The Arid West—Where Water Is Scarce - The West's Fragile Ecosystem

The natural environmental systems of the West are very fragile. Because much of the West is arid or semiarid in climate, the ecosystems are in precarious balance. Alteration of the life-sustaining water supply can dramatically affect habitat and the plant and animal species that reside there. Under natural conditions, most of the surface water and groundwater recharge occurs at higher elevations, resulting in flow toward the center of the basins. Many of the discharge points are wetlands, springs, and streams fed by groundwater. These oases are water-dependent habitats in an otherwise harsh, dry environment and are necessary to the continued survival of plant and animal populations.

When groundwater is continually withdrawn, particularly in excess of replenishment, the effects spread outward from the area of withdrawal, decreasing the amount of water in the aquifer. Entire natural ecosystems can be affected. For example, in 1942 a mesquite woodland was present along the Santa Cruz River near Tucson, Arizona. It was a thriving habitat valued for its wild bird population. By 1989 the woodland was gone. Groundwater levels in the area had declined by more than 100 feet, depriving the plants of their water supply.

In another example, the Cienega de Santa Clara, the largest remaining bird habitat in the Colorado River delta, is now sustained mostly by the agricultural drainage water from the Wellton-Mohawk Irrigation District, a very saline water supply. The salinity of this supply has increased the salinity of the Colorado River water entering Mexico, resulting in a dispute over water quality. The problem is so severe that Congress enacted the Colorado River Basin Salinity Control Act of 1974 to deal with the problem. Because so much of the water's flow has been captured and used long before the river reaches the sea, the Colorado River delta continues to shrink and dry out, cutting off delivery of nutrients to the sea and reducing critical habitat for fisheries. This has had a detrimental effect not only on the environment but also on the economics and society of local communities.

Under Title II of the Colorado River Basin Salinity Control Act of 1974, the U.S. Department of Agriculture and the U.S. Department of the Interior manage the river's salinity, including salinity contributed from public lands. According to the Natural Resources Conservation Service in "Colorado River Basin Salinity Control Program" (http://www.nrcs.usda.gov/programs/salinity/), salts dissolved in the Colorado River cause more than $300 million in damages each year.