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Find video protocols related to scientific articles indexed in Pubmed.
Characterization of methane flux from photosynthetic oxidation ponds in a wastewater treatment plant.
Water Sci. Technol.
PUBLISHED: 09-27-2014
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Photosynthetic oxidation ponds are a low-cost method for secondary treatment of wastewater using natural and more energy-efficient aeration strategies. Methane (CH(4)) is produced during the anaerobic digestion of organic matter, but only some of it is oxidized in the water column, with the remaining CH(4) escaping into the atmosphere. In order to characterize the CH(4) flux in two photosynthetic oxidation ponds in a wastewater treatment plant in northern California, the isotopic compositions and concentrations of CH(4) were measured in the water column, in bubbles and in flux chambers, over a period of 12 to 21 months to account for seasonal trends in CH(4) emissions. Methane flux varied seasonally throughout the year, with an annual average flux of 5.5 g CH(4) m?² d?¹ Over half of the CH(4) flux, 56.1-74.4% v/v, was attributed to ebullition. The oxidation efficiency of this system was estimated at 69.1%, based on stable carbon isotopes and a calculated fractionation factor of 1.028. This is the first time, to our knowledge, that a fractionation factor for CH(4) oxidation has been empirically determined for oxidation ponds. Quantifying CH(4) emissions from these systems is essential to properly identify their contribution and to mitigate their impact on global warming.
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Assessing methods to estimate emissions of non-methane organic compounds from landfills.
Waste Manag
PUBLISHED: 08-06-2014
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The non-methane organic compound (NMOC) emission rate is used to assess compliance with landfill gas emission regulations by the United States Environmental Protection Agency (USEPA). A recent USEPA Report (EPA/600/R-11/033) employed a ratio method to estimate speciated NMOC emissions (i.e., individual NMOC emissions): speciated NMOC emissions=measured methane (CH4) emission multiplied by the ratio of individual NMOCs concentration relative to CH4 concentration (C(NMOCs)/C(CH4)) in the landfill header gas. The objectives of this study were to (1) evaluate the efficacy of the ratio method in estimating speciated NMOC flux from landfills; (2) determine for what types of landfills the ratio method may be in error and why, using recent field data to quantify the spatial variation of (C(NMOCs)/C(CH4)) in landfills; and (3) formulate alternative models for estimating NMOC emissions from landfills for cases in which the ratio method results in biased estimates. This study focuses on emissions through landfill covers measured with flux chambers and evaluates the utility of the ratio method for estimating NMOC emission through this pathway. Evaluation of the ratio method was performed using CH4 and speciated NMOC concentration and flux data from 2012/2013 field sampling of four landfills, an unpublished landfill study, and literature data from three landfills. The ratio method worked well for landfills with thin covers (<40 cm), predicting composite NMOC flux (as hexane-C) to within a factor of 10× for 13 out of 15 measurements. However, for thick covers (?40 cm) the ratio method overestimated NMOC emissions by ?10× for 8 out of 10 measurements. Alternative models were explored incorporating other chemical properties into the ratio method. A molecular weight squared (MW)(2)-modified ratio equation was shown to best address the tendency of the current ratio method to overestimate NMOC fluxes for thick covers. While these analyses were only performed using NMOC fluxes through landfill covers measured with flux chambers, results indicate the current USEPA approach for estimating NMOC emissions may overestimate speciated NMOC emission ?10× for many compounds.
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Changes in peat chemistry associated with permafrost thaw increase greenhouse gas production.
Proc. Natl. Acad. Sci. U.S.A.
