Water pollution describes the contamination of water bodies, such as lakes, rivers, oceans, and groundwater, caused by human activities. A widespread form of this issue is non-point source pollution, which differs from pollution originating from a single, identifiable location. Its diffuse nature means pollutants accumulate from broad areas rather than a specific pipe or discharge point.
Understanding Non-Point Source Pollution
Non-point source (NPS) pollution refers to contamination that does not originate from a single, discrete source. It primarily results from land runoff, precipitation, or snowmelt moving over and through the ground. As this runoff travels, it picks up and carries away both natural and human-made pollutants, eventually depositing them into lakes, rivers, wetlands, coastal waters, and groundwater. Its diffuse nature makes it particularly difficult to monitor and regulate.
Agricultural Activities
Agricultural practices are a major source of non-point source water pollution. Fertilizers, containing nitrogen and phosphorus, lead to nutrient runoff when precipitation washes over farm fields. This excess of nutrients promotes the overgrowth of algae and aquatic weeds, a process known as eutrophication. Pesticides and herbicides used on crops can also be carried into water bodies by runoff or leach into groundwater, harming aquatic life.
Sediment from tilled fields is another agricultural pollutant. Soil erosion, accelerated by farming, transports loose particles into waterways. This sediment can cloud water, reduce sunlight penetration, and impair aquatic habitats by smothering fish spawning grounds and reducing shelter for organisms. Livestock operations contribute through animal waste. Manure contains bacteria, viruses, and excess nutrients that pose health risks and contribute to nutrient pollution and oxygen depletion in water bodies.
Urban and Suburban Areas
Developed urban and suburban areas are major contributors to non-point source pollution due to their extensive impervious surfaces. Roads, rooftops, and parking lots prevent rain and snowmelt from soaking into the ground, increasing the volume and speed of stormwater runoff. This runoff picks up pollutants like oil, grease, and toxic chemicals from motor vehicles, which accumulate on roads.
Chemicals used in lawn care, such as fertilizers and pesticides, along with pet waste, are washed into storm drains by runoff. Unlike wastewater from homes, water entering storm drains typically does not undergo treatment before being discharged directly into rivers and lakes. Construction sites contribute sediment from disturbed soil, along with discarded materials like plastics and chemicals, which are easily transported by runoff.
Other Key Sources
Forestry operations contribute to non-point pollution through timber harvesting and road construction. Sediment runoff from logging roads increases turbidity and harms aquatic organisms. The removal of streamside vegetation can lead to increased water temperatures and reduced streambank stability, affecting aquatic habitats. Chemicals from pesticide or herbicide applications in forests may also enter water systems.
Atmospheric deposition occurs when airborne pollutants settle onto land and water surfaces. Industrial emissions and vehicle exhaust release substances like sulfur dioxide, nitrogen oxides, and heavy metals into the air. These can then be washed down by rain as acid rain or settle as dry particles, contaminating water bodies. Nitrogen compounds from atmospheric deposition are a source of nutrient pollution in some aquatic environments.
Malfunctioning or improperly maintained septic systems represent another non-point source, particularly in areas not connected to centralized sewer systems. These systems can leach nutrients, such as nitrogen and phosphorus, and pathogens like bacteria and viruses into groundwater or surface water. Untreated wastewater from failing septic systems can lead to groundwater contamination and contribute to harmful algal blooms in nearby water bodies.
Abandoned mines are a source of pollution through acid mine drainage and the leaching of heavy metals. When water and oxygen react with sulfur-bearing minerals exposed by mining activities, sulfuric acid can form, dissolving heavy metals into the water. This contaminated water can then flow into streams and groundwater, posing risks to aquatic life and drinking water supplies.