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| Titel |
Aggregates reduce transport distance of soil organic carbon: are our balances correct? |
| VerfasserIn |
Y. Hu, N. J. Kuhn |
| 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 ; 11, no. 22 ; Nr. 11, no. 22 (2014-11-17), S.6209-6219 |
| Datensatznummer |
250117676
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| Publikation (Nr.) |
 copernicus.org/bg-11-6209-2014.pdf |
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| Zusammenfassung |
| The effect of soil erosion on global carbon cycling, especially as a source
or sink for greenhouse gases, has been the subject of intense debate. The
controversy arises mostly from the lack of information on the fate of eroded
soil organic carbon (SOC) whilst in-transit from the site of erosion to the
site of longer-term deposition. Solving this controversy requires an
improved understanding of the transport distance of eroded SOC, which is
principally related to the settling velocity of sediment fractions that
carry the eroded SOC. Although settling velocity has already been included
in some erosion models, it is often based on mineral particle size
distribution. For aggregated soils, settling velocities are affected by
their actual aggregate size rather than by mineral particle size
distribution. Aggregate stability is, in turn, strongly influenced by SOC.
In order to identify the effect of aggregation of source soil on the
transport distance of eroded SOC, and its susceptibility to mineralization
after transport and temporary deposition, a rainfall simulation was carried
out on a silty loam. Both the eroded sediments and undisturbed soils were
fractionated into six different size classes using a settling tube apparatus
according to their settling velocities: > 250, 125 to 250, 63 to
125, 32 to 63, 20 to 32 and < 20 μm. Weight, SOC content and
instantaneous respiration rates were measured for each of the six class
fractions. Our results indicate that (1) 41% of the eroded SOC was
transported with coarse aggregates that would be likely re-deposited down
eroding hillslopes, rather than with fine particles likely transferred to
water courses; (2) erosion was prone to accelerate the mineralization of
eroded SOC, and thus might contribute more CO2 to the atmosphere than
current estimates which often ignore potential effects of aggregation; (3)
preferential deposition of SOC-rich coarse aggregates potentially causes an
increase of SOC remaining in the colluvial system and a reduction of SOC
flux to the alluvial or aquatic system. These findings identify a potential
error of overestimating net erosion-induced carbon sink effects, and thus
add an additional factor to consider when improving our current
understanding of SOC erosion and deposition on hillslopes. |
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