Once circulated water reaches the surface, the air-water interface facilitates the transfer of oxygen to the lake water. Subsurface aeration can be accomplished by the use of jet aerators, which aspirate air, by means of the Venturi principle, and inject the air into the liquid. Subsurface aeration seeks to release bubbles at the bottom of the water body and allow them to rise by the force of buoyancy. Diffused aeration systems utilize bubbles to aerate as well as mix the water.
The barge is capable of dissolving up to 5 tonnes of oxygen in 24 hours. Circulators are commonly used to mix a pond or lake and thus reduce thermal stratification.
However no one has undertaken an project as large as an estuary. The dissolved oxygen concentration within Cardiff Bay are maintained at or above 5 mg/L. Compressed air is pumped, from five sites around the Bay, through a series of steel reinforced rubber pipelines, laid on the beds of the Bay and Rivers Taff and Ely. At times this is insufficient and the Harbour Authority is using a mobile oxygenation barge built by McTay Marine with liquid oxygen stored in a tank. Liquid oxygen is passed through an electrically heated vapouriser and the gas is injected into a stream of water which is pumped from, and returned to, the bay.