Palouse agriculture slice

Nonpoint Pollution from Agriculture

Agricultural-related water quality risks

A stream channel that has been altered by animal grazing. Notice the sediment-laden water, the eroding bank, and the lack of vegetation to shade the stream and filter pollutants.

Here, cattle are excluded from this stream channel which has a riparian (streamside) area. Banks are not eroding and overhanging grasses and shrubs already provide some shade. Later, larger shrubs and trees will grow and provide more shade and woody debris. The riparian area can filter pollutants such as nutrients and fecal coliform before it reaches the stream.
Agricultural-related water quality risks can be classified into three broad categories:
  • Stream Modification
  • Stormwater Runoff
  • Groundwater Contamination

Stream Modification

Various land use activities, such as agriculture, often alter streamside vegetation and sometimes the shape of the stream channel. These changes to stream and riparian area can have a direct and profound impact on the heath of streams and water quality.

A riparian area is a streamside area that is physically linked due to water.

Riparian zones include both the active floodplain (a flat or nearly flat land next to a stream or river, stretching from the banks of its channel to the base of the enclosing valley walls) and the adjacent plant communities.

These plant communities directly influence the stream system by providing:

  • Shade.
  • Fine or large woody material.
  • Nutrients.
  • Organic and inorganic debris.
  • Terrestrial insects.
  • Habitat for riparian-associated wildlife.

Stream-side areas are transition areas between aquatic and upland habitats and contain elements of both ecosystems. Riparian corridors also provide habitat for wildlife, especially migrating and breeding birds.

Riparian vegetation, in turn, influences the water. Riparian vegetation stabilizes stream banks and reduces erosion. Stream bank vegetation protects water quality by filtering sediment and capturing excess nutrients in runoff from upland regions. Stream bank vegetation provides shelter for birds and small animals. Overhanging vegetation cools streams for fish and provides debris and organic matter, as well as food for insects and other life in the water. Approximately 85 percent of terrestrial vertebrate species in Washington State use riparian habitat for essential life activities.

Back to top of page

Stormwater Runoff

Polluted stormwater runoff is rainwater and snowmelt that carries livestock manure, soil, fertilizer, pesticides, and other pollutants downstream into creeks, rivers, and Puget Sound, creating a health problem for people and for aquatic life.

Livestock manure can be a great fertilizer when managed responsibly. But when it’s exposed to the weather or not managed properly, it can also be a source of water pollution.

Bacteria from manure can make shellfish unfit to eat and water unsafe to drink or swim in. Nutrients from manure can promote excessive algae and aquatic plant growth. As plants decay, they deplete the oxygen in the water that fish and other aquatic life need to survive.

Manure storage locations that are not properly constructed or operated generate significant amounts of polluted storm water.

Too much nitrate getting into the ground water can create unsafe drinking water for people. Our state has a number of areas that have too much nitrate and it is contaminating people’s drinking water.

Good manure management:

  • Prevents parasite re-infestation.
  • Keeps ground water clean.
  • Builds goodwill with your neighbors.
  • Supports a healthy watershed.
  • Benefits fisheries and shellfish beds.
  • Grows good crops

Groundwater Contamination

Ground water can become contaminated with nitrate pollution with the over-application of manure, or the application of manure at times when plants do not fully use the applied manure. Commercial fertilizers also can threaten groundwater.

In many cases, the ground water serves as a source of drinking water. Excess nutrients not used by the crop pass beyond the root zone of the plant and may enter the ground water. Over time, nutrients and chemicals may accumulate in the ground water, eventually reaching a level that is harmful to human health.



Back to top of page

Last updated July 2012