In his excellent book, A Dictionary of Modern American Usage, Garner says that impact was traditionally used as a noun and has only recently been used as a verb. He and other stylists consider verb forms of impact to be trendy and recommend that impact be used only as a noun. Garner prefers the verbs affected or influenced to impacted (dentists should consult their own dictionary).
But unless you work with car accidents or asteroids, I suggest that you not use impact or its variants as a verb or as a noun. I suggest that you never utter impact again. Why? It's overused.
Scientists, real estate developers, college administrators (including chancellors, vice chancellors, executive vice chancellors, associate chancellors, deans, vice deans, ...) , advertising executives, and their like frequently use impact to inflate. When developers or deans are trying to separate listeners/readers from their money or their critical sense, effect and affect are too small (their impact is inadequate).
And also consider that, either in verb or noun form, impact, affect/effect, and influence often can be profitably replaced by the more meaningful words increase or decrease.
Moderate disturbance impacts biodiversity.
The impact of moderate disturbance is substantial.
Moderate disturbance affects biodiversity.
The effect of moderate disturbance on biodiversity is substantial.
Moderate disturbance increases biodiversity.
The last sentence is superior to the others because it provides more information and uses no trendy words.
No more impacts, impactions, or impactifications!
For more about this, see impactometer.