RATIOS IN TRANS URANIC ELEMENT STUDIES 203 



The second advantage to the multivariate approach is that it can explain the 

 variability in the ratios. A large ratio can be caused by either a large numerator or a small 

 denominator and a small ratio by the converse. The uncritical use of ratios can obscure 

 information. For example, the apparently strong trend of increasing ratio with increasing 

 distance in Fig. 11 is, in part, due to the two samples at 273 and 306 ft, for which the 

 vegetation concentration is larger than the soil concentration. Admittedly these anomalies 

 may be traceable to the near background levels of ^ ^^ U at greater distances from GZ, but 

 this example illustrates the need for caution when using ratios as input to further 

 statistical analyses. 



Profile Analysis 



In this example a technique called profile analysis by Morrison (1967, pp. 186-197) is 

 used to compare inventory ratios (IR) between ecosystem components at several sites. 

 The elements of the profile are ^^^Pu standing crops in the various ecosystem 

 components at one location. Comparative studies of radionuclide inventories in 

 ecosystems are often based on models such as the simple three-compartment one 

 illustrated in Fig, 12. The box-and-arrow model represents the aboveground components 



Fig. 12 Simple three-compartment model of aboveground components of herbaceous 

 plant community. 



of a herbaceous plant community on an abandoned field. The boxes denote ecosystem 

 compartments (resuspendible surface materials, live vegetation, and Utter), and the arrows 

 denote fluxes of ^^^Pu. Inputs to the model (arrows entering the larger dashed box) 

 represent aerial deposition of ^^^Pu from a reprocessing facility. Outputs (arrows exiting 

 the dashed box) represent either wind dispersal of resuspended ^^^Pu or ^■^^Pu 

 incorporated into the soil. Other potentially important compartments and fluxes have 

 been omitted for simplicity. Resuspendibles are those materials which can be resuspended 

 into the atmosphere by a 6 m/sec wind velocity at ground level (McLendon et al., 1976). 

 The question often asked is whether the radionuclide distribution among compart- 

 ments is the same at each site aUhough the amount of radionuclide per unit area may 

 differ between sites. The question can be stated another way: Are the IR's of the amount 



