Anthropic dark soils horizons in western Siberian taiga: origin, soil chemistry and sustainability of organic matter
Résumé
The impact of human activity on soil carbon stock and soil fertility is at the forefront of scientific research. In the
past, human practices improved soil fertility and increased carbon storage over long periods of time. Studying the
resulting anthrosols provides access to their evolution over time scales that are unavailable otherwise. These
archeological Anthrosols have been extensively investigated in Amazonia and Europe, but are virtually unknown
in Siberia. Here we examined four soil profiles from two archeological sites in western Siberia, along with two
corresponding control profiles. The first site, Ketskii Ostrog, is an ancient 18th century fortress occupied by an
agricultural population. The second site, Shaitan III, is a historical settlement of metallurgists and horse-breeders
active from the 10th through the 17th century. We aimed to understand whether human activity at these two
sites modified soil carbon and chemical fertility, and to compare these soils with other studied global anthrosols.
We revealed a contrasting impact of human activity for these two sites. At Ketskii Ostrog, ancient agricultural
practices improved soil chemical fertility, with the effects persisting until present day. Human activities exhibited
a beneficial influence on deep horizons through improvements in their cation exchange capacity, pH and nutrient
(P and Ca) concentrations. The Ketskii Ostrog soils were similar to plaggic soils documented in Northern Europe,
which are characterized by the addition of fresh organic matter (OM) in the form of manure which was purposefully added to improve soil fertility. At Shaitan III, chemical fertility has also been improved, but to a lesser
extent. In contrast to Ketskii Ostrog, Shaitan III soils are rich in charred organic matter and strongly resemble
Amazonian Dark Earths with their physico-chemical properties. The Shaitan III soils also have a different origin,
as the result of unintentional human impact. Anthropisation has increased carbon stocks in the soil at both sites;
however, Shaitan III soils prove to be a more effective carbon sink than at Ketskii Ostrog. This two-fold dichotomy (intentional/unintentional vs. fresh OM/charred OM) is not limited by geographical borders (Amazonia, Europe, or Siberia) and soil typology as currently proposed in the WRB. This highlights the need for
concerted studies on anthropised archaeological soils in regard to their importance for both soil fertility and
carbon storage.
Domaines
Sciences de la Terre
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