New Mexico Geological Society Annual Spring Meeting — Abstracts

The Malpais Spring and Malpais Salt Marsh are located at the end of the distal section or southwestern edge of the Carrizozo (or Malpais) olivine-basalt lava flow in the northern Tularosa Basin within White Sands Missile Range, New Mexico. The Carrizozo lava flow was originally believed to be about 1,200 years old based on visual observations. Work by Saylards (1991) and Dunbar (1999) determined that the flow was actually about 5,000 years old. The Malpais Spring and Malpais Salt Marsh are one of two endemic localities of the White Sands pupfish (Cyprinodon tularosa).

Most of the groundwater discharge from the Malpais Spring area occurs as several springs and seeps. The aquifer for Malpais Spring consists of the regional Quaternary/Tertiary alluvial bolson-fill and the buried stream-channel sediments underneath the basalt flow. Enough flow occurs in one area to form a stream channel that flows to a wetland or salt marsh. The delineated wetlands, which encompassed approximately 1,188 acres in 1997, have a salt-marsh ecosystem. The dominant species of marsh vegetation are salt grass (Distichlis spicata), iodine bush (Allenrolfea occidentalis), and spike rush (Eleocharis palustris). Some areas of the wetlands are seasonally inundated by water.

The flow of Malpais Spring was estimated to be 2,000 gallons per minute (gpm) in 1911 and 1,500 gpm in 1955. Instantaneous flow rates measured near the top of the main stream channel between 1984 and 2007 ranged from 292 to 987 gpm. These measurements do not include the flow from some seeps and springs that discharge near this stream channel and the upper marsh area. A stream gage was installed on this stream channel by the U.S. Geological Survey and began operation on 25 July 2003. At least two peak flows of about 1,607 gpm were recorded during January 2004 and August 2006.

Water quality at the points of discharge in the Malpais Spring area has remained somewhat constant over recent times. The total dissolved solids (TDS) concentrations (ROE @ 180 oC) for 14 samples collected from 1962 to 2007 varied from 4,760 to 5,200 milligrams per liter. The TDS concentrations at the lower end of the Salt Marsh can be about twice that of the point of discharge due to evapotranspiration from vegetation and evaporation from the water surface.