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Difficulty: MediumEnvironmental Hazards and Degradation

In major low-lying coastal urban zones of southern Nigeria, intense groundwater abstraction combined with frequent ocean storm surges frequently leads to severe subsurface degradation. Which environmental hazard is directly caused by this combination of human action and marine influence?

  1. Salinization of freshwater coastal aquifersAnswer
  2. B
    Rapid downhill displacement of rock scree along highland slopes
  3. C
    Widespread gullying caused by torrential surface runoff on upland soils
  4. D
    Atmospheric temperature inversion leading to persistent dry dust haze

Answer

Salinization of freshwater coastal aquifers
In low-lying coastal settlements, over-extracting groundwater lowers the water table hydrostatic pressure. Combined with ocean storm surges, seawater infiltrates permeable coastal sediments, leading to the salinization of underground freshwater aquifers.

Step-by-Step Solution

1
Analyze the geographical setting and drivers given in the stem.
The setting is low-lying coastal southern Nigeria experiencing high groundwater withdrawal and ocean storm surges.
Identifying the physical environment (coastal aquifer system) isolates hydrological hazards from inland geomorphic or atmospheric hazards.
2
Evaluate the hydraulic mechanisms resulting from excessive groundwater pumping near ocean boundaries.
Excessive abstraction reduces hydraulic head in freshwater aquifers, creating a pressure gradient that enables dense marine saltwater to encroach inland into underground water tables.
Storm surges exacerbate this by depositing saltwater on permeable surface soils, contaminating freshwater supplies.
3
Select the option that correctly identifies this environmental degradation process.
The correct hazard is saltwater intrusion/salinization of freshwater coastal aquifers.
Other listed options describe slope movements, surface soil erosion, or atmospheric phenomena.

Key Concept

Saltwater Intrusion and Coastal Aquifer Degradation
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Topics

Environmental Hazards and Degradation

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