Dendrochronology and Heavy Metal Deposition in Tree Rings of Baldcypress
Latimer, Shane D. | Devall, Margaret S. | Thomas, Charles | Ellgaard, Erik G. | Kumar, Satish D. | Thien, Leonard B.
A chronology (1895–present) based on tree-ring increments was constructed for baldcypress (Taxodium distichum L.) trees in Bayou Trepagnier, in southern Louisiana. The best indicator of growth was precipitation in February of the preceding year and October of the 2 previous years. Crossdated cores were used to reconstruct large historical natural environmental perturbations (hurricanes). Heavy metals and organic pollutants from oil refineries and other sources contaminated the bayou commencing in the early 1900s. The Pb and Zn content of 50 trees along Bayou Trepagnier, analyzed in the growth rings of tree cores using x-ray fluorescent spectrometry, produced an historical record of pollution. High levels of contamination of Pb, as well as Zn, could be correlated with establishment of petroleum refineries (1916) and dredging (1930–1950) of the area, which created spoil banks containing high levels (ca. 300–1600 mg/kg [ppm] Pb) of heavy metals. Concentrations of Pb, per tree, ranged from 0.6 to 14 mg/kg (ppm). Trees in the upper portion of the bayou (near the refinery) contained an average of 4.5 mg/kg (ppm) Pb; trees in the lower portion averaged 2.2 mg/kg (ppm). Concentrations of Zn per tree ranged from 1.7 to 14.8 mg/kg (ppm), but in contrast with Pb did not correlate with distance from pollution sources; trees averaged 5.5 and 5.4 mg/kg (ppm) Zn in the upper and lower portions, respectively, of Bayou Trepagnier. Levels of Pb and Zn in a control ecosystem, Stinking Bayou, were 1.0 and 5.2 mg/kg (ppm), respectively. Research sponsored by the U.S. Dep. of Energy grant to Tulane Univ., Project no. DE-FG01-93EW532023.
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