Urbanization's Watery Downside: Pollution From City Growth

Urbanisation has a significant impact on water pollution. As cities expand, the volume of wastewater discharged into local water bodies increases, carrying with it pollutants such as nutrients, microplastics, chemicals, and pathogens. This can lead to eutrophication, caused by excess nitrogen and phosphorus, and health issues such as diarrhoea caused by pathogens. Urbanisation also alters land use, removing trees and vegetation, and changing water-drainage patterns, leading to increased erosion, sedimentation, and flooding. Furthermore, the density of urban populations means that water pollution affects a large number of people, with 86% of urban dwellers having access to safely managed drinking water services.

Urbanisation increases the amount of water flowing through streams

Urbanisation has had a profound impact on the environment, and water bodies are no exception. With the global population doubling in less than 50 years, the expansion of metropolitan areas has accelerated, leading to significant ecological changes. One notable consequence is the increase in the amount of water flowing through streams, which has several interrelated causes and implications.

The conversion of forests and natural landscapes into urban areas is a primary driver of this phenomenon. When forests are cleared, the land loses its natural ability to absorb and retain water. The removal of trees and vegetation reduces the transpiration and infiltration of water into the soil, resulting in higher surface runoff. This effect is exacerbated by the proliferation of impervious surfaces, such as roads, pavements, and parking lots, that are characteristic of urban environments. These impervious surfaces prevent water from permeating the ground, causing it to flow more rapidly into streams, increasing the overall volume of water.

The impact of impervious surfaces on water flow is significant. Research suggests that when approximately 40% of a watershed is impervious, the amount of runoff can double. This rapid increase in water flow can lead to flooding and changes in water-drainage patterns, further exacerbating the issue. Additionally, the loss of vegetation and the sealing of soils contribute to a reduction in coarse sediment supply, leading to an increase in finer sediment being washed into streams. This increase in sediment load can have detrimental effects on water quality and stream ecology.

Furthermore, urbanisation alters the discharge patterns of streams. The timing and amount of water flow change due to the increased efficiency of stormwater drainage infrastructure. Urban areas often implement improved storm drainage systems to mitigate flooding risks. While these systems effectively reduce localised flooding, they also contribute to the increased volume and speed of water flowing through streams. The complex interplay between natural hydrological processes and urban infrastructure continues to be an area of ongoing research.

The consequences of these changes in water flow extend beyond the streams themselves. Aquatic animals, including fish, amphibians, reptiles, and invertebrates, are affected by increased stream flow, changes in stream bed substrate, and pollution. The combination of higher water volume and increased sediment, nutrient, and contaminant loads can disrupt the delicate balance of aquatic ecosystems, leading to a decline in the abundance, diversity, and health of these organisms. As urbanisation continues to expand, protecting water resources and mitigating its impacts on natural water systems become increasingly crucial.

Urban areas produce more pollutants

Urbanization and population growth have a significant impact on water pollution, with urban areas becoming a common source of multiple pollutants. The high concentration of people and economic activities in cities contribute to the increased generation of waste and pollutants. This includes residential and commercial waste, as well as industrial and mobile sources such as cars and trucks. As a result, urban waters are inundated with a diverse range of contaminants, including pharmaceuticals, pesticides, heavy metals, pathogenic microbial populations, and organic pollutants.

The process of urbanization itself alters the natural landscape, leading to increased pollution. The removal of trees and vegetation during construction reduces the land's ability to absorb and filter water naturally. This leads to higher levels of storm runoff, carrying pollutants such as sediments and nutrients into nearby water bodies. Impervious surfaces like pavement and roads further contribute to this issue, causing water to flow more rapidly into streams and increasing the amount of runoff.

Wastewater management is another critical aspect of the impact of urbanization on water pollution. As urban populations grow, the demand for water increases, and proper wastewater treatment becomes essential. Ineffective or insufficient wastewater treatment can lead to the discharge of untreated or partially treated wastewater into local water bodies, contaminating them with pathogens, chemicals, and other pollutants.

Additionally, urbanization often involves the construction of roads, highways, and bridges, which can contribute to water pollution. The use of toxic chemicals and the generation of nutrient and chemical runoff during construction can contaminate surface water if not properly controlled. Furthermore, the operation and maintenance of these infrastructures can also impact water quality, requiring measures to reduce pollutant loadings to receiving waters.

