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Error analysis of CO2 storage flux in a temperate deciduous broadleaved forest based on different scalar  variables.

WANG Jing, WANG Xing-chang, WANG Chuan-kuan   

  1. (Center for Ecological Research, Northeast Forestry University, Harbin 150040, China)
  • Online:2013-04-18 Published:2013-04-18

Abstract: Using the measurement data from an 8-level vertical profile of CO2/H2O in a temperate deciduous broadleaved forest at the Maoershan Forest Ecosystem Research Station, Northeast China, this paper quantified the errors of CO2 storage flux (Fs) calculated with three scalar  variables, i.e., CO2 density (ρc), molar fraction (cc), and molar mixing ratio relative to dry air (χc). The dry air storage in the control volume of flux measurement was not a constant, and thus, the fluctuation of the dry air storage could cause the CO2molecules transporting out of or into the control volume, i.e., the variation of the dry air storage adjustment term (Fsd). During nighttime and day-night transition periods, the relative magnitude of Fsd to eddy flux  was larger, and ignoring the Fsd could introduce errors in calculating the net CO2 exchange between the forest ecosystem and the atmosphere. Three error sources in the Fs calculation could be introduced from the atmospheric hydrothermal processes, i.e., 1) air temperature fluctuation, which could cause the largest error, with one order of magnitude larger than that caused by atmospheric pressure (P), 2) water vapor, its effect being larger than that of P in warm and moist summer but smaller in cold and dry winter, and 3) P, whose effect was generally smaller throughout the year. In estimating the effective CO2 storage (Fs_E), the Fs value calculated with ρc, cc, and χc was overestimated averagely by 8.5%, 0.6%, and 0.1%, respectively. It was suggested that in the calculation of Fs, adopting the χc conservative to atmospheric hydrothermal processes could be more appropriate to minimize the potential errors.