Salt accumulation and redistribution in the dry plains of Southern South America: Lessons from land use changes

Abstract

We synthesize research on the magnitude and dynamisms of salt stocks in the Chaco-Pampas. While current soil maps characterize one-fourth of the region's soils as saline; integrated soil-hydrology-vegetation studies show salinity to be more widespread and dynamic due to the presence of shallow and stagnant groundwater systems. Two salt retention mechanisms that are turned "off" or "on" by land use changes are proposed: "arrested drainage" and "landscape stagnation." In the Chaco and Espinal, deforestation and cultivation have relaxed arrested drainage, raising the groundwater and bringing a diluted salt pool to the surface that damages crops and soils. Over the shallower and fresher water tables of the Pampas, tree plantations trigger local arrested drainage and in the landscape stagnation context work as virtual lowlands, consuming groundwater and increasing salt pools. While land use changes highlight the dominant role of vegetation dictating the dynamics of salt pools, key fundamental questions about long-term salt dynamics remain open. Rapid and widespread land use changes offered a unique laboratory to understand saline environments showing that they are more dynamic and sensitive to our interventions, than previously thought.