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Stars mark sites where the researchers put the leaf bags, with colors corresponding to levels of radiation. Photo: Mousseau et al., Oecologia.
Stars mark sites where the researchers put the leaf bags, with colors corresponding to levels of radiation. Photo: Mousseau et al., Oecologia.
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  • Mousseau distributing leaf baggies throughout Chernobyl's exclusion zones. Photo: Gennadi Milinevsky.
    Mousseau distributing leaf baggies throughout Chernobyl's exclusion zones. Photo: Gennadi Milinevsky.
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Chernobyl's forests - dead wood and leaves preserved by radiation

Rachel Nuwer / Smithsonian

24th March 2014

It's not just people, animals and trees that suffer from radiation at Chernobyl, writes Rachel Nuwer, but also decomposer fungi and microbes. And with the buildup of dead wood comes the risk of catastrophic fire - which could spread radiation far and wide.

The gist of our results was that the radiation inhibited microbial decomposition of the leaf litter on the top layer of the soil

Nearly 30 years have passed since the Chernobyl plant exploded and caused an unprecedented nuclear disaster.

The effects of that catastrophe, however, are still felt today.

Although no people live in the extensive exclusion zones around the epicenter, animals, trees and other plants still show signs of radiation poisoning.

Birds around Chernobyl have significantly smaller brains that those living in non-radiation poisoned areas. Trees there grow slower. And fewer spiders and insects - including bees, butterflies and grasshoppers-live there.

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.

The ecosystem damage goes deep

However, there are even more fundamental issues going on in the environment. 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."

Chernobyl - where even the trees are petrified

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 is radiation responsible?

But this wasn't enough to prove that radiation was responsible for this difference.

To confirm their hunch, they 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.

Where radiation is strongest, leaves decay slowest

The results were telling. In the areas with no radiation, 70% to 90% of the leaves were gone after a year. But in places where more radiation was present, the leaves retained around 60% 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.

Catastrophic fire would redistribute radiation

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.

This poses a more worrying problem than just environmental destruction. Fires can potentially redistribute radioactive contaminants to places outside of the exclusion zone, Mousseau says: "There is growing concern that there could be a catastrophic fire in the coming years."

Unfortunately, there's no obvious solution for the problem at hand, besides the need to keep a stringent eye on the exclusion zone to try to quickly snuff out potential fires that breaks out.

The researchers are also collaborating with teams in Japan, to determine whether or not Fukushima is suffering from a similar microbial dead zone.

 


 

See also: 27 Years Later, Radiation Still Hides Out in Chernobyl's Trees (Fukushima's Too)

Rachel Nuwer writes for Smart News and is a contributing writer in science for Smithsonian.com. She is a freelance science writer based in Brooklyn. Read more of her work. Follow on Twitter: 

This article was originally published by Smithsonian.com. Follow on Twitter @SmithsonianMag.

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