PARENT SESSION
Oral Session #17: Wetland Ecology. Presiding: E. Weiher.
Monday, August 6, 2001. 1:00 PM to 4:15 PM. Hall of Ideas H.
Oxygen fluxes in constructed wetlands.
Wu, Mei-Yin1, Franz, Eldon2, Chen, Shulin2, 1 2
ABSTRACT- Two dominant routes have been documented for transfer oxygen from air to constructed wetland systems: 1) atmospheric oxygen diffusion and 2) oxygen release from plant roots. This study quantified the atmospheric oxygen diffusion and plant oxygen release rates in constructed wetland systems. We found that oxygen transfer to the constructed wetland was dominated by atmospheric oxygen diffusion. Nitrogen removal efficiency in a constructed wetland is often limited by the amount of oxygen available in the system. The atmospheric oxygen diffusion rates to laboratory-scale subsurface flow constructed wetlands and free water surface constructed wetlands were quantified in this study under two rates of NH4+ loading, 50 mg-N/l and 10 mg-N/l. Appreciable amounts of oxygen were found to diffuse into the subsurface flow constructed wetlands, and the diffusion rates were strongly correlated with the NH4+ concentration in the water. In contrast, little oxygen actually diffused into the free water surface systems. Statistically, the existence of plants on the wetland had no significant impacts on either atmospheric oxygen diffusion rates or NH4+ removal efficiencies in both subsurface flow systems and free water surface systems. This observation was further verified with the tests on oxygen leakage from plant roots. Only approximately 0.023 g/m2/day of oxygen was released from roots of T. latifolia measured using the titanium (III) citrate buffer method. The results of the NH4+ removal rates of the lab scale constructed wetland were further verified with pilot scale constructed treatment wetlands under greenhouse conditions. There was no statistically significant difference between NH4+ removal efficiencies in either lab or greenhouse scale constructed treatment wetland system.
KEY WORDS: constructed wetlands, nitrification, oxygen diffusion, nitrogen removal