Effects of gaseous emissions from the Namakwa Sands Mineral Separation Plant near Lutzville on the adjacent succulent Karoo vegetation : a pilot study
Date
2006-03
Authors
Lukama, Beatice M. K.
Journal Title
Journal ISSN
Volume Title
Publisher
Stellenbosch : University of Stellenbosch
Abstract
A pilot study was conducted at the Namakwa Sands Mineral Separation Plant, to investigate the
effects of acidic gaseous emissions from the Mineral Separation Plant on the adjacent Succulent Karoo
vegetation. Sulphuric acid fumes, a major gaseous emission of the mineral processing, was the subject
of investigation of the present study, due to the potential high negative impact of elevated
concentrations thereof on vegetation in the ecosystem.
Permanent sample plots along three transects radiating from the Mineral Separation Plant were laid out
in the eastern, south-eastern and southern directions following the prevailing wind directions and
practical consideration of land accessibility.
The ecological components assessed as indicators of possible pollution levels in the environment
included percentage plant mortality, foliar sulphur content of selected plant species, chemical
composition of solubles in mist and dust samples, and soil pH. In addition, the vegetation was
screened for plant species suitable to be used as potential bioindicators.
Potential bioindicator plant species were selected on the basis of their relatively wide distribution in
the study area and apparent sensitivity to the ambient air pollutants. The percentage of dead plants of
each species that occurred on the sample plots was used as a criterion of the possible sensitivity of the
plant species towards air pollution. The bioindicator plant species selected for potential monitoring
purposes were: Galenia fruticosa, Lampranthus suavissimus, Lycium ferocissimum and a Ruschia sp.
(SP 9). Plant mortality was greater nearer the emission source, with 28 + 5 % dead plants at 400 m, 19
+ 6 % at 800 m and only 10 + 4 % at 1,200 m from the Mineral Separation Plant. Data summed for all
species recorded and pooled for all three transects per sampling distance.
With the methods used in this study, in the case of all sample plots on the three transects, no
significant difference was found between the mean pH values of soil samples collected from open
spaces without plant cover (8.01 + 0.46) and those collected underneath shrubs (8.91 + 0.96).
Subsequently only the pH values of soil samples collected on open spaces were used to investigate the
variation in soil acidity with distance and direction from the emission source. The means represent
total number of samples from open space versus those collected from underneath shrubs. The pH of soil samples increased with distance from the emission source along the transects to the
south and south-east of the emission source. Eastward of the emission source, soil pH values remained
relatively low at all sample distances. This pilot study could not determine whether the continuous
acidity of the soil along the eastern transect in the direction of the prevailing wind, was caused by
increased deposition of gaseous emissions on the higher lying hilly terrain in this area, or by the
underlying geology.
Ion chromatographic analysis of mist and dust samples collected on each sample plot indicated the
presence of several chemicals that had probably originated from the gaseous emissions from the
Mineral Separation Plant as well as wind blown constituents from the adjacent surroundings of the
sample plots. Of these chemicals, only the sulphate concentrations of the mist and dust samples were
further evaluated, since that could be related to the emission of sulphuric acid fumes by the Mineral
Separation Plant. Results indicated that the mean sulphate concentration of mist and dust samples
collected from sample plots relatively close to the Mineral Separation Plant, 118.8 + 31.6 mg/litre (400
m), were higher than further afield, decreasing to 57 + 30.1 mg/litre at 800 m and 43.1 + 19.6 mg/litre
at 1,200 m. These values, representing the mean sulphate concentrations of mist and dust samples at
each sampling distance (data of the three transects pooled), differ significantly at the 85 % confidence
level.
Statistical evaluation of the data of the mist and dust pH measurements, pooled for the three transects
on the basis of distance, indicated a gradual increase of the mean values from 400 m (7.3 + 0.26),
through 800 m (7.7 + 0.34), to 1,200 m (8.2 + 0.83), although these values were not significantly
different.
A decreasing trend in accordance with that in the case of the sulphate concentrations of mist and dust
samples with distance from the mineral processing plant, was also observed in the sulphur content of
the leaves of selected plant species, with mean sulphur content higher at 400 m sampling distance
(0.29 + 0.091 %) than at 800 m (0.264 + 0.086 %) and a further decline at 1,200 m (0.232 + 0.079 %),
data of the three transects pooled. However, these values were also not significantly different. Although not significantly so, the decreasing trend in the results of the sulphate concentration of mist
and dust samples, the sulphur content of plant leaf samples as well as plant mortality observed, and
increasing soil pH values with distance from the Mineral Separation Plant, suggest that the gaseous
emissions from the Mineral Separation Plant could probably have had a detrimental effect on the
adjacent Succulent Karoo vegetation. A more detailed study is necessary to confirm this trend. In
addition it is recommended that in order to clarify the soil pH measurements outcome along the
eastern transect that were contradicted by the results of the mist and dust pH measurements, a more
intensive survey over a greater distance (at least further than 1.2 km from the Mineral Separation
Plant), be conducted to quantify vegetation damage and acid deposition to the east of the emission
source.
Description
Thesis (MSc (Conservation Ecology and Entomology)--University of Stellenbosch, 2006.
Keywords
Dissertations -- Conservation ecology and entomology, Theses -- Conservation ecology and entomology, Namakwa Sands Mineral Separation Plant, Succulent plants -- Effect of acid deposition on -- South Africa -- Lutzville, Succulent plants -- Effect of gases on -- South Africa -- Lutzville, Mineral industries -- Environmental aspects -- South Africa -- Lutzville, Acid-forming emissions -- Environmental aspects -- South Africa -- Lutzville