210Pb, 137Cs and 239Pu profiles in ombrotrophic peat

210Pb, 137Cs and 239Pu determinations from recent ombrotrophic peat profiles from two sites, Lough Fea Bog, Co. Tyrone, N. Ireland and Bolton Fell Moss, Cumbria, England are reported and discussed. 137Cs profiles reflect both active uptake by contemporary living plants and downward diffusion in the peat. They therefore appear to be of no chronological value. At least at Bolton FEll Moss, 210Pb profiles appear to be affected by sub-lateral and therefore possibly downward mobility of unsupported 210Pb in the peat. They appear to underestimate true age in at least one of the profiles analysed. The 210Pb derived dates appear to come closest to conforming with independent estimates of age based on pollen-analytical evidence, in the more waterlogged microenvironments on the mire surface, though the full effects on the mobility of unsupported 210Pb of regional climate, bog hydrology and peat compaction and humification remain to be evaluated. Comparison of 239Pu and 210Pb derived dates for near surface peat suggest that the clear sub-surface peak in the concentration of fall-out plutonium may pre-date the true 1963 level in the peat. (author)