Gleysols, Stagnosols and Histosols - Major Soil Groups of the World - page 388

insects by secreting enzymes. This is an adaptation for survival because
the roots are submerged in media extremely poor in ions.

12.5.2 Organization of Marshes and Peatlands

(Orbe, Switzerland)
The development of the Great Marsh (Orbe, Switzerland), between
Lausanne and Neuchâtel, will serve as example. The melting of
glaciers on the Swiss Plateau left behind hillocks, which could be
considered totally of morainic origin. In fact, this is the sedimentary rock
that had been carved and rendered undulating (sheepbacks). Moraine
most often represents a very thin layer a few decimetres thick. It is
composed of materials that the glacier moved within itself or on the
surface before melting in place. The organization corresponds to the
pattern in Fig. 12.11.

Landscape position: example of the Great Marsh

Moraine of thickness between zero
and a few metres (gravel)
Wetland (peat)

Hard rock with undulations a
few tens of metres high

Molasse Marl

Molass

Fig. 12.11 Moraine deposits on the Swiss Plateau.

In the initial stages, the closed depressions left by the glacial
morphology gave ponds or lakes. The water that reached them was clear
(reduced plant growth as well as little carbon fixation in soils because
of the cold) and, sometimes, white because of CaCO 3 transported in the
form of powder generated by the nearby glaciers ( glacial flour ). Also, this
water was rich in dissolved CaCO 3 since CO 2 is quite soluble in cold
water. In the lakes and ponds, where the water stagnates and is warmed
by the sun, CO 2 is less soluble. Calcium carbonate then precipitates
as thin sheets. This is marl . It is presently found below peat layers or
mineral-organic materials in marshes.

Sphagnum spreads on the surface of water. It grows indefinitely in
height if conditions are favourable. In Europe, the surface of the peatland
is gradually rising at the rate of 0.2-0.6 mm y -1 . In tropical peatlands, the
upward growth reaches 2.7 mm y -1 . On the contrary, the lower portion of

Vertical organization of peatlands