The Cayuga Fisher

The Water:  Seasonal Variations:  Stratification Details

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Seasonal Variations:  Stratification

Water of different temperatures, and thus densities, does not mix well- the warmer, less dense water floats on top of the colder water.  In a large body of water the warm water floats so well it does not mix with the water below even on the windiest days.  These layers are nearly isolated from one another for the duration of the summer and early fall.  Imagine an oil and vinegar salad dressing with a lot of herbs in it.  The oil and vinegar seperate into the main layers, with (at least in my fridge) the herbs forming a thin layer in the middle.  This is very similar to how the lake stratifies, and tastes better too.

In some lakes the hypolimnion runs out of oxygen during the summer and stresses or kills the coldwater fish and other fauna, an effect known as "oxygen depletion".  Thankfully this does not and will not be a problem for Cayuga Lake in any of our lifetimes, but it does occur in some other local waters.  (It will happen eventually as a part of the natural aging process of the lake, eutrophication.)

The metalimnion (the herb layer in the dressing) is essentially a boundary layer, a slippery surface between the epilimnion and hypolimnion, the warm and the cold, and it keeps them from mixing.  The metalimnion usually contains the bulk of the temperature change between the surface and the bottom.  Over time, though, some heat does begin to mix into and through the metalimnion, and as available sunlight drops quickly in fall, this structure breaks down and the lake fully mixes.  Not to get too far ahead, here is a summary of these layers:

The epilimnion is the warm surface water.  It is a fairly uniform temperature (though solar radiation can create very shallow, very warm layers within it for short periods of time), and where warmwater species of fish are found during the summer months.   It contains the least dense, warmest water, and is located from the surface down to the top of the metalimnion.  Shallow in spring, the epilimnion deepens and thickens through early summer.  From midsummer through fall, the epilimnion cools and continues to widen, losing heat to both to the atmosphere above and to the cooler waters below.

The hypolimnion is the cold bottom water.  "Hypo" means "below", so it's the deepest layer of water.  Though chilly, it supports a lot of life, from mud critters to baitfish and lake trout.  There isn't much in the deepest parts of the lake though, not much biomass exists below ~250 feet in Cayuga.  On the temperature diagram at right, the long, nearly vertical green line below the dotted thermocline shows the hypolimnion.  The nearly vertical section above represents the epilimnion.

The metalimnion is the layer where a steep temperature gradient exists, and it includes the thermocline.  "Meta" means middle, or in-between, and thus the metalimnion is between the other two layers.  Not really the warm water, not really the cold, it is the layer of change.  In the diagram above, the angled middle part of the green line represents the metalimnion.  The point that is "most horizontal" represents the fastest temperature change, the thermocline, and the metalimnion extends above and below it. 

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