Investigation of reservoir age variations in Lake Druksiai caused by anthropogenic factors

The reservoir effect (RE) is defined as the difference between the radiocarbon isotope ratio (¹⁴C/¹²C) in the terrestrial and aquatic samples. Both natural processes and anthropogenic activities affecting carbon cycle in the water ecosystem can lead to changes in the RE. Therefore, reservoir effect studies can help to assess the impact of external factors on a hydrological system [1].

The aim of this research was to evaluate the impact of anthropogenic ¹⁴C contamination from Ignalina nuclear power plant (Ignalina NPP, INPP) on the Lake Drūkšiai system. The lake water was used to cool the reactors of the INPP. The lake sediment and fish (both benthic and pelagic) scale samples were collected from the Drūkšiai lake. ABA (acid-base-acid) chemical pretreatment procedure was used to extract humin (HM) and humic acid (HA) fractions from the sediments. Radiocarbon measurements in these samples were performed using the accelerator mass spectrometer (AMS).

In 1963, increased concentrations of radiocarbon due to the testing of nuclear weapons showed that atmosphere-lake CO₂ exchange accounted for about 22% carbon in bottom sediments. During the first 15 years of operation of the Ignalina Nuclear Power Plant, ¹⁴C-enriched dissolved inorganic carbon (DIC) was continuously released into Lake Druksiai. During that period, an average of about 0.24 GBq of radiocarbon was released per year. Measurements of radiocarbon concentrations in fish confirm that the ¹⁴C contamination was in dissolved inorganic form.

Around 2000, ¹⁴C-enriched DIC (2.3 GBq radiocarbon) was released into Lake Druksiai from Ignalina NPP. In addition, organic compounds were additionally released in the same year. These compounds were not ¹⁴C-enriched but affected the interaction between humic and humic acids. Almost a decade after the end of operation of the Ignalina NPP, there is still some ¹⁴C pollution (from INPP) remaining in Lake Druksiai. The concentration of radiocarbon in the bottom sediments is still higher than in the atmosphere. 

 

[1] R. Barisevičiūtė et al., Tracing Carbon Isotope Variations in Lake Sediments Caused by Environmental Factors During the Past Century: A Case Study of Lake Tapeliai, Lithuania, Radiocarbon 61(4), 885–903, (2019).