An evaluation of the use of dendrochemical analyses in environmental monitoring

Abstract

Dendrochemical techniques have been used to monitor historical changes in soil and atmospheric chemistry since the early 1970s. The development of dendrochemistry in environmental monitoring was prompted by early studies which reported that changes in Pb deposition along roadsides and in industrial areas were reflected by changes in the Pb content of tree rings. Early studies were inconclusive; some authors have stated that tree-ring chemistry is not a useful indicator of pollution episodes and that some tree species are clearly better spatial indicators of pollution than historical monitors. This is due to a number of complicating factors, including potential radial translocation of elements, radial tendencies in element concentration from pith to bark, and physiological differences between heartwood and sapwood. A more detailed understanding of element cycling in trees is needed, as at present, the application of dendrochemistry to historical environmental monitoring is strongly dependent on the choice of tree species and the elements to be studied. There is no general consensus as to which tree species are best suited for dendrochemical studies. There are many reports in which the analyses of tree-ring chemistry have been successfully used to reconstruct trace-metal deposition from a variety of sources, including automobiles, metal refineries, and coal burning. Changes in tree-ring chemistry in recent decades have coincided with hypothesized changes in soil chemistry believed to be a result of acidic deposition onto poorly buffered soils. Indications of changes in groundwater quality, volcanic eruptions, and even climate change have been reported to be preserved in the chemical composition of tree rings. An improvement in analytical techniques has allowed multielement analysis on whole wood samples, with very low detection limits and extremely high spatial resolution, enabling intra-annual changes in element composition of tree rings to be determined. The application of dendrochemistry in environmental monitoring is promising, and with a more detailed understanding of nutrient and metal cycling in trees, dendrochemical studies will continue to provide useful information on historical pollution loadings and changes in soil and atmospheric chemistry that is unobtainable from any other source.