Chernobyl Radiation Slows Decomposition of Vegetation in Red Forest

Mysteriously delayed decomposition of trees, fallen leaves and plant matter in the Red Forest around the site of the 1986 Chernobyl nuclear disaster suggest that the microbes responsible for the breakdown of organic matter in the region have suffered some form of radiological damage, according to new research.

The study, published in the journal Oecologia by Tim Mousseau, a professor of biology and co-director of the Chernobyl and Fukushima Research Initiatives at the University of South Carolina, and Anders Møller of Université Paris-Sud, indicates that the buildup of dry, loose debris poses a wildfire hazard that could threaten to spread radioactivity from the region.

"There's been growing concern by many different groups of the potential for catastrophic forest fires to sweep through this part of the world and redistribute the radioactive contamination that is in the trees and the plant biomass," Mousseau said. "That would end up moving radio-cesium and other contaminants via smoke into populated areas.

When the Chernobyl nuclear facility exploded in the Soviet Union nearly three decades ago, it contaminated a swath of land, and forced an exclusion zone around the fallen reactor. The Red Forest region is the most contaminated part of the Chenobyl nuclear exclusion zone.

"We were stepping over all these dead trees on the ground that had been killed by the initial blast," Mousseau said in a statement. "Some 15 or 20 years later, these tree trunks were in pretty good shape. If a tree had fallen in my backyard, it would be sawdust in 10 years or so."

For their experiment, Mousseau and Møller collected various sorts of uncontaminated leaf litter from pine, oak, maple and birch trees and placed the litter in mesh bags around the forest.

The researchers returned nine months later to assess the decomposition process of the leaves at the different sites, which encompassed a wide range of background radiation doses.

"A statistical analysis of the weight loss of each leaf litter sample after those nine months showed that higher background radiation was associated with less weight loss," the University of South Carolina reported. "The response was proportional to radiation dose, and in the most contaminated regions, the leaf loss was 40 percent less than in control regions in Ukraine with normal background radiation levels."

Additionally, the researchers found that the thickness of the forest floor was greater in places with the highest background radiation, corroborating the evidence that natural decay of organic matter is being slowed by radiation.

The researchers concluded that the bacteria and fungi that decompose plant matter in healthy ecosystems are being hindered by radioactive contamination.

"It's another facet of the impacts of low-dose-rate radioactive contaminants on the broader ecosystem," Mousseau said. "We've looked at many other components, namely the populations of animals in the area, and this was an opportunity for broadening our range of interests to include the plant and microbial communities."

The researchers warn that contaminated plant matter could fuel a wildfire, potentially spreading radioactive material further afield.

"This litter accumulation that we measured, which is likely a direct consequence of reduced microbial decomposing activity, is like kindling," Mousseau said. "It's dry, light and burns quite readily. It adds to the fuel, as well as makes it more likely that catastrophically sized forest fires might start."

Frequent collaborators, Mousseau and Møller released a trio of Chernobyl studies earlier this year, reporting that the nuclear incident has impaired tree growth and the health of birds in and around the region of the Ukraine where the disaster took place.