Preliminary analyses of soils and vegetation in the vicinity of the Mohave Generating Station in southern Nevada

Abstract

Soils and vegetation were characterized at sites distributed over a 27-mile section of Nevada Route 77 and Arizona Route 68 north of the Mohave Generating Station in southern Nevada. Vegetation was also analyzed at two sites along the Colorado River, near River Bend. Sites ranged from 168 to 1069 m in elevation. The soils of this area are generally young and much of their morphology is inherited from parent material. Soils have developed under conditions of high temperatures and low rainfall. Most profiles examined were developed on alluvial deposits containing unconsolidated parent materials low in clay content. Some soils contained restrictive layers of caliche hardpan. Generally, soils were unleached and exhibited a high base status. Vegetation on sites below 800 m (bajadas, alluvial fans, washes) 4 was characteristic of the Mohave Desert. Aggregate densities were some thousands of plants per ha, total coverage was around 10-20%, A and diversities were low (H'<1.0). Based on importance value indexes, the dominant plants were creosotebush (Larrea tridentata) and bursage (Ambrosia dumosa), while other species assumed subdominant roles depending on particular sites (f.6., Krameria grayi, Encelia farinosa, Ephedra sp., and various eacti). Analyses were made of .Zn, Cu, B, V, Cr, Cd, Ni, Pb and Sri in samples of plants collected from sites believed to be exposed to < fallout from the station and from more remote control areas. Unusually high levels of Zn, Cu, B, Cd, Ni, Pb and Sn were detected in some V " samples-levels higher than those normally associated with root uptake. These higher levels were measured in samples from both exposed and control areas. Deposition of airborne particulate material including various trace metals was inferred, but the role of emissions from the Mohave Generating Station vis k vis other sources was not determined. Amounts of trace metals measured at sites along Route 77 and 68 were not obviously correlated with deposition rates predicted by an atmospheric transport model, but the number of samples considered was small.