Gerald Matisoff, chair of the department of geological sciences, and Peter Whiting, professor of geological sciences, are both presenting research today at the 2008 Joint Meeting of the Geological Society of America, Soil Science Society of America, American Society of Agronomy, Crop Science Society of America, and Gulf Coast Association of Geological Societies in Houston.
When a reactor in the Chernobyl nuclear power plant exploded in 1986 in what was then the Soviet republic of Ukraine, radioactive elements were released in the air and dispersed over the Soviet Union, Europe and even eastern portions of North America.
More than 20 years later, researchers from Case Western Reserve University traveled to Sweden and Poland to gain insight into the downward migration of Chernobyl-derived radionuclides in the soil. Among the team's findings was the fact that much more plutonium was found in the Swedish soil at a depth that corresponded with the nuclear explosion than that of Poland.
Radionuclides occur in soil both from natural processes and as fallout from nuclear testing.
Gerald Matisoff, chair of the department of geological sciences at Case Western Reserve University, Lauren Vitko, field assistant from Case Western Reserve, and others took soil samples in various locations in the two countries, measuring the presence and location of cesium (137Cs), plutonium (239, 240Pu), and lead (210Pbxs).
Matisoff will present his findings today at the 2008 Joint Meeting of the Geological Society of America, Soil Science Society of America, American Society of Agronomy, Crop Science Society of America, and Gulf Coast Association of Geological Societies in Houston.
By looking at the magnitude of the radioactive fallout, how fast it moved down into the soil profile and how quickly it eroded and is transported by sediment, Matisoff's research helps shed light on two fronts.
The first is dealing with the public health ramifications, studying such issues as food chain transfer, exposure and cleanup as well as understanding the geologic aftereffects. These issues include measuring erosion rates, how long the radionuclides are retained in the watershed, the source of sediment found in rivers as well as compiling radioactive inventories.
The second is developing an understanding of the differentiation of radioactive elements from a one-time event like Chernobyl and those of fallout created by atmospheric nuclear weapons testing conducted in the 1960s.
Soil samples collected by Matisoff's team reveal insights based on several conditions, such as how the radionuclides were delivered to the soil, whether from a one-time event like the Chernobyl disaster or from atmospheric bomb testing; the half-life of the radionuclides and whether they were absorbed more heavily onto clay particles (such as 137Cs and 7Be) or organic materials (239, 240Pu and 210Pbxs); and the types of soil which may keep the particles at the surface or allow them to permeate to levels below the surface.
As the team examined a range of soil types from the two countries, they found a spike in 239, 240Pu in Sweden's soil at a depth that coincides with the Chernobyl disaster, yet no similar blip in Poland's soil. Meteorological research showed that it rained in Sweden while the radioactive cloud was over that country. Leeched of much of its radionuclides, much less plutonium fell on Poland when the cloud later crossed over its borders.
Matisoff says that his team's findings are preliminary, having raised as many questions as they have answered. His goal is to use this research for even bigger projects and greater, more definitive findings.
Funding for the projects was provided by the National Science Foundation.
Sediment in rivers comes from erosion of the landscape as well as the erosion and collapse of the banks themselves. Just how much each source contributes to a river—and how it affects the flow and path of that river—is the subject of research by Peter Whiting, professor of geological sciences at Case Western Reserve University.
Taking measure of certain radionuclides found in the soil, including beryllium and lead, at various points along a 423-km-long section of the Yellowstone River, Whiting has determined how much of the sediment in the Yellowstone came from runoff and how much came from the streambanks. For example, streambank erosion contributes approximately 50 percent of the sediment at measurement sites up-river, increasing to 89 percent at Billings, Mont. In river basins where significant portions of the surrounding landscape are used for agriculture or forestry, the percentage of sediment coming from streambank erosion drops below 50 percent.
Whiting will present his findings today at the 2008 Joint Meeting of the Geological Society of America, Soil Science Society of America, American Society of Agronomy, Crop Science Society of America, and Gulf Coast Association of Geological Societies in Houston.
Radionuclides occur in soil both from natural processes and as fallout from nuclear testing. Beryllium and lead are found in greater concentrations at the surface of the soil. All the beryllium will be found in the top two centimeters of the surface soil but lead will be found to greater depth.
Beryllium and lead have markedly different half-lives. Lead has a 20-year half life, while that of Beryllium is only 53 days. Comparing the activities of both elements in the river’s suspended sediment to the surrounding landscape and streambanks helps provide a detailed profile of where the sediment originates.
"We need to understand the sources of the sediment in our rivers if we want to address stewardship of our rivers," said Whiting.
For instance, fine sediment carried into rivers can cloud the water and can choke out freshwater bugs and fish that require cleaner water. Fine sediment deposited on the stream bottom can smother eggs laid by fish including salmon and walleye. To preserve these populations of fish, we often try to rehabilitate streams by reducing the amount of sediment supplied to the stream. But to try to reduce the supply, and one needs to understand whether it is activities eroding the landscape—urbanization, farming, or timbering—or it is the streambanks that are the primary cause of the problem.
"In using radionuclides as markers in our research, we are helping to develop new tools for the advancement of soil and river stewardship," said Whiting.
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