Seven decades of management virtually wipes out life from the tidal flats of the Colorado River Delta

(Blacksburg, Va., December 1, 2000) The biological productivity of the Colorado River Delta is only 5 percent of what it was before the mighty Colorado's water was diverted for human uses. Since the 1930's, an environment that supported billions of clams and other life has disappeared because dams and irrigation projects have reduced the flow of nutrient-laden fresh water to the tidal flats of the Colorado Delta.

Islands composed entirely of gleaming white clam shells line the lower reaches of the Colorado Delta, where the river empties into the Gulf of California between the Baja peninsula and the mainland Mexico. Satellite images and field data indicate that at least two trillion (2x 1012) clam shells make up the areas beaches and islands. Seen from the ground, the shells form miles of sun-bleached ridges, originally shaped by spring floods, tides, and the passing of generations of abundant shellfish. In the last seven decades, after the river's flow virtually stopped, the clams have become sparse.

The approach for measuring life on the delta over the last thousand years, pioneered in a study by researchers from four universities, can be used to estimate the prehistoric productivity of coastal ecosystems in other parts of the world. Such estimates will be especially valuable in areas where no biological surveys were made before humans modified the habitat.

"This effort was highly interdisciplinary," says Michal Kowalewski , geological scientist at Virginia Tech. "We used a variety of tools to combine paleontological, biological, geochemical, and satellite image data. It was exciting to find out that we can use fossils to address environmental issues that have direct societal relevance."

The research report by Kowalewski, Guillermo Avila of the Universidad Autonoma de Baja California, Karl Flessa of the University of Arizona, and Glenn Goodfriend of George Washington University will be published in the December issue o

Contact: Michal Kowalewski
Virginia Tech

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