Influence of environmental factors on net N2 and N 2O production in sediment of freshwater rivers
2014
Zhao, Yongqiang | Xia, Yongqiu | Li, Bolun | Yan, Xiaoyuan
Denitrification is an important N removal process in aquatic systems but is also implicated as a potential source of global N₂O emissions. However, the key factors controlling this process as well as N₂O emissions remain unclear. In this study, we identified the main factors that regulate the production of net N₂and N₂O in sediments collected from rivers with a large amount of sewage input in the Taihu Lake region. Net N₂and N₂O production were strongly associated with the addition of NO₃⁻-N and NH₄⁺-N. Specifically, NO₃⁻-N controlled net N₂production following Michaelis–Menten kinetics. The maximum rate of net N₂production (Vₘₐₓ) was 116.3 μmol N₂-N m⁻² h⁻¹, and the apparent half-saturation concentration (kₘ) was 0.65 mg N L⁻¹. N₂O to N₂ratios increased from 0.18 ± 0.03 to 0.68 ± 0.16 with the addition of NO₃⁻-N, suggesting that increasing NO₃⁻-N concentrations favored the production of N₂O more than N₂. The addition of acetate enhanced net N₂production and N₂O to N₂ratios, but the ratios decreased by about 59.5 % when acetate concentrations increased from 50 to 100 mg C L⁻¹, suggesting that the increase of N₂O to N₂ratios had more to do with the net N₂production rate rather than acetate addition in this experiment. The addition of Cl⁻did not affect the net N₂production rates, but significantly enhanced N₂O to N₂ratios (the ratios increased from 0.02 ± 0.00 to 0.10 ± 0.00), demonstrating that the high salinity effect might have a significant regional effect on N₂O production. Our results suggest that the presence of N-enriching sewage discharges appear to stimulate N removal but also increase N₂O to N₂ratios.
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