The bottom isn't completely water. The land portion has a solid piece of polystyrene under it, and only a little area around the edges with gravel and water. It's definitely wet in those photos, but I let it dry a bit before I water it again.
The substrate is peat moss.
I haven't tried these species of ferns before, so it'll be interesting to see how they fair. They're already pretty big for that tank, so I'm not really expecting this to be a long term deal. I have two tanks set up like this, both with different amounts of light. So far the ferns in both tanks look healthy.
This tank was really only intended to be a temporary tank until I set up something nice for them... They had been in a really spartan cage and I wanted something a little nicer for them. I kinda got carried away though. lol That method is one idea I've had, Jennewt. With most of the base being polystyrene, it's actually very light weight, so tipping it is easy.