Seasonal variations of stable hydrogen and carbon isotope ratios of methane in subtropical freshwater sediments

Technical Report · Wed Jan 01 04:00:00 EST 1992

OSTI ID:6995636

Burke, R A; Barber, T R; Sackett, W M

Stable hydrogen (delta D) and carbon (delta(13)C) isotope ratios of sedimentary methane from five subtropical Florida freshwater sites exhibited smaller, less distinct seasonal variations than previously observed in temperate sediments, apparently due to the smaller range of temperatures forcing the subtropical environments. Negative correlations observed between (delta D)-CH4 and (delta(13)C)-CH4 at the sites probably resulted from mixing methane produced via acetate fermentation with methane formed from CO2 and H2O. The inverse (delta D)/(delta(13)C) trends, high sedimentary gas methane concentrations (up to 80 mole%), and visual observations imply that ebullition dominates methane transport from the sediments during at least part of the seasonal cycle. Many values deviated from the main inverse delta D/delta(13)C trend such that bacterial oxidation was not indicated. The deviation may result from the reduction of CO2 with varying delta(13)C under conditions of elevated H2 concentrations or enhanced interspecies hydrogen transfer, which may cause relatively greater hydrogen isotopic fractionation. Alternatively, the deviation may result from fermentation of autotrophically formed, (13)C-depleted acetate. Differences in the delta(13)C of bulk organic matter from two of the sites potentially account for about half of the difference in mean delta(13)C-CH4 between the two sites. In other cases, however, the immediate methanogenic precursor appeared to be the major determinant of methane stable isotopic composition. (Copyright (c) 1992 by the American Geophysical Union.)

• Research Organization: Environmental Protection Agency, Athens, GA (United States). Environmental Research Lab.
• OSTI ID: 6995636
• Report Number(s): PB-92-217181/XAB; EPA--600/J-92/277; CNN: NSF-OCE-8417321; NASA-NAGW-836
• Country of Publication: United States
• Language: English

Related Subjects

29 ENERGY PLANNING, POLICY, AND ECONOMY
290301 -- Energy Planning & Policy-- Environment
Health
& Safety-- Regional & Global Environmental Aspects-- (1992-)
54 ENVIRONMENTAL SCIENCES
540120* -- Environment
Atmospheric-- Chemicals Monitoring & Transport-- (1990-)
540320 -- Environment
Aquatic-- Chemicals Monitoring & Transport-- (1990-)
AIR POLLUTION
AIR-WATER INTERACTIONS
ALKANES
BACTERIA
BIOCONVERSION
CARBON 13
CARBON COMPOUNDS
CARBON DIOXIDE
CARBON ISOTOPES
CARBON OXIDES
CHALCOGENIDES
CLIMATIC CHANGE
CONTAMINATION
DEVELOPED COUNTRIES
ECOLOGICAL CONCENTRATION
ENVIRONMENTAL TRANSPORT
EVEN-ODD NUCLEI
FERMENTATION
FLORIDA
FRESH WATER
GREENHOUSE EFFECT
HYDROCARBONS
HYDROGEN COMPOUNDS
HYDROGEN ISOTOPES
ISOTOPE APPLICATIONS
ISOTOPES
LIGHT NUCLEI
MASS TRANSFER
METHANE
MICROORGANISMS
NORTH AMERICA
NUCLEI
ORGANIC COMPOUNDS
OXIDES
OXYGEN COMPOUNDS
POLLUTION
POLLUTION SOURCES
SEASONAL VARIATIONS
SEDIMENTS
STABLE ISOTOPES
TRACER TECHNIQUES
USA
VARIATIONS
WATER