ECOLOGICAL RELATIONSHIPS OF PLUTONIUM 415 



characteristics of the watershed and the intensity of runoff flow (Purtymun, 1974; 

 Hakonson, Nyhan, and Purtymun, 1976). The dependency of concentrations of 

 suspended sediments and plutonium in runoff on flow rate is indicated in Fig. 3 for one 

 rainstorm runoff event in Mortandad Canyon. Tlie nonlinearity in the curve is due to the 

 relationship of flow rate with the particle size of resuspended material. At flows less than 

 0.25 m^/sec, only the silt— clay size materials were in suspension in the runoff. However, 

 at flows greater than 0.25 m^/sec, coarser sands containing most of the sediment 

 plutonium inventory (Table 5) were resuspended, which resulted in increased suspended 

 sediment and radionucUde concentrations. High flow rates typically occur during the 

 early phases of runoff events at Los Alamos owing to the intense nature and short 

 duration of area rainstorms. We found that nearly 80% of the sediment and 70% of the 

 radioactivity was transported within the first half of such events. 



Additionally, there was a highly significant (P < 0.01 ) relationship between sus- 

 pended sediment and radionuclide concentrations in runoff water. About 99% of the 

 radioactivity in runoff was associated with suspended sediments greater than 0.45 /um in 

 diameter, whereas only 1% of the radioactivity in the liquid phase was associated with 

 sediments less than 0.45 jum in diameter. 



6600 



0.10 



0.15 0.20 0.25 



FLOW RATE, m^/sec 



0.35 



Fig. 3 Concentration of sediment and radioactivity in unfiltered runoff water from 

 Mortandad Canyon as a function of runoff flow rate. 



