Physical versus biological controls of methane partial pressure in shallow lakes under contrasting alternative states

BALIÑA, SOFÍA; IZAGUIRRE, IRINA; SÁNCHEZ, MARÍA LAURA; DEL GIORGIO, PAUL; MUSCARELLA, MARIO

Congreso; ASLO 2021 Aquatic Sciences Meeting; 2021

ASLO

Submerged macrophytes play a key role in maintaining clear vegetated states in shallow lakes with alternative regimes, but their role on methane dynamics has been less explored. They might enhance methane emissions by providing organic matter for methanogenesis but they could also supply oxygen to the sediments therefore increasing methanotrophy, and may also have a physical effect over gas exchange by diminishing wind effect on the water column. Here we explore the contribution of biological and physical factors regulating methane dynamics in shallow lakes under contrasting alternative regimes. We measured seasonal methane fluxes and methane partial pressure (MPP) in 2 clear vegetated and 2 turbid phytoplankton-dominated shallow lakes of the Pampean Plain, Argentina. We estimated methane oxidation, production, and gas exchange velocities standardized to a Schmidt number of 600 (K600), and we found that physical rather than biological factors controlled the observed differences in MPP between alternative regimes. Clear and turbid lakes had similar overall methane oxidation and production, but clear lakes had higher average MPP, which was explained by the systematically lower K600 relative to turbid lakes. Furthermore, while turbid lakes presented the expected positive relationship between K600 and wind speed, in clear lakes this relation was absent. These results suggest that submerged vegetation tend to suppress wind-induced turbulence, diminishing gas exchange velocity and therefore augmenting the amount of methane in surface waters of clear vegetated shallow lakes.