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The colonisation by plants of calcareous wastes from the salt and alkali industry in Cheshire, England
THE COLONISATION BY PLANTS OF CALCAREOUS WASTES FROM THE SALT AND ALKALI INDUSTRY IN CHESHIRE, ENGLAND
.i.A. LEE & BARBARA GREENWOOD
Department o f Botany, The University, Manchester MI 3 9PL, Great Britain
ABSTRACT
Calcareous wastes from the salt industry occupy approximately 150 ha of land in Cheshire, a county devoid of natural calcareous substrata. The wastes are pumped into lagoons and on drying out become colonised by plants. The resulting lime beds vary in the extent to which they are invaded by plants but a number of areas support rich and varied grassland communities. The Witton lime beds, Northwich, support large populations of a number of species of base-rich habitats, which are uncommon in Cheshire and are of restricted distribution in northwest England as a whole. These include a number of orchid species, of which Dactylorhiza praetermissa and Gymnadenia conopsea are the most abundant. Information analysis was used to analyse the vegetation of Witton lime beds and the vegetation groupings recognised were used to examine possible successional sequences. The edaphic factors limiting growth in lime wastes were examined and the effects of fertilizer additions on the growth of indigenous species at Witton are described Phosphorus was the major element limiting growth but on older wastes, with a higher unreacted lime content, phosphorus only partially removed the infertility. The findings are discussed in terms of the conservation and management of Witton lime beds to ensure continued floristic diversity and the possible reclamation of other lime waste areas.
INTRODUCTION
The major part of the United Kingdom salt industry is situated around the Cheshire towns of Middlewich, Northwich, Sandbach and Winsford. The brine is utilized in the salt field as the basis for the heavy chemical industry as well as in the manufacture of salt. A wide range of chemicals is manufactured including soda ash, caustic soda, sodium carbonate and chlorine. Besides these chemicals the industry produces a 131 Biol. Conserv. (10) (1976)--O Applied Science Publishers Ltd, England, 1976 Printed in Great Britain
132
J . A . LEE, B A R B A R A G R E E N W O O D
number of waste products including a calcareous waste from the Solvay process. This waste is now mainly pumped underground into cavities in the 'Keuper' Saliferous Beds formed by controlled brine extraction. Until recently, however, the lime waste was dumped close to the alkali works or pumped as a sludge into lagoons. The waste may be contaminated with brine, and has sometimes been pumped into subsidence flashes which are fed by brine seepages. This has resulted in a range of artificial calcareous habitats varying in salinity. Approximately 150 ha of land, mostly around Northwich, are covered by lime waste and these areas are progressively becoming colonised by plants. The more saline wastes are colonised by a number of halophyte species (Lee, 1975). These sites do not, however, represent the most interesting aspect ecologically of lime waste colonisation, since their vegetation is similar to that of many brine spillage sites in the county. Cheshire is devoid of natural calcareous substrata. The non-saline lime waste areas therefore represent the only extensive calcareous habitats in the county. Although the lime beds are mostly recent in origin (20th century), and are approximately 50 km from the nearest natural calcareous habitats, they have become colonised by a wide range of species, a number of which have no local seed sources. Further, in most cases it is possible to date when the beds were last used for pumping. The lime beds therefore provide an excellent opportunity for the study of primary succession on a unique parent material. This paper describes the vegetation of Cheshire lime beds, the edaphic conditions operating in lime waste and the factors which limit colonisation by plants. Nomenclature of vascular plants follows Clapham et al. (1968). THE NATURE OF THE WASTES The waste is of two kinds. The first is a thixotropic mud known as distiller waste, which never dries out completely; even during long dry spells the water content of the surface 10 cm rarely falls below 60 %. The crude chemical composition of this waste is shown in Table 1. As the waste dries a number of complex inorganic compounds are formed. These include Caa(A103) 2 . CaSO4.12H20, CaSiO3. C a O 3 . 1 5 H 2 0 , and Caa(A103) 2 . 3CASO4.31H 20. This waste displays a distinctive reddish-brown coloration. The second waste product, known as recovered lime-waste, is composed of over 95 ~o calcium carbonate with a certain amount of coke ash. This waste shows a lack of pigmentation. Although the two wastes may become mixed in the lagoons, TABLE 1 THE CHEMICAL COMPOSITION OF DISTILLER WASTE AS PERCENTAGE OF DRY MATTER
CaCOa CaO CaSO4 SiO2
30.0 25.0 20.0 14.0
AI203 MgO Fe20
4.5 3-5" 3-0
PLANTS OF INDUSTRIAL CALCAREOUS WASTES
133
there are some lime beds where either distiller waste or recovered lime waste alone predominate at the surface. Older wastes, produced before the First World War, were of similar composition to the present-day ones but contained a higher unreacted lime content. These wastes dry out to produce concretions which in places give a stony appearance to the surface. The artificial boundary walls of the lagoons are also calcareous. They are made of a mixture of recovered lime waste and cinders, which sets to a concrete-like consistency. After construction these walls are either allowed to become colonised naturally or are fertilized and sown with grass mixtures.
THE L O C A T I O N OF THE WASTES
The largest areas of waste are around Northwich and are owned by Imperial Chemical Industries Ltd. This paper is chiefly concerned with the Witton lime beds (SJ 660746), which are the most extensive tracts of vegetated waste and extend to 40 ha.At the time of the survey (1970) the Witton beds consisted of 5 main beds and a smaller, subsidiary one. These beds first came into use in the mid-1920s. Beds 1-4 have received no waste since 1938, but Bed 5 was in spasmodic use until 1960, receiving only recovered lime-waste. Beds 2-4 contain mainly distiller waste at the surface whereas Beds 1 and 5 contain recovered lime-waste. Tipping with industrial and domestic refuse has now obliterated the surface of Beds 5 and 6. The largest lime beds close to Northwich on Ashton and Neumann's flashes are still in use. They are used as reserve beds when it is impracticable to p u m p the waste undergound. A further lime bed, last used in 1918, is at Plumley (SJ 703748), approximately 4.3 km east of Witton. This is a small bed of 4 ha, but it provides a contrast with the Witton beds because the surface of the waste is in the form of coarser aggregates, is drier and has been much less readily colonised by plants. A number of other small lime beds occur close to Middlewich, Sandbach and Winsford.
THE V E G E T A T I O N
Witton lime beds The vegetation at Witton consists of open grassland and herbaceous communities which are being encroached by scrub. The scrub consists largely of Salix cinerea ssp. oleifolia, but with Betula sp., Crataegus monogyna, and Salix repens ssp. argentea locally abundant. The major interest in these beds is the range of herbaceous species which have colonised them. Several of the species which occur in abundance on the beds are
134
J.A. LEE, BARBARA G R E E N W O O D
extremely local elsewhere in Cheshire (Newton, 1971). These include Blackstonia perfoliata, Dactylorhiza praetermissa, Erigeron acer, Euphrasia borealis, Gymnadenia conopsea, Hirschfeldia incana, Inula conyza, Pastinaca sativa and Sagina nodosa. Gymnadenia conopsea and Dactylorhiza praetermissa are strikingly abundant in certain areas. Other species which occur locally on the beds and rarely elsewhere include Epipactis palustris and Dactylorhiza incarnata ssp. coccinea. Additional local species also occur on the walls of the lagoons. These include Anacamptis pyramidalis, Anthyllis vulneraria, Hieracium grandidans Dahlst., and Hieracium sublepistioides (Zahn) Druce. Many of these characteristic species are adapted for long-range dispersal, having either very small or parachuted seeds. The beds are a large catchment area for wind-blown seed, and the open nature of the existing vegetation ensures little competition to affect establishment. Bare ground still occupies over 50 ~ of the surface in many areas. The waste surface is approximately 2 m below the top of the lagoon walls, and still air close to the walls improves the chances of windblown seed settling on the beds. Many of the species already mentioned have their nearest sizeable populations in dune slacks on the North Wales and Lancashire coasts. A coastal origin for at least some of these species is strengthened by the fact that they are represented by subspecies or growth forms typical of dune slack communities. Such species include Dactylorhiza incarnata, Epipactis palustris, Gymnadenia conopsea and Salix repens. Another feature of the vegetation is the extensive patches of thallose liverworts which are best developed on recovered lime waste. Preissia quadrata (Scop.)Nees and Pellia fabbroniana Raddi are the most widely distributed of these liverworts, but Moerckiaflotowiana (Nees)Schiffn. is locally abundant. Preissia and Moerckia are characteristic plants of dune slacks. Besides the uncommon species of base-rich habitats the beds are colonised by species from the surrounding disturbed ground. The grasses Agrostis stolonifera, Dactylis glomerata, Festuca arundinacea and Festuca rubra are very widely distributed. Chamaenerion angustifolium, Hieracium vulgatum, Hieracium pilosella, Senecio jacobaea, Sonchus arvensis, Taraxacum officinale and Tussilago farfara are abundant on several of the beds. Perhaps the most interesting of this group of species is the alien Hirschfeldia incana, which was first recorded from this area in 1920 (see Newton, 1971) and is now abundant on areas of recovered lime waste. A further group of species, characteristic of salt-contaminated land, occurred very locally on Beds 5 and 6 before the renewal of tipping. These were Atriplex hastata, Puccinellia distans and Spergularia marina.
Plumley lime bed The other Cheshire lime wastes are floristically p o o r e r than the Witton beds, and of these the Plumley bed is the most interesting. The vegetation of this small bed consists of birch scrub with a sparse field layer in which Fragaria vesca, Hypericum perforatum and Linum catharticum are prominent. Other widely distributed species
PLANTS OF INDUSTRIAL CALCAREOUS WASTES
135
include Blackstonia peJJ'oliata, Festuca rubra, Hieracium brunneocroceum Pugsl., Hieracium praealtum (Vill.ex Gochnat), Reseda lutea and Senecio jacobaea. The orchid populations are small. Dactylorhiza fuchsii, Dactylorhiza praetermissa, Dactylorhiza purpurella and Gymnadenia conopsea occur very locally on the lime bed itself, although the first three are also abundant in the surrounding disturbed ground. Hybrids occur between the Dactylorhiza species. The major interest of this lime bed lies not so much in its floristics as in an analysis of the causes for the very sparse vegetation cover developed in the nearly 60 years since dumping ceased. No detailed vegetation analysis of this lime bed has yet been attempted.
Comparison with other lime bed areas Lime beds associated with alkali works also occur in Other European countries. The best documented of these are in the Note~ valley, Poland, where WilkofiMichalska & Sok61 (1968) have recorded 249 angiosperm species from lime spoil mounds surrounding sludge lagoons. As in the case of the Cheshire beds, the list included species rare in the surrounding regions of Pomorze and Kujawy. Further, some of the species recorded from the lime wastes are rare in Poland as a whole. Many of the species have small or parachuted seeds adapted for long-range dispersal but in contrast to the Cheshire beds the Orchidaceae are not represented in this group. The vegetation of both Cheshire and Polish lime waste includes calcicole, halophyte and ruderal species. The last mentioned group includes a number of species characteristic of freely drained habitats which are subjected to summer drought, e.g. Chaenorhinum minus. There are, therefore, similarities between the Cheshire and Polish sites which underline their ecological and floristic interest.
