There’s a time bomb ticking in California’s Sacramento-San Joaquin Delta.

The largest estuary on the West Coast of the Americas, the Delta is a network of some 70 islands protected by more than 1,000 miles of levees. The soil on these islands is some of the richest farmland in the world because it is composed of organic material: decaying plants that accumulated over millennia.

But when the levees were built 150 years ago to create farms, this dried out the soil, causing it to oxidize and decompose. As a result, the surface of many islands has slowly sunk below sea level. This results in a stronger leverage force on the levees, making them more vulnerable to failure.

That’s a problem because the Delta is also the source of freshwater for 25 million Californians and more than 3 million acres of farmland. If numerous islands flooded due to levee failures, seawater could rush into the estuary and compromise the freshwater supply.

One solution to this conundrum is to simply allow the islands to flood again gradually, transforming them back into wetlands. Over time, wetland plants like cattails and tules would grow and die and slowly rebuild the soil elevation. But the process needs an economic incentive on a massive scale.

Now the Delta Conservancy has that incentive. The Conservancy, a state agency that oversees environmental and economic opportunities in the Delta, recently won approval from the American Carbon Registry for a new carbon banking methodology. This means wetland restoration in the Delta (and other coastal areas of the state) can now generate money by selling greenhouse gas credits to polluting industries.

To explain the process, Water Deeply recently interviewed Campbell Ingram, executive officer of the Delta Conservancy, and Steve Deverel, president of Hydrofocus, a consulting firm that helped develop the protocol.

Water Deeply: Why was this carbon methodology developed?

Steve Deverel: What we learned early on from some of the experiments on Twitchell Island, back in the ’90s and into the early 2000s, was that we could reverse the effects of subsidence and actually sequester carbon in permanently flooded wetlands on these islands. So that led to this whole carbon sequestration concept. Basically, if you flood the islands and grow wetland vegetation, these islands could accrete carbon.

Then AB 32 [California’s greenhouse gas reduction law] came along in 2006, and we began to see carbon sequestration methodologies developed for other land uses, such as forestry. There was a methodology developed for tidal wetlands in the Mississippi Delta, and we began to think more about developing a methodology for California. It seemed like an opportune time because, in the early ’90s, the state had purchased a couple western Delta islands and wanted to move forward with subsidence reversal.

Water Deeply: Why is an economic incentive needed?

Campbell Ingram: Currently there are farmers out there leasing land from the state as well as private landowners, and they’re making money off that land. So to ask them to convert to something that doesn’t result in a revenue stream is not really tenable for making a living. So we need to find something that helps replace that income but also accrues these other benefits.

Water Deeply: What other benefits are possible?

Ingram: For every inch of elevation that you don’t lose in a given year due to ongoing agricultural practices, you’re not increasing hydrologic pressure on the levee. And for every inch that you then accrete in elevation, you’re reducing that pressure. It’s a slow process, but it’s at least moving in the right direction.

A wetland compared to a monoculture of corn is typically going to have higher biodiversity, more use by waterfowl and amphibians and giant garter snakes. You can have some water quality benefits. And obviously the greenhouse gas emissions reduction and subsidence reversal.

Water Deeply: How will this protocol be used?

Ingram: One of the things we’re trying to work with right now is the state-owned lands that have existing wetlands. So we might work with the Department of Water Resources and take that land they already have in wetland production, run it through the methodology and actually get contracts to be able to have emissions reduction credits. We can then save those credits and use them to produce revenue.

Secondarily, we’ll be identifying places in the Delta where maybe the land is just getting too wet to farm. As the peat gets thinner, you get less of this hydrologic blanket that holds that water down, and you have more seepage under the levees. So a farmer could then look at that area and think, “I can actually put this land into a managed wetland and get revenue that isn’t from agricultural production.”

Water Deeply: Who would benefit from the greenhouse gas credits produced under this program?

Ingram: It’s whoever actually holds the land and is managing the land. So, essentially, a private landowner. It’s going to take some effort. The procedures early on are very complex. There’s a lot of learning that goes on. We would work with landowners to develop the agreements, and market those credits. But ultimately, it would be the landowner who would get the revenue.

Water Deeply: And who would buy these credits?

Ingram: I think it could run the gamut: anybody who has a responsibility to offset their emissions.

We’ve been working with a couple different carbon financiers who have worked with large companies that are buying carbon. They’ve been marketing the idea of Delta wetlands credits, and they’ve been getting a good response.

Deverel: It’s not necessarily offsetting emissions. We’re talking about a voluntary market. There’s not necessarily an obligation at this point to purchase these carbon credits. But I think there is interest. I think a lot of it is larger companies that just feel they want to invest in this kind of endeavor, because they feel like it’s a good thing to do. Silicon Valley is one example.

Water Deeply: How much carbon can Delta wetlands sequester?

Deverel: In the Delta we’ve established there’s probably 1 million to 2 million tons of CO2 released every year, just from the oxidation of these organic soils. If you implemented wetlands, you stop that ongoing emission. And then you also add a little bit of carbon sequestration to that.

We’ve gone through some of the numbers, and it depends on where you are and what the baseline is. But certainly upwards of 5 to 6 tons of CO2 per acre, per year is reasonable.

Water Deeply: Is it really possible to reverse subsidence and rebuild Delta islands?

Ingram: It’s absolutely possible. It’s a slow process, but anytime you inundate you stop the ongoing subsidence. So theoretically, it’s absolutely capable of restoring the island elevation. On some of these islands, it will take a very long time, say a hundred years. But for every inch you produce, you’re having a significant positive effect on the pressure exerted on that island. The challenge is to really get this concept to spread and catch on and gain acceptance, and have people accept the methodology.

Water Deeply: How does this process work?

Deverel: The key issue is very slow decomposition of the dying wetland vegetation. So every year out there, you have this cycle of wetlands growing and then dying back in winter and then growing again in the spring. That dead vegetation in the winter just basically decomposes and stays in the system and doesn’t oxidize.

You have to go back in geologic history and look at how these organic soils originally formed out in the Delta, which started about 6,500 years ago or so. And it was the result of sea level rise that occurred during the Holocene – the last 10,000 to 11,000 years – which resulted in sea level rising over time and wetland vegetation forming on kind of an outwash plain in the Delta. So you had this continual inundation that resulted in tidal wetlands that allowed them to keep accreting. So over time, you accreted 1 to 2 millimeters a year during that 6,500 years.

The 1850s came along, and the Swamp Land Act allowed people to go in and drain these swamps. In the 1860s, the reclamation of the Delta had begun and all these wetlands were converted to drained islands for farming. Since that happened, we’ve lost about half of that 5 billion cubic meters of organic matter.

Water Deeply: What’s the potential? Where do you see this in, say, another 20 years?

Ingram: There’s a lot of potential. The Air Resources Board recently put out their latest scoping plan, and in that they describe a target of 15,000 to 30,000 acres of managed wetlands in the Delta in the next 13 years. This is one of the best uses of the western Delta because of its importance to the water supply.

The farmers themselves, I think they wake up every morning and realize they are 20-plus feet underwater, and that’s probably not sustainable. So absolutely, it is our hope that we start to see islands in wetland production at scale. But that will definitely take some time, and it’s hard to put out a number on that.

We’re pretty excited, and working hard to get some pilot projects up and running to demonstrate that the methodology is viable. We feel like we’re kind of on the precipice of a great opportunity.