PUBLISHED: 04-07-2014
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Carbon release due to permafrost thaw represents a potentially major positive climate change feedback. The magnitude of carbon loss and the proportion lost as methane (CH4) vs. carbon dioxide (CO2) depend on factors including temperature, mobilization of previously frozen carbon, hydrology, and changes in organic matter chemistry associated with environmental responses to thaw. While the first three of these effects are relatively well understood, the effect of organic matter chemistry remains largely unstudied. To address this gap, we examined the biogeochemistry of peat and dissolved organic matter (DOM) along a ?40-y permafrost thaw progression from recently- to fully thawed sites in Stordalen Mire (68.35°N, 19.05°E), a thawing peat plateau in northern Sweden. Thaw-induced subsidence and the resulting inundation along this progression led to succession in vegetation types accompanied by an evolution in organic matter chemistry. Peat C/N ratios decreased whereas humification rates increased, and DOM shifted toward lower molecular weight compounds with lower aromaticity, lower organic oxygen content, and more abundant microbially produced compounds. Corresponding changes in decomposition along this gradient included increasing CH4 and CO2 production potentials, higher relative CH4/CO2 ratios, and a shift in CH4 production pathway from CO2 reduction to acetate cleavage. These results imply that subsidence and thermokarst-associated increases in organic matter lability cause shifts in biogeochemical processes toward faster decomposition with an increasing proportion of carbon released as CH4. This impact of permafrost thaw on organic matter chemistry could intensify the predicted climate feedbacks of increasing temperatures, permafrost carbon mobilization, and hydrologic changes.
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Microbial community stratification linked to utilization of carbohydrates and phosphorus limitation in a boreal peatland at Marcell Experimental Forest, Minnesota, USA.
Appl. Environ. Microbiol.
PUBLISHED: 03-28-2014
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This study investigated the abundance, distribution, and composition of microbial communities at the watershed scale in a boreal peatland within the Marcell Experimental Forest (MEF), Minnesota, USA. Through a close coupling of next-generation sequencing, biogeochemistry, and advanced analytical chemistry, a biogeochemical hot spot was revealed in the mesotelm (30- to 50-cm depth) as a pronounced shift in microbial community composition in parallel with elevated peat decomposition. The relative abundance of Acidobacteria and the Syntrophobacteraceae, including known hydrocarbon-utilizing genera, was positively correlated with carbohydrate and organic acid content, showing a maximum in the mesotelm. The abundance of Archaea (primarily crenarchaeal groups 1.1c and 1.3) increased with depth, reaching up to 60% of total small-subunit (SSU) rRNA gene sequences in the deep peat below the 75-cm depth. Stable isotope geochemistry and potential rates of methane production paralleled vertical changes in methanogen community composition to indicate a predominance of acetoclastic methanogenesis mediated by the Methanosarcinales in the mesotelm, while hydrogen-utilizing methanogens predominated in the deeper catotelm. RNA-derived pyrosequence libraries corroborated DNA sequence data to indicate that the above-mentioned microbial groups are metabolically active in the mid-depth zone. Fungi showed a maximum in rRNA gene abundance above the 30-cm depth, which comprised only an average of 0.1% of total bacterial and archaeal rRNA gene abundance, indicating prokaryotic dominance. Ratios of C to P enzyme activities approached 0.5 at the acrotelm and catotelm, indicating phosphorus limitation. In contrast, P limitation pressure appeared to be relieved in the mesotelm, likely due to P solubilization by microbial production of organic acids and C-P lyases. Based on path analysis and the modeling of community spatial turnover, we hypothesize that P limitation outweighs N limitation at MEF, and microbial communities are structured by the dominant shrub, Chamaedaphne calyculata, which may act as a carbon source for major consumers in the peatland.
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Microbial metabolic potential for carbon degradation and nutrient (nitrogen and phosphorus) acquisition in an ombrotrophic peatland.
Appl. Environ. Microbiol.
PUBLISHED: 03-28-2014
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This study integrated metagenomic and nuclear magnetic resonance (NMR) spectroscopic approaches to investigate microbial metabolic potential for organic matter decomposition and nitrogen (N) and phosphorus (P) acquisition in soils of an ombrotrophic peatland in the Marcell Experimental Forest (MEF), Minnesota, USA. This analysis revealed vertical stratification in key enzymatic pathways and taxa containing these pathways. Metagenomic analyses revealed that genes encoding laccases and dioxygenases, involved in aromatic compound degradation, declined in relative abundance with depth, while the relative abundance of genes encoding metabolism of amino sugars and all four saccharide groups increased with depth in parallel with a 50% reduction in carbohydrate content. Most Cu-oxidases were closely related to genes from Proteobacteria and Acidobacteria, and type 4 laccase-like Cu-oxidase genes were >8 times more abundant than type 3 genes, suggesting an important and overlooked role for type 4 Cu-oxidase in phenolic compound degradation. Genes associated with sulfate reduction and methanogenesis were the most abundant anaerobic respiration genes in these systems, with low levels of detection observed for genes of denitrification and Fe(III) reduction. Fermentation genes increased in relative abundance with depth and were largely affiliated with Syntrophobacter. Methylocystaceae-like small-subunit (SSU) rRNA genes, pmoA, and mmoX genes were more abundant among methanotrophs. Genes encoding N2 fixation, P uptake, and P regulons were significantly enriched in the surface peat and in comparison to other ecosystems, indicating N and P limitation. Persistence of inorganic orthophosphate throughout the peat profile in this P-limiting environment indicates that P may be bound to recalcitrant organic compounds, thus limiting P bioavailability in the subsurface. Comparative metagenomic analysis revealed a high metabolic potential for P transport and starvation, N2 fixation, and oligosaccharide degradation at MEF relative to other wetland and soil environments, consistent with the nutrient-poor and carbohydrate-rich conditions found in this Sphagnum-dominated boreal peatland.
