Photosynthesis-driven methane production in oxic lake water as an important contributor to methane emission

Recent discovery of methane (CH4) production in oxic waters challenges the conventional understanding of strict anoxic requirement for biological CH(4)production. High-resolution field measurements in Lake Stechlin, as well as incubation experiments, suggested that oxic-water CH(4)production occurred throughout much of the water column and was associated with phytoplankton especially diatoms, cyanobacteria, green algae, and cryptophytes. In situ concentrations and delta C-13 values of CH(4)in oxic water were negatively correlated with soluble reactive phosphorus concentrations. Using(13)C-labeling techniques, we showed that bicarbonate was converted to CH4, and the production exceeded oxidation at day, but was comparable at night. These experimental data, along with complementary field observations, indicate a clear link between photosynthesis and the CH(4)production-consumption balance in phosphorus-limited epilimnic waters. Comparison between surface CH(4)emission data and experimental CH(4)production rates suggested that the oxic CH(4)source significantly contributed to surface emission in Lake Stechlin. These findings call for re-examination of the aquatic CH(4)cycle and climate predictions.