Researchers uncover mystery of charcoal's fate
An international team of researchers, led by chemistry professor Rudolf Jaffé and Thorsten Dittmar of the German Max Planck Society, has uncovered one of nature’s long-kept secrets — the true fate of charcoal in the world’s soils.
A seemingly ordinary topic, being able to determine the fate of charcoal is critical in helping scientists balance the global carbon budget, which in turn can help understand and mitigate climate change. However, until now, scientists only had scientific guesses as to what happens to charcoal once it’s incorporated into soil. Surprisingly, most were wrong.
“Most scientists thought charcoal was resistant. They thought, once it’s incorporated into the soils, it would stay there,” Jaffé said. “But if that were the case, the soils would be black.”
Charcoal, or black carbon, is a residue generated by combustion sources including wild fires and the burning of fossil fuels. Most of the charcoal in nature is from wild fires and combustion of biomass in general, according to Jaffé. When charcoal forms, it is typically deposited into the soil.
“From a chemical perspective, no one really thought charcoal would dissolve, but it does,” Jaffé said. “It doesn’t accumulate as well as we had believed for a long time. Rather, it is exported into wetlands and rivers, eventually making its way to the oceans.”
The findings are outlined in the paper “Global Charcoal Mobilization from Soils via Dissolution and Riverine Transport to the Oceans,” which was published this week in Science, one of the most prestigious peer-reviewed journals for general science in the world.
For Jaffé, it all started with a strange finding in the Everglades. As the Barley Professor in Everglades Research and researcher with FIU’s Southeast Environmental Research Center, Jaffé has built a career studying the environmental chemistry of the river of grass.
Dissolved organic carbon is known to be abundant in wetlands, such as the Everglades, and plays a critical role in the ecology of these systems. In fact, the entire food chain of the Everglades is dependent on it. Jaffé wanted to learn more about what actually comprised the dissolved organic carbon in the Everglades. Through a research project funded by the National Science Foundation, Jaffé discovered that as much as 20 percent of the total dissolved organic carbon in the Everglades is charcoal. Surprised by the finding, his team shifted their focus to the origin of this dissolved charcoal.
In an almost serendipitous scientific journey, Dittmar, head of the Max Planck Research Group for Marine Geochemistry at the University Oldenburg in Germany, was also tracing the paths of charcoal, only from an oceanography perspective. To map out a much more comprehensive picture, the research teams joined forces, along with researchers from Skidaway Institute of Oceanography in Georgia, Woods Hole Research Center in Massachusetts, the USDA Forest Service, and the University of Helsinki in Finland. The collaborative efforts have mapped out the conclusion that charcoal is making its way to the world’s waters.
“Now, we have shown that fire is probably an integral part of the global carbon cycle,” Dittmar said.
This one single discovery, according the team of researchers, carries significant implications for bioengineering. The global carbon budget is a balancing act between sources that produce carbon and sources that remove it. According to the research, the amount of dissolved charcoal transported to the oceans is keeping pace with the total charcoal generated by fires annually on a global scale.
While the environmental consequences of the accumulation of black carbon in surface and ocean waters are currently unknown, Jaffé said the team’s findings mean greater consideration must be given to carbon sequestration techniques. Biochar addition to soils is one such technique. Biochar technology is based on vegetation-derived charcoal that is added to agricultural soils as a means to sequester carbon. Although promising in storing carbon, Jaffé points out that as more people implement biochar technology, they must take into consideration the potential dissolution of the charcoal to ensure these techniques are actually sustainable and environmentally friendly.
Jaffé and Dittmar agree that there are still many unknowns when it comes to the environmental fate of charcoal, and both plan to move on to the next phase of the research. They have proven where the charcoal goes. Now, they want to answer how this happens and what the environmental consequences are. Jaffé said the better scientists can understand the process and the environmental factors controlling it, the better chance they have of developing strategies for carbon sequestration and helping to mitigate climate change.