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<p>Urban wetlands in sub-Saharan Africa face increasing pressure from rapid urbanization, yet the geochemical and mineralogical characterization of their sediments crucial for environmental assessment, monitoring, and sustainable management remains limited. This study investigates the recent sediment layers of the Mfoundi floodplain, a heavily urbanized wetland in Yaoundé, Cameroon, to determine their mineralogical and geochemical composition, provenance, and environmental implications. Nine sediment pits, excavated to depths of up to 2&#xa0;m, were logged and sampled for granulometric, mineralogical (XRD and Raman spectroscopy), and geochemical (XRF and ICP-MS) analyses. The sediments are predominantly sandy to silty sand, with a heavy mineral assemblage comprising zircon, tourmaline, rutile, and kyanite, reflecting derivation from proximal metamorphic basement rocks, including gneisses, quartzites, and migmatites. The bulk geochemical data show high SiO<sub>2</sub>, and low concentrations of major and trace elements, consistent with quartz-rich, compositionally mature sediments. The sediments display overall depletion in trace elements and rare earth elements (REEs) relative to the upper continental crust (UCC), attributed to intense chemical weathering, quartz dilution, and low retention in sandy textures. High Chemical Index of Alteration (CIA: 50–98.92%) and Plagioclase Index of Alteration (PIA: 70.57–99.90%) values indicate advanced weathering of felsic source rocks under humid tropical conditions. The bivariate plots of (Zr vs TiO<sub>2</sub>, La/Th vs Hf, Cr/Th, La/Co*10), geochemical ratios (e.g., Zr/TiO<sub>2</sub>, La/Th vs. Hf, La/Yb<sub>N</sub>) and REE fractionation patterns suggest a dominant felsic provenance with limited input from mafic lithologies. The Index of Compositional Variability (ICV &lt; 1 to &gt; 1) reflects both mature and immature sediment fractions, pointing to contributions from both first and second sedimentary cycles. The trace element enrichment factors (EF &gt; 40) in some samples indicate significant enrichment, likely from natural sources, with decreasing intensity up-section and no evidence of anthropogenic pollution. These findings contribute essential baseline data for future environmental assessments and underscore the importance of sediment studies in the sustainable management of urban floodplain wetlands.</p>

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A mineralogical and geochemical approach to characterizing changes in urban agrarian wetlands: case study of the Mfoundi floodplain sediments, Yaoundé, Cameroon

  • 期刊论文

  • 发表日期：

    2025年7月1日

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  • Emmaculate Nuigendia Ngwanwi,
  • Lionel Takem Nkwanyang,
  • Cheo Emmanuel Suh,
  • Oliver A. Njoh,
  • Terence Cho Ngang,
  • George Lemewihbwen Ngiamte,
  • Kedia Arnold Chi

摘要

Urban wetlands in sub-Saharan Africa face increasing pressure from rapid urbanization, yet the geochemical and mineralogical characterization of their sediments crucial for environmental assessment, monitoring, and sustainable management remains limited. This study investigates the recent sediment layers of the Mfoundi floodplain, a heavily urbanized wetland in Yaoundé, Cameroon, to determine their mineralogical and geochemical composition, provenance, and environmental implications. Nine sediment pits, excavated to depths of up to 2 m, were logged and sampled for granulometric, mineralogical (XRD and Raman spectroscopy), and geochemical (XRF and ICP-MS) analyses. The sediments are predominantly sandy to silty sand, with a heavy mineral assemblage comprising zircon, tourmaline, rutile, and kyanite, reflecting derivation from proximal metamorphic basement rocks, including gneisses, quartzites, and migmatites. The bulk geochemical data show high SiO2, and low concentrations of major and trace elements, consistent with quartz-rich, compositionally mature sediments. The sediments display overall depletion in trace elements and rare earth elements (REEs) relative to the upper continental crust (UCC), attributed to intense chemical weathering, quartz dilution, and low retention in sandy textures. High Chemical Index of Alteration (CIA: 50–98.92%) and Plagioclase Index of Alteration (PIA: 70.57–99.90%) values indicate advanced weathering of felsic source rocks under humid tropical conditions. The bivariate plots of (Zr vs TiO2, La/Th vs Hf, Cr/Th, La/Co*10), geochemical ratios (e.g., Zr/TiO2, La/Th vs. Hf, La/YbN) and REE fractionation patterns suggest a dominant felsic provenance with limited input from mafic lithologies. The Index of Compositional Variability (ICV < 1 to > 1) reflects both mature and immature sediment fractions, pointing to contributions from both first and second sedimentary cycles. The trace element enrichment factors (EF > 40) in some samples indicate significant enrichment, likely from natural sources, with decreasing intensity up-section and no evidence of anthropogenic pollution. These findings contribute essential baseline data for future environmental assessments and underscore the importance of sediment studies in the sustainable management of urban floodplain wetlands.