Environmental physiology — Oxygen movement: The rate (flux) of oxygen in air compared with its rate in water is generally…

Introduction / Context:
Oxygen diffusion and flux determine aerobic microbial activity in different environments. Air and water differ markedly in gas solubility and diffusivity, which shapes microbial ecology.

Given Data / Assumptions:

• Flux depends on diffusion coefficients and concentration gradients.
• Diffusivity of O2 in air is orders of magnitude higher than in water.
• We compare qualitative rates, not exact numbers.

Concept / Approach:
Because the diffusion coefficient of oxygen in air is much higher and the medium is less dense and less viscous, oxygen moves far more rapidly through air. Consequently, oxygen supply is less limiting in well-aerated soils and biofilms with accessible air channels than in stagnant waters.

Step-by-Step Solution:
Recall D(O2 in air) » D(O2 in water). Higher diffusion → higher flux given similar gradients. Therefore, oxygen flux in air is greater than in water.

Verification / Alternative check:
Empirical measurements in soil science and limnology consistently show faster oxygen replenishment in gas-filled pores than in water-saturated matrices.

Why Other Options Are Wrong:

• Lesser/approximately equal/half: contradict physical diffusion properties.

Common Pitfalls:
Confusing oxygen solubility (higher in water than some gases) with diffusivity; flux reflects both gradient and medium properties.

Final Answer:
greater