E Hornibrook - Academia.edu (original) (raw)

Papers by E Hornibrook

AGU Fall Meeting Abstracts, Dec 1, 2018

ABSTRACT A range of culture-independent methods, has recently emerged to study environmental micr... more ABSTRACT A range of culture-independent methods, has recently emerged to study environmental microorganisms in situ[1]. One such method is phospholipid fatty acid (PLFA) analysis, wherein these ubiquitous membrane lipids provide a powerful tool for the study of unculturable soil microorganisms. PLFA analyses have been used to investigate the impacts of a wide range of environmental factors on the soil microbial community. An acknowledged shortcoming of the PLFAs approach is the lack the chemotaxonoic specificity, which restricts the ability of the method to probe the activities of specific functional groups of the microbial community selectively. However, the selectivity of PLFAs analyses can be enhanced by incubating soils with 13C- labelled substrates followed by gas chromatography-combustion-isotope ratio mass spectrometry to reveal the specific PLFAs incorporating the 13C-label. The application of this approach will be demonstrated through our recent work on methanotrophic bacteria in soils. We applied this approach initially to mineral soils[2] and then extended chemotaxonomic assessments by using a combination of 13C-labelled PLFAs and hopanoids [3]. We have used this approach to explore the properties of high affinity methanotrophs in a range of environments, investigating the relationship between methane oxidation rates and the nature and magnitude of the methanotrophic community for the first time[4,5] More recently we extended the technique using a novel time series 13C-labelling of PLFAs[6] to estimate the rate and progression of 13C- label incorporation and turnover of methanotrophic populations. This modified approach has been used to investigate the impacts of various environmental variables, e.g. soil type, vegetation cover and land use, on the methanotrophic biomass[7.8]. The unique nature of the 13CH4 as a gaseous substate/carbon source means that can be readily introduced into soils via a specific subset of the soil microbial biomass, thereby offering many opportunities for studying the fate of microbially fixed carbon in soils. This paper will review the techniques employed and results obtained from our new generation of pulse-chase experiments. References 1. Evershed et al., 2006, Curr. Opin. Biotech. 17, 72. 2. Bull et al., 2000, Nature 405, 175. 3. Crossman et al., 2005, Org. Geochem. 32, 359. 4. Crossman et al., 2006, Soil Biol. Biochem. 38, 983. 5. Crossman et al., 2004, Environ. Sci. Tech. 38, 1359. 6. Maxfield et al., 2006, Appl. Environ. Microbiol. 72, 3901. 7. Maxfield et al., 2008, Evviron. Microbiol. 10, 1917-1924. 8. Maxfield et al., in press Environ. Sci. Technol.

Abstract. Low affinity methanotrophic bacteria consume a significant quantity of methane in wetla... more Abstract. Low affinity methanotrophic bacteria consume a significant quantity of methane in wetland soils in the vicin-ity of plant roots and at the oxic-anoxic interface. Estimates of the efficiency of methanotrophy in peat soils vary widely in part because of differences in approaches employed to quantify methane cycling. High resolution profiles of dis-solved methane abundance measured during the summer of 2003 were used to quantity rates of upward methane flux in four peatlands situated in Wales, UK. Aerobic incubations of peat from a minerotrophic and an ombrotrophic mire were used to determine depth distributions of kinetic parameters associated with methane oxidation. The capacity for methan-otrophy in a 3 cm thick zone immediately beneath the depth of nil methane abundance in pore water was significantly greater than the rate of upward diffusion of methane in all

Geoscientific Model Development Discussions, 2017

Soil bacteria known as methanotrophs are the sole biological sink for atmospheric methane (CH<... more Soil bacteria known as methanotrophs are the sole biological sink for atmospheric methane (CH₄), a powerful greenhouse gas that is responsible for ~ 20 % of the human-driven increase in radiative forcing since pre-industrial times. Soil methanotrophy is controlled by a plethora of different factors, including temperature, soil texture and moisture or nitrogen content, resulting in spatially and temporally heterogeneous rates of soil methanotrophy. As a consequence, the exact magnitude of the global soil sink, as well as its temporal and spatial variability remains poorly constrained. We developed a process-based model (Methanotrophy Model; MeMo v1.0) to simulate and quantify the uptake of atmospheric CH₄ by soils on the global scale. MeMo builds on previous models by Ridgwell et al. (1999) and Curry (2007) by introducing several advances, including: (1) a general analytical solution of the one-dimensional diffusion-reaction...

