Collembola of pulverised fuel ash sites in east London

European Journal of Soil Biology 39 (2003) 1–8 www.elsevier.com/locate/ejsobi

Collembola of pulverised fuel ash sites in east London Peter Shaw School of Life Sciences, University of Surrey Roehampton, Whitelands College, West Hill, London SW15 3SN, UK Received 6 November 2000; accepted 14 January 2002

Abstract Collembola were extracted from surface layers of four lagoons in east London (UK) of the industrial waste pulverised fuel ash (PFA). One lagoon was subject to seasonal inundation, while the other lagoons were dry, and ranged from 4 to 40 years. Twenty-one species were recorded, with both species richness and community diversity increasing steadily with site age. Early successional species were primarily epi-edaphic, while eu-edaphic species were largely confined to the woodland phase of the succession. The first axis of a canonical correspondence analysis detected the difference between early and late stage sites, while the second axis separated out the wet lagoon community from the dry sites. The data include the first record of Isotoma riparia Nicolet for the UK. © 2003 Éditions scientifiques et médicales Elsevier SAS. All rights reserved. Keywords: Collembola; Succession; Colonisation; PFA; Industrial wastes

1. Introduction Usher and Parr [32] formalised the notion of succession in soil decomposer communities, distinguishing between community change driven by alteration in the substrate and changes resulting from inter-specific competition. There have been a number of published examples of successions in Collembolan communities [9,12,13,19,26,28], with the usual pattern being for species richness and community diversity to increase as the successional progresses [10,32]. Despite the potential offered by post-industrial sites for studying successions [31], relatively little has been published about their Collembolan communities. Most of the work has focussed on minespoil [3,4,12–14,16,18,30], although Greenslade and Majer [7] reported on the Collembola of bauxite wastes in Australia. To date, no work has been published on the Collembola of the industrial waste pulverised fuel ash (PFA), despite it being a significant landscape-forming waste whose chemical properties and botanical characteristics are well studied [8,24]. PFA is the fine powdery ash that results from burning powdered coal in power stations, and when first produced, is E-mail address: [email protected] (P. Shaw)

strongly alkaline (pH > 9), due to free calcium oxide, strongly saline and contains phytotoxic levels of boron. In the first few years after production, the plant community that appears is dominated by ruderals, especially members of the Chenopodiaceae (which combine salt-tolerance with an annual life cycle and the ability to flourish without Vesicular Arbuscular mycorrhizas). As the material weathers down, a more diverse flora colonises dominated by legumes, grasses and composites. After 5–10 years orchids, and calcicoles often appear along with the seedlings of Betula spp and Salix spp. The scrub woodland thickens until canopy closure around 25 years, after which the floral diversity declines due to shading [24]. As the succession proceeds, a basic soil profile starts to develop, characterised by an unmixed or poorly mixed surface organic horizon whose depth increases steadily with site age, while the pH falls. After 30 years, the surface organic mat is around 1 cm thick with a pH around 7.0 [23]. It is evident that fresh PFA is a biologically hostile material, but that during its weathering process, a succession occurs akin to that found on sand dunes [20]. This process must be presumed to include the development of a subterranean ecosystem, but to date, virtually no work has been undertaken in this area. The only previous research on the

© 2003 Éditions scientifiques et médicales Elsevier SAS. All rights reserved. PII: S 1 1 6 4 - 5 5 6 3 ( 0 2 ) 0 0 0 0 2 - X

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P. Shaw / European Journal of Soil Biology 39 (2003) 1–8

cerned one site, where 5 years earlier, fertiliser treatments had been applied in a factorial design, allowing the residual influence of fertilisers to be determined.

2. Methods 2.1. Site descriptions

Fig. 1. Map showing site locations.

invertebrate fauna of terrestrial PFA sites consists of an unpublished study of the earthworms of PFA sites [21], which found fresh PFA to be toxic to all worms, while partially weathered PFA was tolerated by epigeic (but not anecic) lumbricids. Most workers studying the colonisation of industrial wastes agree that the key process facilitating the colonisation of a site by soil fauna is the development of plant cover, with the consequent development of a litter layer [7,18]. The aim of this work was to explore the Collembola succession on PFA, with the intention of defining the principal species, and exploring the relationship of communities to habitats. To this end, samples were taken from PFA sites at differing stages in their succession. The data described below were collected from two grass-herb stage and two woodlandphase PFA habitats, all located in Thames-side habitats east of London. An additional component of the research con-

