Environmental Engineering Reference
In-Depth Information
related to a physical property, mixing depth. A general model of this property must
account for the scale of the system. In this sense then the heterogeneity of ecosystems is
not a weakness, but instead leads to the development and application of scaling rules that
help promote understanding of similarities and differences.
INCLUSIVENESS AND FLEXIBILITY
Ecosystems include all biotic and abiotic components within—that's everything! Thus,
ecosystems are inclusive. Biotic properties are not more important than abiotic properties.
Mammals are not more important than microbes or vice versa. An ecosystem scientist may
need to consider rocks, rainfall, and reindeer all in the same study. Ecosystem research
seeks to integrate and synthesize knowledge about ecosystem components to arrive at a
broad understanding (
Likens 1992
). The inclusiveness of ecosystem research seems, at first
glance, to contrast with standard scientific approaches that seek to reduce the number of
variables under consideration through isolation and control to study and understand
mechanisms. The inclusive property of ecosystems might lead to the view that it is neces-
sary to study everything in the system—an inherently difficult prospect and a poor scien-
tific strategy.
The answer to this apparent contradiction is that ecosystem studies are not about every-
thing. While an ecosystem is inclusive, research problems are specific and the investigator
defines the components of an ecosystem to approach a question. In the simplest case, an
ecosystem can be considered a “black box” with inputs and outputs and where no internal
components are considered (
Eq. 9.1
). A study of carbon storage in an ecosystem might
focus on only three internal components such as primary producers, heterotrophs, and the
accumulation of organic carbon in long-term storage pools like sediments and wood.
Another study of the carbon cycling might focus on energy flow and include a number of
trophic groups such as producers, herbivores, decomposers, and predators, as well as a
variety of biotic (e.g., respiratory) and abiotic (e.g., detrital sedimentation) flows. The defi-
nition of ecosystem components is particular to a study. This flexibility is a powerful fea-
ture of the ecosystem approach because of the potential for application to many problems
and a variety of conceptual frameworks.
Consider the following hypothetical examples of possible questions and necessary com-
ponents for an ecosystem study. One study asks for a set of lakes if these ecosystems are
sinks for organic carbon—meaning, do the inputs of organic carbon to lakes exceed the
outputs? The study lakes can be treated as a black box and the question resolved merely
by measuring the balance of inputs and outputs (
Figure 9.5a
). A second study might ask if
lakes are sinks for organic carbon and if the variation in sink strength among lakes is
related to the efficiency of organic matter sedimentation and burial. In this study the
inputs and outputs of organic carbon would need to be measured and internal processes
that control sedimentation and burial would also need to be measured (
Figure 9.5b
). A
third study, pursuing the same line of investigation, might ask if lakes are sinks for
organic carbon and if the variation in sink strength among lakes is related to system respi-
ration as well as sedimentation and burial processes. This study would need to consider
the additional components controlling respiration (
Figure 9.5c
).
