Long-term trends of radiocesium activity concentrations in vegetation in Irish semi-natural ecosystems

Cs-137 activity concentrations were determined in vegetation from four Irish blanket bog ecosystems during the summer months of 1989-1997, The dominant and abundant vegetation species were sampled at each site and the data were used to estimate long-term trends of Cs-137 activity concentrations. A general decline in the Cs-137 activity concentrations in vegetation was observed from all sites sampled. The fastest and most consistent long-term rates of Cs-137 decline were observed in the bryophyte and lichen vegetation group with Cs-137 effective half-life (T-ef) values of 2.2 to 10.7 y. The ericoid group with the exception of one case also showed a significant long-term decline in Cs-137 activity concentrations with T-ef values of 35 to 12.4 y as did the rush species Juncus squarrosus (T-ef range 9.3 to 12.8 y). The sedge and grass groups showed the slowest and the least consistent rates of Cs-137 decline, with T-ef values of 2.9 to 59.8 y. Preliminary evaluation of Cs-137 activity concentrations in sheep from some of the studied sites suggests that the decline found in vegetation is reflected in sheep.