Water and Environmental Research Center
Seminars
9 October 2009
Bubble Trouble: Long-term methane ebullition dynamics for an interior Alaskan lake using high temporal-resolution automated bubble traps
Dragos A. Vas
Dragos Vas kneels next to a large methane bubble
Abstract
Arctic lakes are significant sources of atmospheric methane CH4, the third most important greenhouse gas (IPCC 2007), primarily via the emission pathway of ebullition (bubbling). In open freshwater ecosystems, ebullition can account for as much as 80% [Wassmann et al., 1992] to 95% (Walter et al. 2006) of the total methane released. Measuring methane ebullition rates from lakes is challenging due to temporal and spatial CH4 flux variations. Previous work conducted by Walter et al. (2006, 2007) identified four types of CH4 bubbling point-sources which they classified as A, B, C, and Hotspot. During short term (21-day monitoring) they measured the bubbling rate associated with these four point-source types. In my research I designed, built, and trouble shot the high temporal resolution automated bubble traps which I used to monitor 12 methane seeps for a period of one year. I found that there are three distinctive types of methane seeps: type A seeps with a flux of 3±1 mg CH4 spot -1 day -1, type B seeps with a flux of 50±71 mg CH4 spot -1 day -1, and type C/Hotspot seeps with a flux of 1667±1149 mg CH4 spot -1 day -1. I also found that there is a strong correlation between changes in atmospheric pressure and ebullition rates (r² value as high as .82) and that seasonal patterns show a continued increase in CH4 ebullition during the summer with a peak in the fall, which suggests that temperature plays an important role in CH4 production in lake sediments, leading to the release of more gas. The technique of mapping ebullition seeps used together with the methane flux values calculated in this study is more accurate in estimating whole lake methane emissions than previous techniques in which chambers were placed randomly on lakes very likely missing the ebullition seeps.