The main mechanisms for Nitrate Nitrogen removal in wetland systems include plant absorption, the dissimilation, denitrification, and assimilation of microorganism, and ion exchange in the soil. However, under high Nitrate Nitrogen concentrations, microbial denitrification is regarded as the primary mechanism to remove Nitrate Nitrogen from a wetland system. Denitrification occurs due to an anoxic environment and adequate carbon source. The sediment in a wetland and biofilms, which form on small rocks or plant tissues can create anoxic environments. Thus, the amount of carbon source becomes the main constraint for Nitrate Nitrogen removal in wetland systems (Hoek and Klapwijk, 1987; Ingersoll and Baker, 1998; Iwa, 2000; Lin et al., 2002). In this study, the highly concentratedinfluxcausedthedeclineoftheremovalrateinthetwosystemsafterthefortieth day. However, the removal rates increased and stabilized after day 60, suggesting that the
greater dominant plant coverage in the two zones supplied the necessary carbon sources for denitrification and subsequent nitrogen removal. In addition, more plant coverage would lead to greater microbial populations in the soil due to the rhizosphere effect. Presumably, these increased microbial populations would also create enhanced conditions for denitrification