Acids and bases affect the environment by altering habitats so that they are more favorable to some organisms than others. Acids and bases naturally occur in the environment, and organisms have adapted to the pH of their local habitat over evolutionary time. If the pH of a habitat changes, some organisms may thrive, others may fail, and others simply flee the habitat.
The pH of the air does not change much, so terrestrial organisms are only concerned with the pH of the soil and local water. The primary reason that soil pH is important to terrestrial animals is because soil pH influences which plants live in the area. Some plants thrive in high pH soils, while others thrive in low pH, or acidic, soils. Drinking water must have a pH near the neutral point for most terrestrial animals. Aquatic animals are susceptible to changes in the pH of their water. For fish or frogs that live in small, isolated waters, a change in pH could kill the entire population.
Acids and bases can also exacerbate the rate of erosion. For example, acidic rain water may quickly carve caves and channels through a bed of high pH rocks, such as limestone.