Study of the Water Solubility and Sorption on Particulate Matters of Phthalate in the Presence of Humic Acid Using 14C Labelled Di-(2-Ethylhexyl)Phthalate

Phthalate esters have become widespread contaminants in the aquatic environment, because of their extensive use as non-reactive plasticizers. There is, however, little accurate data on their solubility, transportation, and distribution in the aquatic environment. In this work, we have investigated the influence of humic acid on the water solubility of di-(2-ethylhexyl)phthalate (DEHP), one of the most frequently used phthalate esters in the laboratory studies for DEHP. We have also studied the solid–water distribution of DEHP in the presence of humic acid and particulate matter (activated carbon, ferrihydrite, and kaolinite) to simulate their distribution in a natural aquifer (ternary system). The results show that the water solubility of DEHP can be significantly increased by humic acid. The shape K _eq value, the binding constant of DEHP between water and humic acid at equilibrium, was obtained by fitting experimental data for each humic acid. The shape K _eq values in the ternary system apparently decreased in the order of ferrihydrite ≤ kaolinite ≈ octanol/water partition activated carbon systems. This result shows that the increase in the hydrophobicity of HA remaining in the solution will lead to the apparent increase of shape K _eq in the system since more hydrophilic solid sorbs relatively more hydrophilic HA molecule. The solid–water partition coefficient (shape K _W-P ) for DEHP in the environment estimated from this study is consistent with those reported based on the experiments for natural samples. Quantitative values obtained in this study, such as K'_ow, shape K _eq, and shape K _W-P , can be useful for estimating the behavior of DEHP.     

Greenhouse gas diffusive fluxes at the sediment–water interface of sewage-draining rivers

Purpose

The purposes of this study were to analyse the spatiotemporal variations in greenhouse gas diffusive fluxes at the sediment–water interface of sewage-draining rivers and natural rivers, and investigate the factors responsible for the changes in greenhouse gas diffusive fluxes.

Materials and methods

Greenhouse gas diffusive fluxes at the sediment–water interface of rivers in Tianjin city (Haihe watershed) were investigated during July and October 2014, and January and April 2015 by laboratory incubation experiments. The influence of environmental variables on greenhouse gas diffusive fluxes was evaluated by Spearman’s correlation analysis and a multiple stepwise regression analysis.

Results and discussion

Sewage-draining rivers were more seriously polluted by human sewage discharge than natural rivers. The greenhouse gas diffusive fluxes at the sediment–water interface exhibited obvious spatiotemporal variations. The mean absolute value of the CO₂ diffusive fluxes was seasonally variable with spring>winter>fall>summer, while the mean absolute values of the CH₄ and N₂O diffusive fluxes were both higher in summer and winter, and lower in fall and spring. The annual mean values of the CO₂, CH₄ and N₂O diffusive fluxes at the sewage-draining river sediment–water interface were ??123.26?±?233.78 μmol m^?2 h^?1, 1.88?±?6.89 μmol m^?2 h^?1 and 1505.03?±?2388.46 nmol m^?2 h^?1, respectively, which were 1.22, 4.37 and 134.50 times those at the natural river sediment–water interface, respectively. The spatial variation of the N₂O diffusive fluxes in the sewage-draining rivers and the natural rivers was the most significant. As a general rule, the more serious the river pollution was, the greater the diffusive fluxes of the greenhouse gases were. On average for the whole year, the river sediment was the sink of CO₂ and the source of CH₄ and N₂O. There were positive correlations among the CO₂, CH₄ and N₂O diffusive fluxes. The main influencing factor for CO₂ and N₂O diffusive fluxes was the water temperature of the overlying water; however, the key factors for CH₄ diffusive fluxes were the Eh of the sediment and the NH₄⁺-N of the overlying water.

Conclusions

River sediment can be either a sink or a source of greenhouse gases, which varies in different levels of pollution and different seasons. Human sewage discharge has greatly affected the carbon and nitrogen cycling of urban rivers.

