Small lakes have been identified as a significant source of methane in the global methane budget. These lakes have higher methane fluxes per unit area than large lakes and contribute a major fraction of global methane emissions from lakes. However, the estimation of lake-wide methane emissions underlies large uncertainties, because measurements and model approaches that account for the temporal and spatial variability of methane in lakes are rare. The aims of the project are to investigate methane dynamics and distribution patterns in and methane emissions from small lakes as well as to characterize lake properties and to quantify processes that determine the lake-wide methane emissions from small lakes. Thereby, the focus will be on the relative importance and temporal variability of spatial gradients in methane, autumn overturn, and the different flux paths for annual, lake-wide methane emissions. Intensive field experiments will be conducted measuring the internal dynamics, spatial heterogeneity, lake-wide distribution, and temporal variability of dissolved methane and methane emissions that account for the main emission pathways together with abiotic conditions on the example of six lakes having different properties. State of the art measuring techniques (e.g., an eddy-covariance system, single- and multi-beam echosounder, methane and carbon dioxide probes, automated ebullition flux funnels and diffusive flux chambers, an ultraportable greenhouse gas analyzer, oxygen and carbon dioxide optodes) will be combined with intensive water sampling and water sample analysis (dissolved methane, methane isotopic composition, oxidation rates, and other water constituents) to meet the requirements of sufficient temporal and spatial resolution and reliable absolute data on all abiotic parameters and in specific on the dissolved methane concentration. These field experiments will be complemented by numerical simulations of the methane dynamics conducted with a 3D Methane Model. The purpose of the numerical approaches is to simulate horizontal transport, exchange and distribution dynamics of dissolved methane, and the lake-wide diffusive flux of methane to the atmosphere under changing boundary conditions in small lakes as well as to investigate how climate change and different wind forcing affect the diffusive flux of methane to the atmosphere during overturn periods and their relative contribution to the annual, lake-wide emissions.
