Ecological status of the River Tana phytobenthos

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Ecological status of the River Tana - phytobenthos
Juha Miettinen Regional Environment Centre of
Lapland
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MATERIAL
Phytobenthos was sampled in 9 sites along
the River Tana and 24 sites in its tributaries
in September 2003. Phytobenthos was studied by
community analysis of diatoms on stones.
Diatoms form the majority of the species
diversity in phytobenthos of the northern
rivers, and also a large proportion of
the phytobenthos biomass.
3 samples, composed of 5 cobbles each, were
collected in every site, and diatoms were brushed
off the cobbles. About 400 diatom frustules were
counted from each of the samples.
Fig. 1. Sampling sites.
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TYPICAL DIATOM TAXA FOUND IN THE AREA A total of
109 diatom taxa were identified. The most
abundant species were Tabellaria flocculosa,
Achnanthes minutissima and Fragilaria capucina,
all common species in northern rivers and also
elsewhere.
Indicators of ultraoligotrophy Achnanthes
pusilla Eunotia implicata Fragilaria
arcus Frustulia rhomboides
Indicators of eutrophy (pollution) Achnanthes
minutissima var. saprophila Diatoma
tenuis Hantzschia amphioxys

• COMPARISON TO THE DIATOMS IN RIVER TORNE (Niemelä
  et al.)
• The abundant species are mostly the same.
• Achnanthes pusilla with Tabellaria flocculosa
  are found in the reference sites.
• The major difference appears to be the more
  abundant Gomphonema spp. at
• the downstream sites in River Torne.
• - The indicator values of Van Dam et al. (1994)
  resulted in similar trophy
• classifications in the rivers.

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ORDINATION In Fig. 2 the 33 sites are plotted on
two-dimensional space, using Detrended
Correspondence analysis (DCA). The ordination
techniques are based on a distance measure, so
that the closer two sites are, the more similar
diatom assemblages they have. The sites are
marked by their type according to the Finnish
draft for river typology (Pilke et al. 2002)
2a (small catchment area, low humic content,
altitude lt 200 m) x 2b (small catchment area,
low humic content, altitude 200-800 m) Open
square 5a (mid-sized catchment, low humic
content, alt. lt 200 m) Turned square 5b
(mid-sized catchment, low humic content, alt.
200-800 m) Filled square 8a (large catchment,
low humic content, altitude lt 200 m).
The variation among the samples is at an usual
level for regional diatom studies - eigenvalue
I axis 0.467, II axis 0.180. - length of
gradient I axis 2.78, II axis 2.06

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Fig. 2. DCA ordination plot of the sites. or x
small catchmen area, open square mid-size
catchment filled square large catchment
area. Altitude for all lt 200 m, except for x and
turned square about 300 m.
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Fig. 4.
Fig. 3.
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• INFERRED pH (index of Renberg Hellberg, 1982)
• In Fig. 3 the diatom inferred pH of 8.8 for the
  site B6, Jauvvajohka, demonstrates how the site
  is different from the others based on species
  requiring alcaline conditions.
• The only site with slightly acidic water (pH lt 6)
  was B2, Ailikaspuro, a higher altitude small
  catchment brook site.
• BIOLOGICAL DIATOM INDEX (IBD)
• The general water quality index IBD appears to
  work well with the large rivers, but is not
  capable of inferring the water quality in both
  acidic and alcaline, smaller rivers.
• The elevated pH and nutrient levels in Tana sites
  T12-T14 (Nuorgam-Seida) are reflected in the
  inferred pH and IBD values.

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Fig. 6. Selected diatom taxa in the River Tana,
presented from upstream site Rovisuvanto (no. 1)
to downstream Seida (no. 9) on the vertical
axis. Downstream sites 7-9 (Nuorgam, Tana Bru,
Seida) differ markedly from the other sites, by
the low proportion of Tabellaria flocculosa and
occurrence of more eutraphentic (Fragilaria
capucina var. mesolepta, Cymbella minuta) and
alkaliphilic (Epithemia adnata) taxa.
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• ECOLOGICAL QUALITY RATIOS (EQRs)
• EQR was calculated for some sites (types 5a and
  8a) maybe having some
• significant human impacts. The other sites of
  mid-sized and large river sites,
• presumed pristine, were used as type spesific
  reference sites.
• Predicted values of ecological quality were
  derived by summing the percentage
• proportions of typical diatom taxa (occurring
  at least in 50 of the reference sites).
• For example, 36 taxa were found typical for
  the middle sized, low altitude river sites (type
  5a). In the reference samples, the proportion of
  these taxa varied between 89.3 and 98.3 of the
  total diatom sum. In the three sites defined as
  impacted, the sum of these 36 taxa were
  between 52.8 and 84.0 .
• 99 confidence intervals were calculated for
  the sum of the reference taxa in pristine sites.
  Sites having the sum of these reference taxa
  outside the confidence interval do not reach high
  ecological status according to the phytobenthos.

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Fig. 5. Prequaternary rocks. From Geochemical
Atlas of Finland.
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Fig. 7. The same DCA ordination plot of the sites
as Fig. 2. The sites from Polmak area with
ultramafic intrusive bedrock are marked with red
circles.
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• CONCLUSIONS
• Generally the waters appear in pristine or near
  pristine conditions.
• In the Polmak-Tana Bru area, with differing
  geology and possibly more nutrient loading, the
  alkalinity and nutrient levels are slightly
  elevated.
• The critical points in defining the ecological
  status are the appropriate selection of the
  reference sites and typology of the natural
  environment.
• In the typology of the rivers, the occurrence of
  calcareous and phosphate rich bedrocks should be
  taken into account. For example, river sites in
  the areas of ultramafic intrusive bedrocks could
  be allotted to naturally eutrophic types (in
  addition to the clay soil areas in
  South-Finland).