Final answer:
The low pH layer in bodies of water is caused by increased erosion of acid-containing rocks, and water draining into the ocean from freshwater input and glacial melting.
Step-by-step explanation:
The low pH layer in bodies of water can be primarily attributed to increased erosion of acid-containing rocks and water draining into the ocean from freshwater input and glacial melting. Increased erosion of acid-containing rocks releases acidic substances that lower the pH of the water. Additionally, freshwater input and glacial melting can introduce pollutants that increase the acidity of the water.