thermal properties of water and lakes

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Heat Budgets and
Thermal Stratification

• thermal properties of water and lakes
• annual stratification
• lake classification based on thermal
  stratification patterns

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Thermal Properties of Lakes

• Sources of heat
• Solar radiation
• Sensible heat conduction
• Stream Input
• Sediment absorption of sunlight
• Geothermal
• Biogenic

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Thermal Properties of Lakes

• Sinks of heat
• Evaporation
• Sensible heat conduction
• Back radiation from lake surface
• Stream inputs (snow melt)
• Surface outflow

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Lake Tahoe, CA-NV
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Lake Mendota, WI
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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

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Lakes stratify because water density varies with
temperature
Figure 3-4 in Horne and Goldman
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Thermal Stratification for a typical temperate
lake
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Castle Lake Stratification
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Lake Classification Based on Thermal
Stratification Patterns

• Holomixis
• monomictic mixes once per year
• warm monomictic never below 4C
• cold monomictic never above 4C
• ex Lake Tahoe
• large volume and large depth
• no winter ice cover

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• dimictic mixes twice per year
• ex Castle Lake and Lake Mendota
• small temperate lake
• freezes over during winter

• amictic does not mix, permanently ice-covered
• ex Lake Vanda, Antarctic
• high latitude lake

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Lake Vanda, Antarctica
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• oligomictic mixes rarely, thaws rarely
• ex small lakes at high altitude or latitude

• polymictic mixes many times per year
• warm polymictic
• cold polymictic
• ex Clear Lake
• shallow lake
• exposed to strong winds

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• Meromixis
• structure of a meromictic lake
• mixolimnion
• chemocline
• monimolimnion