Interpreting Phosphorus Test Results

Phosphorus is an essential nutrient that is quickly taken up and "stored" by plants and animals. Phosphates "free" in the environment are usually found dissolved in only low concentrations. High amounts of orthophosphate may indicate the presence of chemical fertilizers, polluted storm water run-off, poorly treated sewage or leaking septic systems.

• The following RiverWatch chart can be used as a guideline for interpreting the orthophosphate concentrations in a river.

  Orthophosphate Concentration	mg/L	River Water Quality	Aquatic Ecosystem
  Low	0.01 - 0.05	Good	Healthy
  Medium	0.05 - 0.1	Fair	Borderline healthy
  High	0.1 - 10	Poor	Unhealthy

• The Environmental Protection Agency in the United States has suggested that healthy aquatic ecosystems and the control of algae growth can be achieved with the following guidelines:

  

• Consider the following range of phosphorus concentrations when analyzing river data in Alberta:

  0.01 mg/L	Total dissolved phosphorus (orthophosphate) along the length of the Bow River rarely exceeds 0.01 mg/L. Alberta Environmental Protection (AEP) 1995
  0.01 mg/L	The average value of total phosphorus in the Athabasca River at Jasper 1970-1983 and in the Bow River at Cochrane 1985-1990. (Shaw Consulting, 1994)
  0.03 mg/L	Total phosphorus levels above .03 mg/L contributes to increased plant growth.
  0.035 mg/L	The average value of total phosphorus in the North Saskatchewan River at the Alberta/Saskatchewan border 1985-1989. (Shaw Consulting, 1994)
  0.05 mg/L	The Alberta Water Quality Guidelines (AWQG) for total phosphorus is 0.05 mg/L.
  0.091 mg/L	The average value of total phosphorus in the South Saskatchewan River at Medicine Hat 1985-1990. (Shaw Consulting, 1994)
  0.1 mg/L	Concentrations of total phosphorus over 0.1 mg/L stimulates plant growth above natural levels and lowers dissolved oxygen levels.
  0.3 mg/L	Total dissolved phosphorus levels of 0.3-0.4 mg/L have been measured below Calgary's wastewater treatment plants. AEP 1995
  0.5 mg/L	The average total phosphorus expelled during the first flush of storm water from outfalls in Calgary (B2, B5, B96) can range from 0.5-1.5 mg/L. City of Calgary Report 1997
  6.7 mg/L	Total dissolved phosphorus levels of 6.7 mg/L were measured below Cochrane's wastewater treatment plant. AEP 1995

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