Permafrost and Periglacial Processes, 2014

Permafrost peatlands are both an important source of atmospheric CH 4 and a substantial sink for ... more Permafrost peatlands are both an important source of atmospheric CH 4 and a substantial sink for atmospheric CO 2. Climate change can affect this balance, with higher temperatures resulting in the conversion of permafrost soils to wetlands and associated accelerated mineralisation and increased CH 4 emission. To better understand the impact of such processes on methanogen populations, we investigated the anaerobic decay of soil carbon in a low Arctic, discontinuous permafrost peatland. Cores were collected monthly from sedge and Sphagnum mires in north Sweden during the summer of 2006. We determined CH 4 concentrations and production potentials, together with variations in the size of the methanogenic community as indicated by concentrations of archaeal lipid biomarkers (phosphorylated archaeol, archaeol and hydroxyarchaeol). Concentrations of methanogen biomarkers generally were higher at the sedge site, increased with depth for all sites and months, and were usually below the detection limits in shallow (<10 cm) Sphagnum peat. The distribution of biomarkers reflects the strong influence of water table depth on anaerobic conditions and methanogen populations, while differences in biomarker concentrations can be explained by differences in vegetation cover and pH. However, methanogen populations inferred from biomarker data show a decoupling from in-situ CH 4 production over the season and from CH 4 production potential, suggesting that other factors such as the availability of labile organic substrates can influence methanogen abundance. Archaeal lipid biomarkers appear to offer a potential new means to investigate permafrost biogeochemical processes but the interpretation of signals remains complex.

ABSTRACT Whilst much attention is focused on CH4 emission inventories, CH4 sinks are sometimes ov... more ABSTRACT Whilst much attention is focused on CH4 emission inventories, CH4 sinks are sometimes overlooked and not accurately accounted for in national budgets. Two primary reasons for this disjunction include uncertainties about the magnitude and mechanism of terrestrial CH4 oxidation, and an under-appreciation of the quantity of CH4 that is removed from the atmosphere by microorganisms. These uncertainties in part are caused by a lack of high-resolution field data that quantify microbial soil CH4 sink. To fully characterize the soil CH4 sink, isotopic fractionation of CH4during uptake and the fate of CH4 carbon following oxidation by soil microorganisms should be quantified in addition to CH4 fluxes. Here we report on field tests studying CH4 uptake in soil using a Picarro G2201-i cavity ringdown spectrometer (CRDS). Short term atmospheric CH4 uptake was continuously measured in a forest soil in Leigh Woods, UK where the soil methanotrophic community and soil CH4 uptake kinetic isotopic effect (KIE) had been previously quantified using stable isotope probing and conventional stable isotope analysis techniques (Maxfield et al., 2008). Two methodological approaches were tested: (i) direct measurement of the soil CH4 uptake KIE at subambient CH4 concentrations, and (ii) methanotrophic carbon conversion efficiency (CCE) where CCE was evaluated through monitoring the direct conversion of 13C-labelled CH4 to 13C-labelled CO2. The suitability of the G2201-i analyzer as a continuous isotopic CH4 and CO2 analyzer for use at both subambient CH4 concentrations and high 13C-enrichments will be discussed. Maxfield, P.J., Evershed, R.P. and Hornibrook, E.R.C. (2008) Physical and biological controls on the in situ kinetic isotope effect associated with oxidation of atmospheric CH4 in mineral soils. Environmental Science &amp; Technology, 42, 7824-7830.

Andrew (2013). Reassessing the stable isotope composition assigned to methane flux from natural w... more Andrew (2013). Reassessing the stable isotope composition assigned to methane flux from natural wetlands in isotope-constrained budgets.

Wetland-adapted trees are known to transport and release soil-produced methane to the atmosphere ... more Wetland-adapted trees are known to transport and release soil-produced methane to the atmosphere through woody stem surfaces, yet the magnitude and controls of tree-mediated methane emissions remain unknown for mature forests. Although 60% of global wetlands are forested, and many tropical forests are either permanently or seasonally flooded, the ecosystem level contribution of tree-mediated methane flux relative to other gas transport pathways (e.g., ebullition, pore-water diffusion and via aerenchyma of herbaceous plants) has received limited attention. The role of trees as a conduit for methane export from soil to the atmosphere was assessed in situ in a temperate forested wetland (Flitwick Moor, UK) and tropical forested wetlands in Borneo, Indonesia and Amazonia, Brazil. Mesocosm experiments also were conducted in the temperate region to characterise emission characteristics of Alnus glutinosa saplings subjected to different water-table treatments. Methane emissions from trees were compared to fluxes from the soil surface in both the in situ and mesocosm studies. Temperate and tropical tree species both released significant quantities of methane from stem surfaces. Emission rates for young trees exceeded that of mature trees by several orders of magnitude on a stem surface area basis. Key factors controlling rates of tree-mediated flux were tree physiology (e.g., wood specific density, stem lenticel density), abiotic conditions (e.g., soil temperature) and methane gas transport mechanisms (e.g., passive diffusion, convective transport). Tree-mediated methane emissions contributed 6 to 87% of total ecosystem methane flux with the largest relative contribution from trees occurring in tropical wetlands. Recent data from Amazonian wetlands demonstrate very high rates of tree-mediated methane emission relative to other types of forested wetlands. These results indicate that exclusion of tree-mediated methane fluxes from measurement campaigns conducted in forested wetlands may result in a significant underestimate of total methane flux from such ecosystems.

