______ aerators use low-pressure air blowers that force air through stones to release air bubbles at the ponds bottom or several feet below the water surface.

• A. Propeller-aspirator Pumps
• B. Paddlewheels
• C. Surface spray or vertical pumps
• D. Diffused air systems

Answer: (D)

Diffused aeration. This approach uses a low-pressure air blower that pushes air through diffuser stones placed on the pond bottom. As air passes through the stones, tiny bubbles are released and rise through the water, transferring oxygen from the air into the water and promoting mixing throughout the water column. This method is especially effective for oxygenating deeper or larger ponds and can be tuned by changing blower rate and diffuser spacing.

The other methods rely on surface agitation rather than releasing air from bottom diffusers: paddlewheels splash and aerate at the surface, surface spray or vertical pumps spray water into the air or push it upward, and they don’t continuously inject air bubbles through stones at depth.