A reconstruction of historical changes in sediment sources, sediment transfer and sediment yield for a small, semi-arid Karoo catchment, South Africa

Kate M Rowntree, Ian D L Foster

Research output: Contribution to JournalArticle

Abstract

Land degradation is widespread in South Africa but few long-term data sets are available to help identify the timing of this degradation and its impact on catchment sediment yields. We report a case study reconstructing the erosion history of a small upland catchment in the Sneeuberg mountains of South Africa based on the dating of reservoir sediments using 210Pb and 137Cs. Sediment sources have been identified using mineral magnetic measurements. Additional information has been derived from the analysis of aerial photographs and satellite images and the measurement of badland erosion using erosion pins. Results suggest that sediment yields increased dramatically from < 30 t km-2 yr-1 in the early part of the 20th Century to ∼1600 t km-2 yr-1 in the 1970s, subsequently falling to ∼850 t km-2 yr-1 in the last decade. Contemporary erosion pin measurements suggest that badlands are still extremely active and help maintain current high yields. Analysis of aerial photographs and satellite images indicate that badlands and extensive gullies existed in the catchment before 1945. An analysis of mineral magnetic signatures suggested that badlands made some contribution to the reservoir sediment in the 1930s, but did not significantly increase sediment yields. Photographic evidence suggests that a major badland became connected to the main channel network (and to the reservoir) from the early 1960s onwards. This interpretation was confirmed by significant and sustained changes in the mineral magnetic signatures of the reservoir sediments. The results indicated that a delayed increase in sediment yield, despite extensive badland development much earlier, appears to have been caused by changes in catchment connectivity rather than being a direct response to contemporary changes in land degradation within the catchment. These results add additional complications to our understanding of the relationship between the response to, and recovery from, periods of overgrazing in the 1930s that probably initiated the badland development.
Original languageEnglish
JournalZeitschrift fur Geomorphologie, Supplementary Issues
Volume56
Issue numberSupp 1
DOIs
Publication statusPublished - 1 Jan 2012

Fingerprint

badlands
sediment yield
catchment
magnetic mineral
sediment
erosion
land degradation
aerial photograph
overgrazing
gully
Africa
connectivity
mountain
history

Keywords

  • sediment yield
  • badlands
  • connectivity
  • gamma spectrometry
  • mineral magnetic signatures
  • Karoo
  • South Africa

Cite this

@article{13a08c2027fa42b484461cb3bd62f87f,
title = "A reconstruction of historical changes in sediment sources, sediment transfer and sediment yield for a small, semi-arid Karoo catchment, South Africa",
abstract = "Land degradation is widespread in South Africa but few long-term data sets are available to help identify the timing of this degradation and its impact on catchment sediment yields. We report a case study reconstructing the erosion history of a small upland catchment in the Sneeuberg mountains of South Africa based on the dating of reservoir sediments using 210Pb and 137Cs. Sediment sources have been identified using mineral magnetic measurements. Additional information has been derived from the analysis of aerial photographs and satellite images and the measurement of badland erosion using erosion pins. Results suggest that sediment yields increased dramatically from < 30 t km-2 yr-1 in the early part of the 20th Century to ∼1600 t km-2 yr-1 in the 1970s, subsequently falling to ∼850 t km-2 yr-1 in the last decade. Contemporary erosion pin measurements suggest that badlands are still extremely active and help maintain current high yields. Analysis of aerial photographs and satellite images indicate that badlands and extensive gullies existed in the catchment before 1945. An analysis of mineral magnetic signatures suggested that badlands made some contribution to the reservoir sediment in the 1930s, but did not significantly increase sediment yields. Photographic evidence suggests that a major badland became connected to the main channel network (and to the reservoir) from the early 1960s onwards. This interpretation was confirmed by significant and sustained changes in the mineral magnetic signatures of the reservoir sediments. The results indicated that a delayed increase in sediment yield, despite extensive badland development much earlier, appears to have been caused by changes in catchment connectivity rather than being a direct response to contemporary changes in land degradation within the catchment. These results add additional complications to our understanding of the relationship between the response to, and recovery from, periods of overgrazing in the 1930s that probably initiated the badland development.",
keywords = "sediment yield, badlands, connectivity, gamma spectrometry, mineral magnetic signatures, Karoo, South Africa",
author = "Rowntree, {Kate M} and Foster, {Ian D L}",
year = "2012",
month = "1",
day = "1",
doi = "10.1127/0372-8854/2012/S-00074",
language = "English",
volume = "56",
journal = "Zeitschrift fur Geomorphologie, Supplementary Issues",
issn = "0372-8854",
publisher = "E Schweizerbart Science Publishers",
number = "Supp 1",

