The Effects of Thermal Effluents on
Marine Organisms
J. E. WARINNER, Assistant Marine Scientist
M. L. BREHMER, Senior Marine Scientist
Virginia Institute of Marine Science
Gloucester Point, Virginia
INTRODUCTION
Urbanization and industrialization along with the rapid increase in population
since World War II have placed a great demand on our waterways. The water
available must serve several purposes including domestic water supplies, water
for industrial consumption, sewage disposal, irrigation, commercial fishing,
transportation, and recreation. A number of industries utilizing water must locate on rivers and streams and along the estuaries. Those which use water for
cooling purposes do not consume appreciable amounts of water nor contaminate
the water supply but they do return the water to the stream at a higher temperature. The largest use of cooling water is by the rapidly expanding steam electric generating industry. The thermal efficiency of steam turbines which turn
the generators is increased by condensing the steam on the exhaust side of the
turbines, thus creating a partial vacuum. The temperature of the cooling water
is raised six to 9.5 C generally but may be raised under some circumstances to
as much as 24.0 C.
One of the earliest investigations into the effects of thermal discharges upon
aquatic life was reported by Van Vliet (1). Moore (2) used the term thermal
pollution" in 1958. "Pollution" of rivers was discussed by Herry (3); and Mar-
kowski (4) published the first of a series of papers on the thermal discharges of a
number of power stations in Great Britain. Since that time research has been continued at an accelerated pace by ecologists, government, and industry in order
to evaluate the effects of thermal elevation on aquatic life. Limitations on maximum temperatures and maximum allowable areas of thermal elevation have been
established by several states in the interest of pollution abatement.
Most of the work has been done on fresh-water streams because of the possibility of low flow conditions and the subsequent use of water for domestic purposes. The volume of water in the typical coastal plain estuary and the presence
of tidal currents favor the utilization of these waters for the discharge of thermal
effluents. However, there is a fundamental difference between inland streams
and tidal estuaries. The introduction of a biocide, whether chemical or physical,
into an inland stream may destroy aquatic organisms in a given section ot the
stream, but the stream may be classified as healthy" upstream from the point
of discharge and below the zone of recovery. A similar introduction into a restricted estuary could easily affect populations in the entire estuary and contiguous
waters. This is because many of the animals have retained a link somewhere in
their life histories between marine and fresh water. The Atlantic and Pacific
salmon are classical examples of fish that require a healthy aquatic environment
from the open sea all the way to fresh headwaters in order to reproduce and survive as a species. The striped bass, shad, herring, and smelt, to name a few of
the better known species, have similar life histories. Less generally known are
those species which spend part of their lives in the estuaries but migrate to higher
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