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| Titel |
Depth and rate of secondary carbonate accumulation in loess - 14C pulse labeling column experiment |
| VerfasserIn |
Martina Gocke, Konstantin Pustovoytov, Yakov Kuzyakov |
| Konferenz |
EGU General Assembly 2010
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250042258
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| Zusammenfassung |
| Pedogenic (secondary) carbonates are formed under arid and semiarid climatic conditions
by reprecipitation of Ca2+ in soil solution with CO2 in soil air. In calcareous soil
parent material, e.g. loess, this process leads to exchange of primary (lithogenic)
carbon (C) with C from CO2, derived mainly from root respiration and microbial
decomposition of plant remains. The resulting relation between δ13C values of
soil CO2 and of secondary carbonate is used for reconstruction of paleovegetation
and paleoenvironmental conditions. For such studies, the time frame of pedogenic
carbonate formation is crucial, but still unknown. Several environmental factors, e.g.
vegetation, temperature, moisture, affect rate and depth of secondary carbonate
accumulation.
Most soils of arid and semiarid regions contain a carbonate accumulation horizon (Bk,
Ck, K), the depth of which is related to climatic conditions and properties of parent
material. Based on C isotopic exchange during secondary carbonate formation,
the aim of this study was to determine recrystallization rates and to localize the
accumulation depth of secondary carbonate in an experiment with alternating moisture
conditions.
Acrylglas columns of 1 m height were filled with loess and planted with maize for six
months. Contrary to soil, this loess contains solely primary CaCO3, has high CaCO3 content
(29%) and nearly no organic carbon. Thus, we simulated initial soil formation on loess.
Maize plants were pulse labeled in 14CO2 atmosphere at regular intervals of 3 weeks. Loess
was wetted down to a maximum depth of 45 cm, and subsequent waterings were applied after
the water level had decreased due to plant transpiration to less than 40% of WHC. After
six months, plants were harvested and loess was cut into 5 cm slices. Amounts of
secondary (recrystallized) CaCO3 were determined in each of the segments based on the
14C tracer assimilated by plants, then respired into rhizosphere and subsequently
incorporated into newly formed secondary carbonate. After six months, 80% of
recrystallized carbonate were leached from the uppermost 15 cm of the loess column, and
75% of total secondary carbonate were accumulated in a depth between 15 and 35
cm.
The experiment confirmed the hypotheses that
water movement in loess leads to a clear accumulation zone of recrystallized
carbonate (although total CaCO3 content in loess was not changed after six
months),
the depth of carbonate accumulation is not related to depth of root penetration,
the carbonate accumulation horizon correspond to the depth of wetting and
drying.
Based on calculated recrystallization rates (in the range of 10-5 day-1), leaching and
accumulation of secondary carbonate, 1400 years are necessary for complete decalcification
of the uppermost 15 cm of loess. Under the experimental conditions, this time interval
represents the minimum age for formation of a calcic horizon. |
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