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Phosphate fertilizers & water pollution

Phosphates are a major source of pollution in lakes and streams, and result in over-production of algae and water weeds. However, many of us have misconceptions regarding the source of polluting phosphates, and many homeowners unknowingly contribute to the problem.

Lawn and garden fertilizers often are implicated as the major source of phosphate pollution. However, research clearly demonstrates that with proper application, fertilizer does not pollute. When phosphates are applied to soils, they quickly bind to soil particles, much like a magnet picks up paper clips. Soil-bound phosphates contribute to pollution only when soil erosion occurs. Research studies found little or no difference in the phosphate content of storm runoff from lawn fertilizers with and without phosphate.

Problems arise, however, when fertilizer is over-spread or spilled onto hard surfaces like streets, driveways and sidewalks. Here, the phosphate washes with rain through the storm drains into lakes and rivers.

Likewise, grass clippings and leaves that fall on hard surfaces release their phosphorous into water sources. Research studies indicate that 80 percent of the phosphorous from urban settings comes from lawn clippings and leaves that end up in street gutters. While a few grass clippings mowed into the street look rather innocent, collectively they have a major impact on our water quality. Using a mulching lawn mower to keep lawn clippings on your lawn is especially useful.

Another important source of phosphate pollution comes from soil erosion caused by water or wind. When soil moves, it takes the soil-bound phosphates with it. Construction sites and sparsely vegetated ground are common causes of erosion.

You can take an active part in protecting Colorado's water quality by keeping fertilizers, leaves and grass clippings off streets and driveways. Prevent soil erosion by planting slopes with grass or other plants. We all have a part in protecting our water, one of Colorado's most valuable resources!

For more information, see the following Colorado State Extension fact sheet(s).


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Updated Monday, July 21, 2014