Evaluation of two, current approaches for the measurement of carbon dioxide diffusive fluxes from lentic ecosystems

The dry ice sowing experiment (DISE) consisted in adding dry ice to a lake and monitoring the subsequent evasion of carbon dioxide (CO2). DISE allowed us to evaluate two approaches commonly used for measuring aquatic CO2 diffusive fluxes: the boundary layer equation (BLE) from Cole and Caraco (1998) and a particular model of static chamber (SC). CO2 evasion measurements with both approaches were compared to CO2 mass budgets as a relative reference to define their recovery coefficients (rho). rho for the BLE and the SC over the whole measurement period were 101 +/- 14%and 115 +/- 56%, respectively. Results from discrete sampling intervals revealed that the BLE generally provided estimations in good agreement (80-130%) with the mass budgets during both daytime and nighttime. Variations in rho for the BLE were related to wind speed and, consequently, piston velocity (k(600)). The SC overestimated CO2 evasion during daytime (149 +/- 39%), and underestimated it during nighttime (57 +/- 18%). Variations in rho for the SC were related to k(600), stemming mainly from the alteration of the air/water temperature gradient.