Parametrization of Air/Lake Gas Exchange
The wind speed dependence of air/water gas exchange in natural systems is controversial, since field measurements failed to verify such a dependence, whereas wind/wave tunnel data show a strong increase of the gas exchange rate with wind speed. This turns out to be no real discrepancy, since the mechanisms controlling gas exchange are not well understood yet and a simultaneous view on recent wind tunnel results shows that other parameters beside the windspeed, dependent on the water surface waves, are influencing the exchange. In this paper we present gas exchange rates obtained with the Tritium/Helium-3 method from 4 lakes. The measured transfer velocities range from 0.4 to 11 m/d. Despite the large uncertaincies both of the exchange rates and the friction velocity, a significant windspeed dependence is found. Finally we describe how to improve measurements in order to get better parametrization and present our investigation started in autumn 1982 at Lake Sempach, Switzerland. In the middle of the lake a buoy is anchored measuring all important meteorological and limnological parameters. The study is closely linked with a project of the EAWAG, during which the internal mixing of the lake is studied with the same data sets.
KeywordsWind Speed Friction Velocity Schmidt Number Transfer Velocity Wind Tunnel Data
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