Geology Reference
In-Depth Information
CHAPTER 7
Biogeochemical Cycling of Chemicals
ROY M. HARRISON
Division of Environmental Health & Risk Management, School of
Geography, Earth & Environmental Sciences, University of Birmingham,
Edgbaston, Birmingham B15 2TT, UK
7.1 INTRODUCTION: BIOGEOCHEMICAL CYCLING
The earlier chapters of this topic have followed the traditional sub-
division of the environment into compartments (e.g. atmosphere, oceans,
etc.). While the sub-divisions accord with human perceptions and have
certain scientific logic, they encourage the idea that each compartment is
an entirely separate entity and that no exchanges occur between them.
This, of course, is far from the truth. Important exchanges of mass and
energy occur at the boundaries of the compartments and many processes
of great scientific interest and environmental importance occur at these
interfaces. A physical example is that of transfer of heat between the
ocean surfaces and the atmosphere, which has a major impact upon
climate and a great influence upon the general circulation of the atmos-
phere. A chemically based example is the oceanic release of dime-
thylsulfide to the atmosphere, which may, through its decomposition
products, act as a climate regulator (see Chapters 2 and 4).
Pollutants emitted into one environmental compartment will, unless
carefully controlled, enter others. Figure 1 illustrates the processes
affecting a pollutant discharged into the atmosphere.
1
As mixing proc-
esses dilute it, it may undergo chemical and physical transformations
before depositing in rain or snow (wet deposition) or as dry gas or
particles (dry deposition). The deposition processes cause pollution of
land, freshwater, or the seas, according to where they occur. Similarly,
pollutants discharged into a river will, unless degraded, enter the seas.
Solid wastes are often disposed into a landfill. Nowadays these are
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