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Methane dynamics regulated by microbial community response to permafrost thaw.
Nature
PUBLISHED: 03-19-2014
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Permafrost contains about 50% of the global soil carbon. It is thought that the thawing of permafrost can lead to a loss of soil carbon in the form of methane and carbon dioxide emissions. The magnitude of the resulting positive climate feedback of such greenhouse gas emissions is still unknown and may to a large extent depend on the poorly understood role of microbial community composition in regulating the metabolic processes that drive such ecosystem-scale greenhouse gas fluxes. Here we show that changes in vegetation and increasing methane emissions with permafrost thaw are associated with a switch from hydrogenotrophic to partly acetoclastic methanogenesis, resulting in a large shift in the ?(13)C signature (10-15‰) of emitted methane. We used a natural landscape gradient of permafrost thaw in northern Sweden as a model to investigate the role of microbial communities in regulating methane cycling, and to test whether a knowledge of community dynamics could improve predictions of carbon emissions under loss of permafrost. Abundance of the methanogen Candidatus 'Methanoflorens stordalenmirensis' is a key predictor of the shifts in methane isotopes, which in turn predicts the proportions of carbon emitted as methane and as carbon dioxide, an important factor for simulating the climate feedback associated with permafrost thaw in global models. By showing that the abundance of key microbial lineages can be used to predict atmospherically relevant patterns in methane isotopes and the proportion of carbon metabolized to methane during permafrost thaw, we establish a basis for scaling changing microbial communities to ecosystem isotope dynamics. Our findings indicate that microbial ecology may be important in ecosystem-scale responses to global change.
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Discovery of a novel methanogen prevalent in thawing permafrost.
Nat Commun
PUBLISHED: 01-07-2014
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Thawing permafrost promotes microbial degradation of cryo-sequestered and new carbon leading to the biogenic production of methane, creating a positive feedback to climate change. Here we determine microbial community composition along a permafrost thaw gradient in northern Sweden. Partially thawed sites were frequently dominated by a single archaeal phylotype, Candidatus 'Methanoflorens stordalenmirensis' gen. nov. sp. nov., belonging to the uncultivated lineage 'Rice Cluster II' (Candidatus 'Methanoflorentaceae' fam. nov.). Metagenomic sequencing led to the recovery of its near-complete genome, revealing the genes necessary for hydrogenotrophic methanogenesis. These genes are highly expressed and methane carbon isotope data are consistent with hydrogenotrophic production of methane in the partially thawed site. In addition to permafrost wetlands, 'Methanoflorentaceae' are widespread in high methane-flux habitats suggesting that this lineage is both prevalent and a major contributor to global methane production. In thawing permafrost, Candidatus 'M. stordalenmirensis' appears to be a key mediator of methane-based positive feedback to climate warming.
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Measurement of carbon storage in landfills from the biogenic carbon content of excavated waste samples.
