Papers by Burke, A. Roger
Organic Geochemistry, 1997
ÐSimultaneous mass spectral detection and stable carbon isotope analysis was performed on individ... more ÐSimultaneous mass spectral detection and stable carbon isotope analysis was performed on individual indigenous n-alkanes isolated from single C 4 and C 3 plant species and on a series of aliphatic and polycyclic aromatic hydrocarbons (PAH) produced from the combustion of these same biomass materials. The analysis technique used a combined gas chromatograph±mass spectrometer/combustion/ isotope ratio mass spectrometer (GC±MS/C/IRMS). Precision (2s) for replicate measurements of individual compounds in standard solutions using this novel con®guration ranged between 0.2 and 0.5for n-alkanes and 0.3 and 0.8-for PAH. Accuracy of the n-alkane measurements ranged between 0.1 and 0.4-and that of the PAH measurements ranged between 0.2 and 0.9-. Replicate GC±MS/C/ IRMS measurements on the combustion-derived n-alkene/alkane pairs were performed to within a precision of between 0.1 and 1.1-and the precision for the combustion PAH was similar to the standard PAH solution. No notable isotopic eects were observed when altering the temperature of the combustion process from 900 to 7008C, or as a result of the individual n-alkenes/alkanes partitioning between the gaseous and condensate fractions. Combustion-derived n-alkenes/alkanes ranged from C 11 to C 31 , and the C 4-derived n-alkenes/alkanes were approx. 8-more enriched in 13 C than the C 3-derived compounds. Both the C 4 and C 3-derived n-alkenes/alkanes (C 20 ±C 30) were isotopically similar to the indigenous n-alkanes and were 2±3-more depleted in 13 C than the lower mol. wt (C 11 ±C 19) n-alkenes/ alkanes, suggesting an independent origin for the lower mol. wt compounds. Combustion-generated C 4 and C 3-derived 2-, 3-, and 4-ring PAH were also isotopically distinct (Dd = 10-). Unlike the nalkenes/alkanes, no compound-to-compound variations were observed between the low and high mol. wt PAH. This study demonstrates that the isotopic composition of original plant biomass material is mainly preserved in the aliphatic hydrocarbons and PAH generated by its combustion. Consequently, analyses of these compounds in sediments impacted by ®re occurrences may provide useful information about paleo-®re activity that may help elucidate the impact biomass burning may have had and could have on climate±biosphere interactions.
Organic Geochemistry, 1997
ÐSimultaneous mass spectral detection and stable carbon isotope analysis was performed on individ... more ÐSimultaneous mass spectral detection and stable carbon isotope analysis was performed on individual indigenous n-alkanes isolated from single C 4 and C 3 plant species and on a series of aliphatic and polycyclic aromatic hydrocarbons (PAH) produced from the combustion of these same biomass materials. The analysis technique used a combined gas chromatograph±mass spectrometer/combustion/ isotope ratio mass spectrometer (GC±MS/C/IRMS). Precision (2s) for replicate measurements of individual compounds in standard solutions using this novel con®guration ranged between 0.2 and 0.5for n-alkanes and 0.3 and 0.8-for PAH. Accuracy of the n-alkane measurements ranged between 0.1 and 0.4-and that of the PAH measurements ranged between 0.2 and 0.9-. Replicate GC±MS/C/ IRMS measurements on the combustion-derived n-alkene/alkane pairs were performed to within a precision of between 0.1 and 1.1-and the precision for the combustion PAH was similar to the standard PAH solution. No notable isotopic eects were observed when altering the temperature of the combustion process from 900 to 7008C, or as a result of the individual n-alkenes/alkanes partitioning between the gaseous and condensate fractions. Combustion-derived n-alkenes/alkanes ranged from C 11 to C 31 , and the C 4-derived n-alkenes/alkanes were approx. 8-more enriched in 13 C than the C 3-derived compounds. Both the C 4 and C 3-derived n-alkenes/alkanes (C 20 ±C 30) were isotopically similar to the indigenous n-alkanes and were 2±3-more depleted in 13 C than the lower mol. wt (C 11 ±C 19) n-alkenes/ alkanes, suggesting an independent origin for the lower mol. wt compounds. Combustion-generated C 4 and C 3-derived 2-, 3-, and 4-ring PAH were also isotopically distinct (Dd = 10-). Unlike the nalkenes/alkanes, no compound-to-compound variations were observed between the low and high mol. wt PAH. This study demonstrates that the isotopic composition of original plant biomass material is mainly preserved in the aliphatic hydrocarbons and PAH generated by its combustion. Consequently, analyses of these compounds in sediments impacted by ®re occurrences may provide useful information about paleo-®re activity that may help elucidate the impact biomass burning may have had and could have on climate±biosphere interactions.
