A Southern Forest Story
Soil Opens Window to the Past and the Future p.2
Using observations and models, Richter and Dan Markewitz,
a 1996 Nicholas School Ph.D. graduate and now assistant professor
of forest soils at the University of Georgia, estimated that
about 40 percent of the acidification of Calhoun soils was
attributable to acid rain and about 60 percent to natural
forest processes. "One of the hardest problems in understanding
the acid rain problem was to quantify the pollutant inputs
of acids relative to natural contributions," Richter says.
The study has contributed special data to other issues
of environmental significance, namely how much acid rain and
other air pollutants have altered calcium, nitrogen, and lead
in eastern forest soils. According to Richter, these issues
have been contentious in the past because of the notable absence
of direct observations of how soils change over time scales
of decades.
• "The Calhoun experiment also is helping to solve
the riddle of the carbon cycle, literally one of the great
scientific issues of our age," says Richter. Carbon dioxide
is increasing in the world’s atmosphere mainly due to fossil
fuel burning and will perhaps double in concentration by the
end of the 21st century. This has raised keen interest in
how the world’s forests incorporate a portion of the excess
carbon dioxide into tree biomass and soil.
Since the Calhoun Experiment includes such an extensive
soil archive, much about the forest-carbon cycle is contained
within the archive’s collection of small jars, including the
story of "bomb carbon." Bomb carbon – carbon that weighs 14
rather than 12 grams per mole – was greatly increased by above-ground
testing of nuclear weapons in the 1950s and 1960s, about the
time the Calhoun forest was being established. This meant
that bomb carbon "labeled" the carbon that was added and stored
in the forest, and can be used to follow it into and out of
the forest ecosystem.
Richter led a study to investigate bomb carbon within
the Calhoun ecosystem from 1957 to 1997, which resulted in
a report published in the scientific journal, Nature, in 1999.
The study estimates the rapid rate with which the
whole forest (trees and soil) can store carbon and quantifies
the soil-carbon cycle like few other long- term ecological
studies.
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