Winter has come and the field season is now ended...
At the end of October we pulled up the Thermistors chain we deployed at the beginning of June. The T chain (see image below) is just a simple rope with small electronic devices that measure continuously the water temperature at different depths. The string has an anchor on the bottom and a buoy on the surface to keep the rope straight and the thermistors at the same depths.
For the past season we have cable-tied 15 thermistors from the surface up to 25m. Each thermistor saves one temperature value every 5 minutes. Considering the deployment time (5 months) we have a lots of data to deal with, but that's not a problem at all!
After the recovery few thermistors were completely full of tiny zebra mussels which Vobster is rich. But they did their job.
The interesting thing about lake temperature is how it changes with time at different depths (click on the image below to see the zoomed plot). Here are some important features:
- The temperature in the several layers increases during summer as expected. The surface is heated up by the su. After September the air temperature decreases and the surface temperature starts decreasing as well.
- From August the water up to ~6m has the same temperature. The blue, orange, yellow and purple lines merge together. This water is completely mixed.
- The lake bottom (22m, bottom green line in the plot) has roughly a constant temperature during the summer below 8C. So divers please use a proper diving suit there. Bottom layers are isolated from the surface and that's a normal feature of lakes during summer.
- After October the water from the surface up to 15m is completely mixed because of the same temperature (~14C). That's a common behaviour of the lake and during winter the water should reach the same temperature in the whole body and the lake become completely mixed.