The conversion of watersheds from forests to urban areas can have a significant impact on water quality. The loss of forests reduces the natural filtration and retention capacity of the land, leading to elevated sediment and nutrient concentrations in surface waters. This, coupled with the increased use of fertilizers and pesticides in urban areas, further contributes to the degradation of water quality.

Urban waterways are more susceptible to pollution from runoff

The types of pollutants found in urban runoff include sediments, nutrients, oxygen-demanding substances, road salts, heavy metals, petroleum hydrocarbons, pathogenic bacteria, and viruses. Sediment erosion, a significant issue in construction sites, constitutes the largest mass of pollutant loadings in urban waterways. Fertilizer usage, pet wastes, faulty septic tanks, and automobile emissions are additional sources of nutrient and bacterial contamination.

Furthermore, urban areas generate a higher volume of wastewater, which is often discharged into local streams. The increased population density and various industrial activities contribute to this issue. As a result, the watersheds in urban areas lose their ability to hold and retain water effectively due to the reduction in natural absorption areas and the increased water flow. This can lead to flooding and further erosion, exacerbating the pollution problem.

The vehicular transportation sector and atmospheric deposition are also major contributors to water pollution in urban areas. Automobiles release pollutants such as petroleum hydrocarbons, while atmospheric deposition includes the release of chemicals and pollutants into the atmosphere, which eventually find their way into water bodies through rainfall or snowmelt. As urbanisation continues to expand, the impact of these pollution sources on urban waterways becomes more pronounced, posing a threat to the health and diversity of aquatic life.

Urbanisation affects the local hydrologic system

Secondly, urbanisation contributes to water pollution through various sources of contaminants. Urban surfaces, such as roads and buildings, generate runoff that carry a range of pollutants, including heavy metals, nutrients like sodium and nitrate, litter, and rubber residue. In addition, vehicular emissions release polycyclic aromatic hydrocarbons (PAHs), which, along with microbial contaminants, pharmaceutical concentrations, and pesticides, end up in urban water bodies. The complex mix of pollutants in urban streams poses a significant challenge for urban hydrologists in terms of sampling, analysis, and prediction of pollutant concentrations.

Thirdly, urbanisation impacts stormwater management and drainage systems. The removal of natural vegetation and the implementation of impervious surfaces during urban development affect the natural absorption and filtration of stormwater. This leads to increased surface runoff, overwhelming drainage systems and potentially causing combined sewer overflows, where untreated sewage and stormwater are discharged into water bodies, further degrading water quality.

Lastly, urbanisation affects groundwater recharge and aquifer levels. The construction of buildings and infrastructure can interfere with groundwater recharge processes, altering the natural replenishment of underground water sources. Additionally, the extraction of groundwater for urban water supply can impact aquifer levels, potentially leading to land subsidence and further compromising the local hydrologic system.

The effects of urbanisation on the local hydrologic system are complex and interconnected. While urban development brings about convenience and economic growth, it is essential to implement sustainable urban planning and water management practices to mitigate the negative impacts on the local hydrologic system and ensure the health and well-being of urban residents and the surrounding natural environment.

Urban waters contain pharmaceuticals, pesticides, heavy metals, and pathogenic microbial populations

Urbanisation has been linked to the degradation of urban waterways. Urban waters contain a range of pollutants, including pharmaceuticals, pesticides, heavy metals, and pathogenic microbial populations.

Pharmaceuticals

The disposal of medications and personal care products has led to the presence of pharmaceuticals in urban waters. This includes antibiotics, analgesics, narcotics, and psychotherapeutics. The overuse of antibiotics has resulted in the emergence of antibiotic-resistant microbial populations, which poses a significant threat to public health.

Pesticides

The use of pesticides in agriculture and residential areas has led to their presence in urban waters. Pesticides can be toxic to aquatic life and contribute to the degradation of water quality.

Heavy Metals

Heavy metals, such as cadmium, mercury, lead, chromium, and zinc, enter aquatic ecosystems through direct discharges or indirect routes like atmospheric deposition and surface runoff. These metals can be toxic to aquatic life and accumulate in the food chain, posing risks to human health.

Pathogenic Microbial Populations

Pathogenic bacteria, viruses, and microorganisms can contaminate urban waters through sewage, septic tanks, and runoff. These pathogens can cause a range of infectious diseases, including dysentery, diarrhea, and jaundice, contributing to a significant number of deaths worldwide.

The presence of these pollutants in urban waters is a cause for concern and requires proper management and treatment practices to ensure the protection of aquatic ecosystems and public health.

Frequently asked questions