Waste Manag
PUBLISHED: 01-15-2013
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Landfills are an anaerobic ecosystem and represent the major disposal alternative for municipal solid waste (MSW) in the U.S. While some fraction of the biogenic carbon, primarily cellulose (Cel) and hemicellulose (H), is converted to carbon dioxide and methane, lignin (L) is essentially recalcitrant. The biogenic carbon that is not mineralized is stored within the landfill. This carbon storage represents a significant component of a landfill carbon balance. The fraction of biogenic carbon that is not reactive in the landfill environment and therefore stored was derived for samples of excavated waste by measurement of the total organic carbon, its biogenic fraction, and the remaining methane potential. The average biogenic carbon content of the excavated samples was 64.6±18.0% (average±standard deviation), while the average carbon storage factor was 0.09±0.06g biogenic-C stored per g dry sample or 0.66±0.16g biogenic-C stored per g biogenic C.
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Observations on the methane oxidation capacity of landfill soils.
Waste Manag
PUBLISHED: 06-23-2011
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The objective of this study was to determine the role of CH(4) loading to a landfill cover in the control of CH(4) oxidation rate (gCH(4)m(-2)d(-1)) and CH(4) oxidation efficiency (% CH(4) oxidation) in a field setting. Specifically, we wanted to assess how much CH(4) a cover soil could handle. To achieve this objective we conducted synoptic measurements of landfill CH(4) emission and CH(4) oxidation in a single season at two Southeastern USA landfills. We hypothesized that percent oxidation would be greatest at sites of low CH(4) emission and would decrease as CH(4) emission rates increased. The trends in the experimental results were then compared to the predictions of two differing numerical models designed to simulate gas transport in landfill covers, one by modeling transport by diffusion only and the second allowing both advection and diffusion. In both field measurements and in modeling, we found that percent oxidation is a decreasing exponential function of the total CH(4) flux rate (CH(4) loading) into the cover. When CH(4) is supplied, a covers rate of CH(4) uptake (gCH(4)m(-2)d(-2)) is linear to a point, after which the system becomes saturated. Both field data and modeling results indicate that percent oxidation should not be considered as a constant value. Percent oxidation is a changing quantity and is a function of cover type, climatic conditions and CH(4) loading to the bottom of the cover. The data indicate that an effective way to increase the % oxidation of a landfill cover is to limit the amount of CH(4) delivered to it.
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Influence of acidification on the optical properties and molecular composition of dissolved organic matter.
Anal. Chim. Acta
PUBLISHED: 05-26-2011
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Acidification is a common method for preserving dissolved organic matter (DOM) in natural water samples until sophisticated laboratory analyses can be performed. However, little is known about the effects of this practice on the composition and optical properties of DOM. In this study, the effects of acidification on DOM in porewater samples collected from the RL IV bog system of the Glacial Lake Agassiz Peatlands in northern Minnesota were characterized. Molecular composition was determined by ultrahigh resolution mass spectrometry and optical properties by UV absorption and three-dimensional fluorescence spectroscopy. Excitation-emission matrix fluorescence spectroscopy results indicate that the fluorescence properties of the peatland porewater DOM were sensitive to pH and that the observed changes were fluorophore dependent. Ultrahigh resolution Fourier transform ion cyclotron resonance mass spectrometry revealed the appearance of newly formed, oxygen-rich compounds upon acidification. The extent to which these oxygen-rich compounds were formed was also dependent on the composition of the DOM.
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Seasonal greenhouse gas emissions (methane, carbon dioxide, nitrous oxide) from engineered landfills: daily, intermediate, and final California cover soils.
J. Environ. Qual.
PUBLISHED: 05-07-2011
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Compared with natural ecosystems and managed agricultural systems, engineered landfills represent a highly managed soil system for which there has been no systematic quantification of emissions from coexisting daily, intermediate, and final cover materials. We quantified the seasonal variability of CH, CO, and NO emissions from fresh refuse (no cover) and daily, intermediate, and final cover materials at northern and southern California landfill sites with engineered gas extraction systems. Fresh refuse fluxes (g m d [± SD]) averaged CH 0.053 (± 0.03), CO 135 (± 117), and NO 0.063 (± 0.059). Average CH emissions across all cover types and wet/dry seasons ranged over more than four orders of magnitude (<0.01-100 g m d) with most cover types, including both final covers, averaging <0.1 g m d with 10 to 40% of surface areas characterized by negative fluxes (uptake of atmospheric CH). The northern California intermediate cover (50 cm) had the highest CH fluxes. For both the intermediate (50-100 cm) and final (>200 cm) cover materials, below which methanogenesis was well established, the variability in gaseous fluxes was attributable to cover thickness, texture, density, and seasonally variable soil moisture and temperature at suboptimal conditions for CH oxidation. Thin daily covers (30 cm local soil) and fresh refuse generally had the highest CO and NO fluxes, indicating rapid onset of aerobic and semi-aerobic processes in recently buried refuse, with rates similar to soil ecosystems and windrow composting of organic waste. This study has emphasized the need for more systematic field quantification of seasonal emissions from multiple types of engineered covers.
