Topsoil and the Carbon Cycle: Soil Carbon Farming Test Plots in California Set to Expand

Twitchell Island shows efficacy of soil reclamation for sequestering carbonScientists and researchers from the U.S. Geological Survey and University of California at Davis are expanding a pilot project to test a version of “carbon farming” in parts of the San Joaquin Delta of California.

Instead of growing crops the project aims to produce soil, specifically the peatland found here when the delta was mostly marsh and wetland. When the peat returns so does the ability of the soil to store carbon and reduce emissions from unsustainable agricultural practices. Farmers are thus provided an economic incentive to practice sustainable land management.

From the ground up

Despite all the high technology and gleaming infrastructure of modern civilization, our advanced society rests firmly in the soil. If the health of the world’s topsoil declines, so eventually must the health of all from which it comes.

Organic topsoil and peatland are essential not only for the production of food, but also for maintenance of the carbon cycle, already out of balance from the rapid increase in atmospheric CO2 from burning fossil fuels.

Lester Brown of the Earth Policy Institute, writing in his book Plan B 3.0 Mobilizing to Save Civilization, says that one-third of all cropland worldwide is losing its topsoil from erosion faster than it is being replaced, with the situation worsening with each passing year.

According to the United Nations Food & Agriculture Organization 650 gigatons of carbon is stored in vegetation, 750 gigatons in the atmosphere, with fully 1500 gigatons of carbon stored in organic topsoil. Says the UNFAO:

“Soil organic carbon is the largest reservoir in interaction with the atmosphere”

Clearly, a key element of both food security and carbon mitigation lay in soil and range management.

Dr. Tim Flannery of the Australian Museum in Sydney says that

The broad figures are that we can store enough carbon in the living biosphere … of our planet, to offset all of the carbon emissions since the beginning of the industrial revolution”.

The answer is blowin’ in the wind.

The California gold rush and that sinking feeling

Back in the mid-nineteenth century a rush of humanity came from the east (and everywhere else) in search of gold. At the time the San Joaquin Delta in the central valley of California was rich in peat soil supporting vast tracts of marsh and wetland.

With the rush came settlers and the need to “reclaim” the rich delta for agriculture, mostly through a network of levees to drain the land. In the century-and-a-half since then the exposed soil has continually degraded through wind, rain, and oxidation.

The persistent alteration of land caused most of the carbon stored in the peat to “liberate” from the soil and much of the drained land to subside.

Some islands farmed in the delta are as much as 20 feet below the surrounding water levee, kept dry only by the network of increasingly strained levees.

Carbon farming, California style

In 2005, the California Department of Water Resources completed the first phase of a pilot project aimed at replanting test plots in the delta with cattails, tules and other plants that existed in these parts when the land was marsh and wetland.

As this vegetation cycles through growth, reproduction, death, and decay the peat soil is restored. With the restored soil comes new wetland – nature’s carbon sponge.

Between 1997 and 2005, 10 inches of peat soil was restored on the two 7-acre test plots on Twitchell Island in the delta. The plots demonstrated the ability to sequester 25 tons of carbon per acre per year while further eliminating additional CO2 emissions by offering an economically viable means of sustainable land management.

This initial success has led the DWR to award a three-year, $12.3 million grant to the U.S. Geological Survey and U.C. Davis to expand the carbon farming project on 400 acres in the western delta beginning in the spring of 2009.

The idea of “carbon farming” is beginning to catch on in other parts of the world, often entailing no more than paying farmers to plant trees and other carbon-sponge vegetation.

The California delta style carbon farming, specifically paying farmers to “grow” wetlands, is not without its risks, as a USGS briefing paper notes:

“Large scale efforts to manage the environment have a decidedly mixed record of success”

Those risks include the release of methane, a greenhouse gas more potent than CO2, and the possibility that the sequestered carbon could produce the neurotoxin methylmercury that can accumulate in the food chain.

Measurements of those risks during the initial pilot project showed varying results, so one principal aim of the expanded plots is to further refine those measurements to better assess the potential risks of the carbon farming concept.

A promising start

What is known is that peat soil is a natural store of carbon and with sustained erosion from land alteration a significant amount of stored carbon is released to the atmosphere. Rebuilding the soil will begin to reverse that process as well as build up subsidence, helping to protect the region’s levees and waterways.

As California works to meet its deadline of reducing it CO2 emissions to 1990 levels by 2020, the upcoming test plots in the San Joaquin Delta may provide both an environmental and economic model for others to follow.

As project director Roger Fuji puts it:

“This project is an investment in California’s future that could reap multiple benefits over several decades – for California, the nation and the world.”

Thomas Schueneman
Thomas Schueneman
Tom is the founder and managing editor of and the PlanetWatch Group. His work appears in Triple Pundit, Slate, Cleantechnia, Planetsave, Earth911, and several other sustainability-focused publications. Tom is a member of the Society of Environmental Journalists.

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  1. American scientists research on topsoil and the carbon cycle. Peat land is specially maintenance for carbon cycle. What do you say?

    Sam Martian

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  3. ‘If the health of the world’s topsoil declines, so eventually must the health of all from which it comes’. What a great point, a point that most people tend to overlook.


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