Lakes Flashcards
What is Schmidt stability
States level of resistance to mixing.
What is wedderburn number?
A number indicating the likelihood of wind-driven upwelling events (when hypolimnion comes to the surface) If Wedderburn number is < 1, thermocline is likely to tilt to the surface allowing the epilimnion to mix with the hypolimnion
What is lake number?
A number indicating the likelihood of wind-driven internal mixing events.
Which factors promote instability in the water column
-Large, deep lakes -deep metalimnion -low temperature differntial -long fetch
How and why do emergent plants provide oxygen to roots?
- Gas tubes in the stem take oxygenated gas from the upper part (exposed part) and pump it down to the roots. - Without that process they would not be able to maintain roots in reducing sediments at great depths.
Why are emergent plants vital in small lakes?
-Buffer role for lake systems -Modifying water as it moves from groundwater & land through to emergent vegetation, -slowing the flow of water & changing geochemistry, -Habitat for wildlife.
Describe the mixing stages of a monomictic lake (warm and cold)
- A monomictic lake mixes once a year.
- Warm monomictic lakes never freeze and are thermally stratified during summer. Winter, Autumn, Spring = Holomixis.
- Cold monomictic lakes freeze over during winter so there is no mixing. Spring, Summer, Autumn = Holomixis.
What is the Profundal Zone?
The Profundal zone is the deep, dark bottom part of a lake where there is no primary production therefore material falling down from the shallower depths are relied on as a source of energy.
What is the Pelagic Zone?
- The Pelagic Zone is the middle, open part of a lake.
- Phytoplanktonic processes dominate
- Phytoplanton, Zooplankton, Fish
Why is Stratification important?
- Seperates photosynthesis from the bottom of the lake
- Oxygen not replaced
- Material in hypolimnion decomposes
- Bacteria respires away oxygen
- Small, organic-rich hypolimnion can become anoxic
What are optically active materials?
Materials that absorb or scatter light in water
- water
- cdom
- sediments
- algae
What are the features of a glacial lake?
- Found in mountainous areas
- Ice gouged out basins form most of the south island lakes
- deep, steep-sided, morraine-dammed, elongated, large
- Lake Wanaka
What are the features of a Dune lake?
- Low nutrient
- small, shallow, oligotrophic
- formed behind wind-blown sand and sediments
Lake Ototoa
Features of a coastal barrier lake
- formed behind bars created across river mouths by large longshore drift
- shallow, fertile, young
Features of a Volcanic Lake?
- Created in the hollows of volcanic craters for most of the larger North island lakes
- Often steep sided, round, small catchments, very old
Lake Taupo, Lake Rotorua
