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Titel |
Bayesian calibration of a soil organic carbon model with radiocarbon measurements of heterotrophic respiration and soil organic carbon as joint constraints |
VerfasserIn |
B. Ahrens, W. Borken, J. Muhr, K. Savage, T. Wutzler, S. Trumbore, M. Reichstein |
Konferenz |
EGU General Assembly 2012
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Medientyp |
Artikel
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Sprache |
Englisch
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Digitales Dokument |
PDF |
Erschienen |
In: GRA - Volume 14 (2012) |
Datensatznummer |
250066212
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Zusammenfassung |
Soils of temperate forests store significant amounts of organic matter and are considered to be
net sinks of atmospheric CO2. Soil organic carbon (SOC) dynamics have been studied using
the Δ14C signature of bulk SOC or different SOC fractions as observational constraints in
SOC models. Further, the Δ14C signature of CO2 evolved during the incubation of
soil and roots has been widely used together with Δ14C of total soil respiration
to partition soil respiration into heterotrophic respiration (HR) and rhizosphere
respiration.
However, this data has not been used as joint observational constraints to determine SOC
turnover times. Thus, we want to present: (1) how different combinations of observational
constraints help to narrow estimates of turnover times and other parameters of a simple
two-pool model, ICBM; (2) if a multiple constraints approach allows determining whether a
forest soil has been storing or losing SOC. To this end ICBM was adapted to model SOC
and SO14C in parallel with litterfall and the Δ14C signature of litterfall as driving
variables. The Δ14C signature of the atmosphere with its prominent bomb peak
was used as a proxy for the Δ14C signature of litterfall. Data from three spruce
dominated temperate forests in Germany and the USA (Coulissenhieb II, Solling D0 and
Howland Tower site) were used to estimate the parameters of ICBM via Bayesian
calibration.
Key findings are: (1) the joint use of all 4 observational constraints helped to considerably
narrow turnover times of the young pool (primarily by Δ14C of HR) and the old pool
(primarily by Δ14C of SOC). Furthermore, the joint use all observational constraints allowed
constraining the humification factor in ICBM, which describes the fraction of the annual
outflux from the young pool that enters the old pool. The Bayesian parameter estimation
yielded the following turnover times (median ± interquartile range) for SOC in
the young pool: Coulissenhieb II 2.9 ± 2.1 years, Solling D0 8.4 ± 1.6 years and
Howland Tower 3.3 ± 2.4 years. Turnover times for the old pool were 385 ± 92 years
(Coulissenhieb II), 134 ± 38 years (Solling D0) and 205 ± 76 years (Howland Tower),
respectively.
(2) At all three sites the multiple constraints approach was not able to determine if
the soil has been losing or storing carbon. Nevertheless, the relaxed steady state
assumption hardly introduced any additional uncertainty for the other parameter
estimates.
Overall the results suggest that using Δ14C data from more than one carbon pool or flux
helps to better constrain SOC models. |
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