T H E C O L O N I S A T I O N O F W I T T O N LIME BEDS
Vegetation analysis A survey of the vegetation of Witton lime beds was made by recording the presence of species in 1 m 2 quadrats along with a subjective estimate of cover. A minimum of 20 quadrats was placed at random on Beds 1-4. Twelve quadrats were placed on Bed 5. A total of 67 species were recorded from 117 quadrats. The relev6s~were analysed by information analysis. The analysis was performed by the Manchester Regional ICL 1906A/CDC computer. No entirely objective method of determining the level used for group recognition is available. The procedure adopted was similar to that of Lloyd (1972), in which the rate of increase in information (AI) with successive fusions is examined. The level of recognition is based on a marked discontinuity in the rate of increase which occurs around the value of AI = 1000. The hierarchy of the information analysis is shown in Fig. 1 in which the levels of fusion are plotted according to the change in information. Six groups result from the analysis but the pattern of fusion within each group is not shown in the dendrogram. Table 2
136
J . A . LEE, BARBARA G R E E N W O O D
5000 A!
4000
3000
2000
I000
Fig. 1. The hierarchy of the information analysis. For details see text. summarises the a p p o r t i o n m e n t o f relev6s belonging to the six groups a m o n g the individual lime beds. It can be seen that relev6s within a given g r o u p are largely confined to a single waste type, thus underlining the importance o f the substrate in determining the vegetation developed. Whilst certain groups are largely confined to a particular bed (e.g. 19 o f the 24 relev6s belonging to G r o u p 5 come from Bed 1), others by contrast (e.g. G r o u p B) have their c o m p o n e n t relev6s fairly evenly divided between two or more beds. The fact that the groups are largely associated with a particular waste type and occur o n several beds argues against the possibility that TABLE 2 THE DISTRIBUTION OF RELEVI~-.SBELONGING TO THE INFORMATION ANALYSIS GROUPINGS AMONG THE INDIVIDUAL BEDS
Group A No. of relcv6s per bed 1. Lime waste 2. Distiller waste 3. Distiller w a s t e 4. Distiller w a s t e 5. L i m e w a s t e
Total No. relcv6s Total No. species Mean angiosperm cover
Group B
11 1 1 1 9
23 50 37
4 6 7 --
17 28 41
Group C
Group D
5 1 6 4 1
17 43 73
Group E
Group F
4
2
19
9 1
13 2 3 --
2 l 1 1
14 29 102
20 28 53
24 41 61
137
PLANTS OF INDUSTRIAL CALCAREOUS WASTES
,_\\ " ' /
c
C C
B
3
6
\
c C
C B
c
c F
C
C
c A
-\
B
C
B E
B E
AA
C
B C
E E
c
C B
E
CC~~CC "
4 A
'
E2 E
E E E B B ~ c E B
B
B
( l
B B
A A ,,, C C
;~~E
c
B B ~,
C B
C
C
A
C
cIA' N
~
A
C
C A
A
C 5
A A
o.ls km
Fig. 2.
The distribution of vegetation groups on the Witton lime beds 1-5. For details of the groups s e e text.
138
J.A. LEE, BARBARA GREENWOOD
they arise simply from the chance position of establishment. However, clearly, the waste type is not the major factor affecting group fusion in the information analysis since the final fusion is not between groups of the 2 waste types (as might be expected if the edaphic sieves operating in the 2 wastes resulted in strongly contrasted vegetation types). Nor is the final fusion relatable to trends in total cover or species number. Nevertheless the groups produced by information analysis do represent recognisable associations. The groups are found in extensive areas on the beds and have been used to produce a vegetation map. Figure 2 shows the approximate areas of the beds occupied by the individual groups. C h a r a c t e r i s a t i o n o f the g r o u p s
The species c o m p o s i t i o n of the six g r o u p s is shown in T a b l e 3 - i n terms o f % TABLE 3 THE MEAN PERCENTAGE COVER (c) AND FREQUENCY (f) OF SPECIES IN RELEVES BELONGING TO THE INDIVIDUAL GROUPS
Group A cf
Group B cf
Group C cf
1 65 + 12 3 77 1 41 2 65 2 100 + 6 13 88 8 88
12 1 1 1 3 1 7 1 5
Group D cf
Group E cf
Group F cf
1 1 11 19 10 2 + + 1
4 2 37 1 1 2 1 + 1
C O N S T A N T SPECIES
Agrostis stoionifera Centaurium erythraea Festuca rubra Hieracium pilosella Hieracium vulgatum Linum catharticum Salix cinerea Sonchus arvensis Tussilago farfara SPECIES GROUP
CONFINED
TO
Artemisia vulgaris Atriplex hastata Cerastium fontanum Dactylorhiza fuchsii Hypochaeris radicata Juncus articulatus Lotus corniculatus Mentha aquatica Plantago lanceolata Puccinellia distans Reseda lutea Rhinanthus minor Sagina procumbens Salix pentandra Salix viminalis Salix alba Spergularia marina Tragop ogon pratensis Trifolium repens Vicia sativa Campylium stellatum (Hedw.) Longs. & C. Jens.
3 1 7 1 1 1 1 1 9
83 52 83 30 48 61 39 4 96
+ +
4 9
53 3 64 53 1 43 3 5 - 18 86 41 1 4 64 65 7 100 53 1 79 41 28 100 18 4 43 82 15 71
30 60 ~0 95 100 100 10 20 40
71 96 100 33 54 96 25 12 50
ONE
+
6
+
+
+..
9
+
4
+
17
+ + + +
4 9 4 4
+
6
+
6 +
+
4
+
4 +
+
4
+
8
+
8
6 5
7
139
PLANTS OF INDUSTRIAL CALCAREOUS WASTES T A B L E 3--continued THE MEAN PERCENTAGE COVER (c) AND FREQUENCY (f) OF SPECIES IN RELEVES BELONGING TO THE INDIVIDUAL GROUPS
WIDESPREAD
Group B cf
Group C ef
Group D cf
Group E cf
Group F cf
+ + + 1 + + 2 1 1 1
4 17 13 26 4 9 52 52 57 57
2 1 1 1 + 1 1 1 1 1
35 35 29 65 12 29 65 47 52 41
8 1 3 14 + 2 3 + 1 1
47 41 29 59 6 47 65 29 41 29
7 1 1 + + + + 1 1 +
1 + + + + 1 1 + + +
45 15 5 5 10 45 25 20 15 15
+ 4 + 8 + 12 + 12 1 29 + 12 + 8 + 17 1 29 2. 58
+
4
1
35
+
12
+
9
+
5
+
5
+
5
SPECIES
Chamaenerion angustiJblium Cirsiurn arvense Dactylis glomerata Festuca arundinacea lnula conyza Seneciojacobaea Taraxacum off~cinale Funaria hygrometrica Hedw. Pelliafabbroniana Preissia quadrata DIFFERENTIAL
Group A cf
64 12 7 14 21 7 21 21 36 7
SPECIES
Angelica sylvestris Bellis perennis Betula pendula Betula pubescens Blackstonia perfoliata Centaurea nigra Cirsium vulgare Crataegus monogyna Dactylorhizapraetermissa Erigeron acer Eupatorium cannabinum Gymnadenia conopsea Hieracium vagum Hirschfeldia incana Holcus lanatus Leontodon autumnalis Leontodon taraxacoides Pastinaca sativa Prunella vulgaris Ranunculus acris Ranunculus repens Rubus caesius Sagina nodosa Salix repens Senecio erucifolius Ceratodon purpureus (Hedw.)Brid. Moerckiaflotowiana
1
1
12
+
6
5
+ 13
+ + + 1
13 4 9 26
1 1 + + + +
26 26 17 9 13 17
+ 1 + +
+
+
4
1 1
30 13
+ + +
9 9
+
6 35
+ 1 +
18 24 12
18
1 1
12 24
+
18
+
12
+ + + + I
6 12 12 6 18
+ +
6 6
+
7 14
8
+
7
+
7
+
7
3
14
6
+
6
+
7
6 12
+
7
6
+ +
+
4
1
33
+
4 4 4 50 4
2 ÷
35 5
+ + 2 +
1
15
+
4
2 +
42 8
+ + +
12 4 4
+
12
+
12
+ +
12 4
6
6
4
+
21
35
+
+
+
10
+
5
C o n s t a n t species are those species present in each g r o u p with a frequency in one g r o u p of > 80 %. W i d e s p r e a d species are those species present in each g r o u p b u t with a m a x i t n u m frequency in any one g r o u p o f < 80 %. + indicates a m e a n percentage cover o f < 1%.
