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At least 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

CO2 and CH4 leaf-level fluxes and soil porewater concentrations from common vegetation patches in Louisiana’s coastal wetlands

This dataset contains leaf-level flux and soil porewater concentration measurements of carbon dioxide (CO2) and methane (CH4 ) in plots in the footprint of Ameriflux sites US-LA2 and US-LA3. Leaf fluxes in US-LA2 were measured on patches dominated by Sagittaria lancifolia and co-dominated by Sagittaria lancifolia and Typha latifolia. In US-LA3, fluxes were measured from distinct Juncus roemerianus and Spartina alterniflora patches. The porewater concentrations were collected across a vertical profile (~50 cm depth) at centric locations within 25 m2 plots where we measured the leaf fluxes. US-LA3 included an additional set of measurements in open water spots. We aimed to evaluate differences in leaf fluxes and porewater pools of CO2 and CH4 of representative ecohydrological patches across a salinity gradient. We also used this dataset to help develop ELM-Wet, a more realistic representation of wetland carbon biogeochemical processes within the U.S. Department of Energy’s Energy Exascale Earth System Model (E3SM) Land Model version 1 (ELM v.1). The files can be opened with regular text editors or spreadsheet programs. Version 2.0 (8/26/2025): This is the latest version of this dataset. The update includes additional samples of soil porewater CH4/CO2 concentrations from June-2021 to November-2022, as well as minor adjustments made to V1 samples via changing Henry's solubility to account for porewater salinity. Additionally leaf-level measurments of spectral indices, PSRI, NDVI, and PRI have been added to complement Leaf-level flux measurements. All V1 data sets have been integrated into V2 sheets, ensuring data from the previous version is contained with the additional samples and consistent with V2 metadata.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2024

Patch-level CO2 and CH4 fluxes and porewater concentrations in experimental wetlands, 2 PPT saltwater intrusion simulations, Aug-Oct 2022: Louisiana

This dataset contains carbon dioxide (CO2) and methane (CH4) flux measurements from patches of wetland vegetation dominated by Typha domingensis and Panicum hemitomon, which were conducted to assess flux responses to acute saltwater intrusion. The measurements occurred before, during, and after simulated acute saltwater intrusion events of low concentrations of ~ 2 PPT. The measurements comprise gas fluxes from the wetland surface (i.e., soil-water column and vegetation) and fluxes from the soil-water column exclusively. These two sets of fluxes are separated into two files and are complemented with four more files containing porewater concentrations of CO2 and CH4 collected at 0-5 cm, 10-15 cm, and 20-25 cm depth increments, spectral indices measurements, biomass, and sediment elevation table measurements. The files can be opened with regular text editors or spreadsheet programs.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2026

Patch-level CO2 and CH4 fluxes and porewater concentrations in experimental wetlands, 5 and 10 PPT saltwater intrusion simulations, Louisiana 2023-2024

This dataset containes carbon dioxide (CO2) and methane (CH4) flux measurements collected from wetland vegetation patches dominated by Typha domingensis and Panicum hemitomon to assess greenhouse gas flux responses to experimental saltwater intrusion (SWI) pulses. Measurements were conducted before, during, and after simulated SWI events at target salinities of approximately 5 parts per thousand (ppt) with durations of 6, 10, and 17 days and 10 ppt with a duration of 48 days, alongside a control wetland (with no salinity added, flood manipulation only). These data were generated to evaluate how the magnitude and duration of SWI alter wetland carbon exchange and related biogeochemical and plant responses. This data package includes flux measurements from the wetland surface (i.e, soil/water surface and enclosed vegetation) and from the soil/water surface only; porewater and surface water concentrations of CO2 and CH4; salinity, pH, electrical conductivity collected in porewater (at 5, 10, and 20 cm soil depths) and in surface water; soil redox potential; leaf spectral indices, leaf vapor pressure deficit, stomatal conductance; water level, salinity, and photosynthetically active radiation; and aboveground biomass.

