Helena Joyce
Urban streams are often teeming with life, but they are also susceptible to pollution from various sources. With 80% of Americans living in metropolitan areas, the environmental changes associated with urban development are evident in these water bodies. Urban streams are affected by contaminants, habitat destruction, and streamflow flashiness, which disrupt biological communities and harm sensitive aquatic species. Chemical contaminants, nutrients, heavy metals, and waste are carried from farms, factories, and cities into rivers and streams, ultimately reaching the ocean. This pollution can be categorised as point source and non-point source pollution. Non-point source pollution, such as stormwater runoff, is a significant threat to aquatic ecosystems as it carries contaminants and soil into waterways. Urban-specific issues, such as increased conductivity and nitrogen loading, also impact water quality. Additionally, commonly used products like coal-tar-based pavement sealcoats contribute to toxicity in streams.
| Characteristics | Values |
|---|---|
| Common Pollutants | Chemicals, nutrients, heavy metals, plastic, waste, marine debris, pathogens, microorganisms, sediments, litter, nitrogen, polycyclic aromatic hydrocarbons (PAHs), etc. |
| Sources of Pollutants | Farms, factories, cities, sewage treatment facilities, runoff from farms and urban areas, vehicle emissions, fertilizers, oil leakage, vehicle exhaust, tire and brake wear, pavement erosion, etc. |
| Effects of Pollution | Degradation of water quality, harm to biological communities, economic losses, health issues including Legionnaires' disease and lead contamination, toxic effects on aquatic organisms, etc. |
| Actions to Address Pollution | Local cleanups, reductions in polluted runoff, installation of green roofs, rain gardens or rain barrels, use of porous surfaces, redirection of home downspouts, proper disposal of chemicals, etc. |
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What You'll Learn
- Urban runoff, including agricultural and industrial waste
- Impervious surfaces and their impact on water quality
- Parking lots and roads as sources of polycyclic aromatic hydrocarbons (PAHs)
- Dams, culverts, and other structures altering water flow and health
- The role of urban streams in the wider water network
Urban runoff, including agricultural and industrial waste
In the context of urban runoff, industrial waste and construction site waste are notable contributors to water pollution. Industrial facilities release pollutants directly into waterways, while construction sites flush debris and residues into adjacent bodies of water during storms. To address this issue, some metropolitan areas require the treatment of runoff and domestic waste at regional treatment plants or the use of large containment structures to store and treat stormwater before release. However, not all communities have the necessary funds to expand wastewater treatment or construct stormwater storage capacity.
Agricultural runoff is another critical component of urban runoff pollution. Farms often use inorganic fertilizers, insecticides, and manure, which contain high levels of nitrogen, phosphorus, potassium, and organic carbon. Consequently, agricultural runoff carries various pollutants, including pesticides, heavy metals, and nutrients, into nearby waterways. This type of pollution is classified as non-point source pollution, and it has detrimental effects on aquatic ecosystems, leading to algal blooms that poison freshwater life by depleting oxygen and limiting sunlight for photosynthetic species.
The impact of urban runoff pollution extends beyond environmental concerns, affecting both residents of the watershed regions and economic activities. Polluted runoff can contaminate drinking water sources, requiring more expensive treatment processes, and can carry bacteria that pose serious health risks. Additionally, the presence of contaminants in recreational areas has led to warnings against swimming in waterways for a certain period after heavy rainfall. Furthermore, urban areas with a high proportion of hard surfaces experience increased flooding due to the lack of absorption, resulting in repeated damage to homes and businesses.
To mitigate the effects of urban runoff, including agricultural and industrial waste, several strategies have been proposed. One promising approach is the creation of "green infrastructure," which aims to slow down and absorb polluted runoff through the development of natural spaces, rain gardens, and the use of pervious pavement. On agricultural lands, regenerative agriculture practices and cost-share programs can help reduce polluted runoff by implementing conservation measures with federal and state funding support. By addressing the diverse sources of urban runoff pollution and adopting effective management strategies, it is possible to improve water quality, protect aquatic ecosystems, and safeguard the health and well-being of residents in urban areas.
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Impervious surfaces and their impact on water quality
As cities expand and develop, the natural landscape is replaced by impervious surfaces such as roads, buildings, parking lots, and driveways. These impervious surfaces have a significant impact on water quality, particularly in urban streams.