Four sites were visited in the study, all in the Thames basin east of London (Fig. 1), representing a range of successional ages and vegetational development (Table 1). One site consisted of a long-term revegetation trial of PFA at Tilbury power station. Here, 24 PFA plots (each 5 m × 5 m) were set up in 1991 to research techniques for the management of the floral succession on PFA [25], and during the sampling described in this paper, were undergoing colonisation by a range of grasses and forbs (principally legumes). The plots were laid out randomly within one block (eight replicates × three treatments), and had received applications of fertiliser treatments at their creation (manure raked in at 1 kg m–2, a 15:15:15 agricultural NPK fertiliser at 20 g m–2, or and an unfertilised control), and soil cores were removed equally from all fertiliser treatments. The number of cores removed from each treatment is given in Table 1. The remaining three sites were studied over a shorter time period. Two sites were geographically contiguous, but differed in their developmental stage: these were both found at the disused PFA lagoons at West Thurrock power station, Essex. The majority of this site had been subjected to irregular flooding with saline water, and was covered in lowgrowing halophytic plants. At the northern end of this site

Table 1 Site descriptions Site name and grid reference Tilbury power station PFA trials

Dominant vegetation

Grasses (Agrostis stolonifera, Vulpia myuros), legumes (Medicago lupulina, Melilotus offıcinalis, Lotus corniculatus, Trifolium spp), asteracea (Senecio jacobea, Picris hieraceoides) and ruderals (Plantago coronopus, Centaurium erythraea, Blackstonia TQ657761 perfoliata). Three fertiliser treatments were applied in 1991: O = organic fertiliser, C = chemical fertiliser, Z = unfertilised. Total plant cover increased significantly in all treatments over the sampling period (Fig. 4) Thurrock lagoon Open lagoon bed dominated by halophytes: Spergularia marina, TQ585765 Honkenkya peploides, Puccinellia sp., Aster tripolium, Atriplex prostata, Salicornia sp. Also Centaurium eryrthraea, Blackstonia perfoliata, Melilotus offıcinalis Vicia cracca in the drier areas. Vegetation cover > 95%, and did not alter during the sampling period, being apparently held at a saltmarsh plagioclimax by winter flooding with saline water Barking woods Birch/willow scrub, ca. 5 m high, with ground flora of grasses and Dactylorhiza orchids TQ465825 Thurrock woods Birch/willow scrub, ca. 3 m high, with ground flora of grasses and Dactylorhiza orchids TQ587768

When sampled

Age, years

Number of cores taken Fertiliser treatment

May 1995

4

O 8

C 16

Z 16

January 1996

5

12

12

6

June 1996

6

5

10

5

June 1997

7

8

8

8

June 1998

8

12

12

8

June 1997

<5

12

June 1998

<6

5

February1997 July 1997 June 1997 June 1998

ca. 40

24 16 8 8

ca. 30

P. Shaw / European Journal of Soil Biology 39 (2003) 1–8

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Table 2 Summary soil properties of the 4 sites, expressed as mean ± standard error Site name Thurrock lagoon Tilbury PFA trials, by fertiliser treatment

Barking woods Thurrock woods

Surface pH

Percent mass loss on ignition

7.70 ± 0.15

12.16 ± 0.28

O: 7.77 ± 0.15 C: 8.37 ± 0.13 Z: 8.37 ± 0.13 7.10 ± 0.10 7.53 ± 0.03

O: 15.57 ± 0.48 C: 12.53 ± 0.50 Z: 12.19 ± 0.60 34.92 ± 0.69 13.20 ± 0.59

Extractable P, mg 100 g–1 5.29 ± 0.17 O: 10.55 ± 0.12 C: 8.75 ± 0.07 Z: 9.87 ± 0.05 2.20 ± 0.07 2.58 ± 0.02

Conductivity mS cm–1 4794 ± 1398 O: 1694 ± 171 C: 773 ± 37 Z: 1182 ± 31 576 ± 40 292 ± 9

Abbreviations: O, manure; C, chemical; Z, unfertilised.

