Environmental Engineering Reference
In-Depth Information
BOX 1.1
SOME NONECOLOGICAL SYSTEMS
Thinking about some of the many famil-
iar examples of nonecological systems may
help you understand how ecosystems are
described and compared. A system is just a
collection of more than one interacting
object. A few familiar systems include the
group of planets rotating around the sun as
a system (the solar system); the group of
electrons, protons, and neutrons forming an
atom; and the system of banks that controls
the money supply of the United States (the
Federal Reserve System). Just as with eco-
systems, we can describe these systems by
their structures, their functions, and the fac-
tors that control them.
A description of system structure often
begins with the number and kinds of
objects in the system. Thus, we might note
that our solar system contains eight or nine
planets; or that the copper atom has 29
electrons, 29 protons, and 35 neutrons; or
that the Federal Reserve System contains a
seven-member Board of Governors, 12
banks, and 26 branch banks. Systems have
functional properties as well—the copper
atom exchanges electrons with other atoms
in chemical reactions, and the Federal
Reserve System exchanges money with
other banks. Systems may be described
according to their controls as well. Gravity
and rotational dynamics control the
motions of the planets, and the copper
atom is controlled by strong and weak
atomic forces, whereas the Federal Reserve
System is controlled by the decisions of its
Board of Governors (who, in turn are cho-
sen by a president who is elected by the
voters of the United States). All of these
descriptions allow us to understand how
each system works. Perhaps more impor-
tantly, they let us compare one system to
another—our solar system with those of
other stars; the copper atom with the cad-
mium atom; our current banking system in
the United States with that of France,
or with that of the United States in the
nineteenth century. Ecosystem scientists
likewise describe ecosystems in various
ways to understand them better, and to
allow comparisons across ecosystems.
Systems science, the general field of
understanding all kinds of systems, is well
developed. Many of the conceptual frame-
works for ecosystem science are those of
system science (e.g., Hogan and Weathers
2003 ).
other place for the material to go. Mass balance offers a convenient quantitative tool for
measuring the integrated activity of entire, complicated systems without having to mea-
sure the properties and interactions of each of its parts. It also allows ecosystem scientists
to estimate the size of a single unknown flux by difference. Consequently, it will become
evident throughout the topic that ecosystem scientists often use the powerful tool of mass
balance.
Second, defining an ecosystem as we have done makes it possible to measure the total
activity of an ecosystem without having to measure all the parts and exchanges within the
ecosystem. This is sometimes referred to as a “black-box” approach, because we can
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