     

Biodegradability of Di(2-Ethylhexyl) Phthalate by Pseudomonas Fluorescens FS1

Di(2-ethylhexyl)phthalate (DEHP), one of high-molecular weightphthalate esters (PAEs), is used in the manufacturing of polyvinylchloride (PVC) resins, polyvinyl acetate, cellulosics,and polyurethanes, and contributes to environmental pollution. In this article, the characteristics of DEHP biodegradation by aneffective degradation bacterium, Pseudomonasfluorescens FS1 that isolated from the activated sludge at a petrochemicalfactory, was capable of using phthalate esters as the sole carbonand energy source, were investigated. Experimental results showedthat the biodegradation of DEHP by P. fluorescens FS1 could be described by the first-order reaction model, whichcould be expressed as: lnC = –0.0688t + A, and the half-life ofDEHP biodegradation was 10.07 d when the initial concentrations of DEHP were less than 50 mg L^-1. The inhibition effects ofDEHP as a substrate had become predominant above the concentration of 50 mg L^-1. The PAEs-degrading enzyme of P. fluorescens FS1, mainly located in the soluble part andthe particle of cytoplasm, was an intracellular enzyme. The metabolites of DEHP degradation by P. fluorescens FS1, which monoester, phthalic acid, benzonic acid, phenol, wereextracted using dichloromethane at different time intervals and identified by the GC-MS. The tentative pathway proposed for degradation of DEHP by P. fluorescens FS1 under aerobic condition is monoester in the beginning, further enzymatic degradation of the monoester produces phthalic acid, benzonic acid, phenol and finally CO₂ and H₂O.     

Effect of moisture,texture and aggregate size of paddy soil on production and consumption of CH4

Laboratory experiments were conducted to find out under which conditions the soil from Italian rice fields could change from a source into a sink of atmospheric CH₄. Moist (30% H₂O=68% of the maximum water holding capacity (whc)) rice field soil oxidized CH₄ with biphasic kinetics, exhibiting both a low (145 ppmv CH₄) and a high (20,200 ppmv CH₄) K_m value and V_max values of 16.8 and 839 nmol gdw⁻¹ h⁻¹, respectively. The activity with the low K_m allowed the oxidation of atmospheric CH₄. Uptake rates of high CH₄ concentrations (16.5% v/v) and of O₂ linearly decreased with aggregate size of soil between 2 and 10 mm. Atmospheric CH₄ (1.8 ppmv) was consumed in soil aggregates <6 mm, but soil aggregates >6 mm released CH₄ into the atmosphere. Similarly, net uptake of atmospheric CH₄ turned into net release of CH₄ when the soil moisture was decreased below a water content of about 20% whc. The uptake rate of atmospheric CH₄ increased threefold when the soil was amended with sterile quartz sand. Flooded microcosms with non-amended and quartz-amended soil emitted CH₄ into the atmosphere. The CH₄ emission rate increased when the flux was measured under an atmosphere of N₂ instead of air, indicating that 30–99% of the produced CH₄ was oxidized in the oxic soil surface layer. Removal of the flood water resulted in increase of CH₄ emission rates until a water content of about 75–82% whc was reached, and subsequently in a rapid decrease. However, the soil microcosms never showed net uptake of atmospheric CH₄. Our results show that the microorganisms consuming atmospheric CH₄ were inactivated at an earlier stage of drainage than the microorganisms producing CH₄, irrespective of the soil porosity which was adjusted by addition of quartz sand. Hence, it is unlikely that the Italian rice fields can act as a net sink for atmospheric CH₄ even when drained.     

