Lake Water Mixing is Slowing - Should we be Worried?
I came across THIS ARTICLE in Quanta magazine and found it very interesting. The bit which caught my imagination was the method of measuring water clarity.
The disc pictured above is lowered into the lake and when it disappears from the observers sight - that is the Secchi depth.
The lake with the longest history of clarity readings is Crater Lake in Oregon in the USA. And lately the lake has been getting clearer. And that is the result of less mixing of the lakes water.
Lake water mixing is the result of many things, but one of them is the surface water becoming warmer, therefore lighter and less likely to descend and mix. In winter the surface water cools and therefore sinks and mixes. But, in many places this no longer happens.
And as a result the water at the bottom of lakes becomes depleted in oxygen.
In Crater Lake another result is that the warm surface layer becomes thinner - the energy (wind) needed to mix the surface layers becomes greater and it does not happen. The thinner surface layer means less phytoplankton and clearer water.
The article goes on to look at other lakes, especially Lake Tahoe, which used to be very similar to Crater, but shows more signs of deterioration.
This is an article well worth reading.
