John Butnor, Chris Maier, and Kurt Johnson from the SRS Biological Foundations of Southern Forest Productivity and Sustainability unit developed the Automatic Carbon Efflux System (ACES) to more effectively measure the carbon that moves out through the soil as part of the carbon cycle.
As a key element in the process of photosynthesis, carbon dioxide is absorbed through the leafy canopy of the forest, then released back into the atmosphere by living organisms: as much as half of this respiration comes from decomposition in the forest soil. Tree roots, living wood, and nocturnal respiration are also part of this efflux of carbon dioxide from forest ecosystems.
"There is a great deal of interest in determining how much carbon dioxide forests can remove from the atmosphere and retain, or sequester, as carbon pools or sinks," says inventor John Butnor. "Accurately measuring carbon dioxide respiration from the forest is essential to truly understanding the carbon cycle. The ACES system gives us a way to dynamically measure soil and woody tissue respiration rates as they fluctuate during the day and change with the seasons."
Several methods have been used to measure carbon flux before ACES. In one method, a closed, static chamber is placed on the ground, using an alkali trap to catch carbon dioxide emitted from the soil. Another method involves taking periodic samples of soil in the same location and running gas chromatography tests to determine changes in carbon concentration over time. Both of these methods are time-consuming, require a technician to take measurements manually, and are sometimes inaccurate. Recent studies have demonstrated that closed measurement techniques underestimate gas flux.
ACES is a dynamic system that uses an open, flow-through design to measure carbon dioxide as it is emitted from the forest floor or from the woody tissue of trees. The system uses a series of chambers and pumps to maintain a constant flow and evacuation of air. Sixteen soil chambers are measured sequentially using a single infrared gas analyzer and a datalogger. Since chambers are constantly cleared when not being sampled, the carbon dioxide does not build up in the soil sample and skew the readings, as it does in the static chambers used in previous systems. ACES runs continuously and is fully automatic, requiring only calibration checks twice a week.
ACES units are being used in several long-term ecological studies to collect data on a continuous basis across the southeastern United States. Current research cooperators include: Duke University (Durham, NC), USDA Agricultural Research Service (Auburn, AL), the SRS Center for Forested Wetlands Research (Charleston, SC), SRS Disturbance and Management of Southern Pine Ecosystems unit (Athens, GA), Auburn University (Auburn, AL), Westvaco Corporation, and International Paper Corporation.
ACES units have also been used in a variety of short-term studies in the United States and Canada, including black spruce plantations in the Petawawa Experimental Forest (Deep River, ON), native fir/pine ecosystems in the Teakettle Experimental Forest (east of Fresno, CA), and old-growth forests in the Pacific Northwest (Wind River Canopy Crane, near Stevenson, WA).
"We have now built 17 ACES that we have used in cooperative research projects across the country," says Kurt Johnsen, project leader of the Research Triangle Park unit. "We worked hard to develop and test this system. Now that it is patented, we hope the technology will be used in even more forested ecosystems, so that our knowledge of and ability to predict forest carbon cycling will increase even more rapidly."
For more information: John Butnor at (802-951-6771 x1230) or jbutnor@fs.fed.us
ACES: http://www.srs.fs.usda.gov/soils/research/aces.html
SRS Biological Foundations of Southern Forest Productivity and Sustainability: http://www.srs.fs.usda.gov/soils/soilhome.htm