The Varying Radiocarbon Activity of Some Recent Submerged Estonian Plants Grown in the Early 1990s

Abstract

Eleven samples of aquatic plants from three Estonian lakes were analyzed for their radiocarbon content in a collaboration between the laboratories in Tallinn and Uppsala. delta-13C values for the actual species were compiled to allow normalization of activities measured in Tallinn without delta-13C values. The range for well determined species is usually a few per mil and the statistical uncertainty greater than or equal to 1 per mil delta-13C values vary considerably for different Potamogeton species and Myriophyllum spp. Lake Antu Sinijarv and Lake Päidre are hard-water lakes containing 300 and 200 mg HCO3-/L, respectively. One sample consisted of a carbonate crust deposited on a Ceratophyllum demersum plant in L. Antu Sinijarv. Its Delta-14C value was -147.3 +/6.7 per mil in 1990, whereas the plant had a value of -74.1 +/8.0 per mil (delta-13C = -35.0 per mil). The same species in L. Päidre had a Delta-14C value of +8.0 +/8.8 per mil (delta-13C = -25.2 per mil) in 1992. Other species in L. Päidre contained more 14C, from a Delta-14C value of about +30 per mil to about +155 per mil, the latter value measured in Tallinn on floating leaves of Nuphar lutea, close to that of the contemporaneous atmospheric CO2. In the third lake, Lake Punso, containing >30 mg HCO3-/L, the stems of Nuphar lutea exhibited in 1990 a memory effect: the activity, Delta-14C = 209.6 +/10.3 per mil, significantly exceeded that of the contemporaneous atmospheric CO2. However, the floating leaves of the same plant had the Delta-14C value 143.1 +/10.0 per mil, close to the atmospheric 14C level in 1990. The memory is explained by nutrients stored in the root stock, used when the growth starts.