Stormwater Runoff: Pollutants And Their Impact On The Environment

Stormwater runoff is one of the greatest threats to clean water in the US, with the potential to cause serious damage to streams, lakes, and estuaries. As stormwater passes over developed land, it picks up a variety of pollutants, including fertilizers, oil, pesticides, dirt, bacteria, and microplastics, which are then carried into local waterways. These pollutants can have harmful effects on water quality and aquatic life, causing physical damage such as flooding and streambank erosion, as well as water pollution.

Fertiliser, oil, pesticides, dirt, bacteria and other pollutants

Stormwater runoff is a significant contributor to water pollution, as it often contains harmful materials picked up from the land. This is particularly true in urban environments, where impervious surfaces such as roads, sidewalks, and parking lots can accumulate various pollutants. When it rains, stormwater washes across these surfaces, collecting contaminants and transporting them into nearby waterways, leading to detrimental effects on the environment and human health.

One of the key pollutants in stormwater runoff is fertiliser. Excess fertiliser on lawns, gardens, and agricultural fields can be washed into storm drains during heavy rains or flooding. This fertiliser ends up in rivers, lakes, bays, and other local waterways, leading to excessive growth of algae and other aquatic plants. The resulting algal blooms can be toxic, harming aquatic life and even posing risks to humans and their pets. For example, nitrates, a common ingredient in fertilisers, can cause methemoglobinemia, or "blue-baby syndrome," in infants.

Oil is another pollutant commonly found in stormwater runoff. Motor oil, grease, automotive antifreeze, and other toxic chemicals from vehicles can contaminate stormwater. These substances can have devastating effects on aquatic organisms, impairing their health, growth, and reproductive abilities. Oil can also mix with road salt, creating a toxic combination for aquatic life. Additionally, oil can pick up and transport heavy metals, further increasing the toxicity of the runoff.

Pesticides are also a significant concern in stormwater runoff. When used on lawns, gardens, or agricultural lands, pesticides can be washed into nearby water bodies by stormwater runoff. Pesticides include insecticides, herbicides, and fungicides, which can contaminate drinking water, harm aquatic plants and animals, and restrict recreational activities such as swimming and fishing. Pesticides can also be toxic to birds and other wildlife, disrupting the natural balance of the ecosystem.

Dirt and sediment are often mobilised by stormwater runoff, particularly when soil is left bare and exposed. Construction sites, freeways, industrial sites, and residential areas can contribute significant amounts of sediment to stormwater. This sediment can smother stream habitats, alter stream flow, and increase nutrient levels to harmful degrees. Sediment deposition can destroy fish spawning areas and aquatic habitats, leading to physical damage and loss of fish habitat.

Lastly, stormwater runoff can carry harmful bacteria, viruses, and other pathogens. These microorganisms can originate from pet waste, bird droppings, wildlife, sanitary sewer overflows, and failing septic systems. High bacteria counts can make waterways unsafe for swimming and other recreational activities, potentially endangering human health.

Nitrogen and phosphorus

Phosphorus, in particular, is a concern in urban stormwater runoff, where it can lead to the eutrophication of water bodies. Sources of phosphorus include pet waste, livestock manure, and failing home septic systems, as well as fertilizer. Pretreatment is generally ineffective for treating dissolved phosphorus, although some practices can be modified to enhance phosphorus removal. Infiltration practices are among the most effective treatment methods for removing dissolved phosphorus.

Nitrogen is also a concern in urban stormwater, and understanding its role in runoff is essential for effective stormwater management. Sources of nitrogen include organic fertilizers such as compost and mulch, as well as pet waste and yard waste.

To reduce the impact of nitrogen and phosphorus in stormwater, it is important to apply fertilizers at the right time of year and in the right amounts, avoiding high-risk spots like waterways, sinkholes, and wells. Properly disposing of pet waste and yard clippings, as well as managing manure and septic systems, can also help reduce the presence of these pollutants in stormwater.

Sediment and debris

The presence of sediment in water bodies can have several detrimental effects. It can smother stream habitats, alter stream flow, and increase nutrient levels to harmful concentrations. Sediment deposition can also fill in lagoons, streams, lake beds, or wetlands, destroying fish spawning areas and other aquatic habitats. Additionally, sediments act as carriers for heavy metals, bacteria, and other pollutants, further exacerbating the problem.

Debris in stormwater runoff can include a variety of materials, such as yard clippings, leaves, grass clippings, litter, and pet waste. These organic materials can use up oxygen as they decay, creating an oxygen-depleted environment that harms aquatic life. Debris can also cause blockages in storm drains and ditches, leading to flooding and other issues.

