Extraction of water from Eucalyptus trees for analysis of deuterium and oxygen-18: laboratory and field techniques |
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Authors: | P. J. THORBURN G. R. WALKER J.-P. BRUNEL |
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Affiliation: | Centre for Groundwater Studies and CSIRO Division of Water Resources, Private Bag 2, Glen Osmond, SA 5064, Australia |
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Abstract: | This study investigated a methodology for sampling and extracting water from Eucalyptus spp. for analysis of stable isotopes of water. Firstly, water of known isotopic composition was extracted from stems of seedlings of Eucalyptus spp. by azeotropic distillation using three solvents (hexane, toluene and kerosene) in laboratory and glasshouse experiments. Kerosene and toluene gave the most accurate extractions, with a small negative bias (~-2‰ for δ2H and ~-0.4‰ for δ18O) due to incomplete extraction. This bias was not evident in further experiments, using kerosene, where water was extracted from stems and roots that had been pre-treated in a manner that more closely reflected field conditions. Secondly, variation in δ2H in trees was investigated in the field to determine an accurate and convenient place for sampling. There was no significant difference in δ2H between water extracted from trunk sapwood and whole twigs, even twigs close to leaves, in samples taken from four Eucalyptus spp. at two field sites. The results mean that the most convenient part of the tree can be sampled. Also, there was little difference in δ2H between sapwood and heart-wood samples, although small increases (~ 2‰) in δ2H were observed in bark of trunks and twigs. Tree roots (15–25 mm diameter) had similar δ2H values to the surrounding soil in many cases, especially surface (<0.2 m depth) roots, rather than having δ2H values similar to twigs of the trees. These roots were absorbing water from surrounding soil, but not contributing significant quantities of water to the tree canopy. Thus, the δ2H of root water is not a good indicator of the isotopic composition of water in the upper parts of Eucalyptus trees. |
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Keywords: | Eucalyptus camaldulensis Eucalyptus largiflorens Eucalyptus oleosa Eucalyptus gracilis river red gum black box mallee stable isotopes azeotropic distillation root function |
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