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Mitigation of methane emission from Fakse landfill using a biowindow system.
Waste Manag
PUBLISHED: 01-18-2011
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Landfills are significant sources of atmospheric methane (CH(4)) that contributes to climate change, and therefore there is a need to reduce CH(4) emissions from landfills. A promising cost efficient technology is to integrate compost into landfill covers (so-called "biocovers") to enhance biological oxidation of CH(4). A full scale biocover system to reduce CH(4) emissions was installed at Fakse landfill, Denmark using composted yard waste as active material supporting CH(4) oxidation. Ten biowindows with a total area of 5000 m(2) were integrated into the existing cover at the 12 ha site. To increase CH(4) load to the biowindows, leachate wells were capped, and clay was added to slopes at the site. Point measurements using flux chambers suggested in most cases that almost all CH(4) was oxidized, but more detailed studies on emissions from the site after installation of the biocover as well as measurements of total CH(4) emissions showed that a significant portion of the emission quantified in the baseline study continued unabated from the site. Total emission measurements suggested a reduction in CH(4) emission of approximately 28% at the end of the one year monitoring period. This was supported by analysis of stable carbon isotopes which showed an increase in oxidation efficiency from 16% to 41%. The project documented that integrating approaches such a whole landfill emission measurements using tracer techniques or stable carbon isotope measurements of ambient air samples are needed to document CH(4) mitigation efficiencies of biocover systems. The study also revealed that there still exist several challenges to better optimize the functionality. The most important challenges are to control gas flow and evenly distribute the gas into the biocovers.
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Landfill methane oxidation across climate types in the U.S.
Environ. Sci. Technol.
PUBLISHED: 12-06-2010
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Methane oxidation in landfill covers was determined by stable isotope analyses over 37 seasonal sampling events at 20 landfills with intermediate covers over four years. Values were calculated two ways: by assuming no isotopic fractionation during gas transport, which produces a conservative or minimum estimate, and by assuming limited isotopic fractionation with gas transport producing a higher estimate. Thus bracketed, the best assessment of mean oxidation within the soil covers from chamber captured emitted CH(4) was 37.5 ± 3.5%. The fraction of CH(4) oxidized refers to the fraction of CH(4) delivered to the base of the cover that was oxidized to CO(2) and partitioned to microbial biomass instead of being emitted to the atmosphere as CH(4) expressed as a percentage. Air samples were also collected at the surface of the landfill, and represent CH(4) from soil, from leaking infrastructure, and from cover defects. A similar assessment of this data set yields 36.1 ± 7.2% oxidation. Landfills in five climate types were investigated. The fraction oxidized in arid sites was significantly greater than oxidation in mediterranean sites, or cool and warm continental sites. Sub tropical sites had significantly lower CH(4) oxidation than the other types of sites. This relationship may be explained by the observed inverse relationship between cover loading and fractional CH(4) oxidation.
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Fate of effluent-borne contaminants beneath septic tank drainfields overlying a Karst aquifer.
