BENTHIC ALGAE AND LIGHT IN LAKE VIREN

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BENTHIC ALGAE AND LIGHT IN LAKE VIREN

• Malin Ranft Malmgren and Krista Takkis
• Supervisor Maria Kahlert

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Benthic algae

• Benthic algae are
• algae that grow in the
• profundal and littoral
• zones of aquatic systems
• and that are attached to a
• substrate, like stones,
• plants, other algae
• and animals.
• 
  
• 
  
• 
  Sebastian
  the Diatom
• 
  (Pediastrum boryanum)

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Hypotheses

• The quality and quantity of benthic algae are
  mostly depending on the quality and quantity of
  the light.
• Benthic algal community composition is different
  in the three lakes (Viren, Erken and Largen) due
  to a different underwater light climate.

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Importance of the benthic algae and our project

• Contribution to the primary production in aquatic
  ecosystem
• Food for grazers
• Used for bioindication
• Subject little
• researched

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Lake Viren

• Located 30 km south from Norrtälje
• Area 1,4 km2
• Maximum depth 10 m
• Euthophic
• Very humic
• Impounded lake

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• Sampling points A (10 m), B (7.5 m), C (6.5 m), D
  (3.5 m) and S (shoreline).

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Methods (field work)

• Water samples with Ruttner sampler
• Sediment samples with Willner sampler
• Secchi depth
• Light measurements
• Stone (shoreline) samples
• Ruttner sampler, Willner
• sampler and Quantum
• (PAR) sensor

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Results
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Temperature in Viren declines with depth
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Water in Viren

• Nutrient-rich
• ? Total N (670 µg/l 1200,µg/l)
• ? Total P (22 µg/l 90 µg/l)
• Silica-rich (1576 µg/l 3604 µg/l)
• Humic

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Light quantity and quality
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Algae and light

• Incoming light is scattered by silica
• Light reaches 7 m depth
• Red, green and yellow light reach the greatest
  depth
• Amount of pigments increases with depth
• Taxa within one algae group vary at different
  depths

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Pigment quantities at different depths
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Two analyse methods

• The spectrophotometer showed small amount of
  chlorophyll c
• Clorophyll c is present in diatoms
• In microscope we saw that diatoms were dominating

• DF analyse shows increase of green algae in
  deeper areas of the lake
• Identification of algae with microscope showed
  more green algae taxa in shallower areas
• DF analyse shows increse of blue-greens in
  shallow areas
• In microscope we saw one taxa of blue-greens at
  each depth

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Identified taxa

• The dominant group in all samples was diatoms
• sediment samples - Aulacoseira
• shoreline samples - Navicula
• Average number of taxa in one sample was 19
• Diatom Green
  Blue-green Bacteria
• Asterionella Ulothrix
  Anabaena Beggiatoa

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Comparison of lakes Viren, Erken and Largen

• Total chlorophyll amount in sediment samples
• Viren increasing with depth
• Largen slightly increasing with depth
• Erken decresing and at 15 m vaguely increasing

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Biodiversity in three lakes

• Most of the benthic algae taxa are the same in
  all three lakes but there are some differences.
• Biodiversity changes with depth
• Viren ?
• Largen ? ?
• Erken ? ? ?
• No connections between biodiversity and light
  quantity and quality could be found as the light
  quantity decrease in all three lakes followed the
  same pattern (exponential).

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Conclusions

• Quantity and quality of algae is to some extent
  dependant on quantity of light. We were not able
  to make any reliable conclusions about the effect
  of the quality of light due to inadequate data.
• In spite of the differences in underwater climate
  the taxa of benthic algae are not significantly
  different.

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