Environmental Engineering Reference
In-Depth Information
Main species
a light microscope is available. Round (1993) con-
cluded that identification to species level for these
was unnecessary and merely to record their pres-
ence in large numbers is enough. If the pollution is
not extreme there may be associated species present
such as Go.parvulum,Amphoraveneta and Navicula
accomoda. Other pollution-tolerant species include
Navicula goeppertiana and Gomphonema augur.
Round's diatom assessment for British Rivers is
compared with those of other analysts in Table 3.9
for categories of moderate and severe pollution.
Although there is substantial similarity in terms of
species composition, differences do occur - to some
extent reflecting differences in river sizes and geo-
graphical location. These differences highlight the
problems involved in attempting to establish standard
species listings for water quality evaluation.
Various authors have considered different levels of
water quality in terms of distinctive diatom assem-
blages. Round(1993) proposedthefollowingclassii-
cation, based on results from a range of British rivers.
In this assessment, five major zones (categories) of
increasing pollution (inorganic and organic soluble
nutrients) were described.
Zone 1:Cleanwater inthe uppermostreaches
of a river (low pH) Here the dominant species
were the small Eunotia exigua and Achnanthes
microcephala, both of which attached strongly to
stone surfaces.
Zone 2: Richer in nutrients and a little higher
pH (around 5.6-7.1) This zone was dominated
by Hannaea arcus , Fragilaria capucina var. lance-
olata and A. minutissima . T. flocculosa and Peronia
fibula were also common in some instances.
Multivariate analysis
Multivariate analysis can be used to compare diatom
assemblages and to make an objective assessment of
speciesgroupingsinrelationtoenvironmentalparam-
eters. Soininen et al . (2004) analysed benthic diatom
communities in approximately 200 Finnish stream
sites to determine the major environmental correlates
in boreal running waters. Multivariate statistical anal-
ysis was used to define
Zone 3: Nutrient rich with a higher pH (6.5-
7.3) Dominant diatoms included A. minutissima
with Cymbella minuta in the middle reaches and
Cocconeis placetula , Reimeria sinuate and Amphora
pediculus in the lower reaches.
Zone 4: Eutrophic but flora restricted
through other inputs Fewer sites in this cat-
egory were found and more work was considered
necessary to precisely typify its flora. However, the
major diatom associated with the decline in water
quality was Gomphonema parvulum together with
the absence of species in the Amphora, Cocconeis ,
Reimeria group.
diatom assemblage types
key indicator species that differentiated between
the various assemblage groups
relative contribution of local environmental factors
and broader geographical parameters in determin-
ing diatom community structure.
Zone 5: Severely polluted sites, where the
diatom flora is very restricted As with zone 4
not many sites in this category have been investigated
and more work is needed. The flora was frequently
dominated by small species of Navicula (e.g. N. ato-
mus and N. pelliculosa ). Detailed identification of
these small species can be difficult, especially if only
The results showed that the ∼200 sites sampled
could be resolved into major diatom groupings which
corresponded to distinctive ecoregions (Table 3.10).
These authors concluded that although analysis of
diatom communities provides a useful indication of
water quality, hydrology and regional factors must
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