A Novel Method for Characterizing the Inter‐ and Intra‐Lake Variability of CH4 Emissions: Validation and Application Across a Latitudinal Transect in the Alpine Region.

Lakes in the Alpine region are recognized as critical methane (CH4) emitters, but a robust characterization of the magnitude and variability of CH4 fluxes is missing. We developed a mobile platform for CH4 eddy covariance (EC) flux measurements to tackle this gap. The mobile system was deployed at nine lakes across a latitudinal transect in the Alps and validated by comparing the measured fluxes with fixed on‐shore EC station and to chamber and boundary layer flux estimates. Our approach was shown to be well suited to capture different CH4 emission pathways and to integrate the within lake variability, therefore, overcoming the limitations of other methods (e.g., boundary layer method). Additionally, this mobile system offers a tool to characterize inter‐lake variability of fluxes with consistent measurements. Methane fluxes were explained by dissolved nitrogen, total phosphorus, dissolved oxygen, seston and lake size. The highest fluxes and most substantial seasonal variability were found in a shallow low‐altitude lake in the Southern Alps. We suggest that characterizing the intra‐lake emission heterogeneity and consistent measurements for a better understanding of inter‐lake emission differences is fundamental for a solid estimate of freshwater CH4 budgets. Plain Language Summary: Our paper focuses on lakes in the Alpine region that release a greenhouse gas called methane (CH4) which is relevant for global warming. Even though we know these lakes emit methane, there is still the need to understand how much is released and how it changes over time. To address this, we built a special mobile tool to measure methane emissions using a method called eddy covariance. Eddy covariance is used to measure the exchange of gases, like methane, between the Earth's surface and the atmosphere by tracking the local changes in wind speed and gas concentration. We tested our mobile tool at nine different lakes across the eastern Alps and compared our measurements with data from common methods like estimating methane from the water close to the lake's surface. We found that the presence of nutrients, the lake's size, and the organic material in the water were associated with how much methane is released. Our mobile tool also helped us describe the variability of methane emissions among different parts of the same lake. This information is crucial because it helps us figure out how much methane these lakes are releasing and better understand the differences between lakes. Key Points: We developed and validated a mobile eddy covariance platform for capturing CH4 fluxes across lakes in the Alpine region for 2 yearsCH4 emissions varied substantially within and among the studied lakes which need consideration for accurate emission assessmentsStatistical models with a few in situ physicochemical and biological variables could describe the observed CH4 fluxes [ABSTRACT FROM AUTHOR]