was an elevated section of dry PFA covered in birch/willow scrub woodland with an understorey of grasses and marsh orchids, indicative of PFA that has been undisturbed for at least 20 years [24]. The final site was an area of birch/willow woodland at Barking Reach, which results from natural colonisation of PFA from the Belvedere power station, with colonisation starting around 1960 (D. Vickers, pers. comm.). 2.2. Sampling methods Soil cores (3 cm deep) were removed from randomly selected areas at each site using a 9 cm internal diameter steel corer [22], and immediately wrapped in a plastic film to be returned to the laboratory. Once returned, Collembola were extracted into 5% ethanol using a standard high gradient Tullgren funnel [29] prior to storage in 70% ethanol. Identifications were performed using a draft of a new key to UK Collembola [10], but reference was made to older standard keys [5,6]; nomenclature follows [10]. Work focused on the surface 3 cm because Collembola densities are invariably highest in this region [32], and preliminary work suggested that their population densities at greater depth in PFA sites were negligible (unpublished data). The majority of the samples were taken in June, coinciding with floral surveys of the same sites, although for two sites (Barking and Tilbury), February samples were also collected (Table 1). The sampling period was from 1995 to 1998, during which time, the sites remained approximately unchanged except for the Tilbury trial plots, where a significant degree of colonisation occurred. The 4 years of data from this site therefore allow a limited observation of true successional change within one location. Soil chemical data are from five replicate random subsamples of PFA after extraction of Collembola. pH and conductivity were determined by a 10 g:25 ml extract, phosphate was extracted with Truog’s reagent and determined by the molybdate blue method [1]. Soil data are summarised in Table 2, showing pH and organic matter content to increase with site age, while salinity (hence conductivity) falls. Data are listed by fertiliser treatment for the Tilbury trial site, because ANOVA showed all properties to differ significantly between treatments.

2.3. Statistical methods The significance of differences between sites was estimated using one-way analysis of variance for soil properties (whose distribution was found to approximate to normality), and by non-parametric tests (Kruskal–Wallis ANOVA and Spearman’s correlation coefficient) for all Collembola data due to their highly clumped distributions. The ordination techniques used (based on log-transformed data) were PCA for data exploration, and Canonical Correspondence Analysis with a Monte-Carlo test to examine community-habitat relationships [2]. Calculations were performed using SPSS 8.0 and Pc-Ord for Windows. 3. Results 3.1. Successional changes observed over the entire data set A total of 26 species of Collembola were recorded during the survey. Table 3 lists the species, their density at each site (mean and standard error), and the significance of the differences between sites. There was a general trend for species richness, diversity and density to increase with increasing age of the site. The Thurrock lagoon community was dominated by just two species (Isotoma riparia and Entomobrya nicoleti), reflecting its disturbed and saline nature. This is the first UK record for I. riparia (Hopkin, pers. comm.), a species that would key to I. viridis under standard Collembolan keys [5,6,10] but has a bold dark dorsal mid-line and is found in aquatic edge habitats [27]. In contrast, the woodland communities produced upwards of eight species in most cores, including smaller species that may be assumed to inhabit the subsurface soil (Isotomodes productus, Megalothorax minimus, Friesea mirabilis). Multivariate analyses on Collembolan population data excluded species occurring in three or fewer soil cores (to reduce noise in the data), and were performed on data after transformation by log(X + 1). PCA was chosen to identify major trends within the dataset, being the simplest and most natural ordination technique. Species scores and eigenvalues for the first two principal axes are summarised in Table 4, while Fig. 2 portrays the ordination as a function of site. The

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P. Shaw / European Journal of Soil Biology 39 (2003) 1–8

Table 3 Summary data for all Collembola as mean ± standard error for each site, and significance of between-site differences calculated by the Kruskal–Wallis test Species Family: Poduridae Brachystomella parvula (Schäffer) Friesea mirabilis (Tullberg) Hypogastrura manubrialis (Tullberg) Micranurida pygmaea (Borner) Family: Isotomidae Cryptopygus thermophilus (Axelson) Folsomia candida (Willem) Folsomia quadrioculata (Tullberg) Isotoma maritima (Tullberg) Isotoma notabilis (Schäffer) Isotoma riparia (Nicolet) Isotoma viridis (Bourlet) Isotomodes productus (Axelson) Isotomurus palustris (Muller) Family: Entomobryidae Entomobrya corticalis (Nicolet) Entomobrya marginata (Tullberg) Entomobrya multifasciata (Tullberg) Entomobrya nicoleti (Lubbock) Lepidocyrtus cyaneus (Tullberg) Lepidocyrtus lignorum (Fabricius) Family: Tomoceridae Cyphoderus albinus (Nicolet) Tomocerus vulgaris (Tullberg) Family: Neelidae Megalothorax minimus (Willem) Family: Sminthuridae Sminthurides malmgreni Sminthurinus elegans (Fitch) Sminthurus viridis (L.) Family: Onychiuridae Mesaphorura spp. Total Collembola m–2 Species richness Simpson’s diversity index

