Geoscience Reference
In-Depth Information
except for nitrogen and phosphorus which are almost totally lacking. Some plants are
sensitive to boron but after about two years of natural weathering the concentration of
this element is reduced by leaching to non-toxic levels.
The high salinity of raw PFA is illustrated by the fact that a coastal plant, hastate
orache
Atriplex hastata
, is often one of the first colonists. If left to Nature, grasses,
clovers and other plants soon appear, and eventually build up a mat of roots and un-
decayed vegetation near the surface. This enables surface-living earthworms to col-
onize, especially the red worm
Lumbricus rubellus.
Worms cannot survive in the raw
PFA because of the high concentration of salts, but as these are leached out, and or-
ganic matter is incorporated into the soil from plant roots, burrowing species are able
to colonize the PFA. They continue to diversify and build up in numbers until, after
about 20 years, a 'mature' worm community with some 15 species is established (
Fig.
bushes, and one would only be able to identify its industrial origin by digging a soil
pit.
T
ABLE 13
Soil profile on Leblanc process waste after 60-80 years. (From E.F.Greenwood and
R.P.Gemmell 1978)
depth (cm)
pH
Profile description
0-5
7.7
Black, surface humus
5-15
7.7
Dark, partially humified waste
15-35
7.8-8.0 Yellowish-brown waste stained with deposited ferric salts
35-55
9.4-9.7 Yellowish, partially weathered waste. Ferric salts present
55-75
12.2
White, unweathered waste, calcium hydroxide present
T
ABLE 14
Some rare plants in South and West Lancashire found on industrial spoil. (From
E.F.Greenwood & R.P.Gemmell 1978)
Yellow-wort
Blackstonia perfoliata
Early marsh-orchid
Dactylorhiza incarnata
Southern marsh-orchid
Dactylorhiza praetermissa
