Effect of dissolved oxygen on nitrogen purification of microbial ecosystem in sediments

Key groups of nitrogen transforming bacteria and enzyme activities in sediments developed in response to dissolved oxygen (DO) concentration were investigated at four different oxygen supply levels, namely, oxygen saturation condition (DO = 8.60 mg L-1), aerobic condition (DO = 6.00 mg L-1), anoxic condition (DO = 2.00 mg L-1), and anaerobic condition (DO = 0.70 mg L-1). The results showed that aerobic heterotrophic bacteria, ammonifying bacteria and nitrifying bacteria in the sediments were positively correlated with DO concentration (r = 0.815-0.897, P 0.01). Among the four oxygen supply levels, the population of denitrifying bacteria was highest in the sediment under anoxic condition during the whole experiment. The enhanced oxygen supply inhibited the activities of urease, nitrate reductase and nitrite reductase in the sediments. However, A positive correlation (r = 0.841, P 0.01) between the activity of protease and DO concentration was found in the sediments. The increase in oxygen supply for the overlying water might give a positive effect on nitrification and coupled nitrification-denitrification. Nitrogen released from the sediment was low in the aerobic and oxygen saturation condition.