APES 8.1-8.2: Sources of Pollution and Human Impact

Point source pollution

Pollution released from a single, identifiable source with negligible spatial extent, such as a factory pipe, sewage treatment plant outfall, or power plant discharge.

Why is a pollution source called a "point source"?

In mathematical and environmental models, the source can be approximated as a single point because its spatial extent is negligible relative to the affected environment.

Give three examples of point sources of water pollution.

Examples include industrial wastewater pipes, municipal sewage-treatment outfalls, and discharges from power plants. Some concentrated animal-feeding operations and regulated stormwater discharges are also point sources.

Give examples of point sources outside water pollution.

A smokestack can be an air-pollution point source, a jet engine a noise point source, an intrusive streetlight a light-pollution point source, and an interfering electrical device a radio-emission point source.

Nonpoint source pollution

Diffuse pollution that originates from many scattered sources over a broad area rather than from one identifiable discharge point. It is commonly transported by runoff, atmospheric deposition, drainage, seepage, or snowmelt.

How do point and nonpoint pollution differ in terms of monitoring and regulation?

Point-source discharges can usually be traced to a particular facility or outlet and regulated directly. Nonpoint pollution is harder to control because it results from many activities distributed across a watershed.

How can pollutants from a point source become widespread nonpoint pollution?

A pollutant may be emitted from a discrete source but then transported long distances through air or water and deposited over a broad region. The resulting environmental contamination is diffuse even though the original emission was point-source.

Why is nonpoint pollution often called cumulative pollution?

Many individual sources may each release small amounts of contaminants, but their combined input over a watershed can produce substantial environmental effects such as turbidity, eutrophication, or toxicity.

What are the principal categories of nonpoint-source water pollutants?

The major categories are sediment, nutrients, toxic contaminants and chemicals, and pathogens.

How can water pollutants be classified as physical, chemical, or biological?

Sediment is primarily a physical pollutant because it increases suspended solids and turbidity. Nutrients, pesticides, metals, acids, and salts are chemical pollutants, while pathogens such as bacteria, viruses, and parasites are biological pollutants.

Urban runoff

Stormwater flowing over impervious urban surfaces such as roads, roofs, parking lots, and sidewalks, carrying sediment, nutrients, oil, metals, and other contaminants into the environment.

How do impervious surfaces affect the water balance during a storm?

They decrease infiltration and increase the fraction of precipitation becoming surface runoff. This increases the rapid transport of contaminants to streams and reduces natural soil filtration.

Why can urban runoff sometimes be classified as a point source?

Although runoff is collected from a broad area, it may be channeled through a municipal storm-drain system and discharged through a single pipe. The final discharge point can therefore be treated as a point source.

Why is urban runoff often treated as true nonpoint pollution despite storm drains?

Urban runoff usually comes from many activities and surfaces rather than one easily identified activity. Some runoff also flows directly into water bodies without passing through a storm-drain pipe.

Sediment as a water pollutant

Sediment consists of eroded soil particles, including fine silt and larger suspended solids. It commonly enters water through agricultural runoff, construction, disturbed land, and eroding stream banks.

How does sediment increase turbidity?

Suspended soil particles scatter and absorb light, making water cloudy. The resulting turbidity can reduce light penetration and interfere with aquatic photosynthesis and drinking-water treatment.

How can excessive sediment harm aquatic ecosystems?

Sediment can reduce light available to submerged plants, damage habitat, transport attached pollutants, and contribute to oxygen depletion. Accumulated sediment can also reduce channel capacity and increase flooding.

What is eutrophication?

Eutrophication is the enrichment of an aquatic system with bioavailable nutrients, especially nitrogen or phosphorus, causing excessive algal or phytoplankton growth.

Which nutrient is often limiting in freshwater systems, and which is often limiting in marine or estuarine systems?

Phosphorus is often the limiting nutrient in freshwater systems, whereas nitrogen is frequently limiting in marine and brackish estuarine systems. Adding the limiting nutrient can stimulate primary production and eutrophication.

