In general, acid deposition has harmful effects for terrestrial ecosystems when it falls below a pH level of AP Environmental Science In general, acid deposition has harmful effects for terrestrial ecosystems when it falls below a pH level of a. 3.6 b. 4.6 c. 5.6 d. 6.6 e. 7.6 Answer: C Share this Share on FacebookTweet on TwitterPlus on Google+