Algae as Bioindicators - Freshwater Algae: Identification, Enumeration and Use as Bioindicators - page 130

Ta b l e 3 . 1 3 Calculation of the Diatom Index ( I d ): River Semois.

Diatom a j v j a j × v j s j a j × v j × s j I d

Achnanthes lanceolata 0.9% 1 0.9 3 2.7

Gomphonema parvulum 0.5% 1 0.5 2 1.0

Navicula accomoda 78.7% 3 235.1 1 235.1

Nitzschia palea 19.7% 2 39.4 1 39.4

Others 0.2%

Total 275.9 278.2 278.2/275.9 = 1.0

Source : Round, 1993.
See text for symbols and I d calculation (Equation 3.2).

and Gomphonema parvalum .The I d value obtained
(1.0) signals heavy pollution, in agreement with the
observed sewage contamination.
Some workers have reported that this index tends
to give high values and thus underestimates heavy
pollution (Leclercq and Manquet, 1987).

and ease of identification. The index was determined
as the weighted mean sensitivity (WMS: Equation
3.2), with pollution sensitivity values ( s j )from1to
5, and indicator values ( v j ) from 1 to 3. The value of
TDI ranged from 1 (very low nutrient concentrations)
to 5 (very high nutrients).
This index has now been modified (Kelly, 2002) to
increase the range from 0 to 100, where

CEE index (Descy and Coste, 1991) This
index of general pollution is based on a total of 223
diatom taxa. The index ranges from 0 to 10 (polluted
to non-polluted water).

TDI = (WMS × 25) − 25 (3.3)

ISL index (index of saprobic load) (Slade-
cek, 1986) This index of soluble organic pollution
(saprobity) is based on 323 diatom taxa, each with a
designated saprobic value. Values range from 4.5 to
0 (polluted to non-polluted water).

GDI index (generic diatom index) (Coste and
Ayphassorho, 1991) An index of organic and
inorganic nutrient pollution, based on 44 diatom gen-
era.Valuesrangefrom1to5(pollutedtonon-polluted
water).

3.4.6 Practical applications of diatom indices

IDAP index (Prygiel et al., 1996) Index based
on a combination of 45 genera and 91 diatom species.
Values range from 1 to 5 (polluted to non-polluted
water).

The diversity of available and currently used diatom
indicespresentsacomplexandconfusingpictureasto
which ones should be used to ensure comparability
of studies and consistency of approach. A further
potentialsourceofconfusionisthatsomeindices(e.g.
TDI, see above) have been subsequently modified
to give a wider range of values in relation to water
quality. The range of available diatom indices raises
a number of key practical issues, including
which index? Ease of use

IPS index (specific pollution index) (Coste,
in CEMAGREF, 1982) This index for pollution
sensitivity is based on organic load and nutrient con-
centrations. Values range from 1 to 5 (polluted to
non-polluted water).

comparability between diatom indices
comparability between diatoms and other bioindi-
cator organisms

TDI (trophic diatom index) (Kelly and Whit-
ton, 1995) In its original formulation, this index
was based on a suite of 86 diatom taxa selected for
their indicator value (tolerance to inorganic nutrients)