How is phosphorus commonly transported from land into water?

Many phosphorus compounds adsorb to soil particles, so erosion and sediment runoff are important transport pathways. Phosphorus also enters water from fertilizers, sewage sludge, manure, and wastewater.

How is nitrogen commonly transported through a watershed?

Nitrogen may enter soil as organic nitrogen or ammonia, $\mathrm{NH_3}$. Oxidation converts it to nitrate, $\mathrm{NO_3^-}$, which is soluble and is readily transported by infiltrating water, tile drainage, and groundwater flow.

Why can an algal bloom create surface scums and reduce plant growth?

Dense algae can accumulate at the water surface, forming scums and blocking light from reaching submerged plants. Some algae also produce compounds that cause taste and odor problems or toxins.

Hypoxia

A condition in which dissolved oxygen concentration is too low to support many aquatic organisms. It can result from microbial decomposition following nutrient-driven algal blooms.

Why can eutrophication lead to hypoxia?

When an algal bloom dies, microorganisms decompose its organic matter and consume dissolved oxygen. If oxygen consumption exceeds replenishment, the water becomes hypoxic, creating harmful conditions for fish and aquatic invertebrates.

What is the relationship among excess nutrients, algal growth, decomposition, and fish mortality?

Excess nitrogen or phosphorus stimulates algal growth. Decomposition of the resulting biomass consumes dissolved oxygen, potentially producing hypoxia or anoxia that stresses or kills fish and aquatic invertebrates.

What are the major environmental concerns associated with toxic nonpoint contaminants?

Toxic contaminants can harm humans and aquatic organisms, persist because they resist environmental breakdown, and accumulate or remain mobile in soil, water, or air.

Examples of toxic contaminants in nonpoint pollution

Examples include heavy metals such as lead, mercury, zinc, and cadmium; persistent organic compounds such as PCBs and PAHs; pesticides; fire retardants; acids; and salts.

Why are heavy metals important water pollutants?

Metals such as lead, mercury, zinc, and cadmium do not readily decompose. They can persist in sediments and water and may be toxic to organisms even at relatively low concentrations.

Pathogens in nonpoint-source pollution

Pathogens are disease-causing organisms, including bacteria, viruses, and parasites, that can enter runoff from livestock, septic systems, sewage overflows, pet waste, and contaminated stormwater.

What is the significance of coliform bacteria in water-quality testing?

Coliforms and fecal indicators are commonly measured as evidence of contamination by fecal material and the possible presence of pathogens. They are indicators of pollution, not necessarily the organisms causing disease.

Examples of pathogens associated with contaminated runoff

Examples include $\textit{Cryptosporidium}$, $\textit{Giardia}$, $\textit{Salmonella}$, noroviruses, and parasitic worms.

How do agricultural activities contribute to nonpoint pollution?

Fertilizers, manure, pesticides, and sediment can be carried from fields by runoff, erosion, or drainage. Crop residues, irrigation water, wildlife waste, and atmospheric deposition can also add contaminants.

Why does plowing increase agricultural pollution?

Plowing exposes and loosens soil, making it more vulnerable to erosion during precipitation. It can also increase the amount of fertilizer and pesticides transported into nearby water bodies.

How can pesticides reach water or air from agricultural land?

Pesticides can move with surface runoff, infiltrating water, or atmospheric deposition. Wind can carry suspended pesticide droplets away from the application site, a process called spray drift.

Why are concentrated animal-feeding operations potentially treated differently from ordinary agricultural runoff?

Large livestock operations can concentrate wastes and release them from identifiable locations, making their discharges more like point sources and subject to increased regulation.

Atmospheric deposition as nonpoint pollution

Pollutants emitted into the atmosphere can return to land or water through dry deposition between storms or wet deposition during precipitation. Because the deposited material may have multiple sources and travel long distances, its environmental impact is often classified as nonpoint.

