Fate of 15NO3− and 15NH4+ in the Treatment of Eutrophic Water Using the Floating Macrophyte, Eichhornia crassipes
- Yan Gao *a,
- Neng Yib,
- Zhiyong Zhanga,
- Haiqin Liua and
- Shaohua Yan *a
Use of the floating aquatic macrophyte, Eichhornia crassipes, to improve eutrophic water quality is practiced on a large scale in China. Limited information is available on the relative importance of the biological NO3− or NH4+ removal process during the treatment of eutrophic water using Eichhornia crassipes. To investigate the key process responsible for the removal of NO3− and NH4+, 15N-NO3− (9.98 atom % [at.%] 15N) or 15N-NH4+ (10.08 at.% 15N) was added to obtain eutrophic water with or without the cultivation of Eichhornia crassipes. In the unplanted water, considerable proportions of the added 15N-NO3− (27.13 ± 4.87%) or 15N-NH4+ (42.08 ± 7.22%) were assimilated by the developed algae. The growth of Eichhornia crassipes controlled algae development in the planted water. Furthermore, the cultivation of Eichhornia crassipes stimulated gaseous loss of N by microbial denitrification (8.61 ± 1.70% N2O-N loss from 15N-NO3−–labeled water). Apart from N loss by denitrification, considerable proportions of the added 15N-NO3− (62.01 ± 6.93%) or 15N-NH4+ (76.76 ± 6.21%) were assimilated into the macrophyte N pools. The fine root detritus of Eichhornia crassipes contained a proportion of N (4.37 ± 1.39% in 15NO3−–labeled water, 2.03 ± 0.52% in 15NH4+–labeled water) that will be returned to the water after decomposition. In addition to 15N loss via N2O emission, an unaccounted proportion of 15N could be mainly due to gaseous loss as N2 by denitrification (25.00% in 15N-NO3−–labeled water with Eichhornia crassipes).Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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