Stream Pollution: Where Does It Hurt The Most?

Streams are affected by pollution from a variety of sources, including agricultural runoff, urban areas, and industrial effluents. These pollutants can be physical, chemical, or biological in nature, and have detrimental effects on the health of the stream ecosystem. Fine sediments, plastics, pesticides, and metals are some of the major streambed pollutants, with agricultural activities being a significant contributor. The impact of this pollution is far-reaching, as streams flow into larger water bodies, affecting the health of aquatic life and humans who depend on these water sources.

Industrial and agricultural sites

Agricultural operations have a significant impact on water quality due to the extent of farm activities on the landscape, the soil-disturbing nature of those activities, and the associated impacts from sediment, nutrients, pesticides, and herbicides. The National Water Quality Assessment shows that agricultural runoff is the leading cause of water quality impairments in rivers and streams, the third leading source for lakes, and the second-largest source of impairments in wetlands.

Soil erosion, nutrient loss, bacteria from livestock manure, and pesticides are the primary stressors on water quality. These contaminants can enter water bodies through runoff, infiltration, and irrigation return flows. Rainfall and snowmelt transport the majority of these pollutants to surface waters, but other factors such as cattle loafing in stream corridors and stream channel erosion can also degrade water quality.

Concentrated animal feeding operations (CAFOs) are a specific type of animal feeding operation where animals are kept and raised in confined situations for their entire lives. These operations create a significant amount of animal waste, which, if released, can have a devastating impact on the environment. The waste is often spread untreated on land, leading to runoff into water sources. Lagoons are used to store the waste, but they are often prone to overflows, leaks, and spills, causing the contents to leach into the soil and groundwater.

Intensive agriculture practices, such as those found in the Midwestern Corn Belt region of the U.S., can also have a significant impact on water quality and the physical habitat of small streams. The use of pesticides and fertilizers in agriculture has led to changes in water quality and the health of stream ecosystems. Increased levels of nutrients from fertilizers draining into streams can stimulate algal blooms, affecting stream health and recreational uses of local streams, downstream reservoirs, and estuaries.

To mitigate the impacts of agricultural pollution, farmers can adopt soil and water conservation practices to reduce the runoff of sediment, nutrients, bacteria, pesticides, and other pollutants. Buffer strips, conservation tillage, cover crops, and improved irrigation practices can help to reduce nutrient runoff and improve soil health. Establishing protection zones along surface watercourses and buffer zones around farms have also been shown to be effective in reducing pollution migration into water bodies.

Urban areas

Sources of pollutants in urban streams include:

• Oil, grease, and toxic chemicals from motor vehicles
• Pesticides and nutrients from lawns and gardens
• Viruses, bacteria, and nutrients from pet waste and failing septic systems
• Heavy metals from roof shingles, motor vehicles, and other sources
• Thermal pollution from impervious surfaces such as streets and rooftops
• Fertilizers and pesticides
• Animal wastes
• Seepage from septic tanks
• Liquids from sewage lines
• Erosion from construction sites
• Automobile fluids
• Vehicle and industrial emissions

The impact of urban areas on stream ecosystems has been studied in different regions. For example, a study in Poland examined the effects of five towns on river water pollution along the Łyna River. It found that the river water quality deteriorated as it passed through the towns, with an increase in nutrients and indicator bacteria. A similar study in the United States found that urban development significantly affected biological communities in 8 out of 9 metropolitan study areas.

The effects of urbanization on stream ecosystems can be complex and vary depending on the region. Management strategies to protect urban streams may need to be tailored to the specific characteristics of each region.

Natural sources

Streams are affected by pollution from a variety of natural sources. These include:

Natural Runoff

Dirt, topsoil, and silt from fields, construction sites, and other human activities can run off into waterways, harming fish and wildlife habitats. This is a significant contributor to nonpoint source pollution, which is the result of runoff from many small sources, such as septic tanks, cars, trucks, and boats, as well as larger sources like farms and ranches.

Algae

Algae are tiny, one-celled organisms that live in streams and rivers. While algae are a natural part of these ecosystems, human activities such as agricultural runoff can cause excess nutrients (such as nitrogen and phosphorus) to enter the water, leading to algal blooms. These blooms can be toxic to people and wildlife and deplete oxygen levels in the water, creating "dead zones" where no life can survive.

