Delta Conservancy Awarded for New Carbon Methodology

Levees and subsided farmland in the Delta (photo: Department of Water Resources)

In April, the American Carbon Registry presented the Innovation Award to the Delta Conservancy and its partners for the development of a landmark carbon offset methodology to quantify greenhouse gas emission reductions from the restoration of wetlands in the Delta and along the California coast. The new science-based methodology combines data and restoration techniques to create a carbon offset project development framework, which can then be used to seek funding for restoration or habitat enhancement projects.

The completion of this methodology marks the successful implementation of Estuary Blueprint Task 11.3:

Support the carbon market by completing relevant offset protocols for wetlands and by developing reference sites and standard carbon monitoring and accounting practices that reduce reporting costs for participants.

Research in freshwater emergent wetlands on delta organic soils shows that carbon capture wetlands are the most carbon-rich landscape per acre. Over 2.5 billion cubic meters of organic soils have disappeared since the late 1800s, resulting in subsidence up to 25 feet below sea level in some parts of the Delta. These drained and cultivated organic soils continue to emit an estimated 1.5-2 million metric tons of CO2-equivalent annually, equal to annual emissions from over 300,000 passenger vehicles.

Delta subsidence graphic

This illustration from Restoration of California Deltaic and Tidal Wetlands (2017) demonstrates the effects of subsidence on carbon sequestration and emissions in the Delta.

Research in the Delta conducted by DWR, USGS, and the University of California has shown that flooded wetlands and rice fields, when managed correctly, not only stop subsidence but reverse it by increasing the accretion of decaying plant matter and sediment. A carbon offset project development can provide much-needed funds for refuges and managed agricultural land in exchange for enhancing and restoring marsh habitat for the purpose of carbon sequestration.

As Campbell Ingram, Executive Officer of the Sacramento-San Joaquin Delta Conservancy, says, “State and federal funding remains insufficient to address land subsidence that threatens the California water system, and carbon market revenues could help fill the funding gap. The new ACR methodology provides an incentive to landowners in the Sacramento-San Joaquin Delta, Suisun Marsh, and other historically natural wetland areas in California to convert their most subsided and marginal agricultural lands to wetlands or to produce wetlands crops such as rice, which will stop land subsidence and reverse it over time.”

The Delta Conservancy led development of the methodology in partnership with HydroFocus, University of California at Berkeley and Tierra Resources. Funding was provided by the Sacramento Municipal Utility District (SMUD), the California Coastal Conservancy, the Metropolitan Water District and California Department of Water Resources (DWR).

Written by Darcie Luce