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
0·
m
bad
+ 25·
m
poor
+ 50·
m
moderate
+75·
m
good
+ 100·
m
high
.