HR: 1340h
AN: B53A-0942    [Abstracts]
TI: Magnitude and Spatio-Temporal Variability of Methane Export From a Seasonally Stratified, Eutrophic Lake
AU: * Varadharajan, C
EM: charuv@mit.edu
AF: Dept of Civil and Environmental Engineering, Massachusetts Institute of Technology, Bldg 48, 77 Massachusetts Avenue, Cambridge, MA 02139, United States
AU: Hemond, H F
EM: hfhemond@mit.edu
AF: Dept of Civil and Environmental Engineering, Massachusetts Institute of Technology, Bldg 48, 77 Massachusetts Avenue, Cambridge, MA 02139, United States
AB: Recent studies have suggested that significant amounts of methane can be released to the atmosphere from freshwater lakes, particularly through bubbling. Yet the relative importance of ebullition in the methane cycle of aquatic ecosystems is poorly understood, since it is a spatially and temporally heterogeneous process. The primary intent of this research is to measure the magnitude, rate and distribution of methane loss from lakes to the atmosphere due to both bubbling and diffusion, using the eutrophic Upper Mystic Lake in Massachusetts as a case study. Over the summer of 2007, under-water conical chambers were deployed to provide an estimate of bubbling fluxes, and the composition of the gases released in this process. Most of the bubbling occurred during short episodes with peak flux rates approaching 200 ml/m²/d, while average ebullition was approximately 30- 45 ml/m²/d. Spatial variability in fluxes was also observed - shallower locations had approximately 3 to 5 times less flux than deeper stations. The mixing ratio of methane present in the collected gas varied across stations and ranged from ~50% to 90%, except at some shallow locations where it was less than 10%. Concentrations of dissolved methane at the surface were less than 1uM leading to calculated rates of diffusive loss that are less than 20 ml/m²/d. This suggests that bubbling, rather than diffusion, is likely to be the more important pathway for methane release to the atmosphere.
DE: 0414 Biogeochemical cycles, processes, and modeling (0412, 0793, 1615, 4805, 4912)
DE: 0428 Carbon cycling (4806)
DE: 0458 Limnology (1845, 4239, 4942)
SC: Biogeosciences [B]
MN: 2007 Fall Meeting