Agriculture Reference
In-Depth Information
M
INING
AND
I
NDUSTRIAL
W
ASTES
Most mining and industrial waste sites present conditions that are extremely hostile to biological
activity (Ma and Eijsackers 1989; Hossner and Hons 1992; Logan 1992). Features of unameliorated
sites likely to inhibit earthworm establishment include lack of organic matter, poor physical struc-
ture, compaction, poor drainage and unfavorable moisture conditions, excessive fluctuations in
surface temperatures, and extreme acidity resulting from the reduction of sulfides and other materials
in tailings ponds. Most soil-dwelling earthworms avoid low pH soils, although epigeic species such
as
Lumbricus eiseni
and
Dendrodrilus
and
Dendrobaena
spp. may be found in the surface litter
even in very acid soils. Very alkaline wastes such as pulverized fly ash (PFA) and wastes, following
aluminum extraction with NaOH from bauxite, can also be toxic to the soil fauna (Satchell and
Stone 1977; Southwell and Majer 1982; Eijsackers et al. 1983). High salinity is probably the main
reason for PFA toxicity; this declines to harmless levels after weathering for 2 to 3 years (Townsend
and Hodgson 1973). Mine tailings from low-grade copper and uranium mining can also be highly
saline (Nielson and Peterson 1973).
Metal toxicity can seriously impede the rehabilitation of mine spoil, adversely affecting reveg-
etation and litter decomposition processes. Earthworms can tolerate fairly high levels of most heavy
metals (Ireland 1983), although depressions in populations close to a copper refinery have been
reported (Hunter and Johnson 1982). Metals in ionic form pose greater risks than organically bound
forms (Malecki et al. 1982), and adverse effects on earthworm populations are more likely to occur
in acidic soils (Ma 1988).
Prerequisites for earthworm reestablishment in severely degraded soils include the amelioration
of adverse conditions such as low pH, the stabilization of the physicochemical environment, and
the provision of a suitable food supply. Liming and organic matter amendment can counteract the
effects of acidity and metal toxicity and facilitate the initial stages of earthworm establishment, but
long-term community development depends greatly on the nature and extent of revegetation and
the litter supply.
The rate and extent of earthworm population establishment varies, depending on factors such
as the extent of initial disturbance and depopulation, the size and shape of the area affected, the
degree and kind of restoration work carried out, and the availability of colonizers. In the case of
rehabilitated coal mining dumps in the former German Democratic Republic, earthworm establish-
ment reflected the main features of vegetation succession (Dunger 1989). Early colonizing species
such as
A. caliginosa
and
Dendrodrilus/Dendrobaena
spp. made their appearance when a herb
layer had developed and litter had begun to accumulate. The development of a shrub layer and
well-developed litter layer was accompanied by the appearance of large populations of
Dendrodri-
lus/Dendrobaena
spp. and later
L. rubellus,
with activities that rapidly reduced the litter layer. By
the time a closed tree canopy had developed, anecic species such as
L. terrestris
were well
established, and during the transition to a fully woodland stage, further immigration of other species
occurred. Under optimum conditions, the woodland stage with a species-rich and abundant earth-
worm fauna commenced 20 to 25 years after rehabilitation, but little earthworm community
development occurred on acidic, infertile dumps.
Earthworm population establishment can occur quite rapidly in grassland on mined sites
restored to a high level of fertility. Purvis (1984) reported population densities in sites restored for
5 years or longer comparable with those in unmined sites in the English Midlands. However,
earthworm biomass was low because large, deep-burrowing species were scarce:
Lumbricus ter-
restris
in particular was still largely confined to the edges of reclaimed fields after 10 years.
Significant earthworm populations (9 to 10 spp., ca. 270 individuals m
−2
) were also found in 5- to
6-year-old productive grass leys on cutover peat in Ireland, although under less-favorable conditions,
earthworm establishment occurred much more slowly (Curry and Cotton 1983).
Because natural rates of earthworm dispersal into new habitats are low, at most 10 to 15 m
year
−1
and no more than 2 to 3 m year
−1
for many species (Dunger 1969; Hoogerkamp et al. 1983;
