Algae as Bioindicators - Freshwater Algae: Identification, Enumeration and Use as Bioindicators - page 123

3.3.2 Peatlands

The use of microalgae as bioindicators was pio-
neered by Patrick (Patrick et al ., 1954) and has con-
centrated particularly on benthic organisms, since the
rapid transit of phytoplankton with water flow means
that these algae have little time to adapt to envi-
ronmental changes at any point in the river system.
In contrast, benthic algae (periphyton and biofilms)
are permanently located at particular sites, integrat-
ing physical and chemical characteristics over time,
and are ideal for monitoring environmental qual-
ity. Examples of benthic algae present on rocks and
stones within a fast-flowing stream are shown in
Fig. 2.23. The use of the periphyton community
for biomonitoring normally involves either the entire
community or specific taxonomic groups - partic-
ularly diatoms and N 2 -ixing (heterocystous) blue-
green algae.

Peatlands differ from marshes in having an imbalance
between decomposition and accumulation of organic
matter, resulting in the long-term deposition of peat.
They are of two main types:

Ombrotrophic bogs Fed by precipitation (rain,
snow, mist). Typically highly acidic (pH 3.5-4.6),
poor in minerals (conductivity 80 iS cm −1 ) with <

2mgl −1 ). Dominated by low Ca concentrations ( <

Sphagnum moss.

Minerotrophic fens Fed by groundwater. Typ-
ically moderately acidic (pH 4.6-7.5), mineral-rich
(conductivity 80 iS cm −1 ) with high Ca concentra-

tions (2-50 mg l −1 ). Dominated by moss and sedges.
In both cases, the major micro-algae present are
desmids (e.g. Closterium, Cosmarium, Staurastrum )
and diatoms ( Eunotia, Gomphonema, Pinnularia ).
Studies by Neustupa et al . (2013) on European
peatlands have shown that algal species composi-
tion and richness are primarily controlled by pH
levels. The mean cell size of desmids relates to
pH and mineral concentration, with low biovolumes
in acidic ombrotrophic bogs, large biovolumes in
minerotrophic fens. Cell sizes of desmids can thus
be used to monitor environmental processes such
as the transition from minerotrophy to ombrotrophy,
and acidification. In contrast to desmids, mean cell
sizes of diatoms did not relate to the minerotrophic-
ombrotrophic gradient.

>

3.4.1 The periphyton community

Analysis of the entire periphyton community clearly
gives a broader taxonomic assessment of the ben-
thic algal population compared to diatoms only, but
the predominance of filamentous algae makes quan-
titative analysis difficult. Various authors have used
periphyton analysis to characterise water quality,
including a study of fluvial lakes by Cattaneo et al .
(1995; Section 3.2.1). This showed that epiphytic
communities could be monitored both in terms of
size structure and taxonomic composition, leading to
statistical resolution of physical (substrate) and water
quality (mercury toxicity) parameters.

3.4 Rivers

3.4.2 River diatoms

Until recently, monitoring of river water quality in
many countries (Kwandrans et al ., 1998) was based
mainly on Escherichia coli titre (sewage contamina-
tion)andchlorophyll- a concentration(trophicstatus).
Chlorophyll- a classification of the French National
Basin Network (RNB), for example, distinguished
five water quality levels (Prygiel and Coste, 1996) -
normal (chl- a concentration

Contemporary biomonitoring of river water quality
has tended to concentrate on just one periphyton
constituent - the diatoms. These have various
advantages as bioindicators - including predictable
tolerances to environmental variables, widespread
occurrence within lotic systems, ease of counting and
a species diversity that permits a detailed evaluation
of environmental parameters. The major drawbacks
to diatoms in this respect are the requirement for com-
plex specimen preparation and the need for expert
identification.

10 μgml −1 ), moderate

≤

pollution (10 to 60), distinct pollution (60 to 120),

≤ ≤

severe pollution (120 to 300) and catastrophic pol-

≤

lution ( > 300).