Thursday, March 9, 2017

Streams in the Desert: Ash Meadows National Wildlife Refuge

Ash Meadows National Wildlife Refuge, about 30 miles east of Death Valley in the Nevada desert, is a first-rate example of an ecological island.  It is a place that owes its uniqueness to the underlying rocks, an oasis in the desert made possible by its geology.  Ash Meadows National Wildlife Refuge was another stop on our rainy geology trip through the Mojave and Basin and Range regions.

Streams in the desert - Ash Meadows doesn't normally look quite like this!  Although, a surprising abundance of water
flows here, hidden beneath the surface.

During the Pleistocene ice ages of the last 2.5 million years ago, this area received much more precipitation than it does now.  Much of this water seeped into the ground and flowed along fissures and underground drainages, where it has remained as "fossil water" for thousands of years.  Water in underground drainages is able to percolate through the surrounding limestone mountains, but in places with extensive faulting, underlying impermeable bedrock forces water to the surface from deep underground.  In the Ash Meadows vicinity, this geologic phenomenon has resulted in a series of about 30 springs.  Because the water originates from so deep below the surface, it is heated and springs in the area maintain temperatures around 90 degrees Fahrenheit.  Some springs have a flow of thousands of cubic feet of water per minute.

Crystal Spring, home of the Ash Meadows Amargosa Pupfish (Cyprinodon nevadensis mionectes)

The springs in Ash Meadows provide an oasis for a number of species of plants and animals, places where speciation has been occurring for the last 20,000 years.  27 endemic species of plants and animals occur here and only here; they are found nowhere else on the planet.  Ash Meadows has the world's highest number of endemic species for an area its size (23,000 acres).  Endemic species include 9 species of plant (one is federally endangered), 3 insect species, 10 native aquatic snails (an eleventh species is extinct), 4 native fish (a fifth is extinct, the Ash Meadows Killifish, and all four extant species are listed as federally endangered) and one mammal species, the Ash Meadows Montane Vole.  A number of birds also flock to the oases, including the Phainopepla which feeds on the berries of desert mistletoe in mesquite trees and wild grapes growing near the springs.

The Devil's Hole Pupfish (Cyprinodon diabolis) is the most geographically restricted and rarest vertebrate on the planet; the entire species, a single population whose numbers have fluctuated from 22 to 300 individuals, lives in a pool called Devil's Hole that measures about 40 feet by 10 feet.  (Due to the rain, the road to Devil's Hole had turned into a mess of slick, sticky clay mud and our vans weren't able to make the drive out to the site without getting stuck.)  Invasive species in the springs of Ash Meadows include Western Mosquito fish (I saw far more of these little guys than the native pupfish), Red Swamp Crayfish and the American Bullfrog.  And of course, the most destructive of them all: humans.

Sheer isolation protected this area from human encroachment for a while, but the entire ecosystem was nearly wiped out in the 1970's and 1980's.  Farming attempts diverted water from springs and pumped groundwater for irrigation, dropping the water table drastically.  In 1976, the Supreme Court ruled to limit pumping.  But in the 1980's, developers proposed a housing development of 30,000 homes, and all the urban trappings to go along with it: schools, shopping centers, casinos.  This too went to the Supreme Court, which ruled to protect the area.  The National Wildlife Refuge was established in 1984.  Thankfully, this remarkable place, this literal island in the desert, will be preserved.

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