Oracle Text

Whenever a player taps a land for mana, that player adds one mana of any type that land produced, and Overabundance deals 1 damage to the player.

Card Rulings

10/4/2004 The ability deals one damage even if the land produces no mana when it was tapped to use a mana ability. This can happen with lands that produce a variable amount of mana.
10/4/2004 This card’s ability is a mana ability. There is no chance to respond to it in order to prevent the damage. If you want to prevent the damage, you need to use a prevention spell or ability prior to tapping the land for mana.