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- 9 4 -<br />
9 . DISCUSSION<br />
9 .1 . Organic Soils<br />
Organic soils are one of the major soil types occurring in the<br />
Mackenzie River area .<br />
Their depth varies but most of them are moderately<br />
deep (greater than 160 cm) .<br />
They are composed basically of three types<br />
of peat materials : sphagnum, forest and fen peat . The rate of<br />
accumulation of these peats was determined using the White River<br />
volcanic ash as a datum line . Based on this, it was found that<br />
sphagnum peat provided the greatest accumulation,<br />
being 2 .94 cm per<br />
100 years ( Sph . fuscum ) and 6 .93 cm per 100 years (Sph . riparium ,<br />
in open water), followed by forest peat at 2 .54 cm per 100 years and<br />
fen peat at 1 .47 cm per 100 years .<br />
The soils developed from the above peat materials are classified<br />
into two groups Mesisols and Fibrisols . The Mesisols developed<br />
mainly from fen and forest peat materials,<br />
and the Fibrisols developed<br />
mainly from sphagnum peat materials .<br />
The Mesisols are better supplied<br />
with nutrients and have a higher pH than do the Fibrisols which are<br />
extremely acid and very low in nutrients .<br />
The temperature of these soils is<br />
generally lower than that of the<br />
mineral soils, thus, on the southern portion of the study area permafrost<br />
occurs mainly in these soils . The ice content of the frozen peat<br />
materials ranges between 75 and 90 percent on a volume basis, approximately .<br />
The ice is found mainly in the form of crystals and veins . Large<br />
amounts of ground ice were also found in these soils, e .g . wooded palsa<br />
with pure ice layer (site T29B)<br />
and ice wedges associated with peat<br />
polygons .
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