Earthworms in Soil Restoration: Lessons Learned
from United Kingdom Case Studies of Land
Reclamation
Kevin R. Butt1,2
Abstract
Restoration ecology requires theoretical consideration of
a habitat’s former structure and function before the practice
of ecological restoration is applied. However, experience
has shown that this does not always occur and aspects such
as soil ecology have often been an afterthought. Here, case
study material relates the use of earthworms at selected
sites in the United Kingdom. Due to their soil-forming capabilities, these organisms may be essential to reconstruction of soils when drastic activities have despoiled an area.
Introduction
For the past 20 years, the science of restoration ecology
has grown from virtually nothing to an expanding area of
research and associated practice. Seminal publications
that brought together thinking of numerous experts in the
field (e.g., Jordan et al. 1987; Perrow & Davy 2002) are
now regarded as key texts in educational spheres with the
number of research publications in this area continuing to
grow rapidly (e.g., Ormerod 2003). Many research projects sensibly focus on well-defined habitats, giving specific
emphasis to the plants that are present and how their
establishment and survival will lead to the desired restoration trajectory. However, during this process, much less
emphasis may be given to the soils in which these plants
are expected to grow. Habitat degradation may rapidly
lead to localized (easily observed) faunal extinctions
followed by the gradual or perhaps rapid destruction of
the flora. Often, though, soil-related problems are not
addressed, and in extreme cases, the soil may be deliberately removed. Restoration or even rehabilitation of a habitat thereafter becomes increasingly difficult.
In many soils, earthworms are essential components of
the fauna. As detritivores, they are partially responsible for
the breakdown and recycling of dead organic matter. This
may involve direct incorporation of vegetation such as leaves
or by production of feces (casts) deposited at the soil surface
and thereby assisting burial. The intimate mixing of soil by
1
School of Built and Natural Environment, University of Central Lancashire,
Preston PR1 2HE, U.K.
2
Address correspondence to K. R. Butt; email krbutt@uclan.ac.uk
Ó 2008 Society for Ecological Restoration International
doi: 10.1111/j.1526-100X.2008.00483.x
DECEMBER 2008
Restoration Ecology Vol. 16, No. 4, pp. 637–641
While describing in brief the type of work undertaken,
these case studies seek to illustrate some of the misunderstandings/problems/deliberately negative acts that have too
often accompanied use of earthworms in soil restoration.
From such experiences, implications for practice are suggested that should lead to a greater understanding and
appropriate utilization of earthworms in future projects.
Key words: case studies, earthworms, landfill site, reclamation, soil restoration.
horizontal burrowing (endogeic) species, such as Aporrectodea caliginosa and Allolobophora chlorotica, causes mineral
components and organic fragments to become closely associated. The crumb structure of earthworm casts is unique and
an ideal substrate for promoting plant growth due to a rich
assemblage of microorganisms and nutrients compared with
the contents of the surrounding soil. Passage of soil through
the gut of an earthworm therefore adds to soil status and
improves soil quality (e.g., Edwards & Bohlen 1996).
Other activities of some (deep burrowing) earthworms,
such as Lumbricus terrestris and Ap. longa, include the formation of vertical burrows. These provide channels that
allow circulation of air and also permit rainwater infiltration, leading to reduced erosion through surface run-off.
Earthworm and soil–water relationships are now thought to
be of some importance, particularly within agricultural and
restored sites (e.g., Shipitalo et al. 2004). The very presence
of earthworms may be a contributory factor in pedogenesis,
and because they actively change and ameliorate their soil
environment, they are now regarded as ecosystem engineers (Lavelle et al. 1997). With increased attention placed
on the restoration of derelict and degraded land, there is
a need to ensure that soil rehabilitation is achieved using
the best practicable option but at acceptable cost. This
compromise may lead to use of subsoil, lacking organic
matter and a resident fauna. In extreme situations, such as
landfill caps, such material may also be deliberately compacted creating a particularly hostile environment for
development of sustainable earthworm populations.
