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1.0
A
Ultra-oligotrophic
0.9
Hypertrophic
0.8
Oligotrophic
Eutrophic
0.7
Mes
otro
phic
0.6
0.5
0.4
0.3
0.2
0.1
0.0
1
10
100
g L
-1
)
Chl (
μ
B
0
1
0.1
10
20
10.0
30
1.0
10
40
50
10.0
1.0
60
70
100
100.0
80
90
0.1
1000.0
100
FIGURE 17.2
Two trophic classification systems for lakes. (A) Probability distribution for
chlorophyll related to trophic state. The
y
axis is the probability that a lake will have a spe-
cific trophic state given a set value of chlorophyll. For example, at 10
g chl liter
1
, the
chances are approximately 0% that the lake is ultraoligotrophic,
5% that the lake is olig-
otrophic, 50% that it is mesotrophic, 45% that it is eutrophic, and 5% that it is hypertrophic
(adapted from
Eutrophication of Waters. Monitoring and Assessment and Control
© OECD,
1982). (B) A logarithmic scale that allows a continuous index to be derived from Secchi depth,
total phosphorus, or chlorophyll
a
(plotted from data of Carlson, 1977).
Trophic classification in streams can be based on suspended algae, at-
tached algal biomass, or nutrients. Suspended algal mass in streams is usu-
ally a function of how much phytoplankton has entered the water column
from the stream bottom, except where water flow is slow enough to allow
development of a truly planktonic algal assemblage. Trophic classification
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