Environmental and biological characteristics of springs in Lake Mead National Recreation Area, Nevada and Arizona

Sada, Donald; Jacobs, Corey

INTRODUCTION Lake Mead National Recreation Area (LAME) encompasses approximately 607,000 hectares (1,500,000 acres) of southeastern Nevada and northwestern Arizona and portions of the Colorado, Mojave, and Sonoran deserts. Elevation in the park ranges from approximately 275 m (900 ft) in valleys to 1,200 m (4,000 ft) in mountains. Average annual rainfall is approximately 11 cm (4.5 in), and heaviest precipitation occurs during the summer monsoon season. The average summer time high temperature is approximately 46oC (115oF) and annual evaporation ranges from 28 cm (70 in) to 63 cm (160 in). Lake Mead National Recreation Area encompasses some of the driest landscapes in North America and it is defined by its aridity. Water in the park comes from seasonal runoff, thundershowers, and aquifers that support springs. Runoff and thundershowers often produce scouring flows that quickly pass through ephemeral streams, and springs provide the only persistent, reliable water for humans and wildlife. Springs are also windows into groundwater systems that are supported by local and regional precipitation (Harrill et al. 1988, Thomas et al. 1996). The importance of springs as aquatic and riparian habitats for wildlife has also become increasingly apparent (Hubbs 1995), and they are now known as “biodiversity hotspots” that support a large proportion of the aquatic and riparian species in arid regions (Fisher et al. 1972, Williams and Koenig 1980, Gubanich and Panik 1986, Myers and Resh 1999). Several hundred species or subspecies of fishes, mollusks, crustaceans, aquatic insects, and plants are endemic to western U.S. springs, which shows that they are also important to a wide variety of rare plants and animals (e.g., Hubbs and Miller 1948, Hubbs et al. 1974, Williams et al. 1985, Minckley et al. 1986, Hershler and Sada 1987, Wiggins and Erman 1987, Hershler and Frest 1996, Hershler 1998, 1999, Schmude 1999, Polhemus and Polhemus 2002, Sada and Vinyard 2002, Smith et al. 2002).

Environmental and biological characteristics of springs in Lake Mead National Recreation Area, Nevada and Arizona

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