Total Phosphorus

Phosphorus: What is it?

Figure 1: Illustrates the phosphorus cycle. Nutrient runoff and soil erosion are two sources of concern.
  • Phosphorus is a nutrient that is naturally found at low levels in water, plants, and animals.
  • Phosphorus is commonly found unnaturally in fertilizers (used in agriculture and lawn care), cleaners (used in industry), and wastewater (from household and industrial waste).

Total Phosphorus: 

  • Total Phosphorus (TP), as its name implies, is a measurement that includes all forms of phosphorus (dissolved and particulate, organic and inorganic).
  • TP is the unit of measurement used in the TMDL.

Why should we care about phosphorus in our water?

  • Phosphorus in low levels is necessary for life!
  • Phosphorus is used to grow healthy crops. It helps provide a strong and resilient root system, which ultimately helps the plant grow. Therefore, people often put it on the landscape to help fields maintain productive crop yields and for lush lawns.
  • However, high levels of phosphorus can cause problems in our streams, rivers, lakes, and oceans.
  • Because phosphorus helps plants grow on the land, it does the same for aquatic vegetation. High levels of phosphorus results in unhealthy levels of plant growth and specifically, harmful algal blooms.
Light green on aerial shot indicates algae bloom on the bay of Green Bay and Lower Fox River
Image 1: Photo credit, Sam Battle, 1999. Light green on aerial shot indicates an algal bloom on the bay of Green Bay and Lower Fox River

What are harmful algal blooms and why should we care?

While some algae, like green-algae, are an essential component of the food chain and essential to maintaining a healthy ecosystem, there are others, like cyanobacteria (blue-green algae), that can cause more harm than good. Cyanobacteria are generally not eaten by other aquatic organisms; therefore, there is not a natural “check and balance” system to help regulate its growth, which can lead to harmful algal blooms (Image 1). When an algal bloom forms, it creates a “green blanket” of algae that covers the water’s surface and can negatively impact both human health and water quality.

For more information about the impacts of harmful algal blooms, check out the “Don’t Get Sick, Avoid the Ick.”

Impacts of algal blooms:

  • Dead Zones: The thick blanket of green algae blocks sunlight from penetrating the waters’ surface and reaching underwater plants. Without sunlight, the plants are unable to perform photosynthesis, which produces oxygen; therefore, resulting in hypoxic (low-oxygen) conditions. When algae die, it sinks to the bottom of the river or lake, where it is then decomposed. The breakdown of plant material requires oxygen; therefore, exasperating the already hypoxic conditions. When a large algal bloom dies the decomposition process can consume most or all of the dissolved oxygen; thus, creating a “dead zone,” where most aquatic life either dies or is forced to seek refuge elsewhere (Figure 2).
  • Most fish species are capable of seeking refuge outside the dead zone; however, leaving their natural habitat requires them to compete for food and shelter in another area of the river or lake. This can have negative impacts on the rest of the ecosystem.
  • Stationary organisms (i.e., plants or benthic life forms) cannot seek oxygen elsewhere and therefore, hypoxic conditions may be fatal.
Figure 2: Graphic credit, Hans Hillewaert. Illustrates the processes that lead up to the creation of a dead zone in a salt water system. Nutrient loading, sediments, and organic carbon are factors that impact dissolved oxygen in both fresh and saltwater systems.
    Image 2: Photo credit, Mike Mushinski, 2017.    30 inch walleye caught on the Fox River.