Algae as Bioindicators - Freshwater Algae: Identification, Enumeration and Use as Bioindicators - page 108

in providing a measure of the general ecology of
the lake. This is recognised in the European Union
Water Framework Directive (WFD; European Union,
2000), which requires Member States to monitor the
ecology of water bodies to achieve 'good ecological
status'. Macrophytes and attached algae together
form one 'biological element' that needs to be
assessed under this environmental programme (see
also 'Multi-proxy approach' - Section 3.2.2).

ate analysis or by determination of bioindices, has
the potential to provide information on water quality
at particular sites along the edge of the lake in rela-
tion to point discharges (stream inflows, industrial
and sewage discharges) and diffuse loadings. The lat-
ter include input from surrounding agricultural land,
discharges from domestic areas, traffic pollutants and
loading from local ecosystems such as forests and
peat bogs (Eloranta, 2000; Fig. 3.2).

Local water quality Various authors have
analysed benthic or epiphytic algal populations in
relation to water quality, including the extensive peri-
phyton growths that occur in the littoral region of
many lakes. These algae are particularly useful in
relation to local water conditions (e.g. localised accu-
mulations of metal toxins, point source and diffuse
loading at the edge of the lake), since their perma-
nent location at particular sites gives a high degree of
spatial resolution within the water body.
Localised metal accumulations . Cattaneo et al .
(1995) studied periphyton growing epiphytically in
macrophyte beds of a fluvial lake in the St. Lawrence
River (Canada), to see if they could resolve periphy-
ton communities in relation to water quality (toxic
and non-toxic levels of mercury) under differing eco-
logical conditions (e.g. fine vs. coarse sediment). The
periphyton, composed of green algae (40%), blue-
greens (25%), diatoms (25%) and other phyla, was
collected from various sites and analysed in terms
of taxonomic composition and size profile. Multi-
variate (cluster and biotic index) analysis of periphy-
ton communities gave greatest separation in relation
to physical ecological (particularly substrate) con-
ditions rather than water quality. The authors rec-
ommended that the use of benthic algae as aquatic
bioindicators should involve sampling from similar
substrate sites to eliminate ecological variation other
than water quality.
Point source and diffuse loading at the edge of the
lake . Water quality in the littoral zone may differ con-
siderably from that in the main part of the lake. This
is partly due to the proximity of the terrestrial ecosys-
tem (with inflow from the surrounding catchment
area) and partly due to the distinctive zone of littoral
macrophyte vegetation, making an important buffer
zone between the shore and open water (Eloranta,
2000). Analysis of littoral algae, either by multivari-

Sampling and analysis of littoral algae
Although attached algal communities (as with phyto-
plankton) can theoretically be related to water quality
in terms of total biomass, this does not correlate well
with nutrient loading (King et al ., 2006) - chiefly
due to grazing and (in eutrophic waters) competition
with phytoplankton. Also, nutrients in the water can
be supplemented by nutrients arising from the sub-
stratum.
Species counts, on the other hand, can provide
a useful measure of water quality. Recent recom-
mendations for littoral sampling (King et al ., 2006;
see also Section 2.10) concentrate particularly on
diatoms - collecting specimens from stones and
macrophytes (Fig. 2.29), since these substrata are
particularly common at the edge of lakes. Epipelic
diatoms (present on mud and silt) are probably less
useful as bioindicators since they are particularly
liable to respond to substrate 'pore water' chemistry
rather than general water quality. The epipelic diatom
community of many lowland lakes also tends to be
dominated by Fragilaria species, which take advan-
tage of favourable light conditions in the shallow
waters, but are poor indicators of water quality - hav-
ing wide tolerance to nutrient concentrations. Having
obtained samples and carried out species counts of
diatoms from habitats within the defined littoral sam-
pling area, weighted-average indices can be calcu-
lated as with river diatoms (Sections 3.4.5 and 3.4.6)
and related to water quality.

3.2.2 Fossil algae as bioindicators: lake sediment
analysis

Recent water legislation, including the US Clean
Water Act (Barbour et al ., 2000) and the European