J. Environ. Qual.
PUBLISHED: 09-14-2010
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Groundwater quality effects from septic tanks were investigated in the Woodville Karst Plain, an area that contains numerous sinkholes and a thin veneer of sands and clays overlying the Upper Floridan aquifer (UFA). Concerns have emerged about elevated nitrate concentrations in the UFA, which is the source of water supply in this area of northern Florida. At three sites during dry and wet periods in 2007-2008, water samples were collected from the septic tank, shallow and deep lysimeters, and drainfield and background wells in the UFA and analyzed for multiple chemical indicators including nutrients, nitrate isotopes, organic wastewater compounds (OWCs), pharmaceutical compounds, and microbiological indicators (bacteria and viruses). Median NO3-N concentration in groundwater beneath the septic tank drainfields was 20 mg L(-1) (8.0-26 mg L(-1)). After adjusting for dilution, about 25 to 40% N loss (from denitrification, ammonium sorption, and ammonia volatilization) occurs as septic tank effluent moves through the unsaturated zone to the water table. Nitrogen loading rates to groundwater were highly variable at each site (3.9-12 kg N yr(-1)), as were N and chloride depth profiles in the unsaturated zone. Most OWCs and pharmaceutical compounds were highly attenuated beneath the drainfields; however, five Cs (caffeine, 1,7-dimethylxanthine, phenol, galaxolide, and tris(dichloroisotopropyl)phosphate) and two pharmaceutical compounds (acetaminophen and sulfamethoxazole) were detected in groundwater samples. Indicator bacteria and human enteric viruses were detected in septic tank effluent samples but only intermittently in soil water and groundwater. Contaminant movement to groundwater beneath each septic tank system also was related to water use and differences in lithology at each site.
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Effectiveness of a Florida landfill biocover for reduction of CH4 and NMHC emissions.
Environ. Sci. Technol.
PUBLISHED: 01-16-2010
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Methane-oxidizing "biocovers" were constructed at the Leon County Landfill (Florida). The primary goal was to determine if a biocover placed above the existing thin (15 cm) intermediate clay cover would be capable of mitigating CH(4) and nonmethane hydrocarbon (NMHC) emissions to the atmosphere in this subtropical environment. A secondary goal was to maximize the use of locally recycled materials for biocover construction. The biocovers consisted of 30 or 60 cm of ground garden waste placed over a 15 cm gas distribution layer (clean crushed recycled glass from discarded fluorescent lights). The deep biocover reduced methane fluxes relative to the controls during temporal monitoring over more than a year; in large part, these reductions were attributable to increased methane oxidation. Both the shallow and the deep biocover exhibited significant percentages of negative fluxes (uptake of atmospheric methane) relative to the nonbiocover controls which had consistently positive fluxes. The overall annual effectiveness/performance of the biocover was limited by seasonally high moisture contents and the thin gas distribution layer. For NMHCs, the deep biocover demonstrated substantial reductions for nonmethane hydrocarbon emissions with high percentages of negative fluxes for several hydrocarbon groups, especially the aromatics, alkanes, and lower chlorinated compounds. Ranges of measured NMHC emissions (10(-9) to 10(-3) g m(-2) d(-1)) were similar to previous studies in the literature. Conservative calculations based on field data for total NMHC emissions from the 60 cm biocover area indicate that current U.S. Environmental Protection Agency (EPA) regulatory methods overestimate emissions by more than 2 orders of magnitude, suggesting that improved field-validated methods are needed.
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Spatial structure and activity of sedimentary microbial communities underlying a Beggiatoa spp. mat in a Gulf of Mexico hydrocarbon seep.
PLoS ONE
PUBLISHED: 01-15-2010
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Subsurface fluids from deep-sea hydrocarbon seeps undergo methane- and sulfur-cycling microbial transformations near the sediment surface. Hydrocarbon seep habitats are naturally patchy, with a mosaic of active seep sediments and non-seep sediments. Microbial community shifts and changing activity patterns on small spatial scales from seep to non-seep sediment remain to be examined in a comprehensive habitat study.
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Does the (13)C of foliage-respired CO(2) and biochemical pools reflect the (13)C of recently assimilated carbon?
Plant Cell Environ.
PUBLISHED: 05-15-2009
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Isotopic labelling experiments were conducted to assess relationships among (13)C of recently assimilated carbon (deltaC(A)), foliage respiration (deltaC(F)), soluble carbohydrate (deltaC(SC)), leaf waxes (deltaC(LW)) and bulk organic matter (deltaC(OM)). Slash pine, sweetgum and maize were grown under (13)C depleted CO(2) to label biomass and then placed under ambient conditions to monitor the loss of label. In pine and sweetgum, deltaC(F) of labelled plants (approximately -44 and -35 per thousand, respectively) rapidly approached control values but remained depleted by approximately 4-6 per thousand after 3-4 months. For these tree species, no or minimal label was lost from deltaC(SC), deltaC(LW) and deltaC(OM) during the observation periods. deltaC(F) and deltaC(SC) of labelled maize plants rapidly changed and were indistinguishable from controls after 1 month, while deltaC(LW) and deltaC(OM) more slowly approached control values and remained depleted by 2-6 per thousand. Changes in deltaC(F) in slash pine and sweetgum fit a two-pool exponential model, with the fast turnover metabolic pool (approximately 3-4 d half-life) constituting only 1-2% of the total. In maize, change in deltaC(F) fits a single pool model with a half-life of 6.4 d. The (13)C of foliage respiration and biochemical pools reflect temporally integrated values of deltaC(A), with change in isotopic composition dampened by the size of metabolic carbon reserves and turnover rates.
