[ Main ] Educator's Guide
Outreach Initiatives
[ Site Map ]
Geology | Lehigh River Watershed Explorations | Weather | Environmental Issues | Data Collection Activities

What is pH?
It is a general measurement of the acidity or alkalinity of a water sample. The symbol pH stands for the "potential for hydrogen".

What factors influence the pH of water?
1. Rainwater provides a significant amount of water to a watershed. Acid rain is caused by increased amount of nitrogen oxides and sulfur dioxides automobile and coal-fired power plant emissions. Nitrogen oxides and sulfur dioxides are changed to nitric acid and sulfuric acid when they interact with water in the atmosphere. These acids combine with moisture in the air and fall to the earth as acid rain or snow. Consequently, the pH of rain influences the overall pH of the watershed.
2. The kind of rocks or soil around a watershed over which runoff passes can also affect the overall pH. If limestone is present, the alkaline rocks may neutralize the acidic water.
3. Algal blooms may cause the water’s pH to become more basic.
4. As aquatic plants decompose, they release carbonic acid into the water.

What is the optimal pH for most aquatic plants and animals?
1. Most living organisms require a pH that is near neutral (pH=7). Pure deionized water has a pH that is neutral because it has an equal number of hydrogen (H+) and hydroxide (OH-) ions.
2. A pH level between 6.5-7.5 is considered to be excellent.
3. A pH level between 6.0-6.4 or 7.6-8.0 is considered to be good.
4. A pH level between 5.5-5.9 or 8.1-8.5 is considered to be fair.
5. When the water becomes too acidic (pH=0-7) or basic (pH=7-14), few organisms survive. Serious problems occur when the pH is below 5 or above 8.5.

What factors are affected by your watershed’s pH?
1. Most aquatic organisms are adapted to a specific pH level. When the pH increases or decreases rapidly, the diversity of a water ecosystem can change dramatically.
2. Immature stages of aquatic insects and young fish are extremely sensitive to low pH values, thus, pH can affect hatching and development of aquatic animals. Fish larvae and eggs usually have a narrower pH requirement than adult fish. Also, the optimal pH of Brine Shrimp embryos to leave their shell is 7.5-8.5.
3. When acidic water comes in contact with certain chemicals and metals that occur in soil and bedrock, these toxic sediments are often released into the waters causing the water to be more toxic than normal. Very acidic water can cause heavy metals, such as copper and aluminum, to be released into the water. Heavy metals can collect on fish gills or cause deformities in young fish, making it hard for them to survive.



Water Quality Background | Water Quality Data Collection Procedures | Water Quality Data Links

Curricular Activities | Lehigh River Photojournal | Water Quality | GIS | History | River Exploration | Fast Facts
LEO EnviroSci Inquiry is brought to you by the Lehigh Environmental Initiative at Lehigh University.
Copyright ©2000-2011 Lehigh Environmental Initiative at Lehigh University. All rights reserved.