The time looks frozen, at Chernobyl. 27 years after the nuclear disaster, trees there grow slower, birds have significantly smaller brains and fewer spiders and insects live the surrounding forests. Additionally, game animals such as wild boar caught outside of the exclusion zone -including some bagged as far away as Germany- continue to show abnormal and dangerous levels of radiation. But there is more. According to a new study published in Oecologia, decomposers—organisms such as microbes, fungi and some types of insects that drive the process of decay—have also suffered from the contamination.
These creatures are responsible for an essential component of any ecosystem: recycling organic matter back into the soil. Issues with such a basic-level process, the authors of the study think, could have compounding effects for the entire ecosystem. The team decided to investigate this question in part because of a peculiar field observation. “We have conducted research in Chernobyl since 1991 and have noticed a significant accumulation of litter over time,” the write. Moreover, trees in the infamous Red Forest—an area where all of the pine trees turned a reddish color and then died shortly after the accident—did not seem to be decaying, even 15 to 20 years after the meltdown. “Apart from a few ants, the dead tree trunks were largely unscathed when we first encountered them,” says Timothy Mousseau, a biologist at the University of South Carolina, Columbia, and lead author of the study. “It was striking, given that in the forests where I live, a fallen tree is mostly sawdust after a decade of lying on the ground.” Wondering whether that seeming increase in dead leaves on the forest floor and those petrified-looking pine trees were indicative of something larger, Mousseau and his colleagues decided to run some field tests. When they measured leaf litter in different parts of the exclusion zones, they found that the litter layer itself was two to three times thicker in the “hottest” areas of Chernobyl, where radiation poisoning was most intense. But this wasn’t enough to prove that radiation was responsible for this difference.
Mousseau and his team created around 600 small mesh bags and stuffed them each with leaves, collected at an uncontaminated site, from one of four different tree species: oak, maple, birch or pine. They took care to ensure that no insects were in the bags at first, and then lined half of them with women’s pantyhose to keep insects from getting in from the outside, unlike the wider mesh-only versions. Like a decomposer Easter egg hunt, they then scattered the bags in numerous locations throughout the exclusion zone, all of which experienced varying degrees of radiation contamination (including no contamination at all). They left the bags and waited for nearly a year—normally, an ample amount of time for microbes, fungi and insects to make short work of dead organic material, and the pantyhose-lined bags could help them assess whether insects or microbes were mainly responsible for breaking down the leaves. The results were telling. In the areas with no radiation, 70 to 90 percent of the leaves were gone after a year. But in places where more radiation was present, the leaves retained around 60 percent of their original weight.
By comparing the mesh with the panty hose-lined bags, they found that insects play a significant role in getting rid of the leaves, but that the microbes and fungi played a much more important role. Because they had so many bags placed in so many different locations, they were able to statistically control for outside factors such as humidity, temperature and forest and soil type to make sure that there wasn’t anything besides radiation levels impacting the leaves’ decomposition. “The gist of our results was that the radiation inhibited microbial decomposition of the leaf litter on the top layer of the soil,” Mousseau says. This means that nutrients aren’t being efficiently returned to the soil, he adds, which could be one of the causes behind the slower rates of tree growth surrounding Chernobyl.
Other studies have found that the Chernobyl area is at risk of fire, and 27 years’ worth of leaf litter, Mousseau and his colleagues think, would likely make a good fuel source for such a forest fire. Fires can potentially redistribute radioactive contaminants to places outside of the exclusion zone.
The researchers are also collaborating with teams in Japan, to determine whether or not Fukushima is suffering from a similar microbial dead zone.