How do you control drainage out of the sectioned compartment? I am assuming you are going to add water to the outer rim and land to the inside. I bet if you drilled a hole with a bulkhead in the back of your tank (so it drains the inner rim) only 1 inch above the bottom and filled that island with 1.5 inch of hydroton bioballs, then screen, then dirt... you would have one awesomely self sufficient habitat going on. You could even get a aqualifter to move 3.5 gallons of water a day from the outer rim, into the inner rim (island) and then out the back of the tank. Sorry I just really like vivariums so I get too excited sometimes.