Influences of plant species and radial oxygen loss on nitrous oxide fluxes in constructed wetlands

Abstract

Constructed wetlands have been used as a green technology to treat wastewaters for several decades. However, constructed wetlands are considered to be great sources of nitrous oxide, a potent greenhouse gas contributing to global warming. Plants play an important role in the nitrogen cycling in wetland ecosystems. To investigate the effects of wetland plants on nitrous oxide fluxes through radial oxygen loss and nutrient removal, integrated vertical flow constructed wetlands were used and planted with three wetland plants (Canna indica L. (C. indica), Acorus calamus L. (A. calamus) and Scirpus validus Vahl (S. validus)). The results showed that integrated vertical flow constructed wetlands were significant sources of nitrous oxide fluxes. However, the nitrous oxide fluxes from the C. indica, A. calamus and S. validus wetlands differed substantially, ranging from 0.05 ± 0.01 to 1.80 ± 0.34, 0.08 ± 0.00 to 0.62 ± 0.20, and 0.03 ± 0.00 to 0.27 ± 0.01 mg N2O-N/m2/h, respectively, and had a similar tendency of seasonal variations: summer > autumn > spring > winter. The nitrous oxide fluxes from the down-flow cells were higher than those from the up-flow cells in every season. Among the three plant species, S. validus was most efficient in removing total nitrogen and ammonium nitrogen while minimizing nitrous oxide fluxes, and could be utilized preferentially as wetland plant. The radial oxygen loss of species has a seasonal tendency: summer > autumn > spring > winter. The nitrous oxide fluxes had positive significant correlations with temperatures, ammonium nitrogen and total nitrogen removal efficiencies and radial oxygen loss. These results contributed to linear prediction and reduction for nitrous oxide fluxes in constructed wetlands.