A long-term study of catchment inputs of 137Cs to a subalpine lake in the form of allochthonous terrestrial plant material

Abstract

The input of allochthonous plant material, largely terrestrial in origin, during the spring spate is a major source of primary production for montane lake ecosystems such as Ovre Heimdalsvatn and is readily incorporated into the food chain leading to fish. The transport from the lake catchment of allochthonous plant material contaminated with Chernobyl 137Cs in 1986 was investigated from 1989 to 2008. 137Cs activity concentrations were determined for both total samples before sorting and for the separate components in the two main tributary streams, Brurskardbekken and Lektorbekken, as well as the outflow river, Hinogla. The total samples showed a similar long-term decline at all sites, although 137Cs activity concentrations were generally somewhat higher in Hinogla compared to the tributary streams. For the total samples, ecological half-lives were in the region of 4–5 years. However, there were major differences between components. The 137Cs activity content of most components, including mosses, leaves of willow and woody material, decreased significantly over time. Lichens and juniper declined, but the relationship was not significant, while leaves of mountain birch and dwarf birch showed no obvious trend over the 20-year period.