Weather Events

Rainstorms and floods can carry pollutants from land into streams and rivers. For example, when large tracts of land are plowed, the exposed soil can erode during rainstorms, carrying agricultural fertilizers and pesticides into waterways. Similarly, heavy rainfall can cause sewer overflows, resulting in the release of untreated sewage into streams and rivers.

Natural Contaminants in Groundwater

Groundwater can become contaminated with natural contaminants, such as arsenic or fluoride, which can pose risks to public health if consumed.

Sewage systems

In the US, there are 600,000 miles of sewer pipes, with an average age of 33 years. Some pipes in older cities are nearly 200 years old and made of wood. This ageing infrastructure, combined with poorly planned urban development, exacerbates the problem of sewage overflows. As cities expand, more concrete and asphalt increase stormwater runoff into sewers, overwhelming the system and leading to untreated sewage spilling into nearby bodies of water.

Similarly, in the UK, years of underfunding, deregulation, and population growth have pushed the sewage system to a breaking point. In 2020, there were over 400,000 discharges of raw sewage into rivers in England and Wales, and dozens of beaches had to be closed due to high levels of toxic waste in 2022. The privatisation of the sewage system has led to a focus on profits over adequate wastewater treatment, and water companies frequently exceed permitted limits for sewage releases.

The consequences of sewage pollution are dire for both human health and the environment. Sewage contains harmful chemicals, bacteria, and pathogens, including salmonella, hepatitis, cholera, and E. coli. According to the World Health Organization (WHO), 3.4 million people die annually from waterborne diseases. Sewage pollution also threatens biodiversity and ecosystems. When sewage enters waterways, it introduces high levels of nitrogen and phosphorus, leading to eutrophication and algal blooms. These blooms block light for photosynthesis, causing the death of plants and leading to a buildup of bacteria that reduces oxygen levels, killing fish and other aquatic organisms.

To address sewage pollution, governments must prioritise investment in wastewater infrastructure and enforce stricter regulations on water companies. Community-led initiatives, such as the Riverfly Partnership in the UK, which monitors water quality and detects incidents of pollution, are also crucial. Additionally, natural solutions like planting trees, restoring wetlands, and creating green roofs can effectively expand the capacity of sewer systems and mitigate overflows.

Oil and its derivatives

The transportation of oil by tankers or pipelines presents a significant risk of spills. Human error, such as groundings, collisions, and equipment failure, is a common cause of tanker accidents. Inadequate maintenance, faulty construction, and improper handling can also lead to leaks and spills during transportation. Additionally, the use of hydraulic fracturing, or fracking, in oil production has raised concerns about water contamination and availability, as it requires large amounts of water and hazardous chemicals.

Oil spills can have severe impacts on the coastal ecosystem, including direct lethal and sublethal effects on organisms. Lethal effects include smothering, hypothermia, coating, and acute toxicity. Sublethal effects can alter the physiology, behaviour, and reproductive capabilities of affected species, leading to changes in community structure and diversity. Oil spills can also have indirect effects, such as changes in habitat, predator-prey dynamics, and food webs.

The response to oil spills typically involves physical, chemical, and biological methods for cleanup and mitigation. Physical methods include booming and skimming, wiping with absorbent materials, mechanical collection, washing, and in-situ burning. Chemical methods, such as dispersants, are used to break down oil slicks and prevent them from reaching shorelines. Biological methods, like bioremediation, enhance natural biodegradation processes by adding nutrients and fertilizers.

Several major oil spills have occurred in recent decades, including the Deepwater Horizon spill in the Gulf of Mexico in 2010, the Exxon Valdez spill in Prince William Sound, Alaska, in 1989, and the Prestige spill off the coast of Galicia, Spain, in 2002. These spills have had long-lasting ecological and economic impacts, affecting marine life, fisheries, tourism, and local communities.

To prevent and mitigate the effects of oil spills, regulations such as the Oil Pollution Act have been implemented. This act requires oil storage facilities and vessels to submit response plans and enhances enforcement of safety and environmental laws. Additionally, advancements in technology, such as remote sensing and improved drilling techniques, help reduce the environmental impact of oil exploration and production.

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