Radiating wildlife: the resurgence of biodiversity in the Chernobyl exclusion zone

The Disaster

As the worst nuclear disaster in all of history, the meltdown and subsequent explosion of reactor four at Chernobyl nuclear power plant on 26th April, 1986 caused widespread irradiation of the surrounding area. The fallout from the ejected nuclear matter affected wildlife as far as Rome and Sweden, and even today there is a 4,200km2 exclusion zone, from which 116,000 people were initially evacuated. Radiation levels were between 40 and 100 times higher than background levels, and the area is thought to be uninhabitable for at least the next 20,000 years.

chernobyl map

Figure 1: Map showing the extend of radiation spread and caesium deposition after the disaster. The effects were widespread across most of the continent. Caesium deposition is measured in kilobecquerel per meter squared. (Photo: BBC news)

With this in mind, it is hard to see how anything could possibly survive here. If humans cannot survive, surely not much else can. The idea that animal and plant reproduction/survival was being reduced as a result of high levels of radiation was the general consensus amongst the scientific community in the years following the disaster. Now however, there is a growing body of evidence which swings in the opposite direction.

The Comeback

Contrary to the idea that large doses of radiation should prevent an ecosystem from thriving, both animal and plant populations have been shown to stay stable, and in some instances increase in irradiated areas. A previously rare apex predator within the exclusion zone, grey wolf (Canis lupus) numbers have surged by up to 7 times the levels recorded at 4 non-contaminated nature reserves in Belarus (1). Even the Eurasian lynx (Lynx lynx) has increased by 1.3 times. Elk (Cervus canadensis), roe deer (Capreolus capreolus), red deer (Cervus elaphus) and wild boar (Sus scrofa) all have roughly the same relative abundance at the non-contaminated reserves, and within the exclusion zone itself their numbers have increased significantly in the 10 years succeeding the meltdown. The numbers of these large mammals were estimated by aerial survey counts and track counts in the snow. The excessive rise grey wolf numbers is thought to be due to lack of hunting within the exclusion zone, which unfortunately still takes place even in the nature reserves of Belarus.

chernobyl graph

Figure 2: Graph showing the relative abundance of elk, roe deer and wild boar within the exclusion zone. The sharp decrease in wild boar is likely due to the increase in grey wolf and lynx numbers. (Photo: (1))

Similarly, smaller mammals have also been studied and have been found in comparable abundance and species richness between irradiated areas in the exclusion zone and those outside (2). Comparing specimens captured within and outside of the exclusion zone, 355 individuals from 11 species and 224 individuals from 12 species were found respectively.

Arguably more important is the effect upon plant and invertebrate communities, despite their less glamorous image. Both were severely affected in the immediate aftermath, with extremely high mortality rates in pine tress and other plant types, and high rates of mortality and loss of species diversity in invertebrates. However, although it has taken some time, both have recovered remarkably, showcasing the resilience of nature, given half a chance. Invertebrate species diversity has recovered to pre-disaster levels, and although there was mass die off of coniferous pine trees and subsequent shift in vegetation type within the ‘red forest’, even they are now in a state of recovery (3). Due to their longer life span, the rate of recovery is understandably slower than other organisms in the area.

The Message

It should be noted, however, that this success is not necessarily due to a reduced susceptibility to the debilitating effects of radiation. This should not come as a major shock. It has never been claimed that the radiation has no effect upon or that it improves animal/plant fecundity or health directly. Some sources have shown evidence to the contrary, even citing that certain species are in fact in a worse state than before the accident. It has, for example, been shown that species richness and abundance of forest birds in Chernobyl decreases in relation to increasing levels of radiation within the Chernobyl area (4). Barn swallows have also been reported to have reduced reproductive success and survival, and, without migration from other populations outside the exclusion zone, it is unlikely that an effective population size will be maintainable in Chernobyl (5), meaning we may see the loss of them at the site at some point in the future.

Overall, however, many species seem to be surviving, if not thriving. A recent report by the United Nations has concluded that there is an overall increase in various forms of organism across the exclusion zone, including plants, fish, terrestrial animals and invertebrates (3). All of this, whilst exposed to doses of radiation that is in many aspects having a detrimental effect to the health of the organism. And that is the fascinating, and ultimately crucial point – that most of these species are thriving in spite of the environment they are in. And so this once again leads us to point the finger of blame squarely at ourselves, and with renewed ignominy. The fact that many species prefer a radiation rich environment to one containing humans and their collateral effects should speak volumes as to our destructive nature.

References

  1. T. G. Deryabina et al., Long-term census data reveal abundant wildlife populations at Chernobyl. Curr. Biol. 25, R824–R826 (2015).
  2. R. J. Baker et al., Small Mammals from the most Radioactive Sites Near Chernobyl Nuclear Power Plant. J. Mammal. 77, 155–170 (1996).
  3. T. G. Hinton et al., Radiation-induced effects on plants and animals: findings of the United Nations Chernobyl Forum. Health Phys. 93, 427–440 (2007).
  4. a P. Moller, T. a Mousseau, Species richness and abundance of forest birds in relation to radiation at Chernobyl. Biol. Lett. 3, 483–6 (2007).
  5. a. P. Møller et al., Condition, reproduction and survival of barn swallows from Chernobyl. J. Anim. Ecol. 74, 1102–1111 (2005).
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