lake_ecosystems

Most lakes are of glacial origin
-Michigan Great Lakes
Most lakes are small; very few are huge

Photosynthesis is greatest and water temperatures warmest in the surface layers

Water reaches its maximum density at 4 degrees C
-this is why ice floats, and the coldest water sinks

The hypolimnion stays at about 4 degrees C year round
-strong thermal stratification
-resistance to mixing

a lake is isothermal if it is the same temperature from top to bottom

What determines the depth of the thermocline?
-force of wind
-latitude
-warmth of sun (seasonal)
-depth/shape of basin

nutrients get used up during summer

a monomictic lake mixes once a year
an amictic lake never mixes (saline lakes)
a polymictic lake mixes several times a year
adimictic lake mixes twice a year

light attenuation is logarithmic
-attenuates with depth

Nitrogen and Phosphorous overwhelmingly found in plant tissue

Liebig's Law of the Minimum:
-growth is controlled by the scarcest resource

Paradox of the Plankton:
-algae all require same nutrients distributed in a well-mixed environment,
-this is a challenge to Gause's principle

Complications:
-algae may differ in their relative dependency on different nutrients
-co-limitation

human-caused eutrophication is referred to as "cultural eutrophication"

Redfield Ratio:
106:16:1 C:N:P

when N:P> 16, phosphorous is limiting
when N:P< 16, nitrogen is limiting

The saturation value for oxygen in water is inversely related to temperature
-warmer water, less oxygen

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