Environmental Science

Choose the Correct Answer

Correct Answer : Option c

Explanation
Correct factors:
● Salinity: Higher salinity reduces oxygen solubility. Freshwater holds more dissolved oxygen (DO) than saline water like in seas and oceans.
● Temperature: Colder water holds more oxygen than warmer water as the intermolecular spaces are less which does not allow the oxygen to escape.
● Surface Turbulence: Waves, currents, and aeration increase oxygen diffusion from the atmosphere into the water. Stagnant water does not experience such turbulence, hence has lower DO levels.
● Pollution: Excess nutrients (from fertilizers, sewage, industrial wastes, etc.) cause algal blooms, which deplete oxygen when they decay or decompose.
● Seasonal variations: In colder seasons the colder surface water can hold a higher amount of dissolved oxygen than warmer waters in warmer seasons.
Incorrect factor:
● Sunlight below the euphotic zone: Sunlight is almost absent below the Euphotic or photic zone, not allowing for the photosynthesis, hence does not contribute to the variation in dissolved oxygen.