Ecological half-times of ¹³⁷Cs and ⁹⁰Sr in forest and freshwater ecosystems

Abstract

More than 200 data sets from the literature of measured time series of activity concentrations and transfer factors concerning: (1) soil, green plants, mushrooms, and game in forests and (2) water, particulate matter, and fish in rivers, reservoirs and lakes in Europe have been analyzed. We used a sum of up to 3 exponential functions to evaluate ecological half-times (T$_{\scriptsize\textrm{eco}}$). In fresh water systems we fitted lognormal distributions of T$_{\scriptsize\textrm{eco}}$ for ¹³⁷Cs (e.g. in the water of 32 European lakes, T$_{\scriptsize\textrm{eco}1}$ = (0.3*2.2$^{\pm 1}$) years and T$_{\scriptsize\textrm{eco}2}$ = (5.7*3.9$^{\pm 1}$) years as geometric mean value and standard deviation). Pronounced seasonal variations were observed in suspended matter of Lake Lugano, reflecting the bio-mass cycle of this lake. In forests, ecological half-times for ¹³⁷Cs can also be fitted by a lognormal distribution. For Central Europe T$_{\scriptsize\textrm{eco}}\:<$ 12 years. Extraordinarily high ¹³⁷Cs activity concentrations were observed recently in wild boar in Germany. For Eastern Europe the physical half-time is dominant and in some components of the ecosystem the activity concentration is still increasing.