Manage appropriate marshes in the Delta to sequester carbon and reverse land subsidence.

The Measure

Increase acres with subsidence reversal or carbon sequestration practices.

  • Expectations

    Land management practices on subsided land in the Delta rebuild soil, reverse subsidence, and sequester carbon.

  • Performance Metrics

    • Number of carbon sequestration projects and acres of subsidence reversal, evaluated annually.

Number of carbon sequestration projects

This chart shows the number of carbon sequestration projects in the Delta. The map shows their location.

Carbon sequestration Projects in the Delta

Acres of subsidence reversal

This chart shows acres of subsidence reversal in the Delta. Projects are Twitchell Rice Research, Twitchell Rice Expansion Project, Twitchell Island East End Habitat Restoration Project, Mayberry Farms Subsidence Reversal and Carbon Sequestration Project, Sherman Island Whale’s Mouth Wetland Restoration. Target: 30,000 acres by January 1, 2030.

Much of the Delta is sinking through due to a process called subsidence which is caused by the drainage of Delta wetlands and the subsequent oxidation of peat soil. This results in elevation loss and the release of carbon dioxide. In some areas of the Delta, the land has subsided to 25 feet below sea level. Subsidence has made Delta levees less stable, increased flood risk, caused soil loss, and released vast quantities of carbon dioxide from oxidation. Continued land subsidence harms Delta agriculture because cultivation now requires expensive drainage systems and levee maintenance. It also reduces the space on the Delta landscape that is capable of supporting restored wetland habitat.

Subsidence can be reversed through a slow accumulation of new sediment on managed wetlands and mixed wetland-rice farms. Subsidence reversal projects can also sequester carbon allowing them to take advantage of carbon credit markets while helping California meet its greenhouse gas targets. As more subsidence reversal projects are implemented we will learn more about subsidence reversal technology and enhance the Delta landscape.

Subsidence in the Delta began in the 19th century when the native wetlands were drained to allow for farming. The Delta soils are highly organic formed through centuries of decaying wetland plants. When exposed to the atmosphere these peat soils naturally oxidize. In the present day Delta, microbial oxidation is the driver of subsidence. The result of this process is that much of the soil matter in the Delta is processed and released into the atmosphere as carbon dioxide and nitrous oxide. Both carbon dioxide and nitrous oxide are greenhouse gases which contribute to climate change. In the central Delta, subsidence is occurring quickly enough that more than one centimeter of elevation is being lost per year (Deverel et al, 2016).

Each chapter of the Delta plan includes strategies to achieve the goals of the plan. These strategies are general guidance on achieving the objective laid out in the plan and in the Delta Reform Act of 2009. Associated with these strategies are recommendations. The recommendations describe more specific and implementable actions to support the achievement of Delta Plan strategies. Strategies may also have associated performance measures. Delta Plan performance measures track progress in achieving desired outcomes for the Delta Plan. Below are the strategies and recommendations associated with this performance measure. 

Delta Plan Strategy
  • Plan to Protect the Delta’s Lands and Communities

Delta Plan Recommendations
  • Plan for the Vitality and Preservation of Legacy Communities
  • Buy Rights of Way from Willing Sellers When Feasible
  • Provide Adequate Infrastructure
  • Plan for State Highways
  • Subsidence Reduction and Reversal
Metric

Acres of subsidence reversal and carbon sequestration projects, evaluated annually.

Baseline

Set at zero as of 2008.

Target

30,000 acres by January 1, 2030 (905 acres were converted in 2008 – 2011 and will be included towards meeting the target).

Data above includes the following projects:

  1. Twitchell Rice Research Project (2008; 300 acres)
  2. Twitchell Rice Expansion Project (2011; 300 acres)
  3. Twitchell Island East End Habitat Restoration Project (2013; 740 acres)
  4. Mayberry Farms Subsidence Reversal and Carbon Sequestration Project, Permanent Wetland (2010; 307 acres)
  5. Sherman Island Whale’s Mouth Wetland Restoration Project (2015; 650 acres)

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