Greenhouse gas emissions and pollutant removal in treatment wetlands with ornamental plants under subtropical conditions

Methane (CH4) and nitrous oxide (N2O) emissions, and pollutant removal were investigated in constructed wetland (CW) mesocosms planted with the ornamental plant Zantedeschia aethiopica to treat polluted river water. We used two types of CWs, surface flow (SF) and subsurface flow (SSF), and two plant densities, high density HD (32 plants m(-2)) and low density LD (16 plants m(-2)). We also compared CH4 and N2O emissions in zones planted with macrophytes (Typha sp and Cyperus papyrus) versus zones planted with Zantedeschia aethiopica in a pilot scaled CW treating municipal wastewater. In the mesocosms, average CH4 emissions were significantly higher in SFCW (436 +/- 32 and 518 +/- 46 mg m(-2) d(-1)). than SSFCW (319 +/- 65 and 210 +/- 74 mg m(-2) d(-1)), and plant density did not affect such emissions. SSFCW showed higher ammonia and nitrate removal efficiencies than SFCW and also showed higher N2O emissions (17 +/- 3 and 23 +/- 5 mg m(-2) d(-1)). Phosphate removal efficiencies were significantly higher in SFCW than SSFCW. In the pilot scale CW, no nitrous oxide emissions were observed and average CH4 emission (11,000 +/- 930 mg m(-2) d(-2)) was higher in the zones near the outflow planted with Zantedeschia aethiopica than in the zones near the inflow planted with Typha sp (4500 +/- 800 mg m(-2) d(-2)) and Cyperus papyrus (5500 +/- 600 mg m(-2) d(-2)), although TOC was higher in the zones near the inflow. We concluded that substrate and water flow are important factors controlling greenhouse gas emissions in CW and the amount of Zantedeschia aethiopica plants did not influence the emissions. Differences in methane emissions in the zones planted with native wetland plants in comparison with zones planted with Zantedeschia aethiopica might indicate that methane production and consumption in CW is influenced differently by the ornamental plants than by native wetland plants. (c) 2017 Elsevier B.V. All rights reserved.