Geoscience Reference
In-Depth Information
teristics have changed. The biological possibilities for soil life will also have changed,
while the inherent soil structural framework remains.
Erosion is an outcome of historic and recent activity by man. Although there is
a tendency to think of soil erosion as a problem only for other parts of the world, this
is not so, and some recent aspects of soil erosion in Britain are considered in
chapter
surface layers of exposed soil, complete with seeds and seedlings. In the hills, the
natural erosive forces of wind, rain, frost, and steep slopes, are added to by heavy
grazing, by burning, and by access roads and other forestry and recreational activities.
Together, these produce landslips, gullying, the wash of eroded material downslope,
the destruction or burial of original soil profiles, and the supply of sediment to rivers,
lakes and reservoirs. In the geological long term, of course, erosion from the land, and
sedimentation in the seas, is part of the cycle of creation of new rocks and continents.
On a human time-scale, such a philosophical view of the world ecosystem is more
difficult to accept.
The pedogenic factors of climate, landform, and biological influences have had,
in general, some 10-14,000 years of post-Glacial time to achieve their effects on par-
ent materials in Britain. During such a period, there have been long spells with differ-
ing climates, and, in the latter half of this period, the progressive effects of man as set-
tler and cultivator. These natural and human factors have both affected trends in soil
development. Soil scientists, archaeologists, and palaeobotanists (specialists in pol-
len analysis) have been able to understand some of these effects through time, from
evidence preserved in some soils and peats. The onset of peat growth on the Pennines
between 7500 and 5000 years ago is one finding. Another is the increased leaching
of lime, and consequent soil acidification, that apparently affected some upland and
hill areas in the Bronze Age around 3500 years ago. As a result of deforestation for
agriculture during the relatively warm and dry continental climate, the rather finely
poised stability of the existing soils was disturbed. The initial impetus caused by ve-
getation changes was accentuated by later climatic deterioration to a cool, wet, ocean-
ic climate. This brought about extensive podzolic soil development (see below), and
the acceleration and spread of the trend to more extensive moorland soils.
It is sometimes possible to follow profile development more directly over quite
short time scales. An example comes from a sand dune system in Norfolk. Here, a
series of linear dune ridges has formed, and is still actively developing successively
to seaward, with new ridges protecting the older, inland, dunes from fresh supplies
of wind-blown sand. Thin continuous mull humus horizons become distinct within a
few decades under dune grassland on the youngest stabilized ('fixed') dunes. After 15
