Phosphorus is usually present in natural waters as phosphate .Organic phosphate is a part of living plants and animals, their by-products, and their remains. Inorganic phosphates include the ions (H2PO-2, HPO=4, and PO-4) bonded to soil particles and phosphates present in laundry detergents.

Phosphorus is an essential element for life. It is a plant nutrient needed for growth, and a fundamental element in the metabolic reactions of plants and animals. Plant growth is limited by the amount of phosphorus available. In most waters, phosphorus functions as a "growth-limiting" factor because it is usually present in very low concentrations.

The natural scarcity of phosphorus can be explained by its attraction to organic matter and soil particles. Any unattached or “free" phosphorus, in the form of inorganic phosphates, is rapidly taken up by algae and larger aquatic plants. Because algae only require small amounts of phosphorus to live, excess phosphorus causes extensive algal growth called "blooms." Algal blooms are a classic symptom of cultural eutrophication. (Eutrophication means when a body of water has an increased amount of minerals and nutrients. This change favors the growth of plants over animals.)

Cultural eutrophication is the human-caused enrichment of water with nutrients, usually phosphorus. Most of the eutrophication occurring today is human-caused. Natural eutrophication also takes place, but it is insignificant by comparison. Phosphorus from natural sources generally becomes trapped in bottom sediments or is rapidly taken up by aquatic plants. Forest fires and fallout from volcanic eruptions are natural events that cause eutrophication. Lakes that receive no inputs of phosphorus from human activities age very slowly

Sources of Phosphorus

Phosphorus comes from several sources: human wastes, animal wastes, industrial wastes, and human disturbance of the land and its vegetation.

Sewage from wastewater treatment plants and septic tanks is one source of phosphorus in rivers. Sewage effluent (out flow) should not contain more than 1 mg/ L phosphorus according to the U.S. Environmental Protection Agency, but outdated wastewater treatment plants often fail to meet this standard. Also, some types of industrial wastes interfere with the removal of phosphorus at wastewater treatment plants.

Storm sewers sometimes contain illegal connections to sanitary sewers. Sewage from these connections can be carried into waterways by rainfall and melting snow. Phosphorus-containing animal wastes sometimes find their way into rivers and lakes in the runoff from feedlots and barnyards.

Soil erosion contributes phosphorus to rivers. The removal of natural vegetation for farming or construction for example, exposes soil to the eroding action of rain and melting snow. Soil particles washed into waterways contribute more phosphorus.

Fertilizers used for crops, lawns, and home gardens usually contain phosphorus. When used in excess, much of the phosphorus in these fertilizers eventually finds its way into lakes and rivers.

Draining swamps and marshes for farmland or shopping malls releases nutrients like phosphorus that have remained dormant in years of accumulated organic deposits. Also, drained wetlands no longer function as filters of silt and phosphorus, allowing more runoff -and phosphorus- to enter waterways.

Impacts of Cultural Eutrophication

Shallow lakes and impounded river reaches, where the water is shallow and very slow-moving, are most vulnerable to the effects of cultural eutrophication. Phosphorus stimulates the growth of rooted aquatic vegetation. These plants, in turn, draw phosphorus previously locked within bottom sediments and release it into the water, causing further eutrophication. Eventually, the entire lake or river stretch may fill with aquatic vegetation.

The first symptom of cultural eutrophication is an algal bloom that colors the water a pea-soup green. As eutrophication increases, algal blooms become more frequent. Aquatic plants that normally grow in shallow waters become very dense. Swimming and boating may become impossible.

The advanced stages of cultural eutrophication can produce anaerobic conditions in which oxygen in the water is completely depleted. These conditions usually occur near the bottom of a lake or impounded river stretch, and produce gases like hydrogen sulfide, unmistakable for its "rotten egg" smell.

