density, layering, and lake mixing - Limnology Exam 2

what factors cause and disrupt lake stratification?

• density differences which are altered by temperature

• wind

• inflows and outflows

• sunlight warming the epilimnion

• wind and cooling events causes temperature changes and mixing to occur

what are the layers of thermal stratification?

• epilimnion

• hypolimnion

• metalimnion/ thermocline

what is the epilimnion?

upper warm water region that gets mixed to uniform temperature by wind. surface waters.

what is the hypolimnion?

the colder, denser, layer that is little affected by wind. (bottom layer)

what is the metalimnion?

the layer of the lake where temperature transitions from warmer to colder. (middle layer)

this layer experiences a sharp decrease in temperature and a sharp increase in density.

what is Isothermal?

when the lake/ water body is at a uniform temperature

what is the thermocline?

the inflection point in the thermal profile. found at a specific depth. the depth at which we find the highest relative thermal resistance.

what is relative thermal resistance?

the amount of energy needed to mix water of two different temperatures.

what is density current?

a flow of a fluid caused by differences in density, which are influenced by factors such as temperature and salinity.

what is an amictic lake?

a lake who’s water column never circulates

what is holomixis?

the period when the entire lake mixes

what is an oligomictic lake?

a lake that is stratified most of the time but occasional cooling of surface causes mixing irregularly and for a short time.

what is a monomictic lake?

a lake that experiences one mixing event per year

what are the two main types of monomictic mixing?

cold- frozen over in winter but isothermal during summer (don’t stratify")

warm- no ice cover in winter and therefore circulate in winter stratify in summer

what is a dimictic lake?

a lake that undergoes two periods of mixing annually (vernal and autumnal turnovers)

what is a polymictic lake?

a lake that undergoes many mixing periods or continuous circulation throughout the year.

what are the types of holomixis?

• oligomictic

• monomictic

• dimictic

• polymictic

what is meromictic?

only incomplete circulation (not entire water column) at surface layer; bottom layer high in solute concentration and is stable.

layers: mixolimnion (mixed), chemocline, monimolimnion (unmixed)