Aquatic ecosystems, including lakes and wetlands, are responsible for approximately 80% of global natural methane (CH₄) emissions. Scientists long believed that CH₄ production occurs exclusively under anoxic conditions. However, CH₄ supersaturation has been frequently observed in oxygenated water bodies, and after excluding CH₄ transport processes, oxic CH₄ production has been confirmed. This supersaturation phenomenon, referred to as the “methane paradox”, has drawn significant scientific interest, yet direct empirical evidence and mechanistic understanding remain limited. 

Detecting this methane production was a major challenge. Traditional methods struggled because oxygen in water creates false signals. Given that oxic CH₄ production often involves rapid, subtle concentration fluctuations—particularly in algal-driven processes—a high-sensitivity, real-time monitoring method is indispensable. 

Led by Prof. Lu ZHANG from the Nanjing Institute of Geography and Limnology, Chinese Academy of Sciences, the researchers developed new tracking technology to reveal that algal (especially cyanobacterial) metabolism is a key player in CH₄ production in oxic environments of cold-temperate mountainous lakes. This study was recently published in Water Research.

“The research enhances our understanding of the aquatic CH₄ cycle by providing valuable insights into the role of algae in CH₄ production,” said Prof. ZHANG, “It also highlights the importance of preserving environmental balance in freshwater ecosystems, with minimal human disturbance.”