Study On CO₂Flux Of Desert-wetland Ecosystem In Ebinur Lake Area

By studying the changing features of CO2fluxes and its mechanism ofenvironmental responses, this thesis try to study on the desert-wetland ecosystemcarbon cycle. Study on arid areas is very important for the carbon cycle of desert-wetland ecosystem and the exploration the processes of climate change on carbonfluxes in arid areas. Based on the eddy covariance technique, a long-term observationwas taken in2012in the Ebinur Lake, where with the desert-wetland ecosystem. Thediurnal monthly and seasonal variations of carbon dioxide flux are analyzed in thispaper, while the carbon exchange threshold approach and magnitude estimates. Thencombining the main environmental factors to further reveal the response mechanismof CO2flux. The main results are as follows:1. Diurnal variation of CO2fluxes. Besides winter, the diurnal variation of CO2flux is substantially U-shaped curve. Maximum net CO2absorption peaks usuallyappeared at12:00to5:00, and the maximum net release of CO2peak usually occurredin one hour after sunset. Because of the cold weather in winter, the diurnal variationof the CO2fluxes was not so obvious, generally to absorb carbon at noon and releasein other time of the day.During the observation, the threshold value of desert-wetlandecosystem NEE diurnal variation was-0.700mg/m2s-1to0.699mg/m2s-1. To seefrom the annual level performance for carbon sequestration, the desert-wetlandecosystem assumed for carbon sink.2.Seasonal variation of CO2fluxes. It shows that the net ecosystem CO2exchange (NEE) in the study area was small in spring, but rapid rise in summer, in fall,it decline slowly, and the minimum amplitude is in winter. The maximum monthlyaverage daily change NEE occurred in the summer of June (-0.568mg/m2s-1), and inAugust (0.272mg/m2s-1). The spring average NEE at Desert-wetland ecosystemswas0.020mg/m2s-1, expressed as carbon source; summer average NEE was-0.076 mg/m2s-1, expressed as carbon sinks; autumn average NEE was0.028mg/m2s-1,expressed as carbon source; winter average NEE was0.028mg/m2s-1, expressed ascarbon source.3. Response of CO2fluxes to air temperature. Changes in the annual averagedaily data analysis showed that the determination coefficient between the airtemperature and NEE coefficient R2=0.5497(P<0.01), which was highly correlated,indicating that at annual level, the air temperature have great influence on NEE. Inspring when Ta <7.00℃, as the Ta elevating, the NEE increased as follow; while Ta>7.00℃, with the increasing temperature, the NEE decreased. In summer, as thetemperatures were rising, NEE maintained a downward trend. In fall when Ta>3.00℃,with the increasing of Ta, NEE decreased, and the ecosystem showed carbon sinks;When the Ta<3.00℃, as the Ta reducing, the NEE raised. Ecosystem was graduallychanging from carbon sink to carbon source. Due to the low temperatures in winter,NEE was substantially near0.4. Response of CO2fluxes to soil temperature. In consideration of annual level,the soil temperature has great impact on NEE. The coefficient of determinationbetween5cm soil temperature and NEE R2is greater than10cm. The correlationcoefficient between soil temperature and NEE r had much difference in day andnight. In spring, there was a moderate soil temperature associated with NEE, therewere little correlation between nighttime soil temperature and NEE in other seasons.But in winter, since the snow was thick at the research area, the correlation betweensoil temperatures and NEE was lower.5. Response of CO2fluxes to wind speeds. There was a certain relationshipbetween wind speeds and NEE. In the breeze weather, when the wind speed was small,the change in the value of NEE was relatively flat; when the wind speed is larger orwind speed change was dramatic, NEE value changes also more intense. In the breezestrong weather, as the wind speed elevating, the NEE decreased as follow; as the wind speed elevating, the NEE increased as follow, expect in winter. In winter noon, theNEE increased as follow, expect in winter.In summary, the desert-wetland ecosystem had certain carbon sequestrationability. Meanwhile, there were obvious diurnal and seasonal variations in CO2fluxes.For the correlation between the carbon flux of air temperature, soil temperature, andwind speed and other environmental factors, different seasons have differentperformances.