Environmental Engineering Reference
In-Depth Information
thus more of the carbon dioxide is likely to stay in the atmosphere [
2
]. Some studies
suggest that warming itself leads to less carbon dioxide being taken up by the land
and ocean [
2
], although this also depends on the cycling of other nutrients such as
nitrogen as well [
3
]. Thus understanding the biogeochemistry of carbon is required
to understand how much carbon can be emitted in the future.
The atmospheric transport and subsequent deposition of trace gases and aerosols
can provide an important mechanism for circulation of different constituents.
Whether this deposition serves as a nutrient or a pollutant usually depends on the
deposition level, as well as the ability of the biota to process these compounds.
Some compounds can be nutrients at low levels, but pollutants at high levels. Thus,
referring to the atmospheric transport of nutrients and pollutants as “atmospheric
biogeochemistry” allows for these changes in impacts depending on amount. For
transport from the land to ocean, many constituents can also be carried by rivers; in
the sections below, the relative importance of atmospheric versus riverine inputs is
discussed. The atmosphere tends to be able to transport species more quickly and
farther distances; however the mass of the atmosphere is much less that of water,
providing a constraint on the amount of constituent the atmosphere can transport.
For the cases of constituent transport from the oceans to land, or upstream on land,
atmospheric transport on short timescales is often the most important, as the only
other mechanism would be geological changes in orography.
The final important aspect of atmospheric biogeochemistry is that it allows us to
understand the composition of the atmosphere, and the fluctuation in this composition,
in an earth system context. Thus understanding atmospheric biogeochemistry
represents an integrative approach to understanding the atmosphere and its relation-
ship with the land, ocean, and crysophere.
Cycling in the Atmosphere
Since most nutrients cycle through the atmosphere, the atmospheric portion of their
biogeochemistry is important. The most important nutrients to sustain life are
carbon, nitrogen, and phosphorus, but many other nutrients are required. Here
some of the most important nutrient cycles for the earth system are discussed,
and cycles that are being perturbed due to human activities have to be focused upon.
Carbon Cycle
The carbon cycle receives substantial interest today because of the anthropogenic
perturbation of the carbon cycle and the documentation of global warming. The
carbon cycle represents the most important of the nutrient cycles, with the exception
of water, for living organisms because living tissue is primarily composed of carbon.
The dominant form of carbon in the atmosphere is carbon dioxide, a chemically
inactive, but radiatively important species in the atmosphere. The riverine flux
of carbon is 0.8 Tg/year, while the gross land and ocean fluxes with the atmosphere
