The Carbon Quandary: Essential and Detrimental - Sustainable Design: The Science of Sustainability and Green Engineering - page 278

agricultural productivity. The very essence of a soil's “value” has been its
capacity to support plant life, especially crops. Even forest soil knowledge owes
much to the agricultural perspective, since much of the reason for investing in
forests has been monetary. A stand of trees is seen by many to be a standing crop .
In the United States, for example, the Forest Service is an agency of the U.S.
Department of Agriculture. Engineers have been concerned about the statics
and dynamics of soil systems, improving the understanding of soil mechanics
so that they may support, literally and figuratively, the built environment. The
agricultural and engineering perspectives have provided valuable information
about soil that environmental professionals can put to use. The information
is certainly necessary, but not completely sufficient, to an understanding of
how pollutants move through soils, how the soils themselves are affected by
the pollutants (e.g., loss of productivity, diversity of soil microbes), and how
soils and contaminants interact chemically (e.g., changes in soil pH change
the chemical and biochemical transformation of organic compounds). At a
minimum, environmental scientists must understand and classify soils according
to their texture or grain size (see Table B7.1), ion-exchange capacities, ionic
strength, pH, microbial populations, and soil organic matter content. These
factors are crucial to green design.

Table B7.1 Commonly Used Soil Texture Classifications

Name Size Range (mm)

Gravel > 2.0

Very coarse sand 1.0-1.999

Coarse sand 0.500-0.999

Medium sand 0.250-0.499

Fine sand 0.100-0.249

Very fine sand 0.050-0.099

Silt 0.002-0.049

Clay < 0.002

Source: T. Loxnachar, K. Brown, T. Cooper, and M. Milford, Sustaining Our Soils
and Society, American Geological Institute, Soil Science Society of America,
USDA Natural Resource Conservation Service, Washington, DC, 1999.

Whereas air and water are fluids, sediment is a lot like soil in that it is a matrix
made up of various components, including organic matter and unconsolidated
material. The matrix contains liquids ( substrate to the chemist and engineer)
within its interstices. Much of the substrate of this matrix is water, with varying
amounts of solutes. At least for most environmental conditions, air and water
are solutions of very dilute amounts of compounds. For example, air's solutes
represent small percentages of the solution at the highest concentrations (e.g.,