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Title: ESTIMATION OF THE UNSATURATED HYDRAULIC CONDUCTIVITY OF PEAT SOILS: LABORATORY VERSUS FIELD DATA

Author
item SCHWARZEL, K - TECH UNIV OF BERLIN
item SIMUNEK, J - UC RIVERSIDE, CA
item STOFFREGEN, H - TECH UNIV OF BERLIN
item WESSOLEK, G - TECH UNIV OF BERLIN
item Van Genuchten, Martinus

Submitted to: Vadose Zone Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/10/2005
Publication Date: 5/26/2006
Citation: Schwarzel, K., Simunek, J., Stoffregen, H., Wessolek, G., Van Genuchten, M.T. 2006. Estimation of the unsaturated hydraulic conductivity of peat soils: laboratory versus field data. Vadose Zone Journal. 5:628-640

Interpretive Summary: Understanding the processes that control the retention and movement of water in peat soils is critical to effective management of such soils from both agricultural and ecological perspectives. In contrast to mineral soils, much less is known about the hydraulic behavior of peat soils, especially its hydraulic conductivity as a function of water content. This is probably in part due to the unique nature of the physical and hydraulic properties of peat soils, including volume changes upon dewatering. Only a relatively few measurements of unsaturated hydraulic conductivities of peat soils have been reported in the literature. Most of these involved direct measurements of the unsaturated hydraulic conductivity using steady-state methods on small cores in the laboratory. In this study we used parameter estimation (inverse) methods to estimate the water retention and hydraulic conductivity functions of drained peat soils from both laboratory and field data. The laboratory data were obtained on small cores using the traditional evaporation method, while the field data were obtained by means of evaporation experiments using groundwater lysimeters with and without vegetation. The field experiments without vegetation produced highly uncertain parameters, and were limited to a relatively small pressure head range. Better results were obtained for the lysimeter with a grass cover that caused the peat soil to dry out more. The hydraulic functions were subsequently tested by comparing forward simulations with measured pressure heads and water contents of an additional lysimeter experiment under grass. The dynamics of the drying process was described well using the optimized hydraulic properties. Results of this study should be of interests to researchers, extension personnel, groundwater professionals, and others dealing with the management of peat soils.

Technical Abstract: As compared to mineral soils, few in-situ measurements are currently available of the unsaturated hydraulic properties of peat soils. We used parameter estimation (inverse) methods to estimate the water retention and hydraulic conductivity functions of drained peat soils from both laboratory and field data. The laboratory data were obtained on small cores using the traditional evaporation method, while the field data were obtained by means of evaporation experiments using groundwater lysimeters with and without vegetation. The field experiments without vegetation produced highly uncertain parameters, and were limited to a relatively small pressure head range. Better results were obtained for the lysimeter with a grass cover that caused the peat soil to dry out more. However, a minimum of the objective function for the plant-covered lysimeter could be found only when prior information about some of the parameters was included in the optimization. Good agreement was obtained between the laboratory and field measurements. The hydraulic functions were subsequently tested by comparing forward simulations with measured pressure heads and water contents of an additional lysimeter experiment under grass. The dynamics of the drying process was described well using the optimized hydraulic properties.