Tree rings as Pb pollution archives? A comparison of Pb-206/Pb-207 isotope ratios in pine and other environmental media

Abstract

Tree rings, if validated as an environmental archive for pollution, would provide a convenient, geographically widespread archive for studying the temporal and spatial distribution of atmospheric pollutants. We collected tree-ring records from Scots pine (Pinus sylvestris L.), ranging in age from 100 to 300 years and from one spruce (Picea abies), from sites in southern and northern Sweden and analyzed their stable lead isotopic composition (Pb-206/Pb-207). These results are compared to the Pb isotopic composition in soil profiles from each of the sites and temporal changes in the Pb-206/Pb-207 ratio in peat and lake sediment deposits in Sweden. The mineral soils at each site are characterized by high Pb-206/Pb-207 ratios ( > 1.35), while the ratios in the mor layer are low (1.14-1.16) and characterized by atmospheric lead pollution. The Pb-206/Pb-207 ratios of the tree rings, typically approximately 1.18-1.20, indicate a significant (10-30%) contribution of Pb derived from the underlying mineral soil. While peat and lake sediment records show that the Pb-206/Pb-207 ratio of atmospheric deposition has varied over time, with a pronounced trough between approximately 1930 and 1990, the tree rings show no similar trend. Further comparison of published Pb isotope data from other tree-ring records with time series from peat bogs and herbarium samples also shows poor agreement, and indicates that tree rings always contain a mixture of pollution Pb and Pb from the underlying mineral soil. The majority of Pb in the wood is derived from atmospheric pollution either directly, through aerial interception, or indirectly, through uptake from the large pool of accumulated pollution Pb in the soil. Since the Pb isotope ratios of the wood indicate that some natural Pb is taken up into the tree, then it must also be concluded that some fraction of the pollution Pb in the wood is likewise taken up from the forest soil. Based on the Pb isotope analyses, we can only conclude that dendrochemical records are not useful in temporal studies of metal pollution. (C) 2003 Elsevier B.V. All rights reserved

Published in

Science of the Total Environment
2004, Volume: 319, number: 1-3, pages: 173-183 Publisher: ELSEVIER SCIENCE BV

SLU Authors

• Emteryd, Ove

  • Department of Forest Ecology, Swedish University of Agricultural Sciences
    

UKÄ Subject classification

Environmental Sciences related to Agriculture and Land-use


Publication identifier

DOI: https://doi.org/10.1016/S0048-9697(03)00397-8

Permanent link to this page (URI)

https://res.slu.se/id/publ/3625