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

Abstract

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 105ppm of NO3–N and 100ppm of NH4–N in 2008 for a cumulative nitrogen load of 86g/m2 and with increased concentration in 2009 from 104ppm of NO3–N and 119ppm NH4–N, to 200ppm of NO3–N and 207ppm of NH4–N for a cumulative nitrogen load of 222g/m2. 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 82g/m2 (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 216g/m2 (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 51g/m2 in Ty to 114g/m2 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 227g/m2 over the two years.