Vegetation and Soil Characteristics of Abandoned Copper Mines
John Breen and Ann Lenihan
Introduction
Mining wastes often expose the
local environment to toxic levels of
metals such as copper.
Understanding the ecology of
mined sites can lead to an
approach to the "rehabilitation" of
mining wastes. In this project the
ecology of long abandoned mines is
being studied to see how nature
itself has coped with the problem.
Some plants are able to tolerate
levels of copper - and other metals
which are toxic to other species.
For example grass seed of
copper-tolerant varieties is
commercially available and used to
rehabilitate the waste or "tailings"
of modern mines.
Copper mines in Killarney
In the Killarney area there are a
number of small copper mines
which were mined for centuries but
are now abandoned for over 100
years. Similar mines of "historical"
interest occur in Berehaven in Co.
Cork and throughout the Burren.
The Killarney mines are located in
natural oak forest. Oak forests have
a great variety of plant species
("high species diversity"). As a long
time has elapsed since mining
activity the natural environment has
had time to colonize the mine
waste. Thus this site is a good
place to investigate the ecology of
copper mines.
The Project
This project began as a final year
undergraduate project by Anne
Lenihan. One of the study sites is
located on the Muckross Peninsula
in Killarney National Park. It is
small, about 50 metres across with
an old mine shaft (about 4 metres
square) in the centre. It is located
on limestone and surrounded by
oak forest. This means that mature
trees such as oak, Arbutus
(strawberry tree) and yew are
nearby. However the actual site
itself, which consists of limestone rubble with the typical signs of copper ore (green patches of copper salts on the rock), is mainly bare of vegetation. By "bare" we mean an almost complete absence of trees. There are some stunted
birch trees. However a very
interesting plant community, is
present. Species found include the
white flowered bladder campion,
the pink sea thrift and the very
thorny spiny rose. These species
are common by the sea. Inland they
only occur on old mine tips.
Investigations
The project was to relate the
distribution of plants to copper
levels on and near the mine. To do
this all the plants were identified in
0.5 meter square quadrats located
along transects (30 metre lengths of
rope) starting at the centre of the
mine and extendlng into the
"natural" oak forest nearby. A soil
sample was taken in each quadrat.
In the laboratory the conductivity,
organic matter and copper levels
were measured Conductivity is a
measure of the number of free ions
present in a material - the higher
the conductivity the more free ions.
The unit of conductivity is the
Siemens, S (in this case S x 10-4).
Organic matter was estimated by
burning a weighed sample in a
furnace at 400ºC for 8 hours and
noting the loss of weight (The
organic matter is burnt away at this
temperature). The copper levels
wee determined by making a
solution of soil in E.D.T.A. This substance (it is a "chelating agent") "mops" up the copper from the sample. This solution was then
analysed in an Atomic Absorption
Spectrophotometer to give the
copper levels in mg/litre (= parts
per million).
Some results
Examine the graph in Figure 1. The
left hand side of the graph
represents the centre of the mine
and the transect extended into the
nearby forest area. The histograms
show the number of plant species
on and off the mine. The number of
plant species is higher in the forest.
Only a small but consistent group of
species (the important ones are
named above) were found on the
mine itself.
A big surprise was the distribution
of copper. The highest copper level
was actually in the forest not on the
mine. Now look at the organic
matter and conductivity levels.
Notice that the highest organic
matter levels were in the forest but
that, in general, the higher values
for conductivity were located on the
mine.
Why, so, because?
We know from published work that
organic matter actually binds copper. The organic matter levels
are low on the mine itself and this
means that only plants which can
tolerate high copper levels survive
there. In the forest the organic
matter levels are high. This masks
the real levels of copper and the
plant species found are similar to
those found elsewhere in Killarney's
oakwoods.
Current research
Anne Lenihan is continuing this
research at postgraduate level
Questions being asked include: Is
copper the only element involved or
are other elements present also? Is
it possible to propagate the tolerant
species of plants so that they might
be used elsewhere?
Micropropagation, if successful,
would be a suitable form of
vegetative reproduction which
would "clone" these plants with their
desirable, copper-tolerant
characteristics. Can organic matter
(e.g. peat) be introducd to mine
wastes so as to bind the toxic
elements and allow "normal"
vegetation to grow on them?
Dr. John Breen is a lecturer in Biology at UL. His research interests include ecology and the environment.
Anne Lenihan is a research student in the Chemical and Life Sciences Department.
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Last updated 26th January 1996 by Stephen Childs