Lakes Concerns in Lakes Eutrophication Toxics Dissolved Oxygen - - PDF document

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Lecture #24 Limnology: More on Stratification

(Chapra, L16)

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Updated: 28 March 2013

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Lakes

 Concerns in Lakes

 Eutrophication  Toxics  Dissolved Oxygen

 Aging of Lakes

 Oligotrophic  Mesotrophic  Eutrophic  Extinction

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Succession: natural course of events (eutrophication), but can be accelerated by human activities (cultural eutrophication).

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Lakes and Lake Modeling

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Hypolimnion Epilimnion Thermocline

Lakes and Lake Modeling (cont.)

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WQ Profiles in Stratified Lakes

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Concentration Manganese Dissolved oxygen Temperature Epilimnion Thermocline Hypolimnion

• Temp. Profiles in Stratified Lakes

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Temperature Spring Epilimnion Thermocline Hypolimnion Fall Winter Summer

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7 From: http://www.ouc.bc.ca/fwsc/oklimnol/FIG1.JPG

Completely mixed lake model

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V dc dt W t Qc kVcn    ( )

dc dt c W t V    ( )    Q V k

For a 1st order reaction (n=1): Where:

c W Q kV  

Steady State Solution: V Q W(t) [accumulation] = [loadings] ± [transport] ± [reactions]

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Stratified Lake Model

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Hypolimnion Epilimnion

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V dc dt W Qc E c c k V c V dc dt W E c c k V c

1 1 1 1 12 2 1 1 1 1 2 1 2 12 1 2 2 2 2

           ( ) ( )

Thermal Lake Types vs Latitude

 From

Limnology, by Wetzel

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Lake Types

 Amictic: lakes permanently covered with ice  Cold Monomictic: temperature is always <4oC, mixes

• nly in summer, when T~4oC

 Dimictic: circulates freely twice a year, temperature

ranges above and below 4oC

 Warm Monomictic: temperature is always >4oC.

Mixes only in winter

 Oligomictic: warm lakes (usually tropical) with rare

and irregular mixing

 Polymictic: frequent or continuous circulation

(possibly even diurnal)

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 To next lecture

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