The gas-exchange potential of three wetland species (helophytes) was examined in an aquatic model vegetation facility (AMOVA) using sulfur hexafluoride (SF 6 ) as a tracer. Three beds containing gravel and vegetated with Phragmites australis, Typha latifolia and Schoenoplectus lacustris were compared to an unvegetated gravel bed as a reference. A mass balance of SF 6 emissions revealed a different seasonal emission pattern for the three species investigated. Helophytes capable of pressurized ventilation, e.g. Phragmites and Typha, showed the highest gas-exchange values. On an annual basis net SF 6 emission values of Phragmites were the highest in the autumn month of October (65.8%) and the lowest in the winter month of January (37.1%). P. australis represents a helophyte species with highly developed gas-exchange tissues facilitating diffusion and transport of the tracer gas SF 6 to the atmosphere via the intercellular lacunar system.