EFFECT ON THE BIOTURBATION OF CARPS IN DIFFERENT DENSITY ON DENITRIFICATION, NITRIFICATION AND NITRATE AMMONIFICATION RATES ON SEDIMENT-WATER INTERFACE

Carp (Cyprinus carpio) is a common freshwater fish in China, and it widely cultivates in freshwater ponds. As a benthic fish, it makes a bioturbation to the procedures on sediment-water interface, including denitrification, nitrification and nitrate ammonification. To explore the effect of different density's carps' bioturbation on denitrification, nitrification and nitrate ammonification rates, six treatments were set in this research: treatment with no fish (C0); treatments with 2, 4, 6, 8 and 10 carps in each flume (C2, C4, C6, C8 and C10). Sediment samples were collected regularly with a sediment sampler with no boundary perturbation; denitrification, nitrification and nitrate ammonifi cation rates were measured using AIT (acetylene inhibition); tracers were used to determine the depth of the carps' physical disturbance. The results showed that: (1) In the five treatments with carps, the depth of the carps' physical disturbance was mainly in 15 cm; (2) Nitrification rate in C0 was significantly faster than that in the other treatments (P0.05), while the rates in C8 and C10 which had a higher density of carps were significantly faster than that in C2, C4 and C6 (P0.05); (3) Denitrification rate was almost to 0 in C0 during the research, but in C2, C4, C6, C8 and C10, the rate got faster in the treatment with carps of higher density; (4) Nitrate ammonification rate changed a little in each treatment, but the rate in C8 and C10 was relatively faster than that in the other treatments. The present study suggested that carps' bioturbation could evidently promote denitrification, nitrification and nitrate ammonification, when there was enough organic carbon in the sediment, carps' bioturbation would have a positive affect on the procedure of removing nitrogen in eutrophic ponds.