Organisms and Environmental Factors 23
• Aphotic zone, which no light reaches and where no photosynthesis
takes place
Radiation decreases exponentially in water, that is, the correlation of
strength at the surface I o and strength I z at a depth z is given by the relationship:
I
I e
z
kz
0
where z = depth below the surface (Chapter 8).
In temperate oceans k = 0,10 – 0,20 m –1 has been measured, whereas in
coastal waters, the coefficient k can be as high as k = 1,0 m –1 . In very turbid
lakes values for k as high as 3–4 m –1 have been measured.
Organisms, like all bodies for that matter, have a specific distribution
of the spectrum of absorbed visible and infrared radiation. Thus, various organisms exposed to a given radiation can absorb different amounts
of energy. On the other hand, all the bodies on the surface of the Earth,
including organisms, radiate energy in the infrared part of the spectrum, at
wavelengths of 9–11 μ. The intensity of the emitted radiation depends on
surface temperature.
According to the Stefan-Boltzmann relationship, this is:
R
T
0
4
2
HV cal cm sec ,
where:
T = temperature in Kelvin
σ = Stefan-Boltzmann’s constant
ε = ratio of the actual radiation to the radiation of a perfect radiator/
absorber (black body), at the same temperature
For almost all bodies of ecological importance, such as plant leaves,
animals, etc. ε ranges between 0.95 and 0.98.
The Stefan-Boltzmann relationship explains the manner in which the
planet’s thermal equilibrium is achieved. Earth receives huge amounts
of solar energy capable of causing a constant increase in its temperature.
This does not occur, however, because the rise in temperature very rapidly increases (in proportion to T 4 ) the emission of energy in the form of
infrared radiation, ultimately resulting in the maintenance of the thermal
equilibrium. Thus, on average the planet’s surface temperature remains
constant. The greenhouse effect (Chapter 9) tends to raise the temperature
at which thermal equilibrium occurs.
• Aphotic zone, which no light reaches and where no photosynthesis
takes place
Radiation decreases exponentially in water, that is, the correlation of
strength at the surface I o and strength I z at a depth z is given by the relationship:
I
I e
z
kz
0
where z = depth below the surface (Chapter 8).
In temperate oceans k = 0,10 – 0,20 m –1 has been measured, whereas in
coastal waters, the coefficient k can be as high as k = 1,0 m –1 . In very turbid
lakes values for k as high as 3–4 m –1 have been measured.
Organisms, like all bodies for that matter, have a specific distribution
of the spectrum of absorbed visible and infrared radiation. Thus, various organisms exposed to a given radiation can absorb different amounts
of energy. On the other hand, all the bodies on the surface of the Earth,
including organisms, radiate energy in the infrared part of the spectrum, at
wavelengths of 9–11 μ. The intensity of the emitted radiation depends on
surface temperature.
According to the Stefan-Boltzmann relationship, this is:
R
T
0
4
2
HV cal cm sec ,
where:
T = temperature in Kelvin
σ = Stefan-Boltzmann’s constant
ε = ratio of the actual radiation to the radiation of a perfect radiator/
absorber (black body), at the same temperature
For almost all bodies of ecological importance, such as plant leaves,
animals, etc. ε ranges between 0.95 and 0.98.
The Stefan-Boltzmann relationship explains the manner in which the
planet’s thermal equilibrium is achieved. Earth receives huge amounts
of solar energy capable of causing a constant increase in its temperature.
This does not occur, however, because the rise in temperature very rapidly increases (in proportion to T 4 ) the emission of energy in the form of
infrared radiation, ultimately resulting in the maintenance of the thermal
equilibrium. Thus, on average the planet’s surface temperature remains
constant. The greenhouse effect (Chapter 9) tends to raise the temperature
at which thermal equilibrium occurs.