Soil structure development and preferential solute flow

Abstract

Abstract. Soil structure and preferential flow are thought to be highly related, but quantification of this relationship has remained problematic. A combination of experiments on two soils at local and field scale was used to study the relationships between the degree of structural development, saturated conductivities Ks, moisture release, breakthrough parameters, and observations of preferential flow at the field scale. The convection dispersion equation and mobile-immobile model were fitted to breakthrough curves, and flow channels were stained with dye. Well-developed structure was associated with high dispersivities, a high coefficient of variation of Ks, and low mobile water contents, low exchange coefficients, and a low dyed area. Field-scale observations matched the differences in structure and preferential flow parameters observed at the local scales. Local-scale preferential flow appeared to highly influence field-scale solute transport, indicating that this is an important local-scale process which is not dampened at the field scale. A conceptual model of subsoil structural development was expanded with physical parameters matching the structural development stage to predict the likelihood of preferential flow on the basis of the saturation regime of the horizon or pedon. IntroductionSoil structure is important in many soil processes, especially in fine-textured soils. Surface soil structure and aggregate stability are important factors in erosion control in that structural It is even more difficult to quantify soil structure. Aggregate stability has been used as a measure of soil structure, but this is usually confined to soil surface measurements [Kemper and Rosenau, 1986]

Caracterização hidrodispersiva de dois solos da região irrigada do Vale do São Francisco

“…Os valores determinados para a dispersividade estão de acordo com os valores encontrados em trabalhos na literatura (Perfect et al, 2002;Vervoort et al, 1999;Gist et al, 1999). 2.…”

A review of model applications for structured soils: a) Water flow and tracer transport

“…The relation between lateral dispersivity, unsaturated hydraulic conductivity, and soil morphological properties, was studied in tracer experiments carried out in columns and field plots with key Belgian soil types (Vanderborght et al, 2001). Procedures based on combined analyses of soil hydraulic measurements, tracer BTCs, and dye stained soil fractions have been proposed to relate MIM parameters to soil clay content (Shaw et al, 2000), or to soil structure formation (Vervoort et al, 1999). The latter authors conceptually linked soil structure development to the predominant state of saturation of a soil horizon as depending on its location in pedon and landscape position.…”

“…Gaur et al, 2006) should be further developed for integrating both spatial and temporal flow-transport observations. The processes linking 'form' (soil structure, layering, interfaces) and 'functions' (solute transport patterns) should be further explored utilizing tracer experiments (Kulli et al, 2003;Kasteel et al, 2005) for structure based prediction of solute transport (Vervoort et al, 1999;Vogel et al, 2006).…”

Meta-analysis of the effects of soil properties, site factors and experimental conditions on solute transport

“…Some approaches for identifying "local" PTFs for parameters of the convection-dispersion equation (CDE) or the mobileimmobile model (MIM) have been published based on relatively small datasets (less than 25 samples in all cases) that had been collected explicitly for the purpose (e.g. Goncalves et al, 2001;Perfect et al, 2002;Shaw et al, 2000;Vervoort et al, 1999). In other studies, data from peer-reviewed literature were assembled to construct larger databases of solute breakthrough curve (BTC) experiments (e.g.…”