Environmental Engineering Reference
In-Depth Information
where
I
is the summed ingestion by all consumers in the ecosystem, and
ε
a
is the
(weighted) mean assimilation efficiency of these consumers. Solutions for these equations
for a range of conditions are shown in
Figure 3.8
. Because
ε
a
varies over a wide range
with diet of the consumer, estimates of
I
from
Eq. (3.14)
are extremely approximate, and
rarely will be useful. Often
S
and
L
are known with some precision, but
g
is variable, so
estimates of total secondary production using this approach are likewise approximate.
A reasonable guess for
ε
ε
g
for many ecosystems might be about 0.3, but it may vary from
less than 0.1 to about 0.6 (
Schroeder 1981; del Giorgio and Cole 1998; Rivkin and Legendre
(a)
150
Retentiveness = 100%
Retentiveness = 50%
100
50
0
0 0 0 0 0 0 0
(b)
250
200
150
100
50
0
0 0 0 0 0 0 0
(c)
1000
800
ε
a
= 0.2
600
ε
a
= 0.2
400
ε
a
= 0.5
ε
a
= 0.5
200
0
0 0 0 0 0 0 0
Net growth efficiency (%)
FIGURE 3.8
Calculated (a) production, (b) assimilation, and (c) ingestion by the entire community of con-
sumers for a few combinations of net growth efficiency, assimilation efficiency, and ecosystem retentiveness.
Production, assimilation, and ingestion are expressed as a percentage of net organic inputs to the ecosystem.
Retentiveness is the fraction of organic inputs not subject to nonrespiratory losses (i.e., (
S-L)/S
).
(Modified from
Strayer 1988
.)