I usually point wave makers or powerhead toward the surface, to facilitate gas exchange.
Consider that the fish species that require a highest dissolved oxygen levels (trout, Geophagines, Hydrocynus, some tetras) live in riffles, even rapids, or in the turbulent counter current surf zones.
Below are natural areas where I have caught the tetras that require high O2 lately
Because I like to keep Rheophillic, riverine fish species, I also like to put sump return lines above the water surface to create as much turbulence as possible, to get the highest dissolve oxygen levels as possible.
This can be problematic for some plant species, so I choose plant species easily adaptable to high flow in those areas, but place others like lilies in lower flow zones created by floating logs, or other barriers that temper flow.