Eutrophication reduces temperature dependence of diffusive methane emissions in freshwater lakes

Eutrophic lakes are considered as an important source of methane (CH₄) to the atmosphere. However, the prediction for CH₄ emission from lakes with different trophic states under warming is still enigmatic. Here, we found temperature dependence of diffusive methane emissions was lower in phytoplankton-dominated zone than that in macrophyte-dominated zone in two typical shallow lakes. Furthermore, an investigation on twenty lakes from the middle and lower reaches of Yangtze River showed that diffusive CH₄ flux was significantly higher in summer than that in winter, with the ecosystem-level Q₁₀ ranged from 0.77 to 3.94 and significantly decreased with increasing phytoplankton. This indicates that eutrophication reduces temperature dependence of diffusive methane emissions in freshwater lakes. When the view extends to diffusive CH₄ emission in global lakes, the estimation regarding temperature dependence as a constant in the past overestimated global methane release for 2.3%-30% under warming for 1-2 °C. This weak positive feedback of CH₄ emission suggests that climate warming may have a lesser exacerbating effect on atmospheric CH₄ concentrations than predicted.