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RESEARCH ARTICLE

Coastal acid sulfate soils in the Saloum River basin, Senegal

Aïdara C. A. Lamine Fall A D , Jean-Pierre Montoroi B and Karl Stahr C
+ Author Affiliations
- Author Affiliations

A Department of Geography, University of Ziguinchor, BP 523 Ziguinchor, Senegal.

B Institute of Research for Development (IRD), UMR 242, IEES Paris, 32 Avenue Henri Varagnat, 93143 Bondy, France.

C Institute of Soil Science and Land Evaluation, University of Hohenheim, 70593 Stuttgart, Germany.

D Corresponding author. Email: chérif.fall@univ-zig.sn

Soil Research 52(7) 671-684 https://doi.org/10.1071/SR14033
Submitted: 4 February 2014  Accepted: 19 June 2014   Published: 10 October 2014

Abstract

Soils in boundary conditions of contrasting ecosystems generally show unique features. Transition often leads to changes in soil-forming processes, whereby the environment never comes to equilibrium and therefore the soil chemistry and mineralogy show different influences. Such an environment was analysed in the Saloum River basin, west-central Senegal. The objective was to identify the main pedogenic processes prevailing in this saline and acid pedoenvironment and to assess the influence of environmental factors (climate, topography, soil salinity and acidity) on local soil formation and mineral distribution. The terrace landscape is built up by a floodplain, a low terrace, which is still influenced by groundwater, and a middle terrace. The results show that soil properties are strongly influenced by hydrology, salinity and acidity in the entire toposequence: Gleyic Hyposalic and Hypersalic Solonchaks (Sulfatic) in the floodplain, Haplic Gleysols (Thionic) in the low terrace, and Endogleyic Arenosols in the middle terrace. The oxidation of pyrite followed by the redistribution of the main products (Fe2+ and SO42–) represents the major chemical process responsible for iron oxide and jarosite formation. Mineral distribution and crystallinity are linked to the landscape position, which controls the hydrological behaviour and reactions of Fe and S ions. Finally, we observed intrapedon processes such as gleysation, sulfidisation and sulfurisation, as well as interpedon processes such as salinisation, colluvio-alluviation and lateral eluviation. The combination of processes depends strongly on the landscape positions.

Additional keywords: acidity, acid sulfate soil, iron oxide, jarosite, salinity, Senegal.


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