EARTH SCIENCE > AGRICULTURE > SOILS > SOIL RESPIRA↗
DOE OSTI2024

Effects of Rapid Permafrost Thaw on CO2 and CH4 Fluxes in a Warmer and Wetter Future (Final Technical Report)

When ice-rich permafrost thaws, the ground subsides, creating thermokarst landscapes with dramatically different soil conditions and carbon fluxes than the original ecosystem. Roughly 20% of the northern permafrost region is susceptible to thermokarst formation (Olefeldt et al., 2016). Thermokarst formation is often rapid; tens of meters of permafrost can thaw within a few years (Schuur et al., 2015). In topographically low areas, thermokarst thaw converts boreal forest or tundra dry shrub ecosystems into sedge or Sphagnum moss wetlands (Olefeldt et al., 2016). While this type of landscape transformation releases carbon stored in permafrost into the atmosphere, on longer time scales, it facilitates sequestration of atmospheric carbon in plant biomass because permafrost thaw releases plant-available nutrients and wetlands are highly productive (M. C. Jones et al., 2017). However, wetlands also generate methane, which is a potent greenhouse gas. Methane emissions from thermokarst wetlands can cause these carbon-sequestering systems to have a positive global warming potential (Johansson et al., 2006; Turetsky et al., 2007). Our project objective was to improve Earth System and environmental predictability by advancing understanding of how CO 2 and CH 4 flux in permafrost thaw-induced wetlands (thermokarst) will change in the future as temperatures and climate conditions shift. Northern latitudes are expected to get warmer and wetter (IPCC 2013), and initiation and expansion of thermokarst thaw is expected to increase (Jorgenson et al. 2006; Zhang et al. 2017). Given these expected changes, our work sought to address three broad questions: Q1) How will northern latitude CO2 and CH4 emissions respond to warming temperatures? Q2) What is the impact of precipitation on permafrost thaw and carbon emissions? Q3) How do CO2 and CH4 emissions change as wetlands age after permafrost thaw? To answer these questions, we took both a modeling and measurement approach. Modeling work was conducted with DOE’s Energy Exascale Earth System Model (E3SM) land model (ELM). Empirical work took place in two primary locations. The first was a thermokarst site near Fairbanks, AK. The site is part of the Bonanza Creek Long Term Ecological Research program and is well instrumented (Neumann et al., 2019). The second was an isolated thawing permafrost wetland located on Kenai Peninsula — Brown’s Lake bog (B. M. Jones et al., 2016) — where the current climate is representative of what is expected at higher latitudes in the future. This site provides an ideal opportunity to test our hypotheses about how thermokarst wetland dynamics will respond to future environmental conditions. In addition, the project collaborated with researchers asking similar questions who were collecting measurements in high latitude post-glacial lakes located in collaborators tackling similar questions in Sweden (Stordalen Mire) (Emerson et al., 2021). Project efforts directly aligned with the stated goal of the funding opportunity announcement (FOA), which was “to improve the understanding and representation of terrestrial ecosystems in ways that advance Earth system model parameterizations and capabilities... thereby improving the quality of Earth and environmental model projections and providing the scientific foundation needed to support DOE’s science and energy missions.” Specifically, the project improved sophistication and accuracy of the Energy Exascale Earth System Model (E3SM), which is being developed primarily at DOE National Laboratories to support scientific research and decision-making.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2023

Soil CO2 and CH4 Chamber Fluxes in Tussock Tundra, Council Road Mile Marker 71, Seward Peninsula, Alaska, 2016-2019

In August-September 2016, June-August 2017, June-August 2018, and June 2019, co-located measurements were made of surface CH4 and CO2 flux, soil temperature, moisture, and thaw depth. Measurements were made at 35 chamber locations at the Council Mile Marker 71 Site (CN_MM71) on the Seward Peninsula, Alaska. Chamber locations include upland moist acidic tussock tundra, thermo-erosional slopes, and periodically inundated lowland water channels. The dataset includes three *.csv data files with measurements using transparent and opaque chambers (CO2 and CH4 fluxes in light and dark) plus one *.pdf user guide.The Next-Generation Ecosystem Experiments: Arctic (NGEE Arctic), was a research effort to reduce uncertainty in Earth System Models by developing a predictive understanding of carbon-rich Arctic ecosystems and feedbacks to climate. NGEE Arctic was supported by the Department of Energy's Office of Biological and Environmental Research. The NGEE Arctic project had two field research sites: 1) located within the Arctic polygonal tundra coastal region on the Barrow Environmental Observatory (BEO) and the North Slope near Utqiagvik (Barrow), Alaska and 2) multiple areas on the discontinuous permafrost region of the Seward Peninsula north of Nome, Alaska. Through observations, experiments, and synthesis with existing datasets, NGEE Arctic provided an enhanced knowledge base for multi-scale modeling and contributed to improved process representation at global pan-Arctic scales within the Department of Energy's Earth system Model (the Energy Exascale Earth System Model, or E3SM), and specifically within the E3SM Land Model component (ELM).

