Environmental Engineering Reference
In-Depth Information
(a)
(b)
(c)
(d)
(e)
(f)
(g)
FIGURE 1.1
Some examples of ecosystems: (a) the frigid Salmon River, Idaho; (b) a residential neighborhood in
Baltimore, Maryland; (c) a biofilm on a rock in a stream; (d) a section of the southern ocean containing a phyto-
plankton bloom; (e) a redwood forest in the fog in California; (f) a tree cavity; (g) the Earth (Photocredits: 1a - John
Davis; 1b - Baltimore Ecosystem Study LTER; 1c - Colden Baxter; 1d - US government, public domain; 1e -Samuel
M. Simkin; 1f -Ian Walker; 1g - NASA,
http://visibleearth.nasa.gov/
).
an ecosystem, and therefore equally valid objects of study. This viewpoint contrasts with
physiology and population ecology, for example, in which the organism is the object of
study, and the nonliving environment is conceived of as an external influence on the object
of study. Finally, the definition implies that ecosystems have definite boundaries, but does
not tell us how we might go about setting or finding the boundaries to an ecosystem.
There are some unexpectedly powerful advantages to this simple definition. First, by
including all living and nonliving objects in a specified space, it is possible to use the tool
of mass balance to follow the movement and fate of materials (
Box 1.2
). Material that
comes into an ecosystem must either stay in the ecosystem or leave—there is simply no
