Geochemical evolution and elemental behaviour of playa sediments: impacts of natural weathering and agricultural practices

Abstract

Playas are predominantly alkaline wetlands common in arid and semi-arid regions. These unique ecosystems are heavily influenced by climatic and hydrological processes, such as high evapotranspiration rates and negative water balance. Numerous studies have documented the ecological degradation of these saline ecosystems due to both anthropogenic and natural processes. The present research analyses the mineralogical and elemental changes in six representative playas at different degradation stages in the western External Betics. Chemical weathering and element fractionation were examined to identify the key geochemical factors involved in the degradation of these playa wetlands. A novel methodology for calculating the Fractionation Index (FI) has been developed and applied alongside established geochemical indices, such as the Chemical Index of Alteration (CIA), Chemical Index of Weathering (CIW), and Vogt’s Residual Index (VRI), as well as analyses of elemental distribution. This approach allows for a comprehensive differentiation of the geochemical processes occurring in nonsaline-alkali, saline-alkali, and degraded playas. The study highlights the role of alkalinity in promoting clay mineral formation, with Na+ and Ca2+ dominating the cationic composition. These findings provide insights into the dynamics of playa ecosystems and inform conservation strategies for managing these vulnerable environments.