Groundwater dynamics, land cover and salinization in the dry Chaco in Paraguay

Abstract

A two-year experimental study on saline groundwater dynamics in the Paraguayan dry Chaco is reported. This study was designed to better understand dryland salinity as a natural phenomenon and a potential consequence of land use changes, in order to avoid adverse economic and environmental impacts. A total of 28 wells at two study sites located nearby Loma Plata were monitored approximately every two weeks for groundwater conductivity and water table level, following transects from sown pasture to native forest and topographic gradients from bush or pasture to a nearby temporarily flooded lagoon. Results show a relation among topography, land cover, precipitation, groundwater salinity and surface salinization. Under pasture, groundwater was less saline in the average and the water table was slightly higher than under adjacent forest. Under forest, infiltrating rainwater never reached groundwater level, whereas under pasture, rainwater diluted the groundwater at several occasions during the observation period. Along the topographic gradients, there was a fringe prone to surface salinization along the borderline of the lagoon. At higher topographic levels, the saline ground water was low enough to not reach the surface by capillary ascension. On the other hand, high water table in the center of the lagoon fed by inflowing rainwaters (which had a slightly higher altitude level than the water table under adjacent land covers), displaced the saline groundwater vertically and horizontally. These findings provide information for land use planning in the region, which is prone to dryland salinity due to a generally high saline water table.