Environmental Engineering Reference
In-Depth Information
Wet deposition
Process by which an atmospheric constituent is removed by precipi-
tation. This is especially important for water-soluble and aerosol
species.
Definition of the Subject and Its Importance
Biogeochemistry represents the interaction of biology, chemistry, and geology in
the Earth system. For many processes, an understanding of biological uptake and
emission, chemical processing, and geological sequestration is necessary to resolve
the sources and sinks of a particular constituent. For example, to discover the
sources and sinks of atmospheric carbon dioxide, it is important to understand
how biota take up carbon dioxide and chemically convert the carbon to organic
carbon, and then how this organic carbon is used either to produce energy by biota or
is deposited to the land or ocean surface and can become sequestered in geological
formations. Often when biogeochemistry is referred to, one refers to the nutrient
cycling of important nutrients. Atmospheric biogeochemistry, as defined in its
narrowest sense, is the flux of nutrients and pollutants important for biogeochem-
istry through the atmosphere. In its broadest sense, atmospheric biogeochemistry is
the interaction of the atmosphere and atmospheric processes with the biogeochem-
istry of the earth system. This broader definition is used here. The hydrologic cycle
is one of the most important biogeochemistry cycles, and is a worthy topic of its
own. It is discussed in several other sections of this encyclopedia (e.g., Climate
Change and Global Water Sustainability, Water Resource and Quality Management
for Adaptation to Climate Change, Water Availability and Quality, Sustainable).
Introduction
Atmospheric biogeochemistry is increasingly relevant for today's society, as
evidenced by the changing composition of the atmosphere. Atmospheric biogeo-
chemistry views these changes in the composition as part of a collection of changes
to the earth system occurring during the anthropocene. One very serious
sustainability issue at the core of atmospheric biogeochemistry is the accumulation
of carbon dioxide in the atmosphere. This is a result of human emissions of carbon
dioxide both directly from fossil fuel burning, and from land use change, especially
tropical deforestation [
1
]. Interestingly, only about ½ of the carbon dioxide emitted
into the atmosphere remains there: The rest is taken up by the land and ocean. This
important negative feedback on human emissions of carbon dioxide is a result of
biogeochemical cycling of carbon in the system. As human emissions of carbon
dioxide grow, it is not clear that the land and the ocean will be able to keep up, and
