Study Of On Methane Emission From A Typical Hydro-Fluctuation Belt Under Water Level Change In Three Gorges Reservoir

Climate warming is a global environmental issue, the main reason is the increase of greenhouse gases concentration in atmosphere. CO2, N2O and CH4are considered to be the most important three greenhouse gases. IPCC (2007) report pointed out that the GWP value of the unit molecule of methane is25times as that of CO2in the100-year scale. The concentration of methane in the atmosphere is about1774ppb in2005, more than twice of the pre-industrial concentration. Sources of methane emissions in the atmosphere including natural wetlands, farmland, forests, oceans, fossil fuel combustion, biomass burning, plant and litter. A large number of recent studies have shown that the release of methane in the reservoir is an important source of atmospheric methane source.The Three Gorges Reservoir is currently the world’s largest artificial reservoir for hydropower. So far, there is little research reports on greenhouse gas emissions in the Three Gorges Reservoir. It has great significance to carry out the greenhouse gas emissions in this area, can be accurately calculated, explore its impact mechanisms and provide a reference for reduce greenhouse gases in the reservoirs water conservancy and hydropower development process.The study sites established in the Wangjiagou Village. Fuling District, Chongqing City. choosing a typical, flat and wide Hydro-Fluctuation Belt in Three Gorges Reservoir. The object of study is the elevation of water level Hydro-Fluctuation Belt of ecological system in the same watershed. Five elevations be chose, there are180m,175m.165m,155m,145m and140m (180m water level elevation is the permanent none flooding control point,140m water level elevation is the permanent flooding control point), the static opaque chamber-GC method is used to study the methane emissions in different water level elevation ecosystems and explore the methane emissions law in drawdown area and the reservoir area of environmental factors on methane emission. The study lays a good foundation for the next step to estimate the reservoir greenhouse gas emissions reduction and provide a basis to help our government seize the initiative negotiations and compliance action in the United Nations Climate Change Framework Convention. The main results are as follows.1. The seasonal variation of methane emissions in different elevationIn the flooding period, methane emission flux in175m elevation ranged from-0.25-0.45mg·m-2·h-1with an average flux of0.17±0.19mg·m-2·h-1. Two observations of methane emissions in October2010are lower than other months, emission peak values appear in the November9to January24in the following year, compared to175m elevation, methane emissions flux is relatively low in permanent flooding control point180m elevation, the average flux was0.05±0.07mg·m-2·-1,180m elevation is maintained at a relatively low low-level emission and absorption state during this period. The single-factor analysis of variance between175m elevation and180m elevation methane emission showed that the175m elevation methane flux significantly higher than the180m elevation (P<0.05).The methane emission flux in145m elevation of the water point ranged of0.23-1.9mg·m-2·h-1, the average flux is1.294±0.49mg·m-2·h-1,the emission characteristics of fluctuations is gradually increased. Compared to the145m elevation surface of the water points, the emission of control points(140m elevation) has no large fluctuations, the methane emission flux ranged from0.37-1.49mg-m-2·h-1with the average value of0.975±0.32mg·m-2·h-1, single-factor variance analysis showed that the140m and145m elevation water point reach the significant difference (P=0.010),145m elevation surface points methane flux significantly higher than140m.In Dry period, methane emission flux in175m elevation ranged from-0.27-0.16mg·m-2·h-1. the average emission flux is0.00±0.08mg·m-2·h-1. There was not appear significantly increase or decrease seasonal discharge law during this period; emission flux in165m elevation ranged from-0.19-0.27mg·m-2·h-1, the average emission flux is0.07±0.11mg·m-2·h-1. The emission peak appear on March29,2011, with the value of0.27mg·m-2·h-1. Elevation is maintained at a relatively low low-level emission and absorption state In the subsequent observations. The methane emissions in155m elevation ranged from0.25-0.61mg·m-2·h-1and average emission flux is0.10±0.25mg·m-2·h-1. On May22and August15,2011, appeared two emission peak, respectively,0.61,0.59mg·m-2·h-1 AN OVA analysis showed that:155m and180m elevation methane emission, reached a significant level of difference. P values were0.015, respectively. the165m and175m elevation methane emission flux have no significant correlation with180m elevation (P>0.05). in the155m elevation observation period, three elevations among methane emission fluxes have no significant differences, only155m elevation and180m elevation methane emission reached a significant level of difference (P=0.028).2. Environmental factors on the impact of the drawdown area of methane emissionsStudies have shown that all the elevation of methane emission flux and soil water content showed a significant positive correlation (P<0.05) throughout the observation period, which up to175m elevation soil moisture correlation reached a significant level (P=0.000). Each the correlation of elevation of soil temperature and methane flux is not significant (P>0.05), but the water temperature and surface point of methane emissions has reached a significant positive correlation. Carbon content is not the main factors that affect the terrestrial methane emissions,there is not correlation among them; but the water methane emissions and water DOC concentration achieve a significant positive correlation relationship, wind speed, pH, NO3-, NH4+and other nutrients have weak relation of the surface methane emission flux.