Pycnocline - Layers forming with different densities

- Thermocline - layers forming between different temperatures.

- Halocline - layers forming between different salinity.

Epilimnion - top layer formed by temperature in lakes

Metalimnion - middle layer

Hypolimnion - bottom layer

Spring - Layers mix (overturn) no density variations

Summer - epilimnion warms up and gets bigger. Phytoplankton phototaxis and wave action causes high O2 levels in epilimnion. Hypolimnion can become anaerobic as fish and bacteria use up O2

Fall - Epilimnion cools. Cold water sinks and causes overturn can cause fish kill if hypolimnion is largely anaerobic. Not common because cold water holds more O2 than warm.

Winter - surface cools more - sometimes faster than metalimnion up north in extreme weather changes. Ice on surface will insulate metalimnion - warms up to 40 F.

Monomictic - when a lake only turns over 1x per year (common in AZ and other warm climates)

Dimictic - 2 turnovers /year - common in northern temperate climates.

Amictic - No turn over - tropical lakes - permanent thermoclines.

Important because if they get stuck in the metalimnion or below the compensation depth there won't be enough O2 to photosynthesize and respire and create the energy to go back up.

Methods of flotation:

Morphologic:

- Small size - less surface area

- Elongated shape filaments/diatoms

- spines protrusions - keeps algae from sinking

Behavioral

- + or - phototaxis swimming to and from light

Physiological

- Gas vacules

- oil vacules

- mucilage

- ionic regulation: using salt and fresh water for differing densities.

V= 2gr^2 (p^1-p)/9n0 Tells how fast a population of algae is sinking.

Grazing, what is eating the algae? rotifers, small cladocerans

Microplankton - 20-200um - crustaceans

Nanoplankton - 2-20um - jelly fish

Picoplankton - < 2um - Protozoans

As algae dies and sinks benthic bacteria decompose and nutrients are released.