Dynamics of Land use Around the Micro-Dam Anti-Salt in the Sub-Watershed of Agnack Lower Casamance (Senegal)

Abstract

Agriculture, mainly based on rain, is one the most important economic activities in Lower Casamance region. Its agricultural production is vulnerable to climatic variability. The water management has become an important issue for rural populations food security. This research aims at the characterization of environmental evolution and agricultural production, around the anti-salt micro-dams in Lower Casamance area, which has a high rainfall and a rich potential of water resources. This study examines the hydro-agricultural planning issues in Lower Casamance and aims at the analysis of the land use change and its evolution in the Agnack sub-basin around anti-salt micro-dam between 1984 and 2010. Based on the importance of rice production area around micro-dams, the analysis focus on eight sites. Using satellite imagery Landsat TM of 1984 and 1992 and ETM of 2000 and 2010 combined with ground, socio-economic survey and soil analysis data, this research investigates land use change through image classifications, change detection and landscape pattern analysis. We conducted a mapping of the rice paddies to determine the evolution of riceland during these dates. Through a pseudo-supervised classification coupled with field data, we characterized the different types of land use and cover. Results of land use/cover change analysis showed a decrease of riceland area; while there is a relative vegetation regeneration between 1984 and 2010. The soil analysis showed a deterioration in soil quality which is showed by a very high acidity in all sites and a soil salinity of riceland in the upstream developed valleys. Socio-economic surveys showed the importance of the micro-dams. In the term, the micro-dam did not achieve the expected results. It could not solve the problem of degraded soil desalination and intensification of rice growing.

Improving the Chemical Properties of Acid Sulphate Soils from the Casamance River Basin

“…Different studies conducted under pot or field conditions have indicated that appropriate agronomic management increases rice production in ASS. To cope with iron toxicity, several strategies have been proposed: add mineral fertilisers to improve soil fertility [38]; apply phosphogypsum and lime to increase available Ca and soil pH and lower toxic iron and aluminium levels [34,39,52]; add organic residue, which could stimulate the activity of reducing bacteria [32] to lead to a rise in pH under flooded conditions.…”

“…The quantitative results of the land-use dynamics based on satellite data showed a significant decline in the rice area for 1984-2010 in the subwatersheds of the lower Casamance basin. However, increased rainfall reversed this trend between 2000 and 2010 [32].…”