Phosphates

Background Information

Phosphorus is usually present in natural waters as phosphate and is an essential element of life. Phosphates can come from fertlizers, human or animal wastes, soaps or detergents, or industrial waste. When too much phosphorus becomes available, plants grow rapidly. Phosphates that enter a stream may cause algae to multiply and grow quickly. This may result in an algae bloom. Algae blooms are thick layers of green slime that cover the surface of ponds or slow moving streams.

Algae blooms are harmful to most aquatic organisms. They cause a decrease in the dissolved oxygen levels of the water. They prevent waves and the surface of the water from coming into contact with the air which provides the main source of oxygen for the water. Their dark color absorbs more heat energy from sunlight causing the water temperature to rise. Warm water holds less oxygen than cold and it causes the metabolic rate of aquatic organisms to increase. In addition, the algae which grow rapidly near the surface block sunlight to plants that live on the bottom causing them to die. Plants which grow fast die fast and sink to the bottom. Dead plant material is decomposed by bacteria increasing the biological oxygen demand (BOD). All of these factors combine to cause oxygen levels in the water to decrease rapidly. This can result in a fish kill and the death of many organisms.

Algae blooms are indicators of cultural eutrophication. Eutrophication refers to the aging of a lake or other body of water. Cultural eutrophication occurs when nutrients (such as nitrates and phosphates) are added from agricultural runoff, sewage, detergents or other sources such as golf courses or lawns. Advanced stages of cultural eutrophication can be detected by an unmistakable "rotten egg" smell.

Test Procedure

Test for phosphates by using the phosphate test kit provided by LaMotte (or other supplier). Follow the instructions provided with the kit. It is important that the vials or test tubes used in the test be extremely clean. Preferably they should be rinsed with distilled or demineralized water prior to the test. Record your results for the phosphate test in ppm.

What to Expect

A reading of 1.0 ppm or less is considered excellent. A phosphate level between 1.1-4 ppm is good. A level between 4.1-9.9 ppm is fair, and a level greater than 10 ppm is poor.

References