frequency and mean % cover within the component releves of each group. Group A is species-rich with a low angiosperm cover, and largely confined to recovered lime waste. It includes the majority of very low cover relev6s on the recently used (1960) areas of Bed 5. The group is very heterogeneous and may be capable of further subdivision. Of particular interest in this context is a small group of relev~s
140
J.A. LEE, BARBARA GREENWOOD
containing Atriplex hastata, Puccinellia distans, and Spergularia marina, which probably reflects the continued contamination of parts of Bed 5 by brine. Two species with restricted distributions on the beds as a whole are found with relatively high percentage occurrences in Group A, viz. Blackstonia perfoliata and Sagina
nodosa. Group B contains relev6s low in grass and shrub cover. It is essentially a herbaceous association in which Sonchus arvensis and Tussilago farfara are the major contributors to the total cover. All the relev6s are from distiller waste. In some relev6s attributable to this group Dactylorhiza praetermissa and Gymnadenia conopsea are strikingly abundant. The low total cover associated with relev6s of Group B probably reflects the fact that the group represents an early stage of colonisation on distiller waste. Group C has the second highest angiosperm cover (73~), with major contributions from Agrostis stolonifera, Chamaenerion angustifoiium, Festuca arundinacea and Salix cinerea. It is a heterogeneous, species-rich group which represents a later stage ofcolonisation than A or B, and is found on bothwaste types. In some quadrats Festuca arundinacea and Dactylis glomerata were present as large tussocks. Both species are prominent and vigorous in certain areas, notably on Bed 4, and this may be a response to the increase in nutrient status of the wastes as a result of successional events. Areas of localised organic enrichment as a result of illicit domestic refuse tipping in particular support large tussocks of Festuca arundinacea. Group D is the only one with a closed vegetation cover and is confined to stands within the dense scrub areas of Beds 1, 2 and 3. Salix cinerea is the dominant plant, although Betula pendula, Crataegus monogyna, Salix repens and Salix alba are also present. A feature of the scrub areas is the luxuriant growth of certain associated species, notably Festuca rubra and Tussilago farfara, around the bushes of Salix cinerea. These represent the only widely distributed areas of continuous ground cover on the beds. Group E is, in contrast, low in shrub cover and is predominantly found on distiller waste. It has no very close attiIlities with Group B which is also low in total cover. Thus Group E is characterised by the ubiquitous presence of Hieracium vulgatum ~/nd Hieracium pilosella, these tw o species contributing 60 ~o of the total plant cover, whilst in Group B Sonchus arvensis and Tussilagofarfara make large contributions to the total cover. Dactylorhiza praetermissa is, however, locally abundant in both groups. Group E probably represents an alternative early stage of colonisation on distiller waste to Group B. Group F is found on recovered lime waste and is largely confined to the northern half of Bed 1. It occupies better drained areas of the bed, where water does not lie on the surface for prolonged periods during the winter. Group F is characterised in part by a 100 ~ frequency of Festuca rubra and by a large contribution of this species to the total cover. Other species with a relatively high percentage frequency in this group are Blackstonia perfoliata, Centaurium erythraea, Erigeron acer and
PLANTS OF INDUSTRIAL C A L C A R E O U S WASTES
141
Hirschfeldia incana. The relatively low percentage cover and frequency of perennial composite species is also a feature of the group. Successional relationships of the groups The beds contain wastes of different ages with limited edaphic variation. Therefore vegetation types associated with these wastes may represent different successional stages, and this should be reflected in the total angiosperm cover. It can be readily seen (Table 2) that Group A, the predominant group on Bed 5, the youngest bed, has the lowest percentage cover. Similarly Group D, the scrub association with the highest percentage cover, is confined to older beds. However, there are a variety of successional sequences observable on the two wastes, and these are not always simply relatable to changes in percentage cover. On recovered lime waste, the very open association of Group A, which may have a total cover of less than 10 %, is succeeded by Groups C and F or may pass directly to scrub. The spread of Dactylis glomerata and other coarse grasses in chalk grassland as the result of nutrient build-up in the soil has been reported by Green (1972), and a similar phenomenon may account for the spread of Group C on the lime beds. It is doubtful, however, whether Groups C and F are successionally related. Group F is more localised than Group C and although Festuca arundinacea is present in 12 % of the relev6s it seldom occurs as large, vigorous tussocks. In contrast, Salix cinerea is present in 25 9/o of the relevbs belonging to Group F, and this probably reflects succession from Group F to scrub without another intermediate grassland stage. The initial stages ofcolonisation on distiller waste may involve Groups A, B and E. The relationships between these groups are uncertain. Group A is so heterogeneous that it may represent an earlier stage than either Groups B or E. No recent areas of distiller waste tipping exist to confirm this point. Groups B and E are not successionally related and represent alternative early stages of colonisation. Scrub may invade these groups directly or they may pass through a coarse grassland association (Group C). Therefore succession on both wastes passes through Groups C and D. However, the initial, stages are perhaps more characteristic of a particular waste type (Table 2) and this may indicate the presence of a number of convergent seres. The essential open nature of the grass and herbaceous associations even after more than 30 years following pumping must reflect that the successional events in these groups have proceeded at a slow rate in the past. In contrast there is good evidence for the rapid spread of Salix cinerea scrub in recent years. Aerial photographs for 1953, 15 years after pumping ceased on Beds 1-4, show no scrub at all, whereas 1973 photographs clearly show the two scrub areas depicted in Fig. 2. Further, Salix cinerea is present in a third of all the relev~s. During the five years since the survey there is evidence for a more rapid expansion ofFestuca arundinacea and to a lesser extent Pastinaca sativa and Angelica sylvestris. This may indicate that successional events as a result of nutrient build-up are gaining momentum.
142
J.A. LEE, BARBARA GREENWOOD
F A C T O R S A F F E C T I N G C O L O N I S A T I O N O N W I T T O N L I M E BEDS
Physical factors The wastes differ quite markedly in their physical features. Recovered lime waste is highly compacted at the surface and is heavy to dig. In some localised areas water stands on the surface for much of the year, This compaction almost certainly means that the surface layers are poorly aerated. Distiller waste areas are not compacted, do not form a surface crust and are much less heavy to dig. The water content of both wastes is always high within the rooting zone and rarely falls below 60 %, although progressive drying of the wastes has taken place since pumping ceased. The importance of physical features on establishment and subsequent colonisation is readily observable on Bed 5. On this bed the recovered lime waste has dried to produce a hard smooth crust over the surface several centimetres thick. This crust is impenetrable to seminal roots of the colonising species. The further drying of the waste has resulted in the crust splitting to form polygons approximately 50 cm across with cracks 1 cm wide at the surface. These cracks provide niches in which seedlings become established. At the time of the survey, 13 years after pumping of recovered lime waste ceased, colonisation was largely confined to the polygonal cracks. After the initial colonisation of these cracks the rhizomes of established plants helped to cause some further cracking by growing into the surface crust. On Bed 1, although the surface crust has been considerably altered by plant colonisation, the compaction in the subsurface layer again represents a restriction on rhizome growth and therefore on the vegetative spread of certain species. In contrast the loose, structureless surface layers of distiller waste beds provide little physical resistance to rhizome growth.
Chemical characteristics of the waste soils The waste soils are primosols with a very thin ( < 5 cm) surface organic stained layer overlying the little altered parent material. Some chemical properties of 2 horizons of the soils from 3 beds are shown in Table 4. The sample areas were chosen to include both wastes and a range of vegetation cover. The Bed 1 samples are from a Festuca rubra-Agrostis stolonifera-rich area referable to Group F. The Bed 2 samples are from a Sonchus arvensis-rich area in Group B which is low in total grass cover. The Bed 5 samples are from the narrow vegetated areas in the polygonal cracks formed in the surface crust by drying (Group A). Although the vegetation in these cracks is sparse, Festuca rubra and Agrostis stolonifera are the most abundant species. The organic carbon contents reflect the build up in organic matter as succession proceeds. The surface samples from Bed 5 have a significantly lower organic carbon content than those from the other 2 beds. The sub-surface samples from all 3 beds show similar organic carbon contents. The low total organic matter content in these samples is principally composed of root fragments.
0-2cm 9-11 cm 0-2cm 9-11 cm 0-2cm 9-11 cm
70.6 91-2 49-3 65.1 95.2 87-8
+ 13.1 +4.7 _ 16.6 _ 15.3 + 6.6 + 14.3
% CaCO 3
8.4+0.5 8-7 _+ 0.4 8.6 -+ 0.1 8.7 _+ 0.2 8.6 _+ 0.3 9.6_+1-1
5.9+0.4 0.8 _+ 0.4 5.7 -+ 0.3 0.9 _ 0.4 1.0 _ 0.5 0.7_+0.3
% organic carbon
14.3 2.2 27.4 0.9 3.9 1.4
-+_3.7 +0.3 _+ 1.2 +0.4 + 7.6 -I- 1.3
NO3N mg/lOOg
316-7+111-5 217-0 ___43.5 533.9 -+ 166.0 419.7 -+ 127.0 219.9 _+ 64-9 196-3_+38.2
Ca
Mineralised nitrogen
2-4+4.2 16-6 -+ 10-0 8-3 + 3-2 6.5 ~ 2-9 0.5 _+ 0-3 0.8_+0.9
Mg
Exchangeable cations rag~l O0g
52.5 -0-7 -0-5 1:9 10.8 3.6
+__5.0 _ 1.6 _ 1.6 +0.5 + 1.2 -+- 4-4
NH4N mg/lOOg
4.3_+1-8 3.1 _+ 2.5 10-4 _+ 3.1 8.6 _ 3.7 5.3 __+2.5 22.0_+16.4
Na
9.5_+3-6 1.7 __+0-4 19.8 _+ 1.5 3.1 _+ 0.4 2-8 _+ 2.5 2-0_+1.4
K
Results are shown as mean figures along with the confidence limits at the 95 ~ level. Exchangeable cations were determined by leaching 10 g oven-dried soil with 100 ml of ~).1 N ammonium acetate. The resulting solution was analysed by atomic absorption spectrophotometry. Mineralised nitrogen was determined by the technique of Eagle (1961). Organic carbon was determined by the method of Walkley & Black (1934). Calcium carbonate was determined in a calcimeter.
Bed 1 0-2cm 9-11 cm Bed 2 0-2cm 9-11 cm Bed 5 0-2cm 9-11 cm
Bed 5
Bed 2
Bedl
pH
TABLE 4 CHEMICAL ANALYSIS OF THE WASTE SOILS
-t
O
144
J.A. LEE, BARBARA GREENWOOD
The nitrogen mineralisation shows a number of interesting features, and is correlated with the organic carbon content of the soils, being much higher in the surface than in the sub-surface samples of the older wastes. Samples from the older wastes (1938) show over twice the total mineralised nitrogen in the recovered limewaste as compared with distiller waste. The form in which nitrogen became available is strikingly different: in the recovered lime waste samples ammonium is the predominant form of nitrogen, whereas nitrate accumulates in the distiller waste samples. Further support for this distinction is provided by the surface samples of Bed 5 in which ammonium accumulates in greater quantities than nitrate. On both ~ecovered lime waste sample areas Festuca rubra is the most abundant species; however, at the distiller waste site it is present with very low total cover. It is possible that the difference between the wastes results from inhibition of nitrification by Festuca rubra. If this is so it represents a very important way in which Festuca rubra could affect the subsequent establishment of other species. The soil samples all have high calcium carbonate contents and are alkaline. The alkalinity may be an important factor in restricting early colonisation. The subsurface samples of Bed 5 have very high pHs. The sub-surface samples from recovered lime waste have calcium carbonate contents similar tO those in the original waste, indicating little alteration of the parent material except near the surface. The distiller waste samples have higher calcium carbonate contents than might be expected from a knowledge of the chemical composition of the waste (Table 1). This presumably results principally from the conversion of calcium oxide to calcium carbonate with a concomitant lowering of the alkalinity and also from some contamination of the distiller waste with recovered lime waste. There is no clear evidence that the difference in calcium carbonate content is an important factor affecting the distribution of plants. Of the more calcicolous species only Erigeron acer is more or less restricted to recovered lime waste. It is doubtful whether the unaltered wastes show a significant cation exchange capacity. The development of an appreciable exchange capacity is probably the result of the build-up o f organic matter within the soil. Thus the base exchange capacity as measured by the sum of the exchangeable calcium, magnesium, sodium and potassium contents is higher in the surface than the sub-surface samples of the older wastes. The exchangeable base content as determined by 0-1 N ammonium acetate leaching probably includes additional important components due to the concentration of ions in the soil solution and to the solubility of calcium carbonate in ammonium acetate solutions. 0.1 N ammonium acetate was preferred to 1 N in order to minimise the solution effect. 1 N solutions extracted approximately double the calcium content but even if these figures are taken, the exchangeable calcium content of both wastes is low compared with those observed by other workers in natural British calcareous soils (see e.g. Fearn, 1973). However, as the waste soils develop there will be a considerable increase in the organic matter content and
PLANTS O F INDUSTRIAL C A L C A R E O U S WASTES
145
therefore in cation exchange sites. Concomitantly there will be an increase in microbial respiration raising the partial pressure of carbon dioxide within the soil. This should lead to a considerable increase in the exchangeable calcium content of the surface soils. The sub-surface sample of Bed 5 has the highest exchangeable sodium content and this represents continued contamination with brine. This is further borne out by the very local occurrence of Puccinellia distans and Spergularia marina on this bed. With the exception of the sodium contents it is difficult to relate the different associations to any of the chemical features measured. However, it must be remembered that the chemical differences are probably more marked in the younger wastes. Freshly deposited distiller waste has a more alkaline reaction than recovered lime waste resulting from a higher calcium hydroxide concentration in solution. It is tempting to conclude that whereas physical features are particularly important in the initial colonisation of recovered lime-waste chemical factors (perhaps hydroxyl ion concentration) provide the major limitation on distiller waste. These differences in the little-altered wastes may be partly responsible for the different association observable today.