Hydrobiologia, Sep 4, 2009
Page 1. PRIMARY RESEARCH PAPER Effects of land use on dissolved organic matter biogeochemistry in... more Page 1. PRIMARY RESEARCH PAPER Effects of land use on dissolved organic matter biogeochemistry in piedmont headwater streams of the Southeastern United States Jon Molinero Æ Roger A. Burke Received: 9 July 2007 ...
We have been measuring concentrations of the trace gases nitrous oxide (N2O), methane (CH4), and ... more We have been measuring concentrations of the trace gases nitrous oxide (N2O), methane (CH4), and carbon dioxide (CO2) and other parameters in 17 headwater streams within the South Fork Broad River (SFBR) watershed on a monthly basis since January 2001. Land use within each watershed was calculated from the National Land Cover Data (NLCD) database. The concentrations of all three
We monitored concentrations of dissolved organic carbon (DOC) and dissolved oxygen (DO), and othe... more We monitored concentrations of dissolved organic carbon (DOC) and dissolved oxygen (DO), and other parameters in 17 small streams of the South Fork Broad River watershed on a monthly basis for 15 months. We observed a strong inverse relationship between mean DOC and mean DO, and low DO concentrations (2 mg/L) during summer in some of the streams. Elevated DOC levels and corresponding low DO may result from watershed sources of organic wastes and/or nutrients. Potential sources of watershed organic wastes include animal manure applied to the land and/or human wastes from wastewater treatment plants or septic tanks. Here we present estimates of the amounts of organic waste input to these watersheds and evaluate the possible impact of the waste on stream DOC concentrations. Our results suggest that application of poultry litter at recommended rates may impact stream DOC levels if applied to a high enough percentage of the watershed land area. We also present a few measurements of the stable nitrogen isotope ratio of plants growing in the channel and of potential denitrification rate in the sediments of a few of these streams on a few dates shortly after the monthly monitoring ended. These preliminary results suggest that stable nitrogen isotope ratios and potential denitrification rates are positively correlated with estimates of stream watershed human waste loading and thus are potentially effective indicators of waste contamination in these watersheds. In some cases, stable isotopic, potential denitrification rate, and other biogeochemical indicators of organic waste and/or nutrient contamination may be useful to regulators and managers charged with protecting water quality.
We have been sampling nutrient concentrations in 17 headwater streams within the South Fork Broad... more We have been sampling nutrient concentrations in 17 headwater streams within the South Fork Broad River (SFBR) watershed on a monthly basis since November 2001. The streams were classified as either developed (n=4), agriculture/pasture (n=4), mixed land use (n=6) or forested (n=3) based on information from the National Land Cover Data (NLCD) database. The lowest mean nitrogen concentrations were observed in streams draining forested watersheds. A set of landscape indicators explained 93 % of the spatial variability in the total nitrogen concentrations which suggests that watershed land use has an important effect on stream nitrogen levels. Total phosphorus varied seasonally at some of the sites, with high concentrations observed during the summer and low concentrations in winter. Only 4 out of 14 non-forested sites showed higher mean total phosphorus concentrations and no relationships were found between the landscape indicators and the total phosphorus concentrations in the streams...
