Footprint Analysis In A Poplar Plantation Ecosystem

Footprint source area analysis is an important approach to study qualitatively and quantitatively the relationship between the flux information and the surface condition. Because the nature vegetation is inhomogeneous distribution and the measurement surface is usually sloping, the credibility of flux exchanges between the atmosphere and the land surface could be questionable. Therefore, it is critically important to identify the fluxes measurements by improved understanding the footprint source area.In this thesis, we calculated flux footprint and NEP (net ecosystem productivity), RE (ecosystem respiration) and GPP (gross primary productivity) weighted footprint with FLEM model by using continuous flux measurements from year2008to year2010, summarized the distributions of daily, monthly and annual footprint source areas under different stabilities, analyzed the representativeness of the carbon flux explained the relationship of land use changes and flux changes. To ensure the quality of model inputs, flux data and the sensibility of inputs on the FLEM model are evaluated. These results are helpful to interpret flux data and to provide a basic method to collect high quality data in the future. With model results, we found that:In the three years, the quality of heat flux was the best and then the carbon flux. Data quality was best in2009and worst in2010. FLEM model was sensible to all the parameters under unstable condition, to undervaluation of z0and zm, and to very stable and very unstable condition. Footprints modeled by using FLEM and FSAM models were similar while the affect areas are larger by using FLEM model under unstable condition.Daily and monthly variation showed a big-small-big tendency.70%to90%cumulative footprints extended to the south in growth season, to both south and north in dormant season and no larger than300m in the west and the east. The source area was largest and northernmost in2008.Carbon flux weighted footprint was affected by carbon components, wind direction and stability. GPP and RE weighted footprint gradually moved to the south during the year, GPP weighted footprint was mainly controlled by southwest wind, while RE weighted footprint was controlled by both southwest and northwest wind. NEP weighted footprint showed an integrated effect of GPP and RE. NEP weighted footprint mainly effected the southern part of the research area. Due to the land use change in this area, there was an obvious carbon source in growing season of2010. In the northern area, the change of NEP was caused by newly planted aspens. The small interannual variability of carbon flux exchange in the residential area indicated that the effect of residents on flux was smaller than the effect of land use change.