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Universiteit Gent (2010)

Formation and properties of badlands in Lusitu area, Southern province, Zambia

Mulalabungu Brian

Titre : Formation and properties of badlands in Lusitu area, Southern province, Zambia

Auteur : Mulalabungu Brian

Université de soutenance : Universiteit Gent

Grade : Master of Science (MS) Physical Land Resources 2010

Résumé
Soil erosion is one of the major threats for land degradation in dryland areas. This study intended to study the formation and the properties of the Lusitu badlands in the Southern Province of Zambia. The badlands are associated with severe problems of erosion ranging from ordinary wind erosion to rill and gully erosion and the more severe piping erosion which is at the origin of large underground cavities. The different horizons of a representative soil profile onto a gully of a seasonal stream were sampled for physico-chemical and mineralogical analyses. Salt evaporated from the ground water and some suspected crystals of gypsum occurring as infillings in the B horizon were also collected. The formation of gullies and piping erosion are related to the unstable subsoil. The physical soil properties of the subsoil are at the origin of its instability relative to the upper horizons. The amounts of water dispersible clay show that most of the clay minerals in the subsoil are easily dispersed by rain water and hence the instability. The instability is also shown by the calculated index of structure which is higher for the upper horizons compared to the subsoil. The aggregate instability show that the aggregates in the lower horizons are very unstable and easily slake. The instability of the aggregates is also due to the chemical dispersion. The chemical characteristics of the soil and the salts evaporated from the ground water show that Na+ and SO4-2 are the dominant ions. XRD analysis of the salts leached from the different horizons revealed that thernadite (Na2SO4) is the dominant mineral in the subsoil. The open 2:1 phyllosilicates (smectites) being dominant in the subsoil are predominantly Na+- saturated and therefore are easily dispersed by rain water. However, kaolinite, a 1:1 phyllosilicate, dominates the upper horizons. When the soil aggregates are broken up, they clog up the soil pores reducing the soil permeability. This eventually leads to the runoff and erosion and hence the formation of rills and gullies. The formation of pipes is related to the sodicity of the subsoil. Therefore when the rain water reaches the subsoil, through cracks or root channels, the subsoil disperses and goes into suspension which starts to flow out through available channels. This results in the formation of cavities in the subsoil as the material is removed. The cavities created leads to the subsidence of the upper more stable soil layers and finally results in the formation of the badland

Source : Pedon 22 - Physical Land Resources - Universiteit Gent

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