Climate Change

Wetlands Help Fight Climate Change, But the Kind of Wetland Matters

February 24, 2022

On a rainy fall morning, a pair of research technicians from the Berkeley Biometeorology Lab travel in a white pickup truck along a tongue of land where the Sacramento and San Joaquin Rivers converge and then finally join. Even though the road is paved with gravel, the tires kick up dust and mix with the scent of wild fennel. At a nearby pasture, cows chew cud unfazed by the sound of the rattling truck bed or river otters splashing. Sandhill cranes soar above crackling high-tension power lines. Once threatened American white pelicans fly in formation against the backdrop of slow turning wind turbines.

By the time the pickup reaches the 307-acre Mayberry Wetland, the rain lightens to a drizzle and the noise from nearby State Route 160 dissipates. Joe Verfaillie and Daphne Szutu grab their backpacks and toolkits, and walk towards the water’s edge. Here, in a flooded area once dominated by pepperweed and upland grasses, the researchers have constructed a tower, a bristling array of instruments zip-tied to metal scaffolding. “This is basically a fancy weather station,” Verfaillie says. He wears oval clip-on sunglasses and an aged brimmer hat that tames his shoulder-length hair. “It measures relative humidity, air and water temperature, rain, air pressure, salinity, and methane.” The wetlands are constantly exchanging gases, like breathing. Verfaillie and Szutu are here to measure the breath of the wetland.

Verfaillie climbs the scaffolding the way a schoolkid navigates a jungle gym during recess. By the time he reaches the second level, he appears to be hovering just above the cattails, tules, and reeds. Verfaillie cleans and adjusts a weatherproof digital camera while Szutu turns a laptop on and connects it to a terminal from one of the sensors. She adds desiccant to some instruments and mothballs to others. She then downloads the data. One more stop on the breathing-measuring tour is complete. From Mayberry they’ll go to East End and West Pond on Twitchell Island, then to Hill Slough, near Suisun. The data collection tour will take eight hours in all.

As slow-moving as it seems, driving through the wetlands where the mud and tides ooze around the gently blowing reeds, Verfaillie and Szutu feel a sense of urgency. The team is fascinated with a process most people only get from science textbooks: something called carbon sequestration. “There’s a local, regional, global push to figure out ways to pull carbon out of the air and growing wetlands is one way to do it,” Verfaillie says.

In 2018, then California Governor Jerry Brown signed an executive order calling for the state to cut its overall emissions to zero by 2045. Global leaders pledged to reduce global emissions by 45 percent by 2030 at the recent COP26. To meet those goals, Verfaillie and Szutu and many others have concluded, we need more carbon-sequestering wetlands, and fast. 

researchers check a wetland monitoring station
UC Berkeley research technicians Joe Verfaillie and Daphne Szutu check a wetland monitoring station in the Delta. (Photo by Francisco Martínezcuello)

Back at a lab tucked inside UC Berkeley’s Hilgard Hall, postdoctoral researcher Ariane Arias-Ortiz interprets the data and checks for errors. Arias-Ortiz wants to better understand the way different types of wetlands breathe, and how they can maximize carbon sequestration and minimize methane emissions. She also wants to know how this may differ with the effects of climate change, such as rising sea levels and extreme weather events. The measurements can also help maintain wetlands. For example, they might help managers determine when to implement water drawdowns to reduce the amount of methane emissions, or determine optimal water levels to maximize plant growth and carbon sequestration in the soil.

There are different types of carbon sequestration. Geological carbon sequestration is when carbon dioxide is stored in underground geologic formations like rocks. Some cement or steel production companies or energy-related sources like power plants or natural gas processing facilities will inject their CO2 emissions into porous rocks for long-term storage. Technological carbon sequestration is a relatively new method where CO2 is used as a resource, like in the production of graphene, which is then used to create screens for devices like smart phones and in fast charging batteries. Industrial carbon sequestration involves the capture of carbon from a power plant: pre-combustion, post-combustion, and oxyfuel. All these carbon sequestration types are expensive. A cheaper, more natural method of carbon sequestration is the biological one – plants and algae, whether in a forest, a grassland, or a wetland like Mayberry, draw CO2 out of the air to build themselves. When they die, that carbon is buried with them instead of being released into the atmosphere. 

