Air-water gas transfer coefficient for shallow water

Fluxes of GH gases across the water surface constitute an important part of the global climate. Because of the combination of small concentrations and  small fluxes, the determination of air–water gas fluxes presents unusual measurement difficulties. Direct measurements (i.e., eddy correlation) of the fluxes are rarely attempted.  Used in gas transport parameterization models were mainly developed for the open ocean. The differences, especially those between shallow sheltered systems and the open waters best fit by some published relationships, are ecologically important and do not appear yet to be measurable by other methods.

The report discusses the determination of the transfer coefficient from direct measurements of methane and carbon dioxide fluxes in the case of shallow water bodies. Coastal zones, an estuary, a small lake and a river of differing bathymetry and local terrain are considered. The influence of footprint, surface condition, and atmospheric stability is investigated. In the case of a river, the current may also have an influence. It is shown that the inhomogeneous relief significantly affects the results of the convergence of measurements and model calculations. Determined that the model overestimates the fluxes in low winds. For CH₄, most of the transport appears to be by ebullition rather than diffusion and model would have underestimated the exchange by two orders of magnitude. New dependencies are proposed for determining the gas transfer coefficient for methane and carbon dioxide under conditions of shallow water and inhomogeneous relief. The work was supported by the Russian Science Foundation grant 22-47-04408.