Radioecology of natural systems in Colorado. Thirteenth technical progress report, May 1, 1974--April 30, 1975

Progress is reported on studies on the behavior of fallout radionuclides (137Cs and 90Sr) in selected organisms and natural ecosystems in Colorado. Components of alpine tundra, montane forests, shortgrass plains, and freshwater lakes and streams are currently under investigation. A study on the effect of gut passage on the mean diameter of monodisperse PuO2 microspheres was initiated. Studies on plutonium in the terrestrial environs of Rocky Flats were initiated in the summer of 1972. Soil movement measurements were conducted to bear on the question of plutonium stability in contaminated areas. The relative importance of root uptake versus aerial deposition was evaluated in the field utilizing a sod block transplant procedure. The study on radiation effects on shortgrass plains vegetation was continued with emphasis on long-term changes in community structure under chronic irradiation stress and recovery patterns. (U.S.)