Atlantic Geology, 1991

Drift prospecting surveys in New Brunswick have previously had limited success in recognizing dis... more Drift prospecting surveys in New Brunswick have previously had limited success in recognizing dispersal plumes through geochemical or mineralogical analyses of tills. This study was undertaken in the Todd Mountain - Trout Lake area of central New Brunswick to define possible constraints on glacial dispersal and assist in related prospecting activities. Dispersal patterns for specific heavy minerals in the silt to fine sand (0.125 mm - 0.250 mm) fraction of 63 till samples were investigated over a 12 km x 25 km area. Twelve minerals, confirmed by Scanning Electron Microscopy, were selected for study on the basis of local geology and ease of recognition. In this area of New Brunswick, eastward-trending dispersal plumes can be distinguished over short distances (<5 km) only for rare indicator minerals that characterize specific sources (e.g., coticules or zircon grains). When sampled at intervals of 100 m the mineral dispersal patterns more clearly reflect the nature and trend of un...

Eos, Transactions American Geophysical Union, 2004

Sedimentary Geology, 1994

ABSTRACT Polished epoxy grain mounts are commonly used for optical analyses of the heavy mineral ... more ABSTRACT Polished epoxy grain mounts are commonly used for optical analyses of the heavy mineral fraction of unconsolidated sediments. Yet there has been limited discussion of contamination particular to the preparation of epoxy grain mounts. Examination of 116 thin sections under transmitted and reflected light revealed tin—lead and diamond paste contamination in mineral samples from till collected in central New Brunswick. The contamination was found as fracture infillings and as a separate opaque phase with inclusions of other material. Although it has a striking resemblance to naturally occurring mineralization, the contamination was found to have been introduced during the lapping stage of the preparation of the grain mounts. Such contamination must be expected and identified as a preliminary step in heavy mineral analysis. Misidentification of this contamination could result in erroneous conclusions of syngenesis between it and resistant mineral content of the sample. This could be especially problematic in studies of garnet or sulfide mineralogy.

Rapid Communications in Mass Spectrometry, 2012

2012 Stable isotope switching (SIS): a new stable isotope probing (SIP) approach to determine car... more 2012 Stable isotope switching (SIS): a new stable isotope probing (SIP) approach to determine carbon flow in the soil food web and dynamics in organic matter pools. Rapid Communications in Mass Spectrometry, 26 (8).

Proceedings of the Royal Society B: Biological Sciences, 2009

It has been proposed that plants are capable of producing methane by a novel and unidentified bio... more It has been proposed that plants are capable of producing methane by a novel and unidentified biochemical pathway. Emission of methane with an apparently biological origin was recorded from both whole plants and detached leaves. This was the first report of methanogenesis in an aerobic setting, and was estimated to account for 10–45 per cent of the global methane source. Here, we show that plants do not contain a known biochemical pathway to synthesize methane. However, under high UV stress conditions, there may be spontaneous breakdown of plant material, which releases methane. In addition, plants take up and transpire water containing dissolved methane, leading to the observation that methane is released. Together with a new analysis of global methane levels from satellite retrievals, we conclude that plants are not a major source of the global methane production.

