Every year I try to measure a water quality depth profile in the middle of lake Liesjärvi. At every 1 m depth the temperature (degrees Celsius), pH, and conductivity (microSiemens) are measured in the middle of the lake were the lake is about 18.0-18.5 m deep.
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Figure 1. Temperature profile in lake Liesjärvi. Spring 2017 (11 days after disappearance of the ice cover) stands out with its
relatively low temperatures. In summer (i.e. all other observations), differences in temperatures in the first two metres depend
on summer weather conditons. At 6 m depth temperature is constant with depth and varies between 8-10 degrees Celsius.
Figure 2. pH profile in lake Liesjärvi. pH decreases with water depth, and it seems as if the pH is higher in spring compared to summer.
Figure 3. EC profile in lake Liesjärvi. Electric conductivity increases with water depth, but this increase is rather small.
Figures 4-9 are based on water quality measurements by a commercial chemical laboratory in the years 2010-2018. Summer measurements were collected in June-July, autumn in August, and winter in March-April. The solid line represents the long-term average, the dotted lines the minimum and maximum values between 2010-2018.
Figure 4. In summer and autumn, water temperature decreases with depth. In contrast, in winter water temperature increases with depth. Differences between years (2010-2018) are small (dotted lines: minimum and maximum temperature; Summer=June/July, Autumn=August, Winter=March/April)
Figure 5. In winter, the oxygen concentration is >10 mg/l, and decreases with depth. In autumn, oxygen concentrations are lower, but not near the bottom. (dotted lines are minimum and maximum values for 2010-2018)
Figure 6. Nitrate concentrations are near zero at the end of the summer and increase during winter. At the end of winter time, the nitrate concentrations are similar throughout the water column. (dotted lines are minimum and maximum values for 2010-2018).
Figure 7. Water pH is highest near the surface and decreases from summer to autumn to winter. The year to year variation is considerable.
Figure 8. Turbidity is lowest near the bottom of the lake, and varies a lot from year to year. Near the surface, turbidity is lowest in winter time.
Figure 9. At the end of the winter (March/April) ice thickness varies between 26-60 cm. Snow cover varied between no snow cover to 25 cm snow.