HYPOLIMNETIC O-2 CONSUMPTION, DENITRIFICATION, AND METHANOGENESIS IN A THERMALLY STRATIFIED LAKE

Hypolimnetic O2 consumption, methanogenesis, and denitrification were estimated from concentration changes in O2, CH4, and nitrogen oxides (NO3-, NO2-, N2O), respectively, in the eastern basin of Lake St. George, Ontario, during thermal stratification from 1980 to 1984. NH4+ accumulated in the hypolimnion throughout the period of stratification and provided an overall measure of organic matter mineralization. Anaerobic metabolism, particularly methanogenesis, predominated because anoxia was total within less than 2 mo of spring water column turnover and nitrogen oxides were always completely depleted before fall turnover. The time of onset and rate of NO3- depletion varied considerably between years and were not always directly correlated with O2 concentration. It was estimated that, on average, O2 consumption, denitrification, and methanogenesis accounted for approximately 80% of hypolimnetic organic C mineralization in the periods surveyed.