Open-file Report - 526
Final report on the geochemistry of Bitter Lake National Wildlife Refuge, Roswell, New Mexico

Water is one of our most important natural resources, and ascertaining its quality is crucial for both human and aquatic life. Water bodies such as the sinkholes, springs and lakes at Bitter Lake National Wildlife Refuge (BLNWR) provide habitat for a number of threatened and endangered species. These features are formed in gypsum bedrock, which serves as a leaky confining unit for an artesian aquifer in the underlying San Andres limestone, and are fed by upward seepage of groundwater from the aquifer (Land and Huff, 2010a; 2010b). However, the processes that control or influence groundwater quality at Bitter Lake are poorly understood. Managers at BLNWR observed that certain aquatic species are restricted to specific springs and sinkholes. Their first hypothesis was that species distribution might be related to the high salt content of some of the water bodies in the area.

Staff of the New Mexico Bureau of Geology and Mineral Resources (NMBGMR) were contracted to construct a conductivity map to aid in determining the relationship between groundwater chemistry and the distribution of aquatic species for the summer of 2008. Water samples were collected for measurements of pH, conductivity and major ions. With these data, diagrams were made to demonstrate the distribution of various salts. For example, Box and Whisker plots have been constructed to show major chemical constituents in water bodies in the study area. Stiff diagrams and Piper Plots for the springs and sinkholes have also been used to classify the water by hydrochemical facies and to indicate the relative proportions of ions. A conductivity map was constructed to show the distribution of electrical conductivity of groundwater in and around BLNWR. Because electrical conductivity is directly related to variations in dissolved solids (mostly mineral salts), other diagrams, such as total dissolved solids, pH and bicarbonate maps have also been constructed to confirm the spatial distribution of conductivity in the area.

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