Nitrogen and phosphorus standing stock inPhalaris arundinaceaandPhragmites australisin a constructed treatment wetland: 3-year study

Constructed wetland with sub-surface horizontal flow at Břehov near České Budějovice, Czech Republic is designed to treat sewage from 100 population equivalent. The system was put into operation in late 2003 and it consists of two rectangular beds (28 (L) × 9 (W) m each) planted with Reed canarygrass (Phalaris arundinacea) and Common reed (Phragmites australis) in bands parallel to the flow. Aboveground biomass of Phalaris and Phragmites was harvested in 2004, 2005 and 2006 during the peak standing crop of both species, i.e. in July for Phalaris and the early September for Phragmites. In 2004 and 2005, also belowground biomass was harvested. The major objective of the study was to evaluate the amount of nutrients sequestered in plant biomass and compare it with inflow loading. The analysis of the biomass indicated that the concentrations of nitrogen and phosphorus in various parts of both species were comparable in all three years. However, due to the higher biomass in 2005 and 2006 the nutrient standing stocks increased between 2004 and 2006 indicating that the most important factor for standing stock is the plant biomass. The results revealed that the amount of nutrients sequestered in the aboveground biomass and hence available for harvesting was low as compared to inflow load.