Weapon element is trumped by arrow element, which is trumped by an endowed element from an expendable item or skill. The exception is 'neutral' arrows which won't pass their element on.
Examples (Rudra's Bow is a [Holy] attribute Bow, Elven Arrow is neutral, elven bow is neutral)
Elven Arrow w/ Elven Bow = neutral attack
Elven Arrow w/ Rudra's Bow = holy attack
Fire Arrow with w/ Elven Bow = fire attack
Fire Arrow with w/ Rudra's Bow = fire attack
Fire Arrow with w/ Rudra's Bow w/ a water converter spent = water attack
Fire Arrow with w/ Rudra's Bow w/ Endow Tsunami from a sage = water attack