Pedological criteria for estimating the importance of subsurface lateral flow in E horizons in South African soils

Abstract

E horizons formed in soils by reduction and eluviation are considered to be an indicator of subsurface lateral flow (SLF) between the A and B horizons -a hydrological process important in generating streamflow. There is, however, uncertainty in the interpretation of the hydropedological behaviour of some E horizons. This study used a physical index (SLFI) to estimate the importance of SLF in profiles with E horizons, where SLFI is . Data were obtained from the South African Land Type database. For criteria development, 156 profiles were used and an additional 80 profiles were used to validate the criteria. SLFI values were determined for the 156 profiles and then divided into 3 groups, with high, medium and low values. The basic hypothesis was that the individual quantifiable and qualitative soil and landscape properties influencing the pedogenesis of E horizons, and their integrated pedogenetic expression in soil forms, would be most and least strongly expressed in the profiles of the 'high' and 'low' SLFI groups, respectively. This concept was employed in a unique way to allocate numerical values expressing the estimated importance of the criteria with regard to SLF. In order to validate the pedological criteria the 80 test profiles were subjected to a similar procedure to that used to develop the criteria, resulting in an integrated pedological criterion value for each profile, which was then correlated against its SLFI value. Selected measured properties, i.e. organic matter, Fe, Mn and clay content, of the test profiles were also correlated against their SLFI values in the validation process. The results provide supporting evidence for the validity of the pedological criteria.

Identification of hydropedological flowpaths in Stevenson–Hamilton catena from soil morphological, chemical and hydraulic properties

“…The lateral flowing water continues to accumulate until it reaches the prismatcutanic horizon in the Estcourt soil. Estcourt soils are known for the generation of lateral flow (Van Tol et al 2013). The prismacutanic horizon acts as a clay plug and governs the lateral flowing water to return to the surface, forming a seepline.…”

Using ancient and recent soil properties to design a conceptual hydrological response model

“…Soil distribution patterns control the hydrological processes such as flowpaths, residence times and storage mechanisms (Soulsby et al, 2006) which influence the quantity and chemical composition of the water exiting the soilscape (Jacks and Norrström, 2004). Soils have specific hydrological functions (Van Tol et al, 2010;Kuenene et al, 2011) and can be divided into horizons with specific hydrological functions (Kuenene et al, 2011;Van Tol et al, 2013).…”

Review of soil form and wetness indicators for wetland delineation in South Africa

“…Since the early 2000s, the discipline of hydropedology has developed rapidly in South Africa by generating a growing understanding of soil water flow mechanisms linked to morphological soil properties (Van Huyssteen et al, 2007;Le Roux et al, 2011;Van Tol et al, 2010a;2010b;2013a;2013b). The hydrological functioning of soil forms was categorised by Van Tol et al (2013a) with this process informing the expansion of soil classification into the NAS, with a subsequent proliferation of soil forms with specific hydrological criteria.…”

“…Laker (2003) emphasises the difference between continental, predominantly cold climate, elevated organic carbon soils due to recent glaciation with resultant pedologically young Northern Hemisphere landscapes, and the geologically old, hard and highly weathered subtropical to arid Southern African landscapes. The different settings yield highly diverging soils that are dealt with in the South African Classification System in a philosophically different, but regionally relevant manner for local landscape-and classification-based wetland and hydropedology interpretations (Van Huyssteen et al, 2007;Le Roux et al, 2011;Van Tol et al, 2010a;2010b;2013a;2013b, Pretorius et al, 2020Van Zijl et al, 2020).…”

“…The occurrence of depletions in deeper horizons without roots, such as grey gleyed (G) and plinthic horizons as well as lowerlying bleached eluvial (E) and albic horizons/pallid zones, requires selective application of the stipulation. In many landscapes, anoxic hillslope-or shallow groundwater drive redox depletions at depth in soils (Van Tol et al, 2010a;2010b;2013b;Le Roux et al, 2011). It is therefore proposed to rephrase the stipulation for South African conditions as follows: "Redox depletions often occur at depth, associated with oxygen-depleted water in hillslope flow paths or shallow groundwater in mature landscapes. "…”