Wildfires in the Chornobyl Exclusion Zone

Wildfires are an annual event in the Chornobyl Exclusion Zone (CEZ), with more than 1250 fires recorded between 1993 and 2014 in the Ukrainian CEZ. Severe and acute radiation from the Chornobyl accident killed most coniferous trees in an area of approximately 4-6 km2 to the west of the power plant. This area, now known as the 'Red Forest', subsequently partially regenerated with understory vegetation and deciduous trees. In July 2016, a fire burnt c.80% of the Red Forest presenting a unique opportunity to study the effect of fire on radionuclide biogeochemistry and the impact of radiation on the recovery of forest ecosystems exposed to a secondary stressor (fire). In early April 2020, fires started to burn in the Ukrainian CEZ and eventually spread over the subsequent month to become the largest wildfire in the 34-year history of the CEZ. The total area burnt has been estimated to be 870 km2 or about one-third of the land area of the Ukrainian CEZ. This presentation will discuss the results of our studies following both of these major fire events. In autumn 2016 we established 60 study plots in the Red Forest incorporating burnt and unburnt areas; control plots (n=9) were also established in a deciduous woodland approximately 4.5 km to the west of the Red Forest study area. Over the next year, we monitored changes in soil biological activity (using ‘bait lamina’ sticks); soil biological activity data for many of the plots were available from before the fire. Over the period September 2016 to September 2017 motion activated cameras (n=21) were established across the Red Forest to capture information on the presence of medium-large mammal species. Data from a preceding motion-activated camera study at sites across the Chornobyl Exclusion Zone (https://tree.ceh.ac.uk/content/exposure-uncertainty) are available for comparison to the Red Forest observations. To study small mammals, trapping grids were established at eight sites (including burnt and unburnt sites) in the Red Forest during summer 2018. Results (trapping success and number of species) from the Red Forest trapping study can be compared to historical data held by Chornobyl Center. There is the possibility that a fire in a contaminated area, such as the Red Forest, could change the bioavailability of radionuclides in the ecosystem. Samples of ash and soil were subjected to extractions to determine the likely contribution of ash to readily available pools of Sr-90 and Cs-137. There has previously been concern over likely inhalation doses to people as a consequence of fires in the Chornobyl Exclusion Zone. We will present dose estimates for the 2020 fires to firefighters and local population.