Methane cycling in a eutrophic shield lake and its effects on whole lake metabolism 1

The methane cycle of an artificially eutrophic shield lake is considered by relating in situ rates of production to rates of oxidation and evasion. Methane production rates f’or oxygenated and anoxic sediments were quite consistant throughout the year, ranging from ~1.0 to ~10 mmol m −2 sediment d −1 . Methane oxidation rates were highly variable (0.02–32 mmol m − 2 lake surface d − 1 ) as were evasion rates (0.0–60 mmol m − 2 lake surface d −1 ). Oxidation and evasion rates both peaked during fall overturn and were very low during the remainder of the year. Methane production was important in regenerating carbon from sediments. Fifty‐five percent of total carbon input was regenerated as methane during 1 year and 36% of this total carbon input was recycled by methane oxidation. Methane oxidation was not an important source of carbon dioxide for primary producers or of seston for secondary grazers during the summer. During some winters production of particulate carbon by methane oxidizers may have been an important source of seston for grazers. Methane oxidation was the most important contributor to the development of total lake anoxia under ice cover.