neW urBan environmenTs, C.1860–1950^181thus appeared in the main river valleys around London, especially beside
the Colne between Uxbridge and Rickmansworth, the Lea from Ware to
Hackney and also around Darenth in Kent.^110 Other notable concentrations
developed elsewhere, especially in the east Midlands, along the valleys of
the Trent in Derbyshire and Nottinghamshire. These workings were further
expanded in the post-War years, and new ones added, so that by the end of
the twentieth century there were around 15,000 hectares of flooded gravel
pits in the United Kingdom, mostly in England.
The extraction of gravel unquestionably led to localized plant extinctions.
But the resulting pits were a boon for wildlife, especially as they were not
kept neat and tidy like urban reservoirs or the lakes in country house parks.
Not only were they soon fringed by areas of reedswamp, marginal vegetation
and willow scrub, but adjacent spoil heaps also provided a wide range of
additional habitats.^111 Flooded pits attracted, in particular, flocks of wintering
wildfowl, including pochard and tufted duck; today around 60 per cent of
breeding little ringed plovers and over a third of breeding great crested grebes
depend on flooded pits.^112 Indeed, the recovery in numbers of both species in
the course of the twentieth century is almost entirely due to their proliferation.
Flooded pits also provided conditions in which rare species of dragonfly, such
as the keeled skimmer (Orthetrum coerulensis), could flourish. The number
now used as reserves and even designated as SSSIs throughout England,
and especially lowland England, is astonishing. Among many noteworthy
examples is the Attenborough reserve near in Nottinghamshire, close to the
border with Derbyshire, created by gravel extraction from 1929 until 1967;
Felmersham Pits in Bedfordshire; and Old Slade in Buckinghamshire, which
‘although surrounded by human activity and despoiled countryside, supports
200 plants and 100 bird species (45 breed there)’.^113
Alongside gravel pits, reservoirs and rubbish dumps, the ‘edgelands’ were
also often the locations of coal-fired power stations, many of which were,
by the 1940s, using pulverized coal as their main fuel. The combustion of
this material produces a residue of ‘fly ash’ or pulverized fuel ash which is
principally composed of glassy spheres of alumnosilicates. This material is
now often used as an engineering fill, or as a component in concrete, but in
the past much was simply pumped into lagoons. Its extreme alkalinity and
salinity, and high levels of boron, ensured that it underwent only a slow
succession, resembling in some ways that which occurs on sand dunes or
infertile calcareous silts. Salt-tolerant wind-blown species, such as coltsfoot
(Tussilago farfara) or varieties of hawkweed, were gradually displaced by
legumes like ribbed melilot (Melilotus officinalis) and colourful perennials
like yellow-wort (Blackstonia perfoliata) and yellow rattle (Rhinanthus
minor), sometimes accompanied by southern marsh orchid (Dactylorhiza
majalis) or common spotted orchid (Dactylorhiza fuchsii), the process
culminating in the development of birch/willow woodland. Some fly ash
contains hollow spheres which float on the surface of the lagoon as ‘islands’
which are gradually colonized by reed, reed-mace and floating sweet grass.^114