I am looking to build a small natural pond (no filters or pumps) in a polytunnel. The last step in designing this is the water aeration method. I've seen various options for solar-powered aeration devices but I'd like to aerate it in a completely natural way if possible. Is this possible? If so how?
One method that has been used to aerate water in larger water treatment plants is to cascade the water.
Depending on the amount of land available, you might be able to install a stepped cascade, prior to the water entering the main pond - see page 43 in the link.