Lake Stratification
Layers of
lakes
ßEpilimnion
ßThermocline
ßHypolimnion
Dimictic
lakes
ßOverturn occurs twice each year
| STRATIFICATION |
|
| Stratification is the
division of a lake into layers due to density differences as a result of
temperature - water is most dense at 4ºC |
|
| layers of a lake: the
top layer of a lake is the epilimnion which is made up of the warmer
less dense water in the summer and the cooler less dense water in the winter
– the thermocline (metalimnion) is the layer of sharp
temperature difference between the upper and lower layers – the hypolimnion
is the bottom layer of a lake and is the colder water in the summer and
the warmer water in the winter, if a lake suffers from oxygen depletion it
will be most felt in the bottom layer of the lake because oxygen is not
replenished while the lake is stratified |
|
| Summer - warmer water
on top, cold bottom |
|
| Winter - colder water
on top, warmer on bottom |
|
| Overturn - spring and in the fall – fall
the colder weather cools the water in the epilimnion until the water becomes
more dense than the water in the lower layers so the dense water displaces
the less dense water at the bottom of the lake – in the spring
the water at the surfaces warms to a temperature of 4°C and sinks to the
botttom bringing the water at the bottom to the top of the water column |
|
| Overturn replenishes
the oxygen to the hypolimnion and creates a constant profile of temperature
and dissolved oxygen throughout the water column |