Effects of nitrogen and sulfur deposition on CH4 and N2O fluxes in high-altitude peatland soil under different water tables in the Tibetan Plateau

Abstract

The effects of nitrogen (N) and sulfur (S) deposition on methane (CH₄) and nitrous oxide (N₂O) emissions under low (10 cm below soil surface) and high (at soil surface) water tables were investigated in the laboratory. Undisturbed soil columns from the alpine peatland of the Tibetan Plateau were analyzed. CH₄ emission was higher and N₂O emission was lower at the high water table than those at the low water table regardless of nutrient application. Addition of N (NH₄NO₃ (ammonium nitrate), 5 g N m^?2) decreased CH₄ emission up to 57% and 50% at low and high water tables, respectively, but correspondingly increased N₂O emission by 2.5 and 10.4 times. Addition of S (Na₂SO₄ (sodium sulfate), 2.5 g S m^?2) decreased CH₄ and N₂O emission by 64% and 79% at the low water table, respectively, but had a slightly positive effect at the high water table. These results indicated that the responses of CH₄ and N₂O emissions to the S deposition depend on the water table condition in the high-altitude peatland.     

Effect of rice straw application on stable carbon isotopes,methanogenic pathway,and fraction of CH4 oxidized in a continuously flooded rice field in winter season

Straw application is a common practice in rice agriculture, but its effect on stable carbon isotopes (δ¹³C) in each process of CH₄ emission, relative contribution of acetate to CH₄ production (F_ac), and fraction of the CH₄ that is oxidized (F_ox) in the winter season is not well known. We investigated CH₄ production and oxidation potentials in paddy soil, CH₄ concentrations in soil pore water and floodwater, and CH₄ emission as well as their δ¹³C from a continuously flooded paddy field with rice straw application (RSA) during the 2007 and 2008 winter seasons and quantified the F_ac and F_ox using the isotopic data. RSA significantly increased CH₄ emission (p < 0.05) but made δ¹³CH_{4 (emission)} lower by 5–8‰. RSA obviously increased CH₄ concentrations in soil pore water and floodwater, but it played a slight role in porewater δ¹³CH₄ while caused floodwater δ¹³CH₄ 4‰ lower. A relatively low contribution of acetate-dependent methanogenesis (about 50%) was observed, and RSA slightly increased F_ac (about 0–10%) at a relatively low temperature whereas greatly decreased it (about 10–20%) at a high temperature. Floodwater CH₄ was much more ¹³C-enriched than porewater CH₄ (p < 0.05), suggesting that about 60–70% of the CH₄ was oxidized at the soil–water interface. F_ox generally decreased in the winter season and it was reduced by RSA (about 10%). Soil temperature was positively correlated with CH₄ flux and CH₄ flux was negatively related to δ¹³CH_{4 (emission)}, suggesting that temperature might be an important factor influencing F_ox, thus CH₄ emission and δ¹³CH_{4 (emission)}. The findings suggest that RSA significantly increased CH₄ production while little affected CH₄ oxidation, thus decreasing F_ox. Moreover, the effect of RSA on methanogenic pathway might be controlled by soil temperature, and RSA generally reduced F_ac and F_ox was the main reason for the emitted CH₄ depleted in ¹³C.     

Function of the methanogenic community in mangrove soils as influenced by the chemical properties of the hydrosphere

Coastal ecosystems represent a potential additional source of the greenhouse gas methane (CH₄) that has been insufficiently quantified. Thus, to understand the mechanisms controlling greenhouse gas emissions in these ecosystems, this study investigated CH₄ emissions from and the related microbial properties of mangrove soils. Soil and gas samples were collected from several plots at different distances from the seashore in Soc Trang and Ca Mau in Vietnam, and the Sundarbans in India. Soil samples were incubated under different conditions, i.e., anaerobic or aerobic, and the microbial properties of each soil sample with the addition of different amounts of seawater were analyzed. Relatively high CH₄ fluxes and production were detected during the aerobic incubation of samples from the seashore plots in Soc Trang and Ca Mau. However, CH₄ production was reduced under anaerobic conditions [soil electrical conductivity (EC): 179–289 mS m^?1, pH (H₂O): 7.45–8.10] compared with aerobic conditions [water content: 38.9–109.2%, EC: 187–299 mS m^?1, pH (H₂O): 6.86–7.72], but it increased with increasing sulfate concentration, soil EC and cellulase activity and lowering soil pH under anaerobic conditions. Furthermore, mangrove soil with a relatively high level of total organic carbon (C) exhibited relatively high CH₄ production when diluted 4-fold with seawater under anaerobic conditions [water content: 38.9–109.2%, EC: 533 mS m^?1, pH (H₂O): 6.67]. Nearly all of the DNA bands excised from polymerase chain reaction-denaturing gradient gel electrophoresis contained identical sequences related to archaea from the class Halobacteria. The high potential of the seashore plot for CH₄ emissions could be due to the enhancement of cellulase activity under the intermittent oxygen supply, which promotes polysaccharide depolymerization and subsequently increases anaerobic methanogenic activities during tidal flooding. This study also indicates that the major archaea responsible for CH₄ production require a particular hydrospheric salt concentration and soil pH.     

