Some properties of methane oxidation in a thermally stratified lake

Abstract

Profiles of14CH4and14CO oxidation and concentrations of CH4, NH4+, and nitrogen oxides (N2O, NH2-, NH3-) were studied in Lake St. George, Ontario, during late summer stratification. Metalimnetic maxima of the nitrogen oxides occurred and high rates of oxidation of CH4and CO were limited to a narrow band (<1 m) below the nitrogen oxide peaks at the oxic-anoxic interface. Oxidation of CH4and CO was strongly inhibited by the nitrification inhibitor allylthiourea. The affinity of the oxidizers for CH4(approximate Km= 4.6 µM), their sensitivity to picolinic acid, and the ratio of CH4oxidation to allylthiourea-sensitive CO oxidation together suggest that methanotrophs were responsible for the observed CH4oxidation. Pure cultures of Nitrosomonas europaea, although less sensitive to picolinic acid than the CH4oxidizers of Lake St. George, were affected by the inhibitor (approximate Kifor inhibition of NH4+oxidation = 51 µM).