54 ENVIRONMENTAL SCIENCES↗
NASA NTRS1972

Phase equilibria in fluid mixtures at high pressures - The He-CH4 system.

An experimental study of phase equilibria in the He-CH4 system has been carried out over the temperature range 95 to 290 K and at pressures to 10,000 atm. The experimental results consist of equilibrium phase composition for twenty-eight isotherms in the region of coexistence of two fluid phases, together with the pressure-temperature trace of the three-phase boundary at which a CH4-rich solid phase is in equilibrium with the two fluid phases. The system exhibits a fluid-fluid phase separation which persists to temperatures and pressures beyond the range of this experiment. These findings are relevant to problems of deep atmosphere and interior structures in the outer planets.-

Streett, W. B.↗
NASA NTRS1972

Phase equilibria in fluid mixtures at high pressures: The He-CH4 system

An experimental study of phase equilibria in the He-CH4 system was carried out over the temperature range 95 to 290 K and at pressures to 10,000 atm. The experimental results consist of equilibrium phase composition for twenty-eight isotherms in the region of coexistence of two fluid phases, together with the pressure-temperature trace of the three-phase boundary at which a CH4-rich solid phase is in equilibrium with the two fluid phases. The system exhibits a fluid-fluid phase separation which persists to temperatures and pressures beyond the range of this experiment. These results, together with those recently obtained for other binary systems, provide information about the form of phase diagrams for binary gas mixtures in the region of pressure induced phase transitions at high pressures. These findings are relevant to problems of deep atmosphere and interior structures in the outer planets.

Streett, W. B.↗
NASA NTRS1974

A search for H2O and CH4 in Comet Kohoutek

A spectroscopic search for H2O and CH4 in Comet Kohoutek (1973f) was made using a Pepsios interferometer. No evidence was found for either molecule, allowing to set an upper limit on their production rates (on about Jan. 21, 1974) of Q(H2O) less than 6.2 times 10 to the 28th power per sec and Q(CH4) less than 20 times 10 to the 30th power per sec.

Traub, W. A.↗
NASA NTRS1975

Shock tube measurements of specific reaction rates in the branched chain CH4-CO-O2 system

Growth constants, obtained by measuring the blue CO flame band emission behind incident shock waves, were obtained for two elementary bimolecular reactions involved in the oxidation of methane. Gas mixtures containing small amounts of CH4 with varying amounts of CO, O2, and in one case CO2, diluted with argon, were investigated, and exponential growth constants were derived from plots of the logarithm of observed light intensity versus gas time. The rate constant for the reaction O + CH4 yields CH3 + OH was found to be 1.9 times 10 to the 14th exp(-5900/T) cu cm per mole per sec in the range 1300-2000 K; for the reaction CH3 + O2 yields CH3O + O, the rate constant was determined to be 2.4 times 10 to the 13th exp(-14,500/T) cu cm per mole per sec in the range 1200 to 1900 K.

Brabbs, T. A.↗
NASA NTRS1976

Interactions of CH4 and CO in the earth's atmosphere

Global distributions, sources, and sinks of methane and carbon monoxide in upper and lower levels of the earth's atmosphere, and the global budgets of methane and carbon monoxide, are studied, with emphasis on cumulative pollution. Stratospheric contents, vertical profiles of concentrations, simulation of vertical transport through the atmosphere, and latitudinal distributions are examined. Diffuse and localized (urban) concentrations of CO as pollutant are studied, and anthropogenic sources and sinks for CH4 and CO are considered. Perturbation of the CH4-CO-CO2 cycle, crucial to self-cleansing mechanisms of the troposphere, by anthropogenic CO emissions, and the effect of CO long life as global pollutant, are investigated.

