Meghan Hodges
Watersheds are vital to our communities, providing drinking water, recreational opportunities, and aesthetic beauty. However, pollutants can contaminate watersheds and have detrimental effects on aquatic ecosystems and human health. Pollution in watersheds can come from various sources, such as industrial waste, agricultural runoff, erosion, and improper disposal of household chemicals. These pollutants can flow through the watershed, contaminating water supplies and disrupting aquatic habitats. Understanding how pollutants move through a watershed is crucial for effective watershed protection and preserving the health of aquatic ecosystems and the communities that depend on them.
| Characteristics | Values |
|---|---|
| Pollutants | Oil, pesticides, dirt, bacteria, fertilizer, insecticides, microorganisms, fossil fuels, heavy metals, nutrients, sediments, mercury, lead, and sewage |
| Sources of Pollutants | Roads, parking lots, rooftops, driveways, industrial sites, agricultural fields, lawns, and improper waste disposal |
| Effects of Pollutants | Degraded wildlife habitats, contaminated water sources, flooding, destruction of habitats for fish and other water-dependent species, sewage overflows, algal blooms, and harm to aquatic life |
| Prevention and Mitigation | Reducing runoff, soaking up rainwater, using green infrastructure, preserving natural features, minimizing impervious surfaces, and proper watershed management |
| Watershed Management Challenges | Accommodating competing needs, such as balancing grazing and stream bank shade for trout habitats, and addressing rising populations, changing climate, and development pressures |
| Watershed Management Success Stories | Cleanup of the Connecticut River, Chesapeake Bay Program, and specific goals set by multiple states to reduce pollution, restore habitats, and protect watershed land |
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What You'll Learn
Urbanization and the replacement of vegetation
Urbanization has a detrimental effect on watersheds, leading to decreased vegetation and an increase in impervious surfaces. This transformation of the landscape has a significant impact on the flow of pollutants through a watershed.
The replacement of vegetation with impervious surfaces, such as paved roads, parking lots, and buildings, reduces the ability of the soil to absorb and retain water. This leads to increased surface runoff, where water flows over the land instead of being absorbed, picking up pollutants along the way. The increased volume and velocity of runoff can cause erosion, turbidity, and habitat degradation, further contributing to the pollution of the watershed.
Research has shown that urban channels tend to widen due to increased peak flows and reduced sediment inputs. This widening is influenced by the presence or absence of riparian vegetation, which can affect floodplain accretion processes. The loss of vegetation also reduces the capacity of the watershed to retain nutrients, leading to increased nutrient delivery through stormwater conveyance systems and wastewater treatment plant effluents.
The effects of urbanization on watersheds can be mitigated through urban planning that incorporates green infrastructure. Retaining and restoring native vegetation, protecting wetlands, and incorporating urban tree cover can help reduce the impact of urbanization on watershed health. For example, trees in urban catchments can intercept a significant portion of precipitation during storm events, reducing the amount of runoff and the associated pollutant load.
Overall, the replacement of vegetation with impervious surfaces due to urbanization has significant effects on the flow of pollutants through a watershed. The reduced ability of the soil to absorb and retain water, coupled with the loss of vegetation's filtering capacity, leads to increased surface runoff and nutrient delivery, contributing to the pollution of the watershed. Mitigation strategies through urban planning and the incorporation of green infrastructure can help reduce these impacts and protect the health of watersheds.
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Impervious surfaces and increased runoff
Impervious surfaces are hard, non-porous surfaces that cover the soil and do not allow water to pass through them. These include roads, streets, sidewalks, driveways, parking lots, roofs, sports courts, and some types of artificial turf. As communities develop and urbanize, natural landscapes are replaced by these impervious surfaces, reducing the area where water can infiltrate the groundwater. This leads to increased stormwater runoff, which must be collected by drainage systems and carried to streams.
The increase in impervious surfaces alters the pathways by which water and associated contaminants reach urban streams. The velocity and volume of runoff increase, causing erosion, turbidity, and degraded wildlife habitats. This runoff picks up pollutants such as oil, bacteria, nutrients, sediment, and metals, carrying them into surface waters. The pollutants enter waterways through storm drains and other surface entry points, leading to nonpoint source pollution, which is a significant contributor to water quality impairment.
The effects of impervious surfaces on stream ecosystems are evident in physical, chemical, and biological parameters. As the amount of impervious cover increases, stream conditions decline, leading to more frequent and severe flooding. The transfer of heat from impervious surfaces to stormwater also increases stream temperatures, impacting aquatic organisms. Additionally, water that ponds on impervious surfaces can increase vector-borne diseases, such as the West Nile Virus, by providing breeding grounds for mosquitoes and other insects.
Minimizing impervious surfaces and promoting infiltration practices are watershed-friendly approaches to improving water quality and flood resilience. By reducing the coverage of impervious materials, communities can help mitigate the negative impacts on watershed health, including increased runoff, pollution, and flooding. Preserving vegetation and natural landscapes plays a crucial role in maintaining the health of watersheds and ensuring the proper filtration and release of water.
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Pollutants in stormwater runoff
Stormwater runoff is one of the leading causes of water pollution. As rainwater flows across the land, it can pick up harmful materials and pollutants, which are then carried into local waterways. This can cause physical damage to creeks, rivers, and lakes, as well as contaminating the water.
