Fluxes of turbulent momentum, heat, moisture, as well as carbon dioxide associated with a prescribed Gulf Coast prairie fire, were documented quantitatively using a 42-m instrumented flux tower within the burn perimeter and a tethered balloon sounding system immediately downwind of the fire. The measurements revealed significant increases of temperature (up to 20 oC), heat flux (greater than 1000 W m-2), and CO2 (larger than 2000 ppmv) within the smoke plumes as well as an intensification of turbulent mixing as indicated by an increase in turbulent kinetic energy and decrease in flux Richardson number. Furthermore, the observations revealed an increase in water vapor mixing ratio of more than 2 g kg-1 or nearly 30% over the ambient air, which is in good agreement with theoretical estimate of the amount of water vapor release expected as a combustion byproduct from a grass fire. These observations provide direct evidence that natural fuel load grass fire plumes may modify the dynamic environment of the lower atmosphere through not only heat release and intense mixing, but large addition of water vapor.