To mitigate the impact of sediment and debris in stormwater runoff, several measures can be implemented. Properly disposing of yard waste and using organic fertilizers, such as compost and mulch, can help reduce the amount of debris entering stormwater systems. Covering bare soil with garden mulches or crop residues can prevent soil erosion and sedimentation. Additionally, implementing erosion control measures, such as sediment traps, filters, and vegetative ground cover, can effectively capture and remove sediments from stormwater before it is discharged into natural water bodies.

It is important to note that the specific strategies for managing sediment and debris in stormwater runoff may vary depending on the location and the type of land use. Different sites, such as parklands, residential areas, and commercial sites, will require tailored sedimentation and erosion control measures. Regular maintenance and cleaning of filtration systems are also crucial to ensure their effectiveness in capturing and removing sediments and debris from stormwater runoff.

Microplastics

Stormwater runoff is a significant source of microplastic pollution in aquatic environments. Urbanization plays a crucial role in the abundance of microplastics in waterways, with higher quantities found near urban centres. The concentration of microplastics in stormwater can vary widely, from 1.1 to 24.6 particles per litre, and even up to 6,000 particles per litre in certain cases. Fibres and black rubbery fragments, possibly from tyres and road wear, are the most common forms of microplastics found in stormwater. These microplastics can be transported over significant distances, affecting even remote aquatic ecosystems.

The impact of stormwater runoff on the introduction of microplastics into aquatic habitats is significant. Studies have shown that all stormwater runoff contains anthropogenic microparticles, including microplastics. This is particularly prominent in urban areas, where stormwater washes microplastics from impervious surfaces into storm drains and, ultimately, into local waterways. The high variability in microplastic concentrations in stormwater runoff makes it challenging to fully understand the extent of the problem.

The presence of microplastics in aquatic ecosystems has severe ecological implications. These tiny plastic particles can be ingested by aquatic organisms, leading to potential health risks and ecological disruptions. The fibres found in stormwater, for instance, can be mistaken for food by fish and other aquatic creatures, causing blockages in their digestive systems. Microplastics can also absorb and release toxic chemicals, posing additional threats to the health of aquatic life and potentially entering the food chain.

Mitigating the impact of microplastics in stormwater requires a range of strategies. These include the use of permeable pavements, which can reduce the volume of stormwater runoff and provide habitats for insects and pollinators. Implementing green infrastructure, such as rain gardens, can also help capture microplastics and prevent them from reaching aquatic ecosystems. Additionally, proper waste management practices, such as collecting yard clippings and disposing of them in covered trash cans, can prevent the release of microplastics into stormwater.

Per-and Polyfluoroalkyl Substances (PFAS)

Stormwater runoff is one of the greatest threats to clean water in the US. As stormwater washes across the land, it picks up harmful materials, including trash, dirt, bacteria, and other pollutants, which can cause physical damage and water pollution to local creeks, rivers, and lakes.

Per- and Polyfluoroalkyl Substances (PFAS) are a group of nearly 15,000 synthetic chemicals that have been used in various consumer products since the 1950s. PFAS are used in everyday products, such as food packaging, cookware, textiles, and firefighting foam, due to their ability to repel water and oil. PFAS molecules are highly stable, with a strong carbon-fluorine bond that prevents them from breaking down easily in the environment. This stability leads to the persistence of PFAS in the environment and contributes to their widespread occurrence.

PFAS exposure can occur through multiple routes, including contaminated water, food, consumer products, and air. Over time, PFAS can accumulate in the body, leading to potential health risks. Studies have found PFAS in the blood and urine of people worldwide, raising concerns about their impact on human health. PFAS have been detected in drinking water, food, and human serum, even in countries with strict environmental regulations, indicating their pervasive presence.

The health effects of PFAS exposure are a growing concern. While the full extent of their toxicity is not yet fully understood, scientific studies have linked PFAS exposure to adverse effects on human health and the environment. The long-term persistence of PFAS in the body and the environment, coupled with their widespread use and distribution, poses a significant challenge in mitigating their impact.

Regulatory measures are being considered in various countries, including the US, to address the concerns associated with PFAS. Several countries, such as Canada, the UK, Sweden, Norway, Germany, and Australia, have already provided administrative guidelines for PFAS in water to protect public health and the environment. However, the complex nature of PFAS compounds and their varying regulatory values across the globe present challenges in developing consistent and effective regulations.

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