13C NMR studies of organic matter in whole soils: I. Quantitation possibilities

A detailed discussion of the quantitative nature of ¹³C CPMAS NMR spectra as applied to solid samples, such as soil, is given. In particular, the influence of the cross-polarization (CP) time constant (T_CH), the relaxation time constant of protons in the rotating frame (T_1pH) and the contact time (t_c) in the CPMAS experiment are considered. Three distinct quantitation regimes are numerically identified according to sample parameters t_CH and T_1PH > and the experimental choice of t_c: (i) quantitation obtainable from a single CPMAS spectrum; (ii) quantitation obtainable from a series of CPMAS spectra; and (iii) quantitation not possible using CPMAS. Strategies for the measurement of sample parameters T_CH and Ti_pH are reviewed. When quantitation is not possible using CPMAS it is necessary to regress to the direct polarization (DP) of ¹³C nuclei. The sensitivity problems of DPMAS are discussed, as too are general factors that affect the quantitation of ¹³C data such as spinning sidebands. More specifically in relation to soil samples, the effects on quantitation arising from the presence of paramagnetics and the actual methods for the measurement of signal intensities are covered.     

中国亚热带中部三峡库区不同土地利用方式下甲烷氧化潜力研究

To compare the CH4 oxidation potential among diferent land uses and seasons,and to observe its response to monsoon precipitation pattern and carbon and nitrogen parameters,a one-year study was conducted for diferent land uses (vegetable field,tilled and non-tilled orchard,upland crops and pine forest) in central subtropical China.Results showed significant diferences in CH4 oxidation potential among diferent land uses(ranging from 3.08 to 0.36 kg CH4 ha-1 year-1).Upland with corn-peanut-sweet potato rotation showed the highest CH4 emission,while pine forest showed the highest CH4 oxidation potential among all land uses.Non-tilled citrus orchard (0.72±0.08 kg CH4 ha-1 year-1)absorbed two times more CH4 than tilled citrus orchard(0.38±0.06kg CH4 ha-1 year-1).Irrespective of diferent vegetation,inorganic N fertilizer application significantly influenced CH4 fluxes across the sites (R2=0.86,P=0.002).Water-filled pore space,soil microbial biomass carbon,and dissolved nitrogen showed significant efects across diferent land uses (31% to 38% of variability)in one linear regression model.However,their cumulative interaction was significant for pine forest only,which might be attributed to undisturbed microbial communities legitimately responding to other variables,leading to net CH4 oxidation in the soil.These results suggested that i)natural soil condition tended to create win-win situation for CH4 oxidation,and agricultural activities could disrupt the oxidation potentials of the soils;and ii)specific management practices including but not limiting to efficient fertilizer application and utilization,water use efciency,and less soil disruption might be required to increase the CH4 uptake from the soil.     

Adsorption of Dimethyl Phthalate on Marine Sediments

Experiments were performed to investigate the sorption behaviors of dimethyl phthalate on marine sediments. The sorption of dimethyl phthalate on marine sediments reached equilibrium within 10 h. The sorption behavior of dimethyl phthalate on HCl-treated and untreated sediments accorded well with the linear sorption isotherm. The sorption occurred primarily via partition function of organic carbon of marine sediments. The sorption behavior of dimethyl phthalate on H₂O₂-treated sediment was nonlinear and conformed to Freundlich isotherm. Sorption of dimethyl phthalate on H₂O₂-treated sediment was chiefly through surface function of clay in marine sediments. Salinity of seawater had an important effect on the sorption of dimethyl phthalate. As the salinity of seawater increased, both the partitioning coefficients K _d and empirical constant K would increase.     