Nutrient factors limiting colonisation The differences in mineralised nitrogen and the poor growth of some species in certain areas of the beds suggest the possible importance of macronutrient availability in limiting growth after initial establishment. The effects of fertilizer addition on the growth of species was therefore investigated. Three sites on different beds were chosen in close proximity to the areas from which the soil samples had been taken. A randomised block design was used to study the response of indigenous species to nitrogen, phosphorus and potassium addition alone and in all combinations. The experimental treatment plots were 1 m 2 and the blocks were replicated 4 times on each bed. Two applications of fertilizers were made. The first was in October 1970, and the second in March 1971. Nitrogen was added as sodium nitrate at 5 g N / m z at each addition. Phosphorus was added as calcium tetrahydrogen orthophosphate at 5 g P/m 2. Potassium was added as potassium carbonate at 1 0 g K / m 2. Between the first and second additions there was a noticeable growth response by the bryophytes. This response on both wastes was to phosphorus addition alone. The angiosperm cover was recorded during August 1971, as the number of hits on ten vertical pins distributed at random in each plot. The results for the two beds last tipped on in 1938 are shown in Table 5. The recovered lime waste plots showed a significant response to phosphorus alone and support the view that phosphorus is the primary element limiting growth. Phosphorus addition caused nitrogen to become limiting. The large increase in cover in the phosphorus plots was due mainly to the increase in grass cover. A similar but less well marked response was shown on
20-5 10.8 28.3 1-5
Angiosperm cover Gramineae cover
Angiosperm cover Gramineae cover
N
31-8 3-0
62.5 36.8
P
24-5 3-0
20-5 12-0
K
For details see text.
Above ground biomass g/m 2
15
N
23-0 2-8
61.3 10-0
TABLE 6
18.3 9.5
NK
149.0 127.8
NP
41.0 6.3
63.0 41.8
Treatments PK
68.0 17.0
188.0 163.5
NPK
133
P 11
K
156
NP
31
NK
118
Treatments PK
170
NPK
THE RESPONSE OF VEGETATION ON BED 5 T O FERTILIZER ADDITION
Cover was measured as the number of hits on 10 pins per plot. For details see text.
Bed 1 Total Total Bed 2 Total Total
TABLE 5 THE RESPONSE OF LIME WASTE VEGETATION TO FERTILIZER A D D I T I O N
19
Control
23.8 1.8
17.8 9.5
C
52
LSD 5 %
19-4 8.0
43.9 44.7
LSD 5 %
m
t"
7.
PLANTS OF INDUSTRIAL CALCAREOUS WASTES
147
the distiller waste. On this waste only the combined nitrogen and phosphorus treatments showed a significant growth response and this is consistent with the nitrogen mineralisation results. However, there was some response to phosphorus and phosphorus plus potassium treatments. There was little response to nitrogen or potassium treatments alone. The increase in total cover in combined nitrogen and phosphorus treatments was less marked on distiller waste than on recovered limewaste. This may have been the result of the sparse grass cover at the distiller waste site but there remains the possibility that factors other than the availability of phosphorus and nitrogen were limiting growth. However, in laboratory experiments using both wastes the primary growth response in Chamaenerion angustifolium, Erigeron acer, Festuca arundinacea and Festuca rubra was to phosphorus. The magnitude of the response for all four species was similar on both wastes. The £ertilizer experiment on Bed 5 was harvested in July 1973, prior to the destruction of the site by tipping. The vegetation of each plot was cut at approximately 1 cm above the ground, and sorted in the laboratory before drying at 100 °. The yield is shown in Table 6. Here again a pronounced effect of phosphorus addition alone was observed in spite of the very low rate of nitrogen mineralisation in the untreated waste. The addition of phosphorus could have had a marked effect on the activities of the soil micro-organisms involved in nitrogen mineralisation, thereby increasing the nitrogen supply. In the three growing seasons after fertilizer addition a nearly closed sward was produced as a result of the response by the indigenous grasses Agrostis stolonifera, Festuea arundinacea and Festuca rubra. This was accompanied by the break-up of the surface lime waste crust. The vegetation of some calcareous wastes, however, does not respond to fertilizer addition with a marked increase in growth. A number of nutrient addition experiments have been carried out on the sparsely colonised beds at Plumley. The vegetation here has shown only avery small response to phosphorus (which does not remove the infertility) and no response to nitrogen at application rates similar to those applied at Witton. The addition of micro-elements in mixtures or singly to phosphorus treatments had little effect. Ferric citrate sprayed on to the foliage removed chlorosis which is visible, notably on Hyperieum perforatum, early in the summer. However, iron addition to the soil or to the foliage did not result in a marked growth response. Toxicity factors in the waste are presumably largely responsible for the infertility. Of these the calcium hydroxide concentration in the soil solution would appear the most likely. A free calcium hydroxide content of 14 at 15 cm and 30 ~ at 30 cm was recorded by ICI chemists in 1965. The reclamation of similar lime waste sites with a high unreacted lime content is probably best achieved by organic mulching plus phosphorus fertilizer addition. THE M A N A G E M E N T O F LIME BED V E G E T A T I O N
While inevitably the large orchid populations have attracted interest in the lime bed
148
.I.A. LEE, BARBARA GREENWOOD
vegetation in Cheshire, there are other reasons why these areas should be considered important. First, they represent the only extensive calcareous habitats in Cheshire, a county of intensive agriculture and industrial areas with few marginal sites. Secondly, they support sizeable populations of a number of species and hybrids with restricted distributions in North West England. Thirdly, they provide a good opportunity for the study of primary succession on unique parent materials which could produce valuable information for the professional ecologist. Fourthly, they are useful as sites for teaching ecology and taxonomy for both schools and universities. The most important lime waste site is the Witton lime beds, which until recently have been little disturbed since the cessation of pumping. The renewed tipping of chemical waste and domestic refuse in 1970 has not so far obliterated much of ecological interest except the initial stages of colonisation onrecovered limewaste. Although tipping will continue, it is hoped that this will be confined to Beds 4, 5 and the western part of Bed 1, leaving an area of approximately 15 ha undisturbed. This area is the most interesting ecologically, containing all the groups recognised by information analysis. However, if this area is to maintain its floristic diversity it is important that some form of management is introduced in the next few years. This is conditioned by two factors--the rapid encroachment of herbaceous communities by scrub and the spread of coarse grasses, notably Festuca arundinacea and Dactylis glomerata. The scrub is best developed close under the lagoon walls at the northern end of Beds 2 and 3, but there is an interesting small area on the south eastern part of Bed 1 which includes Salix x subsericea. The area of the beds remaining undisturbed is sufficient to allow for the succession through scrub to continue in the already dense area of scrub. The immediate management problem is the limitation of the scrub within the areas shown in Fig. 2. Many young Salix cinerea bushes must be removed from the southern half of Beds 2 and 3 and the northern half of Bed 1. This would allow woodland to develop on both recovered lime waste and distiller waste while ensuring large areas for grass and herb communities. The spread of Festuca arundinacea and Dactylis glomerata is not a significant problem at the present over much of the remaining beds themselves, but the luxuriant growth of these species and Festuca rubra on the walls of the lagoon already considerably reduces the species diversity in many areas and threatens to oust species such as Anacamptispyramidalis and Anthyllis vulneraria. Two factors might increase the growth of the tussockforming grasses on the beds themselves. The first is flash fires which have occurred locally on Bed 1 in areas where these grasses are well established. The second is the eutrophication which could result from large seagull flocks resting on the beds. While fires need not result from domestic waste tipping large seagull flocks inevitably will. It would therefore seem preferable to limit refuse tipping and use the beds for chemical waste only. It must be emphasized that the spread of Festuca arundinacea and Dactylis glomerata on the beds is probably part of succession as a result of nutrient build-up within the developing soils, but every effort must be made not to accelerate it artificially.
PLANTS OF INDUSTRIALCALCAREOUSWASTES
149
The large growth response o f indigenous grasses to p h o s p h o r u s fertilizer on recovered lime waste points to the possibility o f producing a rapid vegetation cover on lime beds by fertilizer addition alone. This is o f no immediate application as far as W i t t o n is concerned, but it is a potentially important finding because there are a n u m b e r o f lime beds still in use. The largest o f these are the beds on Ashton's and N e u m m a n ' s flashes adjoining the W i t t o n beds, a m o u n t i n g to approximately 70 ha. There would seem to be little need for tipping followed by top soil addition for the reclamation o f these and other beds. Some m a n a g e m e n t o f lime bed vegetation has been carried out at Plumley by the Cheshire Conservation Trust. This has consisted o f the removal o f birch scrub in an attempt, in part, to encourage the orchid populations. In six years this has had very little effect on the orchids or other herbaceous species. While this management scheme is eminently a sensible one, its aims are unlikely to be realised in the short term. This is because the edaphic factors which result in the very slow and restricted colonisation will also limit the rate at which changes occur as a result o f management practice. The reclamation o f similar wastes with a high unreacted lime content c a n n o t readily be achieved by fertilizer addition alone and requires further investigation. ACKNOWLEDGEMENTS The authors are indebted to Imperial Chemical Industries Ltd for permission to work on Witton lime beds and to the Cheshire Conservation Trust for permission to work at Plumley. Imperial Chemical Industries also kindly supplied information on p u m p i n g and on the chemical composition o f the wastes. The authors are also indebted to D r J. H. Tallis for his helpful criticism o f the manuscript. The skilled assistance o f Mrs Helen Vickers is gratefully acknowledged and Barbara G r e e n w o o d is indebted to the N a t u r a l Environment Research Council for financial support. REFERENCES CLAPHAM,A. R., TUTIN,T. G. & WARBURG,E. F. (1968). Excursion Flora of the British Isles, 2nd edn. London, Cambridge University Press. EAGLE,O. J. (1961). Determination of nitrogen status of soils in the West Midlands. J. Sci. Food Agric., 12, 712-7. FEARN,G. M. (1973). Biological flora of the British Isles. Hippocrepis comosa L. J. Ecol., 61,915-26. GREEN,B. H. (1972). The relevance of seral eutrophication and plant competition to the management of successional communities. Biol. Conserv., 4, 378-84. LEE, J. A. (1975). The conservation of British inland salt marshes. Biol. Conserv., 8, 143-51. LLOYD,P. S. (1972). The grassland vegetation of the Sheffieldregion. I I. Classification of grassland types. J. Ecol., 60, 739-76. NEWTON,A. (1971). Flora of Cheshire. Chester, Cheshire Community Council. WALKLEY,A. ,~" BLACK,I. A. (1934). An examination of the Degtjareff method for determining soil organic matter and a proposed modification of the chromic acid titration method. Soil Sci., 37, 29-38. W1LKOIq-MICHALSKA,J. & SOKOL, M. (1968). Flora of the lime spoil mounds of Inouwroclaw and Janikowo Soda Factory. Zesz. nauk. Uniw. Mikolaja Kopernika Torun. Nauki MatematycznoPrzyrodnicze, 21, Biologia, XI, 173-208.
