New Mexico Geological Society Annual Spring Meeting — Abstracts

A significant proportion of groundwater originating in highlands of the 5000 krn² Estancia basin, central New Mexico is discharged to the surface at lower elevations where it is removed by evaporation. As a result, the basin-center landscape has changed dramatically in response to large, late Quaternary changes in climate (precipitation and evaporation). Evaporation during the last glacial episode occurred from a perennial lake which covered an area of up to 1000 km². Following desiccation of the lake, a 400 km² playa extended over the floor of the basin. Further reductions in effective moisture during the Holocene resulted in wind deflation and excavation of numerous, discrete depressions into the floor of the basin. This incision resulted in an 8-fold decrease, when compared to late-glacial conditions, in the area susceptible to evaporative removal of groundwater.

Our research will gather hydrologic and hydrogeologic information from the playa complex to document rates of groundwater discharge/evaporation under modem climatic conditions. Meteorological data are being collected in order to provide independent estimates of evaporation. Evaporation estimates and associated meteorological data will be used to constrain a landscape-scale model which, in conjunction with lake morphometric and playa surface-area reconstruction, may be used to simulate hydrologic/climatic changes that have occurred during the last glacial/interglacial period.

At playa "E12", along the southeastern margin of the groundwater discharge area, piezometers have been installed at depths of approximately 210 cm ("shallow") and 430 cm ("deep"). Transects of shallow and deep piezometer clusters across the playa provide information about the distribution of hydraulic head beneath the playa. Initial data show that the upward flow of groundwater is strongest around the margin ofthe playa, and that the position of the piezometric surface varies seasonally. Salinity increases from deep to shallow levels due to evaporative concentration, and increases from east to west along lateral flow paths.