Thesis (MScAgric (Soil Science))--University of Stellenbosch, 2005. / The purpose of this study was to investigate and identify the occurrence of specific
soil properties that may be important for vegetation functioning and the possible
effect of the loss of or changes in these properties on rehabilitation success on the
sandy coastal plains of the West Coast, South Africa. The study area covered
approximately 9 400 ha on the Namaqualand coast in the vicinity of Brand-se-Baai
(31º18'S 17º54'E), approximately 350 km north of Cape Town and 70 km north-west
of the nearest town, Lutzville.
A soil survey was done to reveal the presence of important pedological features. The
20 soil profiles surveyed are situated within six vegetation communities. Pedological
features such as surface water repellency, permeable apedal subsurface horizons,
subsurface impediments such as cemented (calcrete or dorbank) hardpans and
significantly more clayey (cutanic, luvic) horizons were identified.
A comparative study between rehabilitated and natural soils indicates that mining
operations result in the formation of saline sand tailings, stripped of a large portion of
the clay and organic matter fraction. The natural leaching of solutes, over a period of
25 months, is sufficient to lower salinity of the tailings to levels comparable to natural
soils. This leaching can also results in lowering of soil fertility. Removal of the
dorbank and the dense neocutanic horizon in the western side of the mine, loss of
topographical features such as small dune systems and heuweltjies, destruction of
natural soil profile morphology and the lowering of organic carbon and clay plus silt
fraction can have detrimental effects on attempts at rehabilitation of this area to a
natural condition similar to that which preceded the mining operation.
Infiltration fingering and deep percolation results in the development of an aquifer
below the reach of shallow-rooted desert shrubs. A method of water acquisition by
vegetation through water distillation is investigated as a possible solution to the
apparent discontinuum between the shallow root systems and deeper-lying aquifer.
Volumetric water content measurements indicated that precipitation of 29.5 mm, over
a period of 10 days, did not result in any variation at 235 mm, 360 mm and 900 mm depths. An average volumetric water content increase of 0.4 mm per night was
measured in the first 23.5 cm of soil surface. This amount is a significant source of
water that can explain the shallow root distribution. Water vapour movement due to
temperature gradients can explain the diurnal volumetric water content fluctuations
observed. Further studies are necessary to determine to what extent the depth of water
infiltration influences the capacity of subsurface dew to provide plants with a
nocturnal water source.
Findings of this study can be summarised into two concepts namely:
• Heuweltjies, small dune systems, and variation in depth of cemented hardpans
are the main features that contribute to pedosphere variation and possibly to
biodiversity.
• Pedogenic features such as topsoil hydrophobicity, and cemented dorbank and
dense more clayey (cutanic, luvic) subsurface horizons are important
components of a soil water distillation process that could be a driving force
behind vegetation functioning in this region.
Mine activities result in the loss of certain pedogenic features and soil properties that
that could be key ingredients to ecosystem functioning. The inability to recognise
their significance and ignorance thereof when planning rehabilitation methods might
prevent sustainable restoration of the environment.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/1918 |
| Date | 03 1900 |
| Creators | Prinsloo, H. P. |
| Contributors | Fey, M. V., Ellis, F., University of Stellenbosch. Faculty of Agrisciences. Dept. of Soil Science. |
| Publisher | Stellenbosch : University of Stellenbosch |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Rights | University of Stellenbosch |
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