High Variability of the Metal Content of Tree Growth Rings as Measured by Synchrotron Micro X-Ray Fluorescence Spectrometry

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Synchrotron radiation analysis was used to investigate the metal content of tree rings collected from paper birch, Betula papyrifera Marsh, on transects downwind from two metal smelters (nickel and copper). Individual trees reflected changes in ring metal content with time, which may be presumed to represent changes in local metal bioavailability. However, between-tree variations were large and no statistically significant differences in metal content as a function of time were found within or between sites. Although concentrations of both total and exchangeable copper and nickel in the soil increased with proximity to the respective smelter, this pattern was reflected only in the nickel content of rings near the nickel smelter; copper content did not vary with distance from either smelter. The sites did differ with respect to lead, manganese and zinc content of the rings, which may be related to pH. In conclusion, the variability between trees at each site suggests that dendroanalysis is a poor method for evaluating metal exposure at a large (site) scale. Tree ring metal content may be used to evaluate the metal uptake by individual trees but metal mobility in the stem makes it difficult to establish a reliable chronology.



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