Hydrogen- and carbon-isotope compositions of methane (δ D-CH4 and δ13C-CH4) and pore water hydrog... more Hydrogen- and carbon-isotope compositions of methane (δ D-CH4 and δ13C-CH4) and pore water hydrogen-isotope compositions (δD-H2O) in several samples from the uppermost 100 m of Orca Basin sediments show little variation with depth and have mean values of - 184, -73.5, and 7‰, respectively. The δD-CH4 is typical of that generally found in deep-sea sediments and suggests that the methane was produced biologically almost entirely via the CO2 reduction pathway. Production of small amounts of methane (-15% of the total) from acetate dissimilation cannot be com- pletely ruled out, however. The pore water is more enriched in deuterium than present day Gulf of Mexico deep water, suggesting that the brine found at the bottom of Orca Basin was formed at a time when appreciably more isotopically light water was tied up in continental ice sheets than is at present. The δ13C-CH4 values reported here are similar to pre- viously determined brine δ13C-CH4, but substantially more enriched in 13C tha...
Marine Ecology Progress Series
Methane seeps in shallow waters In the northern Kattegat off the Danish coast form spectacular su... more Methane seeps in shallow waters In the northern Kattegat off the Danish coast form spectacular submarine landscapes - the 'bubbling reefs' - due to carbonate-cemented sandstone structures which are colonized by brightly coloured animals and plants. These structures may be 100 m2 in area and consist of pavements, complex formations of overlying slab-type layers, and pillars up to 4 m high. The carbonate cement (high-magnesium calcite, dolomite or aragonite) is 13C-depleted, indicating that it originated as a result of microbial methane oxidation. It is believed that the cementation occurred in the subsurface and that the rocks were exposed by subsequent erosion of the surrounding unconsolidated sediment. The formations are interspersed with gas vents that intermittently release gas, primarily methane, at up to 25 1 h-1. The methane most likely originated from the microbial decomposition of plant material deposited during the Eemian and early Weichselian periods, i.e. l00 000 ...
The BOReal Ecosystem-Atmosphere Study Trace Gas Biogeochemistry (BOREAS TGB-5) team collected a v... more The BOReal Ecosystem-Atmosphere Study Trace Gas Biogeochemistry (BOREAS TGB-5) team collected a variety of trace gas concentration and flux measurements at several NSA sites. This data set contains carbon dioxide (CO2), methane (CH4), and carbon monoxide (CO) chamber flux measurements conducted in 1994 at upland forest sites that experienced stand-replacement fires. These measurements were acquired to understand the impact of fires on soil biogeochemistry and related changes in trace gas exchange in boreal forest soils. Relevant ancillary data, including data concerning the soil temperature, solar irradiance, and information from nearby un-burned control sites, are included to provide a basis for modeling the regional impacts of fire and climate changes on trace gas biogeochemistry. The data are provided in tabular ASCII files.
Ciencias Marinas, 2013
An unusual combination of features makes the Midriff Islands region of the northern Gulf of Calif... more An unusual combination of features makes the Midriff Islands region of the northern Gulf of California (NGC) a strong atmospheric methane source. Oceanographic isolation by a series of sills and islands along with upward transport of nutrient-rich water enhanced by tidal currents, upwelling, and overflows results in high productivity. The resulting high phytoplankton biomass likely stimulates biogeochemical cycling that, in turn, may stimulate biological methane production in the water column and sediments. Additionally, venting of abiogenic methane-rich hydrothermal fluids in this tectonically active area and seepage of biogenic or thermogenic methane gas from the sediments may also be important sources. We found elevated methane concentrations throughout our study area, the highest within the Ballenas Channel, which was supersaturated with respect to atmospheric methane at all depths. Our vertical methane profiles show that elevated dissolved methane concentrations in the NGC are mainly associated with Gulf of California Water (GCW). Data from 22 stations suggest southward advection of methane via the methane-rich GCW, and lower methane concentrations south of the sills area. Our observations of supersaturated methane concentrations at all stations and all depths in the Ballenas Channel suggest that it is a strong source of methane to the atmosphere and to other parts of the NGC. In particular, station 7 at 50, 20, and 0 m depths had methane (CH 4) concentrations of 49.1, 48.3, and 43.5 nM, respectively, corresponding to saturation values of 2090%, 2050%, and 1850%, respectively. Our calculated NGC fluxes ranged from 3.4 to 103.4 mol CH 4 m-2 d-1. The average methane flux calculated for our entire study area was 21.1 mol CH 4 m-2 d-1. These values are higher than those measured at many other high productivity sites worldwide including upwelling sites, and suggest input of methane via hydrothermal fluids or seepage from the sediments.
