Thermal Pollution

Introduction

Thermal Pollution is the harmful increase in water temperature in streams, rivers, lakes, or occasionally, coastal ocean waters.

It is the degradation of water quality by any process that changes ambient water temperature.

A temperature increase as small as 1 or 2 Celsius degrees (about 2 to 4 Fahrenheit degrees) can kill native fish, shellfish, and plants, or drive them out in favor of other species, often with undesirable effects.

Causes

The major sources of thermal pollution are electric power plants and industrial factories.

Another cause is the use of water as a coolant by power plants and industrial manufacturers. When water used as a coolant is returned to the natural environment at a higher temperature, the change in temperature decreases oxygen supply, and affects ecosystem composition.

When a power plant first opens or shuts down for repair or other causes, fish and other organisms adapted to particular temperature range can be killed by the abrupt change in water temperature known as "thermal shock."

Causes

Streams and small lakes are naturally kept cool by trees and other tall plants that block sunlight. People often remove this shading vegetation in order to harvest the wood in the trees, to make room for crops, or to construct buildings, roads, and other structures.

Even the removal of vegetation far away from a stream or lake can contribute to thermal pollution by speeding up the erosion of soil into the water, making it muddy.

IMPACTS

All plant and animal species that live in water are adapted to temperatures within a certain range.

This can harm aquatic animals such as fish, amphibians and other aquatic organisms. Thermal pollution may also increase the metabolic rate of aquatic animals, as enzyme activity, resulting in these organisms consuming more food in a shorter time than if their environment were not changed.

Some organisms do thrive in warm water, often with undesirable effects. Algae and other plants grow more rapidly in warm water than in cold, but they also die more rapidly.

IMPACTS

Primary producers are affected by warm water because higher water temperature increases plant growth rates, resulting in a shorter lifespan and species overpopulation.

Temperature changes of even one to two degrees Celsius can cause significant changes in organism metabolism and other adverse cellular biology effects. Principal adverse changes can include rendering cell walls less permeable to necessary osmosis, coagulation of cell proteins, and alteration of enzyme metabolism.

CONTROLS

Thermal pollution from power plants and factories is relatively easy to control. Instead of discharging heated water into lakes and streams, power plants and factories can pass the heated water through cooling towers or cooling ponds, where evaporation cools the water before it is discharged.

Alternatively, power plants can be designed or refitted to be more efficient and to produce less waste heat in the first place.

CONTROLS

In the United States, about 75 to 82 percent of thermal pollution is generated by power plants. The remainder is from industrial sources such as petroleum refineries, pulp and paper mills, chemical plants, steel mills and smelters. Heated water from these sources may be controlled with:

cooling ponds, man-made bodies of water designed for cooling by evaporation, convection, and radiation

cooling towers, which transfer waste heat to the atmosphere through evaporation and/or heat transfer

cogeneration, a process where waste heat is recycled for domestic and/or industrial heating purposes.

CONTROLS

Thermal pollution from devegetation is quite hard to control because it is caused by the cumulative effect of many peoples’ actions, most of which are individually minor.

There should be implemented laws that will help control, conserve, and protect resources to counter thermal pollution.

To prevent thermal pollution due to devegetation, the prescription is simple: do not devegetate. All efforts to control erosion also have the effect of keeping water clearer and, thus, cooler.

CONTROLS

In the United States, the problem of industrial thermal pollution was first addressed in 1970, when Congress gave the Atomic Energy Commission authority to regulate thermal pollution from nuclear power plants. In 1972, the comprehensive Clean Water Act instructed the Environmental Protection Agency to issue regulations to clean up all hot water discharges from all power plants, nuclear or conventional. Since then, thermal pollution from power plants has not been a major issue in the United States.