| In recent years, because of the rising concentrations of greenhouse gases in the atmosphere, global warming has become a major environmental issue global concerned. Many studies showed that hydropower, which had been widely accepted as a clean energy at past, may be an important source of atmospheric CO2and CH4. Especially in the tropic areas, where large number of submerged vegetations under high temperature, cause large emissions of greenhouse gases; there were also some reports of N2O emissions from reservoirs in the tropics and high latitudes. As the world’s largest artificial reservoirs used for power generation, there will form a huge seasonal water level fluctuating zone in Three Gorges Reservoir due to the regular discharge and storage of water. The water level fluctuating zone, as a special and complex environment, is a junction of terresial and aquicolous ecosystems, where takes place many complex processes in the migration and transformation of substances, and is very different from natural ecosystems in carbon and nitrogen cycles, so there may be have huge of potential of producing CO2and N2O. So far, however, reports about greenhouse gases emission from Three Gorges reservoir was rare, so it is significance of carrying out the research about CO2and N2O emissions from water level fluctuating zone and water-air interface in Three Gorges Reservoir.In this study, a typical water level fluctuating zone was selected as the the research area, where located in Wangjiagou of Zhenxi town in Fuling district of Chongqing city from August2010to August2012. The seasonal variation of the ecosystem respiration and the flux of N2O from ecosystems of three elevations (155,165and175m) in water level fluctuating zone and180m elevation as a control of never flooding area was observed using static opaque chamber-GC techniques for two year. The flux of CO2and N2O across the water-air interface about two elevations (155and175m) in water level fluctuating zone and140m elevation was measured with floating static opaque chamber-GC techniques. In addition, the impact of environmental factors on the drop-dry and flooding of two greenhouse gas emissions, more systematic analysis was carried out on the influencing factors like as environmental, physical and chemical factors. The mian results were showed as follows: (1) The flux of CO2about the different elevations in water level fluctuating zone has obvious seasonal change, mainly as following:the summer than in the winter, fall dry period higher than the flooding period. The flux of CO2about each elevation reached to a maximum in summer. From August2011to August2012, the order of annual CO2emissions in different elevations in water level fluctuating zone was175m (59.37t-hm-2)>155m (49.34t-hm-2)>180m (45.43t·hm-2)>140m (10.71t·hm-2), the longer the drying time performance of the drawdown area, the greater the amount of CO2emissions; perennial flood elevation of140m of the annual flux (10.71t·hm-2) below the fall dry control point180m elevation (45.43t·hm-2).①The observation result during the non-flooding periodFrom August2010to August2012, the order of ecosystem respiration for different elevations was175m (1126.6mg·m-2·h-1)>165m (1052.5mg·m-2·h-1)>155m (876.7mg·m-2·h-1)>180m (668.1mg·m-2·h-1). The single factor analysis about the ecosystem respiration for different elevations on May23,2011to September14,2011shows that the difference of ecosystem respiration rate in180m elevation and175m elevation is significant, the difference of ecosystem respiration rate in180m elevation and165m or155m elevation are not significant; there are significant differences between any two of the three elevations (175,165and155m) during the same observation non-flooding period.In the non-flooding period, relationship between ecosystem respiration in all elevation and soil temperature in5cm depth reached a significant level; the results of correlation analysis showed between ecosystem respiration in180m elevation and soil moisture, TN and DOC contents in topsoil reached a significant level; The ecosystem respiration in175m elevation and the pH, SOC contents in topsoil has a significant correlation; ecosystem respiration in155m elevation and SOC and TN contents in topsoil was correlated significantly.②The observation component of water-air interface in flooding timeThroughout the flooding time, the average flux of CO2about each elevation in flooding time was140m (111.8mg·m-2·h-1)>155m (109.5mg·m-2·h-1)>175m (69.1mg·m-2·h-1). The single factor variance analysis about the flux of CO2in different elevations from November21,2011to February2,2012showed that there were significant differences between the175m elevation and155m,140m elevation, and there was no significant difference between the155m elevation and140m elevation.The results show that through the analysis of various environmental factors:during the flooding period, correlation analysis showed that a significantly positive correlation was observed between the flux of CO2across the water-air interface in140m elevation and the DOC concentrations in surface water, relationship between the fluxes of CO2across the water-air interface and the temperature in surface water, wind speed, water pH did not reach a significant level.(2) The flux of N2O about the different elevations in water level fluctuating zone has obvious seasonal change, the general performance:lower in summer, and even the absorption of N2O, higher in autumn; It is generally presented as a N2O resource during the flooding period. From August2011to August2012, the annual flux of N2O in different elevation of the level fluctuation zone,175m (771.22mg·m-2)>180m (666.46mg·m-2)>155m (373.18mg·m-2)>140m (244.91mg·m-2), all of the four elevation showed emissions of N2O.①The observation result during the non-flooding periodDuring the entire non-flooding period, the order of the average annual flux N2O from ecosystems of four elevations was175m (498.2mg-m-2)>180m (362.3mg-m-2)>155m (95.3mg·m-2)>165m (16.9mg-m-2). The single factor variance analysis about the flux of N2O for different elevations shows that there are no significant differences between any two of the four elevations during the same time in dry-time period.In the non-flooding period, the results of correlation analysis showed between the flux of N2O in180m elevation and the pH in topsoil, SMBN contents in topsoil reached a significant level; Other factors as temperature, soil moisture, soil DOC with the flux of N2O have no significant correlation.②The observation component of water-air interface in flooding time.Throughout the flooding period, the average flux of N2O about each elevation in flooding time was175m (49.2μg·m-2·h-1)>155m (31.7μg·m-2·h-1)>140m (26.9μg·m-2·h-1), which can show that the flux of N2O in deep water area less than the nearshore area. The single factor variance analysis about the flux of N2O for different elevations shows that there are no significant differences between any two of the three elevations during the same time in flooding period.During the flooding period, the results of correlation analysis showed that between the flux of N2O in155m elevation and the nitrate nitrogen contents in topsoil reached a significant level; The temperature of surface water, wind speed, pH and DOC concentrations in surface water with the flux of N2O across the water-air interface in others elevation have no significant correlation. |
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