What Is the Cause of pH in a Lake?

Bedrock and Soils

• The composition of bedrock near or within the lake can greatly affect the pH of the water itself. Acidic rocks and soils which are high in silica cause the water they surround or are submerged in to be more acidic. Areas with limestone-based bedrock tend to be more basic and, in turn, give lake waters a higher pH. In both cases, rain waters can wash the minerals from inside the rocks into the lakes, altering the water's pH.

Plant Growth and Activity

• The activity of aquatic plants can also have temporary and seasonal effects on the pH of lake water. During the daylight hours and the peak growing season, the process of photosynthesis can cause lake water to become more basic. The plants use up hydrogen ions from the water in the photosynthesis process, which decreases the pH of the water. These changes do not tend to last long, however, as complex chemical reactions take place in the water to counter the pH change.

Pollution

• High levels of pollution can alter the pH of lake water. Pollutants can cause increases in water temperature or changes in the nutrients within the water. These changes can cause pH to increase in areas where the pollutants are introduced into the lake water.

Acid Rain

• Acid rain can greatly affect the pH of lake water, especially following prolonged heavy rainfall. The heavy burning of fossil fuels in certain areas causes sulfur dioxide and nitrous oxides to be present in rainwater, making it more acidic. When the rain falls heavily, it dilutes the lake water by both directly falling into the lake and flowing in via streams and rivers. The acidic water causes the lake water to become more acidic as well.