干旱区生态环境知识资源中心

Deserts are major areas of wind erosion releasing each year about 1500 Mt of mineral dust in the troposphere. Nevertheless recent works suggest that semi-arid areas become other important mineral dust sources because human activities and mainly agriculture extend the surfaces prone to wind erosion, This is particularly the case in the Sahel where the fast population growth causes changes in land use: surfaces occupied by fallows tend to decrease for cultivated fields. But the Sahel is also on the trajectory of the Saharan dust plumes giving high rate of aerosol deposition. Thus it is still unclear if Sahel is net dust deposition or net wind erosion area,

To assess the mass budget of aeolian sediments < 20 mum transported by wind (erosion vs. deposition) at the scale of a village land unit (25 km x 25 km), measurements have been carried out near Niamey (Niger) during 3 years ( 1996-1998) in a cultivated field and in a fallow area.

Values of deposition recorded in the field and in the fallow were similar. In the field, wind erosion reached its maximum in May and June when the vegetation cover was minimal. The net balance between deposition and erosion was negative in 1996 and 1998 and slightly positive in 1997, In the fallow area, wind erosion was always very low in comparison with the field leading to systematic positive net balance between deposition and erosion, These results have been extrapolated at the scale of the village land unit based on the current land use. At this scale, this balance was positive for the arable soils, indicating a net deposition of aeolian sediments 0.36 t ha(-1) yr(-1)).