Geoscience Reference
In-Depth Information
Lastly, there are intermediate taxa related to moderately long periods
of waterlogging. Soil Taxonomy introduced Folists that are saturated
with water for less than a total of 30 days in a year. In WRB it is
the same thing (Folic Histosols). These are approximate equivalents of
the hydromulls and hydromoders appearing in different classification
systems.
12.5.5 Destruction/Protection of Wetlands
Examples of landscapes of wetlands (Fig. 12.13)
Fig. 12.13
Left: landscape of Scotland with moor and heather favouring formation of
peat soils on the shelves and in the depressions. Right: peatland of the Canadian forest,
waterlogged and covered with spruce.
Photos
: author.
Peatlands, being highly organic, form an unstable environment, in
which it is almost impossible to install underground drains because
they would move. With time, reverse slopes could be obtained that
modify the working of the drainage network. In ancient times, drainage
was effected with bundles of branches representing a cross-section of a
large 'pipe'. These bundles were approximately aligned. They did not rot
because of saturation of the system with water. Nowadays, peatlands are
drained through very wide, spaced ditches open to the sky. As peat is
very porous, this is sufficient to lower the water table. However, it must
be done judiciously. The density of peat is very low (0.20); it, therefore,
contains 80 per cent water or sometimes more. When drained out, it is
mineralized and sinks into itself until it finds its stable level that is a
few cm above the new water table! This is subsidence. The record is 2.80
m of sinking in 100 years (Gobat
et al
. 2003). This can continue until the
organic matter totally disappears, which is not in the interest of farmers
or environmentalists.
In very dry years in the intertropical zone, the water table
falls to 40 cm below the peat. This results in danger of wildfires
(Wösten
et al.
2008).
Drainage and exploitation of peatlands
