Field Course in Winter Ecology 24'28'2' 2003 Lake ecosystem

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Field Course in Winter Ecology 24.-28.2. 2003
Lake ecosystem
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Ice and snow
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Ice and Snow

• Snow and ice cover affect all life in lake
  ecosystems in winter
• ice protects the life in lakes from lethally low
  temperatures
• Insulating ice cover forms on top of the water
• Rapid freezing can result in lack of oxygen
• Ice grows fast at first --gt steel ice
• Melting snow on top of steel ice forms milky ice

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Ice and Snow

• Snow depth (cm, averages) in Lakes Mekrijärvi and
  Iso-Suokko

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Ice and Snow

• Ice thickness averages (cm) in Lakes Mekrijärvi
  and Iso-Suokko

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Ice and Snow

• The Northern Atlantic Oscilation (NAO)
• Measured by air pressure differences between
  Iceland and the Azores
• Positive NAO index -gt wet and warm winters in
  Europe
• Negative NAO index -gt cold winters in Europe
• Correlation between NAO and break-up dates of
  Lake Mekrijärvi
• negative, ice breaks up earlier

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Ice and Snow

• The Northern Atlantic Oscilation (NAO)

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ZoobenthosBenthos are an important part of the
food chain, because of their abundance and
position as "middleman" in the aquatic food
chain. Benthos play a critical role in the
natural flow of energy and nutrients. Benthic
macroinvertebrates can also be used as biological
indicators because they are reliable and
sensitive indicators of habitat quality in
aquatic environments.
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ZoobenthosUsually the benthic animals of lakes
constitute an extremely diverse assembly, both
taxonomically and ecologically. Benthic animals
contain representatives of almost every major
group of invertebrates living in fresh water.
They include segmented worms, insect larvae,
crustaceans and molluscs. These animals have to
be able to tolerate large differences of
temperature.
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ZoobenthosDistribution and abundance of
zoobenthos depends largely on water depth, bottom
sedimentand oxygen concentration. During the
winter course 2003, differences both in the
number of individuals and in species were found
between the two lakes studied - lake Mekrijärvi
and lake Iso-Suokko.
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Table Zoobenthos (individuals per m2) in lake
Mekrijärvi and Iso-suokko
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ZoobenthosBy comparing the results we mark that
there were more species and more individuals in
lake Mekrijärvi than in lake Iso-suokko.
In the lake
Mekrijärvi the most abundant taxon was
Chironomidae ( chironomid larvae ) and in lake
Iso-Suokko only five different taxa werefound
and the most abundant of them was Chaororidae (
phantom midges ).
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Zooplankton

• Students found 11 different kind of zooplankton
• Members of Phylums Rotifera, Crustacea, Rhizopoda
  and Tardigrada
• Trends of research
• - More organisms found in
• surface
• - Higher concentration of animals in Lake
  Mekrijärvi
• Most organisms collected were of phylum Rotifera

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Zooplankton

• Individuals Per 10L Samples Taken From Lake
  Mekrijärvi and Iso-Suokko

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Water quality

• pH and Conductivity
• pH values lie generally between 6 and 9 in fresh
  water
• pH values in Lake Mekrijärvi are approximately
  around 6,2. The pH value nearly reaches the
  minimum amount. This value is caused by the
  amount of organic acids in the lake. Values are
  similar between both lakes.
• Conductivity levels are also low in both lakes
  compared to other lakes around the world. High
  conductivity is caused by nutrients, which cause
  pollution. So we can confirm both lakes are clean
  and non polluted.

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Water quality

• Colour and Transparency
• colour dissolved organic matter
• transparency how much light penetrate through
  water
• in winter does not matter,
  cheap control
• Lake Iso-Suokko darker than Lake Mekrijärvi
• both surrounded by peat bogs
• Lake Iso-Suokko, colour surface - 170, bottom-
  290
• Lake Mekrijärv, colouri surface - 125, bottom-
  137,5
• trnasparency LI-99,5 cm x LM-112,5 cm
• gt higher release of organic matter
• date of ice appearance and oxygen content in the
  bottom not enogh mixing period lead to poor
  content of oxygen during the winter.

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Water quality
Oxygen and temperature

• Oxygen saturation level is higher when
  conductivity and temperature are lower
• Temperature affects the density of the water
  (most dense at 4 C) lack of wind due to ice
  cover and other forces avoids mixis
  stratification.
• Lake Mekrijärvi shows higher oxygen concentration
  than Iso-Suokko as it is shallower (mixis of
  layers)

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Water quality

• In lake Iso-Suokko the temperature is higher in
  bottom layers than in surface
• There is also stratification in oxigen content
• These two parameters are conected. Accumulation
  of organic matter in the bottom and the higher
  temperature, make the deep water be more oxygen
  consuming.

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Water quality

• Observing data from earlier years, there is
  correlation between the