Environmental Engineering Reference
In-Depth Information
Although individual algal species can be rated pri-
marily in terms of trophic preferences, they are also
frequently adapted to other related ecological factors.
Acidity
.Oligotrophicwatersarefrequentlyslightly
acid with low Ca concentrations, and vice versa for
eutrophic conditions.
Nutrient balance
. Mesotrophic waters may be
nitrogen-limiting (high P/N ratio), promoting the
growth of nitrogen-fixing (e.g.
Anabaena
) but not
non-fixing (e.g.
Oscillatoria
) colonial blue-green
algae.
Long-term stability
. In hypertrophic waters, dom-
ination by particular algal groups may vary with
the long-term stability of the water body. High-
nutrient lakes, with established populations of
blue-greensanddinolagellates,oftenhavetheseas
dominant algae during the summer months. Small
newly-formed ponds, however, are often domi-
nated by rapidly growing chlorococcales (green
algae) and euglenoids. The latter are particularly
prominent at high levels of soluble organics (e.g.
sewage ponds), using ammonium as a nitrogen
source. Some of the most hypertrophic and eco-
logically unstable waters are represented by arti-
ficially fertilised fish ponds, such as those of the
Trebon wetlands, Czech Republic (Pokorny
et al
.,
2002a,b).
Figure 3.5
Eutrophic lake (Rostherne Mere, UK).
The high nutrient status of the lake is indicated by
water analyses (mean annual total phosphorus
50 μg
l
−1
), high productivity (maximum chl-
a
concentration
typically
>
60 μgl
−1
) and characteristic bioindicator
algae. These include planktonic blooms of
Anabaena
,
Aphanizomenon
,
Microcystis
(colonial blue-greens) plus
other eutrophic algae (see text). Attached macroalgae
(Cladophora,
Fig. 2.28) and periphyton communities
(present on the fringing reed beds, Fig. 2.29) are also
well-developed.
>
is possible to list organisms that are typical of sum-
mer growths in different standing waters (Table 3.3).
Identiicationofsuchindicatorspecies,particularlyat
high population levels, gives a good qualitative indi-
cation of nutrient state. As an example of this, the
high-nutrient lake illustrated in Fig. 3.5 is character-
istic of temperate eutrophic water bodies, with high
productivity,characteristicseasonalprogression(Fig.
2.8)andwiththeeutrophicbioindicatoralgaelistedin
Table 3.3. In addition to phytoplankton bioindicators,
the trophic status of the lake is also reflected in exten-
sive growths of attached algae such as
Cladophora
(Fig. 2.28) and in the dense periphyton communi-
ties (Fig. 2.29) that occur in the littoral reed beds.
Analysis of lake sediments (Capstick, unpublished
observations) indicates increased eutrophication in
recent historical times, with higher proportions of
the diatoms
Asterionella formosa
plus
Aulacoseira
granulata
var.
angustissima
and marked decreases in
Cyclotella ocellata
and
Tabellaria flocculosa
(more
typical of low-nutrient waters) over the last 50 years.
In addition to considering individual algal species,
taxonomic grouping (assemblages) may also be
useful environmental indicators. Reynolds (1980)
considered species assemblages in relation to
seasonal changes and trophic status, with some
groupings (e.g.
Cyclotella comensis
/
Rhizosolenia
)
typical of oligotrophic waters and others were
typical of eutrophic (e.g.
Anabaena
/
Aphanizomeno
/
Gloeotrichia
) and hypertrophic (
Pediastrum
/
Coelas-
trum
/
Oocystis
) states. Consideration of algae as
groups rather than individual species leads on to
quantitative analysis and determination of trophic
indices.
4.
Phytoplankton trophic indices
. In mixed phy-
toplanktonsamples,algalcountscanbequantitatively
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