Field experiments of aeolian dust accumulation on rock fragment substrata

The effect of rock fragments and rock fragment cover on the accumulation of airborne dust was examined in a long-term field experiment in the Negev desert of Israel. Four parameters were studied: pebble eccentricity, pebble size, pebble flattening and cover density. The effect of these parameters on the accumulation of dust on the pebbles, on the accumulation of dust between and underneath the pebbles, and on total dust accumulation (pebbles+interpebble space) was measured separately. Accumulation on the pebbles increased as the pebbles became larger, less flattened and more elongated, and as cover density increased. Accumulation between and underneath the pebbles increased as the pebbles became smaller, more flattened and more elongated, and as cover density increased (although the accumulation area available became smaller). Total dust accumulation increased as the pebbles became smaller, more flattened and more elongated, and as cover density increased. Rock fragments act as a dust trap as dust accumulation on pebble-covered surfaces is several tens of times larger than dust accumulation on similar but pebble-free surfaces. However, less than 20% of the initially settled dust is protected from further erosion. In the Negev desert, dust erosion by wind is of the order of 10 times larger than dust erosion by water. The rate of long-term dust accumulation in the Negev is of the order of 15–30 g.m^?2.yr^?1. This is considerably lower than the rates proposed elsewhere in the literature, which are based upon over optimistic dust retainment percentages.