One of the main sources of stormwater pollution is sediment, which is often the result of soil erosion. When stormwater washes bare soil into streams, it can smother stream habitats, alter stream flow, and increase nutrient levels, leading to plant and algae blooms that can be harmful to humans and animals.
Another concern is the presence of harmful bacteria, protozoa, and viruses in stormwater. These pathogens can cause gastrointestinal illnesses and are often the reason for swim advisories at public beaches. They can come from improperly disposed pet waste, livestock manure, and failing home septic systems.
Everyday compounds can also contribute to stormwater pollution when they are overused or used improperly. Pesticides, excess winter salt, and leaks of gas, oil, and antifreeze from vehicles are all common sources of toxic compounds in stormwater.
To reduce stormwater pollution, it is important to properly dispose of waste, including pet waste and yard clippings, and to use organic fertilizers and biodegradable soaps. Preventing oil spills and leaks from vehicles and properly maintaining irrigation systems can also help to minimize the impact on local waterways.
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Nonpoint source pollution
Nonpoint source (NPS) pollution is a significant environmental issue that affects watersheds. Unlike pollution from industrial or wastewater treatment plants, which have single sources, NPS pollution arises from various diffuse sources. It is caused by rainfall or snowmelt, which picks up and carries natural and human-made pollutants as it moves over and through the ground. These pollutants are then deposited into lakes, rivers, wetlands, coastal waters, and groundwater.
NPS pollution is a pressing issue for watersheds as it can originate from a range of locations, including farm fields, construction sites, and streambanks. The pollutants carried by stormwater and other runoff include heavy metals, organic compounds, oils, bacteria, nutrients, and sediments. These pollutants can have detrimental effects on aquatic life and the health of the watershed. For example, sediments can cloud the water, impairing the vision and feeding abilities of aquatic organisms, damaging fish gills, and reducing sunlight penetration, which is necessary for plant growth.
Moreover, NPS pollution can infiltrate the groundwater basin, contaminating the water supply for those living and working near the affected waterways. This contamination can render the water unsuitable for drinking, swimming, or fishing, posing health risks to the surrounding communities. The impact of NPS pollution on recreational activities and wildlife further underscores the importance of addressing this issue.
The prevention of NPS pollution is crucial to minimizing its impact on watersheds. Unlike point-source pollution, NPS pollution does not have treatment plants to manage it in creeks, streams, and bays. Therefore, implementing measures to reduce the runoff of pollutants into water bodies is essential. This includes managing stormwater effectively and adopting environmentally sound practices in agriculture, construction, and other industries that contribute to NPS pollution.
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Sewage overflows
Combined sewer systems, which collect and convey both sewage and stormwater in one pipe, have been in existence for over a century. They were designed to dry out streets by collecting rainwater runoff, domestic sewage, and industrial wastewater. While these systems were once adequate most of the time, higher-intensity storms caused by climate change can now overload the pipes, resulting in combined sewer overflows (CSOs). CSOs discharge untreated sewage and stormwater into nearby water bodies, including lakes, rivers, and coastal waters. This can have negative impacts on public health and the environment, as the overflow contains bacteria and chemicals that can increase the risk of getting sick from swallowing water or eating fish in the affected areas.
During rainfall events, the carrying capacity of the pipes in combined sewer systems can be exceeded, leading to overflows. These overflows occur when there is too much stormwater mixed with raw sewage, resulting in the discharge of untreated waste into water bodies. CSOs were designed to protect cities from backups of raw sewage into homes and to reduce the potential for street flooding. They also help safeguard the pipes and treatment systems from damage due to overloading.
While most modern communities have separate collection systems for sewage and stormwater, some older urbanized areas, such as Connecticut, still have combined sewer systems. Six municipalities in Connecticut continue to have CSOs, and they are required to post permanent signs near all CSO outfalls to warn people of the potential risks. Swimmers are advised to follow local health guidelines and avoid swimming or fishing in water that may be impacted by sewer pipe overflows.
To address the issue of CSOs, the U.S. Environmental Protection Agency (EPA) issued the CSO Control Policy in 1994. This policy mandated that communities reduce or eliminate their CSOs and work towards improving their sewage systems to meet Clean Water Act goals. Some communities have increased sewer rates to raise funds for infrastructure upgrades, but many localities struggle to finance large-scale treatment facilities without federal and state aid.
In conclusion, sewage overflows, such as CSOs, are a significant concern for water pollution and public health. They occur when combined sewer systems are overwhelmed during heavy rainfall or when there is insufficient capacity to handle the volume of sewage and stormwater. While efforts are being made to reduce and control CSOs, it is a challenging and costly process that requires investment in infrastructure upgrades and the implementation of alternative treatment approaches.
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Frequently asked questions
A watershed is an area of land that drains into a body of water, such as a river, lake, or ocean. Watersheds come in a variety of sizes and shapes and can span for miles.
Pollutants enter a watershed through runoff, which is when rainwater or snowmelt picks up pollutants as it flows over the ground and into nearby water bodies. This can include pollutants such as oil, bacteria, nutrients, sediment, and metals.
Pollutants in a watershed can have negative effects on the health of the ecosystem and nearby communities. They can contaminate drinking water supplies, making them unsafe for consumption, and can also harm wildlife and plant habitats. Additionally, pollutants can cause algal blooms, which can suffocate fisheries and create an imbalance in the ecosystem.
