Environmental Engineering Reference
In-Depth Information
Definition
Ecosystem services provide the basis for all human activity. Maintaining their
sustained function is of critical concern to the issues of sustainability addressed
here in this encyclopedia. At root, the ecosystem is a thermodynamic system
receiving, collecting, transforming, and dissipating solar energy. The energy
pathways are varied and complex and lead to the diversity of form and services
available on the earth. Therefore, it is necessary to understand the ecosystem as
a thermodynamic system and how the energy flows enter, interconnect, and disperse
from the environmental system. Ecological network methodologies exist to inves-
tigate and analyze these flows. In particular, partitioning the flow into boundary
input, noncycled internal flow, and cycled internal flow shows the extent to which
reuse and recycling arise in ecosystems. The intricate, complex network structures
are responsible for these processes all within the given thermodynamic constraints.
Design of sustainable human systems could be informed by these organizational
patterns, in order to use effectively the energy available. This article demonstrates
the need for flow analysis, provides a brief example using a well-studied ecosystem,
and discusses some of the ecosystem development
tendencies which can be
addressed using ecosystem flow analysis.
Introduction
Ecosystems, like all environmental systems, are open, thermodynamic systems
(
Fig. 5.1
). They take in energy from an external energy source - almost entirely
from solar energy, although geothermal or geochemical energy drives some
systems. Ecosystem structure is built with the energy, and then the degraded energy
is passed back to the environment. For some time period the “stored solar energy”
persists in the forms perceived on the earth's surface as biomass stores of living and
nonliving organic material - such as all of us. In Frank Herbert's novel
Dune
,he
envisioned that on an arid planet an important functional role of each individual was
“carrying” water in oneself. In a world dominated by thermodynamic constraints,
such as ours, everyone is an energy carrier. These stores are temporary and fluid.
Environment
Source/
High quality
energy input
Sink/
Low quality
energy output
System
Fig. 5.1 Environmental
systems are open systems,
connecting to the
environment through inputs
of high-quality energy and
discarding low-quality
outputs
Input-State-Output
