Fate of 15NO3− and 15NH4+ in the Treatment of Eutrophic Water Using the Floating Macrophyte, Eichhornia crassipes

Abstract

Use of the floating aquatic macrophyte, , to improve eutrophic water quality is practiced on a large scale in China. Limited information is available on the relative importance of the biological NO or NH removal process during the treatment of eutrophic water using . To investigate the key process responsible for the removal of NO and NH, N-NO (9.98 atom % [at.%] N) or N-NH (10.08 at.% N) was added to obtain eutrophic water with or without the cultivation of . In the unplanted water, considerable proportions of the added N-NO (27.13 ± 4.87%) or N-NH (42.08 ± 7.22%) were assimilated by the developed algae. The growth of controlled algae development in the planted water. Furthermore, the cultivation of stimulated gaseous loss of N by microbial denitrification (8.61 ± 1.70% NO-N loss from N-NO-labeled water). Apart from N loss by denitrification, considerable proportions of the added N-NO (62.01 ± 6.93%) or N-NH (76.76 ± 6.21%) were assimilated into the macrophyte N pools. The fine root detritus of contained a proportion of N (4.37 ± 1.39% in NO-labeled water, 2.03 ± 0.52% in NH-labeled water) that will be returned to the water after decomposition. In addition to N loss via NO emission, an unaccounted proportion of N could be mainly due to gaseous loss as N by denitrification (25.00% in N-NO-labeled water with Eichhornia crassipes)