Cattails planted to save sinking delta islands

updated 11:54 a.m. ET Aug. 11, 2008

RIO VISTA, Calif. - On one side of the gravel road are hundreds of acres of corn. On the other is a different crop that scientists hope will enable farmers to rebuild sinking islands in the Sacramento-San Joaquin Delta, combat global warming and make a profit at the same time.

The U.S. Geological Survey is growing tules and cattails on about 15 acres on Twitchell Island, about 5.7 square miles of rich but fragile peat soil 30 miles south of Sacramento.

Twitchell and other delta islands are slowing sinking, their soil eaten away by wind, rain and farming. Most are more than 20 feet below the surrounding water. A levee system keeps them from being flooded.

A collapse of the levees would bring in salt water from San Francisco Bay, damaging delta ecosystems and jeopardizing the state and federal programs that pump fresh water out of the delta for farms and cities to the south.

The Geological Survey project started 15 years ago as a small experiment on two 30-foot by 30-foot plots to see if growing mostly tules and cattails would help rebuild the islands' soil.

The plants can grow high enough to dwarf adults. As they die and decay, they slowly build up the peat. The soil under the 15-acre site has risen 1 to 2 feet since the project was moved there in 1996.

"All that soil out there are plants that grew 6,000 years ago and didn't decompose completely," said Robin Miller, a biogeochemist with the Geological Survey. "That's what peat is. So we're just making the same thing happen that happened here for millennia."

Plants capture carbon, too
About 2 1/2 years ago, scientists noticed that their "big garden," as Miller calls it, was removing carbon dioxide, one of the greenhouse gases blamed for global warming.

"We were capturing a lot of (carbon dioxide) at levels much greater than other systems — marshes and forests, grasslands," said Roger Fujii, the project's director and the bay-delta program chief for the Geological Survey's California Water Science Center.

That revelation persuaded state and federal officials to expand the project. They are now trying to determine whether the tules and cattails could be used to combat global warming through what they call "carbon-capture" farming.

Under that scenario, companies could meet state greenhouse gas limits by paying delta farmers to plant tules and cattails rather than row crops.

"They can just sit back and watch the tules grow, and they should be making money," Fujii said. "That's what the vision is. It's not to do it just on Twitchell Island. It's to see if we can do it throughout the delta on subsided land."

The Sacramento-San Joaquin Delta is at the heart of California's water delivery system. It's the meeting place of some of the state's largest rivers, draining an area stretching from the Cascades in Northern California to the central Sierra Nevada.

The region between the state capital and San Francisco Bay is dotted with dozens of islands, most of them surrounded by narrow canals and many used for farming.

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