Nate, you're not dreaming at all. It's pretty much a reality. We have a few water bodies here with the floating islands, whether we want them or not. They're comprised of the following, according to the layers I'm using as text:
(Air)
* Grass/creeping weeds/flowers
* Mixed 15% fine sedimentary and top soils (can be woody compost), 3 inches,with root zones reaching down to 6 inches
* Intertwining of coarse sediment, dead/live moss bed, mushrooms, and lateral roots from various plants,roughly 2 inches.
* Mixed of rotted woody materials from tree barks and stringy leaves (aquatic grasses). Same as rotting mulch based materials.
(Water)
So, from your composition design, you're not too far off. These islands by far will not be able to support any size human, but it can indeed support migratory birds that feed on the insects. There are various designs on YouTube, wetland and habitat restoration agencies that you can take a check upon.
