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Sunday, July 25, 2021

UCD researchers to assess potential of large-scale carbon farming in delta

UC Davis will partner with state, federal and private agencies to study carbon capture farming in the Sacramento-San Joaquin River Delta, in an effort to curb greenhouse gas emissions. The collaboration is enabled by a three-year $12.3 million grant awarded by the state Department of Water Resources to the U.S. Geological Survey.

Carbon-capture farming involves restoring wetland plants on delta islands to absorb atmospheric carbon dioxide and rebuild the soil base, according to the USGS. The peat soils have decomposed to the point that many delta islands have subsided 20 feet or more below sea level. The ongoing elevation loss, which is accelerated by farming, will put more pressure on the levee systems that not only protect the islands from flooding, but also channel fresh water to two-thirds of California’s population.

Growing wetland plants on subsiding delta islands is a possible solution to these threatening problems. A USGS pilot project using two 7-acre test plots on Twitchell Island showed that more than 10 inches of elevation were regained from 1997-2005 through processes that add natural organic matter from wetland plants back into the soil.

“The potential [for carbon capture farming] is tremendous, but we don’t know what the effects of it will be on a large scale,” said Jim Nickles, public affairs officer for the USGS.

UC Davis soil experts will measure the potential negative side effects of the carbon-capture process.

“Wetlands are good at producing methane, a greenhouse gas 23 times more potent than carbon dioxide as far as warming the atmosphere,” said William Horwath, a principal investigator on the grant and vice chair of the department of land, air, and water resources. “We are wondering if these wetlands capture more carbon than they emit in greenhouse gases. The win-win situation is that they can.”

USGS project director Roger Fujii emphasized a need to study effects of carbon capture farming on the output of metabolic byproducts from delta soil microbes. These include the greenhouse gases methane and nitrous oxide, as well as methylmercury, a compound linked to adverse fetal development that can accumulate to toxic levels as it passes along the aquatic food chain to humans.

Horwath added that re-growing wetlands will increase the amount of dissolved organic carbon (DOC) in delta water – another potential health concern if a levee breach mixes this compound into the fresh water supply – where it can combine with disinfection chemicals to produce carcinogenic compounds that end up in drinking water.

He and his colleagues will employ carbon isotope tracing methods to determine whether DOC and methane production on carbon-farmed wetlands stems from existing sediments or from newly established plants. The studies could offer insights to appropriate land management techniques for mitigating harmful carbon emissions, such as controlled flooding.

“This consortium [of research efforts] will provide opportunities for graduate students and undergraduates,” said Horwath. “We still don’t have enough students in natural resource sciences today to tackle all these problems in the future.”

Plans are under way to establish up to 400 acres of new wetlands for study in the spring of 2009.

 

ELAINE HSIA can be reached at campus@californiaaggie.com.

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