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TitlePooling tree-ring samples for determining Zn isotopic signatures in the Athabasca oil sands region
AuthorDinis, L; Savard, M M; Bégin, C; Gammon, P; Girard, I
SourceAmerican Geophysical Union, annual meeting, abstracts; 2013 p. 1
Alt SeriesEarth Sciences Sector, Contribution Series 20130291
PublisherAmerican Geophysical Union
MeetingAmerican Geophysical Union, annual meeting; San Francisco; US; December 9-13, 2013
Mediaon-line; digital
File formathtm
Subjectsfossil fuels; environmental geology; dendrochronology; vegetation; zinc; isotopes; stable isotope studies
ProgramCoal & Oil Resources Environmental Sustainability, Environmental Geoscience
LinksOnline - En ligne
AbstractThe 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.
Summary(Plain Language Summary, not published)
This abstract outlines the development of a method for analysing zinc isotopes present in the growth rings of trees. This method is used on the growth rings of trees from the oil sands region of Alberta to determine whether or not there is contamination related to the oil industry in the forest environment, as well as to better understand biogeochemical processes between trees, atmosphere and soil.