Algae as Bioindicators - Freshwater Algae: Identification, Enumeration and Use as Bioindicators - page 134

Access to common databases Access to web-
based data sites, such as the European Diatom
Database Initiative (EDDI) and the US geological
Survey National water-Quality Assessment program
(NAWQA), promotes a standard approach to identifi-
cation, data acquisition and manipulation. Although
the EDDI site has particular application for lake
palaeolimnology (Section 3.2.2), other databases
specifically on benthic diatoms (Gosselain et al .,
2005) may be more applicable to river studies.

Response to changes in water quality

One important aspect of algal bioindicators is that
they are able to detect a rapid change in water qual-
ity. Because of their shorter generation time, diatom
communities are potentially able to respond more
rapidly than other bioindicator groups (e.g. macroin-
vertebrates, fish), which integrate water quality over
longer time frames.
The time sequence of diatom change can be inves-
tigated by transferring diatom biofilms from polluted
to non-polluted waters, and record

Use of comparable diatom indices The cos-
mopolitan distribution of diatoms, coupled with the
close correlation in results obtained from different
indices, suggests that a single unified index should
be universally applicable within a particular climate
(e.g. temperate) zone.
The use of a single unified index has not been
adopted, however, for two main reasons:

how different diatom indices compare over fixed
time periods,

the time needed for different indices to indicate a
significant change in water quality.

Biofilm studies by Rimet et al . (2005) showed
that some indices (e.g. CEE, TDI - high sensitivity)
responded more rapidly than others (GDI, ILM, SLA
- intermediate sensitivity) to environmental change.
All indices showed significant change (integration
interval) within 40-60 days of biofilm transfer.

Ecologists tend to prefer the security of using mul-
tiple indices, with diatom counts being fed into a
database for multiple determinations. The general
availability of the 'OMNIDIA' database software
(Lecointe et al ., 1993), incorporating indices sum-
marised in Table 3.14, has been particularly useful
in this respect.

Standardisation of approach

Evidence suggests that the use of a particular
index, coupled with key diatom indicator taxa,
will be most usefully applied to the geographic
area where it was developed. This is due both
to floristic differences between geographic regions
and also to environmental differences that modify
species responses to water-quality characteristics
(Potapova and Charles, 2007).

The above studies indicate that benthic diatoms pro-
vide the basis for a standard approach to river moni-
toring, able to be used as an alternative (or addition)
to macroinvertebrate sampling. Individual commonly
used diatom indices appear to correlate significantly
with macroinvertebrate data, and also with each other
(see above). Studies by Kelly et al . (1995) have also
shown that benthic diatom indices do not change
significantly either with season or with major flow
events (both of which can influence invertebrate pop-
ulations) - suggesting that diatom indices are robust
and that consistent results can be obtained throughout
the year.
Standard procedures are important in ensuring
comparability of results. These include a unified
approach to sampling procedures (Kelly etal ., 1998),
access to common databases, use of comparable
diatom indices and quality assurance.

The indices contained in the 'OMNIDIA' soft-
ware are based on European diatom communities
and clearly apply most directly to European rivers.
Application of this software in other parts of the
world requires the incorporation of local (endemic)
species, as emphasised by Taylor et al . (2007) in
their studies on South African rivers. It is also impor-
tant to check that cosmopolitan species have sim-
ilar ecological preferences in different parts of the
world. Dela-Cruz etal . (2006), for example, assessed