Lead-210 chronology of the Scandinavian SWAP sites

In the Surface Water Acidification Project (SWAP) sediment profiles from five Scandinavian sites were analysed for 210Pb by using refined isotope dilution alpha spectrometry. The 210Pb parameters of these lakes were very similar to those obtained for protected forest lakes with no land-use activities. These data demonstrated almost exclusive atmospheric inputs and an internal deposition regulated by the organic fractionation and the grain-size distribution in the sediments. Preliminary speciation experiments showed minor losses of 210Pb (≤ 5%) through enhanced dissolution of fulvic compounds at acid conditions (pH ≥ 4). The sediment accumulation rates (constant rate of unsupported 210Pb supply (CRS) model) of the lakes gradually increased, by at least a factor of three, over the past century although 210Pb parameters did not show any strong signs of enhanced land-use activities. This is perhaps caused by more efficient preservation of the sediments through humic precipitation under more acid conditions. (author)