Wind erosion dynamics associated with land use on sandy soils under
heavy anthropogenic pressure (southwestern Niger)
Abstract
Heavy anthropic pressures and rainfall crises have led to land
degradation and increased the intensity of wind erosion in the Sahel.
This erosion transports soil particles and associated nutrients and
contributes to the degradation of cultivated and grazed land. The aim of
this study is to assess the intensity of wind flux in relation to land
use on the Namaro dune ridge, with sandy soils representative of
south-western Niger. Its surface is essentially dominated by millet
fields and rangelands. The methodological approach consisted in
monitoring soil cover by vegetation on a rangeland and a millet field,
meteorological parameters (rainfall, wind speed and direction) and
associated erosion flux over two annual cycles. Precise, concomitant
measurements of saltation and wind speed were used to determine wind
erosion threshold velocity for both land uses. Wind erosion flux were
measured using sand traps (BSNE) and saltation detectors: sensit and
saltiphone. The potential wind erosion flux was also determined. It
appeared that the millet field is at all times more covered by
vegetation than the rangeland. The two land uses show the lowest land
cover at the end of the dry and beginning of the rainy season when the
winds are strongest. This difference can be explained by the high
grazing pressure on the dune complex, which is maintained throughout the
year. As a result, the threshold velocity, which is always lower on the
rangeland, was 6.1 m.s -1 compared with 7.3 m.s
-1 on the millet field. From July to December, as
vegetation developed, threshold velocities increased, reaching 9.6 and
11.1 m.s -1 respectively on the grazing land and the
field. In agreement with the vegetation cover, DUP and threshold
velocities, horizontal erosion flux and saltation were at least 2 times
greater on the rangeland than on the millet field. This is the first
time in the Sahel that measurements have shown that rangelands can be
more erodible than cultivated fields for the same weather conditions.
This underlines the role of grazing pressure on Sahelian rangelands,
particularly during the rainy season