How can highway runoff become polluted?

Runoff can collect atmospheric fallout, vehicle-related deposits, oil, metals, tire and brake particles, and road-maintenance materials before entering soil or surface water.

How do forestry operations increase nonpoint pollution?

Removing trees reduces protective vegetation and can expose soil. Heavy machinery compacts or disturbs the soil, increasing erosion and sediment delivery to waterways.

Why can abandoned mines contribute to nonpoint water pollution?

Exposed minerals can react with air and water to produce acidic drainage. Water leaving abandoned underground mines may have low pH and can mobilize toxic metals into nearby water bodies.

How do active and abandoned mining operations differ as pollution sources?

Active mining operations can be treated as point sources when their discharges come from identifiable facilities. Runoff and drainage from abandoned mines are diffuse and are therefore commonly considered nonpoint pollution.

What is the chemical significance of acidic mine drainage?

Acidic drainage has elevated $[\mathrm{H^+}]$ and therefore a low pH, since $\mathrm{pH}=-\log[\mathrm{H^+}]$. The acidic water can also increase the solubility and mobility of metal ions.

How do marinas and boating activities contribute to water pollution?

Boat paints, solvents, oils, and fuel can enter water through runoff, spills, or leaks. Poorly maintained sanitary facilities can add nutrients, bacteria, and other pathogens.

What human activities commonly generate nonpoint pollution in developed areas?

Lawn fertilization and pesticide use, road construction, building construction, vehicle activity, stormwater runoff, and poorly maintained septic systems are common contributors.

How can septic systems contribute to nonpoint water pollution?

Faulty or poorly maintained septic systems can release nutrient-rich wastewater, pathogens, and other contaminants into soil and groundwater. These pollutants may eventually reach surface waters.

How do buffer strips reduce nonpoint pollution?

Vegetated strips placed between developed or farmed land and a water body slow runoff, trap sediment, promote infiltration, and allow plants and soil microbes to remove or transform some contaminants.

Retention pond

A constructed basin that temporarily stores stormwater, allowing sediment and some attached pollutants to settle before water leaves the site. It acts as a buffer between runoff and a natural water body.

How does porous pavement help control urban runoff?

Porous pavement allows precipitation to infiltrate into underlying soil rather than becoming direct surface runoff. Infiltration can reduce runoff volume and provide some pollutant removal through soil filtration and adsorption.

Why are wetlands useful in controlling nonpoint pollution?

Wetlands slow water movement, trap suspended particles, promote sedimentation, and provide chemical and biological processes that can remove or transform nutrients and other contaminants.

How do erosion-control measures at construction sites reduce pollution?

Measures such as silt fences, straw barriers, vegetation, and sediment basins reduce the transport of disturbed soil and debris by stormwater. They limit turbidity and sediment deposition in nearby waters.

Contour plowing

A farming practice in which furrows follow the natural contours of a slope. The furrows slow water flow, increase infiltration, and reduce soil erosion and nutrient runoff.

Conservation tillage

A farming method that leaves crop residues on or in the soil instead of removing all plant material. Residues reduce raindrop impact, sheet erosion, runoff, and loss of attached nutrients.

How do crop rotation and perennial crops reduce nonpoint pollution?

They maintain plant cover and root systems for more of the year, helping hold soil in place and improve infiltration. Reduced erosion lowers sediment and particle-bound phosphorus runoff.

Why can phosphorus and nitrogen require different pollution-control strategies?

Phosphorus is often transported attached to eroded soil particles, so erosion control is especially important. Nitrate, $\mathrm{NO_3^-}$, is highly soluble and may require reducing fertilizer application and limiting infiltration or drainage losses.

Why can nonpoint pollution be difficult to solve with a single technological treatment?

The pollution arises from many land uses and transport pathways, so no single discharge can be isolated and treated. Effective control generally combines watershed planning, land-management changes, erosion control, and stormwater management.