Earthworms, rightly or not, have therefore often been targeted as organisms to introduce (inoculate) into soils in the
process of rehabilitation. The following seeks to explore such
practices through examination of case study material drawn
637
638
Ach, Ar, Dr, Ea, Ev
(turf transfer)
As above
As above
Lt (EIU)
Steelworks; created
soil
Restoration Ecology
Ac, Aporrectodea caliginosa; Ar, Ap. rosea; Ach, Allolobophora chlorotica; Al, Ap. longa; Dr, Dendrodrilus rubidus; Ea, Eisenia andrei; Ev, E. veneta; Oc, Octolasion cyaneum; Lr, Lumbricus rubellus; Lt, L. terrestris
using the nomenclature of Sims and Gerard (1999).
Substrate; species;
timing; monitoring;
integration
Substrate; species;
techniques
Trial of method; laboratory comparisons
None recorded
Ev, Lr, Lt (‘‘dug in’’)
Regraded landfill;
created soil
Stockley Park—1992
(Hallows 1993;
Butt 1999)
Hallside—1996/1997
(Craven 1995; Bain
et al. 1999)
(Butt 1999)
Ach, Ac, Al, Lt, Oc
(EIU)
Capped landfill; compacted subsoil
Commercial goals;
biofuel production
Limited survival
Soil very poor;
organic matter
lacking; damage to
site
Timing; species;
numbers
Earthworm survival;
organic matter
incorporation
Survival and spread;
species critical;
positive effect trees
Ac, Al, Lt (broadcast)
Capped landfill; created soil
Hillingdon—1984
(Marfleet 1985;
Butt et al. 1993)
Calvert—1991/1992/
2003 (Butt et al.
1997, 2004)
Test method; confirm
effects of earthworms
Test method/species;
record dispersal;
experiments with
trees
Commercial goals;
golf course
Positive Outcomes
Objectives
Earthworm Species
(Technique Used)
Site Description;
Soil Origin
Location—Inoculation
Date(s) (References)
Choice of Earthworm Species, Number, Technique,
and Timing
The relative merits of major earthworm inoculation techniques are provided in Table 1. Examples of each have
Table 1. Characteristics of selected case study sites of earthworm inoculation.
Locations and Initial Soil Conditions
Case study sites are linked through poor initial site conditions but no more than might be anticipated on reclaimed
industrial sites. No major toxins were present within the
sites, but all were deficient in good quality soils. Hillingdon had a subsoil topped with sewage sludge to provide
adequate physical conditions for earthworms, whereas
Hallside has sewage sludge plowed into the raw, shale-rich
colliery spoil substrate. The sewage sludge content may
initially have been conducive to epigeic earthworms but
contained little mineral soil for geophagous, endogeic species such as Allolobophora chlorotica or deep-burrowing
anecic animals such as Lumbricus terrestris.
Due to the level of compaction (1.6–2 g/cm3) above an
active landfill, high clay content, and no addition of organic
matter, the subsoil medium at Calvert was not ideal for
earthworm inoculation. However, of great value was the
initial support from site managers to assist experiments of
this nature plus a reclaimed soil (in extremis) to trial a novel
technique (earthworm inoculation unit [EIU]). By comparison, the regraded, passive landfill at Stockley Park was
much more conducive to earthworms because a grass covering was established for amenity sport (golf) over a thin layer
of stony soil. All the sites had certain deficiencies/problems
but with appropriate management could have supported
selected earthworms. Nevertheless, the species selected for
use were not always ideal for the given soil conditions.
