Seasonal Change in Gas Content and Buoyancy of Floating Typha Mats

Abstract

(1) In an embanked, freshwater marsh in New Brunswick, Canada, the buoyancy of experimentally isolated Typha fioating mats and release rate of gas bubbles were monitored. Mats were most buoyant and released the greatest quantity of gas in late summer when water temperature in the mat was highest. (2) Nitrogen and methane were the major components of gas bubbles trapped in the organic material in August, but the percentage of methane was relatively lower in May. (3) In a laboratory experiment, Typha mat samples were incubated in growth chambers at 2, 8, 15 or 22 ?C for twelve weeks, and were then held at 2 ?C for thirteen weeks and 15 ?C for ten weeks to simulate winter and summer temperatures, respectively, in floating mats. Samples incubated at 22 ?C reached an equilibrium gas content of 13 7% of total mat volume, while samples at 2 ?C attained a gas content of 6 2%. The magnitude of seasonal change in gas content was estimated at between 2 5 and 4 7% of total mat volume. (4) Seasonal, temperature-dependent change in the rate of anaerobic decomposition is partly responsible for the observed seasonal variation in the gas content and buoyancy of mats, but physical processes such as changes in gas solubility with temperature are also important. The significance of anaerobic decomposition as a biotic factor influencing successional development is discussed.