PI(s): Martin Wahlen, Bruce Deck -- Scripps Institution of Oceanography, University of California, San Diego
Objectives: To determine the isotopic composition (d13CH4, dD in CH4 and 14CH4) in methane emitted to the atmosphere from the boreal forest ecosystems, so that this source, together with the net flux, can be considered in a global isotopic methane budget. The relative importance of methane production versus methane consumption by oxidation in these ecosystems, using the stable isotopes (d13CH4 and dD in CH4) as tracers is also being examined. The isotopic fractionation induced by methane oxidation will be determined. If bacterial methane oxidation is a substantial sink globally (compared to the atmospheric sink) the isotopic consequences of this sink should be determined. Investigations of the dD for methane will allow us to determine the split in methane production from acetate fermentation and CO2 reduction in these ecosystems. Furthermore, we plan to analyze the 14C in the methane emitted from these sites, to investigate the age of the stored carbon, and, to find out if releases of methane highly depleted in 14C could reconcile the discrepancy between statistical estimates for fossil methane releases and those derived from measurements of 14CH4.
Location: NSA and SSA
Sites: SSA wet/dry - possibly fen - black spruce - aspen; NSA wet/dry - possibly beaver pond - old black spruce - jack pine.
To measure oxidation of methane in forest soils and aquatic sediments, Isotopic Fractionation.
Types of Data Collected, Equipment Used:
2 liter gas samples were slowly withdrawn from soil probes at several depths in the forest soil. The depths were chosen to approximate 25% depletion and 50% depletion of soil methane. Several ambient surface air samples were taken. In addition, 2 liter samples were taken from flux chambers on the soil surface equilibrated over a period of several hours to monitor the isotopic changes in methane during direct soil consumption. All samples were returned to the lab for analysis of 13/12 C in methane.
Gas from inverted funnels at the water surface, and from water samples by He equilibrated headspace techniques were made on the NSA Tower beaver pond site. High concentration of methane in some of these samples allows the determination of H/D in addition to 13/12 C in the methane.
Summary of Places and Times of Measurements:
Soil gas samples SSA 8/3-7/94, NSA 8/23-27/94. Soil probes and flux chambers. Beaver pond sediments and waters NSA 8/25+31/94. Surface funnels and water column/sediment water samples.
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Last Updated: November 5, 1997