Thermal Stratification and the Heat Budget - PowerPoint by icecube


									• thermal properties of water and lakes
• annual stratification
• lake classification based on thermal
  stratification patterns
     Thermal Properties of Lakes
             Sources of heat:
•   Solar radiation
•   Sensible heat conduction
•   Stream Input
•   Sediment absorption of sunlight
•   Geothermal
•   Biogenic
     Thermal Properties of Lakes
               Sinks of heat:
•   Evaporation
•   Sensible heat conduction
•   Back radiation from lake surface
•   Stream inputs (snow melt)
•   Surface outflow
Lake Tahoe, CA-NV
Lake Mendota, WI
   Annual Lake Heat Budget
           S = Rn – E – H – Q

where S = storage rate of heat in the lake
      Rn = net radiation
      E = evaporation
      H = sensible heat transfer, conduction
      Q = advective heat transfers due to water
           inflows and outflows
 Lakes stratify because water
density varies with temperature

                      Figure 3-4 in
                      Horne and Goldman
          Thermal Stratification
          for a typical temperate lake
1. Spring Circulation

2. Summer Stratification
Castle Lake
3. Fall Circulation

4. Winter Stratification (inverse stratification)
     Lake Classification Based on
    Thermal Stratification Patterns
1. Holomixis
  a. monomictic – mixes once per year
      • warm monomictic – never below 4°C
      • cold monomictic – never above 4°C
      • ex: Lake Tahoe
             - large volume and large depth
             - no winter ice cover
b. dimictic – mixes twice per year
   • ex: Castle Lake and Lake Mendota
              small temperate lake
              freezes over during winter

c. amictic – does not mix, permanently ice-covered
   • ex: Lake Vanda, Antarctic
              high latitude lake
Lake Vanda, Antarctica
d. oligomictic – mixes rarely, thaws rarely
    • ex: small lakes at high altitude or latitude

e. polymictic – mixes many times per year
    • warm polymictic
    • cold polymictic
    • ex: Clear Lake
        shallow lake

        exposed to strong winds
2. Meromixis
  a. structure of a meromictic lake
        • mixolimnion
        • chemocline
        • monimolimnion

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