A 13‐year record of erosion on badland sites in the Karoo, South Africa

Boardman, John; Favis‐Mortlock, David; Foster, Ian D L

doi:10.1002/esp.3775

Cited by 63 publications

(39 citation statements)

References 45 publications

(71 reference statements)

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“…Land degradation and badland areas were mapped using air photography from 1945,1959,1966,1980,2002 and latterly using Google Earth images from 2010 (Keay-Bright and Boardman, 2006;Boardman et al, 2015). Remotely-sensed images and field mapping were used to delineate formerly cultivated land and identify the locations and state of small farm dams (Boardman and Foster, 2011).…”

Section: Methodsmentioning

confidence: 99%

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Long-term studies of land degradation in the Sneeuberg uplands, eastern Karoo, South Africa: A synthesis

et al. 2017

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For the past 15 yr, the Sneeuberg uplands in the eastern Karoo, South Africa, have been a focus for research on land degradation by the above authors and other colleagues. Earlier work in the Karoo emphasised vegetation change whereas we concentrate on physical changes to the landscape at the small catchment scale, e.g., bare, degraded areas (badlands) and gully (donga) systems. Analysis of sedimentation in farm dams allows for reconstruction of environmental histories using 210 Pb, 137 Cs, geochemical and mineral magnetic properties of the sediments. Erosion rates on badlands are monitored using arrays of erosion pins. A C C E P T E D M A N U S C R I P T ACCEPTED MANUSCRIPT2 Sediment source tracing within small catchments points to the importance of hillslope sources and the relative erosional inactivity of gully systems.Sediment supply from hillslope and colluvial sources is maintained by high rates of weathering on mudstones and sandstones. Current degradation should be viewed in the context of a c. 200 yr history of overgrazing by European-style stock farming and limited areas of former cultivation in the valleys. Grazing pressures are now much reduced but the loss of soils and vegetation suggests that landscape recovery will require several decades.Additional drivers of past degradation are likely to have been periods of drought and fire (natural and managed) and a gradual increase in both rainfall intensity and the frequency of extreme rainfall events. The future of the degraded Sneeuberg landscape will depend on future farming practices. Desirable options include more sustainable livestock practices, adoption of wildlife farming and other more benign regimes involving mixes of agriculture, tourism, and wildlife protection together with landscape rehabilitation measures.

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Section: Methodsmentioning

confidence: 99%

“…4). This approach is discussed in Boardman and Favis-Mortlock (2016) and results have been presented in Keay-Bright and Boardman (2009) and Boardman et al (2015). Table 2 updates these results to 2016.…”

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confidence: 99%

Long-term studies of land degradation in the Sneeuberg uplands, eastern Karoo, South Africa: A synthesis

et al. 2017

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“…We have collected soil and sediment samples from contributing catchments and used a combination of particle size corrected geochemical, mineral magnetic, radionuclide and colour properties to determine the most likely or dominant contemporary sediment sources and to detect any changes in sediment sources through time (see Foster et al, 2012;Pulley and Rowntree, 2016). We have also measured erosion rates on badlands using long term erosion pin surveys (see Boardman et al, 2015).…”

Section: Study Area Materials and Methodsmentioning

confidence: 99%

“…South Africa, and especially the Eastern Cape, has witnessed high rates of erosion and extensive land degradation that appear in significant part to be associated with the arrival of European settlers from the early 19th Century onwards (Hoffmann and Ashwell, 2001;Boardman et al, 2015), yet few recent systematic studies have attempted to measure rates of erosion or fluvial sediment transport across the country. The most recent compilation of sediment transport data for Africa was published by Vanmaercke et al (2014), including an accessible on-line database comprising sediment yield data from reservoir surveys and river monitoring.…”

