Agricultural Runoff is one of the leading causes of water pollution in the United States. Current agricultural practices lead to nutrient loading and in turn to eutrophication. One of the main problems in attempts to regulate this type of pollution is that it is non-point source. The Clean Water Act (CWA) regulates both point source pollution directly and non-point source pollution through ambient water quality standards, yet regulating the latter is much more difficult and ineffective.
Agricultural Runoff 
The picture above shows runoff from a farm in Iowa. Topsoil, fertilizer, pesticides, and other potential pollutants are being carried from the farm to the waterway. Agricultural runoff is a form of non-point source pollution, making it difficult to regulate.
Intensive farming practices strip nutrients from the soil. As a result farmers need to add fertilizers to soil to replace the nutrients.
The picture above shows the visual difference that can be seen between nutrient poor soil (left) and nutrient rich soil (right). Corn (maize) is the number one crop in the United States and is very sensitive to nutrient poor soil. In order to have a high crop yield farmers need to fertilize their crops, because under fertilization causes lower crop yields and poor quality produce farmers tend to error on the side of caution and over fertilize their crops.
Over Fertilization Is Not the Only Cause of Agricultural Runoff
As this excerpt from PBS’s Poisoned Waters discusses, large scale industrial farming leads to increased manure production. These industrialized farms produce so much manure that it cannot all be used, forcing farmers to store it. Yet more is produced than can be dealt with and some ends up as agricultural runoff adding nutrients such as Nitrogen into the water systems.
Agricultural Runoff Leads to Eutrophication
Agricultural runoff adds nutrients like Nitrogen and Phosophorus to the water system causing it to become eutrophic (nutrient rich). Eutrophication can be a natural process, however human intervention such as agriculture dramatically increases the amount of nutrients in water. Algal blooms such as the one pictured above thrive in nutrient rich water.
The Nitrogen Cycle 
Nitrogen is the most common nutrient leading to eutrophication. Above is a pictorial representation of the nitrogen nutrient cycle. Lightning and bacteria fixate nitrogen from atmospheric stores, organic matter, and fertilizers into the soil. Much of the nitrogen is converted into ammonium and later nitrates that plants use. However, through runoff and leaching excess nitrogen enters bodies of water.
Components of Runoff 
The use of excess fertilizer and the presence of excessive amounts of animal waste becomes a problem when the nutrients are carried into a body of water either by runoff or leaching. Runoff occurs when water, either from rainfall or melting snow, picks up the excess nutrients along with other sediment as it moves over and through the ground towards bodies of water.
Eutrophication Leads to Asphyxiation 
The photo above compares ocean floor in a healthy zone (left) and a dead zone (right). Eutrophication leads to dead zones like the one above as a result of algal growth. Algae grow and die at high rates in nutrient rich areas and use up the nutrients. These algal blooms block the sun from penetrating the water’s surface inhibiting photosynthesis. When algae die they sink to the bottom where bacterial composition takes place, a process that uses much of the Oxygen in the water, leading to asphyxiation and the death of marine life.
Agriculture in the Mississippi River Basin 
The photo above shows the tributaries, agricultural land, and urban centers connected to the Mississippi River Basin. These waters lead directly to the Gulf of Mexico. Agricultural runoff leaves the farms into the water system and ends up in the Gulf of Mexico.
Hypoxic Zone in the Gulf of Mexico
The hypoxic zone or “dead zone” in the Gulf of Mexico is an area that runs along the Louisiana and Texas coast lines. The water at the bottom of the gulf in this area contains less than two parts per million of dissolved oxygen. According to the United States Geological Survey, “hypoxia (in the Gulf of Mexico) is believed to be caused primarily by excess nutrients delivered from the Mississippi River in combination with seasonal stratification of Gulf waters.”
Number of Impaired Waterways by State
The number of waterways labeled impaired by the Environmental Protection Agency (EPA) is astounding. Above are the results of a Water Quality Assessment conducted by the EPA. Hypoxia is only one of the ways a waterway can become impaired. However, agricultural runoff is the number one contributor to the impairment of U. S. waterways.
Agricultural Runoff Is Not the Only Type of Runoff Contributing to Non-point Source Pollution 
Urban runoff is another leading cause of Non-point source pollution. As the number of cities grows so does the amount pavement. Almost none of the water flowing over paved surfaces is absorbed, and therefore it carries all the pollutants on the surface to a water body.
Water Pollution and Treatment 1969
This video from 1969 addresses the problems of water pollution and calls for federal regulation of water pollution. Three years later the CWA was passed by congress responding to the call for regulation.
Point Source and Non-Point Source Pollution is regulated by the CWA. 
The EPA uses the CWA to enforce water quality regulations. The CWA was enacted in 1972 and in its early years focused primarily on cleaning up Point-Source Pollution. Non-Point Source Pollution is much harder to regulate.
Three Main Goals of the CWA
The main goal of the CWA was to reclaim the country’s waters to make them swimmable, drinkable, and fishable. The 1972 Act aimed to make all U. S. waters “fishable and swimmable” by 1985. While there have been many success stories, including Lake Pontchartrain in Louisiana, the 1985 goal has yet to be met.
