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TitrePooling tree-ring samples for determining Zn isotopic signatures in the Athabasca oil sands region
AuteurDinis, L; Savard, M M; Bégin, C; Gammon, P; Girard, I
SourceAmerican Geophysical Union, annual meeting, abstracts; 2013 p. 1
LiensOnline - En ligne
Séries alt.Secteur des sciences de la Terre, Contribution externe 20130291
ÉditeurAmerican Geophysical Union
RéunionAmerican Geophysical Union, annual meeting; San Francisco; US; décembre 9-13, 2013
Mediaen ligne; numérique
Sujetsdendrochronologie; végétation; zinc; isotopes; études des isotopes stables; combustibles fossiles; géologie de l'environnement
ProgrammeDéveloppement durable des sables bitumineux, Géosciences environnementales
Résumé(disponible en anglais seulement)
The sampling protocols for trees are primarily determined by the aim of the study and the expected concentrations of targeted elements. For site-specific environmental investigations using C and O stable isotopes, it is common to pool temporally-equivalent samples from different trees to obtain a representative signature for a given site. Furthermore, non-traditional stable isotopic analyses can require significant sample weights due to low elemental concentrations, which can force researchers to pool samples. However, it is unclear whether or not pooling will produce isotopic results representative of a site for elemental distribution of metals within trees. Therefore, this study investigates the validity of pooling sub-samples from several trees to obtain site-averaged Zn-isotopic analyses. We have investigated four white spruce trees from one site about 42 km east of the mining center of the Athabasca oil sands region (Alberta, Canada), and characterized their ring Zn-isotopes. Our specific goal here was to determine if individual determination and/or pooling sub-samples could detect temporal variations in Zn characteristics. We collected and analyzed nine sub-samples per tree, at a resolution of 4 and 2 years, and distributed over a 130 year period (1878-2009) using an ICP-MS. It turned out that the tree rings have very low Zn concentrations (3.8 to 7.6 ppm). The segmented tree-ring series were subsequently analyzed both for d66Zn values in individual tree samples and pooled samples with equally weighted aliquots (total of 45 samples), using a MC-ICP-MS and a standard sample bracketing correction reported against NIST683. The d66Zn results ranged between 0.30 and 0.74‰ ×0.05 (2 SD) for individual samples, and, 0.35 and 0.66‰ ×0.07, for the pooled sample set. As expected, all trees at the investigated site responded similarly, and the weighted average d66Zn value of the individual series closely compared to the d66Zn signature of the pooled sample (r2 = 0.8). For any single pooled versus individual trees comparative data point the d66Zn results are bracketed within 0.2‰ with minimal scatter (generally < 0.1‰), suggesting that at the investigated site the sampling of individual or pooled series gives essentially the same result, and that the pooling technique may be suitable for understanding environmental processes through time. It seems overall that this method has the potential to differentiate Zn sources and emissions, and help understanding local Zn cycling and processes leading to Zn uptake by trees. In order to assess this potential for the oil sands region, we are currently analyzing Zn isotopes for the series from the first investigated site and from a second site, as well as their soil profiles (total of 150 tree and soil samples). Comparison of tree results with the soil Zn-isotopic signatures will help assess the use of tree-ring Zn-isotopes as an environmental tool, as well as the fractionation processes that may be operating at the two sites.
Résumé(Résumé en langage clair et simple, non publié)
Ce résumé présente le développement de méthode permettant d'analyser les isotopes du zinc presents dans les cernes de croissance des arbres. Cette méthode est appliquée sur les cernes de croissance d'arbre provenant de la région des sables bitumineux de l'Alberta, pour déterminer s'il existe une contamination liée à cette industrie dans l'environnement forestier et également pour mieux comprendre les processes biogéochimiques intervenant entre l'atmosphère, le sol et l'arbre.