Phosphorus: Transport to and availability in surface waters

What you need to know

General management practices for areas at high risk for phosphorus loss:

  • Minimize erosion and runoff.

  • Avoid phosphorus additions to very high testing soils where a crop response is unlikely.

  • Incorporate or inject phosphorus inputs, such as fertilizer and manure, below the soil surface.

A number of phosphorus (P) sources contaminate surface waters. These include agriculture, municipal sewage treatment plants, individual septic treatment systems, decaying plant material, runoff from urban areas and construction sites, stream bank erosion and wildlife.

Here, we’ll address the mechanics and sources of P loss from agricultural systems. In some areas and conditions, this can be a major source of P entering lakes and streams.

Phosphorus enters lakes and streams when runoff from landscapes drains to surface water bodies. Phosphorus may dissolve in runoff water (soluble or dissolved P) or become associated with particles such as soil or organic matter particles (particulate P) carried in the runoff.

Factors affecting phosphorus losses

There are two factors affecting P losses from the landscape and movement to surface water: Transport factors and P source and management factors.

Transport factors

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P source and management factors

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Phosphorus availability in surface waters

The addition of nutrients to bodies of surface water accelerates the eutrophication process, in which the water become overly enriched with nutrients. Elevated nutrient levels within the water often causes abnormally high production of algae and aquatic plants.

The eventual decomposition of increased amounts of organic matter can deplete the water’s dissolved oxygen content, resulting in the death of fish and other aquatic organisms.

Of all cropland nutrients inputs, P is the most important nutrient to prevent from reaching surface water bodies. Due to low natural levels of P, P availability usually limits biological productivity in surface waters.

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Daniel E. Kaiser, Extension nutrient management specialist and Paulo Pagliari, Extension soil scientist

Reviewed in 2018

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