Overview of the Clean Water Act
The 303(d) Program creates a list of impaired and threatened waters and identifies all waters where required pollution controls cannot bring the water quality to meet standards. From the list Total Maximum Daily Loads (TMDLs) of pollution are created based on the severity of pollution. A TMDL is a calculation of the maximum amount of a pollutant a water body can receive. Point Sources receive a Waste Load Allocation (WLA) and Non-point sources receive a Load Allocation (LA), the portion of the loading capacity given to one existing Non-point sources. The 40 CFR 130.7 outlines the requirements for States when identifying impaired waters.
Impact of Non-point Source Pollution in Impaired Waters 
The biggest threat to estuaries, lakes, and rivers comes from Non-point source pollution. Of the waterways that have been listed as impaired by the EPA under the CWA, it has been found that Non-point source pollution is the biggest contributor causing the waterways to fail to meet regulatory standards.
Regulation of Non-point Source Pollution 
Section 319 of the CWA implements a Non-point Source Management Program and requires greater federal leadership to regulate non-point source pollution. Local and state governments are responsible for fulfilling Non-point source regulations. Before 1987 the Federal government regulated non-point source pollution through background water quality standards and the impaired waterway lists implementing TMDLs. Section 319 made Federal grant money available to support activities to reduce and clean up non-point source pollution giving them greater responsibility over non-point source pollution.
Regulatory Approaches
- Command and Control-policies created by Federal, State, and Local governments, including the CWA
- Economic Incentives-provides financial reasons for pollution control, includes grants, subsidies, and taxes on Non-point sources
- Design Standards-technology specifications based on a regulatory targets, include Best Management Practices (BMPs), and push polluters to use the best technology available to reduce pollution
- Volunteerism-polluters take action to prevent their own pollution
What You Can Do 
- Apply the proper amount of fertilizer. A soil test will tell you if your lawn needs fertilizer.
- Don’t apply fertilizer at times when it might be washed away by rain.
- Apply pesticides only when necessary and according to the instructions on the label.
- Recycle grass clippings and leaves by mulching or composting.
- Dispose of used motor oil and antifreeze at a recycling depository. Check with local service stations for locations of such facilities.
- Have your septic system inspected and pumped out every three to five years.
- Direct roof runoff into a grassed area. Roof drains should not be connected to a sanitary or storm sewer system.
- Seed grass, install sod or plant ground cover to reduce soil erosion.
- If you notice soil erosion from a construction site, contact the local governing agency responsible for erosion and sediment control. This is usually the county or township.
Suggestions courtesy of the Michigan Department of Environmental Quality. You can find the original document here.
References:
Carpenter, S. R., N. F. Caraco, D. L. Correll, R. W. Howarth, A. N. Sharpley, and V. H. Smith. “Nonpoint Pollution of Surface Waters with Phosphorus and Nitrogen.” Ecological Applications 8.3 (1998): 559. JSTOR. Web. 20 Feb. 2013.
Hascic, Ivan, and JunJie Wu. “Land Use and Watershed Health in the United States.” Land Economics 82.2 (2006): 214-39. JSTOR. Web. 20 Feb. 2013.
Lichtenberg, Erik, and Tony M. Penn. “Prevention versus Treatment under Precautionary Regulation: A Case Study of Groundwater Contamination under Uncertainty.” American Journal of Agricultural Economics 85.1 (2003): 44-58. JSTOR. Web. 20 Feb. 2013.
Rabalais, Nancy N., R. Eugene Turner, and Donald Scavia. “Beyond Science into Policy: Gulf of Mexico Hypoxia and the Mississippi River.” BioScience 52.2 (2002): 129. JSTOR. Web. 20 Feb. 2013.
Smith, Hendrick, and Rick Young. “Poisoned Waters.” Frontline. Dir. Rick Young. PBS. 21 Apr. 2009. Television.
http://toxics.usgs.gov/definitions/
http://water.epa.gov/polwaste/nps/archives/index.cfm
http://water.epa.gov/polwaste/nps/cwact.cfm
http://water.epa.gov/lawsregs/lawsguidance/cwa/tmdl/overview.cfm
http://sci.waikato.ac.nz/farm/content/nutrientcycling.html
My Info:
Eileen Newcomer Class of 2013.
Majors: Environmental Studies and History
Contact Info: newcoet@mx.lakeforest.edu
Definitions:
Eutrophication: the process by which a body of water becomes enriched in dissolved nutrients that stimulate the growth of aquatic plant life usually resulting in the depletion of dissolved oxygen.
Asphyxiation: the condition of being deprived of oxygen.
Hypoxia: the condition in which dissolved oxygen is below the level necessary to sustain most animal life- generally defined by dissolved oxygen levels below 2 ppm.
Point Source Pollution: Water pollution coming from a single point, such as a sewage-outflow pipe.
Non-Point Source Pollution: A contributory factor to water pollution that cannot be traced to a specific spot.