Reply to comment by S. Iden and W. Durner on “Simple consistent models for water retention and hydraulic conductivity in the complete moisture range”

Peters, André

doi:10.1002/2014wr016107

Cited by 70 publications

(79 citation statements)

References 9 publications

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“…The vG‐PDI model expresses water contents as a sum of capillary and non‐capillary (adsorbed) water, and uses a scaling of the original van Genuchten function to ensure that water content at oven dryness is zero. The detailed model specification is given by Peters (2013), Iden and Durner (2014), and Peters (2014). A condensed model description is given in Appendix A of Peters et al (2015).…”

Section: Methodsmentioning

confidence: 99%

Water retention properties of a sandy soil with superabsorbent polymers as affected by aging and water quality

Banedjschafie

Durner

2015

J. Plant Nutr. Soil Sci.

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Hydraulic properties, specifically the water holding capacity of soils, play a key role in the ability of soils to sustain plant growth. Additions of hydrophilic polymers (superabsorbents) can improve the water holding capacity of sandy soils. This has led to practical applications of these materials particularly in arid regions and countries, where water is the limiting factor for plant production. The objectives of this study are to investigate how effective hydraulic properties of polymer-soil mixtures are affected by addition of absorbents in different concentrations. Novel aspects are the investigation of aging under repeated wetting-drying-cycles over an appreciable time in the field and a systematic investigation of the salt influence on the water uptake of polymers. We added the polymer Super AB, A-200 (Iran Polymer Institute), to dune sand in ratios of 0.3%, 0.6%, and 1% w/w. We found that the effective water retention characteristics of the soil-absorbent mixtures were improved with respect to plant-available water compared to the pure sand, and the improvement was related to the respective amount of absorbent in the mixture. The plant available water content (PAW) increased from 0.005 for the untreated sand to 0.06, 0.20, and 0.28 g g -1 , respectively, for the sand with the three polymer additions. Due to aging of the polymers, PAW decreased after 6 months of cyclic drying and wetting to about half of the value immediately after the initial treatment. We attribute this to the effect of salts. This is corroborated by the results from water uptake experiments by the pure polymers. Repeated cycles of water uptake showed that salts in the water greatly reduced the uptake capacity of the polymers after few cycles. The effect was strong for bivalent cations and less pronounced for monovalent cations.

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Section: Methodsmentioning

confidence: 99%

Water retention properties of a sandy soil with superabsorbent polymers as affected by aging and water quality

Banedjschafie

Durner

2015

J. Plant Nutr. Soil Sci.

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“…(1), which is illogical. Peters (2014) required that the conductivity curve monotonically decreases as the soil dries out and derived a minimal value of −2 for τ from that requirement. Indeed, negative values of this parameter have been reported (e.g., Schaap and Leij, 2000), even though the three predictive models mentioned above all have positive values of τ .…”

Section: Hydraulic Conductivity Models and Their Behavior Near Saturamentioning

confidence: 99%

Parametric soil water retention models: a critical evaluation of expressions for the full moisture range

Madi

Rooij

Mielenz

et al. 2018

Hydrol. Earth Syst. Sci.

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Abstract. Few parametric expressions for the soil water retention curve are suitable for dry conditions. Furthermore, expressions for the soil hydraulic conductivity curves associated with parametric retention functions can behave unrealistically near saturation. We developed a general criterion for water retention parameterizations that ensures physically plausible conductivity curves. Only 3 of the 18 tested parameterizations met this criterion without restrictions on the parameters of a popular conductivity curve parameterization. A fourth required one parameter to be fixed.We estimated parameters by shuffled complex evolution (SCE) with the objective function tailored to various observation methods used to obtain retention curve data. We fitted the four parameterizations with physically plausible conductivities as well as the most widely used parameterization. The performance of the resulting 12 combinations of retention and conductivity curves was assessed in a numerical study with 751 days of semiarid atmospheric forcing applied to unvegetated, uniform, 1 m freely draining columns for four textures.Choosing different parameterizations had a minor effect on evaporation, but cumulative bottom fluxes varied by up to an order of magnitude between them. This highlights the need for a careful selection of the soil hydraulic parameterization that ideally does not only rely on goodness of fit to static soil water retention data but also on hydraulic conductivity measurements.Parameter fits for 21 soils showed that extrapolations into the dry range of the retention curve often became physically more realistic when the parameterization had a logarithmic dry branch, particularly in fine-textured soils where high residual water contents would otherwise be fitted.

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“…The WRC of the PDI model family (Peters, 2013(Peters, , 2014Iden and Durner, 2014) is given by the equation…”

Section: Change In Pore-system Characteristics With Depthmentioning

confidence: 99%

“…The equation for K v (h) can be found in Saito et al (2006) and the closed-form equations for the two liquid conductivities are (Peters, 2013(Peters, , 2014 K …”

Section: Change In Pore-system Characteristics With Depthmentioning

confidence: 99%

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

Weber

Iden

Durner

2017

Hydrol. Earth Syst. Sci.

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Abstract. In ombrotrophic peatlands, the moisture content of the acrotelm (vadoze zone) controls oxygen diffusion rates, redox state, and the turnover of organic matter. Thus, variably saturated flow processes determine whether peatlands act as sinks or sources of atmospheric carbon, and modelling these processes is crucial to assess effects of changed environmental conditions on the future development of these ecosystems. We show that the Richards equation can be used to accurately describe the moisture dynamics under evaporative conditions in variably saturated peat soil, encompassing the transition from the topmost living moss layer to the decomposed peat as part of the vadose zone. Soil hydraulic properties (SHP) were identified by inverse simulation of evaporation experiments on samples from the entire acrotelm. To obtain consistent descriptions of the observations, the traditional van GenuchtenMualem model was extended to account for non-capillary water storage and flow. We found that the SHP of the uppermost moss layer reflect a pore-size distribution (PSD) that combines three distinct pore systems of the Sphagnum moss. For deeper samples, acrotelm pedogenesis changes the shape of the SHP due to the collapse of inter-plant pores and an infill with smaller particles. This leads to gradually more homogeneous and bi-modal PSDs with increasing depth, which in turn can serve as a proxy for increasing state of pedogenesis in peatlands. From this, we derive a nomenclature and size classification for the pore spaces of Sphagnum mosses and define inter-, intra-, and inner-plant pore spaces, with effective pore diameters of > 300, 300-30, and 30-10 µm, respectively.

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Reply to comment by S. Iden and W. Durner on “Simple consistent models for water retention and hydraulic conductivity in the complete moisture range”

Cited by 70 publications

References 9 publications

Water retention properties of a sandy soil with superabsorbent polymers as affected by aging and water quality

Water retention properties of a sandy soil with superabsorbent polymers as affected by aging and water quality

Parametric soil water retention models: a critical evaluation of expressions for the full moisture range

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

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