.i.A. LEE & BARBARA GREENWOOD
Department o f Botany, The University, Manchester MI 3 9PL, Great Britain
ABSTRACT
Calcareous wastes from the salt industry occupy approximately 150 ha of land in Cheshire, a county devoid of natural calcareous substrata. The wastes are pumped into lagoons and on drying out become colonised by plants. The resulting lime beds vary in the extent to which they are invaded by plants but a number of areas support rich and varied grassland communities. The Witton lime beds, Northwich, support large populations of a number of species of base-rich habitats, which are uncommon in Cheshire and are of restricted distribution in northwest England as a whole. These include a number of orchid species, of which Dactylorhiza praetermissa and Gymnadenia conopsea are the most abundant. Information analysis was used to analyse the vegetation of Witton lime beds and the vegetation groupings recognised were used to examine possible successional sequences. The edaphic factors limiting growth in lime wastes were examined and the effects of fertilizer additions on the growth of indigenous species at Witton are described Phosphorus was the major element limiting growth but on older wastes, with a higher unreacted lime content, phosphorus only partially removed the infertility. The findings are discussed in terms of the conservation and management of Witton lime beds to ensure continued floristic diversity and the possible reclamation of other lime waste areas.
INTRODUCTION
The major part of the United Kingdom salt industry is situated around the Cheshire towns of Middlewich, Northwich, Sandbach and Winsford. The brine is utilized in the salt field as the basis for the heavy chemical industry as well as in the manufacture of salt. A wide range of chemicals is manufactured including soda ash, caustic soda, sodium carbonate and chlorine. Besides these chemicals the industry produces a 131 Biol. Conserv. (10) (1976)--O Applied Science Publishers Ltd, England, 1976 Printed in Great Britain
132
J . A . LEE, B A R B A R A G R E E N W O O D
number of waste products including a calcareous waste from the Solvay process. This waste is now mainly pumped underground into cavities in the 'Keuper' Saliferous Beds formed by controlled brine extraction. Until recently, however, the lime waste was dumped close to the alkali works or pumped as a sludge into lagoons. The waste may be contaminated with brine, and has sometimes been pumped into subsidence flashes which are fed by brine seepages. This has resulted in a range of artificial calcareous habitats varying in salinity. Approximately 150 ha of land, mostly around Northwich, are covered by lime waste and these areas are progressively becoming colonised by plants. The more saline wastes are colonised by a number of halophyte species (Lee, 1975). These sites do not, however, represent the most interesting aspect ecologically of lime waste colonisation, since their vegetation is similar to that of many brine spillage sites in the county. Cheshire is devoid of natural calcareous substrata. The non-saline lime waste areas therefore represent the only extensive calcareous habitats in the county. Although the lime beds are mostly recent in origin (20th century), and are approximately 50 km from the nearest natural calcareous habitats, they have become colonised by a wide range of species, a number of which have no local seed sources. Further, in most cases it is possible to date when the beds were last used for pumping. The lime beds therefore provide an excellent opportunity for the study of primary succession on a unique parent material. This paper describes the vegetation of Cheshire lime beds, the edaphic conditions operating in lime waste and the factors which limit colonisation by plants. Nomenclature of vascular plants follows Clapham et al. (1968). THE NATURE OF THE WASTES The waste is of two kinds. The first is a thixotropic mud known as distiller waste, which never dries out completely; even during long dry spells the water content of the surface 10 cm rarely falls below 60 %. The crude chemical composition of this waste is shown in Table 1. As the waste dries a number of complex inorganic compounds are formed. These include Caa(A103) 2 . CaSO4.12H20, CaSiO3. C a O 3 . 1 5 H 2 0 , and Caa(A103) 2 . 3CASO4.31H 20. This waste displays a distinctive reddish-brown coloration. The second waste product, known as recovered lime-waste, is composed of over 95 ~o calcium carbonate with a certain amount of coke ash. This waste shows a lack of pigmentation. Although the two wastes may become mixed in the lagoons, TABLE 1 THE CHEMICAL COMPOSITION OF DISTILLER WASTE AS PERCENTAGE OF DRY MATTER
CaCOa CaO CaSO4 SiO2
30.0 25.0 20.0 14.0
AI203 MgO Fe20
4.5 3-5" 3-0
PLANTS OF INDUSTRIAL CALCAREOUS WASTES
133
there are some lime beds where either distiller waste or recovered lime waste alone predominate at the surface. Older wastes, produced before the First World War, were of similar composition to the present-day ones but contained a higher unreacted lime content. These wastes dry out to produce concretions which in places give a stony appearance to the surface. The artificial boundary walls of the lagoons are also calcareous. They are made of a mixture of recovered lime waste and cinders, which sets to a concrete-like consistency. After construction these walls are either allowed to become colonised naturally or are fertilized and sown with grass mixtures.
THE L O C A T I O N OF THE WASTES
The largest areas of waste are around Northwich and are owned by Imperial Chemical Industries Ltd. This paper is chiefly concerned with the Witton lime beds (SJ 660746), which are the most extensive tracts of vegetated waste and extend to 40 ha.At the time of the survey (1970) the Witton beds consisted of 5 main beds and a smaller, subsidiary one. These beds first came into use in the mid-1920s. Beds 1-4 have received no waste since 1938, but Bed 5 was in spasmodic use until 1960, receiving only recovered lime-waste. Beds 2-4 contain mainly distiller waste at the surface whereas Beds 1 and 5 contain recovered lime-waste. Tipping with industrial and domestic refuse has now obliterated the surface of Beds 5 and 6. The largest lime beds close to Northwich on Ashton and Neumann's flashes are still in use. They are used as reserve beds when it is impracticable to p u m p the waste undergound. A further lime bed, last used in 1918, is at Plumley (SJ 703748), approximately 4.3 km east of Witton. This is a small bed of 4 ha, but it provides a contrast with the Witton beds because the surface of the waste is in the form of coarser aggregates, is drier and has been much less readily colonised by plants. A number of other small lime beds occur close to Middlewich, Sandbach and Winsford.
THE V E G E T A T I O N
Witton lime beds The vegetation at Witton consists of open grassland and herbaceous communities which are being encroached by scrub. The scrub consists largely of Salix cinerea ssp. oleifolia, but with Betula sp., Crataegus monogyna, and Salix repens ssp. argentea locally abundant. The major interest in these beds is the range of herbaceous species which have colonised them. Several of the species which occur in abundance on the beds are
134
J.A. LEE, BARBARA G R E E N W O O D
extremely local elsewhere in Cheshire (Newton, 1971). These include Blackstonia perfoliata, Dactylorhiza praetermissa, Erigeron acer, Euphrasia borealis, Gymnadenia conopsea, Hirschfeldia incana, Inula conyza, Pastinaca sativa and Sagina nodosa. Gymnadenia conopsea and Dactylorhiza praetermissa are strikingly abundant in certain areas. Other species which occur locally on the beds and rarely elsewhere include Epipactis palustris and Dactylorhiza incarnata ssp. coccinea. Additional local species also occur on the walls of the lagoons. These include Anacamptis pyramidalis, Anthyllis vulneraria, Hieracium grandidans Dahlst., and Hieracium sublepistioides (Zahn) Druce. Many of these characteristic species are adapted for long-range dispersal, having either very small or parachuted seeds. The beds are a large catchment area for wind-blown seed, and the open nature of the existing vegetation ensures little competition to affect establishment. Bare ground still occupies over 50 ~ of the surface in many areas. The waste surface is approximately 2 m below the top of the lagoon walls, and still air close to the walls improves the chances of windblown seed settling on the beds. Many of the species already mentioned have their nearest sizeable populations in dune slacks on the North Wales and Lancashire coasts. A coastal origin for at least some of these species is strengthened by the fact that they are represented by subspecies or growth forms typical of dune slack communities. Such species include Dactylorhiza incarnata, Epipactis palustris, Gymnadenia conopsea and Salix repens. Another feature of the vegetation is the extensive patches of thallose liverworts which are best developed on recovered lime waste. Preissia quadrata (Scop.)Nees and Pellia fabbroniana Raddi are the most widely distributed of these liverworts, but Moerckiaflotowiana (Nees)Schiffn. is locally abundant. Preissia and Moerckia are characteristic plants of dune slacks. Besides the uncommon species of base-rich habitats the beds are colonised by species from the surrounding disturbed ground. The grasses Agrostis stolonifera, Dactylis glomerata, Festuca arundinacea and Festuca rubra are very widely distributed. Chamaenerion angustifolium, Hieracium vulgatum, Hieracium pilosella, Senecio jacobaea, Sonchus arvensis, Taraxacum officinale and Tussilago farfara are abundant on several of the beds. Perhaps the most interesting of this group of species is the alien Hirschfeldia incana, which was first recorded from this area in 1920 (see Newton, 1971) and is now abundant on areas of recovered lime waste. A further group of species, characteristic of salt-contaminated land, occurred very locally on Beds 5 and 6 before the renewal of tipping. These were Atriplex hastata, Puccinellia distans and Spergularia marina.
Plumley lime bed The other Cheshire lime wastes are floristically p o o r e r than the Witton beds, and of these the Plumley bed is the most interesting. The vegetation of this small bed consists of birch scrub with a sparse field layer in which Fragaria vesca, Hypericum perforatum and Linum catharticum are prominent. Other widely distributed species
PLANTS OF INDUSTRIAL CALCAREOUS WASTES
135
include Blackstonia peJJ'oliata, Festuca rubra, Hieracium brunneocroceum Pugsl., Hieracium praealtum (Vill.ex Gochnat), Reseda lutea and Senecio jacobaea. The orchid populations are small. Dactylorhiza fuchsii, Dactylorhiza praetermissa, Dactylorhiza purpurella and Gymnadenia conopsea occur very locally on the lime bed itself, although the first three are also abundant in the surrounding disturbed ground. Hybrids occur between the Dactylorhiza species. The major interest of this lime bed lies not so much in its floristics as in an analysis of the causes for the very sparse vegetation cover developed in the nearly 60 years since dumping ceased. No detailed vegetation analysis of this lime bed has yet been attempted.
Comparison with other lime bed areas Lime beds associated with alkali works also occur in Other European countries. The best documented of these are in the Note~ valley, Poland, where WilkofiMichalska & Sok61 (1968) have recorded 249 angiosperm species from lime spoil mounds surrounding sludge lagoons. As in the case of the Cheshire beds, the list included species rare in the surrounding regions of Pomorze and Kujawy. Further, some of the species recorded from the lime wastes are rare in Poland as a whole. Many of the species have small or parachuted seeds adapted for long-range dispersal but in contrast to the Cheshire beds the Orchidaceae are not represented in this group. The vegetation of both Cheshire and Polish lime waste includes calcicole, halophyte and ruderal species. The last mentioned group includes a number of species characteristic of freely drained habitats which are subjected to summer drought, e.g. Chaenorhinum minus. There are, therefore, similarities between the Cheshire and Polish sites which underline their ecological and floristic interest.
