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 .)
 
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