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Difficulty: MediumPollution Types, Causes, Effects, and Control

In an industrial area where high concentrations of sulfur dioxide (SO2\text{SO}_2) and nitrogen dioxide (NO2\text{NO}_2) are emitted into the atmosphere, surrounding terrestrial ecosystems receive acid rain with a pH significantly lower than 5.65.6. Which of the following best explains how acid precipitation directly impairs the growth and root development of forest plants?

  1. It mobilizes toxic aluminum ions in the soil while leaching essential mineral cations such as calcium and magnesium below the root zone.Answer
  2. B
    It destroys nitrifying bacteria in the soil, thereby preventing the photolysis of water required for cellular respiration in plant roots.
  3. C
    It forces energy to flow backward from soil decomposers to primary producers, causing an inversion of the ecosystem's pyramid of energy.
  4. D
    It alters soil structure so severely that the community is reset to bare rock, initiating primary ecological succession.

Answer

Acid precipitation mobilizes toxic toxic aluminum ions in the soil while leaching essential nutrient cations like calcium and magnesium below the root zone.
The correct answer explains that elevated soil hydrogen ion concentrations displace essential nutrients like calcium (Ca2+\text{Ca}^{2+}) and magnesium (Mg2+\text{Mg}^{2+}), causing them to leach out of the root zone, while simultaneously releasing soluble aluminum (Al3+\text{Al}^{3+}) ions which are toxic to root systems.

Step-by-Step Solution

1
Identify the primary chemical pollutants responsible for acid precipitation.
Atmospheric SO2\text{SO}_2 and NO2\text{NO}_2 react with atmospheric water vapour to form sulfuric acid (H2SO4\text{H}_2\text{SO}_4) and nitric acid (HNO3\text{HNO}_3).
These strong acids lower the pH of rainfall below natural baseline levels.
2
Analyze the chemical interaction between acidic water (H+\text{H}^+ ions) and soil mineral particles.
Excess H+\text{H}^+ ions replace cations (Ca2+\text{Ca}^{2+}, Mg2+\text{Mg}^{2+}, K+\text{K}^+) bound to soil clay particles, washing them beyond the reach of roots (leaching), while dissolving bound aluminum into toxic Al3+\text{Al}^{3+} ions.
Aluminum toxicity directly damages root apical meristems, while cation depletion leads to severe plant mineral deficiencies.

Key Concept

Effects of Acid Rain on Soil Chemistry and Terrestrial Vegetation
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Topics

Pollution Types, Causes, Effects, and Control

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