Wetlands are particularly good at carbon sequestration, Arias-Ortiz says. One reason is because wetlands are inundated most of the time, so the carbon stored is underwater where there is no oxygen and therefore preserved for longer than it would be if it were exposed to the atmosphere. In fact, according to NOAA, wetlands sequester carbon at rates ten times higher than most forested systems. Even though wetlands represent a much smaller fraction of the surface land area on Earth compared to forests, they are equally as effective as carbon sinks. With one major caveat, Arias-Ortiz says: “if left undisturbed.” If the wetlands are filled for development, drained for agriculture, or modified due to dams or water diversions they no longer function as carbon sinks and become a carbon source – releasing all their stored carbon into the atmosphere.

According to the California Water Quality Monitoring Council, the state has lost more than 90 percent of its historical wetlands. Many remaining wetlands are threatened by rising sea levels, climate change and anthropogenic activities.  

In the San Francisco Bay, wetland extent reached a nadir in the late 1990s. Of what was 200,000 acres of marsh before Europeans arrived, only 40,000 acres remained. In 1999 scientists called for the remaining acres to be protected and for 60,000 additional acres to be restored for a healthier and sustainable ecosystem. A report by the Bay conservation group Save the Bay in April 2021 says that 78,000 acres of wetlands have either been acquired, already existed as healthy wetland, or have been restored, leaving 22,000 acres to reach the 100,000-acre goal.

The question Arias-Ortiz wants answered is how, or whether, restored tidal wetlands are different from nontidal-managed wetlands when it comes to their carbon sequestration power and to the amount of methane they produce. The answer matters because restoring wetlands isn’t easy, and it’s to everyone’s benefit to make sure the process captures the most carbon it can while minimizing methane emissions that may cause unintended warming. Mayberry, for example, was constructed by California’s Department of Water Resources (DWR) in 2010 after three years of planning and permitting with a price tag of $1.6 million. The project restored about 192 acres of emergent wetlands and enhanced roughly 115 acres of seasonally flooded wetlands. Since the fall of 2010, DWR has worked with UC Berkeley and used the greenhouse gas data collection for policymakers and legislators.      

Arias-Ortiz looks in the Mayberry data for carbon storage and methane production. Methane is the second most abundant greenhouse gas after carbon dioxide, but it has more than 80 times the warming power of CO2 over the first 20 years after it reaches the atmosphere. Though the effects of CO2 are longer-lasting, methane sets the pace for warming in the near term.

In wetlands, methane is produced from microbes in the soil called methanogens. These organisms produce methane when they decompose organic matter from the dead plant material that ends up accumulating in soils, and especially in the absence of oxygen – a common condition in waterlogged wetland soils. Once methane is produced, it diffuses from the soil to the atmosphere.

Arias-Ortiz’s experiments have illuminated differences between non-tidal and tidal restored wetlands. In her analysis, non-tidal wetlands stored the most carbon, but also had high methane emissions, meaning on net they would not provide climate benefits for roughly the first two to eight decades after restoration. The restored tidal wetland she studied stored less carbon in the soil than its non-tidal counterpart, because some carbon leaks away with the tides, reducing carbon storage on-site. Overall, however, the tidal wetland was a net greenhouse gas reducer because of its lower methane emissions. Wetland restoration, Arias-Ortiz concludes, should be considered a long-term process.

And even though some wetlands produce methane, they offer numerous other environmental benefits, Arias-Ortiz says. “Wetland restoration is important to maintain critical wildlife habitat, improve water quality, limit flooding, and provide erosion control,” she says. “Wetlands benefit societies and the environment and are also important in mitigating climate change due to their capacity to sequester carbon dioxide and modulate atmospheric concentrations of greenhouse gases.”

The experiment will continue until its funding ends in 2024. Daphne Szutu and Joe Verfaillie will return to these wetlands every two weeks to retrieve the data, maintain equipment, and check on the status of the towers and water levels. The synthesized data will make its way to spreadsheets, presentations, and research papers and funding proposals. Meanwhile, slowly but for as long as it remains intact, the wetland will grow itself from the gases that cause humanity such problems, and keep breathing.

This story was produced with support from the 2021 National Association of Science Writers David Perlman Virtual Mentoring Program.

About the Author

Francisco Martínezcuello is a second year student at UC Berkeley Graduate School of Journalism. He is a narrative writer focusing on science and the environment.