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

• Published in: Limnology and oceanography Vol. 65; no. 12; pp. 2853 - 2865
• Main Authors: Günthel, Marco, Klawonn, Isabell, Woodhouse, Jason, Bižic, Mina, Ionescu, Danny, Ganzert, Lars, Kümmel, Steffen, Nijenhuis, Ivonne, Zoccarato, Luca, Grossart, Hans-Peter, Tang, Kam W.
• Format: Journal Article
• Language: English
• Published: Hoboken, USA John Wiley and Sons, Inc 01-12-2020; John Wiley & Sons, Inc
• ISSN: 0024-3590; 1939-5590
• DOI: 10.1002/lno.11557

Recent discovery of methane (CH₄) production in oxic waters challenges the conventional understanding of strict anoxic requirement for biological CH₄ production. High-resolution field measurements in Lake Stechlin, as well as incubation experiments, suggested that oxic-water CH₄ production occurred throughout much of the water column and was associated with phytoplankton especially diatoms, cyanobacteria, green algae, and cryptophytes. In situ concentrations and δ13C values of CH₄ in oxic water were negatively correlated with soluble reactive phosphorus concentrations. Using 13C-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 CH₄ production-consumption balance in phosphorus-limited epilimnic waters. Comparison between surface CH₄ emission data and experimental CH₄ production rates suggested that the oxic CH₄ source significantly contributed to surface emission in Lake Stechlin. These findings call for re-examination of the aquatic CH₄ cycle and climate predictions.