ecological perturbation acid rain ENVO:03000127 ExO:0000013 OMIT:0016047 An ecological perturbation that is acidic water, usually pH 2.5 to 4.5, which poisons the ecosystem and adversely affects plants, fishes, and mammals. It is caused by industrial pollutants, mainly sulfur oxides and nitrogen oxides, emitted into the atmosphere and returning to earth in the form of acidic rain water.