Effects of grazing and topography on dust flux and deposition in the Xilingele grassland, Inner Mongolia

Abstract

The dynamics of dust emission and deposition in the grasslands of Inner Mongolia were investigated during a measuring campaign from April to May 2005 in grazed and un-grazed plots. Both processes are determined by the grazing intensity, whereas dust deposition rates are modified additionally by the topography. Because grazing intensity influences the height and density of the vegetation, it could therefore be measured through the surface roughness length ( z 0). Almost all strong winds come regularly from the northwest, which give rise to the distinction between exposed windward and mostly sheltered leeward slopes. Dust deposition and dust remobilization are merged processes, which are difficult to separate during dust storms. Airborne sediments that originate from various source areas (supra-regional dust storms and local wind erosion) were distinguished by comparing vertical transport profiles. The average horizontal dust flux measured during the measuring campaign for below the height of 1 m was between 180 and 239 g m −1 width and day. The average proportion of material transported by local wind erosion amounted to only 5% in grazed plots. Evidence of dust emission was found at all grazed sites (up to 0.8 g m −2 d −1) while ungrazed sites seemed well protected. The dust deposition rates on grazed and ungrazed sites were on average 1.3 and 2.4 g m −2 d −1, respectively. Leeward slopes had 29–33% higher deposition rates than windward slopes, summits and plane positions.