Problems
from four locations in the United Kingdom. These sites, at
Hillingdon (Marfleet 1985; Butt et al. 1993), Calvert (Butt
et al. 1997, 2004), Stockley Park (Hallows 1993; Butt 1999),
and Hallside (Craven 1995; Bain et al. 1999), have been the
focus of seven earthworm inoculation trials. Specific aspects
drawn from these case studies (Table 1) where a variety of
inoculation techniques were used (Table 2) cannot fail to
demonstrate some of their achievements and successes,
which are already documented in the literature and reviewed
by Butt (1999). However, a specific aim here is to critically
assess each of the operations by reference to problems, mistakes, or deliberate acts that failed to assist the specifically
stated or inferred objectives. Thereafter, implications for
practice in reclamation schemes are examined.
The case studies chosen all relate to sites in Britain,
simply because the author had a direct input into their
establishment or was involved indirectly (usually through
monitoring) at a later stage. Nevertheless, results have a
wider bearing, and the positive aspects demonstrated can
be transferred and the potential problems avoided in similar reinstated soils across temperate systems worldwide.
Monitoring; methane
Earthworms in Soil Restoration
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Earthworms in Soil Restoration
Table 2. Relative merits of earthworm inoculation techniques (adapted from Butt et al. 1997).
Technique
Advantages
Disadvantages
Broadcast after chemical/
physical extraction
High densities possible; species selection
possible
Turf transfer
Protective microenvironment; cocoons
transferred
EIU
Protective microenvironment; cocoons and
all life stages present; high densities
possible; control over numbers; species
selection/combinations possible; no
collection site to be damaged
been used in the case studies presented (Table 2) plus
a variant at Stockley Park, where broadcast inoculation
was supplemented by earthworms being ‘‘dug in’’ to slots
created in the turf of the receptor site. This cannot be
regarded as a standard practice or one that will assist
earthworm survival. Here, as on a golf course, the slots
were closed (trodden down) after earthworm insertion—
potentially leading to immediate mortality. Timing of this
particular operation (over winter months) may have
necessitated this practice to avoid deposited animals freezing on the soil surface.
Use of broadcast inoculation at Hillingdon in 1984 was
then seen as best practice, but the method of collection
was a potential problem from the outset. This was because
mass spraying of soil with formalin will have harmed the
4,000 collected animals if not washed immediately. Likely
species used, determined by resampling the donor field,
were Aporrectodea caliginosa, Ap. longa, and Lumbricus
terrestris. All may not have been ideal candidates for
the site due to the high organic matter content. Litterdwelling and other shallow-working species such as Red
worm (L. rubellus) and Allolobophora chlorotica, respectively, would have been more suitable (but less easily collected). By contrast, the species used at Stockley Park
were obtained commercially. They did not therefore suffer
from any chemical exposure prior to use, but once again,
the majority (commercially bred epigeic Eisenia veneta) of
the 1.5 million inoculated (Hallows 1993) were not a suitable choice. This was confirmed during monitoring in later
years, when none of this species was located (Butt 1999).
Three trials saw development of the EIU technique
(e.g., Butt et al. 1997). This mass rearing in plastic bags
(Lee 1995) meant that species selection was possible, so
appropriate species could be used as starter cultures.
However, this in itself was part of the development process and species selection shifted in favor of Ap. longa
and Al. chlorotica or a combination of both species over
L. terrestris. The latter was a poor candidate species for
DECEMBER 2008
Restoration Ecology
Protective microenvironment absent; no
cocoon transfer; mainly deep-burrowing
(anecic) worms; worms may be injured
during extraction; laborious and
expensive; damage to collection site
Densities usually low; little control over
species/numbers; mainly surfacedwelling (epigeic and endogeic)
worms; cutting machines/labor
required; damage to collection site
Laborious and expensive
this site because it was less able to burrow into compacted
clays than, e.g., Ap. longa (Kretzschmar 1991). However,
site managers were initially keen to use L. terrestris contrary to the judgment of the scientists involved.
