A5024131798- Methane Hydrates and Related Phenomena
- Atmospheric and Environmental Gas Dynamics
- Geology and Paleoclimatology Research
- Microbial Community Ecology and Physiology
- Hydrocarbon exploration and reservoir analysis
- Isotope Analysis in Ecology
- Marine and coastal ecosystems
- Peatlands and Wetlands Ecology
- Planetary Science and Exploration
- Anaerobic Digestion and Biogas Production
- Coastal wetland ecosystem dynamics
- Air Quality Monitoring and Forecasting
- Space Exploration and Technology
- Climate change and permafrost
- Fish Ecology and Management Studies
- Toxic Organic Pollutants Impact
- Radioactive contamination and transfer
- Geological formations and processes
- Groundwater and Isotope Geochemistry
- Environmental Toxicology and Ecotoxicology
- Aquatic Ecosystems and Phytoplankton Dynamics
- Archaeology and ancient environmental studies
- Marine Biology and Ecology Research
- Forensic Toxicology and Drug Analysis
- Ocean Acidification Effects and Responses
University of Missouri
2004-2024
Weatherford College
2004
United States Naval Research Laboratory
2001
Environmental Protection Agency
1996-1998
National Academies of Sciences, Engineering, and Medicine
1997
Gulf Marine Institute of Technology
1996
University of North Carolina at Chapel Hill
1987-1995
Variations in hydrostatic pressure controlled by diurnal tides triggered ebullition from subtidal freshwater sediments dominated methanogenesis the White Oak River estuary, North Carolina. Pulses of gas consisting 50–80% methane were released when tidal cycle reached its nadir. In August, site‐to‐site variations these fluxes ranged 60 to 650 ml (39–425 mg) CH 4 m −2 d −1 . At a single site, made up 50% total flux out sediments; remainder was transported across sediment‐water interface...
Bogs and fens from northern Minnesota produce large quantities of CH4, which may be either emitted to the atmosphere or stored in below-ground reservoirs. The identity organic materials that support CH4 production has been uncertain, but we present evidence a significant fraction surface emission is derived recently fixed compounds. First, both bogs '4C signature equivalent contemporary values for atmospheric CO2. Second, flooded rates are linearly related CO2 exchange δ13C CH4. Third,...
The cycling of methane across the soils tidally flooded bank margins in tidal freshwater portion White Oak River estuary, North Carolina, was investigated from October 1990 to November 1991. A comparison between these edges and adjacent submerged stations made. showed large seasonal variations production rates, with very little being produced winter amounts (up 1,000 mg m −2 d −1 ) during summer. This seasonality seems be linked cycle growth senescence vascular plants growing soils. In...
The carbon isotopic composition of methane emitted by the Alaskan emergent aquatic plants Arctophila fulva , a tundra mid‐lake macrophyte, and Carex rostrata lake margin was −58.6 ± 0.5 ( n =2) −66.6±2.5 = 6) ‰ respectively. these species found to be depleted in 13 C 12‰ 18‰, relative withdrawn from plant stems 1 2 cm below waterline. As macrophyte‐mediated flux represented approximately 97% sites, results suggest more rapid transport 12 CH 4 through atmosphere. This preferential release...
Rates of microbially mediated sedimentary organic carbon remineralization vary along the salinity gradient White Oak River estuary, N.C. A direct comparison two sites, one upriver dominated by methanogenesis and downriver sulfate reduction, indicates a more rapid rate upriver. Measurements diffusive ∑CO 2 flux plus CH 4 (56%) bubble (44%) fluxes at upriver, freshwater site from June 1986 to March 1988 yield an average yearly 1.35 ± 0.35 mmol m −2 h −1 . At midestuarine site, dominant for...
The total methane flux to the troposphere from tundra environments of Yukon‐Kuskokwim Delta is dominated by emissions wet meadow (∼75%) and small, organic‐rich lakes (∼20%). mean δ 13 C value diffusing into collar‐mounted chambers near Bethel, Alaska, was −65.82 ± 2.21‰ (±1 sigma, n = 18) for period July 10 August 10, 1988. Detritus‐rich sediments lakes, including margins large entire submerged areas smaller ones, are laden with gas bubbles whose concentration ranges 11% 79%. Lowest...
This work was undertaken to investigate the usefulness of stable carbon isotopic analysis as a monitoring tool for contaminant remediation. Concentrations and δ13C values BTEX (benzene, toluene, ethylbenzene, xylenes) were measured at gasoline-contaminated site in southern California. The data determined using purge-and-trap connected gas chromatograph/ion trap mass spectrometer an isotope ratio system. ranged from below detection (<0.5 ppb ≈ 0.05 μM C) about 120 ppm (≈10 000 total BTEX,...
