Pollution's Reach: Upstream's Impact On Downstream Water Quality

Pollution upstream can have a significant impact on water downstream, affecting both its quality and the surrounding environment. Upstream pollution can be caused by a variety of factors, including industrial and municipal wastewater discharge, mining, drilling, and deforestation. These activities can lead to an increase in biochemical oxygen demand (BOD) and a decrease in dissolved oxygen (DO) levels in the water, resulting in a decline in ambient water quality. Additionally, upstream pollution can have far-reaching consequences, such as social injustice to indigenous and underserved areas, habitat destruction, and air and water pollution. Furthermore, the pollutants can enter the water cycle, leading to the contamination of drinking water and the release of methane gas, a potent greenhouse gas. Understanding the impact of upstream pollution on downstream water quality is crucial for effective waste management and the preservation of aquatic ecosystems.

The impact of upstream pollution on downstream water quality

Upstream pollution has a significant impact on downstream water quality. This statement is supported by empirical evidence, which shows that pollutant inputs from major sources worsen the quality of water downstream, even when controlling for upstream pollution levels and location-specific factors.

The US Clean Water Act

The US Clean Water Act recognises nutrient pollution in stream ecosystems as one of the country's most pressing environmental challenges. This type of pollution costs billions of dollars each year and is a causal factor in harmful algal blooms, which can impact the taste and odour of drinking water.

Case Study: Cape Fear River

The Cape Fear River in North Carolina serves as a representative case study of the impact of upstream pollution on downstream water quality. From 2009 to 2012, the river experienced harmful algal blooms, predominantly composed of the cyanobacterium *Microcystis aeruginosa*. These blooms were found to be stimulated by nitrogen loading, with upstream nutrient concentrations influencing downstream chlorophyll a levels.

Point Sources of Pollution

Point sources of pollution, such as industrial and municipal wastewater discharge, have been identified as significant contributors to downstream water quality degradation. In the case of the Cape Fear River, four major point sources were identified as influencing chlorophyll a concentrations.

Policy Implications

The understanding of the impact of upstream pollution on downstream water quality has important policy implications. It underscores the need to reduce nutrient pollution in waterways and to address the various sources of pollution, including both point sources and non-point sources such as agricultural runoff.

In conclusion, upstream pollution has a direct and measurable impact on downstream water quality. This impact can have far-reaching consequences, affecting ecosystems, drinking water sources, and public health. Addressing upstream pollution through regulation, improved waste management, and reduced nutrient pollution is crucial to mitigating these impacts and preserving the health of aquatic environments.

The Clean Water Act and its effectiveness

The Clean Water Act, passed by the US Congress in 1972, has been instrumental in improving the quality of the nation's waterways. The Act set out to restore and maintain the chemical, physical, and biological integrity of America's lakes, rivers, streams, and other bodies of water. It required states to establish clean water standards to benefit drinking water, public health, recreation, and wildlife.

Effectiveness of the Clean Water Act

The Clean Water Act has successfully diverted 700 billion pounds of pollution from America's rivers, and the number of water bodies meeting clean water goals has doubled since 1972. The Act has also provided around 35,000 grants, totaling $1 trillion in funding to combat water pollution.

• Cuyahoga River, Ohio: Once one of the most polluted rivers in America, catching fire multiple times due to industrial pollution, now supports over 70 species of fish and has been designated for recreational use.
• Monterey Bay, California: The Clean Water Act led to the formation of Monterey One Water, a centralized agency that improved wastewater quality standards and conserved land upstream to prevent runoff into the Bay.
• Potomac River: Once severely polluted with sewage and deemed a health hazard, now supports bass and has reduced blue-green algae due to improved sewage treatment and limits on pollutants.
• Des Plaines River, Illinois: Transformed from a degraded stream to a healthy urban fishery, with an increase in the number of fish and the introduction of socioeconomically valuable sport fish.

Despite these successes, challenges remain. The Environmental Protection Agency (EPA) has only assessed about half of US waters, and issues like nonpoint source pollution, PFAS chemicals, and climate change-related disasters continue to threaten water safety.

The impact of nutrient pollution on chlorophyll a

Nutrient pollution in stream ecosystems is considered one of the most pressing environmental challenges in the US. Nitrogen-Phosphorus (NP) pollution is a causal factor in algal blooms, which are often stimulated by phosphorus (P) loading in freshwater and nitrogen (N) loading in coastal waters.