Changes in Aquatic Life

As with other types of water pollution, cultural eutrophication causes a shift in aquatic life to a fewer number of pollution tolerant species. The many different species that exist in clean water are replaced by a fewer number of species that can tolerate low dissolved oxygen levels-carp, midge larvae, sewage worms (Tubifex), and others. For example, waters that once supported bass, walleye, pike, and bluegill may only be able to support carp under eutrophic conditions.

Reversing the Effects of Cultural Eutrophication

Aquatic ecosystems have the capacity to recover if the opportunity is provided by:

  1. Reducing our use of lawn fertilizers (particularly inorganic forms) that drain into waterways;
  2. Encouraging better farming practices: low-till farming to reduce soil erosion; soil- testing to match the amount of fertilizer applied to soil needs, thus preventing excess fertilizer from finding its way into waterways; building storage or collecting areas around cattle feedlots, so that phosphorus containing manure is not carried away with surface runoff;
  3. Preserving natural vegetation whenever possible, particularly near shorelines; preserving wetlands to absorb nutrients and maintain water levels; enacting strict ordinances to prevent soil erosion;
  4. Supporting measures (including taxes) to improve phosphorus removal by wastewater treatment plants and septic systems; treating storm sewer wastes if necessary; encouraging homeowners along lakes and streams to invest in community sewer systems;
  5. Requiring particular industries to pretreat their wastes before sending it to a wastewater treatment plant.

Can you think of any other actions that would prevent or reduce the effects of eutrophication?

Sampling Procedure

It is important that glassware used for measuring total phosphate be “acid-washed," that is, soaked in diluted HCI, and then rinsed thoroughly with distilled water. Please wear protective gloves when handling this glassware. WARNING: Never wash this glassware with phosphorous-containing detergents.

Total Phosphate (PO-4-P) Testing Procedure


Total Phosphate test kit items

  1. Fill the 50 ml graduated cylinder to the 50 ml line with the water sample. Pour into a 125 ml Erlenmeyer flask. Use gloves if drawing the sample by hand.
  2. Use a 1ml pipette to add 1ml, of Sulfuric Acid, 36% to the flask. Swirl to mix.
  3. Use the 0.05 g spoon to add one measure of Ammonium Persulfate. Swirl to dissolve.
  4. Add a few boiling stones. Place the flask on a hot plate, small backpacking stove or Sterno and boil gently for 30 minutes. Add deionized water to the sample during the boiling to maintain a volume between 10 and 50 ml. Permit the volume to decrease to approximately 10 ml (about 1/4 inch of water) at the end of the boiling step, but do not allow the sample to go to dryness or to dense white sulfur trioxide fumes. Remove from the hot plate and cool.

If inside, please boil sample in a well-ventilated place; if outside, please stay upwind of the boiling sample.

  1. Add one drop of Phenolphthalein Indicator, 1% to the cooled sample.
  2. While swirling the flask, use a 1 ml- pipette to add Sodium Hydroxide dropwise until the solution turns faint pink. A volume of slightly less than 3 ml is required.
  3. While swirling the flask, add Sulfuric Acid, 36%, one drop at a time, until the pink color disappears.
  4. Quantitatively transfer the sample, which should be at room temperature, to the 50 ml graduated cylinder. After transferring the solution from the flask to the graduated cylinder, wash the flask with a little deionized water and add it to the solution in the graduated cylinder. Dilute the solution in the graduated cylinder to exactly 50 ml using deionized water and mix well.
  5. Fill a test tube to the 10 ml line with the test sample from step 9.
  6. Use the 1.0 ml pipette to add 1.0 ml of Phosphate Acid Reagent. Cap and mix.


Use of the Axial Reader

  1. Use the 0.1 g spoon to add one level measure of Phosphate Reducing Reagent. Cap and mix until the powder has dissolved. Wait 5 minutes.
  2. Remove the stopper from the test tube. Place the tube in the Phosphate Comparator with Axial Reader. Match the sample color to a color standard. Record the result as mg/L (ppm) Total Phosphate.

Note: Total phosphate concentrations of non-polluted waters are usually less than 0. 1mg/ L.