Responses of an arthropod community to beta and gamma radiation from${}^{137}{\rm Cs}\text{-tagged}$ simulated fallout and the interaction of radiation with other environment parameters are being investigated in a unique experimental facility at Oak Ridge National Laboratory. Lithium fluoride microdosimeters attached to the thorax and abdomen of insects in a fallout field indicate that closely related organisms may receive significantly different doses owing to differences in habitat or behavior. Significant differences in variation between control and contaminated communities appeared in summer 1970 (P ≤ 0.05), disappeared in autumn 1970, and reappeared in summer 1971 (P ≤ 0.01). Population densities of four arthropod taxa had been significantly (P ≤ 0.05) reduced by summer 1970. By summer 1971, three of these taxa had recovered to control levels, but four additional taxa underwent significant (P ≤ 0.05) reductions in population density. This number of affected populations is not statistically significant. No significant increase in dissimilarity in taxa composition between the contaminated and control areas was evident. Consequently, the threshold for long-term effects of fallout radiation on taxa comprising the arthropod community appears to be above the 2.4-13.0 rads/day exposure over the 3-year period.

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