Subsurface sources contribute substantially to fine‐grained suspended sediment transported in a tropical West African watershed in Burkina Faso

Abstract

Increasing watershed sediment yields is an important problem in Africa, but the sources of these sediment yields have only very rarely been investigated. This study therefore aims to discriminate subsurface and surface sources of fine-grained sediments in a representative mesoscale (580 km 2 ) West African savanna watershed.We used a sediment source fingerprinting approach for source apportionment including geochemical and radionuclide ( 137 Cs, 210 Pb ex , and 7 Be) composite signatures where 7 Be was used as a tracer for the first time in the African environment. Two field campaigns were conducted collecting a total of 258 geochemical and 66 isotope samples. We found that subsurface source categories, dominantly river bank, contributed an unexpected high share of 43% (geochemistry) and 45% (radionuclides) to the sampled fine-grained sediments. Pairwise comparison of the averaged frequency distributions for predicted source proportions using five geochemical signatures with the frequency distribution generated using the single radionuclide signature suggested that the two distributions are not statistically different. Extrapolating our measured contribution of subsurface erosion to areas with similar yields in comparable environmental settings, we can assume that subsurface sources are an important component of sediment loss across large areas of West Africa. Subsurface erosion, primarily associated with bank rather than gully erosion, is likely to increase in the future with projected rises in run-off due to land use and climate change. Source tracing studies need to be undertaken more widely across Africa to help mitigation planning for sediment-related and land degradation problems.

A global review of sediment source fingerprinting research incorporating fallout radiocesium (137Cs)

“…In catchments of South Africa, Foster et al (2007) demonstrated the potential for 210 Pb xs to provide an alternative to 137 Cs as the latter will soon become undetectable because of the lack of inputs and its 30-yr half-life. A good relationship between both radionuclides was also found in source and sediment samples collected in a catchment of Burkina Faso (Rode et al, 2018). A similar finding was also demonstrated in a catchment of Southern England by comparing 137 Cs and Pb xs activities in surface, subsurface material and sediment (Walling and Amos, 1999), although the authors outlined a greater enrichment in 210 Pb xs than in 137 Cs in suspended sediment and channel bank material compared to subsoil material.…”

“…In the Southern Hemisphere, where less fallout is estimated to have occurred (~23%) (UNSCEAR, 2000), much less information is available regarding areas where the method is applicable. In Africa, this technique was shown to be applicable in Tunisia (Ben Slimane et al, 2013) as well as in Burkina Faso (Rode et al, 2018). This suggests that the technique can be used in the Maghreb and Sahel countries, at least in areas where soils are not too sandy.…”

Plutonium Isotopes: An Effective Tool for Fluvial Sediment Sourcing in Urbanized Catchments

“…As urban development and agricultural activity increases to meet growing population demands, decreasing sedimentation in fluvial systems will be integral to creating sustainable and efficient urban and agricultural systems. This is particularly important as subsurface erosion is likely to increase in the future with projected rises in runoff due to land use and climate change (Rode et al., 2018).…”

The Role of Paddy Fields in the Sediment of a Small Agricultural Catchment in the Three Gorges Reservoir Region by the Sediment Fingerprinting Method

“…The classification of source groups is a key step in the application of fingerprinting techniques, as they are used to construct field samples of potential sources [34]. Summarizing existing studies, it is common practice to selected priority source groups based on spatial sources subdivided by geological units [35][36][37] or tributary subbasins [38][39][40][41] or source types consisting of surface and subsurface sources [18,[42][43][44]. In practical applications, the sources of different classification methods can be combined.…”