Translocation of 203Hg labelled HgCl2 and CH3HgCl in an iron-humus podzol studied by radio-analytical techniques

Since increased Hg-concentrations in fish in lakes and rivers in northern Europe, northern parts of the U.S.A. and Canada were found, environmental Hg research has focused intensively on the factors determining leaching of mercury from soil into water systems. This article presents the results of a leaching experiment with undisturbed soil columns treated with HgCI₂ and CH₃HgCl using radio-analytical techniques. The columns were irrigated with rain of different acidity, rain volumes and irrigation intensities. The leaching of mercury was traced by detecting the vertical distribution of ²⁰³Hg in the soil profiles. Advantages and disadvantages of radioanalytical scanning techniques are discussed. The results of Hg leaching in the soil columns indicate a considerably stronger leaching of monomethyl mercury compared to inorganic mercury. Leaching of the two Hg-species is ruled by competition of H⁺ induced soil-Hg desorption with DOM-Hg complex formation; both being affected by rain acidity. Rain intensity had no visible effect on leaching of Hg²⁺ and CH₃Hg⁺. An extended rain duration increased the leaching of CH₃Hg⁺.     

Seasonal Variations in Vertical Redox Stratification and Potential Influence on Trace Metal Speciation in Minerotrophic Peat Sediments

Seasonal variations in pore water and solid phase geochemistry were investigated in urbanized minerotrophic peat sediments located in southwestern Michigan, USA. Sediment pore waters were collected anaerobically, using pore water equilibrators with dialysis membranes (“peepers”) and analyzed for pH, alkalinity, dissolved ΣPO₄ ^?3, ΣNH₄ ⁺, ΣS^?2, SO₄ ^?2, Fe⁺³, Fe⁺², and Mn⁺² at 1-2 cm intervals to a depth of 50 cm. Cores collected adjacent to the peepers during all four seasons were analyzed for reactive solid phase Fe according to extraction methods proposed by Kostka and Luther (1994). The association of Fe and trace metals (Mn, Pb, Zn, Cu, Cr, Co, Cd, U) with operationally defined solid phase fractions (carbonates, iron and manganese oxides, sulfides/organics and residual) was assessed for cores extracted during winter and spring using extraction methods proposed by Tessier et al. (1979, 1982). Pore water Fe and S data demonstrate a clear seasonal variation in redox stratification of these sediments. The redox stratification becomes more compressed in spring and summer, with relatively more reducing conditions closer to the sediment water interface (SWI), and less reducing conditions near the SWI in fall and winter. In the upper 10–15 cm of sediment, the pool of ascorbate extractable Fe, thought to be indicative of reactive Fe(III) oxides, diminishes during spring and summer, in agreement with seasonal changes in redox stratification indicated by the pore water data. Tessier extractions indicate that the total extractable quantity of all metals analyzed in this study decrease with depth, and that the majority of the non-residual Fe, Pb, Zn, Cu, Cr, Co, Cd, and U is typically associated with the sulfide/organic fraction of the sediments at all depths. Non-residual Mn, in contrast, is significantly associated with carbonates in the upper 15–25 cm of the sediment, and predominantly associated with the sulfide/organic fraction only in deeper sediments.     

An experimental study of two potential methylation agents of mercury in the atmosphere: CH3I and DMS

Experimental results from a study of the gas and aqueous phase reactions of elemental mercury (Hg⁰) with methyl iodide (CH₃I) and dimethyl sulfide (DMS) are presented. In aqueous phase experiments with CH₃I we found no observable increase in methyl mercury (MeHg). A small formation of MeHg, however, was observed in some (but not all) gas phase experiments in sunlight. A loss of Hg⁰ and a simultaneous formation of oxidized mercury (Hg(II)) was also observed in these experiments. No reaction, neither methylation or oxidation, was found between Hg⁰ and DMS under any conditions investigated. These experiments suggest that a simple homogeneous gas or aqueous phase methylation of Hg⁰ by DMS or CH₃I in the atmosphere cannot account for the significant levels of MeHg observed in precipitation.     

