Preprints
https://doi.org/10.5194/bg-2021-278
https://doi.org/10.5194/bg-2021-278

  04 Nov 2021

04 Nov 2021

Review status: this preprint is currently under review for the journal BG.

Modelling temporal variability of in-situ soil water and vegetation isotopes reveals ecohydrological couplings in a willow plot

Aaron Smith1, Doerthe Tetzlaff1,2,3, Jessica Landgraf1, Maren Dubbert1,4, and Chris Soulsby3,2,5 Aaron Smith et al.
  • 1IGB Leibniz Institute of Freshwater Ecology and Inland Fisheries Berlin, Berlin, Germany
  • 2Humboldt University Berlin, Berlin, Germany
  • 3Northern Rivers Institute, School of Geosciences, University of Aberdeen, UK
  • 4ZALF Leibniz Center for Agricultural Landscape Research, Müncheberg, Germany
  • 5Technische Universitat Berlin, Institut für Bauingenieurwesen, Berlin, Germany

Abstract. The partitioning of water fluxes in the critical zone is of great interest due to the implications for understanding water cycling and quantifying water availability for various ecosystem services. We used the tracer-aided ecohydrological model EcH2O-iso to evaluate water, energy, water stable isotope, and biomass dynamics at an intensively monitored study plot under two willow trees, a riparian species, in Berlin, Germany. Importantly, we assessed the value of in-situ soil and plant water isotope data to quantify xylem water sources and transit times, with coupled estimates of the temporal dynamics and ages of soil and root-uptake water. The willows showed high evapotranspiration water use, with limited percolation of summer precipitation to deeper soil layers due to the dominance of shallow root-uptake (> 80 % in the upper 10 cm). Lower evapotranspiration under grass resulted in higher soil moisture storage, greater soil evaporation and more percolation of soil water. Biomass allocation was predominantly foliage growth (57 % in grass and 78 % in willow). Shallow soil water age under grass was similar to under willows (15–17 days). Considering potential xylem transit times showed a large improvement in the model's capability to estimate xylem isotopic composition and water age, and revealed the high value of in-situ data within modelling. Root-uptake was predominately derived from summer precipitation events (56 %) and had an average age of 35 days, with xylem transport times taking at least 6.2–8.1 days. By evaluating water partitioning, energy and isotope mass-balance, along with biomass allocation, the model revealed multifaceted capabilities for assessing water cycling within the critical zone at high temporal resolution, including xylem water sources and transport, which are all necessary for short and long-term assessment of water availability for plant growth.

Aaron Smith et al.

Status: open (until 16 Dec 2021)

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Aaron Smith et al.

Aaron Smith et al.

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Short summary
This research utilizes high spatio-temporal resolution soil and vegetation measurements, including water stable isotopes, within an ecohydrological model to partition water flux dynamics and identify flow paths and durations. Results showed high vegetation water use and high spatio-temporal dynamics of vegetation water source and vegetation isotopes. The evaluation of these dynamics further revealed relatively fast flow paths through both shallow soil and vegetation.
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