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
(210Pb and 137Cs) to date sediments accumulating in reservoirs, farm dams, wetlands, alluvial fans and
floodouts and have used other fallout nuclides (7Be) and long-lived geogenic radionuclides (e.g. 40K, 235U) 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 137Cs, 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 210Pb 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.
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
(210Pb and 137Cs) to date sediments accumulating in reservoirs, farm dams, wetlands, alluvial fans and
floodouts and have used other fallout nuclides (7Be) and long-lived geogenic radionuclides (e.g. 40K, 235U) 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 137Cs, 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 210Pb 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.
| Original language | English |
|---|---|
| Pages (from-to) | 29-34 |
| Number of pages | 6 |
| Journal | Proceedings of the International Association of Hydrological Sciences |
| Volume | 375 |
| DOIs | |
| Publication status | Published - 3 Mar 2017 |