Tree species affect atmospheric CH4 oxidation without altering community composition of soil methanotrophs

Plant species exert strong effects on ecosystem functions and one of the emerging, and difficult to test hypotheses, is that plants alter soil functions through changing the community structure of soil microorganisms. We tested the hypothesis for atmospheric CH₄ oxidation by using soil samples from a Siberian afforestation experiment and exposing them to ¹³C-CH₄. We determined the activity of the soil methanotrophs under different tree species at three levels of initial CH₄ concentration (30, 200 and 1000 ppm) thus distinguishing the activities of low- and high-affinity methanotrophs. Half of the samples were incubated with ¹³C-enriched CH₄ (99.9%) and half with ¹²C-CH₄. This allowed an estimation of the amount of ¹³C incorporated into individual PLFAs and determination of PLFAs of methanotrophs involved in CH₄ oxidation at the different CH₄ concentrations. Tree species strongly altered the activity of atmospheric CH₄ oxidation without appearing to change the composition of high-affinity methanotrophs as evidenced by PLFA ¹³C labeling. The low diversity of atmospheric CH₄ oxidizers, presumably belonging to the UCSα group, may explain the lack of tree species effects on the composition of soil methanotrophs. We submit that the observed tree species effects on atmospheric CH₄ oxidation indicate an effect on biomass or cell-specific activities rather than by a community change and this may be related to the impact of the tree species on soil N cycling.     

Induction of enhanced CH4 oxidation in soils: NH4 inhibition patterns

The influence of NH₄⁺ on microbial CH₄ oxidation is still poorly understood. Therefore, the influence of NH₄Cl and (NH₄)₂SO₄ on CH₄ oxidation was studied in soils at the different stages of the induction of enhanced methanotrophic activity. After a brief peak in the methanotrophic activity, a steady state was observed in which NH₄⁺ inhibited CH₄ oxidation at low CH₄ concentrations, and stimulated CH₄ oxidation at high concentrations. Chloride did not strongly inhibit CH₄ oxidation during this phase. During a second phase methanotrophic activity increased again. Ammonium no longer stimulated CH₄ oxidation, and Cl⁻ became an important source of uncompetitive inhibition. It was hypothesized that type I methanotrophs dominated during the first, soil-N-dependent phase while N₂-fixing type II methanotrophs dominated the second, soil-N-independent phase.     

Quantitative determination of 2-mercaptoethane sulphonate as biomarker for methanogens in soil by high performance liquid chromatography using UV detector

All methanogens, irrespective of their preferred carbon sources, form coenzyme M (Co-M: 2-mercaptoethane sulphonate) as an intermediate to produce methane (CH₄). But the quantification of Co-M in soil is not done before. In this experiment, the method for quantifying Co-M was standardized by HPLC using UV detector and the values of Co-M were compared with CH₄ emission flux and methanogen activity of soil. The objectives of this experiment were to standardize the Co-M quantification technique and to evaluate its feasibility as a biomarker for methanogens in soil. The Co-M was extracted from soil by rupturing the cell membrane of methanogens using lysis buffer. Trichloroacetic acid solution (0.5 M) and acetonitrile mixture (70: 30, v/v) was used as a mobile phase for measuring Co-M by HPLC at 270 nm. The precision of the method was more than 97% and 90.3 ± 8.1% of the added Co-M standard was recovered from soil by this method. The Co-M concentration in soil was varied at the different rice cultivation stages and the highest concentration of Co-M was recorded at the maximum CH₄ emission period (60 days after seedling transplanting). Application of organic substrates significantly (P ≤ 0.05) increased methanogen activity and Co-M concentration in rice paddy soil. The conversion factor, 155.03 ± 14.20 μg CH₄ produced mmol⁻¹ Co-M d⁻¹, could be used to calculate methanogen activity from Co-M concentration of soil. Based on these results, it could be proposed that the Co-M concentration could be used as a biomarker for methanogen activity and the above-mentioned method can be used for an easy but precise quantification of Co-M in soil.     

