Effects of water level fluctuation on radial oxygen loss, root porosity, and nitrogen removal in subsurface vertical flow wetland mesocosms

Laboratory experiments were conducted to investigate the effects of water level fluctuation on plant radial oxygen loss (ROL), root porosity, plant growth performance, and nitrogen dynamics in vertical subsurface flow wetland mesocosms. Four types of mesocosms were used: control with static water level, control with fluctuating water level, static water level with plants, and fluctuating water level with plants. Typha orientalis, an emergent macrophyte, was used in this study. Changes of ROL, root porosity, and plant biomass were measured every six weeks. Shoot height and density of plants were also observed. Every two weeks, the nitrogen removal efficiency of the four systems was monitored. Maximum ROL values under static and fluctuating conditions were 7.58 and 2.73 μmol/g DW/h, respectively. The porosity values of roots under static and fluctuating conditions ranged between 33-47% and 30-37%, respectively. Average removal efficiency of both total nitrogen (TN) and ammonium nitrogen (NH4-N) in the fluctuating condition with plants was about 65%, and nitrate nitrogen removal in the static condition with plants was about 75%. Although the water level fluctuation caused a considerable reduction in ROL and root porosity, it clearly produced a significant improvement in TN and NH4-N removal.