Transfer of sediment-derived carbon into aquatic plants for ¹⁴C biosphere assessment

Among the released radionuclides from nuclear power plants and radioactive waste repositories, ¹⁴C is of great importance. Continuous discharges of ¹⁴C from nuclear industries, the risk of uncontrolled releases, and possible leaking from facilities may cause a threat to the biosphere. Because of high mobility and a long half-life of ¹⁴C, it has great potential to be released into aquatic ecosystems and to be assimilated by aquatic plants. However, the amount of ¹⁴C incorporated into organic matter and hydrophytes is largely unknown. In this study, the uptake of carbon from sediment into aquatic plants was investigated in a microcosm experiment. The study was carried out based on the natural difference in the isotopic signature of ¹⁴C between the 8000-year-old peat and more enriched sources (water and atmosphere). The two-pool isotope mixing model was applied to determine the relative contribution of each source (sediment vs. air/water) to the hydrophytes. The results indicated the highest contribution of sediment-derived carbon to the free-floating Lemna minor (up to 60%), followed by submerged Littorella uniflora (15-17%) and the emergent species, Stachys palustris and Lysimachia nummularia (up to 10%). Despite the contribution of sediment-derived C to their C source, the hydrophytes incorporated less than 2% of their total C from sediment. The results also indicated the importance of floating plants in more efficient uptake of sediment-derived C available in water column or the air. Furthermore, no significant difference was found in the transfer of sediment-derived C between the roots and the leaves within the species.