Wednesday, July 30, 2014
   
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Total and Dissolved Phosphorus

Phosphorus is another nutrient essential for aquatic plant growth. Total Phosphorus includes particulate as well as dissolved phosphorus, however, it is the latter form that is most readily bioavailable for plant growth.

phosphorus

Phosphorus enters surface waters naturally through runoff, or through human activities such as wastewater discharges and agricultural practices. Elevated concentrations can result in excessive growth of algae and aquatic plants.

A key nutrient that is often in short supply in freshwater environments, and the availability of which can govern the rate of growth of many aquatic organisms. Even small increases in the amount of phosphorous can set off a chain of undesirable events including accelerated plant growth, algae blooms, low dissolved oxygen, and the death of certain invertebrates and fish.

In nature, phosphorus usually exists as part of a phosphate molecule (PO4). Phosphorus in aquatic systems occurs as organic phosphate and inorganic phosphate. Organic phosphate consists of a phosphate molecule associated with a carbon-based molecule, as in plant or animal tissue. Phosphate that is not associated with organic material is inorganic. Animals can use either organic or inorganic phosphate.

Both organic and inorganic phosphorus can either be dissolved in the water or suspended (attached to particles in the water column). Dissolved inorganic phosphorus is the form required by plants.

Based on the Surface Water Quality Guidelines for Use in Alberta, the following has been established as the Total Phosphorus Water Quality Objective (WQO) for the SSRSB:

  • Phosphorus (total inorganic and organic) = 0.05 mg/L
  • Phosphorus (total dissolved) = 0.015 mg/L

In general, rating (condition) of the Total Phosphorus indicator is based on the number of times that recorded measurements over a one year period "exceeded" the Water Quality Objective (WQO) at that location.

  • 0% of recorded measurements exceeded the WQO level = NATURAL condition (blue)
  • 0.1% to 10% of recorded measurements exceeded the WQO level = GOOD condition (green)
  • 10.1% to 50% of recorded measurements exceeded the WQO level = FAIR condition (yellow)
  • more than 50% of recorded measurements exceeded the WQO level = CAUTIONARY condition (red)