Isotopes in Environmental and Health Studies, 2000

Much uncertainty still exists regarding spatial and temporal variability of stable isotope ratios... more Much uncertainty still exists regarding spatial and temporal variability of stable isotope ratios (13C/12C and D/H) in different CH4-emission sources. Such variability is especially prevalent in freshwater wetlands where a range of processes can influence stable isotope compositions, resulting in variations of up to approximately 50% for delta13C-CH4 and approximately 50% for deltaD-CH4 values. Within a temperate-zone bog and marsh situated in southwestern Ontario, Canada, gas bubbles in pond sediments exhibit only minor seasonal and spatial variation in delta13C-CH4, deltaD-CH4 and delta13C-CO2 values. In pond sediments, CO2 appears to be the main source of carbon during methanogenesis either directly via CO2 reduction or indirectly through dissimilation of autotrophic acetate. In contrast, CH4 production occurs primarily via acetate fermentation at shallow depths in peat soils adjacent to ponds at each wetland. At greater depths within soils, sigmaCO2 and H2O increasingly exert an influence on delta13C- and deltaD-CH4 values. Secondary alteration processes (e.g., methanotrophy or diffusive transport) are unlikely to be responsible for depth-related changes in stable isotope values of CH4. Recent models that attempt to predict deltaD-CH4 values in freshwater environments from D/H ratios in local precipitation do not adequately account for such changes with depth. Subenvironments (i.e., soil-forming and open water areas) in wetlands should be considered separately with respect to stable isotope signatures in CH4 emission models.

Geomicrobiology Journal, 2008

... [CrossRef], [Web of Science ®] View all references; Mastalerz et al. 200737. Mastalerz, V, de... more ... [CrossRef], [Web of Science ®] View all references; Mastalerz et al. 200737. Mastalerz, V, de Lange, G, Dahlmann, A and Feseker, T. 2007. Active venting at Isis mud volcano, offshore Egypt: origin and migration of 2 hydrocarbons. Chemical Geology , 246(1–2): 87–106. ...

Geochimica et Cosmochimica Acta, 2007

Mud volcanism in the Gulf of Cadiz occurs over a large area extending from the shelf to more than... more Mud volcanism in the Gulf of Cadiz occurs over a large area extending from the shelf to more than 3500 m water depth and is triggered by compressional stress along the European-African plate boundary, affecting a deeply faulted sedimentary sequence of locally more than 5 km thickness. The investigation of six active sites shows that mud volcano (MV) fluids, on average, are highly enriched in CH 4 , Li, B, and Sr and depleted in Mg, K, and Br. The purity of the fluids is largely controlled by the intensity of upward directed flow. Flow rates could be constrained by numerical modelling and vary between <0.05 and 15 cm yr À1. Application of dD-d 18 O systematics identifies clay mineral dehydration, most likely within Mesozoic and Tertiary shales and marls, as the major source of fluids. Hence, Cl and Na in the pore fluids are mostly depleted below seawater values, following a general trend of dilution. However, deviations from this trend occur and are likely caused by the dissolution of halite in evaporitic deposits. Other secondary processes overprinting the original fluid composition may occur along the flow path, such as dissolution of anhydrite or gypsum and/or the formation of calcite and dolomite. Different sources of fluids are also indicated by variations in 87 Sr/ 86 Sr, which range from 0.7086 to 0.7099 at the different sites. Dehydration may be induced primarily by overburden and tectonic compression; however, very high concentrations of Li and B, specifically at Captain Arutyunov MV (CAMV) indicate additional leaching at temperatures above 150°C, which could be explained by the injection of hot fluids along deep penetrating, major E-W strike-slip fault systems. This hypothesis is supported by the occurrence of generally thermogenic, but significantly CH 4-enriched, light volatile hydrocarbon gases at CAMV which cannot be explained by shallow microbial methanogenesis. Li and Li/B ratios from different types of hot and cold vents are used to infer that high temperature signals seem to be preserved at various cold vent locations and indicate a closer coupling of both systems in continental margin environments than outlined in previous studies.

Environmental Science & Technology, 2008

The amounts and δ 13 C values of CH 4 at subambient concentrations in soil gas were determined al... more The amounts and δ 13 C values of CH 4 at subambient concentrations in soil gas were determined along depth profiles in a U.K. grassland (Bronydd Mawr) and woodland (Leigh Woods). The data were used to determine in situ kinetic isotope effects (KIEs) associated with uptake of atmospheric CH 4 by highaffinity methanotrophic bacteria that inhabit soil. Three independent calculation approaches yielded similar mean KIEs of 1.0211 (0.0020 (n) 18) for Bronydd Mawr and 1.0219 (0.0010 (n) 24) for Leigh Woods. Soil methanotrophy KIEs were largely invariant among oak, beech, and pine forest soils of different ages at Leigh Woods but exhibited a statistically significant relationship with methanotroph biomass in individual plots at Bronydd Mawr and Leigh Woods quantified previously by 13 C stable isotope probing. This finding, albeit based upon a small data set, suggests that 13 C and 12 C partitioning associated with the global soil sink for atmospheric CH 4 may occur in part as a result of biological as well as physical processes. An accurate assessment of the relative importance of each process to the total KIE requires confirmation that significant partitioning of 13 CH 4 and 12 CH 4 occurs in pore spaces as a result of differences in diffusion rates.