Eos, Transactions American Geophysical Union, 1990
Seafloor oil seepage on the continental slope of the Gulf of Mexico drives a number of distinct b... more Seafloor oil seepage on the continental slope of the Gulf of Mexico drives a number of distinct biological, chemical and geological processes. Macroseepage of oil and gas controls the extent and distribution of chemosynthetic ``oil seep'' communities, the seafloor configuration, ...
Limnology and Oceanography, 1983
Page 1. Limnol. Oceanogr., 28(1), 1983, 19-32 © 1983, by the American Society of Limnology and Oc... more Page 1. Limnol. Oceanogr., 28(1), 1983, 19-32 © 1983, by the American Society of Limnology and Oceanography, Inc. Upper water column methane geochemistry in the eastern tropical North Pacific1 Roger A. Burke, Jr.2 Department ...
Water, Air, & Soil Pollution, 2014
ABSTRACT We measured C and N cycling indicators in Appalachian watersheds impacted by mountaintop... more ABSTRACT We measured C and N cycling indicators in Appalachian watersheds impacted by mountaintop removal and valley fill (MTR/VF) coal mining, and in nearby forested watersheds. These watersheds include ephemeral, intermittent, and perennial stream reaches, and the length of time since disturbance in the MTR/VF watersheds was 5 to 11 years. In forest soils compared to VF soils, both denitrification enzyme activity (DEA) and basal respiration (BR) were elevated (factor of 6 for DEA and factor of 1.8 for BR expressed on a weight basis) and bulk density was lower. Organic matter (OM) and moisture were higher in the forest soils, which likely contributed to the elevated DEA and BR levels. Evaluation of soils data from our intermittent watersheds as a chronosequence provides some evidence of soil quality (DEA, BR, and soil moisture) improvement over the course of a decade, at least in the top 5 cm. Across the hydrological permanence gradient, sediment DEA was significantly higher (factor of 1.6) and sediment OM was significantly lower in forested than in VF watersheds, whereas sediment BR did not differ between forested and VF watersheds. Dissolved organic carbon (DOC) concentrations were not different in mining-impacted and forested streams, whereas dissolved inorganic carbon (DIC) concentrations and DOC and DIC stable carbon isotopic compositions ( δ13C) were significantly elevated in VF streams. The δ13C-DIC values indicate that carbonate dissolution was a dominant source of dissolved carbon in MTR/VF mining-impacted streams. The disturbance associated with MTR/VF mining significantly impacts C and N processing in soils, stream sediments, and stream water although our data suggests some improvement of soil quality during the first decade of reclamation.
