The role of wetland plants in the treatment of wastewater was investigated. The research was carried out in the backdrop of conflicting reports about the role wetland plants play in wastewater treatment. The plants' ability to release oxygen through their roots in wastewater environment was investigated in subsurface flow wetlands. The research investigated the role of aerobic and anaerobic processes in constructed treatment wetlands. Oxygen release by the wetland plants has been reported by researchers. One of the most recent studies have reported quantification of wetland plant oxygen release through the use of microelectrodes. However, the microelectrode measurement method had its inherent drawback of possible under or over estimation of oxygen release by wetland plants. This research is an endeavor to model a field wetland based on the assumption that wetland plants do not release enough oxygen for use in biochemical oxygen demand (BOD) removal. The wetland was modeled as an aerobic-anaerobic system. The model takes into account all the possible mechanisms of oxygen addition and consumption. These mechanisms include atmospheric reaeration, plant oxygen release, wastewater oxygen demand, and biomass oxygen demand. The modeling results indicated that ∼ 65% BOD removal occurs aerobically and rest is removed anaerobically.