'Chinampas': The Ancient Aztec Floating Gardens That Hold Promise for Future

They always call these "floating" gardens, but AFAICT they are always firmly attached to the bottom. What they are more like is flooded raised beds. The illustration in the article even seems to show them floating, but the description contradicts it. To make one, you drive in stakes and weave wickerwork in and out between them, and scoop mud from outside into the space. The channels get deeper, and the bed fills up with rich mud, which when high enough becomes dry enough to grow in. They drive in live willow stakes at the corners, which sprout and help hold it all together.

The article says both that the Aztecs developed the method, and that the pre-Aztec Nahuat were already using it.

Chinampas are still in operation in the poorer part of Mexico City, with some effort going into expanding them. They have had to erect filtering dams at the ends of the narrow channels between beds to keep pollution out of the water that feeds them.

Thinking about nitrogen runoff... perhaps easily deployable rafts (fashioned from mycelium, equipped with bioaccumlators?) could be deployed in waterways... or, a quick way to seed mangroves?