374 TRANSURANIC ELEMENTS IN THE ENVIRONMENT 



TABLE 2 Estimates of Mass of the Major 



Components of the Oak Ridge Floodplain and the 



Los Alamos Mortandad Canyon 



*Mass is based on a profile depth of 20 cm and on 

 densities of 1.3 and 1.2 g/cm^ for Oak Ridge and Los 

 Alamos, respectively. 



t Estimated from mensuration data and regression 

 equations (Harris, Goldstein, and Henderson, 1973). 



^Estimated from mensuration data and regression 

 equations (Wheeler, Smith, and Gallegos, 1977). 



§ Estimated from field measurements of populations and 

 biomass. 



floods on litter accumulation; and (3) moist-mesic conditions, which favor rapid 

 decomposition. 



Soil and Biotic Characteristics of Mortandad Canyon 



The canyon soil consists of an alluvial deposit (<30 cm) derived from volcanic tuff. The 

 coarse soil is less than 3% by weight silt and clay (Nyhan, Miera, and Peters, 1976a). 

 Cation-exchange capacity is low (2 to 20 meq per 100 g) (Schiager and Apt, 1974). 

 Organic matter ranges from 0.1 to 0.2%. Calcium as high as 3.7% and soil pH up to 9.2 

 are measurable (Scliiager and Apt, 1974), which reflects the carbonate contribution from 

 liquid waste. Uncontaminated soil from the canyon floor has a pH of 5.7. 



The dominant arborescent species of the canyon are ponderosa pine (Pinus 

 ponderosa), Douglas fir (Pseudotsuga menzeziij, and Gambels oak (Quercus gambelii) 

 (Miera et al., 1977). Dominant forb and grass species are wheat grass (Elymus sp.), 

 bluegrass (Poa pratensis), wild strawberry (Fragaria americana), and dandelion (Taraxa- 

 cum officinale). The most common mammal residents are pinon mouse (Peromyscus 

 tniei), deer mouse (P. maniculatus), and the least chipmunk (Eutamias minimus). 



Standing-crop biomass [grams (dry weight)] for arborescent, herbaceous, and animal 

 components of the floodplain and canyon ecosystems is shown in Table 2. Arborescent 

 species contribute more than 80% of the total mass at the site. 



Characteristics of Plutonium in the Floodplain Soil 



Concentration of plutonium in the floodplain soil ranges from about 10 to 150 pCi/g over 

 a 3-ha area (Fig. 1). The highest concentrations were found behind the former dike, along 



