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What is a Meromictic Lake?

Updated: Sep 5, 2023

A Meromictic Lake is Just another thing we need to know today!

A few people observing a calm lake from a dock.
Calm Lake

There are times when I wish I had paid more attention in science class. Today, I learned what a Meromictic lake is for the first time (that I can remember). To put a lake like this in perspective, I can best relate it to a pool. My parents had a pool they kept covered with a solar cover growing up. When you wanted to swim in the pool, you would roll up the cover and jump in. The first thing you would notice is how warm the top of the pool was compared to the middle layer and down to the bottom.

A Meromictic Lake is much the same way in that the layers do not intermix. You would encounter a hot top and then notice profound temperature changes throughout the pool, almost like someone flipped a switch.

A Meromictic Lake is comprised of three separate layers as described by

The Layers Of A Meromictic Lake
Monimolimnion Layer: The water of this layer of the lake is usually hypoxic (low oxygen) and more saline than the rest of the lake and have little circulation.
Mixolimnion Layer: This is the top layer of the lake which behaves like a holomictic (uniform) lake.
Chemocline: The middle layer between the upper and lower is called the chemocline.

A graphic showing the 3 layers of a meromictic lake.
3 Layers Meromictic Lake (medium by JC)

These three layers have their environment as they exhibit three different oxygen levels, and are home to different organisms. The bottom layer, or the monimolimnion, is an inhospitable layer due to its very low oxygen. It is for this reason scientists are enamored with the data they can gain from studying this layer due to the sediment on the bottom being largely untouched. The lack of oxygen means less living things stirring things up.

This also means if this layer is disturbed for any reason, it can have devastating effects for the lake. One such example could be an earthquake causing the various layers to intermix and vastly decreasing oxygen in the upper layers. This could potentially suffocate the organisms living their best life at the upper levels.

What causes this phenomenon where you would have three separate levels or stratification? Science would tell you there are two reasons revolving around being endogenic or ectogenic.

  1. Endogenic means the stratifications seen in the lake are caused by internal events, such as organic matter accumulating in the sediments and decaying.

  2. Ectogenic means the stratifications seen are caused by external causes, like an intrusion of saline (Saltwater).

Interesting facts:

For every meromictic lake there are 1000 holomictic (common) lakes.

The largest meromictic water source is the Black Sea.

Large body of water with a sailboat.
Large Body of Water

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