A small jar containing a sample of sediment dug from the Kendall-Frost Marsh Reserve in Mission Beach on Sept. 16, 2021. Researchers will use the sample to determine how much carbon is in the marsh. / Photo by Adriana Heldiz

 It may look like a weedy mud flat, and yes, sometimes it burps a bit of sulfuric-scented gas, but the Kendall-Frost marsh in Mission Bay could be worth millions in terms of its ability to help slow global warming.  

New research ascribes a dollar value to one of San Diego’s remaining coastal wetland’s ability to suck carbon dioxide from the atmosphere and bury it underground, a process known as carbon sequestration. Viewing ecosystems this way could help governments like the city of San Diego weigh the cost and benefits of rebuilding wetlands over developed land it once occupied.  

Less than one percent of Mission Bay’s 4,000 acres of wetland remain. In terms of landscapes that are naturally talented at sequestering carbon, wetlands are one of the best. Initial results of a study by Patti Lieberg-Clark, a former student at Scripps Institution of Oceanography, and biological oceanographer Matt Costa, show the top meter of mud in the 40-acre Kendall-Frost marsh contains about 1,052 metric tons of carbon.   

The Kendall-Frost Marsh Reserve in Mission Beach on Sept. 16, 2021. / Photo by Adriana Heldiz

That’s a drop in the bucket compared to how much the city emits, about 9.6 million metric tons of greenhouse gases in 2019. But this marsh is an ecosystem that can bury carbon basically forever at a rate of about 15 metric tons per year, as long as you leave it alone.  

Estimating economic value of carbon sequestering capabilities is more of an art than a science. To do that, Lieberg-Clark assessed the value of the marsh’s carbon against the carbon cap-and-trade marketplace. She figures Kendall-Frost’s carbon-burying capabilities are currently worth anywhere from about $69,000 to $1.6 million.  

The reason why these values vary so much is because the price on a ton of carbon represents the cost to the environment of emitting it. In other words, the question is how much should some pay for damaging the earth, an economic theory known as the social cost of carbon. The answer is highly politicized. 

In California, carbon is tradable on its cap-and-trade marketplace where the state sets a limit on emissions and industries can buy credits, allowing those industries to pollute more if they purchase extra credits. Likewise, a conservation project, like a marsh restoration,which takes carbon out of the atmosphere, could sell its ecosystem benefits as carbon credits. (The state Air Resources Board reduces that cap by a rate of four percent each year, which forces the overall amount of emissions down.) The California marketplace valued a ton of carbon at $18 at the time of the study.  

If you ask President Joe Biden’s Administration, a ton is worth $51. (President Donald Trump priced a ton of carbon as low as $1, according to Yale Climate Connections.) But recent research suggests the price should be much higher, over $400, according to research by Kate Rickey, who is also at Scripps.  

“If you make assumptions about how bad climate change will be for the earth, the damages could be very large, even bigger than (Ricke’s) number,” said Mark Jacobsen, an environmental economist at University of California San Diego. 

None of this means that the city of San Diego can just put the marsh on the market and make a boat load of cash.  

Lieberg-Clark’s research gives an ecosystem a value that the government could compare against when making decisions about land use. For instance, the city considers how much it makes in revenue on land leases and permits for the area surrounding the marsh. In 2015, those leases generated about $30 million for the city. Permit revenues were just over $538,000 that same year.  “The nice feature of this is the city doesn’t need to capture the economic value (restoring marsh) to count it toward its climate goals,” Jacobsen said. “It can count towards the Climate Action Plan goals regardless of whether the city is getting money to get it done.” 

The city already committed to cutting half of its greenhouse gas emissions by 2035 under the first iteration of its Climate Action Plan. But none of the plan’s strategies target habitat restoration projects like this. The closest it gets (but no cigar) is growing the city’s urban tree canopy.  

Costa, the biological oceanographer on Lieberg-Clark’s study, along with members of the University of California Reserve System that manages Kendall-Frost and the San Diego Audubon Society, urged the city to capture the value of the marsh under its Climate Action Plan. 

Coastal vegetated ecosystems, including salt marshes and seagrass beds, sequester carbon more rapidly than most other ecosystems on earth, and far more than any other found in the San Diego region,” the group wrote in a July letter to the city. “Do not fail to take advantage of this opportunity in setting climate action goals for the coming years.”  

Kendall-Frost is locked-in on three sides by apartment complexes, roads and a private campground. There are not many places for the marsh to grow without displacing development other than deeper into Mission Bay waters.  

Matt Costa, a biological oceanographer, uses a tool called the Russian peat corer to dig up samples of sediment from the Kendall-Frost Marsh Reserve in Mission Beach on Sept. 16, 2021. Researchers will use the sample to determine how much carbon is in the marsh. / Photo by Adriana Heldiz

The city still owns some of the land around the marsh occupied by Campland, the private campground on the marsh’s eastern border. But the city just granted a three-year lease extension to Campland, according to the Union-Tribune, settling years of litigation between the business and the city. Campland’s owners did not respond to a request for comment on this story.  

None of the city’s plans to redevelop the area included much wetland restoration. As a result of a settlement agreement with the San Diego Regional Water Quality Control Board, the city agreed to study how to squeeze 80 more acres of marsh in the northeast corner of the bay. But plans for that restoration project won’t be out for a number of years.  

Andrew Meyer, the director of conservation at the San Diego Audubon Society, on Sept. 16, 2021. / Photo by Adriana Heldiz

San Diego Audubon Society has been pushing for exactly that. The marsh serves as habitat for the endangered Ridgway’s Rail bird, which lays eggs on floating nests protected by tall cordgrasses that prosper on swampy land.  

Andrew Meyer, its director of conservation, argues the land where Campland and another abandoned RV park further east was once wetland anyway. Such infill in the bay cut off the marsh from Rose Creek, which naturally feeds sediment and freshwater to wetland habitat.  

“The coast of California has lost 90 percent of its coastal wetlands,” Meyer said. “We’ve prioritized different things in Mission Bay over the years, but this is the only spot left and Ridgway Rails need it.”  

Clarification: This story was updated to reflect more detailed information about how California’s cap and trade system functions.

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