Urban Sprawl's Impact On Water Pollution: A Complex Issue

Urban sprawl has been linked to water pollution, with researchers suggesting that policies aiming to reduce sprawl may be inadvertently increasing water pollution. This phenomenon is attributed to the higher density of impervious surfaces, such as concrete, in urban areas, which can cause water runoff, carrying pollutants like nitrogen, phosphorus, and sediment into bodies of water. Additionally, the combination of sprawl and simultaneous agricultural development can contribute to increased water pollution. The impact of urban sprawl on water quality is also influenced by population density and land-use changes, with suburban and rural areas experiencing higher increases in specific conductance concentration over time compared to central cities.

Increased runoff from impervious surfaces like concrete

Urban sprawl, or the expansion of urban areas onto rural land, has a significant impact on water pollution. One of the primary ways in which this occurs is through increased runoff from impervious surfaces like concrete.

When land is developed, natural landscapes that absorb water, such as fields and meadows, are replaced with impervious surfaces like roads, parking lots, and buildings. These surfaces do not absorb water but instead cause runoff. As a result, water flows across these surfaces and into nearby bodies of water, carrying with it various pollutants.

Concrete surfaces, in particular, have been identified as a major contributor to water pollution in the context of urban sprawl. The higher the density of development, the more concrete and other impervious surfaces are present. This leads to increased runoff and, consequently, higher levels of water pollution.

The impact of concrete on water pollution is twofold. Firstly, the concrete itself can be a source of pollution, as it often contains chemicals and contaminants that can leach into the water supply. Secondly, and more commonly, concrete surfaces facilitate the flow of water into nearby water bodies, carrying with it various pollutants picked up along the way.

This runoff water can pick up a variety of pollutants, including sediment, nitrogen, and phosphorus. These pollutants can cause environmental problems in streams, rivers, and bays. For example, nitrogen and phosphorus can cause excessive algae growth, leading to oxygen depletion and the death of fish and other aquatic organisms. Sediment, on the other hand, can smother aquatic habitats and reduce water quality.

Higher water pollution from agriculture than low-density residential areas

Agriculture is a major contributor to water pollution, accounting for 70% of water withdrawals worldwide. Farms discharge large quantities of agrochemicals, organic matter, drug residues, sediments, and saline drainage into water bodies. The intensive use of pesticides and chemical fertilizers in crop production has led to an increase in water pollution. The growth in livestock production, aquaculture, and the use of antibiotics and other veterinary medicines further contribute to the degradation of water quality.

In contrast, low-density residential areas, such as suburban and rural areas, have a relatively lower impact on water pollution. However, it is important to note that the impact of urban sprawl on water quality is not limited to a single source. The combination of high-density development and agricultural activities in suburban and rural areas can lead to increased water pollution.

Douglas Wrenn, a researcher from Penn State University, found that anti-sprawl policies may be counterproductive and lead to increased water pollution. Higher-density development results in more impervious surfaces, such as concrete, which cause runoff. This runoff carries pollutants such as sediment, nitrogen, and phosphorus into nearby water bodies. By restricting development outside of urban growth boundaries, the opportunity to reduce pollution from agricultural areas is lost.

Agriculture contributes to water pollution through various means. Farms discharge agrochemicals, such as pesticides and fertilizers, into water bodies, leading to contamination. The use of pesticides has seen double-digit growth in countries like Argentina, Malaysia, South Africa, and Pakistan. The expansion of irrigation practices has also played a role, as the area equipped for irrigation has more than doubled from 1961 to 2012, increasing the transfer of agricultural pollution to water bodies.

Additionally, livestock production accounts for a significant portion of agricultural land use, with the total number of livestock rising from 7.3 billion units in 1970 to 24.2 billion units in 2011. Livestock manure contains bacteria and nutrients that can contaminate water sources, impacting both aquatic ecosystems and drinking water supplies. The use of antibiotics and other veterinary medicines in livestock farming further contributes to water pollution, as these substances can enter groundwater and surface water, posing risks to human health.

In conclusion, while low-density residential areas have a relatively lower impact on water pollution, agriculture is a significant contributor to water pollution globally. The intensive farming practices, expansion of irrigation, and livestock production all play a role in degrading water quality. By addressing agricultural practices and implementing effective policies, there is a potential to reduce water pollution and mitigate its impacts on the environment and human health.

More nitrogen, phosphorus, and sediment in streams, rivers, and bays

Urban sprawl can cause more nitrogen, phosphorus, and sediment in streams, rivers, and bays due to the increased number of impervious surfaces, such as concrete. Unlike natural surfaces, these human-made surfaces do not absorb water but cause runoff. As a result, water flows directly into bodies of water, carrying with it pollutants like sediment, nitrogen, and phosphorus.

