Insect-Vegetation Relationships in an Area Contaminated by Radioactive Wastes

Abstract

The development of insect populations on vegetation growing on White Oak Lake bed was followed for 3 years (1956 to 1958), immediately following the draining at White Oak Lake. This lake had served as a final holding basin for Oak Ridge National Laboratory's low-level wastes, and the alluvial terrain exposed upon drainage contained significant concentrations of radioisotopes, including Sr/sup 90/ and Cs/sup 137/. The insect biomass, estimated by sweep-net and box-trap methods, was about 200 to 300 mg/m/sup 2/. No change could be demonstrated during the seasons, and evidently little change occurred between years. Significant concentrations of both Sr9O and Cs/sup 137/ were found in samples of herbivorous insects. Concentrations of Sr/sup 99/ were about 25% of the soil values, and Cs/sup 137/ concentrations were about 1% of the soil values. However, the biomass of insects was minute compared to plant and soil masses, and the herbivorous insects contained but a minute fraction of the fission products in the system, since the bulk of these radioisotopes is in the soil. A sizeable fraction of the materials taken up by plants, however, may pass through the herbivorous insects in the system. Insect populations were followed in 2 areas each of smartweed,more » sedge-rush, and willow vegetation. Each of the vegetation types acquired its own characteristic insects. First-year insect populations tended to be dominated by one or a few species represented by many individuals. The second-year populations showed a reduction in numbers for the dominant species and an influx of additional species, accompanying an increase in plant diversity. No such reduction of the dominant species occurred in the willow areas, presumably because the willows were increasing their coverage each year, and additional species of plants were not invading the willow stands. (auth)« less