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Farming Carbon to Help the Atmosphere and the Land

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Detailed Description

Long-standing farming practices in California's Sacramento-San Joaquin River Delta expose fragile peat soils to wind, rain and cultivation, emit carbon dioxide (CO2) and cause land subsidence. To capture or contain the carbon, farmers would ‘grow’ wetlands. In doing so, they would begin to rebuild the Delta's unique peat soils, take CO2 out of the atmosphere, ease pressure on the Delta's aging levees, and infuse the region with new economic potential. We learn more from USGS bio-geochemist Robin Miller about how this could help California, the nation, and the world.




Public Domain.


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Jim Nickles: Hello and welcome to the USGS CoreCast. This is Jim Nickles. I am here with Robin Miller, USGS biogeochemist. And we are talking about carbon-capture farming in the Sacramento-San Joaquin Delta. 

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The idea that you could convert farmland into wetlands that take carbon out of the atmosphere and also rebuild the region's subsided peat soils.

After several years of a small-scale test that shows promising results, USGS is just beginning a much more ambitious research project to see if this could be done on a large-scale - perhaps on several thousand acres ultimately. 

Robin, what is a carbon-capture farm and how does it work?

Robin Miller: A carbon-capture farm is a wetland built specifically to grow very productive emergent marsh vegetation, in our case, cattails and tules that use photosynthesis to capture carbon dioxide from the atmosphere and put it into their plant tissue

And then the farm would store that carbon in the tissue by minimizing the loss or the decay of that. And since carbon dioxide is a very important greenhouse gas that's been linked to global warming, this could be a method to address that problem. And so our new research project will be testing the feasibility of carbon-capture farming in the Sacramento-San Joaquin Delta where it could have other benefits as well. 

Jim Nickles: What is happening in the Delta and how could carbon-capture farming address some of its problems? What do you hope to accomplish?

Robin Miller: Well, over the last century or more, reclamation of islands in the Delta for agriculture has created the conditions that promote loss of the soil. To grow corn and other row crops, the farmers drain and expose the soil to the atmosphere and this increase in oxygen from the atmosphere promotes soil microbial activity. The microbes oxidize or eat the organic matter in the peat soils.

And so under traditional farming practices, the islands lose up to an inch of surface elevation a year. And now many of the islands are subsided more than 20 feet below sea level and the ground water has to be kept even lower than the land surface to grow crops. And so we have water tables on some of those Delta islands that are 25 feet or more below the surrounding water channels which create a lot of pressure against the levees and make the levees extremely vulnerable to failure. 

And if or when the levees would fail, water would rush on to these islands flooding them, creating 20-feet deep lakes where the crops were growing. And because there's such a limit of fresh water available in the Delta and such a huge amount of land that could be filled with levee failure, we'd very likely be drawing saltwater from the Bay back into the Delta, which would make the water no good for drinking or agricultural purposes.

And this would be incredibly catastrophic to California. I mean imagine all of the water being sent down to LA, to San Joaquin valley farms, and Contra Costa being shut off. I mean what would those people in farms and businesses do without a usable water supply? So by increasing land surface elevations on these islands, the water pressures against the levees are minimized or decreased and the levee systems are a lot less felt vulnerable to failure and so there was less likely levee breaks and if there are, there are less of a problem because there's less space to filled with water. So this helps protect California's water supply. 

But this is a slow process regaining surface elevation and it's going to take many decades to return the Delta islands to sea level, but I think it's a good long term investment.

And we hope to be able to develop a different kind of farming in the Delta. Instead of growing corn or alfalfa or tomatoes, the farmers will grow tules or cattails.

Jim Nickles: So you are talking about a new kind of farming in the Delta. But Robin, how would a farmer potentially generate income from this? How would this work to replace traditional farming?

Robin Miller: Well, the farmer would sell carbon-capture credits which are similar to emission-reduction credits. A greenhouse gas reduction could be sold to an industry for which greenhouse gas reductions are prohibitively expensive or impractical. California's trying to establish a carbon-credit system that would allow carbon credits to be bought and sold. And although the carbon-credit market is not yet established in California, our hope is that carbon farms will be able to sell their credits and make money, essentially replacing conventional farming in the Delta with carbon-capture farming.

Jim Nickles: Robin, what are some of the things your research will be looking at? I've heard, for instance, that wetlands also can be emitters of greenhouse gases?

Robin Miller: We could also be producing a lot of nitrous oxide which is also a big important greenhouse gas much stronger than CO2 or methane. Re-establishing wetlands could sequester CO2 and mitigate some of the nitrous oxide emissions but then by putting out methane, you know, you're introducing another.

So we need to look at the whole balance of those. And another problem in our area is a relic from the Gold Rush era. It's the mercury that's in our system. And when you create wetlands, you create conditions where that mercury can get into the food chain, into the food web. It's called methylmercury. And so we want to see if these wetlands are producing methylmercury at what amounts. We don't know because wetlands are very variable in this.

Not all wetlands produce a lot of methylmercury even if they have mercury in the system. We don't know what will happen in these wetlands and we need to look at that. Another issue is just DOC, dissolved organic carbon, that's produced by wetland plants and is an issue in drinking water because once the drinking water's treated if there's a lot DOC, if there's a lot of dissolved organic carbon in the water, when it's treated, it can become chlorinated and creates disinfection by-products that are regulated and a concern for human health.

So these are all things that need to be looked at and that we'd like to look at more thoroughly so that we can see, really balance the benefits and the potential problems that we could have by doing this.

Jim Nickles: And maybe that you'll be able to-- You know if these are issues, there may be a way to mitigate those issues or manage the wetlands in a way that those issues are minimized.

Robin Miller: And that's what we're finding. We're finding that we can manage the wetland to minimize DOC export, that we can actually manage the hydrology to kind of minimize some of the methane emissions. We need to look at that more closely. An interesting thing about the Delta is that it produces less methylmercury than the surrounding areas. So there's more methylmercury coming in to the system than going out of the system. So even though wetlands are places where methylmercury is produced, these wetlands seem to almost be cleaning and scrubbing.

But we don't have a good handle on these processes and we really need to understand them to find out what would restoration of wetlands in the Delta, what would all of the effects of that be.

Jim Nickles: Thank you Robin for your time and we look forward to seeing your results over the next several years. And thanks to all of you out there for tuning in. 

If you're interested in learning more about the USGS carbon-capture efforts, take a look at the links on the notes for this episode.

CoreCast is a product of the US Geological Survey, Department of the Interior. I'm Jim Nickles. Have a great day.

Music by Dane Klima

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