SOME PROPERTIES OF METHANE OXIDATION IN A THERMALLY STRATIFIED LAKE

Profiles of (CH4)-C-14 and (CO)-C-14 oxidation and concentrations of C H4, NH4+, and nitrogen oxides (N2O, NO2-, NO3-) were studied in Lake S t. George, Ontario, during late summer stratification. Metalimnetic ma xima of the nitrogen oxides occurred and high rates of oxidation of CH 4 and CO were limited to a narrow band (<1 m) below the nitrogen oxide peaks at the oxic-anoxic interface. Oxidation of CH4 and CO was stron gly inhibited by the nitrification inhibitor allylthiourea. The affini ty of the oxidizers for CH4 (approximate K-m = 4.6 mu M), their sensit ivity to picolinic acid, and the ratio of CH4 oxidation to allylthiour ea-sensitive CO oxidation together suggest that methanotrophs were res ponsible for the observed CH4 oxidation. Pure cultures of Nitrosomonas europaea, although less sensitive to picolinic acid than the CH, oxid izers of Lake St. George,were affected by the inhibitor (approximate K -i for inhibition of NH4+ oxidation = 51 mu M).