Thurrock lagoon

Tilbury PFA trials

–

208 ± 77 5±3 994 ± 202 2±2

55 ± 16 8±8 – – – – – – 333 ± 241 – – 333 ± 241 – – –

Thurrock woods

39 ± 39 588 ± 381 – –

1137 ± 463 – – 75 ± 49 656 ± 463 – 386 ± 164 – 54 ± 37

– 344 ± 206 79 ± 48 – 39 ± 28

36 ± 27 95 ± 28 2±2 394 ± 217 27 ± 27

– – –

–

–

–

– –

– –

2±2

10 ± 10

118 ± 80 3±3

** ** ** NS

189 ± 90 4±4

NS NS * NS ** * NS ** *

– – 2232 ± 411 – 106 ± 61 1254 ± 335 4±4 – – –

20 ± 11 79 ± 16 29 ± 29

Significance of site effect

401 ± 92 613 ± 242 29 ± 19 –

127 ± 127 20 ± 20 334 ± 334 39 ± 39 383 ± 383

–

755 ± 313 10 ± 10

Barking woods

28 ± 19 444 ± 88 582 ± 204

** NS ** ** ** NS

4±4

NS NS

9±9

16 ± 12

NS

20 ± 20

59 ± 27 483 ± 168 20 ± 20

NS ** NS

–

– –

–

– –

– 2101 ± 309 3.6 ± 0.24 0.36 ± 0.07

74 ± 39 4268 ± 867 4.6 ± 0.4 0.44 ± 0.05

324 ± 141 2653 ± 823 8.0 ± 0.7 0.71 ± 0.04

680 ± 337 7157 ± 837 10.0 ± 0.7 0.76 ± 0.03

** ** ** **

–: Not recorded. NS: P > 0.05. * P < 0.05. ** P < 0.01. Species richness and diversity were calculated for each soil core individually.

analysis stopped at the second principal axis because the third axis accounted for less variance (9.7%) than expected under the broken stick model (11.0%) [15]. The first axis appears to detect succession in the drier sites, running from the open plots in the Tilbury trials to the woods at Thurrock and Barking, while the second axis detected the difference between the saline lagoon at West Thurrock from the other (drier) sites. CCA was used to explore relationships between communities and environmental factors (Fig. 3). The biplot shows scores for a subset of the species (to minimise overlap on the diagram), showing Entomobrya multifasciata and Hypogastrura manubrialis to be particularly associated with the Tilbury site, Isotomodes productus, Sminthurinus elegans and

Lepidocyrtus lignorum with the wooded sites, and Entomobrya nicoleti plus I. riparia with the saline lagoon. MonteCarlo testing was used to test the null hypothesis of no association between species and environment (9999 iterations), and rejected this hypothesis for the second axis (P = 0.03) but not the first axis (P = 0.10). It also positions the Tilbury ‘Organic’ plots closer to the woodland sites than other Tilbury data, suggesting that the addition of manure has hastened the succession compared with the other fertiliser treatments. 3.2. Analysis of changes within the Tilbury trial plots Data from the Tilbury trial plots could provide for evidence of fertiliser effects (organic, chemical or control) and

P. Shaw / European Journal of Soil Biology 39 (2003) 1–8

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Table 4 The Principal Components Analysis of commoner Collembola after transformation of raw data by log(X+1) Axis Eigenvalue Variance (%) Brachystomella parvula Cryptopygus thermophilus Entomobrya marginata Entomobrya multifasciata Entomobrya nicoleti Friesea mirabilis Hypogastrura manubrialis Isotoma maritima Isotoma notabilis Isotomurus palustris Isotomodes productus Isotoma riparia Isotoma viridis Lepidocyrtus lignorum Lepidocyrtus cyaneus Sminthurides malgreni Sminthurus elegans Mesaphorura spp.

