Brian Barton
Nonpoint source pollution refers to pollution that comes from multiple sources rather than a single identifiable point. This type of pollution is a significant issue for water quality, and agriculture is a major contributor. Agricultural runoff, which includes pesticides, fertilizers, and livestock manure, is a leading cause of water quality degradation in rivers and streams, and it also affects lakes and wetlands. The pollutants in agricultural runoff can be carried by rainfall or snowmelt into water bodies, causing a range of environmental and health issues. The impact of agricultural practices on nonpoint source pollution is well recognized, and various initiatives, such as the National Water Quality Initiative and the Agricultural Nonpoint Source Abatement and Control Program, aim to address these challenges and improve water quality.
| Characteristics | Values |
|---|---|
| Nonpoint source pollutants | Bacteria, excess nutrients, nitrogen, phosphorus, pesticides, manure, fertilizer, herbicides, insecticides |
| Leading cause of water quality issues | Rivers and streams |
| Third leading cause of water quality issues | Lakes |
| Second leading cause of water quality issues | Wetlands |
| Annual application in the US | 0.5 million tons of pesticides, 12 million tons of nitrogen, 4 million tons of phosphorus fertilizer |
| Primary stressors to water quality | Soil erosion, nutrient loss, bacteria from livestock manure, pesticides |
| Nonpoint sources of nitrogen | Commercial fertilizer, animal manure, atmospheric deposition |
| Percentage of total nitrogen added to the environment from point sources | 5.7% |
| Percentage of total nitrogen added to the environment from agricultural nonpoint sources | 93.5% |
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What You'll Learn
Bacteria from livestock manure
Livestock and poultry in the United States produce approximately 1.4 billion tons of manure annually, which is nearly five times the waste of the entire human population of the country. This manure contains bacteria, nutrients, antibiotics residue, and chemicals. When excess manure is spread on land, it can exceed the ground's natural absorption rate, leading to runoff into water sources. Storing manure in large, uncovered lagoons can also increase the risk of runoff into nearby water bodies.
The bacteria and nutrients present in livestock manure can have detrimental effects on water quality. For example, the nutrients in manure can stimulate algal blooms in lakes and rivers, leading to hypoxic (low oxygen) conditions that are harmful to aquatic life. As the algae die off, aerobic bacteria decompose them, further reducing oxygen levels and causing the death of fish and other aquatic organisms. This process has led to the creation of "dead zones," such as the recurring one in the Gulf of Mexico, which is caused by nutrient runoff from the Mississippi River.
Additionally, bacteria from livestock manure can directly impact human health. Contamination of drinking water supplies by manure bacteria can pose risks to human consumers. Furthermore, manure management practices can contribute to air pollution, as the manure emits ammonia, which combines with other air pollutants to form harmful solid particles that can cause heart and lung diseases.
To mitigate the impact of bacteria from livestock manure on nonpoint source pollution, proper manure management practices are essential. This includes storing manure in covered stockpiles or protected upland areas to minimize runoff risks. Implementing conservation practices, such as contour strip cropping, can also help reduce erosion and subsequent runoff of manure into water sources. By adopting these measures, farmers can play a crucial role in protecting water quality and preserving aquatic ecosystems.
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Pesticides
In the context of agriculture, pesticides are applied to crops to control pests and diseases. However, when excess pesticides are used or when they are improperly applied, they can be washed away by rainwater or irrigation and end up in nearby water bodies. This contributes to water pollution and can have harmful effects on aquatic ecosystems, including fish and other organisms.
The National Water Quality Assessment in the United States has found that agricultural runoff is the leading cause of water quality degradation in rivers and streams, the third leading source for lakes, and the second largest source of impairments to wetlands. About half a million tons of pesticides are applied annually to crops in the continental United States. As a result, pesticides are one of the primary stressors on water quality, along with soil erosion, nutrient loss, and bacteria from livestock manure.
To mitigate the negative impacts of pesticide use in agriculture, farmers can implement several best management practices (BMPs). These include adopting integrated pest management (IPM) strategies, such as using beneficial insects to control pests, reducing the overall reliance on chemical pesticides. Other BMPs include utilizing buffer strips, which are areas of vegetation or natural habitat between agricultural fields and nearby water bodies, to capture and filter pesticides and other pollutants before they enter water bodies. Conservation tillage, which involves leaving crop residue from a previous harvest when planting a new crop, can also help reduce erosion and keep pesticides in place.
