CONTINUOUS MEASUREMENT OF CO2 FOR ESTIMATION OF AIR-WATER FLUXES IN LAKES - AN IN-SITU TECHNIQUE

Three parameters must be known to use the thin boundary-layer model (o r other bulk transfer models) for CO2 flux between water and air: the concentration of dissolved CO2, CO2(aq), the concentration of CO2 in t he air immediately above the water, CO2(atm), and the wind velocity, w hich is used to determine the appropriate transfer coefficient. These parameters change hourly and from day to day in a nonlinear fashion, s o the frequency of measurements is an important factor in determining the accuracy of flux estimates for any period. To achieve a high frequ ency measurement, we developed a self-contained, solar-powered, in sit u sampling system that continuously measures and records CO2(aq), CO2( atm), and windspeed. Unique to this technique is an underwater in situ equilibration chamber (ISEC). The ISEC was tested in a shallow wetlan d pond in which changes in both CO2(aq) and CO2(atm) were large. The d ata obtained showed that large errors may result from extrapolating fl ux calculations made from short-term data (e.g. daily) to longer time periods.