Uganda’s scientists plans to restore Queen Elizabeth
National Park through planting trees deemed to be resistant to mineral
pollutants with a view to maximise their potentials for phytoremediation.
Phytoremediation is the direct use of green plants and their
associated micro-organisms to stabilise or reduce contamination with organic
and inorganic pollutants in soils, sledges, sediments, surface water, or ground
water.
The Lead Researcher, Prof Hannington Oryem-Origa said tree species; Eucalyptus grandis and two legume species; Leucaena
glauca and Cassia siamea, are currently under confined trials in the copper
tailings dams in Kilembe and in the pyrite trail in Queen Elizabeth National
Park both in Kasese District, Western Uganda.
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| Eucalyptus trees under confined trials in Queen Elizabeth National Park. |
“These two areas have been contaminated by heavy
metals as a result of dumping of wastes generated from the mining of copper
from Kilembe Mines between 1956 and 1982. The estimated amount of pollutants
dumped in Kilembe area is about 15 million metric tonnes,” Prof Oryem-Origa
said.
Prof Oryem-Origa said conditions in the tailings dams
in Kilembe area and the pyrite trail in Queen Elizabeth National Park are
acidic and inhibit the growth of ordinary plants.
The pyrite materials originally consisted of metal
suphides which were oxidized resulting in the production of sulphuric acid. The
acidic pyrite was then spread into the Park area by storm water and at one time
covering a total area of about 150 hectares within Queen Elizabeth National
Park, threatening the survival of biodiversity.
Queen Elizabeth National Park covers 1978 square
kilometres, with its position providing a magnificent view of the rift valley
floor that occupies Lakes Edward and Gorge.
The Park is believed to have the highest
biodiversity ratings in country with over 500 different bird species and about
100 mammal species.
According to Uganda Wildlife Authority, Queen
Elizabeth National Park is the country’s third highest revenue earner after
Bwindi Impenetrable National Park and Murchison Falls National Park in Uganda.
Prof Oryem-Origa said their interest was to use trees of
economic value to people which could be periodically harvested and transported
away from the polluted habitats while gradually removing the pollutants.
In addition to growing fast, these tree species can
also send deep roots into the soil and extract heavy metals from the polluted
habitat as they grow because they exhibit some degree of tolerance or
resistance to acidity and drought.
“It is in the process of repeated tree harvesting that
the trees will be taking away heavy metals that include lead, cadmium, copper,
cobalt, nickel, manganese and iron among others from the polluted soil and
ultimately leading to its restoration to the original state,” Prof Oryem-Origa
said.
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| A section of pyrite trail in Queen Elizabeth National Park in Uganda |
Prof Oryem-Origa added that there will also be an
element of phytostabilisation of the polluted soils-a subset of
phytoremediation- where growing trees reduce heavy metal mobility by root
adsorption and precipitation resulting from growing the pollutant resistant
trees.
Prof Oryem-Origa said if the new technology succeeds,
then the planted tree in Queen Elizabeth conservation area will be cut down and
completely removed to permit the indigenous vegetation to regenerate in the
restored areas.
The scientists also expect to use the same technology
in restoring vegetation in other mineral polluted environments countrywide.
Though the new development is good news for the restoration
of the Park, Uganda Wildlife Authority believes that the selected tree species
may not be allowed in the park at the moment as they seem to be exotic.
“While the development is a good initiative, I am only
worried that the proposed plant species seem to all be exotic species and would
not be accepted inside the national park,” said Mr. Charles Tumwesigye, a
chief conservation manager at UWA.
Mr. Tumwesigye said the scientists need to identify
indigenous plant species that are resistant to mineral pollutants and they
would be happy to work with them.
In the early 2000s, scientists successfully applied
shallow rooted plant species like Spear Grass (Imperata cylindrica), Barmuda
Grass or Common Star Grass (Cynodon dactylon), Kodo Grass (Paspalum scrobiculatum),
Bulrush millet (Typha latifolia) and Copper ferns in the pyrite trail in Queen
Elizabeth National Park to restore the natural vegetation.
However, the tested shallow-rooted plants improved only
shallow depths of the soil in the pyrite trail.
It is on this basis that Uganda’s scientists have
embarked on new technology that could possibly help restore the polluted soil
permanently.
The project is being conducted by Makerere University
in collaboration with Sorderton University in Sweden.
