Agricultural Runoff: A Major Nonpoint Source Polluter

Nonpoint source pollution is a significant environmental issue that arises from various human activities and natural processes. It is challenging to control due to its diverse sources and locations, and it can have detrimental effects on aquatic ecosystems, drinking water supplies, and recreational activities. Nonpoint source pollution, or NPS pollution, refers to any source of water contamination that does not meet the legal definition of point source outlined in the Clean Water Act. Unlike pollution from industrial or sewage treatment plants, NPS pollution results from runoff, precipitation, drainage, and other factors, carrying natural and human-made pollutants into water bodies. This type of pollution is the leading cause of water quality issues in many states, impacting not only the environment but also the economy and society of coastal communities.

Urban and suburban areas

One major cause of nonpoint source pollution in urban and suburban areas is stormwater runoff. When it rains, water flows across impervious surfaces like roads, parking lots, and rooftops, picking up and carrying away a variety of contaminants.

Agriculture

• Pesticides: The application of pesticides to crops can directly contaminate bodies of water used to control aquatic plants. Additionally, pesticides can indirectly pollute surface waters through air transport and surface water runoff. Pesticide seepage through the soil can also contaminate groundwater.
• Fertilizers: Excessive use of fertilizers can result in increased levels of nitrogen and phosphorus in water bodies, leading to algal blooms and the creation of hypoxic (low oxygen) conditions that are harmful to aquatic life.
• Livestock manure: Bacteria and nutrients from livestock and poultry manure can contaminate water sources, impacting both surface water and groundwater quality.
• Soil erosion: Agricultural practices can lead to soil erosion, causing excessive sedimentation that can smother aquatic ecosystems and degrade coastal and marine environments, including coral reefs.
• Nutrient loss: Fertilizers and livestock manure contain nutrients that can be washed into nearby water bodies through runoff, infiltration, and irrigation return flows.

The impact of agricultural nonpoint source pollution on water quality varies depending on factors such as the type of farming operation, landscape conditions, soils, climate, and farm management practices. To address this issue, organizations like the USDA NRCS have launched initiatives such as the National Water Quality Initiative (NWQI) to reduce the runoff of agriculture-related nutrients, sediments, and pathogens in high-priority watersheds.

Atmospheric inputs

Nonpoint source pollution is a type of diffuse contamination that does not originate from a single discrete source. It is often the result of small amounts of contaminants gathered from a large area. This type of pollution is challenging to control as it arises from various sources and locations, such as runoff from multiple sites.

Highway runoff, which is a small but widespread component of nonpoint source pollution, can be attributed to atmospheric fallout, vehicle deposition, and highway maintenance materials. Atmospheric fallout, which includes air pollution from industrial facilities, can be considered a nonpoint source due to its distributional nature, long-range transport, and multiple sources.

Forestry and mining operations also play a role in nonpoint source pollution. Forestry activities reduce the number of trees, leading to decreased oxygen levels in the area. Additionally, heavy machinery used in forestry and mining can contribute to soil erosion, increasing the risk of pollutants entering nearby water bodies.

Highway runoff

The pollutants associated with highway runoff include heavy metals, oils, toxic substances, debris, and sediment. These contaminants can be absorbed by the soil at construction sites and along roadsides and then carried by runoff water into aquatic ecosystems. Sediment, in particular, can smother aquatic habitats, clog waterways, and hinder the breathing of fish and aquatic insects. It also reduces sunlight penetration, impacting plant growth.

To mitigate the environmental impact of highway runoff, various management practices and regulatory frameworks have been established. The United States Environmental Protection Agency (EPA) has implemented programs such as the National Estuary Program (NEP) and the pesticides program under the Federal Insecticide, Fungicide, and Rodenticide Act to address roadway pollution. Additionally, states with approved coastal zone management programs are required to incorporate guidance management measures to control nonpoint source pollution.

Furthermore, erosion and sediment control measures, such as permanent stormwater retention ponds, slope protection, and temporary sediment traps, play a crucial role in reducing highway runoff pollution. By implementing these measures during the construction of roads, highways, and bridges, the negative impact on the environment can be minimized.

Forestry and mining operations

Nonpoint source (NPS) pollution is caused by rainfall or snowmelt moving over and through the ground, picking up and carrying natural and human-made pollutants, and depositing them into lakes, rivers, wetlands, coastal waters, and groundwater. NPS pollution is the leading remaining cause of water quality problems, and its effects on specific waters can be difficult to fully assess.

To address NPS pollution from forestry activities, the US Environmental Protection Agency (EPA) has developed National Management Measures to Control Nonpoint Source Pollution from Forestry. This report provides scientifically sound techniques and best practices to help forest owners protect lakes and streams from polluted runoff. It also assists states in implementing their nonpoint source control programs. Additionally, forest management certification has emerged as an incentive for landowners to commit to sustainable forest management practices that are environmentally appropriate, socially beneficial, and economically viable.

Mining operations, particularly abandoned subsurface mines, also contribute significantly to NPS pollution. The water that seeps out of abandoned mines can become highly acidic and contaminated with metals and toxic chemicals. For example, in Colorado, several streams were affected by copper, zinc, and arsenic contamination from abandoned mines. Similarly, in the mid-Atlantic and Appalachian regions of the United States, acid mine drainage and associated contamination from abandoned mines have impacted waterbodies.

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