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Diurnal variation in the atmospheric CO2 concentration and the carbon isotopic composition (Δ14C and δ13C) was measured in a forest in an urban area on 9 February 1999. The carbon isotope approach used in the present study differentiated between the quantitative contributions from anthropogenic and biogenic CO2 sources in the urban atmosphere. The anthropogenic (fossil fuel) and biogenic (soil respiration) contributions was estimated, and they ranged from 1 to 16% and from 2 to 8% of the total atmospheric CO2. The diurnal variation of the anthropogenic CO2 was the major cause of the total atmospheric CO2 variation, while the biogenic CO2 remained relatively constant throughout the day. Estimating the contribution of soil respired CO2 provided the mean residence time of soil respired CO2 within the forest atmosphere.  相似文献   

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Oceanic excess radiocarbon data is widely used as a constraint for air–sea gas exchange. However, recent estimates of the global mean piston velocity  〈 k 〉  from Naegler et al., Krakauer et al., Sweeney et al. and Müller et al. differ substantially despite the fact that they all are based on excess radiocarbon data from the GLODAP data base. Here I show that these estimates of  〈 k 〉  can be reconciled if first, the changing oceanic radiocarbon inventory due to net uptake of CO2 is taken into account; second, if realistic reconstructions of sea surface  Δ14C  are used and third, if  〈 k 〉  is consistently reported with or without normalization to a Schmidt number of 660. These corrections applied, unnormalized estimates of  〈 k 〉  from these studies range between 15.1 and 18.2 cm h−1. However, none of these estimates can be regarded as the only correct value for  〈 k 〉  . I thus propose to use the 'average' of the corrected values of  〈 k 〉  presented here (16.5 ± 3.2 cm h−1) as the best available estimate of the global mean unnormalized piston velocity  〈 k 〉  , resulting in a gross ocean-to-atmosphere CO2 flux of 76 ± 15 PgC yr−1 for the mid-1990s.  相似文献   

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The amounts of microbial and root‐respired CO2 in a maize/winter wheat agricultural system in south western Germany were investigated by measurements of the CO2 mixing ratio and the 13C/12C ratio in soil air. CO2 fluxes at the soil surface for the period of investigation (1993–1995) were also determined. Root respired CO2 shows a strong correlation with the plant mass above ground surface of the respective vegetation (R2≥0.88); the maximum CO2 release from roots was in August for the maize (2.0±0.5 mmol m−2 h−1) and in June for winter wheat (1.5±0.5 mmol m−2 h−1). Maximum CO2 production by roots correlate well with the maximum amount of plant root matter. Integrating the CO2 production over the whole growing season and normalizing to the dry root matter yields, the CO2 production per gram dry organic root matter (DORM) of maize was found to be 0.14±0.03 gC (g DORM)−1. At the sites investigated, root‐produced CO2 contributed (16±4)% for maize, and (24±4)% for winter wheat, respectively, to the total annual CO2 production in the soil (450±50 gC m−2 for maize, 210±30 gC m−2 for winter wheat).  相似文献   

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