STRIVE - Environmental Protection Agency

the right side of the dendrogram-isolated Cross Lake,
with the indicator Dinobryon, from the rest of the lakes
constituting assemblage III and containing the indicator
taxon Halteria. Subdivision in assemblage III was based
on the presence of Anabaena in the 16 lakes of the first
group, as opposite to the presence of the indicator taxa
Tabellaria and Dinobryon in the 9 lakes from the second
group.
N. Touzet (2008-FS-EH-3-S5)
Figure 3.10. Groups of lakes identified by Two-Way INdicator Species ANalysis (TWINSPAN). Eigenvalues are
shown at each level together with the indicator taxa.
Figure 3.11 shows a range of taxa that occurred with
varying frequencies across the three assemblages.
The dinoflagellate Ceratium and cyanobacterium
Sphongosphaerium occurred more frequently in
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assemblage I. The lakes grouped in assemblage II
contained, along with Dinobryon, less cyanobacteria
and more diatoms (mostly Tabellaria and Tribonema).
The taxa that occurred the most in assemblage III were
essentially diatoms (Cymbella, Diatoma, Meridion and
Navicula), whose frequency of occurrence was greater
in assemblage III (Kruskal-Wallis, p < 0.05, H = 6.34,
df = 2, n = 49, lake 0212 excluded). About ~75% of the
individual taxa in the lakes grouped in Assemblage
III were less abundant than in Assemblages I and II.
An assessment of variations in the distribution of the
broad phytoplankton taxonomic units among the three
assemblages showed that a significant difference was
Figure 3.11. Occurrence frequency of selected phytoplankton taxa in the 2009 sampled lakes (a). Occurrence
frequency of selected taxa in lakes from the three assemblages defined by Two-Way INdicator Species ANalysis
(TWINSPAN) analysis (b).