The Semi-Arid Land-Surface-Atmosphere Program (SALSA) is a multi-agency, multinational research effort that seeks to evaluate the consequences of natural and human-induced environmental change in semi-arid regions. The ultimate goal of SALSA is to advance scientific understanding of the semi-arid portion of the hydrosphere-biosphere interface in order to provide reliable information for environmental decision making. SALSA approaches this goal through a program of long-term, integrated observations, process research, modeling, assessment, and information management that is sustained by cooperation among scientists and information users. In this preface to the SALSA special issue, general program background information and the critical nature of semi-arid regions is presented. A brief description of the Upper San Pedro River Basin, the initial location for focused SALSA research follows. Several overarching research objectives under which much of the interdisciplinary research contained in the special issue was undertaken are discussed. Principal methods, primary research sites and data collection used by numerous investigators during 1997-1999 are then presented. Scientists from about 20 US, five European (four French and one Dutch), and three Mexican agencies and institutions have collaborated closely to make the research leading to this special issue a reality. The SALSA Program has served as a model of interagency cooperation by breaking new ground in the approach to large scale interdisciplinary science with relatively limited resources. Published by Elsevier Science B.V.
Land management activities that disrupt surface vegetation cover pose a serious threat to the long‐term stability of buried‐waste sites located within the semiarid sagebrush (Artemisia tridentata Nutt.) steppe region of the northwestern USA. In this study, we evaluated the erosion response of a sagebrush hillslope subjected to three vegetation cover treatments: natural (undisturbed), bare (plant canopy and litter cover removed), and clipped (canopy removed). A rotating boom rainfall simulator 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 moisture conditions, and during two late and one early summer seasons. Supplemental overland flow was added at the upper end of each plot to simulate increased slope length during very wet runs. Maximum soil loss rates 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. Cumulative soil loss was typically 100 to 1000 times greater on the bare treatment than on the natural or clipped treatments. Increases in simulated slope length produced a near linear increase in soil loss from the 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 hillslope. Despite high rainfall intensity and surface runoff rates, rill erosion was negligible on both the undisturbed and disturbed portions of the hillslope.
A kinematic wave model of overland flow was used to calculate hydraulic roughness coefficients for earth covers and native hillslope surfaces at a waste burial site located in a cold-desert region of southeast Idaho. Manning n roughness coefficients were greater on earth cover plots planted to crested wheatgrass [Agropyron desertorum (Fisch, ex Link) Schult.] (a bunchgrass, average n = 0.076) than on those planted to streambank wheatgrass [Elymus lancelolatus (Scribner & J. G. Smith) Gould] (a sodgrass, average n = 0.030). Mound and intermound microtopography strongly influenced overland flow geometry on the bare native hillslope plots resulting in low apparent roughness values (average n = 0.013). Time-related changes in hydraulic roughness appeared to be caused by development of a raininduced crust on exposed soil surfaces that reduced infiltration and increased plot smoothness.
Control of runoff (reducing infiltration) and erosion at shallow land burials is necessary in order to assure environmentally safe disposal of low‐level radioactive‐waste and other waste products. This study evaluated the runoff and erosion response of two perennial grass species on simulated waste burial covers at Idaho National Engineering and Environmental Laboratory (INEEL). Rainfall simulations were applied to three plots covered by crested wheatgrass [Agropyron desertorum(Fischer ex Link) Shultes], three plots covered by streambank wheatgrass [Elymus lanceolatus(Scribner and Smith) Gould spp. lanceolaus], and one bare plot. Average total runoff for rainfall simulations in 1987, 1989, and 1990 was 42 percent greater on streambank wheatgrass plots than on crested wheatgrass plots. Average total soil loss for rainfall simulations in 1987 and 1990 was 105 percent greater on streambank wheatgrass plots than on crested wheatgrass plots. Total runoff and soil loss from natural rainfall and snowmelt events during 1987 were 25 and 105 percent greater, respectively, on streambank wheatgrass plots than on crested wheatgrass plots. Thus, crested wheatgrass appears to be better suited in revegetation of waste burial covers at INEEL than streambank wheatgrass due to its much lower erosion rate and only slightly higher infiltration rate (lower runoff rate).
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