Seasonal growth pattern of Phalaris arundinacea in constructed wetlands with horizontal subsurface flow

•Phalaris biomass is much higher in the inflow zone as compared to outflow zone.•The peak aboveground biomass occurs at different times in inflow and outflow zones.•Separate harvest of biomass in inflow and outflow zones enhances nutrient removal.

Plants play import role in constructed wetlands (CWs) with horizontal subsurface flow. It has been well documented that planted constructed wetlands are more efficient that filters with vegetation. Also, it has been found that plant species may differ in their effect on wastewater treatment. However, there has been little attention paid to the management of vegetation with the focus on enhanced nutrient removal. During the period April 2012–March 2013 seasonal development of aboveground biomass of Phalaris arundinacea (Reed canarygrass) has been evaluated at two constructed wetlands in the Czech Republic. Both systems were sampled on a monthly basis and triplicate samples were taken in both inflow and outflow zones. It has been found that the aboveground biomass was substantially higher in the inflow zone in both surveyed CWs and this phenomenon was also found in six other CWs where aboveground biomass was sampled during the peak biomass period. Besides that, it has been found that the peak biomass in the outflow zone occurred about two months later than in the inflow zone. This information could be used for biomass harvest management aimed at enhancing nutrient removal. The results of this study revealed that if inflow and outflow zones are harvested separately at different periods of the growing season, the amount of nitrogen and phosphorus removed via harvesting may increase up to 42% and 43%, respectively as compared to a single harvest of the whole surface of the filtration beds.