High-resolution dendrochemical analysis of flood-affected oaks using laser ablation ICP-mass spectrometry

Dendrochemical analysis was conducted on Quercus macrocarpa Michx. (bur oak) growing within the floodplain of the Red River, Canada, to determine if xylem formed during severe floods contained significantly perturbed chemistry. Wood samples were taken from five living trees in the same stand and from three timbers from a 19^th-century building. Laser ablation ICP-mass spectrometry was used to determine the trace element chemistry in the early wood and latewood of rings formed before, during and after major floods. Between-tree correlations were significant (p < 0.05) for Hg, Mg, Mn, Sr and Zn, suggesting that changes in the abundance of these elements over time might reflect common physiological processes or environmental signals. Mg, Mn and Sr concentrations were higher in the earlywood than in the latewood for both living and historical samples. These intra-annual shifts may reflect varying rates of uptake driven by seasonal changes in anatomical development, as well as stability of these elements after their initial deposition. Although no chemical anomalies are associated with 20^th-century floods, earlywood coinciding with an extreme flood in 1826 contained low levels of Mg, Mn and Sr. These elemental anomalies might represent an independent biochemical flood signature but it is also possible they are a secondary expression of wood formation disrupted by flooding. In either case, elemental analysis does not provide any information beyond that obtained from studying anatomical features, and does not appear to be a viable tool to identify the occurrence of past floods.