Algae as Bioindicators - Freshwater Algae: Identification, Enumeration and Use as Bioindicators - page 131

differences between indices in response to changes
in water quality
adoption of a standard approach to use of diatoms
as bioindicator organisms
quality assurance: reliability of analyst assessment

Comparability between indices

Recent projects using diatoms as bioindicators have
tended to use groups of indices, to eliminate any
irregular conclusions that might have arisen from use
of a single index. Different indices have been com-
pared for assessment of water quality within different
river systems, where there is variation in trophic sta-
tus (inorganic nutrients - particularly phosphates and
nitrates) and a range of other factors such as salin-
ity, organic pollution (related to biological oxygen
demand - BOD) and industrial contamination (metal
pollution and acidity).
A summary of studies is shown in Table 3.14, with
some detailed examples below. In general, different
diatom indices give broadly comparable results. Vari-
ous investigations (e.g. 3, 4 in Case study 3.2) do indi-
cate, however, that the IPS index is particularly useful
for monitoring general changes in water quality. This
index best reflects the combined effects of eutroph-
ication, organic pollution and elevated salt concen-
trations, since it usually integrates all diatom species
recorded within the samples.

Which index? Ease of use

One practical problem with the use of diatoms as
bioindicators is the large number of taxa encountered
in environmental samples. This can be overcome in
two main ways:
Use indices based on genera (e.g. GDI) rather than
species (e.g. SPI, TDI). Various researchers (e.g.
Case study 3.2) have found no significant differ-
ences between the two.
Restrictidentiicationtothemostabundantspecies.
Round (1993), for example, used about 20 key
species for monitoring rivers in the United
Kingdom.

Case study 3.2 Field studies on different diatom indices (see Table 3.14)

1. Greek rivers: variation in trophic status, organic and inorganic chemical pollutants. Iliopoulou-Georgudaki
et al. (2003) used IPS, Descy (1979) and CEE indices as they were considered more representative of environ-
mental conditions (Table 3.14). The indices gave exactly comparable results.

2. Selected rivers inEngland andScotland. Ranging from nutrient-poor upland streams to lowland rivers subject
to varied eutrophication and contamination with organic pollutants, pumped mine water, heavy metals and
agricultural run-off.
Ke l ly et al. (1995a) assessed water quality using four indices based on diatom genera (GDI) and species (SPI,
TDI-P and TDI-NP). The high correlation between indices across the different river sites suggested that any
could be used individually for routine monitoring and that diatom recognition to genus rather than species
level was adequate.

3. Metal pollution in lowland river.DeJongeet al. (2008) assessed diatom populations in relation to metal (ZN)
contamination and related physicochemical variables. The IPS index best reflected changes in water quality -
(pH, conductivity, oxygen concentration, inorganic nutrients) and was the only diatom index that indicated
a significant difference between control and contaminated sites.

4. Rivers of Southern Poland: variation in trophic status andorganic pollution. Kwandrans et al. (1998) used the
suite of eight diatom indices contained in the 'OMNIDIA' database software to evaluate water quality in this
r ive r syste m. Except for S l adek's index, indices t yp i cal l y showed s i gn i fican t cor r e l a t ions with each other and