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. Freshwaters emit significant amounts of CO2 on a global scale.However, emissions remain poorly constrained from the diverse range ofaquatic systems. The drivers and regulators of CO2 gas flux fromstanding waters require further investigation to improve knowledge on bothglobal-scale estimates and system-scale carbon balances. Often,lake–atmosphere gas fluxes are estimated from empirical models of gastransfer velocity and air–water concentration gradient. Directquantification of the gas flux circumvents the uncertainty associated withthe use of empirical models from contrasting systems. Existing methods tomeasure CO2 gas flux are often expensive (e.g. eddy covariance) orrequire a high workload in order to overcome the limitations of single pointmeasurements using floating chambers. We added a small air pump, a timer andan exterior tube to ventilate the floating chamber headspace and passivelyregulate excess air pressure. By automating evacuation of the chamberheadspace, continuous measurements of lake CO2 gas flux can beobtained with minimal effort. We present the chamber modifications and anexample of operation from a small forest lake. The modified floating chamberperformed well in the field and enabled continuous measurements of CO2 gas flux with 40 min intervals. Combining the directmeasurements of gas flux with measurements of air and waterside CO2 partial pressure also enabled calculation of gas exchange velocity. Buildingand using the floating chamber is straightforward. However, because an airpump is used to restart measurements by thinning the chamber headspace withatmospheric air, the duration of the air pump pause–pulse cycle is criticaland should be adjusted depending on system characteristics. This may resultin shorter deployment duration, but this restriction can be circumvented byproviding a stronger power source. The simple design makes modifications ofthe chamber dimensions and technical additions for particular applicationsand systems easy. This should make this approach to measuring gas fluxflexible and appropriate in a wide range of different systems.

Technical note: A simple and cost-efficient automated floating chamber for continuous measurements of carbon dioxide gas flux on lakes