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Shifting precipitation patterns due to climate change may impact peatland methane (CH4) emissions, as precipitation affects water table level which largely controls CH4 cycling. To investigate the impact of variable precipitation on peatland CH4 emissions, we measured CH4 fluxes and their 13C isotope composition (δ13C–CH4) across two summers marked by drought (2020) and heavy precipitation (2021) in a northern temperate poor fen in New Hampshire, USA. Monthly variation in CH4 fluxes and δ13C–CH4 was larger than interannual variation and variation between peatland microforms. While the seasonal pattern of CH4 emissions was not significantly different between years, the magnitude of seasonal changes in CH4 flux and δ13C–CH4 provided insight regarding the processes controlling CH4 emissions. Between July and August 2020, water table levels dropped > 15 cm, CH4 emissions decreased by an order of magnitude, and δ13C–CH4 increased ~ 10‰, suggesting lower water table levels promoted CH4 oxidation and reduced emissions in late summer. Rainstorms in July 2021 caused flooding and stimulated high CH4 emissions, but the impact of increased water table levels due to heavy precipitation on CH4 fluxes was transient and did not have an apparent effect on emitted δ13C–CH4. While drought conditions had a clear impact on CH4 fluxes and δ13C–CH4, our results suggest rainstorms and subsequent flooding do not have a sustained impact on CH4 emissions from temperate peatlands. [ABSTRACT FROM AUTHOR]

A new, integrated methodology to locate and measure methane emissions from natural gas systems has been developed. Atmospheric methane sources are identified by elevated ambient CH4 concentrations measured with a mobile laser-based methane analyzer. The total methane emission rate from a source is obtained by simulating the source with a sulfur hexafluoride (SF6) tracer gas release and by measuring methane and tracer concentrations along downwind sampling paths using mobile, real-time analyzers. Combustion sources of methane are distinguished from noncombustion sources by concurrent ambient carbon dioxide measurements. Three variations on the tracer ratio method are described for application to (1) small underground vaults, (2) aboveground natural gas facilities, and (3) diffuse methane emissions from an entire town. Results from controlled releases and from replicate tests demonstrate that the tracer ratio approach can yield total emission rates to within approximately ±15%. The estimated accuracy of emission estimates for urban areas with a variety of diffuse emissions is ±50%. © 1995, American Chemical Society. All rights reserved.

Water table depth and vegetation are key controls of methane (CH4) emissions from peatlands. Microtopography integrates these factors into features called microforms. Microforms often differ in CH4 emissions, but microform‐dependent patterns of belowground CH4 cycling remain less clearly resolved. To investigate the impact of microtopography on belowground CH4 cycling, we characterized depth profiles of the community composition and activity of CH4‐cycling microbes using 16S rRNA amplicon sequencing, incubations, and measurements of porewater CH4 concentration and isotopic composition from hummocks and lawns at Sallie's Fen in NH, USA. Geochemical proxies of methanogenesis and methanotrophy indicated that microforms differ in dominant microbial CH4 cycling processes. Hummocks, where water table depth is lower, had higher porewater redox potential (Eh) and higher porewater δ13C‐CH4 values in the upper 30 cm than lawns, where water table depth is closer to the peat surface. Porewater δ13C‐CH4 and δD‐CH3D values were highest at the surface of hummocks where the ratio of methanotrophs to methanogens was also greatest. These results suggest that belowground CH4 cycling in hummocks is more strongly regulated by methanotrophy, while in lawns methanogenesis is more dominant. We also investigated controls of porewater CH4 chemistry. The ratio of the relative abundance of methanotrophs to methanogens was the strongest predictor of porewater CH4 concentration and δ13C‐CH4, while vegetation composition had minimal influence. As microbial community composition was strongly influenced by redox conditions but not vegetation, we conclude that water table depth is a stronger control of belowground CH4 cycling across microforms than vegetation. Plain Language Summary: Northern peatlands are significant sources of the greenhouse gas methane (CH4) to the atmosphere. Patterns of CH4 emissions across peatlands often mirror patterns in water table level, vegetation cover, and elevation over small spatial scales as these factors influence microbial CH4 production and consumption. We investigated microbial CH4 production and consumption across areas in a northern peatland with varying water table depth and vegetation cover using measurements of belowground CH4 chemistry and microbial DNA sequencing. We observed consistent signals in the belowground concentration and stable isotope composition of CH4, which can indicate where different microbial processes are occurring, that suggest slightly elevated areas with lower water table depth are hotspots for CH4 consumption while CH4 production is more prominent in areas that are lower and wetter. Overall, both CH4 chemistry and microbial communities were more strongly influenced by changes in moisture than vegetation. These insights are important for understanding how climate change may impact CH4 cycling, as CH4 producing and consuming microbes respond differently to changes in temperature and moisture. Better understanding of the distribution of CH4 production and consumption across the landscape may also help scale predictions of CH4 emissions across larger areas for global modeling efforts. Key Points: Surface porewater δ13C‐CH4 and δD‐CH3D values were more reflective of methanotrophy in hummocks and methanogenesis in lawnsCommunity composition of methanogens and methanotrophs was influenced by redox conditions and water table level across microtopographyVegetation cover had limited influence on microbial community composition and porewater CH4 concentration and stable isotope composition [ABSTRACT FROM AUTHOR]

ABSTRACT We demonstrate the use of an aldehyde scrubber system to resolve isobaric aldehyde/alkene interferences in a proton transfer reaction mass spectrometer (PTR-MS) by selectively removing the aldehydes from the [...]

