| Nitrogen load of river are increasing due to waste water and agricultural runoff flowed into.Microorganism in sediment and water use nitrogen sources to produce variety of by-products such as nitrous oxide?N2O?,which attracted more and more social concern for its huge warming potential.Sediment-water interface?SWI?as an important channel of material and energy exchange whose contribution can not be neglected.There are many factors influencing the flux of N2 O,in this paper,the influence of different hydrodynamic conditions on the N2 O flux of SWI was mainly studied by using the eddy covariance technique.Besides,the nitrogen elements in the sediments mainly included total nitrogen?TN?,ammonia nitrogen?AN?,nitrate nitrogen?NO3--N?and nitrite nitrogen?NO2--N?were studied as well as bacterial diversity to further explore the mechanism of N2 O production and release.The main achievements of this article are summarized as follows:1 In static state?0 ± 0.01m/s?,the N2 O flux?absolute value?of the SWI was in the range of 5.15495.93 umol.m-2.h-1,with an average value of 118.86 umol.m-2.h-1.The N2 O flux range was 7.08 2211.65 umol.m-2.h-1with an average value of 844.38 umol.m-2.h-1,at a flow rate of 0.03 ± 0.02 m/s.When the flow rate was 0.07 ±0.02 m/s,the N2 O flux range was 8.04 3385.75 umol.m-2.h-1 and the average value was1485.45 umol.m-2.h-1.When the flow rate was 0.12 ± 0.02m/s,the N2 O flux range was8.275359.34 umol.m-2.h-1 and the average value was 2302.85 umol.m-2.h-1.When the flow rate was 0.20 ± 0.02m/s,the N2 O flux was in the range of 67.48 24736.00 umol.m-2.h-1,the average value was 10953.82 umol.m-2.h-1.When the flow rate was 0.30± 0.02m/s,the N2 O flux range was 76.64 35879.54 umol.m-2.h-1 and the average flux was 30151.88 umol.m-2.h-1 when the flow rate was 0.35 ± 0.02 m/s.2 The effect of different hydrodynamic conditions on the N2 O flux of SWI was very significant.In general,as the average flow rate increasing,the N2 O flux of SWI increased.The N2 O flux in the stationary state was the smallest;when the velocity was between 0.03 and 0.12 m/s,the sediment had not yet suspended and the flux increased slowly with the increasing of the flow rate.When the average velocity reached 0.20 m/s,the sediment began to suspend largely,and the N2 O flux increased rapidly when the flow rate was in the 0.20 0.35 m/s.3 The coefficient of vertical eddy diffusion?Kv?of N2 O with the average periodof 30 min was 2.565.86×10-10m2.s-1 in the stationary state.Kv was 1.041.81×10-7m2.s-1 when the average velocity was 0.030.12m/s and when the average disturbance rate of water was 0.200.35m/s,Kv was 1.042.52×10-6m2.s-1.In general,with the increase of flow rate,the turbulence degree of water increased,and the Kv increased.and there is a significant positive correlation between velocity and Kv.When the flow rate was between 0.010.14m/s?sediment had not yet suspended?,velocity and Kv has a good linear correlation.The relationship can be expressed by y = 39.980 x +0.970 and R2=0.969.When the flow rate was between 0.180.37m/s,the sediment suspended largely and there is no significant linear relationship between the flow rate and Kv.4 The contents of TN and NO3--N in the sediment before and after the experiment were both reduced,the decrease range of TN was 40.673337.463mg/kg and the decrease of NO3--N was 1.0215.343mg/kg,the content of NO2--N was relatively increased after each experiment and the NH4+-N increased or decreased.5 The bacteria in the sediment are rich,the dominant bacteria in the bacteria were Proteobacteria,Bacteroidetes and Chloroflexi.In addition,Nitrospira and Planctomycetes were also detected and Nitrospira was the main nitrite oxidant bacteria.Besides,many of the bacteria in the Planctomycetes were anaerobic ammonium oxide bacteria.Among the bacteria that may produce N2 O,ammonia oxidizing bacteria?137gene sequences?,nitrite oxidizing bacteria?111 gene sequences?,denitrifying bacteria?43 gene sequences?,anaerobic ammonium oxide?7 Gene sequence?and aerobic denitrifying bacteria?259 gene sequences?.Since the completion of the Three Gorges Reservoir,the change of water level and flow rate caused by reservoir scheduling were bound to have an impact on the generation and emission of greenhouse gases such as N2 O.In this paper,the influence of different hydrodynamic conditions?mainly flow velocity?on the N2 O flux of SWI was studied through the laboratory simulation test whose aim was to contribute to the control of greenhouse gas of the Three Gorges reservoir area. |
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