Critique of Floating-dome Technique for Estimating Reaeration Rates

The task of accurately estimating the reaeration coefficient in oxygenmodeling studies remains a primary concern to researchers. In lotic systems the reaeration coefficient has been directly estimated by deoxygenating a parcel of water and measuring its DO as it travels downstream (Gameson et al. 1955); by measuring the loss of radioactive-gas tracers (Tsivoglou et al. 1965, 1968) or hydrocarbons (Rathburn et al. 1975; Ruane and Kim 1979) from a water parcel; by measuring the rate of change of the concentration of gaseous oxygen (Copeland and Duffer 1964) or carbon dioxide (Hood and Kelley 1976) inside a floating dome, or helmet; and by predictive equations (reviewed by Zison et al. 1978; Wilcock 1982). Predictive equations, for the most part, have not been applied to lentic systems because of their greater complexity and the lack of understanding of the important turbulentmixing processes affecting reaeration. The only direct measurement techniques commonly used in lentic systems are floating-dome, or helmet, techniques. In view of the foregoing, the primary purpose of this study was to evaluate the suitability and effectiveness of the floating-dome oxygen method, as described by Copeland and Duffer (1964) and the U.S. Geological Survey ("Methods" 1987), for providing valid and scientifically sound reaeration estimates in lentic systems. This critique is supported by simple theoretical calculations and experimental data.