Performance evaluation of different horizontal subsurface flow wetland types by characterization of flow behavior, mass removal and depth-dependent contaminant load

► Plants improve the contaminant removal efficiency in the gravel CW. ► The hydroponic plant root mat achieves better contaminant removal than the planted gravel CW. ► Plants induce flow and thus contaminant flux into the root zone of the gravel CW. ► Local residence time distributions allow to observe dead zones and preferential flow paths.