Recent atmospheric Pb deposition at a rural site in southern Germany assessed using a peat core and snowpack, and comparison with other archives

Abstract

In a peat bog from Black Forest, Southern Germany, the rate of atmospheric Pb accumulation was quantified using a peat core dated by 210Pb and 14C. The most recent Pb accumulation rate (2.5 mg m−2 y−1) is similar to that obtained from a snowpack on the bog surface, which was sampled during the winter 2002 (1 to 4 mg m−2 y−1). The Pb accumulation rates recorded by the peat during the last 25 yr are also in agreement with published values of direct atmospheric fluxes in Black Forest. These values are 50 to 200 times greater than the “natural” average background rate of atmospheric Pb accumulation (20 μg m−2 y−1) obtained using peat samples from the same bog dating from 3300 to 1300 cal. yr B.C. The isotopic composition of Pb was measured in both the modern and ancient peat samples as well as in the snow samples, and clearly shows that recent inputs are dominated by anthropogenic Pb. The chronology and isotopic composition of atmospheric Pb accumulation recorded by the peat from the Black Forest is similar to the chronologies reported earlier using peat cores from various peat bogs as well as herbarium samples of Sphagnum and point to a common Pb source to the region for the past 150 years. In contrast, Pb contamination occurring before 1850 in southwestern Germany, differs from the record published for Switzerland mainly due to the mining activity in Black Forest. Taken together, the results show that peat cores from ombrotrophic bogs can yield accurate records of atmospheric Pb deposition, provided that the cores are carefully collected, handled, prepared, and analysed using appropriate methods