Long-Term Trends of Radiocesium Activity Concentrations in Vegetation in Irish Semi-Natural Ecosystems

Abstract

137Cs 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 137Cs activity concentrations. A general decline in the 137Cs activity concentrations in vegetation was observed from all sites sampled. The fastest and most consistent long-term rates of 137Cs decline were observed in the bryophyte and lichen vegetation group with 137Cs 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 137Cs activity concentrations with T ef values of 3.5 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 137Cs decline, with T ef values of 2.9 to 59.8 y. Preliminary evaluation of 137Cs activity concentrations in sheep from some of the studied sites suggests that the decline found in vegetation is reflected in sheep.

Chernobyl radioactivity persists in reindeer

“…In Cetraria nivalis, Cladonia mitis and C. stellaris sampled in the Rondane and Dovrefjell mountains in southern Norway during the period 1987e1999, 137 Cs concentrations decreased with half-times of about 3.4e7.2, 5.2 and 3.6e6.4 years, respectively (Gaare et al, 2000). These halftime values are comparable to other estimates for lichens following fallout from the nuclear weapons tests as well as the Chernobyl fallout (see for instance summary by Synnott et al (2000)). …”

“…Andersson et al (2001) estimated the half-time in composite herbage samples 60e80 km south-east of Østre Namdal to be about 7 years during the period 1990e 1997, while samples of Carex, Betula and Salix had relatively unaltered concentrations. In Irish blanket bog ecosystems radiocaesium concentrations decreased significantly during 1989e1997 in 26 out of 36 plant/site combinations (Synnott et al, 2000): estimated effective half-times for Vaccinium myrtillus were 3.6e6.2 years, Eriophorum angustifolium 2.9e22.0 years and Eriophorum vaginatum 11.2e17.7 years. Plants in the sedge and grass groups had slowest and least consistent rates of 137 Cs decline (Synnott et al, 2000).…”

“…In Irish blanket bog ecosystems radiocaesium concentrations decreased significantly during 1989e1997 in 26 out of 36 plant/site combinations (Synnott et al, 2000): estimated effective half-times for Vaccinium myrtillus were 3.6e6.2 years, Eriophorum angustifolium 2.9e22.0 years and Eriophorum vaginatum 11.2e17.7 years. Plants in the sedge and grass groups had slowest and least consistent rates of 137 Cs decline (Synnott et al, 2000).…”

“…However, lichens in Østre Namdal are generally interspersed and covered with other food plants, which probably reduces the grazing pressure on lichen thalli. Furthermore, leached 137 Cs from taller plants and trapped litterfall may have been absorbed by the lichen thalli, resulting in a slower decline in 137 Cs concentrations (as suggested by Synnott et al (2000)). …”

137Cs and 90Sr in live and dead reindeer lichens (genera Cladonia) from the “Kraton-3” underground nuclear explosion site

“…The biological half-times (T bio ) of the airborne radioactive elements in the epigeic (or terricolous, i.e., ground growing) lichens have been estimated to vary widely from about 1 to 17 years, depending on species, contamination source, environmental and ecological conditions (Hanson, 1967;Hanson et al, 1967;Lidén and Gustafsson, 1967;Miettinen, 1967;Miettinen and Häsänen, 1967;Mattsson, 1975a;Ellis and Smith, 1987;Eriksson et al, 1991;Roos et al, 1991;Gaare and Staaland, 1994;Heinrich et al, 1999;Synnott et al, 2000;Golikov et al, 2004). Such pronounced interception and retention of airborne radionuclides (especially radiocaesium) in reindeer lichens was explained by (1) a prolonged (tens of years) growth period of these organisms in combination with a slow increase in their biomass (e.g., only 3 mm in thickness annually), (2) a large absorption surface (ten to hundred times that of annual grass crops, per unit dry weight) due to the presence of microscopic mycelium, (3) the internal cycling of radionuclides within the tissues of the lichen, and (4) resorption of contamination from the substrate over which the lichens are growing (Hanson, 1967;Nevstrueva et al, 1967;Ramzaev et al, 1970Ramzaev et al, , 1993Troitskaya et al, 1971;Mattsson, 1975a;Whicker and Pinder, 2002).…”