One advantage of natural tracers is their tendency to "average" out 

 short-term trends and provide qualitatively accurate historical background 

 information on transport. Their use requires a minimum amount of field 

 work and a minimum number of technical personnel. Disadvantages include 

 the irregularity of their occurrence, the difficulty in distinguishing the 

 tracer from the sediment itself, and a lack of quantitative control on 

 rates of injection. In addition, natural tracers are unable to reveal 

 short-term changes in the direction of transport and changes in material 

 sources. 



Judge (1970) found that heavy mineral studies were unsatisfactory as 

 indicators of the direction of longshore transport for beaches between 

 Point Conception and Ventura, California, because of the lack of unique 

 mineral species and the lack of distinct longshore trends which could be 

 used to identify source areas. North of Point Conception, grain size and 

 heavy mineral distribution indicated a net southward movement. Cherry 

 (1965) concluded that the use of heavy minerals as an indicator of the 

 direction of coastal sand movement north of Drakes Bay, California was 

 generally successful. 



b. Artificial Tracers . Artificial tracers may be grouped into two 

 general categories: radioactive or nonradioactive. In either case, the 

 tracers represent particles that are placed in an environment selected 

 for study, and are used for relatively short-term studies of sediment 

 dispersion. 



While particular experiments employ specific sampling methods and 

 operational characteristics, there are basic elements in all tracing 

 studies. These are: selection of a suitable tracer material, tagging 

 the particle, placing the particle in the environment, and detection of 

 the particle. 



Colored glass, brick fragments and oolitic grains are a few examples 

 of nonradioactive particles that have been used as tracers. The most com- 

 monly used stable tracer is made by coating indigenous grains with bright 

 colored paint or flourescent dye. (Yasso, 1962; Ingle, 1966; Stuvier and 

 Purpura, 1968; Kidson and Carr, 1962; and Teleki, 1966.) The dyes make 

 the grains readily distinguishable among large sample quantities, but do 

 not significantly alter the physical properties of the grains. The dyes 

 must be durable enough to withstand short-term abrasion. The use of paints 

 and dyes as tracer materials offers advantages over radioactive methods in 

 that they require less sophisticated equipment to tag and detect the grains, 

 and do not require licensing or the same degree of safety precautions. How- 

 ever, less information is obtained for the same costs, and generally in a 

 less timely matter. 



When using nonradioactive tracers, samples must be collected and 

 removed from the environment to be analyzed later by physically counting 

 the grains. For fluorescent dyes and paints, the collected samples are 

 viewed under an ultraviolet lamp and the coated grains counted. 



For radioactive tracer methods, the tracer may be radioactive at the 

 time of injection or it may be a stable isotope capable of being detected 

 by activation after sampling. The tracer in the grains may be introduced 



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