Wofsy, S. C.↗
NASA NTRS1977

A measurement system for the atmospheric trace gases CH4 and CO

A system for measuring ambient clean air levels of the atmospheric trace gases methane and carbon monoxide is described. The analytical method consists of a gas chromatographic technique that incorporates sample preconcentration with catalytic conversion of CO to CH4 and subsequent flame ionization detection of these gases. The system has sufficient sensitivity and repeatability to make the precise measurements required to establish concentration profiles for CO and CH4 in the planetary boundary layer. A discussion of the bottle sampling program being conducted to obtain the samples for the concentration profiles is also presented.

Condon, E. P.↗
NASA NTRS1979

Sensitivity of the predicted CO-OH-CH4 perturbation to tropospheric NOx concentrations

Measurements indicate that ambient NOx(NO + NO2) concentrations vary over at least an order of magnitude in the troposphere. Thus it is of interest to study atmospheric chemistry with NOx concentrations covering this range. In this paper we present steady state calculations which show that as NOx concentrations are increased from very low values, the hydroxyl radical concentration increases at first and then decreases. This change of behavior occurs at a concentration of NO2 of about 0.23 ppb in the model. Also, the response of the atmosphere to increased CO fluxes undergoes a qualitative change as a function of the concentration of NOx. At low levels of NOx concentration, an increase in CO fluxes into the atmosphere depletes the OH concentration and increases the concentrations of CH4 and H2, as reported in the literature. However, at high values of NOx concentration, increased CO fluxes give rise to an increase in the OH concentration and, consequently, a decrease in the concentrations of CH4 and H2.

Hameed, S.↗
NASA NTRS1980

A laser flash photolysis-resonance fluorescence kinetics study of the reaction Cl/2P/ + CH4 yields CH3 + HCl

The technique of laser flash photolysis-resonance fluorescence is employed to study the kinetics of the reaction Cl(2P) + CH4 yields CH3 + HCl over the temperature range 221-375 K. At temperatures less than or equal to 241 K the apparent bimolecular rate constant is found to be dependent upon the identity of the chemically inert gases in the reaction mixture. For Cl2/CH4/He reaction mixtures (total pressure = 50 torr) different bimolecular rate constants are measured at low and high methane concentrations. For Cl2/CH4/CCl/He and Cl2/CH4/Ar reaction mixtures, the bimolecular rate constant is independent of methane concentration, being approximately equal to the rate constant measured at low methane concentrations for Cl2/CH4/He mixtures. These rate constants are in good agreement with previous results obtained using the discharge flow-resonance fluorescence and competitive chlorination techniques. At 298 K the measured bimolecular rate constant is independent of the identity of the chemically inert gases in the reaction mixture and in good agreement with all previous investigations. The low-temperature results obtained in this investigation and all previous investigations can be rationalized in terms of a model which assumes that the Cl(2P 1/2) state reacts with CH4 much faster than the Cl(2P 3/2) state. Extrapolation of this model to higher temperatures, however, is not straightforward.

Ravishankara, A. R.↗
NASA NTRS1983

Prebiotic synthesis in atmospheres containing CH4, CO, and CO2. I - Amino acids

The prebiotic synthesis of amino acids, HCN, H2CO, and NH3 using a spark discharge on various simulated primitive earth atmospheres at 25 C is investigated. Various mixtures of CH4, CO, CO2, N2, NH3, H2O, and H2 were utilized in different experiments. The yields of amino acids (1.2-4.7 percent based on the carbon) are found to be approximately independent of the H2/CH4 ratio and the presence of NH3, and a wide variety of amino acids are obtained. Glycine is found to be almost the only amino acid produced from CO and CO2 model atmospheres, with the maximum yield being about the same for the three carbon sources at high H2/carbon ratios,whereas CH4 is superior at low H2/carbon ratios. In addition, it is found that the directly synthesized NH3 together with the NH3 obtained from the hydrolysis of HCN, nitriles, and urea could have been a major source of ammonia in the atmosphere and oceans of the primitive earth. It is determined that prebiotic syntheses from HCN and H2CO to give products such as purines and sugars and some amino acids could have occurred in primitive atmospheres containing CO and CO2 provided the H2/CO and H2/CO2 ratios were greater than about 1.0.

