The aim of this study was to investigate the effect of dissolved oxygen (DO) on nitrifying bacterial abundance and vertical distribution in sediment of Pearl River (Guangzhou section).Vertical distributions of sediment physical-chemical properties (grain size distribution

concentrations of total organic carbon

total nitrogen

nitrate

ammonium

DO) and nitrifying bacteria abundance were characterized using sediment cores.The experiments were conducted to cultivate bacteria using local bacteria and different DO concentrations.The results showed that DO concentrations decreased from 0.26 to 0.02 mg·L

-1

within sediment depths of 0 to 10 cm

which was attributable to the sandy sediment and perturbation of benthic macrofauna.The nitrifying bacteria were inhibited by low DO condition

resulting in ammonium accumulation in subsurface sediment.With DO

<

0.03 mg·L

-1

the abundance of ammonia oxidizing bacteria was greater than that of nitrite oxidizing bacteria.