Soil material exported from river catchments by soil erosion is a key issue in environmental
sustainability. Although soil erosion processes have been thoroughly investigated, their
dynamics, specifically the continuity of erosion processes and sediment source locality, are
less studied. The aim of this investigation was to evaluate the changes in the fluxes and
characteristics of sediments during their downslope and downstream transport. The study was
conducted in a 1000 ha catchment of the Drakensberg foothills, South Africa. Sediment fluxes
were monitored at nested scales during the 2009-2011 rainy seasons using 1×1m and 2×5 m
erosion plots and H-flumes coupled to automatic samplers from 23 ha, 100 ha catchments. In
addition, soil texture, colour and total organic carbon and nitrogen contents in sediments
exported from the nested scales and a 1000 ha catchment were compared to in-situ surface
and sub-surface soil horizons in a 23 ha catchment river bank and hillslope soils and fluvial
sediments. There was a sharp increase of sediment fluxes with increasing slope length
(846±201 gm-1y-1 for 1 m2 vs 6820±1714 gm-1y-1 for 10 m2), revealing a limited contribution
of splash erosion compared to rain-impacted flow erosion. Sediment fluxes decreased to
500±100 gm-1y-1 and 100±10 gm-1y-1 at the 23 ha and 100 ha catchments respectively,
indicating the occurrence of sedimentation during sediment downslope and downstream
transport. A principal component analysis (PCA) suggested that rain impacted flow erosion
efficiency at the 10 m2 scale was significantly correlated with soil bulk density, clay content
and antecedent rainfall (P<0.05). Moreover, strong correlations existed between runoff,
sediment concentration and soil loss and selected soil surface and environmental variables at
the plot scales. Correlations became weaker at the catchment scales due to increasing
landscape heterogeneity and the complexity of soil erosion dynamics. An additional PCA
suggested that stream bank erosion contributed to 63% of the soil loss from the 23 ha
catchment. During their downstream transport, sediments were discriminated by the second
PCA axis, which correlated with the clay and fine silt content, 100 ha sediments showed
negative coordinates to this axis while 1000 ha catchment sediment had positive coordinates. / Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2011.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:ukzn/oai:http://researchspace.ukzn.ac.za:10413/9420 |
| Date | January 2011 |
| Creators | Oakes, Ernest Gene Martin. |
| Contributors | Chaplot, Vincent A. M., Lorentz, Simon A., Titshall, Louis William. |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | English |
| Type | Thesis |
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