|Herrick, Jeffrey - Jeff|
Submitted to: Earth Surface Processes and Landforms
Publication Type: Peer reviewed journal
Publication Acceptance Date: 2/9/2006
Publication Date: 4/1/2007
Citation: Belnap, J., Phillips, S.L., Herrick, J.E., Johansen, J.R. 2007. Wind erodibility of soils at Fort Irwin, California (Mojave Desert), USA, before and after trampling disturbance: Implications for land management. Earth Surface Processes and Landforms. 32:75-84. Interpretive Summary: Reducing runoff and erosion is a high priority for most land managers, particularly in arid and semiarid ecosystems. The effects of soil surface disturbance on water infiltration in these rangeland soils are poorly understood. We trampled soils at six different sites in the Mojave Desert. Three of the sites had been heavily disturbed by off-road wheeled and track vehicle traffic; the other three had not. Trampling reduced infiltration by 36% at both types of sites. It increased soil loss from the small (50cm x 50cm) plots 240% at the previously disturbed sites and 240% at the relatively undisturbed sites. We concluded that soil surface disturbance negatively affects soil and water conservation on sandy soils in this warm desert environment.
Technical Abstract: Recently disturbed and ‘control’ (i.e. less recently disturbed) soils in the Mojave Desert were compared to their vulnerability to wind erosion, using a wind tunnel, before and after being experimentally trampled. Before trampling, control sites had greater cyanobacterial biomass, soil surface stability, threshold friction velocities (TFV; i.e. the wind speed required to move soil particles), and sediment yield than sites that had been more recently disturbed by military manoeuvres. After trampling, all sites showed a large drop in TFVs and a concomitant increase in sediment yield. Simple correlation analyses showed that the decline in TFVs and the rise in sediment yield were significantly related to cyanobacterial biomass (as indicated by soil chlorophyll a). However, chlorophyll a amounts were very low compared to chlorophyll a amounts found at cooler desert sites, where chlorophyll a is often the most important factor in determining TFV and sediment yield. Multiple regression analyses showed that other factors at Fort Irwin were more important than cyanobacterial biomass in determining the overall site susceptibility to wind erosion. These factors included soil texture (especially the fine, medium and coarse sand fractions), rock cover, and the inherent stability of the soil (as indicated by subsurface soil stability tests). Thus, our results indicate that there is a threshold of biomass below which cyanobacterial crusts are not the dominant factor in soil vulnerability to wind erosion. Most undisturbed soil surfaces in the Mojave Desert region produce very little sediment, but even moderate disturbance increases soil loss from these sites. Because current weathering rates and dust inputs are very low, soil formation rates are low as well. Therefore, soil loss in this region is likely to have long-term effects.