Terrestrial invertebrate population studies in the Chernobyl exclusion zone, Ukraine

Abstract

The Chernobyl reactor accident in April 1986 released some 3-6.10⁵ TBq ¹³⁷Cs and 2-4.10⁵ TBq ⁹⁰Sr to atmosphere. About half of this was deposited within 20 km of the site, leading to extensive death of trees and other biota, and the establishment of a human exclusion zone. High levels of contamination remain in this zone. Nonetheless, birch (Betula spp.) and willow (Salix spp.) have recolonised the forest areas, while abandoned agricultural land has succeeded to tall grassland and scrub. This study summarises observations on invertebrate populations in sites with gamma dose rates varying from 0.1 to 140 μSv h^-1. Corresponding activity concentrations were 3.10³ to 3.10⁶ Bq kg^-1 dw ¹³⁷Cs and 10³ to 2.106 Bq kg^-1 dw ⁹⁰Sr in the top 5 cm of soil. Sub-surface bait lamina penetration decreases with increasing concentrations of ¹³⁷Cs and ⁹⁰Sr in soil. At the highest levels of contamination there is also some loss of above-ground invertebrate diversity; although little change in total biomass. Trials on earthworms in soils from the region and matched soils spiked in the laboratory have proved variable. However, there is a non-significant indication of depressed growth rates in all contaminated regimes compared to control populations.