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Abstract

The objective of this dissertation is to clarify the role of a relatively large Hungarian biosphere region in the carbon cycle. This is accomplished by determining the Net Ecosystem carbon dioxide Exchange (NEE) of an active agricultural region and a small grassland area in Hegyhátsál (western Hungary) using the eddy covariance (EC) technique. NEE is determined as the sum of the CO\( _{2}\protect \) EC flux at 82 m and the rate of change of CO\( _{2}\protect \) storage below the measuring level for the regional scale system. NEE of the grassland is determined directly from the carbon dioxide fluxes measured at 3 m. The temperature dependence of nighttime ecosystem respitation and photosynthetically active photon flux density (PPFD) dependence of daytime NEE is analyzed. The missing measurement intervals are filled with the modified CO\( _{2}\protect \) flux data determined from the parallel profile measurements or with data calculated from the temperature and light dependences. Maximum values of carbon dioxide uptake reached 1.5 mg CO\( _{2}\protect \) m\( ^{-2} \) s\( ^{-1} \) (34.1 \( \mu \)mol m\( ^{-2} \) s\( ^{-1} \)) during summertime, and soil decomposition resulted in net carbon dioxide loss during wintertime. The agricultural region sequestered 134 gC m\( ^{-2} \) in 1997, 146 gC m\( ^{-2} \) in 1998, and 92 gC m\( ^{-2} \) in 1999. The grassland sequestered 86 gC m\( ^{-2} \) in 1999 and 247 gC m\( ^{-2} \) in 2000. The year-round NEE values are comparable with results from boreal environment, temperate croplands or in some cases with results from temperate deciduous forests. More scientific data are needed to understand the behaviour of the ecosystem and to constrain the results.


next up previous contents
Next: Introduction Up: Long term atmosphere/biosphere exchange Previous: Contents   Contents
root 2001-06-16