Redox conditions related to interflow in a soil of the Kroonstad form in the Weatherley catchment

Abstract

The Kroonstad soil form, in the Weatherley catchment, Eastern Cape Province consists of an orthic A / E / G horizon sequence, and is a typical gleyed soil of South Africa. The profile has an uncommon diffuse E / G transition. Water contents from weekly neutron water meter readings and redox response as indicated by dissolved Fe 2+ concentration were correlated with daily rainfall data from automated weather stations. Results showed that reducing conditions were more pronounced in the E horizon than in the orthic A or G horizon as indicated by the Fe 2+ concentration. This is contradictory to what is normally expected. Response in soluble iron concentration in the orthic A horizon was largely associated with rainfall events. Responses in the E horizon could not be linked to current rain events. A time lag was found to exist between a response in the A and the E horizon. The G horizon responded to seasonal changes. The inability to relate current rainfall events to redox conditions as indicated by soluble Fe 2+ response in the E horizon could be attributed to water entering the E horizon laterally through interflow. This would also explain the observed time lag. This is typical of perched water tables. The lack of response in the G-horizon is an indication of a year round flow pattern controlled by seasonal changes and is typical of phreatic water tables. It is postulated that the non-abrupt E / G transition is an indication of the dominant role of the phreatic water table during pedogenesis, with upwards and lateral movement of water into the E horizon. It is further postulated that the nature of the E / G transition could serve as a valuable criterion to distinguish between the wetter and drier soils of the Kroonstad form.

Hydropedological Classification of South African Hillslopes

“…The rate of interflow on the A/B interface mainly depends on the slope (van Tol et al, 2013). Hillslope contribution of water (fractured rock soil return flow) plays a role in the subsoil of footslope soils by creating two flowpaths in the soil body (Jennings et al, 2008). Base flow largely depends on recharge of the fractured rock as leakage from the perched soil water table is probably negligible.…”

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

“…According to Schaetzl et al (2005), Albaqualfs (similar to the Kroonstad form) in landscape positions close to streams have formed entirely by intense reduction and breakdown of organic matter followed by vertical eluviation. Jennings et al (2008) showed that vertical infiltration is impossible during the majority of the year in a Kroonstad soil form in the Weatherley catchment, Eastern Cape, South Africa. This implies that this particular E horizon did not form according to the popular belief of vertical drainage, perching and lateral leaching.…”