Estimating Depth of Water Table in Hydric Soils: A Case Study in Northern Patagonia, Argentina

María Cristina Frugoni, and Gabriel Falbo

Universidad Nacional del Comahue, AUSMA, Argentina

Abstract: This work was carried out in the sector called “Vega Plana” (40°07´02", 40°08´39" LS, 71°15´14" 71°18´17" LO) in San Martín de los Andes, Neuquén, Argentina. It’s inserted into a fluvioglacial valley landscape, surrounded by mountains that drain towards it. Relief is flat and soils are poorly drained, covered by grasses and Cyperaceae. Meadows or “mallines” in the intermontane valleys of Northern Patagonia are frequent and function as regulating units of the landscape hydrology, storing the excess water in times of rain and bringing water to streams during dry season. Soils that develop in these ecosystems are the so-called hydric soils. In this region are derived in volcanic ash, with intrinsic characteristics printed by the parent material, but with an evolution marked by the permanent groundwater table. This regulating role of hydric soils becomes more relevant when development of cities in areas of these characteristics must be resolved. San Martín de los Andes includes meadows in its area, being the most important the “Vega Plana”, on which real estate developments are being carried out, framed by a restrictive regulation in terms of land use percentage. One of the criteria for land occupancy concerns depth of water table. Due to the complexity of these processes and their manifestation in the profile, a series of criteria to estimate that depth was proposed. Redoximorphic features were studied to estimate the least depth that water table can reach. Abundant, precise and coarse redox concentrations would indicate the presence of the capillary fringe; sectors with dominant redox depletions would coincide with the oscillation fringe and the reduced areas, with the presence of free water for most of the year.

Key words: redoximorphic features, volcanic ash soils, San Martín de los Andes