Irrigation and the Colorado River

From the University of Georgia (http://www.ugacfs.org/producesafety/Pages/Steps/USGrowingRegions.html)

One of the country’s most prolific growing regions is in the Mojave Desert

Dams on the Colorado River

Lake Mead

Behind each dam, a lake forms. These are used as reservoirs for cities and for agriculture.

Elevations of Lake Mead

Note the high-water marks

for Lake Mead

Worldwide large aquifers and their “Groundwater Footprint”

From http://www.nature.com/nature/journal/v488/n7410/full/nature11295.html

Location of the Ogallala Aquifer

Center-pivot irrigation circles, Finney County, Kansas. Here, water is pumped from an underground aquifer and distributed through a giant sprinkler, up to 1/2 mile in length, that pivots around a central point.

From http://ga.water.usgs.gov/edu/gallery/irrigation-sprinkler.html

Center-Pivot Sprinkler Irrigated fields

Another typical irrigation sprinkler type

This is in Nebraska (from http://ga.water.usgs.gov/edu/gallery/irrigation-sprinkler.html)

From http://ga.water.usgs.gov/edu/wuir.html

From http://pubs.usgs.gov/sir/2013/5079/SIR2013-5079.pdf

From http://pubs.usgs.gov/sir/2013/5079/SIR2013-5079.pdf

From http://www.irrigation.org/uploadedFiles/Policy/PNP-WesternIrrigationImpact_8-2013.pdf

Should the environment be altered to benefit people by growing food using irrigation in dry-land regions like southern Arizona and the central valley of California?

How about the Great Plains (irrigated by drawing water from the Ogallala aquifer)?  If we “let nature take its course”, in the case of drought, what are the consequences?  The Kesterson Marsh was artificially created by the water diverted from the San Luis drain. If it isn’t natural, why can’t we allow this wetland to dry up, i.e., return to its natural state?

If not already answered, how does the GAIA concept fit here?