Environmental Engineering Reference
In-Depth Information
with boundary growth, but becomes a necessity when boundary growth is limited.
In human systems, those immediate constraints are looming at least given the current
fuel-mix options.
Natural ecosystems, dependent on the solar energy flows developed extremely
complex and beautiful structures within these thermodynamic constraints. And it is
a useful guide to learn from these systems as a more eco-friendly design is
incorporated. Below, some of the ecosystem flow analysis methodologies are
explored and applied.
Investigation of Ecosystem Flows Using Network Analysis
“There are no trash cans in nature.” This is a useful phrase reminding that waste
from one entity is food/input for another. Energy, of course, has a higher dissipative
factor in the reuse than material cycles such as nitrogen, phosphorus, and calcium,
but still there is a complex network of pathways designed to utilize the energy
available in natural ecosystems. In 1973, Hannon [
4
] introduced Leontief's
input-output methodology into ecology, applying it to the energy flow structure
of an ecosystem. The ecosystem is represented by n compartments, and the energy
flowing into compartments, within compartments and exiting compartments.
A network flow model is essentially an ecological food web (energy-matter flow
of who eats whom), which also includes energy input, and nonfeeding pathways
such as dissipative export out of the system and pathways to detritus. The first step
is to identify the system of interest and place a boundary (real or conceptual) around
it. Energy-matter transfers within the system boundary comprise the network;
transfers crossing the boundary are either input or output to the network, and all
transactions starting and ending outside the boundary without crossing it are
external to the system and are not considered. The energy inflows and intra-system
flows can be considered the
production energy flow
and the flows with no
consumers such as metabolic energy and exported biomass are the
respiration
energy flow
[
5
].
The data required for ecological network analysis are as follows: for each
compartment in the network, the biomass and physiological parameters, such as
consumption (C), production (P), respiration (R), and egestion (E), must be
quantified [
6
]. Furthermore, the diet of each compartment must be apportioned
amongst the inputs from other compartments (consumption) in the network. This
apportionment of “who eats whom and by how much” can be depicted in a dietary
flow matrix
, F, where energy flows from column elements j to row elements i. For
all compartments, inputs should balance outputs (C = P + R + E) in accordance with
the conservation of matter and the laws of thermodynamics.
The sum of the flow matrix elements,
f
ij
, gives the total inflow to compartmental
i such that:
