Environmental Engineering Reference
In-Depth Information
forest, soil, and stream water, but sticking when sulfate is taken up by plants and incorpo-
rated into biomass (also a change). Later changes in the chemical form of sulfur—from
organic to inorganic—as litter decomposes allows the sulfur to be more easily lost
from the system. Thus, a description of the sulfur cycle in a forest includes movement
among pools (atmosphere, soil, plant, water), sticking within the system (particularly in
organic forms here), and transformation between inorganic and organic forms.
WHAT KINDS OF QUESTIONS ARE
ASSOCIATED WITH ELEMENT CYCLES?
Ecosystem scientists ask many kinds of questions about element cycles and make com-
parisons among elements and across ecosystems. For example, we might be interested in
whether two systems retain potassium in the same way or whether differences in soils or
crops lead to one farm field being “leakier” than another. Alternatively, a scientist might
be interested in the length of time an element spends in a system—its residence time.
Residence time questions are particularly important in studies of element transport and
sequestration, say, how long carbon arising from fossil fuel burning might be retained in
terrestrial ecosystems or in the ocean. As you will see in the following chapters, a great
deal is already known about how ecologically important the cycle of elements within and
between systems is, but there are important fundamental questions remaining—for exam-
ple, the interplay between biotic and abiotic factors in the release of phosphorus from lake
sediment. Some of these questions, as well as others that might be asked in a management
context, have implications for our actions as individuals and communities, as well as the
policies we make to mitigate disturbances within ecosystems that arise from anthropo-
genic stressors (see Chapters 12
16).
The next three chapters focus on carbon, nitrogen, and phosphorus cycling. We chose
these three elements because they are critical to life. They also provide important con-
trasts in their sources, reactivity, and linkages to each other and across ecosystems. We
encourage readers to explore how other elements move, stick, and change in and among
ecosystems in
Schlesinger and Bernhardt (2013)
. In fact, before you launch into the next
chapters, we encourage you to consider a hypothetical example: suppose a new ele-
ment—fogidium—has been discovered and your task is to research its importance in
ecosystem science. Take 10 minutes to identify what you need to know about fogidium
to assess its importance in the context of ecosystem science. Keep this list in mind when
reading about carbon, nitrogen, and phosphorus (below is a list of what other students
have identified).
SOME CHARACTERISTICS IMPORTANT FOR
UNDERSTANDING AN ELEMENT'S ROLE IN
ECOSYSTEMS
Number of oxidation states
Whether it is involved in oxidation-reduction reactions