T H E C O L O N I S A T I O N O F W I T T O N LIME BEDS
Vegetation analysis A survey of the vegetation of Witton lime beds was made by recording the presence of species in 1 m 2 quadrats along with a subjective estimate of cover. A minimum of 20 quadrats was placed at random on Beds 1-4. Twelve quadrats were placed on Bed 5. A total of 67 species were recorded from 117 quadrats. The relev6s~were analysed by information analysis. The analysis was performed by the Manchester Regional ICL 1906A/CDC computer. No entirely objective method of determining the level used for group recognition is available. The procedure adopted was similar to that of Lloyd (1972), in which the rate of increase in information (AI) with successive fusions is examined. The level of recognition is based on a marked discontinuity in the rate of increase which occurs around the value of AI = 1000. The hierarchy of the information analysis is shown in Fig. 1 in which the levels of fusion are plotted according to the change in information. Six groups result from the analysis but the pattern of fusion within each group is not shown in the dendrogram. Table 2
136
J . A . LEE, BARBARA G R E E N W O O D
5000 A!
4000
3000
2000
I000
Fig. 1. The hierarchy of the information analysis. For details see text. summarises the a p p o r t i o n m e n t o f relev6s belonging to the six groups a m o n g the individual lime beds. It can be seen that relev6s within a given g r o u p are largely confined to a single waste type, thus underlining the importance o f the substrate in determining the vegetation developed. Whilst certain groups are largely confined to a particular bed (e.g. 19 o f the 24 relev6s belonging to G r o u p 5 come from Bed 1), others by contrast (e.g. G r o u p B) have their c o m p o n e n t relev6s fairly evenly divided between two or more beds. The fact that the groups are largely associated with a particular waste type and occur o n several beds argues against the possibility that TABLE 2 THE DISTRIBUTION OF RELEVI~-.SBELONGING TO THE INFORMATION ANALYSIS GROUPINGS AMONG THE INDIVIDUAL BEDS
Group A No. of relcv6s per bed 1. Lime waste 2. Distiller waste 3. Distiller w a s t e 4. Distiller w a s t e 5. L i m e w a s t e
Total No. relcv6s Total No. species Mean angiosperm cover
Group B
11 1 1 1 9
23 50 37
4 6 7 --
17 28 41
Group C
Group D
5 1 6 4 1
17 43 73
Group E
Group F
4
2
19
9 1
13 2 3 --
2 l 1 1
14 29 102
20 28 53
24 41 61
137
PLANTS OF INDUSTRIAL CALCAREOUS WASTES
,_\\ " ' /
c
C C
B
3
6
\
c C
C B
c
c F
C
C
c A
-\
B
C
B E
B E
AA
C
B C
E E
c
C B
E
CC~~CC "
4 A
'
E2 E
E E E B B ~ c E B
B
B
( l
B B
A A ,,, C C
;~~E
c
B B ~,
C B
C
C
A
C
cIA' N
~
A
C
C A
A
C 5
A A
o.ls km
Fig. 2.
The distribution of vegetation groups on the Witton lime beds 1-5. For details of the groups s e e text.
138
J.A. LEE, BARBARA GREENWOOD
they arise simply from the chance position of establishment. However, clearly, the waste type is not the major factor affecting group fusion in the information analysis since the final fusion is not between groups of the 2 waste types (as might be expected if the edaphic sieves operating in the 2 wastes resulted in strongly contrasted vegetation types). Nor is the final fusion relatable to trends in total cover or species number. Nevertheless the groups produced by information analysis do represent recognisable associations. The groups are found in extensive areas on the beds and have been used to produce a vegetation map. Figure 2 shows the approximate areas of the beds occupied by the individual groups. C h a r a c t e r i s a t i o n o f the g r o u p s
The species c o m p o s i t i o n of the six g r o u p s is shown in T a b l e 3 - i n terms o f % TABLE 3 THE MEAN PERCENTAGE COVER (c) AND FREQUENCY (f) OF SPECIES IN RELEVES BELONGING TO THE INDIVIDUAL GROUPS
Group A cf
Group B cf
Group C cf
1 65 + 12 3 77 1 41 2 65 2 100 + 6 13 88 8 88
12 1 1 1 3 1 7 1 5
Group D cf
Group E cf
Group F cf
1 1 11 19 10 2 + + 1
4 2 37 1 1 2 1 + 1
C O N S T A N T SPECIES
Agrostis stoionifera Centaurium erythraea Festuca rubra Hieracium pilosella Hieracium vulgatum Linum catharticum Salix cinerea Sonchus arvensis Tussilago farfara SPECIES GROUP
CONFINED
TO
Artemisia vulgaris Atriplex hastata Cerastium fontanum Dactylorhiza fuchsii Hypochaeris radicata Juncus articulatus Lotus corniculatus Mentha aquatica Plantago lanceolata Puccinellia distans Reseda lutea Rhinanthus minor Sagina procumbens Salix pentandra Salix viminalis Salix alba Spergularia marina Tragop ogon pratensis Trifolium repens Vicia sativa Campylium stellatum (Hedw.) Longs. & C. Jens.
3 1 7 1 1 1 1 1 9
83 52 83 30 48 61 39 4 96
+ +
4 9
53 3 64 53 1 43 3 5 - 18 86 41 1 4 64 65 7 100 53 1 79 41 28 100 18 4 43 82 15 71
30 60 ~0 95 100 100 10 20 40
71 96 100 33 54 96 25 12 50
ONE
+
6
+
+
+..
9
+
4
+
17
+ + + +
4 9 4 4
+
6
+
6 +
+
4
+
4 +
+
4
+
8
+
8
6 5
7
139
PLANTS OF INDUSTRIAL CALCAREOUS WASTES T A B L E 3--continued THE MEAN PERCENTAGE COVER (c) AND FREQUENCY (f) OF SPECIES IN RELEVES BELONGING TO THE INDIVIDUAL GROUPS
WIDESPREAD
Group B cf
Group C ef
Group D cf
Group E cf
Group F cf
+ + + 1 + + 2 1 1 1
4 17 13 26 4 9 52 52 57 57
2 1 1 1 + 1 1 1 1 1
35 35 29 65 12 29 65 47 52 41
8 1 3 14 + 2 3 + 1 1
47 41 29 59 6 47 65 29 41 29
7 1 1 + + + + 1 1 +
1 + + + + 1 1 + + +
45 15 5 5 10 45 25 20 15 15
+ 4 + 8 + 12 + 12 1 29 + 12 + 8 + 17 1 29 2. 58
+
4
1
35
+
12
+
9
+
5
+
5
+
5
SPECIES
Chamaenerion angustiJblium Cirsiurn arvense Dactylis glomerata Festuca arundinacea lnula conyza Seneciojacobaea Taraxacum off~cinale Funaria hygrometrica Hedw. Pelliafabbroniana Preissia quadrata DIFFERENTIAL
Group A cf
64 12 7 14 21 7 21 21 36 7
SPECIES
Angelica sylvestris Bellis perennis Betula pendula Betula pubescens Blackstonia perfoliata Centaurea nigra Cirsium vulgare Crataegus monogyna Dactylorhizapraetermissa Erigeron acer Eupatorium cannabinum Gymnadenia conopsea Hieracium vagum Hirschfeldia incana Holcus lanatus Leontodon autumnalis Leontodon taraxacoides Pastinaca sativa Prunella vulgaris Ranunculus acris Ranunculus repens Rubus caesius Sagina nodosa Salix repens Senecio erucifolius Ceratodon purpureus (Hedw.)Brid. Moerckiaflotowiana
1
1
12
+
6
5
+ 13
+ + + 1
13 4 9 26
1 1 + + + +
26 26 17 9 13 17
+ 1 + +
+
+
4
1 1
30 13
+ + +
9 9
+
6 35
+ 1 +
18 24 12
18
1 1
12 24
+
18
+
12
+ + + + I
6 12 12 6 18
+ +
6 6
+
7 14
8
+
7
+
7
+
7
3
14
6
+
6
+
7
6 12
+
7
6
+ +
+
4
1
33
+
4 4 4 50 4
2 ÷
35 5
+ + 2 +
1
15
+
4
2 +
42 8
+ + +
12 4 4
+
12
+
12
+ +
12 4
6
6
4
+
21
35
+
+
+
10
+
5
C o n s t a n t species are those species present in each g r o u p with a frequency in one g r o u p of > 80 %. W i d e s p r e a d species are those species present in each g r o u p b u t with a m a x i t n u m frequency in any one g r o u p o f < 80 %. + indicates a m e a n percentage cover o f < 1%.