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Methane oxidation in landfill cover soils, is a 10% default value reasonable?
J. Environ. Qual.
PUBLISHED: 01-01-2009
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We reviewed literature results from 42 determinations of the fraction of methane oxidized and 30 determinations of methane oxidation rate in a variety of soil types and landfill covers. Both column measurements and in situ field measurements were included. The means for the fraction of methane oxidized on transit across the soil covers ranged from 22 to 55% from clayey to sandy material. Mean values for oxidation rate ranged from 3.7 to 6.4 mol m(-2) d(-1) (52-102 g m(-2) d(-1)) for the different soil types. The overall mean fraction oxidized across all studies was 36% with a standard error of 6%. The overall mean oxidation rate across all studies was 4.5 mol m(-2) d(-1) +/- 1.0 (72 +/- 16 g m(-2)d(-1)). For the subset of 15 studies conducted over an annual cycle the fraction of methane oxidized ranged from 11 to 89% with a mean value of 35 +/- 6%, nearly identical to the overall mean. Nine of these studies were conducted in north Florida at 30 degrees N latitude and had a fraction oxidized of 27 +/- 4%. Five studies were conducted in northern Europe ( approximately 50-55 degrees N) and exhibited an average of 54 +/- 14%. One study, conducted in New Hampshire, had a value of 10%. The results indicate that the fraction of methane oxidized in landfill greater than the default value of 10%. Of the 42 determinations of methane oxidation reported, only four report values of 10% or less.
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Comparison of dialysis and solid-phase extraction for isolation and concentration of dissolved organic matter prior to Fourier transform ion cyclotron resonance mass spectrometry.
Anal Bioanal Chem
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We compare two methods, solid-phase extraction (SPE) and dialysis, commonly used for extraction and concentration of dissolved organic matter (DOM) prior to molecular characterization by electrospray ionization (ESI) and ultrahigh-resolution Fourier transform ion cyclotron resonance mass spectrometry. Spectra of DOM samples from Minnesota and Sweden peatlands that were extracted with styrene divinyl benzene polymer SPE sorbents included ions with formulas that had higher oxygen to carbon (O/C) ratios than spectra of DOM from the same samples after de-salting by dialysis. The SPE method was not very effective in extracting several major classes of DOM compounds that had high ESI efficiencies, including carboxylic acids and organo-sulfur compounds, and that out-competed other less-functionalized compounds (e.g., carbohydrates) for charge in the ESI source. The large abundance of carboxylic acids in the dialysisextracted DOM, likely the result of in situ microbial production, makes it difficult to see other (mainly hydrophilic) compounds with high O/C ratios. Our results indicate that, while dialysis is generally preferable for the isolation of DOM, for samples with high microbial inputs, the use of both isolation methods is recommended for a more accurate molecular representation.
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Spatial distribution of bottlenose dolphins (Tursiops truncatus) inferred from stable isotopes and priority organic pollutants.
Sci. Total Environ.
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Differences in priority organic pollutants (POPs), analyzed by gas chromatography-mass spectrometry, and stable isotope ratios (?(13)C, ?(34)S, and ?(15)N; analyzed by isotope ratio-mass spectrometry), divide 77 bottlenose dolphins (Tursiops truncatus) from the Florida Gulf Coast into three distinct groups. POP levels reflect human population and historical contamination along the coast. In the least disturbed site, concentrations of ?POP in male dolphins were 18,000 ng g(-1)±6000 (95% confidence interval here and throughout); in the intermediate bay, males had ?POP concentrations of 19,000 ng g(-1)±10,000. St Andrews Bay was home to dolphins with the highest ?POP concentrations: 44,000 ng g(-1)±10,300. ?(34)S and ?(15)N, differed significantly between St. George Sound dolphins and those frequenting each of the other two bays, but not between St. Andrews and St. Joseph Bays. ?POP concentrations were statistically higher in dolphins frequenting St. Andrews Bay, but were not significantly different between dolphins occupying St. Joseph Bay and St. George Sound. Thus, using either POP or isotope values alone, we would only be able to identify two dolphin groups, but when POP and isotope data are viewed cumulatively, the results clearly define three distinct communities occupying this region.
