Eutrophication and ice phenology influence methane storage in north temperate lakes

Abstract Among lakes, eutrophication is positively related to methane emissions, but various processes can alter the seasonal conversion of primary production into stored methane. We used a series of whole‐lake enrichment and shading experiments across three years with varying ice phenology to assess how eutrophication and ice cover affect within‐year methane storage. The seasonal pattern of methane storage was driven in part by cyanobacteria blooms and their influence on light and oxygen availability. Early ice‐off reduced anoxic volume and methane storage in both the manipulated and reference lake, but a subsequent bloom and shading in the manipulated lake drove a rapid increase in methane, with storage reaching similar levels to those of other years. These experiments revealed that interactions between ice phenology and eutrophication can drive shifts in seasonal methane storage trajectories in north temperate lakes. Improved understanding of variability in these drivers could substantially reduce uncertainty in lake methane emissions.