Study Of Nitrous Oxide Emission From A Typical Water Level Fluctuating Zone Under Water Level Change In Three Gorges Reservoir

N2O is an important greenhouse gas except methane and carbon dioxide, whose contribution to atmospheric warming of6percent. In addition, N2O is also involved in photochemical reactions to destroy the ozone layer, which become a great threat to the survival of mankind.At present the researches about reservoir greenhouse gas emissions are also less, and are mainly fucused in some regions, such as Brazil, the United States, French Guiana and northern Canada and other minority reservoir. The water-level-fluctuating zone is a convergence and transition zone of aquatic ecosystems and terrestrial ecosystems, which will be sources of N2O. So the research about the N2O production mechanism, emission process and influencing factors of water-level-fluctuating zone in reservior are meaningful for global environmental protection which can reduce N2O emissions and provide theoretical and technical support.The three Gorges Reservoir is the largest artificial reservoir for hydropower of the world. So far, there is no report about greenhouse gases emission of the Three Gorges Reservoir.So the field experiment was located in Wangjiagou of Zhenxi town in Fuling district of Chongqing city, slecting a typical area of water-level-fluctuating zone along the Three Gorges reservoir area as the research object, using the static opaque chamber to research N2O flux of three different elevation of175,165,155and145m, during the time of submerge compared with180m elevation as for permanent land and140m elevation as for permanent river. At the same time, we also investigated the temperature, wind speed, soil moisture, available nitrogen, dissolved organic nitrogen, soil microbial biomass nitrogen, total nitrogen and pH on the influence of N2O emissions. The results show as follows.(1) The N2O emission flux of different elevationsThe observation result during the non-flooding period. N2O emission of180m elevation as permenent contrast bareness has obvious characteristics of seasonal variation. The remaining three elevations affected by water-level and seasonal variation have the performance of different characteristics of N2O emissions under the control of different environmental factors.175and165m elevation all appear the largest N2O emission peaks, which main reason is the soil frequent and strong dry-wet alternation;155m elevation’s flooding time is the longest, which is a N2O emission source affected by water-level.The observation component of water-air interface in flooding time. The N2O of175,140and145m elevations are based as emission during their observation time becoming emission sources in the water-air interface. The N2O fluxs of140and145m elevation reach to maximum in the summer and the water-level of175m elevation is the highest, but at this time the water environment will limit the N2O emissons because the daily average emissions of N2O in the river time are less than that in the dry-land time.In the continuous observation period between2011-5-23and2011-9-14, we calculate the four elevations of155,165,175and180m then derive that the order of N2O total emissions of the period arranged from large to small is180m(-116.38mg·m-2)<165m(-10.50mg·m-2)<155m(71.11mg·m-2)<175m(154.43mg·m-2). The single factor analysis of variance shows that there are no significant differences between any two of the four elevations during the same observation dry-time period.In the observation river period of2011-3-28to2011-9-13, the order of N2O total emissions is145m(117.84mg·m-2)>140m(91.38mg·m-2). The single factor analysis of variance shows that there is no significant difference between the two elevations.The order of total annual emissions in a whole year observation period from2010-8-31to2011-8-31is175m(769.03mg·m-2)>180m(-92.64mg·m-2). N2O emissions of175m elevation in the high-land of water-level-fluctuating zone are much larger than180m elevation for contrast, indicating that the special habitat of the reservoir water-level-fluctuating zone can greatly facilitate N2O emissions.(2) Diurnal variation research of N2O emission Correlation analysis shows that in the two diurnal variations of2010-11-12and2011-7-17temperature is the main influence factor, but N2O flux is not only affected by temperature, but also by soil moisture, soil conditions, vegetation types, seasonal variations and other factors, which led to the randomness of N2O fluxes.(3)The impact of different environmental factors to N2O emissionFor the river-time experiment, Wind speed and water pH are all important environmental factors affecting the N2O flux of145m elevation which promote N2O emissions within certain ranges.For the non-flooding time experiment:To155m elevation, soil pH is important factor which can be significant with the promotion of N2O the emissions; To165m elevation, Don, SMBN, soil moisture, NH4+-N and NO3--N are all important factors, and soil humidity, SMBN, DON and NH4+-N could significantly promote N2O emission; To175m elevation, soil pH and DON are important factors. DON significantly promotes N2O emission, and the soil pH limits N2O emissions.