Dynamics of 137Cs content in higher aquatic plants of Kyiv and Kaniv Reservoirs
Authors: Volkova O. , Belyaev V. , Pryshliak S. , Skyba V. , Prysiazhniuk N. , Nagorniuk O. 
Published: August 2024

The study aimed to determine the temporal parameters of 137Cs specific activity in higher aquatic plants of Kyiv and Kaniv reservoirs. Parameters characterizing the dynamics of 137Cs content for hydrophytes (Potamogeton perfoliatus and Ceratophyllum demersum) and helophytes (Phragmites australis and Typha angustifolia) were determined based on the results of 137Cs specific activity determination in the aboveground plant organs. Plant samples were collected in 1989–2021 from a polygonal area in the upper part of Kyiv reservoir (shallow waters near Strakholyssia village) and in 2000–2021 from a polygonal area in the middle part of the Kaniv reservoir (shallow waters near Rzhyschiv and the Borispol islands). A model of specific activity of aquatic organisms was substantiated (or developed) in case of exponential decrease in radionuclide levels in the environment. The main parameter of the model is the period of resulting halving of organism specific activity due to the decrease in radionuclide concentration in water, its irreversible fixation in bottom sediments, and radioactive decay. During 1989–2021, the half-life period of 137Cs specific activity in Potamogeton perfoliatus, Ceratophyllum demersum, and Phragmites australis of Kyiv reservoir was 5.4 years. Two time intervals were identified, characterized by different intensities of radionuclide specific activity decrease. During the periods of 1989–1996 (1998), the specific activity of 137Cs in the studied plant species decreased by half in approximately 2 years. For the time interval of 2011(2012)–2021, the half-life period of 137Cs content in Potamogeton perfoliatus and Ceratophyllum demersum increased on average to 12 years. A tendency towards a slowdown in the rate of specific activity decrease was observed for Phragmites australis. During 1987–1996, the half-life period of maximum 137Cs specific activity in higher aquatic plants of Kaniv reservoir was 2.1 years. Thus, during the first decade after the accident, the rates of 137Cs content decrease in plants of Kyiv and Kaniv reservoirs did not differ. In 2000–2021, the rate of 137Cs specific activity decrease in Potamogeton perfoliatus and Ceratophyllum demersum of Kaniv reservoir corresponded on average to a half-life period of about 20 years. For Phragmites australis and Typha angustifolia, only a tendency to decrease in 137Cs activity was noted, corresponding to a half-life period of about 40 years. Over time, the half-life period of 137Cs specific activity in higher aquatic plants of Kyiv and Kaniv reservoirs increases, which is explained by the slowdown in the rate of decrease in volumetric activity of 137Cs in the waters of the Dnipro and Pripyat rivers. A model of 137Cs specific activity in higher aquatic plants of reservoirs for periods exceeding 20 years after accidental radionuclide entry into ecosystems of large plain reservoirs has been proposed. The parameters of the model describing the dynamics of 137Cs specific activity can be used for predictive assessments of 137Cs content in higher aquatic plants in the event of accidental radionuclide entry into ecosystems of large plain reservoirs.