Transport of stable isotopes of water (δ18 O, δ2 H) using HYDRUS-1D
Stable isotopes of water can be used as environmental or artificial tracers to investigate soil water flow and solute transport. In HYDRUS-1D, the solute transport module was modified to account for isotope transport (Stumpp et al., 2012). We assumed that we can neglect fractionation processes and that the relative concentration of isotopes (delta content) does not accumulate at the upper boundary due to evaporation. This is in contrast to the standard treatment of solutes during evaporation in HYDRUS-1D, where solutes stay behind in the soil while water is removed. This modification was implemented only in the standard HYDRUS-1D module (i.e., with single-porosity and MIM models; not in dual-permeability models).
It is important to emphasize that the modified version does not account for fractionation processes. Therefore, it is only applicable in soils where fractionation due to evaporation is of minor importance. It is recommended carefully controlling potential fractionation by plotting water isotope data measured in soil water in a dual-isotope plot and compare it to local values in precipitation (local meteoric water line). Only if slopes of regression lines are similar and soil water data plot close to the local meteoric water line, the modified HYDRUS-1D version can be used.
Stable isotopes of water are reported in the delta notation as the δ-content (‰), which is a relative deviation from the international standard V-SMOW (Vienna-Standard Mean Ocean Water). Mostly, the δ-content is negative. It is not possible to calculate with negative “concentrations” in HYDRUS-1D, and therefore, the user has to add an arbitrary value to all isotope data for the simulations (input and observation data). Do not take the absolute values though!
The example below (Lys3_Stumpp) is taken from the original publication presenting the modified HYDRUS-1D code (Stumpp et al., 2012). Please refer to this reference when using the modified code for isotope transport.
For further questions about the applicability of the model, please contact Christine Stumpp (christine.stumpp@boku.ac.at).
|
Project
|
Description
|
|
Lys3_Stumpp
|
Transport of stable water isotopes in a lysimeter study (Stumpp et al., 2012)
|
Download the computational module (1.1 MB)
Download the demonstrative example (0.7 MB)
To use the code, you can simply replace the h1d_calc.exe file in the HYDRUS installation folder (make a backup of the original file first, so that you can return to it for other than Isotope transport applications), or you can place it anywhere else and run it outside of the GUI (see FAQ4).
The manuscript, for which the Isotope module of HYDRUS-1D has been developed:
- Stumpp, C., W. Stichler, M. Kandolf, and J. Šimůnek, Effects of land cover and fertilization method on water flow and solute transport in five lysimeters: A long-term study using stable water isotopes, Vadose Zone Journal, 11(1), doi:10.2136/vzj2011.0075, 14 pp., 2012.
Other applications of the modified code:
- Stumpp, C., and M. J. Hendry, Spatial and temporal dynamics of water flow and solute transport in a heterogeneous glacial till: The application of high resolution profiles of δ18O and δ2H in pore waters, Journal of Hydrology, 438-439, 203-214, 2012.
- Sprenger, M., T. H. M. Volkmann, T. Blume, and M. Weiler, Estimating flow and transport parameters in the unsaturated zone with pore water stable isotopes, Hydrology and Earth System Sciences, 19, 2617-2635, 2015.
- Huang, M., J. N. Hilderman, and L. Barbour, Transport of stable isotopes of water and sulphate within reclaimed oil sands saline–sodic mine overburden, Journal of Hydrology, 529, 1550-1561, 2015.
- Sprenger, M., M., Erhardt, M., Riedel, and M. Weiler, Historical tracking of nitrate in contrasting vineyards using water isotopes and nitrate depth profiles, Agr. Ecosyst. Environ., 222, 185–192, doi: 10.1016/j.agee.2016.02.014, 2016.
- Sprenger, M., S. Seeger, T. Blume, and M. Weiler, Travel times in the vadose zone: variability in space and time, Water Resour. Res., 52, 5727–5754, doi: 10.1002/2015WR018077, 2016.
- Sprenger, M., D. Tetzlaff, J. Buttle, H. Laudon, H. Leistert, C. P. J. Mitchell, J. Snelgrove, M. Weiler, and C. Soulsby, Measuring and modeling stable isotopes of mobile and bulk soil water, Vadose Zone J., 17, 170149, 18 p., doi: 10.2136/vzj2017.08.0149, 2018.
- Groh, J., C. Stumpp, A. Lücke, T. Pütz, J. Vanderborght, and H. Vereecken, Inverse estimation of soil hydraulic and transport parameters of layered soils from water stable isotope and lysimeter data, Vadose Zone J., 17, 170168, doi: 10.2136/vzj2017.09.0168, 2018.