During development and trialing of this technique at
Calvert, the size of the unit was reduced (2 rather than 4
L) for ease of handling and inoculation into site. To prevent hatchling escape, sealed units were used during the
3-month cultivation phase. Netting was also pegged immediately above each EIU site following inoculation because
site workers after the first trial reported that birds (corvids
and gulls) from the nearby active landfill area had shown
significant interest in the EIUs and likely reduced earthworm numbers through predation. In addition to monitoring the earthworms, their interaction with trees was also
investigated in collaboration with the Forestry Commission. Over a period of a decade, Alder (Alnus glutinosa)
had a significant positive effect on overall earthworm density, likely due to nitrogen additions. However, the earthworm treatments had no significant effect on tree growth,
most likely as a result of extremely hostile soil conditions
with low organic matter content and high compaction
(Butt et al. 2004). The third trial at Calvert (March 2003)
used Ap. caliginosa, Ap. longa, and Octolasion cyaneum
from stock sources (e.g., Lowe & Butt 2005). This compared inoculation of earthworms into two adjacent 400-m2
plots, one of which had 40 tonnes of composted green
waste (CGW) added as a surface dressing. At most recent
sampling (3 years), the inoculated earthworm species were
all recorded from the CGW plot, but only very low numbers of Ap. longa were found in the control plot.
Site managers at Hallside (Scottish Greenbelt Company
[SGC]) considered that provision of earthworms through
use of the EIU technique might be of value to assist willow (Salix sp.) and poplar (Populus sp.) short rotation
coppice production (Craven 1995). SGC therefore commissioned 2,000 (3 L) EIUs following the design of Butt
et al. (1997) but with a substrate similar to that spread on
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Earthworms in Soil Restoration
site (colliery spoil and sewage sludge). The earthworm
starter culture comprised 8,000 L. terrestris (obtained from
a commercial supplier), and EIUs were inoculated into
site by a commercial labor force. However, as at Calvert,
this species was not suitable to the given soil conditions,
and none were recorded during monitoring for the following 2 years (Bain et al. 1999).
Recurring Problems/Specifics
At Hillingdon, the site itself was not stable, and signs in
1990 revealed methane seepage that had reduced earthworm numbers to zero in places, such that no organic matter incorporation had occurred. However, monitoring of
this site was not continuous, so it was difficult to draw firm
conclusions.
An inappropriate choice of earthworm species led to
the failure of trials (or parts thereof) featured here. The
choice of Lumbricus terrestris was a problem at Calvert
and Hallside. Soils were not in a state of development
appropriate for this species, so preventing deep burrowing
and allowing predation. In addition at Hallside, use of
EIUs was compromised at a number of stages. Observation of the labor force employed for inoculation showed
that instructions were not followed, and contents of the
EIUs were often simply emptied on to the soil surface,
totally negating use of this technique (Table 1). The
£40,000 allocated for this earthworm inoculation exercise
(Craven 1995) was effectively wasted. Parallel laboratorybased research using the same materials and commercially
obtained earthworms showed that cocoon production
would have been minimal and adult survival equally low
(Bain et al. 1999). The whole Hallside enterprise involved
a number of major organizations such as the SGC, Scottish Enterprise, and the Forestry Commission but perhaps
paramount was the release of the land for housing from
below the colliery spoil heaps.
Turf transfer inoculation at Hallside was a badly conceived afterthought, conducted during winter, so chances
of earthworm survival were low from the outset. The turfs
were thin (approximately 2 cm), laid on the surface, and
did not integrate with the (hostile, stone rich) substrate.
By the following spring, most had dried and the grass they
contained was dead.
The integrity of the site at Calvert was not always maintained because test drilling by the site operators was
deemed necessary. Eventually, a road (known for some
years in advance) was constructed directly through trial 2.
This was perhaps an unfitting end to what was the largest
earthworm inoculation and tree planting experiment set
up in Britain. However, it could be argued that sustained
site access and provision of a deer- and rabbit-proof fence
(for the trees) were sufficient recompense for the ultimate
loss of the experiment.
