Water Quality Measurement  | Chemical Parameter

Lake Pend Oreille | Pend Oreille River

Phosphorus occurs mostly as phosphates, the most common form being orthophosphate – also known as a reactive phosphate. Orthophosphates are commonly used in fertilizers for agricultural and residential purposes and are often carried into waterbodies through run-off. Orthophosphate is the form of phosphorus most readily utilized by aquatic organisms, such as plants and bacteria. 

Although phosphate is not harmful to humans, anthropogenic inputs of phosphorus are known to have a significant impact on ecosystems and damage the health of rivers and lakes. In high concentrations, orthophosphate, an ingredient in fertilizers, can cause rapid algae growth in surface waters, which can deplete sunlight and oxygen levels and harm fish populations (Gooddy et al. 2015). 

We measure the orthophosphate of the water each time we collect data – once a month for five months out of the year (June – October). The bars represent the upper quartile (75% of the data taken at this site falls below this line), the median (or mid-point of the data) for each site, first quartile (25% of the data taken at this site falls below this line), and the box represents the middle 50% of the data. Please note that the data for this graph has been log-transformed for visual aid purposes. 

Use our interactive graph to check out all the data we have collected since 2012. Hover over a data point to see more information or try clicking on the name of a month to see all the data for just one month!

Some sources of excess phosphorus

  • Stormwater runoff and snow melt
  • Erosion and sedimentation
  • Atmospheric deposition
  • Direct input by animals/wildlife
  • Agricultural runoff
  • Detergents and cleaning fluids
  • Failing septic systems
  • Lake mixing (internal loading of phosphorus from sediment/water interface)
  • Wastewater treatment plants and permitted industrial discharge
  • Fertilizer

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