Schlesinger, G.↗
NASA NTRS1984

Carbon and energy yields in prebiotic syntheses using atmospheres containing CH4, CO and CO2

Yields based on carbon are usually reported in prebiotic experiments, while energy yields (moles/cal) are more useful in estimating the yields of products that would have been obtained from the primitive atmosphere of the earth. Energy yields for the synthesis of HCN and H2CO from a spark discharge were determined for various mixtures of CH4, CO, CO2, H2, H2O, N2 an NH3. The maximum yields of HCN and H2CO from CH4, CO, and CO2 as carbon sources are about 4 x 10 to the -8th moles/cal.

Miller, S. L.↗
NASA NTRS1984

The composition of Saturn's atmosphere at northern temperate latitudes from Voyager IRIS spectra - NH3, PH3, C2H2, C2H6, CH3D, CH4, and the Saturnian D/H isotopic ratio

The vertical distributions and mixing ratios of minor constituents in the northern hemisphere of Saturn are investigated. Results are obtained for NH3, PH3, C2H2, C2H6, CH3D, and CH4; the D/H ratio is obtained from the CH4 and CH3D abundances. The NH3 mixing ratio in the upper atmosphere is found to be compatible with the saturated partial pressure. The inferred PH3/H2 ratio of 1.4 + or - 0.8 x 10 to the -6th is higher than the value derived from the solar P/H ratio. The stratospheric C2H2/H2 and C2H6/H2 ratios are, respectively, 2.1 + or - 1.4 x 10 to the -7th and 3.0 + or - 1.1 x 10 to the -6th; the latter decreases sharply below the 20-50 mbar level. The results for CH3D/H2 and CH4/H2 imply an enrichment of Saturn's upper atmosphere in carbon by a factor of at least three over the solar abundance. The interpretation of two NH3 lines in the five-micron window suggests a NH3/H2 ratio at the two bar level below the solar value.

Courtin, R.↗
NASA NTRS1987

Carbon kinetic isotope effect in the reaction of CH4 with HO

The carbon kinetic isotope effect in the CH4 + HO reaction is measured experimentally and the use of carbon isotope ratios to diagnose atmospheric methane is examined. The chemical, photolysis, and analytical experimental conditions and procedures are described. It is determined that the CH4 + HO reaction has a carbon kinetic isotope effect of 1.010 + or 0.007 for k(12)k(13) (rate constants ratio) at 297 + or - 3 K. This value is compared with the data of Rust and Stevens (1980). Causes for the poor correlation between the data at high methane conversions are discussed. It is supposed that the difference between the k(12) and k(13) values is due to a difference in the activation energy of the two reactions.

Davidson, J. A.↗
NASA NTRS1987

Simultaneous in situ measurements and diurnal variations of NO, NO2, O3, jNO2, CH4, H2O, and CO2 in the 40- to 26-km region using an open path tunable diode laser spectrometer

Simultaneous in situ measurements of temperature, pressure, and the NO, NO2, O3, jNO2, CH4, H2O, and CO2 concentrations were conducted in the 40- to 26-km region of the stratosphere using the JPL Balloon-borne Laser In Situ Sensor, a tunable diode laser absorption spectrometer. The NO, NO2, CH4, H2O, and CO2 concentration measurements generally show good agreement with previous observations, with a tendency for somewhat lower NO2 amounts. Measured O3 concentrations at 38 km agree well with comparable measurements from in situ UV photometers, but at 28 km they are lower by about 10 percent and agree more closely with the solar backscattered UV data. A decline was found in NO2 during the night over a 5-km altitude range, which implies either lower NO2 postsunset profiles, or an NO2 decay rate that is significantly higher than current model predictions that use N2O5 chemistry.

Webster, Christopher R.↗