Provision of CGW as a source of organic matter was
possible because an on-site composting facility was then
in operation. Nevertheless, the 40 tonnes provided were
640
deposited in only one large plot rather than a number of
smaller areas because large plant operators appear to work
on different scales to research scientists. After a period of
2 years, the plot and adjacent control plot had effectively
been isolated from the rest of the landfill cap because plowing took place to the edges to alleviate water-related problems during the summer. Once again, a feature of research
taking place on an active industrial site is that the science is
seldom, if ever, given priority. Monitoring continues, but
the effective barrier formed by plowing may prove a severe
restriction to further dispersal across site.
Conclusions
Earthworms are not a panacea and cannot remedy all
problems associated with soils. They can assist in soil
development and have been used to good effect in some
soil restoration schemes. Nevertheless, use of earthworms
should always be questioned, and unless the points below
are recognized and considered before use, then it is likely
that any efforts made may be wasted. There is a wealth of
material in the scientific literature relating to earthworms
in soil restoration (e.g., Lee 1995; Butt 1999) beyond the
scope of the case studies presented here. Any future soil
restorations must consider these, as appropriate, and learn
from past experiences.
Implications for Practice
The following have arisen from the case study material
presented and serve as a guide for the use of earthworms in soil restoration schemes:
d
d
Is the operation necessary?—This question must first
be addressed, and earthworm introduction into restored soils only employed if really justified. What
are the earthworms expected to do? Is it within the
scope of their known ecology? If natural colonization
will occur from adjacent land, then perhaps inoculation is not required or only additions of deep-burrowing (slow to colonize) species may be necessary? A
significant aspect that must be considered is operational cost and all the points below link to this.
Earthworm selection—An appropriate choice of species (possibly a number from different ecological
groupings—but certainly native to the given area)
must be made for the given restored soil. This must
take into account species requirements with respect
to soil physicochemical conditions. The life stages
used (cocoon/juvenile/adult) and their origin (collected/bred for purpose/purchased) may also be
critical to successful establishment and continued
survival. Just as quality of inoculum is important, the
quantity used is vital but ought to be kept to a minimum while ensuring sustainability (survivorship and
reproduction).
Restoration Ecology
DECEMBER 2008
Earthworms in Soil Restoration
d
d
d
d
Timing—This has a number of facets but primarily
relates to the stage of soil restoration. A ‘‘raw’’
mixture of inorganic and organic components may
be less suitable than a more mature amalgam. Also
for the earthworms introduced, season (spring
or fall advised) and associated soil moisture/temperature conditions are critical to assist long-term
survival.
Inoculation method—The type of earthworm introduction (broadcast/turf transfer/EIU/other) may also
be a critical factor in ensuring earthworm establishment and survival in newly created soils (Table 2).
Density of chosen inoculation affects rate of dispersal across site and is linked to species choice.
Labor—This depends on the method employed but
experienced personnel may be required to ensure
that the earthworms used have the best chances of
survival. Where possible, prevent any activities taking place that will disrupt the (industrial) site after
earthworms are added.
Monitoring—Without this, there is no point in undertaking any form of management. An agreed plan
over a realistic time frame, e.g., annually for 3 years
then at 5 and every 5 years thereafter, must be put in
place. Monitoring of the earthworms themselves,
species, numbers, and dispersal ought to be linked
with measurements of developing soil properties.
Future Developments
Where appropriate, earthworms could be used to greatly
assist soil development in rehabilitated sites. Currently
seen as ‘‘optional extras’’ by site managers, there is a need
to stress the specific role of different earthworm ecological
groups and even species within soil processes to carefully
select suitable inocula. This requires acting on advice from
experts. The use of earthworms in rehabilitation of soils
can, and will, only move forward if ecologists are incorporated into the planning process by environmental managers, engineers, and other stakeholders.
Acknowledgments
The author thanks the colleagues from the past 20 years
who worked on earthworm-related, soil restoration projects,
DECEMBER 2008
Restoration Ecology
and also numerous managers and operators of the case
study sites.
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