How Much of the Colorado River Delta Remains?


The Colorado River is the fifth largest river in the United States, draining parts of seven states in the Southwest as well as parts of northern Mexico. There are thirteen major dams in the river system and more than 90 percent of the river’s water is diverted for agriculture and drinking water. Disputes over water are a permanent feature of public life in the Southwest with some cases reaching the U.S. Supreme Court. However, the natural systems that depended on the river’s water have not received as much attention. In 1922 Aldo Leopold camped and canoed through the river’s delta and called it “a milk and honey wilderness” but in one generation that delta ecosystem was gone. Until recently we didn’t even know how big the original delta ecosystem was or how much life it supported. In a recent paper Karl Flessa and his colleagues used fossil clamshells from the old river estuary to find out how productive the Colorado Delta system was during its heyday. For the last thousand years the river’s delta ebbed and flowed with natural changes in the climate and landscape, but in the last seventy years it has been reduced in area by 95 percent and it’s productivity declined proportionately. We spoke with Michal Kowalewski, one of the authors, about this clever and important contribution.

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