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

•Substrate and water flow are important factors controlling greenhouse gas emissions from CW with ornamental plants.•Surface flow CW measocosms planted with Zantedeschia aethiopica emitted more CH4 than subsurface flow CW mesocosms.•Subsurface flow CW mesocosms planted with Zantedeschia aethiopica removed more nitrogen and emitted more N2O than surface flow CW mesocosms.•In a pilot scale CW, CH4 emissions were higher in zones with Zantedeschia aethiopica than with macrophytes (Typha sp and Cyperus papyrus).