Dynamics of microbial oxidation of methane in the water of stratified lakes

Fluctuations of methane (CH₄) concentration and the dynamics of microbial methane oxidation (MO) were investigated in the water column of freshwater stratified lakes of different trophicity levels during various seasonal periods and throughout the diurnal cycle. Characteristics of vertical CH₄ distribution and ranges of methane transformation rates were determined and found to depend upon the lake productivity as well as seasonal and daily fluctuations of hydrological and hydrochemical parameters. The highest rate of MO was registered in highly eutrophic lakes during summer stagnation under conditions of formation of a distinct metalimnial water layer with MO up to 0.4–1.2 ml CH₄/(l day). Under the same conditions, a maximum amount of bacterioplankton (6–13 × 10⁶ cells/ml) was detected and CO₂ bacterial dark assimilation (DA) reached 50–72 μg C/(l day). In the metalimnion layer, a strong correlation (R = 0.74) was revealed between diurnal fluctuation dynamics of MO and DA.