1

2 5.50 30.60 0.38 – 0.07 – 0.31 – 0.42 0.15 0.78 – 0.61 – 0.39 0.81 – 0.11 0.90 – 0.14 0.22 0.87 0.74 0.31 0.72 0.69

2.84 15.80 0.48 0.66 0.48 0.59 – 0.54 – 0.25 0.56 0.18 0.17 – 0.16 0.16 – 0.72 0.40 0.13 0.18 – 0.05 0.22 0.20

Fig. 3. The Canonical Correspondence Analysis of the Collembola of PFA sites. Some species have been excluded to control overlaps on the diagram. Abbreviations: soil properties: P, extractable phosphorus; LOI, loss on ignition; Cond, conductivity of soil extract; Collembola: Bp, Brachystomella parvula; Ct, Cryptopygus thermophilus; En, Entomobrya nicoleti; Em, Entomobrya multifasciata; Fm, Friesea mirabilis; Hm, Hypogastrura manubrialis; In, Isotoma notabilis; Ip, Isotomurus palustris; Ipd, Isotomodes productus; Ir, Isotoma riparia; Lc, Lepidocyrtus cyaneus; Ll, Lepidocyrtus lignorum; Se, Sminthurinus elegans.

successional changes (between 4 and 7 years). During the sampling period, the total plant cover increased significantly in both the fertiliser treatments, but the application of manure had the greatest beneficial effect (Fig. 4). Despite this, the effects of fertiliser treatments on the Collembola community were at best weakly detectable. The total density and species richness of Collembola both differed significantly between fertiliser treatments, both being highest in the plots treated with organic fertiliser (Figs. 5 and 6). Despite this, the fertiliser effect was not significant for any one species. In contrast, nine species were found by Spearman’s correlation coefficient to vary significantly (P < 0.05) monotonically with time. Of these, six increased (Brachystomella parvula, Entomobrya marginata, I. notabilis, I. viridis, Lepidocyrtus cyaneus, Tullbergia spp) while two declined (Isotoma mar-

itima and Tomocerus vulgaris). The total population density and species richness both rose significantly with time. Results from the Tilbury trials were analysed by a Canonical Correspondence Analysis with four environmental variables: absolute date (defined as the number of days since 1-1-1991), date (defined as the number of days since the most recent 1 January), and binary variables defining the addition of organic or organic fertiliser. The ordination is shown in Fig. 7, which identifies two strong trends. The first pattern involves an outlier group, consisting of samples taken in January 1996. These were characterised by the presence of moisture-loving species (Isotomurus palustris and Sminthurides malmgreni). When collected, these samples were waterlogged, in contrast to the dry nature of the ash during summer, and it is likely that these winter samples are in fact

Fig. 2. PCA ordination of the Collembola communities from the four PFA sites studied, labelled by site.

Fig. 4. Vegetation cover within the Tilbury trial plots as a function of fertiliser treatment and age.

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P. Shaw / European Journal of Soil Biology 39 (2003) 1–8

Fig. 5. Density of Collembola in Tilbury trials as a function of fertiliser treatment.

reflecting water content. The second pattern is a smooth progression along the first canonical axis with increasing successional age. The early successional species are identified as Isotoma marina, Hypogastrura manubrialis and Cryptopygus thermophilus, while Entomobrya nicoleti and Lepidocyrtus cyaneus arrive latest. The canonical coefficients for both fertiliser treatments are too small to be accurately portrayed in the diagram, and although their coefficients on the third canonical axis were rather larger, it only explained 2.9% of the variance, and Monte-Carlo testing (using H0: no relationship between datasets) found that only the first and second axes were significant. This CCA analysis can be summarised as showing one outlier group composed of wet samples, coupled with a steady successional development but with only weak fertiliser effects on the Collembolan community. 4. Discussion The general pattern observed for successional changes in Collembolan communities is that their richness and diversity

Fig. 6. Species richness of Collembola in Tilbury trials as a function of fertiliser treatment.

Fig. 7. The Canonical Correspondence Analysis of the Collembola from the Tilbury fertilisation experiment. Some species have been excluded to control overlaps on the diagram. Abbreviations: Environmental Variables: Day, days since 1-1-1991; Date, days since most recent 1 January, Collembola: As for Fig. 1, with the addition of Sm, Sminthurides malmgreni; Emm, Entomobrya marginata.

