Dashing through the snow....
If one wants to evaluate the impact of light pollution on lakes (or other ecosystems) it is required to put it in context with natural nocturnal but also with daylight. Daylight is supposed to be a lot. If you look into a text book it is 100 000 lx or a bit more....well here in the sub-arctics (Kilpisjärvi is at about 69° N) just 1 month after winter solstice it peaks at around 600 lx on a cloudy "day" (that is less then the textbook value at sunset of around 800lx).
Todays task is to measure the light on the lake and under the ice. So Franz and I jump back into our cool explorer suits and pull the seldge with the equipment onto the lake, where the snowmobile is waiting for a fun ride.
Our lake physics friends drop us off about 500 m from shore with our generator, light measurement devices, shovel, sledge and a drill. Although they have no time, they show us how to drill the hole in the ice....
Their task today is to do a transect. That means measuring temperature gradient of the lake with a spatial resolution of a few hundreds of meters. Going a few meters, drill hole, drop temperature measurement chain, wait, move to next spot etc....its a big lake and it takes about 8 hours and requires two shifts.
We are fine with just one hole to measure the under ice spectra and illuminance levels. Its still a border line experience for light pollution scientists and equipment. We have to cut a line with the saw and hold ropes that are wet and freeze in a few seconds when pulled on land....
This evening we can join our lake physics friends in the sauna - because the weather is exactly the same as yesterday.
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