Concrete and other impervious surfaces contribute to increased levels of dissolved solids in water bodies. This leads to higher conductivity or ionic strength, which has been identified as one of the most consistent indicators of water quality changes associated with urbanization. In addition, the increased use of concrete and other construction materials can lead to concrete weathering, which further increases dissolved solids in water.

Another factor contributing to the issue is the use of fertilizers on lawns and golf courses. Fertilizers often contain nitrogen, which can be washed into nearby water bodies during rainfall or irrigation, leading to increased nitrogen levels in urban streams. Atmospheric deposition from fossil fuel combustion also contributes to elevated nitrogen concentrations.

Furthermore, the development of agricultural land can result in nitrogen-rich runoff, as well as increased sediment and phosphorus levels in water bodies. This is because agricultural activities often involve the use of fertilizers and pesticides, which can be washed into nearby streams, rivers, or bays during rainfall or irrigation.

The combination of these factors leads to higher concentrations of nitrogen, phosphorus, and sediment in water bodies affected by urban sprawl. This can have numerous environmental impacts, including increased toxicity and negative effects on aquatic organisms and ecosystems.

Population and land-use changes

The impact of urban sprawl on water quality is closely tied to population and land-use changes. As urban areas expand outward from city centres, they encroach on agricultural lands and natural habitats, leading to habitat fragmentation and the loss of environmentally sensitive areas. This expansion also results in an increase in impervious surfaces such as concrete, which do not absorb water but instead cause runoff, carrying pollutants such as sediment, nitrogen, and phosphorus into nearby water bodies.

The combination of high population density and a high percentage of developed land use within urbanized watersheds tends to result in higher concentrations of water pollutants. This is further exacerbated by the leapfrogging patterns of development characteristic of urban sprawl, where development favours more distant parcels of land over adjacent vacant lots, leading to a haphazard and disconnected urban form. This type of development consumes large amounts of land, reducing open spaces and natural habitats.

The impact of urban sprawl on water quality is not uniform across all areas. Suburban and rural areas tend to experience greater increases in water pollution over time compared to central cities. This is due to the more dispersed nature of development in these areas, which can result in higher levels of pollution from sources such as agriculture and stormwater runoff.

The automobile dependency that often accompanies urban sprawl also contributes to water pollution. The reliance on cars is due in part to the large distances between dwellings and the segregation of different land uses. This has resulted in a decrease in alternative forms of transportation such as walking and biking. Additionally, the development of roads and parking lots contributes to the increase in impervious surfaces, further exacerbating stormwater runoff and the pollution of water bodies.

To mitigate the negative impacts of urban sprawl on water quality, local planning policies and techniques can be implemented to guide growth towards more sustainable patterns. This includes concentrating development within defined areas, protecting and restoring natural resources, and promoting mixed-use neighbourhoods that are less dependent on automobiles. By understanding the complex relationship between population and land-use changes, policymakers and planners can work towards creating more sustainable and resilient urban environments.

Automobile dependency

Environmental Impact

Firstly, the increase in paved surfaces due to urban sprawl contributes to water pollution. Paved surfaces, such as roads and parking lots, are impervious, meaning they do not absorb water. As a result, stormwater runoff is increased, carrying pollutants such as oil, grease, and chemicals directly into nearby water bodies without treatment. This runoff can also pick up sediment, nitrogen, and phosphorus, which, in high quantities, can cause environmental problems in streams, rivers, and bays.

Secondly, urban sprawl often results in longer commutes and an increase in vehicle miles travelled. This leads to higher emissions of pollutants, including nitrogen oxides, particulate matter, and volatile organic compounds, which contribute to water pollution through acid rain and the deposition of toxic chemicals. Additionally, as vehicles are a significant source of greenhouse gas emissions, urban sprawl-induced automobile dependency contributes to climate change, which further exacerbates water pollution through altered precipitation patterns and increased flooding.

Social and Economic Impact

From an economic perspective, automobile dependency is costly for individuals, businesses, and local governments. The direct costs of owning and maintaining a vehicle can be substantial, impacting family budgets. Businesses may also face higher expenses due to the need for extensive parking lots and landscaping to maintain an appealing appearance. Local governments bear the burden of maintaining expansive road networks and infrastructure, often requiring tax increases or service cuts to cover the costs.

In conclusion, automobile dependency caused by urban sprawl has far-reaching consequences. It contributes to water pollution through increased stormwater runoff and vehicle emissions, while also impacting the social fabric and economic well-being of communities. Addressing these issues requires a shift towards more walkable, bikeable, and transit-friendly neighbourhoods, reducing our reliance on automobiles and mitigating the negative effects of urban sprawl on water pollution.

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