Geoscience Reference
In-Depth Information
based on the relative abundance of pollens present in the profile from
the bottom up (Chap. 2, § 2.1.3). In addition, these peatlands serve to
date the beginnings of agriculture, for example in the vicinity of the
Aigoual massif (France), because they contain the oldest wheat pollens
found in the region. In the Pyrenees, they enable dating of the start
of olive cultivation in Spain. Bogs also preserve trunks of trees that
grow there, die and are swallowed by the peat. They can be located
and studied by dendrochronology for reconstructing climatic sequences
(Chap. 1, § 1.3.4). Because of waterholes, peatlands are dangerous places
and perhaps a gateway to Hell as was believed in ancient times. In the
Northern Hemisphere (Canada, Europe), the bodies were recently found
of more than 1000 persons drowned or perhaps executed from 3500
BC to the 18
th
century. They were still preserved by the cold, the water
and, above all, the low biological activity. Human skin is preserved and
the clothes too. But the bones had often been dissolved by the acidity
(for example in the case of the Lindow Man in the British Museum).
This is the converse of what is usually seen in the residual material
from human bodies. All said and done, these environments preserve
important archives explaining the past.
In addition, the amount of carbon immobilized in the intertropical
zone is between 50 and 150 kg m
-2
(Vegas-Vilarrúbia
et al.
2010). This is
quite large considering the area of peats in that zone. If we also consider
their equivalent of the high latitudes, the atmospheric carbon balance is
therefore linked to soils and particularly to the soils of peatlands.
12.5.4
Classification of Marsh and Peatland Soils
In the field, the elements characterizing the horizons of peats are:
Characterization of peats
content of organic matter generally greater than 40 per cent,
thickness of the peat, which must exceed 40 cm to ensure its
placement in Histosols; but for phytosociologists it is peatland
when sphagnum moss is present, even if in a very thin layer,
colour (light-coloured peat, brown peat, black peat),
the state of the peat (percentage of fibres), feature that goes
with the preceding. We distinguish undecomposed fibrous peat
(
fibrist-peat
), semi-fibrous and decomposed peat (
hemist-mucky
or even
dy
of some old authors) and non-fibrous, highly
decomposed peat with the feel of soft butter (
saprist-muck
),
