Effects of five macrophytes on nitrogen remediation and mass balance in wetland mesocosms

Five macrophyte species, Carex elata All., (Cae), Juncus effusus L (Jue), Typhoides arundinacea (L) Moench (syn. Phalaris arundinacea L) (Pha) var. picta, Phragmites australis (Cav.) Trin. (Phr), and Typha latifolia L (Ty), have been grown in mesocosms fed with a synthetic wastewater to acquire information on nitrogen balance and assess their capacity to abate nitrogen. The experiment, conducted during the growing seasons 2008-09 with four replicates, also included an unvegetated control. The mesocosms, filled with gravel, were fed with a solution of 105 ppm of NO3-N and 100 ppm of NH4-N in 2008 for a cumulative nitrogen load of 86 g/m(2) and with increased concentration in 2009 from 104 ppm of NO3-N and 119 ppm NH4-N, to 200 ppm of NO3-N and 207 ppm of NH4-N for a cumulative nitrogen load of 222 g/m(2). At the end of the experiment plants were harvested and N content in the above and belowground biomass was determined along with the amount of N contained in the roots and gravel microbial communities. In the first growing season (8 months) Ty removed 82 g/m(2) (96% of the cumulative load) of TOT N, followed by Cae (94%),Jue (82%), Pha (81%), Phr (77%) and the control (48%). In the second growing season (6 months) all the vegetated treatments, except Jue, increased their efficiency, with Pha removing 216 g/m(2) (98% of the cumulative load) of TOT N. followed by Phr and Ty (97%), Cae (93%),Jue (75%) and the control (63%). Jue showed lower tolerance than the other species to high N concentration. Depending on the species, plants absorbed 53-75% of the two-seasons load and allocated 51-83% of this amount in the aerial tissues, showing the benefit of harvesting to remove N from the treatment site, at least in the medium short term. Application of the N balance allowed the gaseous losses to be estimated, giving values ranging from 51 g/m(2) in Ty to 114 g/m(2) in Pha, 17% and 37% of the total load respectively. If the target is the definitive elimination of the maximum amount of N from the treatment site, the sum of nitrogen harvested in the aerial part and the gaseous losses has to be considered. This value was maximum with Cae, with 227 g/m(2) over the two years. (C) 2012 Elsevier B.V. All rights reserved.