Tellus B, 1998
Dark or low-light carbon monoxide fluxes at upland Canadian boreal forest sites were measured on-... more Dark or low-light carbon monoxide fluxes at upland Canadian boreal forest sites were measured on-site with static chambers and with a laboratory incubation technique using cores from different depths at the same sites. Three different upland black spruce sites, burned in 1987, 1992 and 1995 and a control site, were chosen to determine the effects of fire, temperature, soil structure and soil covers on CO fluxes. Three different surfaces were observed at the sitesbare mineral soil with little living moss cover; burned feather mosses 5-30 cm deep; and unburned, living, green feather mosses. The static chamber measurements indicated similar deposition velocities for the burned and unburned feather moss sites [(1.54±0.64)Ω 10−2 cm s−1; (1.83±0.63)Ω10−2 cm s−1], but significantly lower rates for sites that had burned down to the mineral soil [(1.08±0.53)Ω10−2 cm s−1, excluding data with net CO emission]. This finding was confirmed by results from the incubation measurements and shows that fire intensities determine the long-term, post-fire effect on soil-atmosphere fluxes of CO. Temperature studies with the cores showed that CO consumption rates increased from (2±1)% at −15°C to −13°C to (43±20)% at 0°C to 1.5°C and (68±15)% at 4°C to 5°C of the deposition velocity values obtained at 20°C. This temperature dependence was consistent with results obtained from the static chamber measurements. The temperature range studied and the dark or low-light conditions were representative for the night-time of nearly the whole six snow-free months in the boreal ecosystem. In nearly all cases, deposition velocities determined for cores from the top 5 cm with the incubation technique were the same, within experimental errors, as those determined with the static chambers. Soil CO concentration profiles taken in situ, moreover, did not show any clear trend below 5 cm. Thus we conclude that the top 5 cm of soils are determining the dark soil-atmosphere CO fluxes at these sites. The top 5 cm of soil columns are most exposed to temperature (and probably moisture) variations and are most affected by fires as well.
Pesquisa Agropecuária Brasileira, 2011
The objective of this work was to evaluate the effects of fire regimes and vegetation cover on th... more The objective of this work was to evaluate the effects of fire regimes and vegetation cover on the structure and dynamics of soil microbial communities, through phospholipid fatty acid (PLFA) analysis. Comparisons were made between native areas with different woody covers ("cerrado stricto sensu" and "campo…
Nature Communications, 2013
A recent review concluded that earthworm presence increases CO 2 emissions by 33% but does not af... more A recent review concluded that earthworm presence increases CO 2 emissions by 33% but does not affect soil organic carbon stocks. However, the findings are controversial and raise new questions. Here we hypothesize that neither an increase in CO 2 emission nor in stabilized carbon would entirely reflect the earthworms' contribution to net carbon sequestration. We show how two widespread earthworm invaders affect net carbon sequestration through impacts on the balance of carbon mineralization and carbon stabilization. Earthworms accelerate carbon activation and induce unequal amplification of carbon stabilization compared with carbon mineralization, which generates an earthworm-mediated 'carbon trap'. We introduce the new concept of sequestration quotient to quantify the unequal processes. The patterns of CO 2 emission and net carbon sequestration are predictable by comparing sequestration quotient values between treatments with and without earthworms. This study clarifies an ecological mechanism by which earthworms may regulate the terrestrial carbon sink.
Marine Ecology Progress Series, 1991
At a large North Sea pockmark, with active methane seeps, surface sediments were found to have hi... more At a large North Sea pockmark, with active methane seeps, surface sediments were found to have higher insoluble sulphide concentrations than sedlments from the surrounding area. The fauna of the pockmark was characterized by 2 species which have not pi-evlously been reported from the Fladen Ground in the northern North Sea. These species were a b~valve, Thyasira sarsi (which is known to contain endosymbiotic sulphur-oxidising bacteria) and a mouthless and gutless nematode, Astomonerna sp., which also contains endosymbiotic bacteria The nematode was the dominant meiofauna species in the pockmark sediments. Both macro-lnfauna and total nematodes were in low abundance in samples taken from the base of the pockmark. Sediment samples from the pockmark contained numerous otoliths, implying that substantial winnowing of the sediment had taken place. This was supported by studies on the sulphide concentrations in the sediment which showed multiple layering of the sediments on the sides of the pockmark, suggesting displacement. The carbon isotope compositions (6I3c) of the tissues of benthic animals from in and around the pockmark were generally in the range-16 to-2O%, indicating that little methane-derived carbon was contributing to their nutrition. T sarsi had the most 13c-depleted tissues,-31.4 to-35.1 L, confirming the nutritional dependence of this species on chemoautotrophic bacteria that utilize reduced sulphur
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Papers by Burke, A. Roger