Long-term changes in ⁹⁰Sr pools of Scots pine biomass in the Chornobyl Red Forest

The trenches of the waste burial site in the Chornobyl Red Forest represent a big reservoir of radionuclides for the artificial plantation of Scots pine established in that area, but the long term dynamics of tree biomass contamination, especially with ⁹⁰Sr, remains unclear. The present study was conducted between 2005 and 2018 on two groups of trees of the same age. The IN group is represented by trees growing on the trench containing highly radioactive contaminated fertile soil and organic matter, while the OUT group is located outside the trench. Within a little more than one decade, the total aboveground biomass doubled in the trees of the group OUT and increased more than four times in the group IN. In the group OUT, the concentrations of ⁹⁰Sr have decreased in all biomass compartments compared to 2005, while in the group IN, the concentrations demonstrated a trend to increase. Regression analysis shows that both decrease in the compartment concentrations in the group OUT (slope coefficient 0.55) and increase in the group IN (1.58) were significant. As a result of the changes in the biomass inventories and ⁹⁰Sr concentrations, in absence of changes in plantation density, the contamination of total aboveground biomass by ⁹⁰Sr in the group OUT would have increased slightly in 2018 (from approximately 18 GBq ha^-1 to 23 GBq ha^-1) compared to 2005, while in the group IN it would have increased almost 6-fold, reaching approximately 560 GBq ha^-1, or about (19 ± 9) % of the total ⁹⁰Sr inventory in the trench area. Trenches of the Red Forest were shown to act as long-lasting hot spots of ⁹⁰Sr bioavailability for forest trees.