frequency and mean % cover within the component releves of each group. Group A is species-rich with a low angiosperm cover, and largely confined to recovered lime waste. It includes the majority of very low cover relev6s on the recently used (1960) areas of Bed 5. The group is very heterogeneous and may be capable of further subdivision. Of particular interest in this context is a small group of relev~s
140
J.A. LEE, BARBARA GREENWOOD
containing Atriplex hastata, Puccinellia distans, and Spergularia marina, which probably reflects the continued contamination of parts of Bed 5 by brine. Two species with restricted distributions on the beds as a whole are found with relatively high percentage occurrences in Group A, viz. Blackstonia perfoliata and Sagina
nodosa. Group B contains relev6s low in grass and shrub cover. It is essentially a herbaceous association in which Sonchus arvensis and Tussilago farfara are the major contributors to the total cover. All the relev6s are from distiller waste. In some relev6s attributable to this group Dactylorhiza praetermissa and Gymnadenia conopsea are strikingly abundant. The low total cover associated with relev6s of Group B probably reflects the fact that the group represents an early stage of colonisation on distiller waste. Group C has the second highest angiosperm cover (73~), with major contributions from Agrostis stolonifera, Chamaenerion angustifoiium, Festuca arundinacea and Salix cinerea. It is a heterogeneous, species-rich group which represents a later stage ofcolonisation than A or B, and is found on bothwaste types. In some quadrats Festuca arundinacea and Dactylis glomerata were present as large tussocks. Both species are prominent and vigorous in certain areas, notably on Bed 4, and this may be a response to the increase in nutrient status of the wastes as a result of successional events. Areas of localised organic enrichment as a result of illicit domestic refuse tipping in particular support large tussocks of Festuca arundinacea. Group D is the only one with a closed vegetation cover and is confined to stands within the dense scrub areas of Beds 1, 2 and 3. Salix cinerea is the dominant plant, although Betula pendula, Crataegus monogyna, Salix repens and Salix alba are also present. A feature of the scrub areas is the luxuriant growth of certain associated species, notably Festuca rubra and Tussilago farfara, around the bushes of Salix cinerea. These represent the only widely distributed areas of continuous ground cover on the beds. Group E is, in contrast, low in shrub cover and is predominantly found on distiller waste. It has no very close attiIlities with Group B which is also low in total cover. Thus Group E is characterised by the ubiquitous presence of Hieracium vulgatum ~/nd Hieracium pilosella, these tw o species contributing 60 ~o of the total plant cover, whilst in Group B Sonchus arvensis and Tussilagofarfara make large contributions to the total cover. Dactylorhiza praetermissa is, however, locally abundant in both groups. Group E probably represents an alternative early stage of colonisation on distiller waste to Group B. Group F is found on recovered lime waste and is largely confined to the northern half of Bed 1. It occupies better drained areas of the bed, where water does not lie on the surface for prolonged periods during the winter. Group F is characterised in part by a 100 ~ frequency of Festuca rubra and by a large contribution of this species to the total cover. Other species with a relatively high percentage frequency in this group are Blackstonia perfoliata, Centaurium erythraea, Erigeron acer and
PLANTS OF INDUSTRIAL C A L C A R E O U S WASTES
141
Hirschfeldia incana. The relatively low percentage cover and frequency of perennial composite species is also a feature of the group. Successional relationships of the groups The beds contain wastes of different ages with limited edaphic variation. Therefore vegetation types associated with these wastes may represent different successional stages, and this should be reflected in the total angiosperm cover. It can be readily seen (Table 2) that Group A, the predominant group on Bed 5, the youngest bed, has the lowest percentage cover. Similarly Group D, the scrub association with the highest percentage cover, is confined to older beds. However, there are a variety of successional sequences observable on the two wastes, and these are not always simply relatable to changes in percentage cover. On recovered lime waste, the very open association of Group A, which may have a total cover of less than 10 %, is succeeded by Groups C and F or may pass directly to scrub. The spread of Dactylis glomerata and other coarse grasses in chalk grassland as the result of nutrient build-up in the soil has been reported by Green (1972), and a similar phenomenon may account for the spread of Group C on the lime beds. It is doubtful, however, whether Groups C and F are successionally related. Group F is more localised than Group C and although Festuca arundinacea is present in 12 % of the relev6s it seldom occurs as large, vigorous tussocks. In contrast, Salix cinerea is present in 25 9/o of the relevbs belonging to Group F, and this probably reflects succession from Group F to scrub without another intermediate grassland stage. The initial stages ofcolonisation on distiller waste may involve Groups A, B and E. The relationships between these groups are uncertain. Group A is so heterogeneous that it may represent an earlier stage than either Groups B or E. No recent areas of distiller waste tipping exist to confirm this point. Groups B and E are not successionally related and represent alternative early stages of colonisation. Scrub may invade these groups directly or they may pass through a coarse grassland association (Group C). Therefore succession on both wastes passes through Groups C and D. However, the initial, stages are perhaps more characteristic of a particular waste type (Table 2) and this may indicate the presence of a number of convergent seres. The essential open nature of the grass and herbaceous associations even after more than 30 years following pumping must reflect that the successional events in these groups have proceeded at a slow rate in the past. In contrast there is good evidence for the rapid spread of Salix cinerea scrub in recent years. Aerial photographs for 1953, 15 years after pumping ceased on Beds 1-4, show no scrub at all, whereas 1973 photographs clearly show the two scrub areas depicted in Fig. 2. Further, Salix cinerea is present in a third of all the relev~s. During the five years since the survey there is evidence for a more rapid expansion ofFestuca arundinacea and to a lesser extent Pastinaca sativa and Angelica sylvestris. This may indicate that successional events as a result of nutrient build-up are gaining momentum.
142
J.A. LEE, BARBARA GREENWOOD
F A C T O R S A F F E C T I N G C O L O N I S A T I O N O N W I T T O N L I M E BEDS
Physical factors The wastes differ quite markedly in their physical features. Recovered lime waste is highly compacted at the surface and is heavy to dig. In some localised areas water stands on the surface for much of the year, This compaction almost certainly means that the surface layers are poorly aerated. Distiller waste areas are not compacted, do not form a surface crust and are much less heavy to dig. The water content of both wastes is always high within the rooting zone and rarely falls below 60 %, although progressive drying of the wastes has taken place since pumping ceased. The importance of physical features on establishment and subsequent colonisation is readily observable on Bed 5. On this bed the recovered lime waste has dried to produce a hard smooth crust over the surface several centimetres thick. This crust is impenetrable to seminal roots of the colonising species. The further drying of the waste has resulted in the crust splitting to form polygons approximately 50 cm across with cracks 1 cm wide at the surface. These cracks provide niches in which seedlings become established. At the time of the survey, 13 years after pumping of recovered lime waste ceased, colonisation was largely confined to the polygonal cracks. After the initial colonisation of these cracks the rhizomes of established plants helped to cause some further cracking by growing into the surface crust. On Bed 1, although the surface crust has been considerably altered by plant colonisation, the compaction in the subsurface layer again represents a restriction on rhizome growth and therefore on the vegetative spread of certain species. In contrast the loose, structureless surface layers of distiller waste beds provide little physical resistance to rhizome growth.
Chemical characteristics of the waste soils The waste soils are primosols with a very thin ( < 5 cm) surface organic stained layer overlying the little altered parent material. Some chemical properties of 2 horizons of the soils from 3 beds are shown in Table 4. The sample areas were chosen to include both wastes and a range of vegetation cover. The Bed 1 samples are from a Festuca rubra-Agrostis stolonifera-rich area referable to Group F. The Bed 2 samples are from a Sonchus arvensis-rich area in Group B which is low in total grass cover. The Bed 5 samples are from the narrow vegetated areas in the polygonal cracks formed in the surface crust by drying (Group A). Although the vegetation in these cracks is sparse, Festuca rubra and Agrostis stolonifera are the most abundant species. The organic carbon contents reflect the build up in organic matter as succession proceeds. The surface samples from Bed 5 have a significantly lower organic carbon content than those from the other 2 beds. The sub-surface samples from all 3 beds show similar organic carbon contents. The low total organic matter content in these samples is principally composed of root fragments.
0-2cm 9-11 cm 0-2cm 9-11 cm 0-2cm 9-11 cm
70.6 91-2 49-3 65.1 95.2 87-8
+ 13.1 +4.7 _ 16.6 _ 15.3 + 6.6 + 14.3
% CaCO 3
8.4+0.5 8-7 _+ 0.4 8.6 -+ 0.1 8.7 _+ 0.2 8.6 _+ 0.3 9.6_+1-1
5.9+0.4 0.8 _+ 0.4 5.7 -+ 0.3 0.9 _ 0.4 1.0 _ 0.5 0.7_+0.3
% organic carbon
14.3 2.2 27.4 0.9 3.9 1.4
-+_3.7 +0.3 _+ 1.2 +0.4 + 7.6 -I- 1.3
NO3N mg/lOOg
316-7+111-5 217-0 ___43.5 533.9 -+ 166.0 419.7 -+ 127.0 219.9 _+ 64-9 196-3_+38.2
Ca
Mineralised nitrogen
2-4+4.2 16-6 -+ 10-0 8-3 + 3-2 6.5 ~ 2-9 0.5 _+ 0-3 0.8_+0.9
Mg
Exchangeable cations rag~l O0g
52.5 -0-7 -0-5 1:9 10.8 3.6
+__5.0 _ 1.6 _ 1.6 +0.5 + 1.2 -+- 4-4
NH4N mg/lOOg
4.3_+1-8 3.1 _+ 2.5 10-4 _+ 3.1 8.6 _ 3.7 5.3 __+2.5 22.0_+16.4
Na
9.5_+3-6 1.7 __+0-4 19.8 _+ 1.5 3.1 _+ 0.4 2-8 _+ 2.5 2-0_+1.4
K
Results are shown as mean figures along with the confidence limits at the 95 ~ level. Exchangeable cations were determined by leaching 10 g oven-dried soil with 100 ml of ~).1 N ammonium acetate. The resulting solution was analysed by atomic absorption spectrophotometry. Mineralised nitrogen was determined by the technique of Eagle (1961). Organic carbon was determined by the method of Walkley & Black (1934). Calcium carbonate was determined in a calcimeter.
Bed 1 0-2cm 9-11 cm Bed 2 0-2cm 9-11 cm Bed 5 0-2cm 9-11 cm
Bed 5
Bed 2
Bedl
pH
TABLE 4 CHEMICAL ANALYSIS OF THE WASTE SOILS
-t
O
144
J.A. LEE, BARBARA GREENWOOD
The nitrogen mineralisation shows a number of interesting features, and is correlated with the organic carbon content of the soils, being much higher in the surface than in the sub-surface samples of the older wastes. Samples from the older wastes (1938) show over twice the total mineralised nitrogen in the recovered limewaste as compared with distiller waste. The form in which nitrogen became available is strikingly different: in the recovered lime waste samples ammonium is the predominant form of nitrogen, whereas nitrate accumulates in the distiller waste samples. Further support for this distinction is provided by the surface samples of Bed 5 in which ammonium accumulates in greater quantities than nitrate. On both ~ecovered lime waste sample areas Festuca rubra is the most abundant species; however, at the distiller waste site it is present with very low total cover. It is possible that the difference between the wastes results from inhibition of nitrification by Festuca rubra. If this is so it represents a very important way in which Festuca rubra could affect the subsequent establishment of other species. The soil samples all have high calcium carbonate contents and are alkaline. The alkalinity may be an important factor in restricting early colonisation. The subsurface samples of Bed 5 have very high pHs. The sub-surface samples from recovered lime waste have calcium carbonate contents similar tO those in the original waste, indicating little alteration of the parent material except near the surface. The distiller waste samples have higher calcium carbonate contents than might be expected from a knowledge of the chemical composition of the waste (Table 1). This presumably results principally from the conversion of calcium oxide to calcium carbonate with a concomitant lowering of the alkalinity and also from some contamination of the distiller waste with recovered lime waste. There is no clear evidence that the difference in calcium carbonate content is an important factor affecting the distribution of plants. Of the more calcicolous species only Erigeron acer is more or less restricted to recovered lime waste. It is doubtful whether the unaltered wastes show a significant cation exchange capacity. The development of an appreciable exchange capacity is probably the result of the build-up o f organic matter within the soil. Thus the base exchange capacity as measured by the sum of the exchangeable calcium, magnesium, sodium and potassium contents is higher in the surface than the sub-surface samples of the older wastes. The exchangeable base content as determined by 0-1 N ammonium acetate leaching probably includes additional important components due to the concentration of ions in the soil solution and to the solubility of calcium carbonate in ammonium acetate solutions. 0.1 N ammonium acetate was preferred to 1 N in order to minimise the solution effect. 1 N solutions extracted approximately double the calcium content but even if these figures are taken, the exchangeable calcium content of both wastes is low compared with those observed by other workers in natural British calcareous soils (see e.g. Fearn, 1973). However, as the waste soils develop there will be a considerable increase in the organic matter content and
PLANTS O F INDUSTRIAL C A L C A R E O U S WASTES
145
therefore in cation exchange sites. Concomitantly there will be an increase in microbial respiration raising the partial pressure of carbon dioxide within the soil. This should lead to a considerable increase in the exchangeable calcium content of the surface soils. The sub-surface sample of Bed 5 has the highest exchangeable sodium content and this represents continued contamination with brine. This is further borne out by the very local occurrence of Puccinellia distans and Spergularia marina on this bed. With the exception of the sodium contents it is difficult to relate the different associations to any of the chemical features measured. However, it must be remembered that the chemical differences are probably more marked in the younger wastes. Freshly deposited distiller waste has a more alkaline reaction than recovered lime waste resulting from a higher calcium hydroxide concentration in solution. It is tempting to conclude that whereas physical features are particularly important in the initial colonisation of recovered lime-waste chemical factors (perhaps hydroxyl ion concentration) provide the major limitation on distiller waste. These differences in the little-altered wastes may be partly responsible for the different association observable today.
