Title: LAKE AND POND ECOSYSTEM FIELD COURSE IN WINTER ECOLOGY 2006 University of Joensuu
1LAKE 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
2INTRODUCTION
- 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
3INTRODUCTION
- 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
4INTRODUCTION
- 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
5METHODS
- 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
6TEMPERATURE
- 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
7TEMPERATURE RESULTS
Water temperature profile of Lake Mekrijärvi
8OXYGEN 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
9OXYGEN SATURATION RESULTS
- oxygen saturation differ largely between the
days of measure-ment
Oxygen saturation in of Lake Mekrijärvi and
lake Iso-Suokko
10CONDUCTIVITY
- 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
11CONDUCTIVITY - RESULTS
12COLOUR
- 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
13COLOUR RESULTS
14TRANSPARENCY
- 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
15TRANSPARENCY 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
16pH - 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)
17pH 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
18DIFFERENCES 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
19ZOOPLANKTON
- 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
20METHODS
- 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
21RESULTS
22RESULTS
23CONCLUSIONS
- 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
24ZOOBENTHOS 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
25ZOOBENTHOS 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
26ZOOBENTHOS RESULTS
- Table Zoobenthos density (individuals per m2) in
lakes Mekrijarvi and Iso Suokko
27ZOOBENTHOS 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
28ZOOBENTHOS 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
29THANK YOU FOR YOUR ATTENTION!