Could Protecting Levees Be a Key in Halting Global Warming?

By Joan Melcher, Miller-McCune.com. Posted January 6, 2009.

This article originally appeared on Miller-McCune.com.

It's obvious that carbon is stored in wetlands. But could it be stored at a rate that would merit their inclusion in carbon cap-and-trade programs?

That question has been asked since researchers looking at the safety of levees uncovered a promising way to capture atmospheric carbon. The preliminary answer is a definite ... maybe.

Well before Katrina, scientists studying central California's Sacramento-San Joaquin River Delta speculated that restoring wetlands on abandoned farmland would mitigate the hydraulic force on miles of delta levees, which in some places hold back 20 feet of water. Then, Katrina's devastation of New Orleans drew national attention to concerns about the delta's aging levees and the potential for another catastrophic failure.

Exacerbating the problem was the likelihood of certain disasters (such as California's looming "Big One") allowing saltwater intrusion from San Francisco Bay, a threat to millions of acres of farmland in the state's Central Valley as well as freshwater supplies for some 25 million Californians.

As U.S. Geological Survey scientists studied the subsidence of land drained for agricultural uses in the delta, they began to notice surprisingly high rates of carbon captured -- or accreted -- in their study plots.

Could restoring these freshwater wetlands not only help save the levees, protect farmland and save freshwater supplies but also address global climate change? That was something USGS scientist Robin Miller said people inside and outside her 10-year-old project on Twitchell Island have started asking.

Let's Find Out

The USGS recently launched a three-year, $12.3 million project that will attempt to answer the question. Scientists from the USGS California Water Science Center and the University of California, Davis have joined Miller at Twitchell Island. If they find that "carbon capture" farming in the delta is a viable idea, farmers could be paid for restoring wetlands while helping save the planet.

Specifically, Miller's research has shown that as tule (a species of sedge grass also known as bulrush) and cattails grow in these soggy study plots, the land surface rises an average of 4 to 6 centimeters a year -- from decomposing plants that form a peat soil -- with some areas rising about 0.63 meter, or two feet, over 10 years. Typical rates documented in scientific literature are a centimeter or less a year, she said.

That decomposed matter contains lots of stored carbon. The project has shown an average of 1,000 grams of carbon per square meter per year has been captured over the past five years. That dwarfs the rate of carbon sequestration achieved in reforested agricultural land, which is typically less than 100 grams of carbon per square meter per year, according to a study by Gail Chmura, associate professor of geography at McGill University and director of the Global Environmental and Climate Change Center of Quebec.

The idea of looking at wetlands as carbon sinks is relatively new, and little scientific quantification has been made of wetlands' potential to offset global warming, Chmura said.

Scientists working with Miller put some numbers to what carbon-capture farming could do for California's efforts to offset greenhouse gas emissions. They claim restoring an area the size of subsided lands in the delta could see greenhouse gas reduction equal to turning all the SUVs in California into small hybrids or turning off all residential air conditioners in the state. They're looking to find a place for carbon farming in California's carbon-trading market, which state law requires be online by 2011.

But There's a Catch

Wait a minute, say other scientists, who note methane is typically released from freshwater wetlands, and methane is a much more potent greenhouse gas than carbon dioxide. To put it in perspective, one molecule of methane is equal to 70 molecules of carbon dioxide in the atmosphere, Chmura said.

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