Estimation of the Unsaturated Hydraulic Conductivity of Peat Soils: Laboratory versus Field Data

Abstract

As compared with mineral soils, there are few in situ measurements of the unsaturated hydraulic properties of peat soils available. 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 physically realistic minimum in the objective function for the plant‐covered lysimeter could be found only when prior information about several 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 independently 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 soil hydraulic properties.

Hydrological properties of duff

“…These equations are somewhat comparable to studies done on peat [Weiss et al, 1998;Schwärzel et al, 2006], particularly in the range of the parameter n. The values determined for a, on the other hand, are higher than those in the peat studies; however, they do follow the trend that a decreases with depth.…”

“…[13] Using the significant desorption characteristic curves, the relative hydraulic conductivity curves, K r (Ày), were determined using the relationship [van Genuchten, 1980] …”

A pore-size classification for peat bogs derived from unsaturated hydraulic properties

“…Subsequently, transient evaporation experiments were carried out (Wendroth et al, 1993;Schwärzel et al, 2006) on samples 5 cm i.h. and 8 cm i.d., starting with fully saturated samples that were exposed to free evaporation in the lab.…”

Inverse estimation of soil hydraulic properties under oil palm trees

“…Inverse solutions based on the Richards equation are now increasingly used for estimating the unsaturated soil hydraulic properties. An advantage of this approach is that the retention and hydraulic conductivity functions can be estimated simultaneously from transient flow data, as shown by many past and recent studies (Abbasi et al, 2003;Abbaspour et al, 1999;Dane and Hruska, 1983;Eching and Hopmans, 1993;Kool and Parker, 1987;Lazarovitch et al, 2007;Minasny and Field, 2005;Ritter et al, 2003;Russo et al, 1991;Schwarzel et al, 2006;Sonnleitner et al, 2003;Zachmann et al, 1981). The soil hydraulic parameters are then obtained by minimizing an objective function, usually defined as the sum of squared deviations between observed and predicted transient water flow variables (Hopmans et al, 2002).…”