Geoscience Reference
In-Depth Information
Sites that have been left for 50-60 years can remain virtually devoid of earth-
worms if pH levels remain around 4.5 due to pyrites oxidation. On the other hand,
less acid coal shales support reasonable populations of six species after a much short-
er period, with the red worm
Lumbricus rubellus
as the most abundant species.
In 1957, I.G.Hall published an account of an extensive survey of over 200 dis-
used pit heaps in England in which he described stages in soil formation. After 20
years, the weathering of shale fragments into fine particles extends down to about 30
cm, but not until it is 40-50 years old can the spoil be said to resemble a normal soil,
and even after 100 years many spoils lack proper soil structure.
Table 12
describes a
profile pit from a 100 year old heap in Somerset with young oakwood on it.
F
IG. 67
Earthworm colonization of pulverized fuel ash on a 9 year old site. (From J.E.Satchell & D.A.Stone,
1972.)
Pulverized fuel ash (PFA) is a waste product which remains after coal has been
ground to a fine powder and burnt in electricity-generating power stations. The ash
consists mainly of spherical glassy particles similar in size to those of a light silty soil,
and therefore it has good water-holding properties. Like china clay wastes, it is com-
posed predominantly of silica (SiO
2
) but with the addition of considerable amounts of
alumina (A1
2
O
3
) and iron oxides. There are also smaller amounts of the oxides of cal-
cium, magnesium and some other elements, including boron. Nutrient ions for plant
growth are therefore present in reasonable quantities - if not immediately available -
