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

Abstract

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.

Keywords:

• Sediment
• dissolved oxygen (DO)
• nitrogen transforming bacteria
• enzyme activities

Acknowledgments

This work was financially supported by State Key Laboratory of Hydrology-Water Resources and Hydraulic Engineering, Hohai University with grant No. 2006412211 and No. 2006412611, Ministry of Education Key Laboratory of Integrated Regulation and Resource Development on Shallow Lakes with grant No. 2084-406054, Ministry of Education Key Lab of Environment Remediation and Ecological Health with grant No. EREH0706, Natural Science Foundation of Hohai University with grant No. 2006407211, and National Science & Technology Pillar Program with grant No. 2007BAC26B03.

Notes

∗DO = 8.60 mg L⁻¹, Oxygen saturation condition; DO = 6.00 mg L⁻¹, Aerobic condition; DO = 2.00 mg L⁻¹, Anoxic condition; DO = 0.70 mg L⁻¹, Anaerobic condition.

∗∗Mean ± S.D. (n = 3).

∗∗∗Means with the same small letter(s) and capital letter(s) are not significantly different at P < 0.05 or P < 0.01, respectively, based on least significant differences (LSD) comparisons.

∗DO = 8.60 mg L⁻¹, Oxygen saturation condition; DO = 6.00 mg L⁻¹, Aerobic condition; DO = 2.00 mg L⁻¹, Anoxic condition; DO = 0.70 mg L⁻¹, Anaerobic condition.

∗∗Mean ± S.D. (n = 3).

∗∗∗Means with the same small letter(s) and capital letter(s) are not significantly different at P < 0.05 or P < 0.01, respectively, based on LSD comparisons.

∗DO = 8.60 mg L⁻¹, Oxygen saturation condition; DO = 6.00 mg L⁻¹, Aerobic condition; DO = 2.00 mg L⁻¹, Anoxic condition; DO = 0.70 mg L⁻¹, Anaerobic condition.

∗∗Mean ± S.D. (n = 3).

∗∗∗Means with the same small letter(s) and capital letter(s) are not significantly different at p < 0.05 or p < 0.01, respectively, based on LSD comparisons.

∗∗∗∗Not detected.

∗DO = 8.60 mg L⁻¹, Oxygen saturation condition; DO = 6.00 mg L⁻¹, Aerobic condition; DO = 2.00 mg L⁻¹, Anoxic condition; DO = 0.70 mg L⁻¹, Anaerobic condition.

∗∗Mean ± S.D. (n = 3).

∗∗∗Means with the same small letter(s) and capital letter(s) are not significantly different at p < 0.05 or p < 0.01, respectively, based on LSD comparisons.

∗ P < 0.05

∗∗ P < 0.01.