Methanogenesis was characterized in hypersaline microbial mats from Guerrero Negro, Baja California Sur, Mexico both situ and after long-term manipulation a greenhouse environment. Substrate addition experiments indicate methanogenesis to occur primarily through the catabolic demethylation of non-competitive substrates, under field conditions. However, evidence for coexistence other metabolic guilds methanogens obtained during previous sulfate concentrations. To fully characterize these...
Abstract Methane (CH 4 ) is a potent greenhouse gas (GHG) with atmospheric concentrations that have nearly tripled since pre‐industrial times. Wetlands account for large share of global CH emissions, yet the magnitude and factors controlling fluxes in tidal wetlands remain uncertain. We synthesized flux data from 100 chamber 9 eddy covariance (EC) sites across marshes conterminous United States to assess improve predictions emissions. This effort included creating an open‐source database...
Motivated by the increasingly abundant evidence for hypersaline environments on Mars and reports of methane in its atmosphere, we examined methanogenesis ponds Baja California Sur, Mexico, northern California, USA. Methane-rich bubbles trapped within or below gypsum/halite crusts have δ¹³C values near -40‰. Methane with these relatively high isotopic would typically be considered thermogenic; however, incubations crust samples resulted biological production similar composition. A series...
Abstract Adverse impacts on the health of some fish populations, such as skewed sex distributions, have been noted in surface waters and laboratory experiments with relatively low concentrations (above 25 ng/L) natural estrogen (17 β‐estradiol—E2). Sources E2 to ground can include avian, human, mammalian waste products. The Ozark Plateau Aquifer (OPA) is a karstic basin that receives significant portion its water through losing reaches rivers. Thus, there direct connection between water. OPA...
Abstract Stable isotope analysis of bacterial nucleic acids can be used to trace carbon that is assimilated and respired by the bacterioplankton in aquatic ecosystems. However, sediment soil environments humic co-extract with acids, resulting inaccurate analysis. In this study we have examined use amino found cell walls as biomarkers sources support growth. development method, peptidoglycan from laboratory grown Pseudomonas sp. was hydrolyzed acids. ratios (δ13C) were analyzed a dual mass...
Water column samples from a transect cruise southern Chile through the Panama Canal to Gulf of Mexico were used determine dissolved methane depth profiles and air‐sea fluxes. In Mexico, surface concentrations approximately 40% supersaturated with respect atmosphere, whereas near equator in Peru upwelling region, 10–20% supersaturation generally occurred. These saturation ratios translate into an average flux sea atmosphere 0.38 μmol m −2 d −1 . addition, water indicate that subsurface maxima...
Modern microbial mats have been used as analogs for early life because of the longevity on Earth. Mats collected from hypersaline salterns in Baja California were maintained over a year and half under both normal (85 ppt salinity, 50 mM SO 4 2− ) reduced salinity (35 salinity; near modern seawater) sulfate concentrations (20 mM, ≤1 to assess carbon processing conditions more similar Archean oceans. As was removed by diffusion out into overlying water, methane within increased. Highest...
Methane production has been observed in a number of hypersaline environments, and it is generally thought that this methane produced through the use noncompetitive substrates, such as methylamines, dimethylsulfide methanol. Stable isotope measurements have also suggested methanogens are operating under conditions substrate limitation. Here, limitation gypsum-hosted endoevaporite soft-mat environments was investigated by addition trimethylamine, for methanogenesis, dried microbial mat, source...
Abstract Diet interactions between native and non‐native fishes may influence the establishment of species within their historical range (i.e., reintroduction). Therefore, we illustrated food web structure followed transition federally endangered humpback chub Gila cypha into a novel following translocation determined potential for species, rainbow trout Oncorhynchus mykiss , to success. Humpback used resources high in assimilated similar proportions fishes, suggesting occupy an ecological...
A set of continuous, high‐resolution atmospheric radon ( 222 Rn) concentration time series and soil flux measurements were acquired during the summer 1990 at a micrometeorological tower site 13 km northwest Schefferville, Quebec, Canada. The was located in dry upland, open‐canopy lichen‐spruce woodland. For period July 23 to August 1, 1990, mean 41.1±4.8 Bq m −2 h −1 . Radon surface from two end‐member forest floor cover types (lichen mat bare soil) 38.8±5.1 61.8±15.6 , respectively. Average...
Abstract Data from a combination of laboratory and fieldwork is presented to initiate testing stable carbon nitrogen isotope ratios trace sources TNT in contaminated soil groundwater. Evaluation these extraction methods resulted 99.9 99.8% recovery with Soxhlet solid‐phase (SPE), respectively. As result the high efficiency, fractionation did not occur, thus providing an accurate value on field samples. Subsequent experiments evaluated stability signatures through incubations lasting up four...
The importance of hypersaline environments over geological time, the discovery similar habitats on Mars, and methane as a biosignature gas combine to compel an understanding factors important in controlling released from microbial mat environments. To further this understanding, changes stable carbon isotopes possible methanogenic substrates communities were investigated function salinity here Earth. Microbial mats sampled four different field sites located within salterns Baja California...