Skip Navigation
Button that takes you to back to the home page. Button that takes you to the teacher pages. Button that takes you to the modules and activities page. Button that takes you to the related links page. Button that takes you to the references page. Button that takes you to the Problem Based Learning model page. Button that takes you to the glossary page.Image map of some Water Quality puzzle pieces.  Please have someone assist you with this.

Button that takes you to the Overview page.
Button that takes you to the Acid Mine Drainage page.Image that says Agriculture.
Button that takes you to the Sewage page.
Button that takes you to the Dredging page.

Water Pollution: Agriculture
Image of a cow standing in a field with some mountains in the background.Agriculture is a common contributor to non-point-source pollution. Pesticides and fertilizers from crop fields, as well as animal wastes from feed lots, are often carried in runoff to streams. Pesticides are generally toxic and may lead to immediate health problems — even death — within the stream. Fertilizers and animal wastes, however, tend to enrich streams with large amounts of nutrients such as nitrogen and phosphorus. The immediate result of increased nutrients in a stream is increased growth of aquatic plants. While this may seem beneficial at first glance, it is actually quite harmful to the ecosystem. The overabundance of plants leads to an overabundance of plant detritus on the streambed at the end of the growing season. Microbes on the streambed must then use larger amounts of oxygen in order to decompose the increased amount of dead plant material. This leads to a depletion of the amount of dissolved oxygen in the streamwater. Macroinvertebrates and larger aquatic animals such as fish can die from a lack of oxygen. With the death of herbivorous (plant-eating) animals, the aquatic plant population will continue to increase. The use of oxygen by microbial decomposers will also continue to increase. This positive feedback process is referred to as eutrophication. Photo 1994

Another indicator of agricultural pollution is the presence of the microbe fecal coliform. Fecal coliform is a non-pathogenic bacteria that naturally occurs in the digestive tracks of warm-blooded animals. "Non-pathogenic" means fecal coliform does not cause diseases. However, it is often found in association with pathogenic (disease-causing) organisms.

Loose dirt, or sediments, from plowed fields is also a form of agricultural pollution. Like pesticides, fertilizers, and animal wastes, dirt from plowed fields can be carried by runoff to streams. Sediments cause increased suspended solids in streamwater. The suspended solids decrease light penetration through the water column. When the sediments finally settle to the bottom of the stream, they suffocate life there. This movement of loose dirt into streams is called siltation. The murkiness of the water is referred to as turbidity.

The problem of pesticides, fertilizers, animal wastes, and sediments in runoff can be increased by livestock grazing along the stream. Vegetation that grows near streams acts as a buffer. This vegetation absorbs toxins and nutrients and traps sediments before they reach the stream. Livestock remove the vegetation. Without a vegetation buffer, pollutants can move freely from a field into a stream. In addition, livestock increase erosion of banks along streams, and thereby increase the occurrence of siltation.


Overview ..|.. Acid Mine Drainage ..|.. Agriculture ..|.. Sewage ..|.. Dredging
Glossary  .|
Related Links  .|.. References ..|.. PBL Model  .|

  Home ..|.. Teacher Pages ..|.. Modules & Activities  

Button that takes you back to the Water Quality main page.

HTML code by Chris Kreger
Maintained by ETE Team
Last updated November 10, 2004

Some images 2004

Privacy Statement and Copyright 1997-2004 by Wheeling Jesuit University/NASA-supported Classroom of the Future. All rights reserved.

Center for Educational Technologies, Circuit Board/Apple graphic logo, and COTF Classroom of the Future logo are registered trademarks of Wheeling Jesuit University.