AGU Fall Meeting Abstracts, Dec 1, 2018

ABSTRACT A range of culture-independent methods, has recently emerged to study environmental micr... more ABSTRACT A range of culture-independent methods, has recently emerged to study environmental microorganisms in situ[1]. One such method is phospholipid fatty acid (PLFA) analysis, wherein these ubiquitous membrane lipids provide a powerful tool for the study of unculturable soil microorganisms. PLFA analyses have been used to investigate the impacts of a wide range of environmental factors on the soil microbial community. An acknowledged shortcoming of the PLFAs approach is the lack the chemotaxonoic specificity, which restricts the ability of the method to probe the activities of specific functional groups of the microbial community selectively. However, the selectivity of PLFAs analyses can be enhanced by incubating soils with 13C- labelled substrates followed by gas chromatography-combustion-isotope ratio mass spectrometry to reveal the specific PLFAs incorporating the 13C-label. The application of this approach will be demonstrated through our recent work on methanotrophic bacteria in soils. We applied this approach initially to mineral soils[2] and then extended chemotaxonomic assessments by using a combination of 13C-labelled PLFAs and hopanoids [3]. We have used this approach to explore the properties of high affinity methanotrophs in a range of environments, investigating the relationship between methane oxidation rates and the nature and magnitude of the methanotrophic community for the first time[4,5] More recently we extended the technique using a novel time series 13C-labelling of PLFAs[6] to estimate the rate and progression of 13C- label incorporation and turnover of methanotrophic populations. This modified approach has been used to investigate the impacts of various environmental variables, e.g. soil type, vegetation cover and land use, on the methanotrophic biomass[7.8]. The unique nature of the 13CH4 as a gaseous substate/carbon source means that can be readily introduced into soils via a specific subset of the soil microbial biomass, thereby offering many opportunities for studying the fate of microbially fixed carbon in soils. This paper will review the techniques employed and results obtained from our new generation of pulse-chase experiments. References 1. Evershed et al., 2006, Curr. Opin. Biotech. 17, 72. 2. Bull et al., 2000, Nature 405, 175. 3. Crossman et al., 2005, Org. Geochem. 32, 359. 4. Crossman et al., 2006, Soil Biol. Biochem. 38, 983. 5. Crossman et al., 2004, Environ. Sci. Tech. 38, 1359. 6. Maxfield et al., 2006, Appl. Environ. Microbiol. 72, 3901. 7. Maxfield et al., 2008, Evviron. Microbiol. 10, 1917-1924. 8. Maxfield et al., in press Environ. Sci. Technol.

Abstract. Low affinity methanotrophic bacteria consume a significant quantity of methane in wetla... more Abstract. Low affinity methanotrophic bacteria consume a significant quantity of methane in wetland soils in the vicin-ity of plant roots and at the oxic-anoxic interface. Estimates of the efficiency of methanotrophy in peat soils vary widely in part because of differences in approaches employed to quantify methane cycling. High resolution profiles of dis-solved methane abundance measured during the summer of 2003 were used to quantity rates of upward methane flux in four peatlands situated in Wales, UK. Aerobic incubations of peat from a minerotrophic and an ombrotrophic mire were used to determine depth distributions of kinetic parameters associated with methane oxidation. The capacity for methan-otrophy in a 3 cm thick zone immediately beneath the depth of nil methane abundance in pore water was significantly greater than the rate of upward diffusion of methane in all

Geoscientific Model Development Discussions, 2017

Soil bacteria known as methanotrophs are the sole biological sink for atmospheric methane (CH<... more Soil bacteria known as methanotrophs are the sole biological sink for atmospheric methane (CH₄), a powerful greenhouse gas that is responsible for ~ 20 % of the human-driven increase in radiative forcing since pre-industrial times. Soil methanotrophy is controlled by a plethora of different factors, including temperature, soil texture and moisture or nitrogen content, resulting in spatially and temporally heterogeneous rates of soil methanotrophy. As a consequence, the exact magnitude of the global soil sink, as well as its temporal and spatial variability remains poorly constrained. We developed a process-based model (Methanotrophy Model; MeMo v1.0) to simulate and quantify the uptake of atmospheric CH₄ by soils on the global scale. MeMo builds on previous models by Ridgwell et al. (1999) and Curry (2007) by introducing several advances, including: (1) a general analytical solution of the one-dimensional diffusion-reaction...

