increased from -27.5/1000 PDB (L) to -26.0/1000 PDB (Oh) which reflects the lack of mixing by animals. In the upper 2-4 cm of the mineral soil, i.e., in the eluvial horizons Aeh, 13C values showed a minimum at the spruce sites which was presumably related to a translocation of 13C enriched fulvic acids. Depthwise changes in delta 15N values were not related to podzolisation processes. At all three sites, a 13N enrichment with depth occurred in the mineral soil which is the result of the discrimination of 15N by microbial decomposition.     

Elasticity and active force generation of cochlear outer hair cells.

The cochlear outer hair cell is described by a cylindrical membrane model, characterized by area and shear moduli for a passive elastic element and an active tension element dependent on the membrane potential. In passive experiments, these moduli are determined from the pressure-strain relations. The area modulus obtained is 0.07 N m-1, similar to a lipid bilayer and the shear modulus is 0.007 N m-1. These moduli combined with previous active experiments show that the active tension is nearly isotropic and is about 1.6 x 10(-2) N m-1 V-1, resulting in a 0.5 nN/mV force per cell. This implies that the receptor potential for acoustical stimulation produces an active force comparable to the acoustic force applied to the basilar membrane per outer hair cell. This finding supports the hypothesis that the outer hair cell acts as feedback motor in the fine tuning mechanism of the mammalian ear.