Impervious surfaces are surfaces that do not allow water to seep through and instead cause water to run off into storm sewers and local creeks and streams. Examples of impervious surfaces include superhighways, streets, pavement, driveways, and house roofs. As the number of impervious surfaces in a watershed increases, the risk of flooding events also increases. This is because, in natural landscapes like forests and grassy areas, a significant portion of rainfall is absorbed into the soil, reducing the amount of runoff. In contrast, impervious surfaces prevent infiltration, leading to increased water flow into streams and rivers.
The impact of impervious surfaces on water quality is twofold. Firstly, construction sites with exposed dirt and sediment can cause sediment-laden water to enter local waterways, degrading water quality and harming aquatic ecosystems. Secondly, impervious surfaces contribute to nonpoint source pollution. As water runs off impervious surfaces, it picks up and carries contaminants, such as pollutants, soil, and even trash. These pollutants are then carried into waterways, where they can infiltrate groundwater and concentrate in streams and rivers.
Nonpoint source pollution is a significant threat to aquatic life and ecosystems. It can lead to the formation of large dead zones with minimal oxygen in oceans and also endanger coral reef ecosystems. Additionally, contaminants from urban development can disrupt biological communities, particularly sensitive aquatic species, and harm economically valuable resources such as fisheries and tourism.
Understanding the impact of impervious surfaces on water quality is crucial for managing urban development and protecting the health of urban streams and the larger water bodies they flow into. By recognizing the connection between impervious surfaces and water pollution, cities can implement measures to mitigate these effects, such as improving infiltration through the use of permeable surfaces and implementing better erosion control practices at construction sites.
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Parking lots and roads as sources of polycyclic aromatic hydrocarbons (PAHs)
Urban streams are often teeming with life, weaving through cities and towns. However, the environmental changes associated with urban development are evident in these water bodies. Contaminants, habitat destruction, and streamflow flashiness from urban development can disrupt biological communities, especially sensitive aquatic species. As watersheds in urban areas are dominated by concrete, pavement, and roofs, they quickly shed water, flushing pollutants and soil into nearby rivers and streams.
One significant source of pollution in urban streams is polycyclic aromatic hydrocarbons (PAHs). PAHs are persistent organic pollutants (POPs) composed of two or more fused aromatic rings of carbon and hydrogen atoms. They are typically characterized by biological enrichment, hydrophobicity, anti-degradation, carcinogenicity, mutagenicity, and teratogenicity. Long-term exposure to PAHs can damage human organs and lead to various cancers. PAHs are widespread due to long-term anthropogenic sources of pollution, and their inherent properties make them highly persistent in the environment.
Parking lots and roads are significant sources of PAHs. In Harbin, China, concentrations of 32 PAHs in road dust, green belt soil, and parking lot dust samples were quantified. The total PAH concentrations in road dust ranged from 0.95 to 40.7 μg/g, while in green belt soil, they ranged from 0.39 to 43.9 μg/g. For parking lot dust, the range was 0.81–190 μg/g, with higher concentrations in underground parking lots compared to surface lots. The composition profile of PAHs was similar across road types, dominated by high molecular weight PAHs (HMW-PAHs).
The use of coal-tar-based pavement sealcoat on asphalt driveways and parking lots is another source of PAHs in urban streams. This product is commonly applied in urban and suburban areas across the central, eastern, and southern United States, contributing to the toxicity of runoff and particles washed from these surfaces.
Overall, parking lots and roads are significant sources of PAHs, which are toxic pollutants that can have detrimental effects on both human health and the environment. As urban development continues, managing these sources of pollution is crucial to protecting the health of urban streams and the biological communities they support.
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Dams, culverts, and other structures altering water flow and health
Urban streams are often teeming with life, weaving through cities and towns. However, the environmental changes associated with urban development are evident in these water bodies. One significant issue is the impact of dams, culverts, and other structures that alter water flow and, consequently, the health of aquatic ecosystems.
Dams are constructed for various reasons, including irrigation, water storage, flood control, and hydroelectric power generation. While they offer significant benefits, their environmental costs are often overlooked. One of the most significant ways dams impact river health is by disrupting the natural flow of water. Rivers have seasonal flow patterns that are critical for maintaining ecosystems. For instance, many aquatic species rely on seasonal flooding for spawning or accessing habitats. By controlling the volume and timing of water release, dams can permanently alter habitats and ecosystems downstream.
Another critical issue with dam construction is sediment trapping. Rivers naturally carry sediment downstream, essential for maintaining riverbeds, deltas, and coastal areas. Sediment replenishes shorelines, creates fertile deltas, and provides essential nutrients to aquatic ecosystems. When a dam is built, it traps sediment in the reservoir, preventing it from reaching downstream areas. This sediment trapping leads to receding deltas, loss of wetlands, and increased vulnerability to storms and sea-level rise.