Permafrost and Periglacial Processes, 2014

Permafrost peatlands are both an important source of atmospheric CH 4 and a substantial sink for ... more Permafrost peatlands are both an important source of atmospheric CH 4 and a substantial sink for atmospheric CO 2. Climate change can affect this balance, with higher temperatures resulting in the conversion of permafrost soils to wetlands and associated accelerated mineralisation and increased CH 4 emission. To better understand the impact of such processes on methanogen populations, we investigated the anaerobic decay of soil carbon in a low Arctic, discontinuous permafrost peatland. Cores were collected monthly from sedge and Sphagnum mires in north Sweden during the summer of 2006. We determined CH 4 concentrations and production potentials, together with variations in the size of the methanogenic community as indicated by concentrations of archaeal lipid biomarkers (phosphorylated archaeol, archaeol and hydroxyarchaeol). Concentrations of methanogen biomarkers generally were higher at the sedge site, increased with depth for all sites and months, and were usually below the detection limits in shallow (<10 cm) Sphagnum peat. The distribution of biomarkers reflects the strong influence of water table depth on anaerobic conditions and methanogen populations, while differences in biomarker concentrations can be explained by differences in vegetation cover and pH. However, methanogen populations inferred from biomarker data show a decoupling from in-situ CH 4 production over the season and from CH 4 production potential, suggesting that other factors such as the availability of labile organic substrates can influence methanogen abundance. Archaeal lipid biomarkers appear to offer a potential new means to investigate permafrost biogeochemical processes but the interpretation of signals remains complex.

ABSTRACT Whilst much attention is focused on CH4 emission inventories, CH4 sinks are sometimes ov... more ABSTRACT Whilst much attention is focused on CH4 emission inventories, CH4 sinks are sometimes overlooked and not accurately accounted for in national budgets. Two primary reasons for this disjunction include uncertainties about the magnitude and mechanism of terrestrial CH4 oxidation, and an under-appreciation of the quantity of CH4 that is removed from the atmosphere by microorganisms. These uncertainties in part are caused by a lack of high-resolution field data that quantify microbial soil CH4 sink. To fully characterize the soil CH4 sink, isotopic fractionation of CH4during uptake and the fate of CH4 carbon following oxidation by soil microorganisms should be quantified in addition to CH4 fluxes. Here we report on field tests studying CH4 uptake in soil using a Picarro G2201-i cavity ringdown spectrometer (CRDS). Short term atmospheric CH4 uptake was continuously measured in a forest soil in Leigh Woods, UK where the soil methanotrophic community and soil CH4 uptake kinetic isotopic effect (KIE) had been previously quantified using stable isotope probing and conventional stable isotope analysis techniques (Maxfield et al., 2008). Two methodological approaches were tested: (i) direct measurement of the soil CH4 uptake KIE at subambient CH4 concentrations, and (ii) methanotrophic carbon conversion efficiency (CCE) where CCE was evaluated through monitoring the direct conversion of 13C-labelled CH4 to 13C-labelled CO2. The suitability of the G2201-i analyzer as a continuous isotopic CH4 and CO2 analyzer for use at both subambient CH4 concentrations and high 13C-enrichments will be discussed. Maxfield, P.J., Evershed, R.P. and Hornibrook, E.R.C. (2008) Physical and biological controls on the in situ kinetic isotope effect associated with oxidation of atmospheric CH4 in mineral soils. Environmental Science &amp; Technology, 42, 7824-7830.

Andrew (2013). Reassessing the stable isotope composition assigned to methane flux from natural w... more Andrew (2013). Reassessing the stable isotope composition assigned to methane flux from natural wetlands in isotope-constrained budgets.

Wetland-adapted trees are known to transport and release soil-produced methane to the atmosphere ... more Wetland-adapted trees are known to transport and release soil-produced methane to the atmosphere through woody stem surfaces, yet the magnitude and controls of tree-mediated methane emissions remain unknown for mature forests. Although 60% of global wetlands are forested, and many tropical forests are either permanently or seasonally flooded, the ecosystem level contribution of tree-mediated methane flux relative to other gas transport pathways (e.g., ebullition, pore-water diffusion and via aerenchyma of herbaceous plants) has received limited attention. The role of trees as a conduit for methane export from soil to the atmosphere was assessed in situ in a temperate forested wetland (Flitwick Moor, UK) and tropical forested wetlands in Borneo, Indonesia and Amazonia, Brazil. Mesocosm experiments also were conducted in the temperate region to characterise emission characteristics of Alnus glutinosa saplings subjected to different water-table treatments. Methane emissions from trees were compared to fluxes from the soil surface in both the in situ and mesocosm studies. Temperate and tropical tree species both released significant quantities of methane from stem surfaces. Emission rates for young trees exceeded that of mature trees by several orders of magnitude on a stem surface area basis. Key factors controlling rates of tree-mediated flux were tree physiology (e.g., wood specific density, stem lenticel density), abiotic conditions (e.g., soil temperature) and methane gas transport mechanisms (e.g., passive diffusion, convective transport). Tree-mediated methane emissions contributed 6 to 87% of total ecosystem methane flux with the largest relative contribution from trees occurring in tropical wetlands. Recent data from Amazonian wetlands demonstrate very high rates of tree-mediated methane emission relative to other types of forested wetlands. These results indicate that exclusion of tree-mediated methane fluxes from measurement campaigns conducted in forested wetlands may result in a significant underestimate of total methane flux from such ecosystems.