Nutrient factors limiting colonisation The differences in mineralised nitrogen and the poor growth of some species in certain areas of the beds suggest the possible importance of macronutrient availability in limiting growth after initial establishment. The effects of fertilizer addition on the growth of species was therefore investigated. Three sites on different beds were chosen in close proximity to the areas from which the soil samples had been taken. A randomised block design was used to study the response of indigenous species to nitrogen, phosphorus and potassium addition alone and in all combinations. The experimental treatment plots were 1 m 2 and the blocks were replicated 4 times on each bed. Two applications of fertilizers were made. The first was in October 1970, and the second in March 1971. Nitrogen was added as sodium nitrate at 5 g N / m z at each addition. Phosphorus was added as calcium tetrahydrogen orthophosphate at 5 g P/m 2. Potassium was added as potassium carbonate at 1 0 g K / m 2. Between the first and second additions there was a noticeable growth response by the bryophytes. This response on both wastes was to phosphorus addition alone. The angiosperm cover was recorded during August 1971, as the number of hits on ten vertical pins distributed at random in each plot. The results for the two beds last tipped on in 1938 are shown in Table 5. The recovered lime waste plots showed a significant response to phosphorus alone and support the view that phosphorus is the primary element limiting growth. Phosphorus addition caused nitrogen to become limiting. The large increase in cover in the phosphorus plots was due mainly to the increase in grass cover. A similar but less well marked response was shown on
20-5 10.8 28.3 1-5
Angiosperm cover Gramineae cover
Angiosperm cover Gramineae cover
N
31-8 3-0
62.5 36.8
P
24-5 3-0
20-5 12-0
K
For details see text.
Above ground biomass g/m 2
15
N
23-0 2-8
61.3 10-0
TABLE 6
18.3 9.5
NK
149.0 127.8
NP
41.0 6.3
63.0 41.8
Treatments PK
68.0 17.0
188.0 163.5
NPK
133
P 11
K
156
NP
31
NK
118
Treatments PK
170
NPK
THE RESPONSE OF VEGETATION ON BED 5 T O FERTILIZER ADDITION
Cover was measured as the number of hits on 10 pins per plot. For details see text.
Bed 1 Total Total Bed 2 Total Total
TABLE 5 THE RESPONSE OF LIME WASTE VEGETATION TO FERTILIZER A D D I T I O N
19
Control
23.8 1.8
17.8 9.5
C
52
LSD 5 %
19-4 8.0
43.9 44.7
LSD 5 %
m
t"
7.
PLANTS OF INDUSTRIAL CALCAREOUS WASTES
147
the distiller waste. On this waste only the combined nitrogen and phosphorus treatments showed a significant growth response and this is consistent with the nitrogen mineralisation results. However, there was some response to phosphorus and phosphorus plus potassium treatments. There was little response to nitrogen or potassium treatments alone. The increase in total cover in combined nitrogen and phosphorus treatments was less marked on distiller waste than on recovered limewaste. This may have been the result of the sparse grass cover at the distiller waste site but there remains the possibility that factors other than the availability of phosphorus and nitrogen were limiting growth. However, in laboratory experiments using both wastes the primary growth response in Chamaenerion angustifolium, Erigeron acer, Festuca arundinacea and Festuca rubra was to phosphorus. The magnitude of the response for all four species was similar on both wastes. The £ertilizer experiment on Bed 5 was harvested in July 1973, prior to the destruction of the site by tipping. The vegetation of each plot was cut at approximately 1 cm above the ground, and sorted in the laboratory before drying at 100 °. The yield is shown in Table 6. Here again a pronounced effect of phosphorus addition alone was observed in spite of the very low rate of nitrogen mineralisation in the untreated waste. The addition of phosphorus could have had a marked effect on the activities of the soil micro-organisms involved in nitrogen mineralisation, thereby increasing the nitrogen supply. In the three growing seasons after fertilizer addition a nearly closed sward was produced as a result of the response by the indigenous grasses Agrostis stolonifera, Festuea arundinacea and Festuca rubra. This was accompanied by the break-up of the surface lime waste crust. The vegetation of some calcareous wastes, however, does not respond to fertilizer addition with a marked increase in growth. A number of nutrient addition experiments have been carried out on the sparsely colonised beds at Plumley. The vegetation here has shown only avery small response to phosphorus (which does not remove the infertility) and no response to nitrogen at application rates similar to those applied at Witton. The addition of micro-elements in mixtures or singly to phosphorus treatments had little effect. Ferric citrate sprayed on to the foliage removed chlorosis which is visible, notably on Hyperieum perforatum, early in the summer. However, iron addition to the soil or to the foliage did not result in a marked growth response. Toxicity factors in the waste are presumably largely responsible for the infertility. Of these the calcium hydroxide concentration in the soil solution would appear the most likely. A free calcium hydroxide content of 14 at 15 cm and 30 ~ at 30 cm was recorded by ICI chemists in 1965. The reclamation of similar lime waste sites with a high unreacted lime content is probably best achieved by organic mulching plus phosphorus fertilizer addition. THE M A N A G E M E N T O F LIME BED V E G E T A T I O N
While inevitably the large orchid populations have attracted interest in the lime bed
148
.I.A. LEE, BARBARA GREENWOOD
vegetation in Cheshire, there are other reasons why these areas should be considered important. First, they represent the only extensive calcareous habitats in Cheshire, a county of intensive agriculture and industrial areas with few marginal sites. Secondly, they support sizeable populations of a number of species and hybrids with restricted distributions in North West England. Thirdly, they provide a good opportunity for the study of primary succession on unique parent materials which could produce valuable information for the professional ecologist. Fourthly, they are useful as sites for teaching ecology and taxonomy for both schools and universities. The most important lime waste site is the Witton lime beds, which until recently have been little disturbed since the cessation of pumping. The renewed tipping of chemical waste and domestic refuse in 1970 has not so far obliterated much of ecological interest except the initial stages of colonisation onrecovered limewaste. Although tipping will continue, it is hoped that this will be confined to Beds 4, 5 and the western part of Bed 1, leaving an area of approximately 15 ha undisturbed. This area is the most interesting ecologically, containing all the groups recognised by information analysis. However, if this area is to maintain its floristic diversity it is important that some form of management is introduced in the next few years. This is conditioned by two factors--the rapid encroachment of herbaceous communities by scrub and the spread of coarse grasses, notably Festuca arundinacea and Dactylis glomerata. The scrub is best developed close under the lagoon walls at the northern end of Beds 2 and 3, but there is an interesting small area on the south eastern part of Bed 1 which includes Salix x subsericea. The area of the beds remaining undisturbed is sufficient to allow for the succession through scrub to continue in the already dense area of scrub. The immediate management problem is the limitation of the scrub within the areas shown in Fig. 2. Many young Salix cinerea bushes must be removed from the southern half of Beds 2 and 3 and the northern half of Bed 1. This would allow woodland to develop on both recovered lime waste and distiller waste while ensuring large areas for grass and herb communities. The spread of Festuca arundinacea and Dactylis glomerata is not a significant problem at the present over much of the remaining beds themselves, but the luxuriant growth of these species and Festuca rubra on the walls of the lagoon already considerably reduces the species diversity in many areas and threatens to oust species such as Anacamptispyramidalis and Anthyllis vulneraria. Two factors might increase the growth of the tussockforming grasses on the beds themselves. The first is flash fires which have occurred locally on Bed 1 in areas where these grasses are well established. The second is the eutrophication which could result from large seagull flocks resting on the beds. While fires need not result from domestic waste tipping large seagull flocks inevitably will. It would therefore seem preferable to limit refuse tipping and use the beds for chemical waste only. It must be emphasized that the spread of Festuca arundinacea and Dactylis glomerata on the beds is probably part of succession as a result of nutrient build-up within the developing soils, but every effort must be made not to accelerate it artificially.
PLANTS OF INDUSTRIALCALCAREOUSWASTES
149
The large growth response o f indigenous grasses to p h o s p h o r u s fertilizer on recovered lime waste points to the possibility o f producing a rapid vegetation cover on lime beds by fertilizer addition alone. This is o f no immediate application as far as W i t t o n is concerned, but it is a potentially important finding because there are a n u m b e r o f lime beds still in use. The largest o f these are the beds on Ashton's and N e u m m a n ' s flashes adjoining the W i t t o n beds, a m o u n t i n g to approximately 70 ha. There would seem to be little need for tipping followed by top soil addition for the reclamation o f these and other beds. Some m a n a g e m e n t o f lime bed vegetation has been carried out at Plumley by the Cheshire Conservation Trust. This has consisted o f the removal o f birch scrub in an attempt, in part, to encourage the orchid populations. In six years this has had very little effect on the orchids or other herbaceous species. While this management scheme is eminently a sensible one, its aims are unlikely to be realised in the short term. This is because the edaphic factors which result in the very slow and restricted colonisation will also limit the rate at which changes occur as a result o f management practice. The reclamation o f similar wastes with a high unreacted lime content c a n n o t readily be achieved by fertilizer addition alone and requires further investigation. ACKNOWLEDGEMENTS The authors are indebted to Imperial Chemical Industries Ltd for permission to work on Witton lime beds and to the Cheshire Conservation Trust for permission to work at Plumley. Imperial Chemical Industries also kindly supplied information on p u m p i n g and on the chemical composition o f the wastes. The authors are also indebted to D r J. H. Tallis for his helpful criticism o f the manuscript. The skilled assistance o f Mrs Helen Vickers is gratefully acknowledged and Barbara G r e e n w o o d is indebted to the N a t u r a l Environment Research Council for financial support. REFERENCES CLAPHAM,A. R., TUTIN,T. G. & WARBURG,E. F. (1968). Excursion Flora of the British Isles, 2nd edn. London, Cambridge University Press. EAGLE,O. J. (1961). Determination of nitrogen status of soils in the West Midlands. J. Sci. Food Agric., 12, 712-7. FEARN,G. M. (1973). Biological flora of the British Isles. Hippocrepis comosa L. J. Ecol., 61,915-26. GREEN,B. H. (1972). The relevance of seral eutrophication and plant competition to the management of successional communities. Biol. Conserv., 4, 378-84. LEE, J. A. (1975). The conservation of British inland salt marshes. Biol. Conserv., 8, 143-51. LLOYD,P. S. (1972). The grassland vegetation of the Sheffieldregion. I I. Classification of grassland types. J. Ecol., 60, 739-76. NEWTON,A. (1971). Flora of Cheshire. Chester, Cheshire Community Council. WALKLEY,A. ,~" BLACK,I. A. (1934). An examination of the Degtjareff method for determining soil organic matter and a proposed modification of the chromic acid titration method. Soil Sci., 37, 29-38. W1LKOIq-MICHALSKA,J. & SOKOL, M. (1968). Flora of the lime spoil mounds of Inouwroclaw and Janikowo Soda Factory. Zesz. nauk. Uniw. Mikolaja Kopernika Torun. Nauki MatematycznoPrzyrodnicze, 21, Biologia, XI, 173-208.