Environmental Engineering Reference
In-Depth Information
high precipitation causes peaty surface horizons. Descending soil water reaches less
weathered iron-rich parent material below seasonally waterlogged upper horizons. The
soils thus show features of both gleying and podzolization, hence their name
stagnopodzols
in the
Soil Map of England and Wales
. The former name for the placic
podzol is the 'peaty gley podzol with ironpan', under which appellation it occurs in older
Soil Survey reports (see Colour Plate 17 between pp. 400 and 401).
It is likely that several different development pathways can lead to this soil profile.
The Scottish pedologist FitzPatrick has suggested an alternative evolutionary sequence
after observing that the ironpan frequently occurs above a dense subsoil; in these cases
the ironpan picks out a physical interface in the subsoil, the interface marking the upper
limit of permafrost conditions in Pleistocene times. Such compact subsoils are termed
fragipans
and they have a high density and low porosity which cause precipitation of the
sesquioxides. Another pathway for the development of soil with thin ironpans is
dependent on vegetation change. From evidence of archaeology and radiocarbon dates, it
is clear that there are
Plate 19.3
Leaching of fluvioglacial sands has produced a
bleached eluvial (Ea) horizon. Precipitation of medium
acidity is made more acid by organic acids from the surface
litter. Profile depth 2m.
Photo: Ken Atkinson.
