pH indicates the acidic or alkaline nature of a substance. The pH is derived by determining the negative log of the hydrogen ion (H+) concentration of liquids and substances. pH values range between 0 to 14. Waters with low pH have more hydrogen ions and are more acidic than waters with higher pH. A pH of 7 indicates neutrality.
Changes in pH
Because pH is based on a logarithmic scale, a decrease in pH from 7 to 6 results in a tenfold increase in acidity. Conversely, a pH increase from 7 to 8 results in a tenfold decrease in acidity. Thus, water with a pH of 5 has 100 times as many hydrogen ions than water with a pH of 7. The acidic or alkaline nature of lake and river water is determined by the rocks and minerals of the basin. The natural system, however, can be influenced by inputs to the system. Areas within a limestone basin have high amounts of bicarbonate and carbonate which help buffer the water from the effects of acid precipitation by neutralizing the hydrogen ions. Changes in pH can have many effects on the biology and chemistry of lakes and rivers. Many organisms are sensitive to changes in pH and may not be able to tolerate changes. Fish spawning of some species may be inhibited with a small drop in pH. Waters with a pH at or less than 4 is toxic to many fish and may result in death. Waters subject to declines in pH may also experience increases in metals, such as aluminum or mercury. These metals may interfere with reproduction of both aquatic organisms and the consumers of these organisms.
