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 km2) West African savanna watershed. We used a sediment source fingerprinting approach for source apportionment including geochemical and radionuclide (137Cs, 210Pbex, and 7Be) composite signatures where 7Be 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.

中文翻译：

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地下源对布基纳法索热带西非流域中细粒悬浮沉积物的输送有很大贡献

增加流域沉积物产量是非洲的一个重要问题，但很少研究这些沉积物产量的来源。因此，本研究旨在区分具有代表性的中尺度（580 平方公里）西非稀树草原流域中细粒沉积物的地下和地表来源。我们使用沉积物源指纹识别方法进行源分配，包括地球化学和放射性核素（137Cs、210Pbex 和 7Be）复合特征，其中 7Be 首次在非洲环境中用作示踪剂。进行了两次实地活动，共收集了 258 个地球化学和 66 个同位素样品。我们发现地下源类别，主要是河岸，对采样的细粒沉积物贡献了 43%（地球化学）和 45%（放射性核素）的意外高份额。将使用五个地球化学特征的预测源比例的平均频率分布与使用单个放射性核素特征生成的频率分布进行成对比较，表明这两种分布在统计上没有差异。将我们测得的地下侵蚀贡献外推到可比较环境条件下具有相似产量的地区，我们可以假设地下来源是西非大片地区沉积物流失的重要组成部分。地下侵蚀主要与河岸侵蚀而非沟壑侵蚀有关，未来可能会增加，预计由于土地利用和气候变化导致径流增加。需要在整个非洲更广泛地开展溯源研究，以帮助制定与沉积物相关和土地退化问题的缓解计划。