Radiation or human intrusion: which factor is the more clear and present danger for animals near Chernobyl?

In a time when countries are looking for any replacement for fossil fuels that are dwindling in supply and isolated to geopolitically unstable regions, nuclear power is an appealing alternative. Despite the huge capital to build a nuclear power plant, the station only requires cheap fuel and limited maintenance once up and running. The radioactive waste does not contribute to global warming, unlike fossil fuels, and some government agencies foresee nuclear energy growth as a requirement for any low-carbon energy future.

But what of the environmental risks: the low-probability, extremely high-risk chance of meltdowns and widespread radiation? Accidents at Fukushima and Chernobyl dramatically sway public opinion away from nuclear options. Chernobyl, in particular, conjures images of a radiation-touched wasteland scattered with crumpled, leafless trees still in the silence of a swath of land devoid of life. At least that's been my fantastical impression of the area surrounding the reactor since I first learned of the disaster as a child.

It turns out this may not be the truth. New research¹ out of Belarus contradicts previous research and common opinion that the region around Chernobyl has never regained its pre-accident levels of wildlife. In fact, the exact opposite may be true, implying conclusions about just what is the most prominent environmental pressure preventing vibrant and diverse ecosystems.

Without a doubt, the Chernobyl accident was a humanitarian, ecological, and economic disaster: 31 casualties, uncounted cancer incidents, and over 10 billion dollars required for recovery.² Within the first six months after the accident, massive levels of radiation suppressed the reproductive ability of deer, wolves, and fox in the area, leading to reduced population levels.³ But what about the long-term effects of the disaster on animal abundance in the region? Has the wildlife never recovered?

To answer this question, the researchers measured population density by counting the number of animal tracks per 10 kilometers along well-known travel routes within the exclusion zone in Belarus. This accounts for about half of the total contaminated area and contains radiation levels similar to the rest of the exclusion zone in Ukraine.

The scientists posed three primary questions to test the radiation-animal abundance connection:

1) Are radiation levels in contaminated zones correlated with animal population density?

The answer is a resounding no. No correlation exists between radiocaesium contamination density and the mean number of tracks per 10 km for elk, wolf, boar, deer, or fox. It is true that track density does not directly measure reproductive success or individual animal longevity, both of which could be affected by chronic radiation. But if these latter variables were decreased while population density remained constant, this would mean that animals from outside the contamination zone were continually entering the exclusion zone to keep the mean number of tracks high. This seems highly unlikely.

This surprising finding does fly in the face of previous research that did find a negative association between radiation levels and population density. However, the earlier work assessed only 1/20^th of the animal routes examined in the new study, and also considered only one time point. In contrast, the present work provides a longitudinal view over 2-3 years.

2) Are mammal densities in the contaminated zones less than those in nearby uncontaminated reserves?

No difference in population levels were found between the contaminated and uncontaminated regions, which were natural preserves established a little distance away from Chernobyl. Deer, fox, and wolves seem to be thriving whether closer or far from the reactor site. This is an especially helpful comparison to make because the same dependent variable is measured in both regions - track density - avoiding the sticky questions in 1) about whether reproductive success or longevity are properly accounted for.

3) Has the density of mammals in the contaminated region decreased over the decade since the accident?

Again, no! Even more surprisingly, wild boar, deer, and elk population levels all increased over the 10 years after the meltdown. Wolf populations increased seven times compared to pre-accident levels!

In summary, chronic radiation over the 30 years since the meltdown has had no negative effects on wildlife population levels around Chernobyl. It is known that extremely high radiation six months after the accident did reduce reproductive success and suppress population levels. But long-term negative effects are non-existent; in fact, the accident has done more good than harm, if 'good' is measured by an increase in population density.

So what changed? While there could be several variables at play here, the most obvious is the exodus of all humans from the 4000 square kilometers around the reactor after the meltdown. Without the pressures of hunting, agriculture, and lumber industries, the animals may have found a return to an ecosystem infused with radiation but also free of a more dangerous factor: humans. This explanation seems especially applicable to the sevenfold increase in wolves since the accident.

This is only speculation at this point - the study cannot directly connect the effect of population density increases to the cause of human vacancy. But the evidence does demonstrate the robust resilience of animals to chronic radiation, and the dramatic dismissal of humans from the area cannot be dismissed when considering the burgeoning ecosystem surrounding the nuclear reactor over the past decade. So what is the worse stressor for animals: radiation or human activities continually closing in on habitats and hunting grounds?

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