Magnitude and spatio-temporal variability of methane emissions from a eutrophic freshwater lake

Methane is the second most important greenhouse gas after carbon dioxide, and it can significantly impact global climate change. Considerable amounts of methane can be released to the atmosphere from freshwater lakes, particularly through bubbling. However, spatial and temporal heterogeneity in ebullition has complicated efforts to accurately measure such methane emissions. This thesis presents the results from a two-year study of methane biogeochemistry conducted at the eutrophic, stratified, Upper Mystic Lake located in eastern Massachusetts, US. Field sampling was done between June and November 2007, and between April and November 2008. In both years, ebullition at the lake was strongly episodic, and the amount and composition of bubbled gas varied considerably between sites. In 2008, under-water bubble traps were equipped with pressure sensors that measured the gas collected every 5 minutes for 4-6 months. The high-temporal resolution data showed that synchronized lake-wide bubbling episodes were triggered when hydrostatic pressures fell below a site-dependent threshold. Twice as much bubbling was observed in 2007 than in 2008. In both years, approximately 70% of the total methane export from the lake occurred through ebullition, and 30% through diffusion across the air-water interface at the lake surface. About 6-11 kg CH4/d was emitted to the atmosphere from the Upper Mystic Lake during the sampling periods of 2007 and 2008.

Department dc:contributor.department

Massachusetts Institute of Technology. Dept. of Civil and Environmental Engineering.

Grantor dc:publisher

Massachusetts Institute of Technology

Year dc:date.issued

2009

Author dc:creator

• Varadharajan, Charuleka, 1980-

Advisor dc:contributor.advisor

• Harold F. Hemond.

• Civil and Environmental Engineering.

Statement dc:rights

• M.I.T. theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission. See provided URL for inquiries about permission.

Licence dc:rights.uri

• http://dspace.mit.edu/handle/1721.1/7582

Language dc:language.iso

eng

Handle dc:identifier.uri

http://hdl.handle.net/1721.1/54879

OAI identifier oai:identifier

oai:dspace.mit.edu:1721.1/54879