Clay composition and properties in termite mounds of the Lubumbashi area, D.R. Congo

The influence of Macrotermes falciger activity on clays, sesquioxides and water-dispersible clay (WDC) content was investigated by a physico-chemical, mineralogical and micromorphological study of termite mound and control soil profiles at various sites near Lubumbashi, SE Katanga, D.R. Congo. X-ray diffraction reveals that the termite-mound materials are enriched in 2:1 clays, especially mica and expandable clay minerals, and selective dissolution analyses show that they contain greater relative amounts of Mn oxides and poorly crystalline Fe oxides, relative to the surrounding Ferralsols. The water-dispersible clay (WDC) content is much higher (4–87 fold) in epigeal mound parts than in the control soils. Enrichment in 2:1 clays of the mounds is attributed to upward transport of mica and smectite as part of soil aggregates or saprolite materials used in mound construction. The difference in nature and abundance of sesquioxides between termite mound and control soil is related to a difference in moisture regime, whereby the basal part of the mounds are characterized by conditions with alternating reducing/oxidizing conditions, in contrast to the surrounding well-drained ferralitic soils. The much greater degree of clay dispersibility in termite mound materials than in the surrounding soils is mainly due to differences in clay properties, primarily surface charge characteristics, and to differences in Fe oxide content and mode of occurrence. The high water-dispersible clay content of termite mound materials is confirmed by micromorphological features, including abundant clay coatings and fragments of coatings.