Geochemistry of Urban Soil in the Fast-Growing Kuito City (Angola)

Abstract

The city of Kuito is located in the Central Plateau of Angola, with elevations above 1500 m high. The soils are classified as ferralsols and arenosols, developed over laterites and clastic recent sediments of the Kalahari Group, respectively. The soils have very low clay contents, less than 3.9%, and loamy sand to sandy loam texture. The urban soil has higher pH (7.4) and electrical conductivity (267 μS/cm) levels than natural soils. To note, the latter usually have an average pH value of 5.8 and an average value of 7.2 μS/cm of electrical conductivity. There is no distinction in the organic matter content in both types of soils. Urban soil has 0.69% and the natural soil has 0.71%, of organic carbon. The urban soils also display higher concentrations of Na, P, Cu, Zn, Sn, Sb, Cd and Pb than the natural ones, and the contaminating elements in the urban soils are Cu, Zn, Sn, Sb, Cd and Pb. These elements are added to the soils by anthropic activities, such as the uncontrolled deposition of domestic and industrial effluents and car traffic. It is actually the type of soil and the modification of its pH which control these elements’ fixation in the urban soils.