Fluxes of methane and carbon dioxide from soil under forest, grazing land, irrigated rice and rainfed field crops in a watershed of Nepal

Field evolution of CH₄ and CO₂ from soils under four dominant land uses in the Mardi watershed, western Nepal, were monitored at 15-day intervals for 1 year using closed chamber techniques. The CH₄ oxidation rate (mean±SE, g CH₄ m^–2 h^–1) in the forest (22.8±6) was significantly higher than under grazing land (14±2) and an upland rainfed maize and millet system (Bari) (2.6±0.9). Irrigated rice fields (Khet) showed an oxidation rate of 6±0.8 g CH₄ m^–2 h^–1 in the dry season (December–May) but emitted a mean rate of 131 g CH₄ m^–2 h^–1 in the rainy season and autumn (June–October). The evolution of CO₂ ranged from 10 mg CO₂ m^–2 h^–1 in the Bari in January to 1,610 mg CO₂ m^–2 h^–1 in the forest in July. Higher evolution of CO₂ (mean±SE, mg CO₂ m^–2 h^–1) was observed in the Bari (399±39) and forest (357±36) compared to Khet (246±25) and grazing (206±20) lands. The annual emission of CO₂ evolution varied from 86.6 to 1,836 g CO₂ m^–2 year^–1. The activation energy for CH₄ and CO₂ varied between 16–283 and 80–117 kJ mol^–1, respectively. The estimated temperature coefficient for CO₂ emission varied from 2.5 to 5.0. Temperature explained 46–51% of the variation in CO₂ evolution, whereas it explained only 4–36% of the variation in CH₄ evolution.     

Activity and composition of the methanogenic archaeal community in soil vegetated with wild versus cultivated rice

Wild rice (Oryza rufipogon) is a problematic weed in fields of cultivated rice (Oryza sativa). We hypothesized that the composition and/or the activity of the methanogenic microbial communities might be different in soil grown with cultivated versus wild rice. We used samples from Hainan, China, where wild rice grew on a field adjacent to cultivated rice. The composition of the methanogenic archaeal community was analyzed in samples of rice soil by targeting the 16S rRNA gene. Analysis of the terminal restriction fragment length polymorphism (T-RFLP) showed similar patterns in soil from wild versus cultivated rice. Sequences of archaeal 16S rRNA genes also showed similar composition in soil from wild versus cultivated rice, revealing the presence of Methanosarcinaceae, Methanosaetaceae, Methanobacteriales, Methanocellales (Rice Cluster I), Rice Cluster II, Crenarchaeota Group I.3 and Crenarchaeota Group I.1b. Incubation of soil samples under anoxic conditions generally resulted in vigorous CH₄ production after a lag phase of 7-8 days. Production of CH₄ was partially inhibited by methyl fluoride, a specific inhibitor of acetoclastic methanogenesis, resulting in nearly stoichiometric accumulation of acetate. CO₂ was produced without lag phase. The δ¹³C of the produced CO₂ was slightly lower in soil grown with cultivated rice versus wild rice, reflecting the δ¹³C of organic matter, which was about −29‰ for cultivated rice soil and about −24‰ for wild rice soil. The δ¹³C of the produced CH₄ and the acetate that accumulated in the presence of CH₃F was much more negative in cultivated versus wild rice soil, mainly since the isotopic fractionation factors for hydrogenotrophic methanogenesis were higher for soil from cultivated rice (α = 1.054) versus wild rice (α = 1.039). However, the percentage contribution of hydrogenotrophic methanogenesis to total CH₄ production was similar in both soils (27-35%). In conclusion, although the two soils exhibited different δ¹³C values of soil organic matter and derived products, they were similar with respect to rates and composition of the methanogenic communities.     

