The role of some site geochemical processes in the development and stabilisation of three badland sites in Almeria, Southern Spain

Samples of both surface and subsurface soils were collected on various surfaces in three badland areas of differing ages (Tabernas, Vera and Mocatan), in Almeria province, southern Spain. Data were explored with the aim of identifying any diagnostic geochemical relationships between site EC, pH, sediment size and SAR, which might constitute typical 'signatures' for site materials, with some success. Data for the three sites are further used to explore the hypothesis that changes in site geochemistry through time are involved in badland stabilisation. It was found that: (1) the physico-chemical properties of the three sites can be differentiated by the functional relationship between EC and SAR, and this may represent a useful tool in characterising sites where piping predominates; (2) there is some (equivocal) evidence that sediment size distribution may play an additional role in site diagnosis and evolution; and (3) surfaces appear to lose sodium over time, the suggestion being that sodium is either progressively buffered by calcium during leaching, or exchanges with hydrogen on the cation exchange sites under a vegetation cover. Since other research suggests that smectite can also relocate down the profile on some marl sites, reducing hydraulic conductivity and suppressing pipes, we argue that the surface at Tabernas may be capable of long-term autostabilisation in which piping intensity progressively reduces. However, this possibility really applies only to fine-grained, densely structured materials, and evidence from the silty Triassic-rich unit in the Mocatan basin suggests that without a high clay content, piping may be expected to increase through time. From this standpoint, contemporary badland morphology at Mocatan does not represent an early stage of the forms seen in Vera and Tabernas. (C) 2000 Elsevier Science B.V. All rights reserved.