Severe Effects of Thermal Pollution

Based on the demands for cooling in industrial processes and power generation coupled with other human and natural events, the extent of the impacts of thermal pollution worldwide is far-reaching. Specifically, highly industrialized nations in Europe, Asia, North America, and Australia suffer the most. In the United Kingdom, for instance, it is estimated that about half of all river flow is used for cooling purposes.

Likewise, various nations in the U.S., Australia, and Asia have recorded numerous instances of thermal discharges into water resourcing after cooling uses hence creating severe stresses on aquatic ecosystems. In general, these kinds of activities have adverse effects on various aquatic life forms and the environment.


Some of the effects of thermal pollution, therefore, include:

  1. Decrease in Dissolved Oxygen (DO)

The heat released into natural waters increases the optimum water temperature, in turn, reducing the concentration of dissolved oxygen (DO) content. Elevated water temperatures lower the level of dissolved oxygen because warm water is incapable of holding sufficient oxygen compared to cold water. This can cause asphyxiation for aquatic plants and animals like fishes, turtles, or other aquatic organisms.

Elevated temperatures also restrict the dispersion of oxygen into deeper waters, which may bring about anaerobic conditions that lead to a rise in bacterial population when there is abundant food supply. Consequently, it promotes the dense growth of algae blooms on the water surface further lessening dissolved oxygen levels in the water.

  1. Migration

Alterations in the marine environment may equally result in migration of species to adaptable alternative environments. Fishes, crustaceans, and amphibians that are used to consistent water temperatures are bound to migrate when water temperatures change. When this happens, the food chain is interrupted since some of the interconnected food supply relationships are broken.

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Food sources may also continue to slim due to increased number of organisms in a localized marine habitat. Also, some more adaptable species may move into the environment and take advantage of those that are unable to adapt. Ultimately, as aquatic organisms try to find suitable ways of survival, they migrate from one region to another consequently decreasing biodiversity.

  1. Affects Reproduction

Since many aquatic organisms are swift at detecting and reacting to temperature changes of as low as 1 degree Celsius, it can adversely affect their biological activities. Among the proven biological activities affected by temperature changes are cellular processes.

This extends to cellular impacts that can harm the success of their reproduction process. Because reproduction entails enzyme activity that only thrives at optimal temperatures, a substantial increase in temperature can cause the release of immature eggs. Alternatively, high temperatures may stop some specific eggs from developing normally.

  1. Elevation of Toxins

Consistent high water discharge into natural water bodies favors the growth of algae especially the blue-green algae which replaces other kinds of algae. When these types of algae dominate the water, they form algal blooms which reduce the water quality by releasing toxins into the water. On the other hand, heated industrial effluent may contain toxins with elements such as radioactive and chemical materials that pile up in the water systems leading to severe consequences on the aquatic ecosystems.

  1. Loss of Biodiversity

According to marine science research, tropical marine species are for the most part incapable of withstanding temperature increases of 2 to 3 degrees Celsius. Mostly, this applies to molluscs, sponges, and crustaceans which die at temperatures more than 37 degrees Celsius. Therefore, it means that any little shift in water temperatures can lead to a considerable loss of biodiversity.

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Changes in the water temperature may also force species to shift their base to other areas, exposing them to predators or unsuitable living conditions that can result in their death. In this sense, significant changes in water temperature reveal the effects it has on the modification of aquatic biological activity which can cause loss of biodiversity.

  1. Decline in the Number of Aquatic Organisms Due to Increased Metabolism

Thermal pollution intensifies enzyme activity resulting in the increase of the metabolic rate of aquatic species. The increase in metabolic rate sequentially makes the aquatic species consume more food than normal within a very short time. On this account, food chain stability is altered due to unavailability of enough food resulting in a sharp decrease in the aquatic species population. Metabolic changes can also transform the balance of species composition as well as lead to species migration to other areas as they struggle to adapt to the aquatic environment changes.

  1. Aquatic Species Malnutrition

The majority of aquatic species are very sensitive to minimal temperature changes of as little as 1 degree Celsius. On these grounds, significant increases in water temperatures affect cellular biological activities and denature life-supporting enzymes in aquatic species.

When the enzyme activities are decreased in aquatic species, it can contribute to problems such as the inability to break down lipids, which causes malnutrition. In many cases, the effects of malnutrition are observable from the mass death of fish that more often float on water bodies or washed to the shores. Young fish, in particular, are frequently heavily affected.

  1. Effects in Cases of Cool Water Injection
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Cool water injection into water sources is also part of thermal pollution since it modifies the average water temperature. In the case of cold water injection from reservoirs into warmer receiving canals, streams, rivers, or ponds, there can be substantial impacts on fish, mostly in the egg and larvae stage. Likewise, cooler water injection can also create a modified marine environment creating entry of foreign species that can have competitive gain over the native species.

Photo by: dren

Sonia Madaan is a writer and founding editor of science education blog EarthEclipse. Her passion for science education drove her to start EarthEclipse with the sole objective of finding and sharing fun and interesting science facts. She loves writing on topics related to space, environment, chemistry, biology, geology and geography. When she is not writing, she loves watching sci-fi movies on Netflix.