Sampling soil water along the pF curve for δ2H and δ18O analysis
Research output: Contribution to journal › Research article › Contributed › peer-review
Contributors
Abstract
Soil water stable isotopes are widely used across disciplines (e.g., hydrology, ecology, soil science, and biogeochemistry). However, the full potential of stables isotopes as a tool for characterizing the origin, flow path, transport processes and residence times of water in different eco-, hydro-, and geological compartments has not yet been exploited. This is mainly due to the large variety of different methods for pore water extraction. While recent work has shown that matric potential affects the equilibrium fractionation, little work has examined how different water retention characteristics might affect the sampled water isotopic composition. Here, we present a simple laboratory experiment with two well-studied standard soils differing in their physico-chemical properties (e.g., clayey loam and silty sand). Samples were sieved, oven-dried and spiked with water of known isotopic composition to full saturation. For investigating the effect of water retention characteristics on the extracted water isotopic composition, we used pressure extractors to sample isotopically labelled soil water along the pF curve. After pressure extraction, we further extracted the soil samples via cryogenic vacuum extraction. The null hypothesis guiding our work was that water held at different tensions shows the same isotopic composition. Our results showed that the sampled soil water differed isotopically from the introduced isotopic label over time and sequentially along the pF curve. Our and previous studies suggest caution in interpreting isotope results of extracted soil water and a need to better characterize processes that govern isotope fractionation with respect to soil water retention characteristics. In the future, knowledge about soil water retention characteristics with respect to soil water isotopic composition could be applied to predict soil water fractionation effects under natural and non-stationary conditions. In this regard, isotope retention characteristics as an analog to water retention characteristics have been proposed as a way forward since matric potential affects the equilibrium fractionation between the bound water and the water vapour.
Details
Original language | English |
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Pages (from-to) | 4959-4972 |
Number of pages | 14 |
Journal | Hydrological processes |
Volume | 34 |
Issue number | 25 |
Publication status | Published - 15 Dec 2020 |
Peer-reviewed | Yes |
External IDs
ORCID | /0000-0003-4368-4580/work/163293734 |
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Keywords
ASJC Scopus subject areas
Keywords
- pF value, soil water isotopes, soil water pool, δH and δO analysis