Comparison of pore water samplers and cryogenic distillation under laboratory and field conditions for soil water stable isotope analysis
2018
Thoma, Michael | Frentress, Jay | Tagliavini, M. (Massimo) | Scandellari, Francesca
We used pore water samplers (PWS) to sample for isotope analysis (1) only water, (2) soil under laboratory conditions, and (3) soil in the field comparing the results with cryogenic extraction (CE). In (1) and (2), no significant differences between source and water extracted with PWS were detected with a mean absolute difference (MAD) always lower than 2 ‰ for δ²H and 1 ‰ for δ¹⁸O. In (2), CE water was more enriched than PWS-extracted water, with a MAD respect to source water of roughly 8 ‰ for δ²H and 4 ‰ for δ¹⁸O. In (3), PWS water was enriched relative to CE water by 3 ‰ for δ²H and 0.9 ‰ for δ¹⁸O. The latter result may be due to the distinct water portions sampled by the two methods. Large pores, easily sampled by PWS, likely retain recent, and enriched, summer precipitation while small pores, only sampled by CE, possibly retain isotopically depleted water from previous winter precipitation or irrigation inputs. Accuracy and precision were greater for PWS relative to CE. PWS is therefore suggested as viable tool to extract soil water for stable isotope analysis, particularly for soils used in this study (sandy and silty loams).
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