Geoscience Reference
In-Depth Information
Aside scheme. A very different restoration scheme was adopted at Martin's Farm, St
Osyth, by Essex County Council, again on an experimental basis. The aim here was to
create a country park over a 24 ha landfill site with picnic areas, wildflower meadows
with butterflies, and patches of woodland. In this instance, the County Council had
taken over an already worked-out gravel pit and filled it in gradually with domestic
waste over an 18 year period up till 1983. There was no stockpile of soil from the
original excavation, so the final covering consisted of lorry loads of sandy clay sub-
soil, available free from various local sources, and spread over the compacted fill to a
depth of about 0.6 metres. This is much less than the 1.2 metres of soil cover used at
Bush Farm and elsewhere, but to have bought in soil would have been very expens-
ive.
Although it might seem that the requirements for establishing native vegetation
were much less demanding than those for arable crops, the scheme posed some inter-
esting problems because of the poor soil properties and the constraints on remedial
measures. It is true that, left to itself, such a site gradually becomes clothed with quite
a variety of self-sown grasses and wildflowers; over 120 such species were recorded
in the first four years after completing the soil cover. However, most of these were
annual plants dependent on bare ground. Without periodic disturbance, creeping bent
grass
Agrostis stolonifera
would soon dominate the area and render it very dull florist-
ically. To create a meadow-like assemblage, it was necessary to cultivate the ground
and sow it with a suitable selection of perennial grasses and wildflowers. It was then
that the low soil fertility and unfavourable physical conditions made themselves ap-
parent.
The poor soil structure and low organic matter content of the soil cover resulted
in low water-holding capacity so plants suffered from drought in the summer. Dry
conditions may have been exacerbated by heat produced through the decomposition
of the refuse, as mentioned earlier, though methane did not appear to be a serious
problem. Winter rainfall created the reverse situation because water could not drain
through the compacted refuse, and there were no field drains as there were at Bush
Farm. The soil therefore quickly became waterlogged, discouraging deeper rooting
by plants, and thus limiting their ability to survive dry conditions. It was a classical
'chicken-and-egg' situation in which poor soil conditions inhibited plant growth
while slow vegetation development limited the rate of soil improvement. This situ-
ation extended also to earthworms. Their rate of colonization depended on vegetation
cover and was limited in the early years mainly to surface-living species such as the
green worm
Allolo-bophora chlorotica
and
Lumbricus castaneus.
The deeper burrow-
ing
Lumbricus terrestris
and
Aporrectodea longa
reproduce more slowly (
chapter 5
),
and colonization was probably limited by the anaerobic conditions in the refuse.
