A tenfold increase in the Orange River mean Holocene mud flux: implications for soil erosion in South Africa

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dc.contributor.authorCompton, John S
dc.contributor.authorHerbert, Caren T
dc.contributor.authorHoffman, M Timm
dc.contributor.authorSchneider, Ralph R
dc.contributor.authorStuut, Jan-Berend
dc.date.accessioned2016-07-27T13:12:08Z
dc.date.available2016-07-27T13:12:08Z
dc.date.issued2010
dc.date.updated2016-07-12T16:44:55Z
dc.description.abstractSoil erosion poses a major threat to sustainable agriculture in southern Africa but is difficult to quantify. One measure of soil erosion is the sediment flux of rivers. The Orange River is the principal source of sediment to the western margin of South Africa with an estimated mean mud flux over the last 11 500 years (the Holocene epoch) of 5.1 (3.2–7.4) million metric tons/year (Mt/yr). A total of 43 gigatons (Gt; 1015 g) representing 72% of the Holocene mud flux has accumulated on the shelf in the Orange River prodelta and mudbelt, a clayey finesilt deposit focused on the inner to middle shelf. Only 8% (5 Gt) of the mud flux occurs in Holocene calcareous ooze on the slope. Comparison of the clay to mud ratio of offshore deposits with Orange River suspended sediment and catchment soils indicates that 20% (11 Gt) of the Holocene mud flux has been lost as clay beyond the margin. The Orange River mud flux prior to the building of large dams (1930–1969) is ten times greater than the mean Holocene mud flux and is reconciled with estimates of soil erosion within the catchment. A tenfold increase in the Orange River mud flux implies up to a hundredfold increase in total soil erosion depending on the extent of mud storage over periods of decades to centuries within the catchment. Erosion has shifted from areas of high relief and rainfall of the Drakensberg escarpment during the Holocene to intensely cultivated lands of low relief having moderate to high rainfall in the eastern catchment and to a lesser extent, grazing areas of the southern Orange River catchment.en_ZA
dc.identifierhttp://dx.doi.org/10.1177/0959683609348860
dc.identifier.apacitationCompton, J. S., Herbert, C. T., Hoffman, M. T., Schneider, R. R., & Stuut, J. (2010). A tenfold increase in the Orange River mean Holocene mud flux: implications for soil erosion in South Africa. <i>The Holocene</i>, http://hdl.handle.net/11427/20898en_ZA
dc.identifier.chicagocitationCompton, John S, Caren T Herbert, M Timm Hoffman, Ralph R Schneider, and Jan-Berend Stuut "A tenfold increase in the Orange River mean Holocene mud flux: implications for soil erosion in South Africa." <i>The Holocene</i> (2010) http://hdl.handle.net/11427/20898en_ZA
dc.identifier.citationCompton, J. S., Herbert, C. T., Hoffman, M. T., Schneider, R. R., & Stuut, J. B. (2010). A tenfold increase in the Orange River mean Holocene mud flux: implications for soil erosion in South Africa. The Holocene, 20(1), 115-122.en_ZA
dc.identifier.issn0959-6836en_ZA
dc.identifier.ris TY - Journal Article AU - Compton, John S AU - Herbert, Caren T AU - Hoffman, M Timm AU - Schneider, Ralph R AU - Stuut, Jan-Berend AB - Soil erosion poses a major threat to sustainable agriculture in southern Africa but is difficult to quantify. One measure of soil erosion is the sediment flux of rivers. The Orange River is the principal source of sediment to the western margin of South Africa with an estimated mean mud flux over the last 11 500 years (the Holocene epoch) of 5.1 (3.2–7.4) million metric tons/year (Mt/yr). A total of 43 gigatons (Gt; 1015 g) representing 72% of the Holocene mud flux has accumulated on the shelf in the Orange River prodelta and mudbelt, a clayey finesilt deposit focused on the inner to middle shelf. Only 8% (5 Gt) of the mud flux occurs in Holocene calcareous ooze on the slope. Comparison of the clay to mud ratio of offshore deposits with Orange River suspended sediment and catchment soils indicates that 20% (11 Gt) of the Holocene mud flux has been lost as clay beyond the margin. The Orange River mud flux prior to the building of large dams (1930–1969) is ten times greater than the mean Holocene mud flux and is reconciled with estimates of soil erosion within the catchment. A tenfold increase in the Orange River mud flux implies up to a hundredfold increase in total soil erosion depending on the extent of mud storage over periods of decades to centuries within the catchment. Erosion has shifted from areas of high relief and rainfall of the Drakensberg escarpment during the Holocene to intensely cultivated lands of low relief having moderate to high rainfall in the eastern catchment and to a lesser extent, grazing areas of the southern Orange River catchment. DA - 2010 DB - OpenUCT DP - University of Cape Town J1 - The Holocene LK - https://open.uct.ac.za PB - University of Cape Town PY - 2010 SM - 0959-6836 T1 - A tenfold increase in the Orange River mean Holocene mud flux: implications for soil erosion in South Africa TI - A tenfold increase in the Orange River mean Holocene mud flux: implications for soil erosion in South Africa UR - http://hdl.handle.net/11427/20898 ER - en_ZA
dc.identifier.urihttp://hdl.handle.net/11427/20898
dc.identifier.vancouvercitationCompton JS, Herbert CT, Hoffman MT, Schneider RR, Stuut J. A tenfold increase in the Orange River mean Holocene mud flux: implications for soil erosion in South Africa. The Holocene. 2010; http://hdl.handle.net/11427/20898.en_ZA
dc.languageengen_ZA
dc.publisherSAGE Publicationsen_ZA
dc.publisher.institutionUniversity of Cape Town
dc.sourceThe Holoceneen_ZA
dc.source.urihttps://uk.sagepub.com/en-gb/afr/journal/holocene
dc.subject.otherSoil, Erosion, Orange River, South Africa, Continental margin, Holocene
dc.titleA tenfold increase in the Orange River mean Holocene mud flux: implications for soil erosion in South Africaen_ZA
dc.typeJournal Articleen_ZA
uct.type.filetypeText
uct.type.filetypeImage
uct.type.publicationResearchen_ZA
uct.type.resourceArticleen_ZA
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