EROSION RESPONSE OF A DISTURBED SAGEBRUSH STEPPE HILLSLOPE

Land management activities that disrupt surface vegetation cover pose a serious threat to the long-term stability of buried-waste sites loca ted within the semiarid sagebrush (Artemisia tridentata Nutt.) steppe region of the northwestern USA. In this study, we evaluated the erosio n response of a sagebrush hillslope subjected to three vegetation cove r treatments: natural (undisturbed), bare (plant canopy and litter cov er removed), and clipped (canopy removed). A rotating boom rainfall si mulator was used to apply rain at 60 or 120 mm/h intensities to runoff plots (3.0 m by 10.7 m) with dry, wet, and very wet antecedent moistu re conditions, and during two late and one early summer seasons. Suppl emental overland flow was added at the upper end of each plot to simul ate increased slope length during very wet runs. Maximum soil loss rat es on the natural, clipped, and bare treatments were, respectively, 1, 5, and 216 mg/m2 per s during the 60 mm/h rainfall intensity, and 13, 79, and 1473 mg/m2 per s during the 120 mm/h rainfall intensity. Cumu lative soil loss was typically 100 to 1000 times greater on the bare t reatment than on the natural or clipped treatments. Increases in simul ated slope length produced a near linear increase in soil loss from th e bare treatment plots (about 0.02 g/m2 per s soil loss per m of slope length) until 30 m, after which the effect of slope length declined. Surface crust development and mound-intermound microtopography played important roles in governing soil detachment and transport on the hill slope. Despite high rainfall intensity and surface runoff rates, rill erosion was negligible on both the undisturbed and disturbed portions of the hillslope.