Have a look through the thread on ground effect a couple months back. Ground Effect and Induced Drag kinda go hand in hand. There are several ways of looking at induced drag, all of them equally valid ways of explaining it. One of them is as follows:
The wingtips make vortices...The kinetic energy used to create these vortices has to come from somewhere. This energy actually comes from the airplane engine (or gravity in the case of a glider), and since the engine has to pull harder to create these vortices, we think of it as an additional drag. That's why contraptions that reduce wingtip vortices (winglets, high aspect ratio, etc.) are really trying to reduce induced drag. Flying close to the ground, "in ground effect" helps destroy wingtip vortices, and therefore reduced induced drag.

See the link below. A discussion on induced drag always comes to ground effect at some point, and a discussion on ground effect always comes back to induced drag...
[link=http://www.rcuniverse.com/forum/m_1887016/anchors_1887016/mpage_1/key_induced%252Cdrag/anchor/tm.htm#1887016]Ground Effect Thread[/link]