Abstract
To model water flow and solute transport in soils, hydrodynamic and hydrodispersive parameters are required as input data in the mathematical models. This work aims to estimate the soil hydraulic and solute transport properties using a ponded axisymmetric infiltration experiment using a single-ring infiltrometer along with a conservative tracer (Cl-) in the field. Single ring infiltration experiments were accomplished on an Oxisol in Areia in the state of Paraíba, Brazil (6o 58' S, 35o 41' W, and 645 m), in a 50 x 50 m grid (16 points). The unsaturated hydraulic conductivity (K) and the sorptivity (S) were estimated for short or long time analysis of cumulative three-dimensional infiltration. The single tracer technique was used to calculate mobile water fraction (Ф) by measuring the solute concentration underneath the ring infiltrometer at the end of the infiltration. Two solute transfer numerical models based on the mobile-immobile water concept were used. The mobile water fraction (Ф), the dispersion coefficient (D), and the mass transfer coefficient (a) between mobile and immobile were estimated from both the measured infiltration depth and the Cl- concentration profile underneath the infiltrometer. The classical convection-dispersion (CD) and the mobile-immobile (MIM) models showed a good agreement between calculated and experimental values. However, the lowest standard errors to the fitted parameters were obtained by the CD model.
Highlights
In many applications dealing with environmental sciences, the knowledge of soil hydraulic properties is essential: (1) to diagnose the hydrodynamic functioning of soils in relation to the natural and/or anthropogenic constraints which are applied, and (2) to simulate the physical processes to establish a prognosis on the order of magnitude of the hydraulic fluxes able, for instance, to make water and nutrients available for the plant rooting system, or to advect chemicals leading to point or diffuse pollution of the groundwater table
Physically-based modeling of coupled water and solute transport requires the knowledge of soil properties that have to be estimated with adequate accuracy
The field transport studies are more complex; the field soils are usually structured by containing large continuous macropores, such as inter-aggregate pores, earthworm burrows, drying cracks, or decayed root channels (Al-Jabri et al 2006; Arora et al, 2019; Köhne et al, 2011; Tabarzad, Sepaskhah, & Farnoud, 2011). These macropores are generally characterized by distinctly different hydraulic properties from the soil matrix and may result in significantly more rapid solute movement through the unsaturated zone as indicated by average flow estimations, due to preferential flow (Ersahin et al, 2002; Gerke & Maximilian Köhne, 2004; Kamra & Lennartz, 2005; Li, Yao, Yan, & Cheng, 2021)
Summary
In many applications dealing with environmental sciences, the knowledge of soil hydraulic properties is essential: (1) to diagnose the hydrodynamic functioning of soils in relation to the natural and/or anthropogenic constraints which are applied, and (2) to simulate the physical processes to establish a prognosis on the order of magnitude of the hydraulic fluxes able, for instance, to make water and nutrients available for the plant rooting system, or to advect chemicals leading to point or diffuse pollution of the groundwater table. The field transport studies are more complex; the field soils are usually structured by containing large continuous macropores, such as inter-aggregate pores, earthworm burrows, drying cracks, or decayed root channels (Al-Jabri et al 2006; Arora et al, 2019; Köhne et al, 2011; Tabarzad, Sepaskhah, & Farnoud, 2011) These macropores are generally characterized by distinctly different hydraulic properties from the soil matrix and may result in significantly more rapid solute movement through the unsaturated zone as indicated by average flow estimations, due to preferential flow (Ersahin et al, 2002; Gerke & Maximilian Köhne, 2004; Kamra & Lennartz, 2005; Li, Yao, Yan, & Cheng, 2021)
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