lakes II Flashcards
what are the 5 biological zones of a lake system?
- littoral zone (coast)
- limnetic zone (inside top lake)
- photic zone (zone that receives light ~2 meters)
- benthic zone (along bottom)
- produndal/aphotic zone (no light)
what is the cause of lake stratification?
due to density differences (in temperature and chemical)
at what temperature is water most dense?
4 degrees celsius
does saltiness increase or decrease density?
increase
what are the three layers of thermal stratification?
- epilimnion (top layer)
- metalimnion (middle)
- hypolimnion (bottom)
what are the characteristics of the epilimnion layer?
in summer, warm and rich in oxygen
what are the characteristics of the metalimnion layer?
steep temperature gradient called a thermocline
what are the characteristics of the hypolimnion layer?
cold, dark and oxygen depleted
what is the added stratification layer in a meromitic lake?
monimolimion -> at bottom no matter the temperature because it is so dense with a solute
what do the four seasons’ lake layers look like?
spring: everything is 4 degrees
summer: 20 degrees at top - thermocline - 4 degrees
fall: 10 degrees all around
winter: ice- 1 degree- thermocline - 4 degrees
how come water is fully mixed in spring and fall?
the denser water sinks + wind
how is oxygen introduced into lakes?
from the atmosphere or photosynthesizing organisms
what are 6 properties that affect lake mixing?
- change in temperature
- wind
- size and depth of lake
- bathymetry and shape of lake
- inflow/outflow of lake
- ice cover
what are the six types of lakes based on mixing behavior?
- holomictic (mixed through entire lake)
- meromictic (some layers never mix)
- amictic (no mixing -> continuous ice cover)
- dimictic (mix twice per year)
- monomictic (mix once per year)
- polymictic (mix often)
what is an example of a monomictic lake?
cold mountain lake that warms up to 4 degrees in the summer or warm lakes that cool to 4 degrees in winter
