A methane bubble curtain in meromictic Sakinaw Lake, British Columbia

Hydroacoustic surveys in meromictic Sakinaw Lake found an approximate 20-m-wide dual-column bubble curtain originating from a depth of 42–60 m all around the main basin at the interface between the chemocline and the sediments. With the exception of the small upper basin, Sakinaw Lake is oligotrophic and permanently salt stratified, with a 30-m mixolimnion overlying an anoxic monimolimnion containing high concentrations of sodium chloride and dissolved sulfide. Nitrogen is the major factor limiting the lake’s phytoplankton productivity. The mainly methane bubbles in the curtain have a fairly narrow range of sizes, with most of the bubbles (75%) having radii between 600 and 850 mm with a peak at 735 mm, which is close to a third of the size of bubbles reported for Kinneret Lake in Israel. We hypothesize that different bubble generation mechanisms cause this difference. A simple bubble evolution model that includes gas dissolution and buoyancy is in good agreement with the acoustically observed bubble characteristics and is used to infer bubble densities and gas flux rates. Few of the bubbles reach the surface with any methane left in them. The bubble flux of methane into the upper part of the lake is 3 mg m22 yr21. The dual-column nature of the bubble plume and the extensive and persistent nature of the bubble curtain around the lake suggest that there may be unique physical and biological conditions in Sakinaw Lake affecting methane generation and bubble ebullition.