Carbon Fluxes And Influence Factors

Under the background of global changing, many researchers focus on terrestrialcarbon cycle, While urban ecosystem as one of the type of terrestrial ecosystem anda major source of atmosphere carbon dioxide, few research has been done in this are.In this study, Based on forest ecological system long-term station in Shanghai suburbfield and eddy covariance technique, carbon dynamic and the main influencingfactors were analyzed, the main results are listed as the following:(1) With the data quality control and evaluation from eddy covariance systemsand gradient meteorological systems. Data quality control including axis rotation theair density correction and data screening in night. According to the different times,different loss characteristics, used MDV(mean diurnal variation) and nonlinearregression method to interpolate the data of2011. The appropriate friction velocity(u*) for flux data quality control could be about0.15m/s. After the data qualitycontrol and quality evaluation, the data will be able to meet the needs of the analysis.Only in this way, those data can represent the relatively real flux exchange processesof this region.(2) The distribution of carbon flux in the area. Based on FSAM(the Flux-SourceArea Model)model, the footprint source area were calculated in urban ecosystem.The distribution of footprint was analyzed in the different atmospheric conditions,including wind directions and the diurnal dynamics. The results shew that: thefootprint source area changed by different seasons, the footprint source area were96~1063m,84~967m,103~1301m, and110~1284m, respectively in spring, summer,autumn, and winter, At a0.9significant stable conditions, the footprint source areawere from94~1047m in main wind direction, the area were from66~491m inunstable conditions.The diurnal variation of footprint appeared a rule that thefootprint was larger in night than in the day, they were113~1024m and59~503mrespectively.(3) Characteristics of carbon flux variation. Carbon fluxes varied in differentseasons, carbon sequestration was most actively in summer, the spring and autumn were at second place. Look from the annual scale, the underlying surface was thecarbon source. In summer, daily average carbon flux was-0.076mg/m2/s, in winterwas0.079mg/m2/s. Daily average carbon flux in2011was0.0291mg/m2/s. Theinitial light energy use efficiency in four seasons weresummer>autumn>spring>winter,in summer,it was0.00365μmol CO2/m2/s. carbonflux exchange process were different in different flux areas,in urban area, dailyaverage carbon flux was0.09mg/m2/s,but in park area, daily average carbon flux wasonly-0.03mg/m2/s,this result prove that urban area was carbon source,park areawas carbon sink. The research area was carbon source in2011.(4) Motor vehicle of the road near the tower show two obvious peaks at eighto clock in the morning and around six oclock in the afternoon, the volume of trafficwas450per hour on average.Traffic influenced observation of carbon flux, In the caseof the confidence level of95%, motor vehicle emissions influenced carbon fluxchange charactation was significant, the ratio of carbon emissions resulting fromtraffic that contributed to CO2flux variation was18%.