TY - JOUR

T1 - Evaporation experiments for the determination of hydraulic properties of peat and other organic soils

T2 - An evaluation of methods based on a large dataset

AU - Dettmann, Ullrich

AU - Bechtold, Michel

AU - Viohl, Thomas

AU - Piayda, Arndt

AU - Sokolowsky, Liv

AU - Tiemeyer, Bärbel

N1 - Funding information: We thank Bernd Lennartz ( Rostock University , Germany) for lending us a ku-pF apparatus. We appreciate laboratory and field support from Astrid Jäger, Frank Hegewald, Bernd Schemschat, Tilmann Dreysse and Annette Freibauer. We also thank Andre Peters for technical support. The samples were provided by the FACCE-JPI ERA-NET Plus project on Climate Smart Agriculture on Organic Soils ( CAOS ) which was funded by the German Federal Ministry of Education and Research (BMBF) under grant No. 031A543A. M. Bechtold thanks the Alexander von Humboldt Foundation for a Feodor Lynen Fellowship. We are grateful to Corrado Corradini as Editor, Magdeline Laba as Associated Editor and the anonymous reviewers for their helpful comments. We thank Bernd Lennartz (Rostock University, Germany) for lending us a ku-pF apparatus. We appreciate laboratory and field support from Astrid Jäger, Frank Hegewald, Bernd Schemschat, Tilmann Dreysse and Annette Freibauer. We also thank Andre Peters for technical support. The samples were provided by the FACCE-JPI ERA-NET Plus project on Climate Smart Agriculture on Organic Soils (CAOS) which was funded by the German Federal Ministry of Education and Research (BMBF) under grant No. 031A543A. M. Bechtold thanks the Alexander von Humboldt Foundation for a Feodor Lynen Fellowship. We are grateful to Corrado Corradini as Editor, Magdeline Laba as Associated Editor and the anonymous reviewers for their helpful comments.

PY - 2019/8

Y1 - 2019/8

N2 - Soil hydraulic properties are frequently obtained from evaporation experiments. Different methods exist to infer soil hydraulic properties from these experiments. Commonly proposed is the ‘direct method’ (or ‘Simplified Evaporation Method’) by which soil hydraulic properties are calculated analytically. An alternative is given by inverse parameter optimization (‘inverse method’). Although soil hydraulic properties are frequently estimated by the ‘direct method’, only very few studies have focused on the question how accurate derived parameters can reproduce laboratory measurements. This can be achieved by modeling the water flow with a processed based numerical forward model, e.g. with HYDRUS-1D. Here, we applied the ‘direct method’ and ‘inverse method’ to a large dataset of evaporation experiments on 431 organic soil samples. The derived soil hydraulic parameters were used in HYDRUS-1D simulations and their performance in reproducing measured states and fluxes was compared. As an additional analysis, we tested how water contents at the permanent wilting point can aid stabilizing parameter estimation by adding information on water retention in the dry range. For all methods, soil hydraulic properties were determined with the soil hydraulic functions of van Genuchten-Mualem and Peters-Durner-Iden. The results show that parameters derived with the ‘direct method’ do often not well reproduce measured pressure heads over the complete pressure head range of the evaporation experiments when they were used for HYDRUS-1D simulations (mean objective function value 0.05831). Parameters derived by the ‘inverse method’ provided a better performance in the HYDRUS-1D simulations if the full pressure head range of the evaporation experiments was considered (mean objective function value 0.00099), but a weaker performance when focusing on wet conditions (pressure heads >−100 cm). Constraining the ‘inverse method’ by additional soil moisture measurements at permanent wilting point improved the prediction of the soil moisture at dry conditions. For the full pressure head range, the hydraulic functions of Peters-Durner-Iden performed better than the ones of van Genuchten-Mualem.

AB - Soil hydraulic properties are frequently obtained from evaporation experiments. Different methods exist to infer soil hydraulic properties from these experiments. Commonly proposed is the ‘direct method’ (or ‘Simplified Evaporation Method’) by which soil hydraulic properties are calculated analytically. An alternative is given by inverse parameter optimization (‘inverse method’). Although soil hydraulic properties are frequently estimated by the ‘direct method’, only very few studies have focused on the question how accurate derived parameters can reproduce laboratory measurements. This can be achieved by modeling the water flow with a processed based numerical forward model, e.g. with HYDRUS-1D. Here, we applied the ‘direct method’ and ‘inverse method’ to a large dataset of evaporation experiments on 431 organic soil samples. The derived soil hydraulic parameters were used in HYDRUS-1D simulations and their performance in reproducing measured states and fluxes was compared. As an additional analysis, we tested how water contents at the permanent wilting point can aid stabilizing parameter estimation by adding information on water retention in the dry range. For all methods, soil hydraulic properties were determined with the soil hydraulic functions of van Genuchten-Mualem and Peters-Durner-Iden. The results show that parameters derived with the ‘direct method’ do often not well reproduce measured pressure heads over the complete pressure head range of the evaporation experiments when they were used for HYDRUS-1D simulations (mean objective function value 0.05831). Parameters derived by the ‘inverse method’ provided a better performance in the HYDRUS-1D simulations if the full pressure head range of the evaporation experiments was considered (mean objective function value 0.00099), but a weaker performance when focusing on wet conditions (pressure heads >−100 cm). Constraining the ‘inverse method’ by additional soil moisture measurements at permanent wilting point improved the prediction of the soil moisture at dry conditions. For the full pressure head range, the hydraulic functions of Peters-Durner-Iden performed better than the ones of van Genuchten-Mualem.

KW - Peatland

KW - Peters-Durner-Iden

KW - Simplified evaporation method

KW - Unsaturated hydraulic conductivity

KW - van Genuchten-Mualem

KW - Water retention characteristics

KW - Wetland

UR - http://www.scopus.com/inward/record.url?scp=85066983333&partnerID=8YFLogxK

U2 - 10.1016/j.jhydrol.2019.05.088

DO - 10.1016/j.jhydrol.2019.05.088

M3 - Article

AN - SCOPUS:85066983333

VL - 575

SP - 933

EP - 944

JO - Journal of hydrology

JF - Journal of hydrology

SN - 0022-1694

ER -