Atlantic Geology, 1991

Drift prospecting surveys in New Brunswick have previously had limited success in recognizing dis... more Drift prospecting surveys in New Brunswick have previously had limited success in recognizing dispersal plumes through geochemical or mineralogical analyses of tills. This study was undertaken in the Todd Mountain - Trout Lake area of central New Brunswick to define possible constraints on glacial dispersal and assist in related prospecting activities. Dispersal patterns for specific heavy minerals in the silt to fine sand (0.125 mm - 0.250 mm) fraction of 63 till samples were investigated over a 12 km x 25 km area. Twelve minerals, confirmed by Scanning Electron Microscopy, were selected for study on the basis of local geology and ease of recognition. In this area of New Brunswick, eastward-trending dispersal plumes can be distinguished over short distances (<5 km) only for rare indicator minerals that characterize specific sources (e.g., coticules or zircon grains). When sampled at intervals of 100 m the mineral dispersal patterns more clearly reflect the nature and trend of un...

Eos, Transactions American Geophysical Union, 2004

Sedimentary Geology, 1994

ABSTRACT Polished epoxy grain mounts are commonly used for optical analyses of the heavy mineral ... more ABSTRACT Polished epoxy grain mounts are commonly used for optical analyses of the heavy mineral fraction of unconsolidated sediments. Yet there has been limited discussion of contamination particular to the preparation of epoxy grain mounts. Examination of 116 thin sections under transmitted and reflected light revealed tin—lead and diamond paste contamination in mineral samples from till collected in central New Brunswick. The contamination was found as fracture infillings and as a separate opaque phase with inclusions of other material. Although it has a striking resemblance to naturally occurring mineralization, the contamination was found to have been introduced during the lapping stage of the preparation of the grain mounts. Such contamination must be expected and identified as a preliminary step in heavy mineral analysis. Misidentification of this contamination could result in erroneous conclusions of syngenesis between it and resistant mineral content of the sample. This could be especially problematic in studies of garnet or sulfide mineralogy.

Rapid Communications in Mass Spectrometry, 2012

2012 Stable isotope switching (SIS): a new stable isotope probing (SIP) approach to determine car... more 2012 Stable isotope switching (SIS): a new stable isotope probing (SIP) approach to determine carbon flow in the soil food web and dynamics in organic matter pools. Rapid Communications in Mass Spectrometry, 26 (8).

Proceedings of the Royal Society B: Biological Sciences, 2009

It has been proposed that plants are capable of producing methane by a novel and unidentified bio... more It has been proposed that plants are capable of producing methane by a novel and unidentified biochemical pathway. Emission of methane with an apparently biological origin was recorded from both whole plants and detached leaves. This was the first report of methanogenesis in an aerobic setting, and was estimated to account for 10–45 per cent of the global methane source. Here, we show that plants do not contain a known biochemical pathway to synthesize methane. However, under high UV stress conditions, there may be spontaneous breakdown of plant material, which releases methane. In addition, plants take up and transpire water containing dissolved methane, leading to the observation that methane is released. Together with a new analysis of global methane levels from satellite retrievals, we conclude that plants are not a major source of the global methane production.

