The boreal forests in the north of Canada, Russia and other countries that ring the Arctic burn every summer after lightning strikes their towering trees, releasing tons of carbon dioxide into the air as they turn to ash and charcoal in the flames. Some scientists have argued, however, that this climate-changing natural disaster might not be all bad from a global warming perspective: Charcoal is a stable way to store carbon in the ground, where the carbon-rich charcoal can safely stay for hundreds if not thousands of years. Or at least that's the theory of so-called biochar. A new study published today in Science shows that such charcoal may not keep as much carbon in the soil as previously believed.

The electrically charged surface of charcoal—the reason it is used in filters—absorbs simple organic compounds that, in turn, "serve as a good food source for microbes," says ecologist and study coauthor David Wardle of the Swedish University of Agricultural Sciences. "Because these compounds are carbon-rich, and are rapidly broken down by microbes on the surface of the charcoal, we get great accelerated [carbon] loss." In other words, instead of trapping carbon in the soil, charcoal, along with microbes, accelerates its release back into the atmosphere.

The ecologists discovered this by leaving hundreds of bags containing either pure charcoal, or the natural leaf litter of the forest floor, or a mix of charcoal and leaf litter at three sites in Sweden for a decade. They report that when they retrieved the bags in 2006, the contents of the bags with the mixture—the most like natural conditions after a forest fire—had shrunk by nearly 25 percent and lost a significant portion of their carbon within the first two years of the 10 year period.

The pure coal, however, remained nearly unchanged. "The amount of soil [carbon] lost as a result of adding charcoal to soil will likely partially counteract the amount of [carbon] sequestered by the charcoal itself," Wardle says.

Some experts have proposed using such charcoal, or biochar, as a way of offsetting the extra carbon dioxide emissions from a forest fire and dead trees. In fact, some have proposed that the vast swathes of forest killed in recent years by the pine beetle in Alaska and western Canada should be turned into such biochar.

But Wardle warns that rather than serve as a carbon sink, trees turned to charcoal could end up releasing even more carbon dioxide from the forest floor.

This does not mean that biochar might not find useful applications in agriculture, where it may enhance soil fertility as well as cut down on carbon emissions. "The most useful and easiest [place to apply biochar] would be to apply the biochar to agricultural soil that does not have a litter layer such as the one studied by the authors," says biogeochemist Johannes Lehmann of Cornell University, who studies the ancient biochar practices of the historical inhabitants of the Amazon.

But that means more research is needed to determine whether more carbon is captured or released using this process. Wardle says it's particularly important to see whether his findings apply to other ecosystems and types of charcoal. "In other words, is what we found a widespread phenomenon and is it ecologically important?"

4 Comments

1. 1. skbarry 02:37 PM 5/2/08

   Wardle makes the common mistake of not differentiating fossil carbon from other carbon. Most other organic carbon will decay and re-enter the atmosphere within 5 to 10 years anyway. Making charcoal out of some organic carbohydrates and putting it in the soil prevents release of that carbon to the atmosphere (at least for several millennia). Even if it accelerates release of some other organic carbon, it does not increase atmospheric carbon concentrations like emissions of fossil carbon does. It would, instead, just increase the rate of natural carbon cycling into and out of the atmosphere. Then again, the microorganisms that he speaks of are also carbon rich and their populations are increased in soil amended with charcoal. Plus, the increased fertility of the soil promotes more vigorous growth by plants and uptake by them of CO2. I think charcoal and leaf litter in a bag is not the same as charcaol-in-soil which has plants growing in it.

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2. 2. erichj 03:14 AM 5/3/08

   Also, Biochar reduces Methane and N2O GHG soil emissions by a factor of ten, reduces water use by 17%, increases yields in some field trials by 200-300% and in each biofuel cycle 1/3 of the biomass feedstock is sequestered.
   
   If you have any other questions please visit the TP web site. http://terrapreta.bioenergylists.org/?q=node

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3. 3. DannyDay 10:59 PM 2/16/09

   The point that charcoal absorbs dissolved organic matter (DOM) and increases microbial activity on the surface of charcoal is true. However, the surface area of low temperature charcoal is small in comparison to high temperature charcoal and preferentially adsorbs decomposing organic matter that would be quickly consumed by microbes when exposed between the particles of soil. When trapped inside charcoal, it becomes the recycled nutrient base picked up by arbuscular mychorizal fungi and transported to roots via microscopic pipelines known as"fungal hyphae". This concentrates available nutrients to plants above. The structural support for these pipelines are glues such as "glomalin" which bind them to the tiny silt and sand particles they criss-cross in the soil. This also knits together soil to form aggregates, providing tilth. This is what you feel when you pick up fertile soil. The small particles of charcoal become building blocks to form much these larger structures with many times the carbon capture capacity of the charcoal which helped to build it. Just like using bricks to build a house, the enclosed volume is many times that of the bricks. During the natural wetting and drying of aggregates, the DOM dries and hardens, much as meat will if left in the sun. This strengthens the aggregates, creating long lasting topsoil and the most beneficial carbon sink in the world.
   
   Microbes will "eat" biochar and the pyrolytic condensates trapped inside. The diverse number of these compounds produced inside natural charcoal support them when the preferred DOM is cut off, as in a drought, when the soil is laid bare, there is no surface litter or compost or when there are no plants growing above to capture CO2 for their microscopic partners below. So yes, charcoal in a bag will be decomposed. So the lesson here is not to put charcoal in a bag or bury it in pits or caves. Rather, place it in the soil, sized appropriately for use in building fertile topsoil. Mix in a diverse group of locally available microbial life (from a small amount of compost). Insure you either have a cover crop growing or surface litter; no bare ground above your biochar. The formation of soil aggregates and restoring the earth's carbon pool in topsoil is the goal. Charcoal is just a natural way to accelerate the process. The pyrolysis gases contain energy, valuable extractives and simple pathways to fuel. This is the path to carbon negative energy, nutrient dense foods and a sustainable role for humankind. Danny Day EPRIDA

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4. 4. shubhamindia 05:25 AM 12/13/10

   Although the term granular activated carbon is used generically, it can refer to dozens of similar - but not identical- adsorbents. Depending on raw material, method and degree of activation and other factors, activated carbons can perform differently in various applications.
   
   Granular activated carbon has a relatively larger particle size compared to powdered activated carbon and consequently, presents a smaller external surface. Diffusion of the adsorbate is thus an important factor. These carbons are therefore preferred for all adsorption of gases and vapours as their rate of diffusion are faster. Granulated carbons are used for water treatment, deodourisation and separation of components of flow system. GAC can be either in the granular form or extruded. GAC is designated by sizes such as 8×20, 20×40, or 8×30 for liquid phase applications and 4×6, 4×8 or 4×10 for vapour phase applications. A 20×40 carbon is made of particles that will pass through a U.S. Standard Mesh Size No. 20 sieve (0.84 mm) (generally specified as 85% passing) but be retained on a U.S. Standard Mesh Size No. 40 sieve (0.42 mm) (generally specified as 95% retained). AWWA (1992) B604 uses the 50-mesh sieve (0.297 mm) as the minimum GAC size. The most popular aqueous phase carbons are the 12×40 and 8×30 sizes
   because they have a good balance of size, surface area, and head loss characteristics.
   
   http://shubhamindia.com

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