Thermal Pollution

Thermal pollution refers to the degradation of water quality caused by processes that increase the ambient water temperature, negatively affecting the ecosystem. The primary issues associated with thermal pollution include a decrease in dissolved oxygen (DO) levels and disruption to the ecosystem’s composition.

Sources of Thermal Pollution

1. Industries:
   • Power plants often use water as a coolant, and the discharge of heated water into water bodies is a major cause of thermal pollution. These include:
     • Hydro-electric power plants
     • Coal-fired power plants
     • Nuclear power plants
     • Effluents from industries like textiles, paper, and pulp
2. Urban Runoff: Stormwater runoff from roads and parking lots, which absorbs heat, is another significant source of elevated water temperatures.

1. Domestic Sewage: Municipal sewage is typically warmer than ambient water, contributing to the temperature increase.

Effects of Thermal Pollution

• Decreased Oxygen Solubility: As the temperature rises, the solubility of oxygen in water decreases, which can harm aquatic life, especially fish and amphibians that rely on sufficient oxygen levels.

• Increased Metabolism of Aquatic Life: Higher temperatures can increase the metabolic rate of aquatic organisms, causing them to consume more food. This can lead to resource depletion, impacting food chains and biodiversity. In some regions, this has caused the elimination of native fish species and altered macroinvertebrate populations.

• Thermal Shock: Sudden temperature changes, such as during the opening or closing of power plants, can lead to “thermal shock,” killing species not adapted to rapid temperature fluctuations.

• Altered Food Chains: The increased metabolic rate caused by elevated temperatures may favor certain species over others, disrupting existing food chains and ecosystems.

• Changes in Water Chemistry: Higher temperatures can alter the physical and chemical properties of water, increasing the toxicity of certain substances. For example, a 1°C increase in temperature can double the toxic effects of chemicals like potassium cyanide.

• Interference with Reproduction: Many aquatic species rely on specific temperature ranges for successful reproduction. Warmer temperatures can disrupt nesting, spawning, hatching, and migration. For instance, lake trout may fail to spawn successfully at temperatures above 8.9°C.

• Increased Vulnerability to Diseases: Higher water temperatures accelerate the activities of pathogenic microorganisms, leading to increased disease outbreaks in aquatic species. For example, hot water can cause bacterial infections in salmon.

• Invasion of Destructive Organisms: Warmer waters may allow the invasion of species that thrive in such conditions, potentially damaging the local ecosystem. An example of this is the invasion of shipworms into New Jersey’s Oyster Creek.

• Thermal Shock in Cooling Systems: In power plants and other industries, cooling systems may kill small organisms (plankton, fish, and insect larvae) through thermal shock, increased pressure, and water viscosity changes.

Control Measures for Thermal Pollution

1. Cooling Ponds and Towers:
   • The heated water can be passed through cooling ponds or cooling towers before being discharged into natural water bodies. Cooling ponds are large, shallow ponds where hot water is pumped in at one end and cooler water is removed at the other. Cooling towers are used to dissipate the heat into the atmosphere.

1. Stormwater Management:
   • Urban runoff can have a significant thermal impact on small streams. To mitigate this, stormwater management systems can be implemented to absorb the runoff or direct it into the groundwater, such as using bioretention systems and infiltration basins.
   • Retention basins, however, are less effective at controlling temperature as the water can be heated by the sun before it is discharged into receiving streams.