LAKE AND POND ECOSYSTEM FIELD COURSE IN WINTER ECOLOGY 2006 University of Joensuu

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LAKE AND POND ECOSYSTEM FIELD COURSE IN WINTER
ECOLOGY 2006 University of Joensuu
A presentation by Antti Kokkonen, Clara Moreno,
Elena Bonet, Elodie Philippe, Harri Eerilä, Heidi
Weber, Heikki Leitala, Robert Klinger, Nadinja
Hettinga, Jonas Linke
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INTRODUCTION

• Overall, two different water bodies were
  studied Lake Mekrijärvi and the pond Iso-Suokko
• located around Ilomansti (6241'N 3057'E, 157m
  above sea-level)
• both drain into the Koitajoki drainage basin
• Data
• Lake Mekrijärvi Mean depth 1.7m, Surface
  area 894 h
• Iso-Suokko Mean depth 7m deep, Surface area
  26 ha

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INTRODUCTION

• Different environmental conditions in winter
  time, e.g. ice cover and low temperature
• Physical, chemical and biological parameters
  were observed (in situ measurements, analyses of
  water samples)
• thickness of the ice cover
• depth colour and transparency of the water
• temperature
• oxygen concentration and saturation
• pH-value
• conductivity
• zooplankton and zoobenthos composition

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INTRODUCTION

• water is dark and humic (particulated and
  suspended organic substances)
• Oligotrophic - low productivity and low amounts
  of macronutrients (P and N)
• located in the boreal climate zone
• dimictic

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METHODS

• water and sediment samples were taken with a
  Ruttner Sampler and a Sormonen Sampler
• physical and chemical water features were
  measured
• samples of sediment, zoobenthos and zooplankton
  were taken
• Snow depth and ice depth were measured with a
  measure stick.
• depth of the water body was determined
  (echo-sounder)
• temperature of the water each two meters
  (transect)
• samples of the surface water layer and the bottom
  layer for determination of the parameters

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TEMPERATURE

• Lake Mekrijärvi 1,50 m (only one measurement,
  cause of total depth 2 m)
• In Lake Iso-Suokko
• Temperature was measured at the surface and at 5
  different depths
• In both lakes the surface temperature at a depth
  of 1,5 meters is between 0,5 C and 1C. the
  temperature is increasing in lake Iso-Suokko
  towards the bottom. In the depth of 10 m it is
  2,3-2,4C.
• Lake Mekrijärvi is very shallow, thus the whole
  water body is rather cool, little stratification

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TEMPERATURE RESULTS
Water temperature profile of Lake Mekrijärvi
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OXYGEN SATURATION

• To determine the oxygen saturation, the
  Winkler-method was applied.
• In Lake Mekrijärvi four water samples in a depth
  of 1,5m were taken, while in Iso-Suokko each
  three samples in a depth of 1,5m and in 10m were
  taken.
• In the laboratory the oxygen content was analyzed
  
• The oxygen content and the percentage of
  saturation were calculated

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OXYGEN SATURATION RESULTS

• oxygen saturation differ largely between the
  days of measure-ment

Oxygen saturation in of Lake Mekrijärvi and
lake Iso-Suokko
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CONDUCTIVITY

• conductivity is a measure of the waters capacity
  to convey an electronic current
• related to nature and concentration of ionized
  substances and temperature
• Conductivity increases when the amount of
  dissociated substances in water increase, e.g. in
  case of eutrophication or pollution
• average concuctivity of Finnish lakes is 6,9 mS
  m-1
• conductivity of each water sample was measured
  with a conductivity meter

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CONDUCTIVITY - RESULTS
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COLOUR

• Water of almost all lakes in Finland are brown,
  due to humic and iron compounds
• colour is measured in mg Pt /l
• average value for Finnish lakes is about 90 Pt
  mg/l

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COLOUR RESULTS
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TRANSPARENCY

• Measurement of spectral quality and light
  extinction in water
• measured by Secchi-Method Secchi value is the
  depth at which the disc cannot be seen any more
• Median in Finnish lakes is 3m
• depth is relative to light reflection from disc
  and governed by light absorption of the water,
  dissolved compounds and particles

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TRANSPARENCY RESULTS

• Very low Secchi values of only 50 and 55cm on all
  four days
• values, due to high amounts of iron and humic
  compounds, implied by the measured colour values
• low values might also be affected by other
  dissolved compounds and particles
• The light reflection from the disc must have been
  very low as well, as both lakes were covered by
  thick ice and snow layers, which avoided light
  penetration into the lakewater

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pH - VALUE

• pH is a measure of acidity negative dec.
  logarithm of concentration of free H - ions in
  a liquid
• reflects the possibility of the water to exchange
  CO2 and its biological activity
• Ice cover (and with it the temperature) influence
  this factors strongly
• pH of finnish lakes is from 6 to 9
• Acidity of lake depends on surrouding and
  substrates (biotic and abiotic factors e.g.
  silica rocks and boreal vegetation) but as well
  on possible pollutants (acid rain)

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pH VALUE RESULTS

• Lake Mekrijärvi pH value of 6
• Pond Iso-Suokko pH of 5,6
• pH at the bottom seems to be slightly higher in
  lake Iso-Suokko

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DIFFERENCES WITHIN THE LAKES

• Temperature Stratification due to depth
• Oxygen content higher in Iso Soukko
• Conductivity at same level
• Colour and transparency at same level
• pH lower in Lake Iso-Suokko

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ZOOPLANKTON

• We studied density of zooplankton in Boreal lake
  and pond
• Samples were taken with ISO standarded
  watersampler from different layers
• Surface samples from Mekrijärvi
• Surface and bottom samples from pond Iso-Suokko

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METHODS

• Samples were taken from depths 1,5 m and 11 m
• Water was filtered through plankton net
• Mesh size 55 µm
• Zooplankton was treated with formalin to settle
  down to counting cuvette
• The number of individuals were counted with light
  microscope

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RESULTS
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RESULTS
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CONCLUSIONS

• Annual changes in numbers of individuals vary a
  lot
• Populations of those few common species express
  high variation
• Possible reasons
• Chemical and physical factors
• Biological factors

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ZOOBENTHOS INTRODUCTION

• Extremely diverse assemblage, both taxonomically
  and ecologically
• Invertebrates larger than 0,5 millimeters, living
  in the sediments and mud
• The presence of this group depends on the depth,
  the oxygen concentration and the quality of the
  sediments
• They are important for the food chain
• They are bioindicators of the water quality

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ZOOBENTHOS METHODS

• Samples from two lakes Mekrijarvi and Iso
  Suokko
• With a Kajak-sampler, three lifts of sediments
  for each subsamples, and five subsamples per
  sample

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ZOOBENTHOS RESULTS

• Table Zoobenthos density (individuals per m2) in
  lakes Mekrijarvi and Iso Suokko

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ZOOBENTHOS CONCLUSION

• Diversity in Mekrijarvi is greater than Iso
  Suokko, because it is shallower.
• Mekrijarvi has more oxygen than Isu Suoko, better
  for spreading of zoobenthos.
• Most abundant taxon Chironomidae
• Dominant species
• Mekrijarvi Copepoda, Oligochaeta and Hydracarina
• Iso Suokko Chaoboridae and Sphaerium

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ZOOBENTHOS SUMMER/ WINTER

• Increase of total density in both lakes
• Bigger increase in Mekrijarvi
• There is the same diversity during winter and
  summer, but lower density in winter
• Effect of the temperature and of the predation on
  density

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THANK YOU FOR YOUR ATTENTION!