If you really care about the science the wikipedia article on difraction is very detailed.
Diffraction - Wikipedia, the free encyclopedia
If your not bothered the best thing you can do is go take some photos. Set up a scene and shoot with various different aperture settings and compare the results.
Just a though, is it definately diffraction? Unless you are printing lagre or pixel peeping the effect is quite slight, especially at f/16. Could it be high ISO or long exposure noise being generate by your camera due to the smaller aperture requiring longer/more sensitive exposures? If you could post a example that would be great.