Assessment of 137Cs and 90Sr removal through the system “soil − rhizosphere – above-ground parts of plants” during annual flooding (Yenisei, KMCC near impact zone)

Abstract

The Yenisei floodplain has long been impacted by the Krasnoyarsk Mining and Chemical Combine (KMCC), leading to significant accumulation of ¹³⁷Cs and ⁹⁰Sr isotopes in soils. Floodplain plants, particularly sedges (Carex L.) with root systems 20–40 cm deep, uptake these isotopes from contaminated layers, depositing them in above-ground parts. Annual floods leach isotopes from the “soil – rhizosphere – above-ground parts of plant” system into river water. This study assesses seasonal isotope removal from two model sites from the KMCC near impact zone: Atamanovskaya spit and Balchugovskaya channel, differing in hydrological conditions. The isotope removal calculation used data on isotope activities in system components, percentages of mobile isotope forms in in system components, component mass per area, and area flooded during normal annual flooding. Considered floods are seasonal rises determined by the operation mode of Krasnoyarsk HPP (40–60 cm in April-June; 30–40 cm in September-November), flooding coastal zones. Results show remobilization of 10⁸–10⁹ Bq per season, comparable to KMCC’s annual input into the Yenisei floodplain (10⁷–10⁹ Bq for ¹³⁷Cs; 10⁸–10¹⁰ Bq for ⁹⁰Sr). A quasi-steady state exists between input and output at the two model sites. No statistically significant correlations were found, except a weak negative one for ¹³⁷Cs specific activities (Bq∙kg⁻¹) in the above-ground parts of plants of the head of the Atamanovskaya spit and ¹³⁷Cs annual input into the Yenisei floodplain (Bq) from the KMCC (R² = 0.8251, p = 0.0122, ρ = -0.07). Secondary isotope migration may come not only from annual KMCC input but also from mobilization of previously deposited inventories. Precise quantitative assessment requires further field studies.