Isotopes in Environmental and Health Studies, 2000

Much uncertainty still exists regarding spatial and temporal variability of stable isotope ratios... more Much uncertainty still exists regarding spatial and temporal variability of stable isotope ratios (13C/12C and D/H) in different CH4-emission sources. Such variability is especially prevalent in freshwater wetlands where a range of processes can influence stable isotope compositions, resulting in variations of up to approximately 50% for delta13C-CH4 and approximately 50% for deltaD-CH4 values. Within a temperate-zone bog and marsh situated in southwestern Ontario, Canada, gas bubbles in pond sediments exhibit only minor seasonal and spatial variation in delta13C-CH4, deltaD-CH4 and delta13C-CO2 values. In pond sediments, CO2 appears to be the main source of carbon during methanogenesis either directly via CO2 reduction or indirectly through dissimilation of autotrophic acetate. In contrast, CH4 production occurs primarily via acetate fermentation at shallow depths in peat soils adjacent to ponds at each wetland. At greater depths within soils, sigmaCO2 and H2O increasingly exert an influence on delta13C- and deltaD-CH4 values. Secondary alteration processes (e.g., methanotrophy or diffusive transport) are unlikely to be responsible for depth-related changes in stable isotope values of CH4. Recent models that attempt to predict deltaD-CH4 values in freshwater environments from D/H ratios in local precipitation do not adequately account for such changes with depth. Subenvironments (i.e., soil-forming and open water areas) in wetlands should be considered separately with respect to stable isotope signatures in CH4 emission models.

Geomicrobiology Journal, 2008

... [CrossRef], [Web of Science ®] View all references; Mastalerz et al. 200737. Mastalerz, V, de... more ... [CrossRef], [Web of Science ®] View all references; Mastalerz et al. 200737. Mastalerz, V, de Lange, G, Dahlmann, A and Feseker, T. 2007. Active venting at Isis mud volcano, offshore Egypt: origin and migration of 2 hydrocarbons. Chemical Geology , 246(1–2): 87–106. ...

Geochimica et Cosmochimica Acta, 2007

Mud volcanism in the Gulf of Cadiz occurs over a large area extending from the shelf to more than... more Mud volcanism in the Gulf of Cadiz occurs over a large area extending from the shelf to more than 3500 m water depth and is triggered by compressional stress along the European-African plate boundary, affecting a deeply faulted sedimentary sequence of locally more than 5 km thickness. The investigation of six active sites shows that mud volcano (MV) fluids, on average, are highly enriched in CH 4 , Li, B, and Sr and depleted in Mg, K, and Br. The purity of the fluids is largely controlled by the intensity of upward directed flow. Flow rates could be constrained by numerical modelling and vary between <0.05 and 15 cm yr À1. Application of dD-d 18 O systematics identifies clay mineral dehydration, most likely within Mesozoic and Tertiary shales and marls, as the major source of fluids. Hence, Cl and Na in the pore fluids are mostly depleted below seawater values, following a general trend of dilution. However, deviations from this trend occur and are likely caused by the dissolution of halite in evaporitic deposits. Other secondary processes overprinting the original fluid composition may occur along the flow path, such as dissolution of anhydrite or gypsum and/or the formation of calcite and dolomite. Different sources of fluids are also indicated by variations in 87 Sr/ 86 Sr, which range from 0.7086 to 0.7099 at the different sites. Dehydration may be induced primarily by overburden and tectonic compression; however, very high concentrations of Li and B, specifically at Captain Arutyunov MV (CAMV) indicate additional leaching at temperatures above 150°C, which could be explained by the injection of hot fluids along deep penetrating, major E-W strike-slip fault systems. This hypothesis is supported by the occurrence of generally thermogenic, but significantly CH 4-enriched, light volatile hydrocarbon gases at CAMV which cannot be explained by shallow microbial methanogenesis. Li and Li/B ratios from different types of hot and cold vents are used to infer that high temperature signals seem to be preserved at various cold vent locations and indicate a closer coupling of both systems in continental margin environments than outlined in previous studies.

Environmental Science & Technology, 2008

The amounts and δ 13 C values of CH 4 at subambient concentrations in soil gas were determined al... more The amounts and δ 13 C values of CH 4 at subambient concentrations in soil gas were determined along depth profiles in a U.K. grassland (Bronydd Mawr) and woodland (Leigh Woods). The data were used to determine in situ kinetic isotope effects (KIEs) associated with uptake of atmospheric CH 4 by highaffinity methanotrophic bacteria that inhabit soil. Three independent calculation approaches yielded similar mean KIEs of 1.0211 (0.0020 (n) 18) for Bronydd Mawr and 1.0219 (0.0010 (n) 24) for Leigh Woods. Soil methanotrophy KIEs were largely invariant among oak, beech, and pine forest soils of different ages at Leigh Woods but exhibited a statistically significant relationship with methanotroph biomass in individual plots at Bronydd Mawr and Leigh Woods quantified previously by 13 C stable isotope probing. This finding, albeit based upon a small data set, suggests that 13 C and 12 C partitioning associated with the global soil sink for atmospheric CH 4 may occur in part as a result of biological as well as physical processes. An accurate assessment of the relative importance of each process to the total KIE requires confirmation that significant partitioning of 13 CH 4 and 12 CH 4 occurs in pore spaces as a result of differences in diffusion rates.