In the United States, agricultural runoff is one of the primary causes of water contamination. Current farming methods contribute to nutrient loading and, therefore, eutrophication. This sort of pollution is a non-point source, which is one of the primary obstacles to its regulation. The Clean Water Act (CWA) regulates both point source pollution and nonpoint source pollution through ambient water quality requirements, however it is significantly more difficult and ineffective to regulate nonpoint source pollution.
Agricultural Runoff
The farm is transporting topsoil, fertiliser, pesticides, and other hazardous pollutants to the river. Agricultural runoff is a type of non-point source pollution, making its regulation problematic.
Intensive agricultural techniques deplete the soil of its nutrients. Therefore, farmers must add fertilisers to the soil to replenish the nutrients.
The most important crop in the United States, corn (maize), is extremely susceptible to nutrient-deficient soil. In order for farmers to obtain a high crop yield, they must fertilise their crops. However, because under fertilisation results in lower crop yields and inferior produce, they prefer to err on the side of caution and over fertilise their crops.
Over Fertilization Is Not the Only Cause of Agricultural Runoff
According to this excerpt from the PBS documentary Poisoned Waters, industrial agriculture on a broad scale increases manure production. These modern farms generate so much manure that not all of it can be used, forcing farmers to stockpile it. However, more waste is created than can be managed, and part of it winds up as agricultural runoff, which adds nutrients such as nitrogen to water systems.
Agricultural Runoff Leads to Eutrophication
Agricultural runoff contributes nutrients such as Nitrogen and Phosphorus to water systems, causing them to become eutrophic (nutrient rich). Despite the fact that eutrophication can be a natural process, human activity such as agriculture greatly increases the nutrient concentration in water. In nutrient-rich water, algal blooms develop, such as the one depicted above.
The Nitrogen Cycle
Nitrogen is the most prevalent nutrient that causes eutrophication. An illustration of the nitrogen nutrient cycle is shown above. Nitrogen from atmospheric storage, organic matter, and fertilisers is fixed in the soil by lightning and bacteria. Much of the nitrogen is transformed to ammonium and then nitrates, which are utilised by plants. However, runoff and leaching allow excess nitrogen to reach water bodies.
Components of Runoff
When nutrients are transferred into a body of water through runoff or leaching, the use of excessive fertiliser and the presence of excessive amounts of animal faeces become problematic. Runoff occurs when water from precipitation or melting snow collects surplus nutrients and other debris as it flows over the ground and into bodies of water.
Eutrophication Leads to Asphyxiation
As a result of algal development, eutrophication causes dead zones such to the one pictured. In nutrient-rich environments, algae grow and die at a rapid rate and eat up the nutrients. These algae blooms prevent sunlight from accessing the surface of the water, so impeding photosynthesis. When algae die, they drop to the ocean floor and undergo bacterial decomposition, a process that consumes a great deal of the oxygen in the water, resulting in the death of marine life.
Agriculture in the Mississippi River Basin
The Mississippi River Basin’s tributaries, agricultural land, and metropolitan centres. These waters flow straight into the Gulf of Mexico. The agricultural runoff enters the water system and eventually reaches the Gulf of Mexico.
Hypoxic Zone in the Gulf of Mexico
The hypoxic zone or “dead zone” in the Gulf of Mexico stretches along the coasts of Louisiana and Texas. Less than two parts per million of dissolved oxygen exist in the water at the bottom of the gulf in this area. According to the United States Geological Survey, “hypoxia (in the Gulf of Mexico) is believed to be principally caused by excess nutrients delivered by the Mississippi River and 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.
It is not only agricultural runoff that contributes to non-point source pollution. Urban runoff is an additional major contributor to Non-point source pollution. As the number of cities increases, so does the quantity of asphalt. Almost none of the water flowing over paved surfaces is absorbed, and as a result, it transports all surface pollutants to a body of water.
Water Pollution and Treatment 1969
This 1969 film highlights water pollution issues and argues for federal regulation of water contamination. Congress passed the CWA three years later in response to the request for regulation.
The CWA regulates Point Source and Nonpoint Source Pollution. The EPA enforces water quality laws using the CWA. In its early years, the CWA, which was adopted in 1972, concentrated primarily on cleaning up Point-Source Pollution. Non-Point Source Pollution is far more difficult to control.
