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| Titel |
Soils apart from equilibrium – consequences for soil carbon balance modelling |
| VerfasserIn |
T. Wutzler, M. Reichstein |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1726-4170
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| Digitales Dokument |
URL |
| Erschienen |
In: Biogeosciences ; 4, no. 1 ; Nr. 4, no. 1 (2007-02-15), S.125-136 |
| Datensatznummer |
250001504
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| Publikation (Nr.) |
 copernicus.org/bg-4-125-2007.pdf |
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| Zusammenfassung |
| Many projections of the soil carbon sink or source are based on kinetically
defined carbon pool models. Para\-meters of these models are often determined
in a way that the steady state of the model matches observed carbon stocks.
The underlying simplifying assumption is that observed carbon stocks are
near equilibrium. This assumption is challenged by observations of very old
soils that do still accumulate carbon. In this modelling study we explored
the consequences of the case where soils are apart from equilibrium.
Calculation of equilibrium states of soils that are currently accumulating
small amounts of carbon were performed using the Yasso model. It was found
that already very small current accumulation rates cause big changes in
theoretical equilibrium stocks, which can virtually approach infinity. We
conclude that soils that have been disturbed several centuries ago are not
in equilibrium but in a transient state because of the slowly ongoing
accumulation of the slowest pool. A first consequence is that model
calibrations to current carbon stocks that assume equilibrium state,
overestimate the decay rate of the slowest pool. A second consequence is
that spin-up runs (simulations until equilibrium) overestimate stocks of
recently disturbed sites. In order to account for these consequences, we
propose a transient correction. This correction prescribes a lower decay
rate of the slowest pool and accounts for disturbances in the past by
decreasing the spin-up-run predicted stocks to match an independent estimate
of current soil carbon stocks. Application of this transient correction at a
Central European beech forest site with a typical disturbance history
resulted in an additional carbon fixation of 5.7±1.5 tC/ha within 100
years. Carbon storage capacity of disturbed forest soils is potentially much
higher than currently assumed. Simulations that do not adequately account
for the transient state of soil carbon stocks neglect a considerable amount
of current carbon accumulation. |
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