AMMONIA CHANGES IN AQUACULTURE PONDS COVERED WITH IPOMOEA AQUATICA FLOATING BEDS

Floating beds were used widely for improving water quality in aquaculture environments, but its effects on ammonia changes in aquaculture environments were still not clear. In this study, the Ipomoea aquatic floating beds were introduced into 2 intensive aquaculture ponds to investigate its effect on ammonia dynamics, and 2 similar ponds set as controls. Throughout the experiment, control ponds were higher than the corresponding floating bed ponds in ammonia concentration by 6.2 similar to 75.7 %, and 12.4 similar to 43.2 %, respectively. The unionized ammonia concentrations of the two control ponds were 2.58 similar to 8.86-fold higher than that of the corresponding experimental ponds. In the Ipomoea aquatica fibrous roots, the amoA copy numbers of ammonia-oxidizing bacteria (AOB) ranged from (1.16 +/- 0.01) x 10(5) to (2.33 +/- 0.24) x 10(6) copy g(-1), and those of ammonia-oxidizing archaea (AOA) ranged from (5.41 +/- 0.25) x 10(3) to (3.82 +/- 0.37) x 10(4) copy g(-1). The Ipomoea aquatica floating bed can efficiently remove ammonia in intensive aquaculture pond, especially can decrease the unionized ammonia level and the unionized ammonia toxicity to fish. It was assumed that the decrease of the unionized ammonia level was resulted from the pH decrease, which was contributed by the floating bed through algal photosynthesis inhibition. High richness of AOB and AOA in the Ipomoea aquatica rhizosphere indicated that the rhizospheric ammonia-oxidizing microorganisms played a vital role in ammonia removal.