More evidence that anaerobic oxidation of methane is prevalent in soils: Is it time to upgrade our biogeochemical models?

Estimating future fluxes of CH₄ between land and atmosphere requires well-conceived process-based biogeochemical models. Current models do not represent the anaerobic oxidation of methane (AOM) in land surface soils, in spite of increasing evidence that this process is widespread. Our objective was to determine whether AOM, or potential AOM, commonly occurs in 20 hydromorphic soils spanning a wide range of chemical properties. Bulk soil samples were collected under shallow water near the shoreline of 15 recently drained fish ponds in southern Bohemia (Czech Republic), as well as from below the water table at 3 peatland locations in northeast Scotland and 2 acid sulfate soils on the southern coast of Finland. Each soil slurry was incubated under both oxic and anoxic conditions, with or without the addition of alternative electron acceptors (SO₄²⁻ and NO₃⁻) or H₂PO₄⁻. Here, “oxic” and “anoxic” conditions refer to anoxic soil respectively incubated in a headspace containing air or argon. Using the isotope dilution method, we determined the gross production and oxidation rates of CH₄ after 2 days incubation under oxic headspace conditions, and after 2, 21 and 60 days incubation under anoxic conditions. Large differences in net CH₄ fluxes were observed between soil types and between incubation conditions. AOM was detected in each of the 20 bulk soil samples, which spanned >6 pH units and 2 orders of magnitude in organic C content. Significant positive relationships were found between AOM and gross CH₄ production rates under anoxic conditions, resulting in AOM rates that were sometimes higher than CH₄ oxidation rates under oxic headspace conditions. There was no relationship between net and gross CH₄ production rates, such that 2 soil types could display similar low net rates, yet conceal very large differences in gross rates. The effects of alternative electron acceptors on AOM were idiosyncratic and resulted in no net trend. We did find, however, a negative effect of SO₄²⁻ and H₂PO₄⁻ on gross CH₄ production rates under anoxic and oxic conditions respectively. Under oxic headspace conditions, CH₄ oxidation was related to soil organic C content. Taken collectively, our results suggest that AOM, or potential AOM, is prevalent over a wide range of soil types, that AOM may contribute substantially to CH₄ oxidation in soils, and that AOM in soils should be integrated to current process-based CH₄ cycling models.     

不同耕作条件下豆麦双序列轮作农田土壤温室气体的排放及影响因素研究

为了研究耕作措施对双序列轮作农田土壤温室气体的排放及影响, 采用CO₂分析仪、静态箱 气相色谱法在陇中黄土高原半干旱区对传统耕作不覆盖、免耕不覆盖、免耕秸秆覆盖和传统耕作+秸秆还田4种耕作措施下豆麦双序列轮作农田土壤温室气体(CO₂、N₂O和CH₄)的排放及影响因素进行了连续测定和分析。结果表明: 测定期内4种耕作措施下农田土壤均表现为CO₂源、N₂O源和CH₄净吸收汇; 除传统耕作不覆盖措施, 其他3种耕作措施不同程度地减少了2种轮作序列土壤的N₂O排放通量, 并显著增加了土壤对CH4的吸收。CO₂和N₂O的排放通量分别与地表、地下5 cm处、地下10 cm处的土壤温度呈极显著和显著正相关关系, 相关系数分别为0.92^**和0.89^**、0.95^**和0.91^**、0.77^*和0.62^*; 而CH₄吸收通量与不同地层的温度之间无明显的相关关系; CO₂和CH₄的通量与0~5 cm、5~10 cm的土壤含水量均呈显著正相关关系, 相关系数分别为0.69^*和0.72^*、0.77^*和0.64^*, 而与10~30 cm土壤含水量无明显相关关系; N₂O排放通量与各层次的土壤含水量之间均呈不显著负相关关系。对2种轮作序列各处理下土壤中排放的3种温室气体的增温潜势计算综合得出: 4种耕作措施中, 免耕不覆盖处理可相对减少土壤温室气体的排放量, 进而降低温室效应。