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

  • Martinsen K
  • Kragh T
  • Sand-Jensen K
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Abstract

Freshwaters emit significant amounts of CO<sub>2</sub> on a global scale. Yet, emissions remain poorly constrained from the diverse range of aquatic systems. The drivers and regulators of CO<sub>2</sub> gas flux from standing waters require further investigation to improve knowledge on both global scale estimates and system scale carbon balances. Often lake-atmosphere gas fluxes are estimated from empirical models of gas transfer velocity and air-water concentration gradient. Direct quantification of the gas flux circumvents the uncertainty associated with the use of empirical models from contrasting systems. Existing methods to measure CO<sub>2</sub> gas flux are often expensive (e.g. eddy-covariance) or require a high workload in order to overcome the limitations of single point-measurements using floating chambers. We added a small air pump, timer and an exterior tube to ventilate the floating chamber headspace and passively regulate excess air pressure. By automating evacuation of the chamber headspace, continuous measurements of lake CO<sub>2</sub> gas flux can be obtained with minimal effort. We present the chamber modifications and an example of operation from a small forest lake. The modified floating chamber performed well in the field and enabled continuous measurements of CO<sub>2</sub> gas flux with 40-minute intervals. Combining the direct measurements of gas flux with measurements of air and waterside CO<sub>2</sub> partial pressure also enabled calculation of gas exchange velocity. Application of the described floating chamber is straightforward and modifications are both simple and cost-efficient to perform. Changing the chamber dimensions to particular applications and systems makes this approach to measure gas flux flexible and appropriate in a range of different systems.

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Martinsen, K. T., Kragh, T., & Sand-Jensen, K. (2018). A simple and cost-efficient automated floating chamber for continuous measurements of carbon dioxide gas flux on lakes. Biogeosciences Discussions, 1–12. https://doi.org/10.5194/bg-2018-61

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