Environmental and Climatic History of the Eastern Kivu Area (D.R. Congo, ex Zaire) from 40 ka to the Present

Abstract

This paper provides a brief review of extensive large-scale terrestrial observations on stratigraphie and pedologie features of soils and sediments in the eastern Kivu region of former Zaire. Along an almost 600 km wide exploration transect from Bukavu in the Western Rift Valley to Kisangani in the Congo basin, Late Quaternary and Holocene environmental changes are discussed. The eastern Kivu has long been believed to be a part of the LGM (Last Glacial Maximum) “core-area” and a refuge area of the central African rain forest, showing more or less environmental stability during drier glacial times. In the course of road building, numerous deep soil openings, especially in the area of Walikale, were subject to palaeoenvironmental interpretation. Yellowish-brown hillwash sediments contained charcoal. These covered stone- lines and fossil tree trunks within the mottled and pallid zone of soils. The resulting many radiocarbon dates allowed for the reconstruction of the environmental frame conditions of the eastern Kivu region between 40 ka to the present. There is considerable evidence for a major forest retreat between 36 ka and 13 ka. Several periods with a pre-LGM age from 36–28 ka, a LGM phase between 21–18 ka and a post-LGM period around 13–12 ka were characterized by alternating and contrasting dry and wet seasons with significantly intensified surface morphodynamic processes (sheet wash erosion, gullying) and stronger fluvial dynamics of rivers (alluviation). Annual rainfall in the lowland is suggested to have reached around 1200 mm only. The vegetation cover was mainly dominated by a savanna-woodland mosaic with extended gallery forest systems. Therefore, the conception of a “fluvial refuge” in the eastern Congo is a preferred environmental view for the LGM. Lowland tropical mean temperatures are supposed to have been slightly cooler in the range of 2–4° C lower than today.