Environmental Engineering Reference
In-Depth Information
builds up organic biomass, stabilizes and influences soils, provides food and shelter for
animals and influences the hydrological cycle. There is no commonly agreed system for
naming Arctic ecosystems, as is illustrated in Figure 24.3, where the US, Canadian and
Russian views are represented. The Canadian view of three zones north of treeline (shrub
tundra, heath tundra, polar desert) contrasts with the US division into Low Arctic and
High Arctic only. The Russian view is more complicated, recognizing five zones, though
other polar scientists would include forest-tundra in the subarctic rather than in the
Arctic. In addition to a recognizable zoning of vegetation
Figure 24.3
Definitions of Arctic ecosystems according to
US, Canadian and Russian usage.
with latitude, there is a strong patterning of plant cover in relation to landforms and soil.
Whilst a superficial glance may suggest uniform plant cover, with little variation from
place to place, in fact there is a high degree of spatial variety which is conditioned by
local variations in microclimates, drainage conditions and particularly soil conditions.
The
soil catena
, the sequence of soils and vegetation communities according to
landforms, is a major unit in polar landscapes. Figure 24.4 shows an example of a soil
catena at Rankin Inlet, Canada, on the western coast of Hudson Bay in the heath tundra
zone (Low Arctic). Topography and depth-to-permafrost are crucial in influencing
vegetation communities and soil profiles. The ridge crests are freely draining and
therefore the permafrost table is relatively deep at 1-2 m. If the ridge is composed of hard
igneous and metamorphic shield rocks, soil formation will have been minimal and the
surface is likely to be bare rock (
Leptosol
soil) with a sparse cover of lichens and
Rhacomitrium
moss. Ridges of glacial till, sand or gravel will have a well drained Arctic
brown soil above permafrost, with a surface vegetation of lichens and dwarf heath
(crowberry,
Empetrum nigrum
; Labrador tea,
Ledum decumbens
) (Plate 24.1). The Arctic
brown profile is slightly acidic and leached, and has a weakly developed surface humus
horizon (Ah) and weathered horizon (Bw) (see Colour Plate 23 between pp. 400 and
401).
On smooth slopes soil drainage deteriorates and the permafrost is shallower. The
summer melt leads to waterlogging and gleying, hence giving tundra gley and tundra
peaty gley soils. Plant communities reflect the change in moisture conditions, with more
wet-tolerant species (mosses and sedges) forming a mixed community. The low points of
the catena in topographical hollows consist of flat, wet meadows where permafrost
occurs at a shallow depth. Typically peaty organic matter, frozen in winter but a black
