How is the ph altered in an ecosystem? (both terrestrial and aquatic)

The pH of a substance refers to the degree of acidity or alkalinity of that substance, that is, pH is a measure of how acidic or basic a substance is. The pH scale ranges from 0 to 14. Point 1 [very acidic] to 6 [slightly acidic] is considered to be acidic while point 8 [very basic] to point 14 [slightly basic] is considered to be basic. Point 7 is neutral. 
In an ecosystem, the pH of the terrestrial or the aquatic environment can be altered by pollution such as mining erosion, radioactive materials, oil spillage, excess nutrients, etc.