In addition to dams, culverts can also hinder or block the migration of aquatic species. Poorly designed or undersized culverts can impede the movement of fish and other wildlife, impacting their reproductive cycles and contributing to population declines. This disruption of migratory patterns has severe economic implications, affecting commercial and recreational fishing industries that generate significant revenue.
The removal of obsolete dams and the restoration of natural river flows are gaining momentum in some regions. Projects aimed at reconnecting rivers and restoring natural meanders are being undertaken to improve stream health and mitigate the environmental and social impacts of these structures. Alternatives to traditional dam construction, such as "run-of-the-river" hydroelectric projects, can also help reduce the disruption of natural flows while still generating power.
In conclusion, dams, culverts, and other structures that alter water flow have significant impacts on the health of urban streams and the ecosystems they support. By disrupting natural flow patterns, blocking fish migration, and trapping sediment, these structures can lead to ecological, social, and economic consequences. Balancing the benefits of these structures with their environmental costs is crucial for sustainable water management and the preservation of aquatic ecosystems.
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The role of urban streams in the wider water network
Urban streams are an integral part of the wider water network, providing freshwater habitats for aquatic life and acting as a source of water for various purposes. However, they are also susceptible to pollution and the impacts of urban development, which can have far-reaching consequences downstream and beyond.
Urban streams are often fed by creeks and tributaries that wind their way through cities and towns. These water bodies are largely unseen by the majority of the population, who are unaware of the rich biodiversity that exists within them. However, the environmental changes associated with urban development are often most evident in these streams. Contaminants, habitat destruction, and altered streamflow resulting from urbanization can disrupt aquatic ecosystems, particularly sensitive species.
One of the significant sources of pollution in urban streams is nonpoint source pollution, where stormwater runoff carries contaminants such as chemicals, nutrients, and sediments from paved surfaces, roofs, and industrial sites. As this polluted water flows downstream, it can infiltrate groundwater and concentrate in rivers and streams, ultimately making its way to the ocean. Here, it contributes to the formation of dead zones with minimal oxygen and threatens coral reef ecosystems.
Another issue is the presence of polycyclic aromatic hydrocarbons (PAHs) in urban streams. PAHs are common pollutants resulting from transportation-related sources such as oil leakage, vehicle exhaust, tire and brake wear, and pavement erosion. Coal-tar-based pavement sealants, often used in parking lots and driveways, are a significant source of PAHs, which have been shown to adversely affect aquatic life.
The health of urban streams is also impacted by excess nutrients, such as nitrogen, entering the water through agricultural and urban runoff, vehicle emissions, and fertilizer use. These nutrients can fuel the growth of harmful algae blooms, blocking sunlight from reaching underwater vegetation and leading to oxygen depletion. Additionally, the installation of dams, culverts, and other structures can alter streamflow, affect fish migration, and accelerate sediment accumulation.
The pollution and degradation of urban streams have far-reaching consequences. As these streams are connected to larger water bodies, including rivers, reservoirs, and coastal waters, the chemical contaminants and sediments introduced can degrade water quality downstream. This not only harms aquatic ecosystems and biodiversity but also impacts economically valuable resources such as fisheries and tourism. Therefore, understanding and managing urban-related stressors are crucial to protecting the health of urban streams and their role in the wider water network.
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Frequently asked questions
Water pollution occurs when harmful substances, often chemicals or microorganisms, contaminate a body of water, degrading water quality and rendering it toxic to humans or the environment.
Water pollution can be classified as point source pollution or nonpoint source pollution. Direct contamination of waterways, such as industrial waste pouring from a factory drain into a river, is an example of point source pollution. Nonpoint source pollution refers to contaminants that are carried by stormwater runoff, such as rainwater and snowmelt, which then infiltrate groundwater and concentrate in streams and rivers.
Common pollutants found in urban streams include polycyclic aromatic hydrocarbons (PAHs), which come from transportation-related sources like oil leakage, vehicle exhaust, tire and brake wear, and pavement erosion. Other pollutants include chemical contaminants, nutrients, sediment, and litter.
Urban development can disrupt biological communities and harm sensitive aquatic species in streams. Contaminants, habitat destruction, and streamflow alterations can degrade water quality downstream, impacting economically valuable resources such as fisheries and tourism.
