Use of a satellite-derived land cover map to estimate transport of radiocaesium to surface waters

During the weeks to months after the deposition of radioactive fallout, the initial concentration of radioactivity in rivers and lakes declines as a result of flushing and removal to bottom sediments. In the long-term, however, radioactivity in the water body can remain at significant levels as a result of secondary contamination processes. In particular, it is known that soils contaminated by long-lived radionuclides such as 137Cs and 90Sr provide a significant source to surface waters over a period of years after fallout. Using The Land Cover Map of Great Britain, a satellite-derived land cover map as a surrogate indicator of soil type, we have related catchment land cover type to long-term 137Cs activity concentrations in 27 lakes in Cumbria, UK. The study has shown that satellite-derived maps could be used to indicate areas vulnerable to high long-term 137Cs transport to surface waters in the event of a nuclear accident. In these Cumbrian lakes, it appears that residual 137Cs levels are determined by transfers of 137Cs from contaminated catchments rather than within-lake processes. Only three of the cover types, open shrub moor, bog and dense shrub moor, as identified by the satellite, are needed to explain over 90% of the variation in long-term 137Cs activity concentrations in the lakes, and these have been shown to correlate spatially with occurrence of organic soils.