Mechanisms of consistently disjunct soil water pools over (pore) space and time
<p>The storage and release of water in soils is critical for sustaining plant transpiration and groundwater recharge. However, how much subsurface mixing of water occurs, and how much of the water is available for plants or otherwise percolates to streams and the groundwater is not yet underst...
| Main Authors: | , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2019-06-01
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| Series: | Hydrology and Earth System Sciences |
| Online Access: | https://www.hydrol-earth-syst-sci.net/23/2751/2019/hess-23-2751-2019.pdf |
| Summary: | <p>The storage and release of water in soils is critical for
sustaining plant transpiration and groundwater recharge. However, how much
subsurface mixing of water occurs, and how much of the water is available for plants or otherwise percolates to streams and the groundwater is not yet
understood. Based on stable isotope (<span class="inline-formula"><sup>2</sup>H</span> and
<span class="inline-formula"><sup>18</sup>O</span>) data, some studies have found that water infiltrating into soils can bypass older pore
water. However, the mechanisms leading to the separation of water routed
to the streams and water held tightly in smaller pores are still unclear.
Here, we address the current limitations of the understanding of subsurface
mixing and their consequences regarding the application of stable isotopes in
ecohydrological studies. We present an extensive data set, for which we
sampled the isotopic composition of mobile and bulk soil water
in parallel with groundwater at a fortnightly temporal resolution and stream water and rainfall at a much higher resolution in a Mediterranean
long-term research catchment, in Vallcebre, Spain. The data reveal that the
mobile and tightly bound water of a silty loam soil in a Scots pine forest
do not mix well; however, they constitute two disjunct subsurface water pools
with little exchange, despite intense rainfall events leading to high soil
wetness. We show that the isotopic compartmentalization results from the rewetting
of small soil pores by isotopically depleted winter/spring rain. Thus,
stable isotopes, and, in turn, water residence times, do not only vary
across soil depth, but also across soil pores. Our findings have important
implications for stable isotope applications in ecohydrological studies
assessing the water uptake by plants or the process realism of hydrological models,
as the observed processes are currently rarely implemented in the simulation
of water partitioning into evapotranspiration and recharge in the critical
zone.</p> |
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| ISSN: | 1027-5606 1607-7938 |