By implementing these and other conservation practices, farmers can play a crucial role in minimizing the impact of pesticides on water quality and protecting the environment.
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Fertilizers
Nitrogen, in the form of nitrate, is a significant component of fertilizers. Nitrate is highly mobile and soluble in water. When excess nitrogen fertilizer is applied, it can easily be washed into adjacent streams by rainfall or snowmelt or leach into groundwater systems. This contributes to an increase in nitrogen levels in these water bodies, leading to a condition known as eutrophication.
Eutrophication can have several ecological consequences. Elevated nitrogen levels can cause excessive growth of algae, leading to algal blooms. These algal blooms can block sunlight from reaching aquatic plants, disrupting the balance of the ecosystem. As the algae die and decompose, they consume oxygen, leading to hypoxic conditions that can be harmful or even fatal to fish and other aquatic organisms.
Phosphorus, another key nutrient in fertilizers, also plays a significant role in nonpoint source pollution. Excess phosphorus from fertilizer runoff can contribute to eutrophication, further exacerbating the problem. Additionally, phosphorus can accumulate in water bodies, leading to nutrient enrichment. This enrichment can stimulate the growth of aquatic plants and algae, altering the natural balance of the ecosystem.
The impact of fertilizer-related nonpoint source pollution extends beyond the immediate ecological effects. It can also affect drinking water supplies, posing risks to human health. When fertilizers contaminate groundwater or surface water sources used for drinking water, there may be increased treatment costs and concerns about the potability of the water.
To mitigate the environmental and health impacts of fertilizer-related nonpoint source pollution, proper fertilizer management practices are essential. This includes applying fertilizers at appropriate rates, adopting conservation tillage practices, and implementing water-saving irrigation techniques. By effectively managing fertilizer usage, the risk of nutrient runoff and its subsequent ecological and health consequences can be significantly reduced.
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Sediment from soil erosion
Soil erosion is a significant issue in agriculture, and sediment from this process is a leading nonpoint source of water pollution. Nonpoint source pollution refers to any source of water pollution that does not meet the legal definition of "point source" as outlined in the Clean Water Act. This means that instead of originating from a single, identifiable source, nonpoint source pollution arises from various diffuse sources, such as land runoff, precipitation, and atmospheric deposition.
Agricultural practices play a crucial role in soil erosion and sedimentation. When natural vegetation is replaced by agricultural fields, topsoil becomes exposed and vulnerable to erosion by wind and water. The conversion of land for crop production or pasture can lead to higher rates of erosion, particularly when trees are removed and replaced with crops that cannot effectively hold onto the soil, such as coffee, cotton, palm oil, soybean, and wheat. As a result, valuable topsoil is lost, and soil characteristics essential for agriculture are altered.
To address the issue of sediment from soil erosion, sustainable land use practices are essential. This includes implementing conservation measures through a systems approach, targeting critical source areas to minimize water quality impacts. Additionally, techniques such as contour strip cropping can help reduce erosion and runoff. By adopting these practices, farmers can not only improve soil health and crop productivity but also mitigate the off-site impacts of sedimentation on aquatic ecosystems and water quality.
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Atmospheric deposition
In the context of agriculture, atmospheric deposition plays a role in the spread of pollutants associated with farming practices. For example, the improper use of fertilizers and pesticides can result in nutrient loss, primarily nitrogen and phosphorus, which can be transported by rainfall and snowmelt into local water bodies. Atmospheric deposition of nitrogen is often highest in areas with greater precipitation, such as the Northeast region of the United States.
Animal manure is another significant contributor to atmospheric deposition of nitrogen, particularly in the South and parts of the Northeast. When manure is left uncovered or improperly managed, nitrogen compounds can volatilize and be released into the atmosphere, subsequently contributing to nitrogen deposition in nearby areas.
Additionally, the combustion processes of power plants and industries release nitrogen oxides into the air, which then contribute to nonpoint source pollution when they return to the Earth's surface through precipitation. While these sources are considered point sources of air pollution, they become nonpoint sources of water pollution when the nitrogen reaches water bodies.
To address atmospheric deposition of nitrogen, efforts have been made to reduce nitrogen oxide emissions from point sources. However, it is important to note that atmospheric deposition is just one aspect of nonpoint source pollution in agriculture, which also includes runoff, infiltration, and irrigation return flows that directly transport pollutants from the landscape into water bodies.
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