Importance of soil surface characteristics on water erosion in a small grazed Sahelian catchment

Abstract

Abstract:This study concerns the problem of water erosion in the Sahel. Surface water and sediment yields (suspended matter and bedload) were monitored for 3 years (1998)(1999)(2000) at the outlet of a small grazed catchment (1Ð4 ha) in the northern part of Burkina Faso. The catchment consists of about 64% sandy deposits (DRY soil surface type), which support most of the vegetation, and about 34% of crusted bare soils (ERO soil surface type). The annual solid-matter export is more than 90% suspended sediment, varying between 4Ð0 and 8Ð4 t ha 1 . The bedload represents less than 10% of soil losses. In a single flood event (10 year return period), the sediment yield can reach 4Ð2 t ha 1 . During the period studied, a small proportion (20 to 32%) of the floods was thus responsible for a large proportion (80%) of the solid transport. Seasonal variation of the suspended-matter content was also observed: high mean values (9 g l 1 ) in June, decreasing in July and stabilizing in August (between 2 and 4 g l 1 ). This behaviour may be a consequence of a reorganization of the soil surfaces that have been destroyed by trampling animals during the previous long dry season, vegetation growth (increase in the protecting effect of the herbaceous cover) and, to a lesser extent, particle-supply limitation (exhaustion of dust deposits during July). The particle-size distribution in the suspended matter collected at the catchment outlet is 60% made up of clay: fraction <2 µm. The contribution of this clay is maximum when the water rises and its kaolinite/quartz ratio is then close to that of the ERO-type surfaces. This indicates that these surfaces are the main source of clay within the catchment.

Soil crusting impact on soil organic carbon losses by water erosion

“…There is a tendency for ERO crusts to develop in clayey soil horizons, DES and STRU to develop under sandy soil conditions and for GRAV crusts to form under the coarsest soil textures (Casenave and Valentin, 1989). Several studies (de Rouw and Rajot, 2004;Graef and Stahr, 2000;Karambiri et al, 2003;Malam-Issa et al, 2011) in the Sahel supplied information on impacts of soil crusting on infiltration and soil erosion, yet, little is known about the impacts of soil crusting on SOC losses.…”

Nutrient dynamics—wind and water erosion at the village scale in the Sahel

“…Their results emphasise the necessity to take into account both wind and water erosion processes to assess the actual land degradation in the Sahel. Furthermore, Rajot et al (2002) and Karambiri et al (2003) have shown that the surface characteristics determine mainly the pattern of erosion and deposition of sediment in a small-scale catchment. This emphasises the need for more research on wind and water erosion at a larger (i.e.…”

Increasing River Flows in the Sahel?

“…For the Niger Republic during the 1999-2006 period, Garba [38] observed a decrease in biomass in a study based on NDVI; but he explains this by the fact that the year 1999-2000 was a humid one. Karambiri et al [39], Diello et al [40] and Hauchart [41] also noticed a reduction in vegetation cover in two different regions of Burkina Faso (the Nakambe and Mouhoun basins). Lié nou et al [42] made similar observations in Cameroon, which are consistent with the works of Amani and Nguetora [9], and Mahé et al [43] on the west bank of the Niger River.…”