A study was conducted to determine roles of soil bacteria in the uptake of methyl bromide in soils. A dilution system that can produce mixing ratios of methyl bromide and an analytical method were utilized. Results revealed that the varied soil moisture and temperature optima from different soils were caused by the diverse consumption activity of soil bacteria. However, soil fungi were not involved in the removal of methyl bromide from the soil.

Gas concentrations and isotopic signatures can unveil microbial metabolisms and their responses to environmental changes in soil. Currently, few methods measure soil trace gases such as the products of nitrogen and carbon cycling, or volatile organic compounds (VOCs), that could constrain microbial biochemical processes like nitrification, methanogenesis, respiration, and microbial communication. Versatile trace gas sampling systems that integrate soil probes with sensitive trace gas analyzers could fill this gap with measurements resolving spatial (centimeter scale) and temporal (minutes) variations in concentrations and isotopic signatures of in situ soil gases. We developed a system that integrates new 15 cm long sintered PTFE diffusive soil gas probes with various infrared spectrometers and a VOC mass spectrometer. The system is based on porous and hydrophobic soil probes that non-disruptively collect and transport gas from multiple probes to one or more central gas analyzers. Here, we demonstrate the feasibility and versatility of an automated multi-probe system for soil gas measurements of isotopic ratios of nitrous oxide (d18O, d15N, and the 15N site-preference of N2O), methane, carbon dioxide (d13C), and VOCs. First, we used an inert silica matrix to challenge probe measurements under controlled gas conditions. By changing and controlling system flow parameters, including probe flow rate, we optimized recovery of representative soil gas samples while reducing sampling artifacts on subsurface concentrations. Second, we forced environmental manipulations in soil-filled columns to demonstrate real time detection of subsurface gas dynamics in response to irrigation and soil redox conditions. In addition, we developed a new laser spectrometer to recover isotope ratios for 14N14N16O ("d446"), 14N15N16O ("d456"), 15N14N16O ("d546"), and 14N14N18O ("d448") with high precision and low concentration dependence. We captured temporal subsurface gas pulses in CO2, N2O, and VOCs. This demonstrated the potential for diffusive-based probes to couple to trace gas sensors for soil health and fertility studies, and to inform high-throughput meta-omics, leading to the development of a suite of powerful new tools for soil analysis. [ABSTRACT FROM AUTHOR]

We have developed a dual-beam tunable diode laser absorption spectroscopy system to follow the cocondensation of water and ethanol in a supersonic Laval nozzle. We determine the D2O monomer concentration in the vapor phase by fitting a Voigt profile to the measured line shape but had to develop a calibration scheme to evaluate the C2H5OD monomer concentration. To measure the temperature of the gas, we seed the flow with CH4 and measure two absorption lines with different lower state energies. These data give a far more detailed picture of binary condensation than axially resolved pressure measurements. In particular, we observe that the C2H5OD monomer starts to be depleted from the gas phase well before D2O begins to condense. [ABSTRACT FROM AUTHOR]

The NO(v,J)-fragment population distributions and recoil energies were measured for the vibrational predissociation of NO·HF following excitation of the H–F stretch. Most of the available energy appears in NO vibration and/or HF rotation. There is little recoil momentum. All NO(v,J) fragments are formed with near δ-function recoil kinetic energies, correlated with HF fragments in a single rotational level. Two dissociation channels proceed with similar probability to produce NO(v=0) and NO(v=1). Only two rotational levels of HF are populated. One of the HF rotational states is correlated exclusively with NO(v=0) fragments, the other is paired with NO(v=1) fragments. Constraints on fragment angular momenta as well as energetics appear important for the dissociation dynamics. The presence of significant amounts of vibrationally excited NO fragments, in the absence of observable spectroscopic perturbations, implies that intramolecular vibrational redistribution proceeds as the dimer dissociates. The data support two possibilities for the NO·HF dimer bond energy: (1) D0=448±5 cm-1 with coincident pairs of fragments NO(v=0)+HF(J=12) and NO(v=1)+HF(J=8); (2) D0=1769±10 cm-1 with JHF=9 and 2, respectively. [ABSTRACT FROM AUTHOR]