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WATER LEVEL DRAWDOWN TRIGGERS SYSTEM-WIDE BUBBLE RELEASE FROM RESERVOIR SEDIMENTS
Citation:
Beaulieu, J., A. Balz, J. Harrison, K. Birchfield, C. Nietch, AND J. Young. WATER LEVEL DRAWDOWN TRIGGERS SYSTEM-WIDE BUBBLE RELEASE FROM RESERVOIR SEDIMENTS. Summer Meeting of the Association for the Sciences of Limnology and Oceanography, Sante Fe, NM, June 05 - 10, 2016.
Impact/Purpose:
To inform the public.
Description:
Reservoirs are an important anthropogenic source of methane and ebullition is a key pathway by which methane stored in reservoir sediments can be released to the atmosphere. Changes in hydrostatic pressure during periods of falling water levels can trigger bubbling events, suggesting that intentional water-level drawdowns may trigger bursts of methane emissions. We measured ebullition at 9 sites in a eutrophic reservoir located in the Midwestern U.S. over a 6-month period. Ebullition rates were threefold higher immediately downstream from the largest tributary (median = 373 mg CH4/m2/day) than at open water sites (median = 114 mg/CH4/ m2/day), but were unrelated to changes in water levels following summer-time precipitation events. However, an intentional drawdown of 0.5m conducted over 24 hours in mid-September caused ebullition rates to increase by an average of 7-fold (range 2–26 fold). This intentional drawdown dropped water levels to their lowest point since early summer, likely triggering the release of stored sediment bubbles. Drawdowns are frequently conducted during the fall in many midwestern reservoirs and may be an important period of methane emissions.