increase in step with the development of vegetation and soil organic matter [7,12,13,17,18,26]. The data presented above concord fully with this model. The four sites studied approximate to a chronosequence, judged by vegetation and soil characteristics (Tables 1 and 2), although only one (the Tilbury trials site) can be dated precisely. The species richness and diversity increase steadily along the chronosequence (Table 3), although the pattern for total density is less clearcut. It is important to examine the assumption that the sites are comparable in all aspects except age. The precise chemistry of PFA varies between batches depending on its source coal, and this essentially random variation may explain the relatively high phosphorus content of PFA in the Tilbury trials (Table 2). It does not explain inter-site variation in pH or conductivity, both of which change rapidly early in the weathering process due (respectively) to carbonation of calcium oxide and leaching of soluble salts. The combustion process destroys essentially all organic matter, so the LOI data must result from material deposited during colonisation. The LOI data given in Table 2 are remarkably high, possibly reflecting the development of a surface organic mat [23]. Other than site age, the biggest difference between sites concerns the hydrological regime. Although no hydrological data were collected, the lagoon bed sampled at Thurrock lagoon was clearly a wetter site than the trial plots at Tilbury power station. It is not clear whether the extremely high conductivity values at this site (Table 2) come from weathering of the PFA particles or from a previous influx of saline water. It is therefore likely that data from the Thurrock lagoon would not correspond to an early stage of succession on a dry site. In contrast, the two woodland sites were approximately equivalent in vegetation structure, and soil development, although the Barking site was apparently older (based on the relative sizes of the Betula and Salix trees at the two sites).

P. Shaw / European Journal of Soil Biology 39 (2003) 1–8

Given this caution, it is possible to examine the community composition at each site. The species-poor assemblage in the highly saline Thurrock lagoon included the first UK record of Isotoma riparia. It also included Entomobrya nicoleti, a species reported by Fjellberg [5] to be halophytic, although Hopkin [10] describes this species as widely distributed. The dominant species in the Tilbury trial plots were Hypogastura manubrialis, Cryptopygus thermophila and Brachystomella parvula. Little is known about the ecology of C. thermophilus [11], but there are several precedents for finding Hypogastrura species in young, disturbed habitats. Parsons and Parkinson [18] recorded H. manubrialis as a co-dominant on the youngest mine spoil sites (along with H. denticulata), and that both species declined with site age. Hutson [13] also found H. manubrialis as a common species on shale sites. Brachystomella parvula was described by Fjellberg [5] as a Collembole of disturbed saline soils, Parr [17] found it in the youngest soils close to a quarry face, and Shaw [26] found it to colonise a fire site so rapidly as to suggest the presence of a dormant egg bank. One unexpected observation at Tilbury was the occurrence of Isotomurus palustris and Sminthurides malmgreni in January 1995, since these are both normally a species of pond edges and wet habitats [5,11]. This coincided with a period when the PFA was waterlogged following heavy rain, suggesting a rapid but temporary invasion of the site by these species. The dominant pattern found in the Tilbury data was a successional change, with CCA identifying Isotoma maritima as the earliest successional species. This could be explained by I. maritima being a halophytic species [11], coupled with the presence of a salt crust on the surface of PFA which dissolves away after a few years [24]. They also showed that the addition of manure increased Collembolan density (Fig. 5), species richness (Fig. 6) but not successional development. This is interpretable as indicating that the addition of manure increased population density without greatly affecting the balance between species. It is not possible for these data to resolve whether this effect was due to changed soil properties (Table 2) or to the increased vegetation cover (Fig. 4). The increases due to litter addition can be contrasted with the observation of Parson and Parkinson [18] who added litter to mine spoil, and found that numbers of Hypogastrura denticulata and Folsomia nivalis were increased in consequence (although total Collembola density was not increased). The two woodland collembolan communities (Barking and Thurrock woods) both held 8–10 species per core, dominated by Lepidocyrtus cyaneus, L. lignorum, Isotomodes productus, I. viridis, Isotoma notabilis, and Friesea mirabilis. Most of these are widespread species, but Isotomodes productus is noteworthy as being recorded by Hutson [13] colonising mine spoil in the British midlands. Slawska [28] also found F. mirabilis and I. notabilis in her sand-dune succession, but in her system, these only appeared at the climax (pine forest) phase. The small blind eu-edaphic collembola in the genus Mesaphorura were at their commonest

7

in these oldest sites, presumably needing the development of organic layers in the soil. In conclusion, these data describe for the first time the colonisation by Collembola of PFA (or indeed any alkaline industrial waste). The pattern observed can be summarised as a small community of early successional (usually epiedaphic) species being replaced by a denser and richer community of generalists which includes eu-edaphic species. This is interpreted as reflecting the improving level of soil development as sites mature, creating new microhabitats within the soil.

Acknowledgements The author would like to thank Mrs Katharine Lankey for help with soil analyses, Dennis Vickers for permission to sample from the Barking woods nature reserve, National Power for permission to visit the Tilbury and Thurrock sites, and Steve Hopkin for his time, encouragement and taxonomic assistance.

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