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Difficulty: MediumPollution Types, Causes, Effects, and Control

A thermal power station regularly discharges high-temperature water effluent directly into a nearby freshwater stream. Which of the following effects will this thermal pollution primarily have on the aquatic organisms in the stream?

  1. It reduces the concentration of dissolved oxygen while simultaneously increasing the metabolic rate of fish.Answer
  2. B
    It increases the solubility of oxygen gas in water, leading to oxygen toxicity in aquatic invertebrates.
  3. C
    It halts the light reaction of photosynthesis by directly decomposing water molecules into oxygen gas.
  4. D
    It stimulates denitrifying bacteria to convert toxic ammonia directly into atmospheric nitrogen.

Answer

Thermal pollution reduces dissolved oxygen concentration in water while raising the metabolic rate and oxygen demand of aquatic organisms.
The correct response accurately describes the dual impact of thermal pollution: as water temperature rises, dissolved oxygen solubility decreases while the metabolic rate of cold-blooded organisms (such as fish) increases, creating acute oxygen stress.

Step-by-Step Solution

1
Analyze physical effect of elevated water temperature on dissolved gases.
The solubility of gases, such as oxygen, decreases as water temperature increases.
Gas molecules gain kinetic energy and escape from the liquid phase into the atmosphere more readily at higher temperatures.
2
Analyze physiological effect of higher water temperature on aquatic organisms (poikilotherms).
Body temperatures of poikilothermic organisms rise, accelerating enzymatic activity and overall metabolic rate.
Higher metabolic rates require greater consumption of oxygen for cellular respiration.
3
Combine physical and physiological impacts to determine net biological effect.
Organisms experience respiratory stress due to decreased oxygen availability combined with heightened oxygen requirements.
This supply-demand mismatch can lead to hypoxia, distress, or death in stream fauna.

Key Concept

Thermal Pollution Effects on Dissolved Oxygen and Aquatic Metabolism
Estimated Time:1m 0s
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Topics

Pollution Types, Causes, Effects, and Control

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