From The Aquarium Wiki
Ripariums are a style of aquaria that utilize a combination of planters, rafts and riparian or emmersed aquatic plants (i.e. Spathiphyllum, Dieffenbachia, Acorus, Pilea, Bacopa, Cryptocornes) to create a riparian-like display. The planters are generally made of plastic with several small holes in it. When planted, they are usually filled with a clay based planting media, planted with a hydrophyte or other water loving plant, then attached close to the water line on the back or sides of the riparium display tank. The rafts are usually small and made of a tough foam with many holes sized for the stems of plants in it. After the stems of the selected plant are placed into the holes of the raft, it is attached to the front of a planter in the display. The roots of the riparium plants then have their root systems completely submerged under water and are able to absorb nutrients including nitrogenious wastes from the water column. Ripariums have been confused with another style of aquaria known as paludariums. The biggest difference between these two styles, is that paludariums have a set land area, while ripariums have no set land area, but are comprised of moveable planters and rafts. Riparium displays have numerous advantages, including providing cover for shy fishes, removing nitgrogenious waste from the water column, adding vibrant colours to a setup, and creating a naturalistic display.