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Light and Temperature

Light and Temperature. Light. photons- packets of electomagnetic energy wavelength: ultraviolet= short; infrared= long ~ 53% of the incident light/radiation is absorbed (transformed into heat) within the 1 st 1M of the water column shorter wavelengths penetrate deeper

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Light and Temperature

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  1. Light and Temperature

  2. Light • photons- packets of electomagnetic energy • wavelength: ultraviolet= short; infrared= long • ~ 53% of the incident light/radiation is absorbed (transformed into heat) within the 1st 1M of the water column • shorter wavelengths penetrate deeper • factors influencing incident radiation: latitude, season, time of day, altitude, & weather conditions

  3. turbidity • decreases water’s ability to transmit light • secchi disk • attenuation- reduction of light energy with depth by scattering & absorption

  4. euphotic zone • the stratum of water receiving adequate light such that photosynthesis exceeds respiration; primary production occurs here

  5. Riparian Vegetation • restricts incident light in woodland streams during the summer; max. illumination occurs in winter & early spring • autochthonous -vs- allochthonous energy input

  6. photosynthesis/respiration CO2 + H2O ----> C6H12O6 + O2 radiation 400-700nm drives the system

  7. Temperature • absorption- the high specific heat of water permits the dissipation of light energy as heat; this process is enhanced by dissolved organic matter. • The thermal conductivity of water is low therefore heat radiation is primarily a surface phenomenon.

  8. In lentic systems, the transfer of heat to lower strata is primarily dependent upon mixing by wind action. • As temperature increases and wind decreases thermal stratification increases; i.e. density differences of strata exceed the mixing power of the wind

  9. Thermocline strata where the change in temperature is >1o C/meter epilimnion- upper stratum characterized by uniformly warm water which constantly mixes metalimnion- characterized by thermal discontinuity hypolimnion- lowest stratification; temporally stable

  10. Mixing • Holomictic Lakes: complete mixing • amictic- perennial ice cover; Antarctic lakes • dimictic- two circulation periods; temperate lakes • polymictic- frequent or continuous mixing • Meromictic Lakes: strata separation • chemocline

  11. Thermal Stratification

  12. Thermal Profile

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