}

TY - JOUR

T1 - A reconstruction of historical changes in sediment sources, sediment transfer and sediment yield for a small, semi-arid Karoo catchment, South Africa

AU - Rowntree, Kate M

AU - Foster, Ian D L

PY - 2012/1/1

Y1 - 2012/1/1

N2 - Land degradation is widespread in South Africa but few long-term data sets are available to help identify the timing of this degradation and its impact on catchment sediment yields. We report a case study reconstructing the erosion history of a small upland catchment in the Sneeuberg mountains of South Africa based on the dating of reservoir sediments using 210Pb and 137Cs. Sediment sources have been identified using mineral magnetic measurements. Additional information has been derived from the analysis of aerial photographs and satellite images and the measurement of badland erosion using erosion pins. Results suggest that sediment yields increased dramatically from < 30 t km-2 yr-1 in the early part of the 20th Century to ∼1600 t km-2 yr-1 in the 1970s, subsequently falling to ∼850 t km-2 yr-1 in the last decade. Contemporary erosion pin measurements suggest that badlands are still extremely active and help maintain current high yields. Analysis of aerial photographs and satellite images indicate that badlands and extensive gullies existed in the catchment before 1945. An analysis of mineral magnetic signatures suggested that badlands made some contribution to the reservoir sediment in the 1930s, but did not significantly increase sediment yields. Photographic evidence suggests that a major badland became connected to the main channel network (and to the reservoir) from the early 1960s onwards. This interpretation was confirmed by significant and sustained changes in the mineral magnetic signatures of the reservoir sediments. The results indicated that a delayed increase in sediment yield, despite extensive badland development much earlier, appears to have been caused by changes in catchment connectivity rather than being a direct response to contemporary changes in land degradation within the catchment. These results add additional complications to our understanding of the relationship between the response to, and recovery from, periods of overgrazing in the 1930s that probably initiated the badland development.

AB - Land degradation is widespread in South Africa but few long-term data sets are available to help identify the timing of this degradation and its impact on catchment sediment yields. We report a case study reconstructing the erosion history of a small upland catchment in the Sneeuberg mountains of South Africa based on the dating of reservoir sediments using 210Pb and 137Cs. Sediment sources have been identified using mineral magnetic measurements. Additional information has been derived from the analysis of aerial photographs and satellite images and the measurement of badland erosion using erosion pins. Results suggest that sediment yields increased dramatically from < 30 t km-2 yr-1 in the early part of the 20th Century to ∼1600 t km-2 yr-1 in the 1970s, subsequently falling to ∼850 t km-2 yr-1 in the last decade. Contemporary erosion pin measurements suggest that badlands are still extremely active and help maintain current high yields. Analysis of aerial photographs and satellite images indicate that badlands and extensive gullies existed in the catchment before 1945. An analysis of mineral magnetic signatures suggested that badlands made some contribution to the reservoir sediment in the 1930s, but did not significantly increase sediment yields. Photographic evidence suggests that a major badland became connected to the main channel network (and to the reservoir) from the early 1960s onwards. This interpretation was confirmed by significant and sustained changes in the mineral magnetic signatures of the reservoir sediments. The results indicated that a delayed increase in sediment yield, despite extensive badland development much earlier, appears to have been caused by changes in catchment connectivity rather than being a direct response to contemporary changes in land degradation within the catchment. These results add additional complications to our understanding of the relationship between the response to, and recovery from, periods of overgrazing in the 1930s that probably initiated the badland development.

KW - sediment yield

KW - badlands

KW - connectivity

KW - gamma spectrometry

KW - mineral magnetic signatures

KW - Karoo

KW - South Africa

UR - http://www.schweizerbart.de/journals/zfg

U2 - 10.1127/0372-8854/2012/S-00074

DO - 10.1127/0372-8854/2012/S-00074

M3 - Article

VL - 56

JO - Zeitschrift fur Geomorphologie, Supplementary Issues

JF - Zeitschrift fur Geomorphologie, Supplementary Issues

SN - 0372-8854

IS - Supp 1

ER -