Environmental Engineering Reference
In-Depth Information
method a : EBI (Breine et al. 2007)
method b : EFCI (Harrison & Whitfield 2004)
method c : EBI (Borja et al. 2004)
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total number of fish species
Limit for low =
threshold of method (a) = 7
Limit for medium =
threshold of method (c) = 3
=
threshold of method (a) = 10
Limit for
medium
Limit for high =
threshold of method (b) = 7
1
high
medium
low
0
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total number of fish species
Fig. 10.2 Definition of the membership functions low , medium and high for the metric “total
number of fish species” based on three published methods ((a), Breine et al. 2007; (b), Harrison
and Whitfield 2004; (c), Borja et al. 2004)
guarantee a smooth variation of the index in response to input variations. Defuzzifica-
tion has been performed by means of the linear combination technique: the five output
classes of ecological status have been weighted to produce a final index value varying
from0 to 100, with 0 representing bad quality and 100 representing high quality status.
The defuzzification weights are as follows:
output index value
¼
m bad + 25·
m poor + 50·
m moderate +75·
m good + 100·
m high .
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