Section: Introductionmentioning

confidence: 99%

The potential for gamma-emitting radionuclides to contribute to an understanding of erosion processes in South Africa

et al. 2017

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Abstract. Several research projects undertaken by the authors and others over the last 14 years have used fallout and geogenic radionuclides for understanding erosion processes and sediment yield dynamics in South Africa over the last 100-200 years as European settlers colonised the interior plains and plateaux of the country and imported new livestock and farming techniques to the region. These projects have used two fallout radionuclides ( 210 Pb and 137 Cs) to date sediments accumulating in reservoirs, farm dams, wetlands, alluvial fans and floodouts and have used other fallout nuclides ( 7 Be) and long-lived geogenic radionuclides (e.g. 40 K, 235 U) as part of a composite fingerprint exploring contemporary sediment sources and changes to sources through time. While successful in many parts of the world, applying these techniques in Southern Africa has posed a number of challenges often not encountered elsewhere. Here we explore some of the benefits and challenges in using gamma-emitting radionuclides, especially 137 Cs, in these landscapes. Benefits include the potential for discriminating gully sidewall from topsoil sources, which has helped to identify contemporary gully systems as sediment conduits, rather than sources, and for providing a time-synchronous marker horizon in a range of sedimentary environments that has helped to develop robust chronologies. Challenges include the spatial variability in soil cover on steep rocky hillslopes, which is likely to challenge assumptions about the uniformity of initial fallout nuclide distribution, the paucity of stable (non-eroding) sites in order to estimate atmospheric fallout inventories, and the limited success of 210 Pb dating in some rapidly accumulating high altitude catchments where sediments often comprise significant amounts of sand and gravel. Despite these challenges we present evidence suggesting that the use of gamma-emitting radionuclides can make a significant contribution to our understanding of erosion processes and sediment yield dynamics. Future research highlighted in the conclusion will try to address current challenges and outline new projects established to address them more fully.

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“…Thus from one statistical perspective, these ten sites are replicates. Nevertheless, there are obvious inter‐site differences in erosion rate, which are greater than the errors associated with pin measurement (see Table in Boardman et al ., ). But between‐site variation in erosion, accumulation and net erosion (i.e.…”

Section: Introductionmentioning

confidence: 97%

‘Local gradient’ and between‐site variability of erosion rate on badlands in the Karoo, South Africa

Favis‐Mortlock

Boardman

Foster

et al. 2017

Earth Surf Processes Landf

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Site‐average values of local gradient, defined as the steepest slope angle measured at a point, are a powerful predictor of long‐term rates of soil loss as measured by erosion pins on the non‐channel floor portions of ten badland study sites in the Karoo area of South Africa. Local gradient may be easily measured using a smartphone clinometer. The successful use of local gradient here is in strong contrast to the previous failure of other site‐specific attributes, including other measures of gradient and relief, to explain between‐site variation in erosion rate on these study sites. Each measurement of local gradient may be thought of as a sample of the site's microtopography. Microrelief is a strong determinant of the emergent patterns of inter‐channel overland flow, and hence of the patterns of inter‐channel erosion by flow. Local gradient changes most rapidly during the initial stages of channel incision. When channels are established, local gradient changes more slowly leading to almost‐parallel retreat of channel sidewalls. A sensitivity analysis suggests that measurements of local gradient are not all equal with regard to prediction of long‐term erosion rate. A greater share of predictive power is contributed by measurements made on very steep or vertical channel side wall areas, and a lesser share is contributed by measurements made on interfluves. Copyright © 2017 John Wiley & Sons, Ltd.

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A 13‐year record of erosion on badland sites in the Karoo, South Africa

Cited by 63 publications

References 45 publications

Long-term studies of land degradation in the Sneeuberg uplands, eastern Karoo, South Africa: A synthesis

Long-term studies of land degradation in the Sneeuberg uplands, eastern Karoo, South Africa: A synthesis

The potential for gamma-emitting radionuclides to contribute to an understanding of erosion processes in South Africa

‘Local gradient’ and between‐site variability of erosion rate on badlands in the Karoo, South Africa

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