Hydropower reservoirs as methane sources
Event details
| Date | 01.03.2010 |
| Hour | 16:15 |
| Speaker | Wehrli, Bernhard (EAWAG) |
| Location |
GR B3 30
|
| Category | Conferences - Seminars |
There is growing interest and concern about methane emissions from reservoirs globally. However, the methane fluxes from reservoirs reported in the literature are very discordant - ranging over an order of magnitude - with tropical ones considered the most important. Organic-rich sediments in lakes and reservoirs are hot spots of methanogenesis, from which methane can escape to the atmosphere via four major pathways - bubbling, diffusion, transport through plants, and exposure of the anoxic methane-rich deep waters to the atmosphere during convective mixing events. We have conducted a detailed systems analysis on the Wohlensee reservoir of the Aare River in Switzerland. Measurements using gas traps indicated very high ebullition rates. Methane diffusion from the sediment was generally low and seasonally stable and could not fully account for methane accumulation during passage through the reservoir. A firm relationship between water temperature and the observed dissolved methane accumulation allowed us to identify and quantify the role of bubble dissolution. The reservoir emitted methane at an average rate of ~150 mg methane per square meter and day (130 tons per year), which is the highest ever recorded for a mid-latitude reservoir. These and further results indicate that temperate water bodies can be an important but overlooked methane source in a warming climate.
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