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Methane emissions from 20 landfills across the United States using vertical radial plume mapping.
J Air Waste Manag Assoc
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Landfill fugitive methane emissions were quantified as a function of climate type and cover type at 20 landfills using US. Environmental Protection Agency (EPA) Other Test Method (OTM)-10 vertical radial plume mapping (VRPM) with tunable diode lasers (TDLs). The VRPM data were initially collected as g CH4/sec emission rates and subsequently converted to g CH4/m2/ day rates using two recently published approaches. The first was based upon field tracer releases of methane or acetylene and multiple linear regression analysis (MLRM). The second was a virtual computer model that was based upon the Industrial Source Complex (ISC3) and Pasquill plume stability class models (PSCMs). Calculated emission results in g CH4/m2/day for each measured VRPM with the two approaches agreed well (r2 = 0.93). The VRPM data were obtained from the working face, temporary soil, intermediate soil, and final soil or synthetic covers. The data show that methane emissions to the atmosphere are a function of climate and cover type. Humid subtropical climates exhibited the highest emissions for all cover types at 207, 127, 102, and 32 g CH4/m2/day, for working face (no cover), temporary, intermediate, and final cover, respectively. Humid continental warm summers showed 67, 51, and 27 g CH4/m2/day for temporary, intermediate, and final covers. Humid continental cool summers were 135, 40, and 26 g CH4/m2/day for the working face, intermediate, and final covers. Mediterranean climates were examined for intermediate and final covers only and found to be 11 and 6 g CH4/m2/day, respectively, whereas semiarid climates showed 85, 11, 3.7, and 2.7 g CH4/m2/day for working face, temporary, intermediate, and final covers. A closed, synthetically capped landfill covered with soil and vegetation with a gas collection system in a humid continental warm summer climate gave mostly background methane readings and average emission rates of only 0.09 g CH4/m2/day flux when measurable.
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Substrate limitation for methanogenesis in hypersaline environments.
Astrobiology
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Motivated by the increasingly abundant evidence for hypersaline environments on Mars and reports of methane in its atmosphere, we examined methanogenesis in hypersaline ponds in Baja California Sur, Mexico, and in northern California, USA. Methane-rich bubbles trapped within or below gypsum/halite crusts have ?¹³C values near -40‰. Methane with these relatively high isotopic values would typically be considered thermogenic; however, incubations of crust samples resulted in the biological production of methane with similar isotopic composition. A series of measurements aimed at understanding the isotopic composition of methane in hypersaline systems was therefore undertaken. Methane production rates, as well as the concentrations and isotopic composition of the particulate organic carbon (POC), were measured. Methane production was highest from microbial communities living within gypsum crusts, whereas POC content at gypsum/halite sites was low, generally less than 1% of the total mass. The isotopic composition of the POC ranged from -26‰ to -10‰. To determine the substrates used by the methanogens, ¹³C-labeled methylamines, methanol, acetate, and bicarbonate were added to individual incubation vials, and the methane produced was monitored for ¹³C content. The main substrates used by the methanogens were the noncompetitive substrates, the methylamines, and methanol. When unlabeled trimethylamine (TMA) was added to incubating gypsum/halite crusts in increasing concentrations, the isotopic composition of the methane produced became progressively lower; the lowest methane ?¹³C values occurred when the most TMA was added (1000 ?M final concentration). This decrease in the isotopic composition of the methane produced with increasing TMA concentrations, along with the high in situ methane ?¹³C values, suggests that the methanogens within the crusts are operating at low substrate concentrations. It appears that substrate limitation is decreasing isotopic fractionation during methanogenesis, which results in these abnormally high biogenic methane ?¹³C values.
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