LIGHT & HEAT

IN INLAND WATERS

Light spectrum at the top and bottom of the atmosphere

Measurable Properties of Light

• Intensity• Quality

Both are dependent on absorption and reflection by the atmosphere

Fates of light in water

Shading of low order streams

Confluence of Kotorosl and Volga Rivers

Walker Lake

Extinction Coefficient

ν (nu) = extinction coefficient of light through water.

Examples:• Crystal Lake v = 0.19• Turbid Pond v = 1 – 10• Muddy Stock Tank

v = >>10-150

• Depends on:• Light absorption by

water• Light scattered and

absorbed by particles• Light absorbed by

dissolved substances• v ~ 1/secci depth

Secci Disk

Typical Secci Depths• Crater Lake 40m• Castle Lake 33m• Lake Texoma 0.75m• Susquehanna River

– West Shore >1.2m– West Center 0.32m– East Center 0.23m– East Shore 0.18m

• Secci Depth measured with Secci Disk in lakes and with a Secci Tube in running water.

• Also measured with Turbidimeter (Jackson Turbidity Units- JTU)

Susquehanna River at Byer’s Island

Lakes Erie and St. Claire following major runoff event

Heat Budget for LakesSources• Solar radiation• Sensible heat

conduction• Stream Input• Sediment absorption

of sunlight• Geothermal• Biogenic

Sinks• Evaporation• Sensible heat

conduction• Back radiation from

lake surface• Stream inputs (snow

melt)• Surface outflow

Annual Lake Heat Budget

where S = storage rate of heat in the lakeRn = net radiationE = evaporationH = sensible heat transfer, conductionQ = advective heat transfers due to water

inflows and outflows

S = Rn – E – H – Q

Lake Tahoe, CA-NV

Lake Mendota, WI

Density and temperature

Stratification

Castle Lake Stratification

Lake Classification Based on Thermal Stratification Patterns

1. Holomixisa. 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

Fall turnover occurs when the center of gravity (M) approaches the center of the volume (X).

Martin Lake

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

Meromixis

Lake Nyos

Lakes Nyos (A&C) and Monoun (B&D)

Polymixis in Clear Lake(Rueda et al. 2003)

Property Rivers Reservoirs LakesTemperature variations Rapid, large Rapid in upper zone;

slow in lower portionSlow, stable

Stratification Rare Irregular Common (monomictic or dimictic)

Spatial differences Headwaters cooler becoming warmer downstream

Large fluctuations in upper reservoir, more stable in main body

Stratification common

Groundwater effects High ratio groundwater to runoff

Small Usually small (high in seepage lakes)

Tributary effects Can be significant Moderate to small Small and localized

Shading effects Considerable, especially in the headwaters

Small to negligible Small to negligible

Winter ice formation Transitory Usually transitory Persistent

Ice scouring effects Extensive Minor Minor