Does a spell with split second stop mana abilities from being activated?

Split second (CR 702.61) prevents players from casting spells or activating non-mana activated abilities while the split second spell is on the stack. However, it explicitly carves out an exception for mana abilities, which may still be activated freely.

A mana ability (CR 605.1) is broadly defined as an activated ability that could produce mana and does not use the stack. Because mana abilities never go on the stack, they are not subject to the timing restrictions imposed by split second. This makes intuitive sense: players still need to be able to float mana to pay costs even during split second windows.

Triggered abilities also still trigger normally during a split second spell's resolution window — split second only locks out spells and non-mana activated abilities (CR 702.61b).

Example: Your opponent casts Sudden Shock (which has split second). You cannot cast instants or activate abilities like Maze of Ith, but you can tap a Forest for one green mana using its mana ability, because tapping a basic land for mana is a mana ability and is explicitly exempt from split second's restriction.

So if you're hoping split second will lock your opponent out of producing mana, it won't — only non-mana activated abilities and spell casting are locked down.