Chapter 9

Thermal  Pollution

  • Defined as: The warming of an aquatic ecosystem to the point where desirable organisms are adversely affected.
    Most significant non-chemical ways humans impact aquatic systems because:

    Aquatic organisms are “stenothermal” or intolerant of temperature fluctuations outside normal extremes.

    Aquatic animals have evolved enzymatic processes designed to function at temperatures natural for that region over millions of years.

    Water temperature doesn't fluctuate relative to air temperature; therefore, no aquatic organism ever evolved to be “homeothermic” or developed the ability to maintain a relative constant and warm body temperature that is independent of environmental temperature.

  • Sources of Thermal Pollution:
    • Natural:    Geothermal vents--geysers.
    Human:      Electric Utility Plants are number one at 9 to 10 billion gallons discharged per day.

    Nuclear powered generation (produces more heated water than an equal sized fossil-fuel plant).
    Fossil powered generation.

    Commercial Air Conditioning Cooling Units.

Directly lethal = “thermal shock”.  Happens with any drastic temperature change, as when a plant begins operation or shuts down.

Upper lethal temperature limit - chronic effects of heat burden can kill or shorten life spans.
a) Cerio-daphnia:  Lives for 108 days at 46 degrees F; lives only 29 days at 82 degrees F.
b) Larger species (fish) even less tolerant.

Reproductive and growth effects = temperature-dependent reproductive cues like spawning (mollusks--hours after certain temperature is reached) and hatching (aquatic insects). 
Migratory patterns.  Areas of elevated temperature may act as a barrier for some species, particularly migratory fish.

Distribution of species.  Warmer water is lighter and generally floats on colder denser water and can affect surface-dwelling species directly or act as a barrier.

Cell permeability.  Temperature will affect permeability of an organisms cells, potentially affecting salt balance as well as toxic chemical penetration/absorption.  Available data have indicated that toxicity increases with temperature.

Photosynthetic Respiration rates increase.  Lower dissolved oxygen because elevated temperature will cause water to hold less oxygen causing respiration to double for each 10 degree C. rise.

Chemical reactions increase 2 to 5 times faster for each 18 degrees F.
Significantly affects photosynthesis and nitrogen fixation by blue-green algae contributing to Eutrophication.

Solubility of Oxygen decreases with higher temperatures.
A carp can survive with as little as .5 ppm dissolved oxygen at 33 degrees F, but at 95 degrees, the requirement is 1.5 ppm.
What is the recommended dissolved oxygen for fresh water?

    • Thermal stratification is a process by which temperature and certain environmental conditions create a situation where a body of water separates into distinct masses or units. In summer, deep penetration of sunlight heat up the surface water of the lake; cooler water sinks to the bottom.  In winter, air temperatures drop, and the surface of the water gradually becomes colder than the deep water and a reverse stratification takes place, this time with the warmer water on the bottom.   When the process of “turnover” takes place, the distinction between the different units disappears as they mix and interact. 

No cooling towers at McGuire.  Cooling towers would reduce hot water discharge by 90%, theoretical max by 95%.  (Catawba has cooling towers   -  a new law requires cooling towers.)
Hot water limits for McGuire is 95 degrees.
EPA recommends a maximum temperature of 90 degrees F. with a maximum delta over background of 3 degrees in lakes.

Dissolved Oxygen Dead Zone.

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