The Carbon Quandary: Essential and Detrimental - Sustainable Design: The Science of Sustainability and Green Engineering - page 280

lie within the physics, chemistry, and biology of the system. It is up to the
designer to apply the principles properly.
CARBON SEQUESTRATION IN SOIL
When tallying the benefits of soil conservation, a few always come to mind,
especially soil's role in sustainable agriculture and food production, keeping soil
from becoming a pollutant in the surface waters, and its ability to sieve and filter
pollutants that would otherwise end up in drinking water. However, another,
less obvious benefit is as a sink for carbon. Soil is lost when land is degraded by
deforestation and as a result of inadequate land use and management in sensitive
soil systems, especially those in the tropics and subtropics, such as slash-and-
burn and other aggressive practices. As is often the case in ecosystems, some of
the most valuable ecosystems in terms of the amount of carbon sequestered and
oxygen generated are also the most sensitive. Tropical systems, for example,
often have some of the least resilient soils, due to the rapid oxidation processes
that take place in humid, oxidized environments.
Sensitive systems are often given value by a society for a single purpose.
Bauxite, for example, is present in tropical soils due to the physical and chem-
ical conditions of the tropics (aluminum in parent-rock material, oxidation,
humidity, and ion-exchange processes). However, from a life-cycle and re-
source planning perspective, such single-mindedness is folly. The decision to
extract bauxite, iron, or other materials from sensitive tropical rain forests must
be seen in terms of local, regional, and global impacts. With this in mind,
international organizations promote improved land-use systems and land man-
agement practices that provide both economic and environmental benefits.
Keeping soil intact protects biological diversity, improves ecosystem condi-
tions, and increases carbon sequestration. This last-mentioned benefit includes
numerous forms of carbon in all physical phases. As discussed and shown in
Table B7.2, soil gases include CO 2 and CH 4 . Plant root systems, fungi, and
other organisms comprised of amino acids, proteins, carbohydrates, and other
organic compounds live in the soil. Even inorganic forms of carbon are held
in soil, such as the carbonate, bicarbonate, and carbonic acid chemical species
in soils resulting from chemical reactions with parent-rock material, especially
limestone and dolomite.
When the soils are lost, all of these carbon compounds become available to
be released to the atmosphere in the form of greenhouse gases.
The principal biological process at work in these systems is photosynthesis,
whereby atmospheric CO 2 is transformed to molecular oxygen by way of the