CA Wetlands Sequester CO2 in Peat

Photo courtesy USDA

By Alex Maleshko, PanXchange Blog

Wetlands are one of the most potent nature-based systems on land that sequester atmospheric CO2. In the Sacramento-San Joaquin River Delta, UC Davis-based scientist Steve Deverel, as first reported by PublicNewsService.com, is hoping to flood the area to create a wetland. In doing so, it would also provide the additional benefit of reversing subsidence by adding as much as two inches of soil a year as watery plants die and form peat. Although it would be a slow process in the delta, every added foot would help buttress the levees that protect the land and a large portion of the area’s fresh-water supply from the Pacific Ocean’s brackish water. Restoring the Delta wetlands would have many other climate and biodiversity benefits as well, as wetlands help filter fresh water and provide a habitat for wildlife. 

“Carbon-farming” in the wetlands

The project, funded to date by California state agencies and the University of California, has so far flooded 1,700 acres of Delta farmland on Twitchell and nearby Sherman island, transforming them wetlands. In October 2020, the American Carbon Registry issued credits for 52,000 tons of CO₂ removed by the experiment, which is still in its very early stage. That makes this the first wetland project (and only one so far) to generate verified carbon credits in the US. The Delta project is also one of very few such efforts around the world, yet its promise is enormous. Wetlands cover just 9% of the Earth’s surface, yet they are the largest natural carbon sink on land, sequestering an estimated 35% of the world’s carbon stored on land, more than all other biomes combined. Since a majority of wetlands are degraded or destroyed, environmental scientists see restoring them as a huge potential source of carbon credits as countries and corporations ramp up their commitments to cut greenhouse gas emissions. 

Peat formed in wetlands is a powerful carbons sequestration vehicle, however, when it “subsides” (dries out when exposed to oxygen, allowing it to evaporate or be swept away by the wind), it releases its stored CO2. Over more than 30 years of careful measurements, Deverel has found that each year, on average, each of those acres of dried-peat farmland emits roughly ten tons of CO₂, roughly equivalent to the annual emissions of 217,000 gas-powered cars. It should be noted that all wetlands emit methane (which is 25 times more potent in terms of its atmospheric heat trapping effect than CO2), as anaerobic soil microbes digest growing plants. However, flooding lands and preventing peat from oxidizing would reduce so much CO2 that it would more than compensate for new methane emissions, according to Deverel’s research. 

Economics

Wetlands restoration is expensive, and the San-Joaquin Delta carbon project is estimated to cost $18.5 million to implement. Currently, many farmers are resistant to change, as they feel that (1) carbon offset prices are not a strong enough incentive to change their agronomic strategy, (2) paying property tax to fund work on the levees continues to work at present, and (3) the farmers can continue farming the land for well over 100 years. Ultimately, a resulting increase in prices for carbon offsets is needed for market-driven solutions, and may likely happen as climate-change mitigation needs intensify.