Pedology of soils within the spray zone of the Victoria Falls (Zimbabwe)

Abstract

Six profiles were sampled in the Victoria Falls National Park (Zimbabwe) in order to investigate the influence of the abundant spray of the falls on the pedogenesis in the otherwise semi-arid environment. Depending upon the thickness of the alluvium, soils developed in the sediment with variable admixture of basalt gravel, or practically directly on the underlying Karroo plateau basalt layer. Those near the gorge are subject to a continuous spray during most of the year; the more remote ones get only the natural precipitation. Chemical, mineralogical and micromorphological analyses indicate that the parent material is a more dominant factor determining chemical, mineralogical and micromorphological characteristics than precipitation. The main active process is bioturbation. Phytolites and sponge spicules are abundant. In most profiles basalt-derived laumontite is observed in thin sections and in the silt fraction. Weathering of the basalt gravel is limited, although pedogenesis has been active for at least 50–100 ka. A subdivision of enaulic c/f related distribution patterns is proposed.