Chlorophyll a is used as a proxy for algal bloom strength and is regularly monitored by regulatory agencies. An increase in nutrient pollution can cause a rise in chlorophyll a levels, which in turn can lead to algal blooms. This was observed in North Carolina's Cape Fear River, where harmful algal blooms were reported near Lock and Dam 1 (LD1) from 2009 to 2012.

A study of the Cape Fear River found that upstream nutrient concentrations, particularly nitrate, positively correlated with chlorophyll a levels at LD1. The highest chlorophyll a levels were observed when nitrate concentrations were above 0.38 mg/L at two upstream locations.

Another study in Himachal Pradesh, India, also found a significant reduction in chlorophyll content in plant leaves growing in highly polluted sites compared to less polluted ones. The study analysed six plant species commonly found along National Highway 5 and found that total chlorophyll content was significantly affected by distance from the highway.

A retrospective study of Machado Lake in California examined the relationship between nutrient pollutants and chlorophyll-a. The study found a positive correlation between total nitrogen and total phosphorus and chlorophyll-a, with approximately 63% of the variability of chlorophyll-a concentration explained by these independent variables.

In summary, nutrient pollution, particularly nitrogen and phosphorus, can have a significant impact on chlorophyll-a levels in water bodies. This, in turn, can lead to algal blooms, which can have detrimental effects on community and public health.

The role of nitrogen and phosphorus in algal blooms

Nitrogen and phosphorus are essential plant nutrients that can cause algal blooms when they are present in excess. Algal blooms are a rapid increase in the density of algae in an aquatic system, which can be harmful to the ecosystem. While algal blooms can sometimes be natural phenomena, their frequency, duration and intensity are increased by nutrient pollution.

Nitrogen and phosphorus are vital to algal growth in aquatic ecosystems. Nitrogen is involved in the synthesis of proteins, amino acids and nucleic acids, while phosphorus is the main component of nucleic acids and phospholipids in algal cells. The optimal ratio of nitrogen to phosphorus for algal growth is 16:1, but this can vary depending on the species of algae. When there is an overabundance of these nutrients in waterways, algae can multiply quickly, particularly when the water is warm and the weather is calm. This proliferation causes blooms of algae that turn the water noticeably green, although other colours can occur.

The US Environmental Protection Agency (EPA) considers nutrient pollution in stream ecosystems to be one of the country's most pressing environmental challenges. The EPA acknowledges that nitrogen-phosphorus pollution is a causal factor in algal blooms. However, as many factors may contribute to a harmful algal bloom, it can be difficult to determine the exact role of nutrient pollution.

Nitrogen and phosphorus-associated metabolic activities have been observed during the development of cyanobacterial blooms. Genes involved in nitrogen fixation and phosphorus scavenging were found to be significantly upregulated during a bloom compared to pre-bloom. The activities of nitrogen fixation occurred during early summer after a late spring phytoplankton bloom, and were associated with high phosphorus and low nitrogen. Following nitrogen fixation and the production of new nitrogen, a shift in dominance from Nostoc and Anabaena to Microcystis and an increase in microcystin and saxitoxin occurred.

Nitrogen and phosphorus can also influence the types of algae that form blooms. For example, in Coastal Plain rivers and streams, algal blooms are largely stimulated by nitrogen loading. In contrast, freshwater algal blooms are often stimulated by phosphorus loading.

Overall, nitrogen and phosphorus play a crucial role in the development and composition of algal blooms. An overabundance of these nutrients in waterways can have significant impacts on the ecosystem, including the proliferation of harmful algal blooms.

The economic costs of nutrient pollution

Nutrient pollution, particularly nitrogen and phosphorus, is a pressing environmental challenge in the US, causing harmful algal blooms (HABs) that damage aquatic life, human health, and local economies. The economic costs of nutrient pollution are significant and far-reaching. Here is a breakdown of the economic impacts:

Property Values

The presence of HABs reduces water clarity, which in turn decreases property values in nearby areas. Dodds et al. estimate that for every meter decrease in water clarity, property values drop by 15.6%. This loss in property values is one of the most significant economic impacts of nutrient pollution, with an estimated average loss of $1.6 billion annually in the US.

Recreational Activities

A decrease in water clarity due to HABs also reduces the demand for recreational activities such as swimming and fishing. Vesterinen et al. developed a model to quantify this change in demand, finding that a reduction in water clarity leads to a decrease in the frequency of participation in recreational activities. This, in turn, results in economic losses for local businesses and industries that depend on tourism and recreation.

Clean-up Expenses

Mitigating the effects of nutrient pollution and HABs can be costly. Treatment technologies such as aeration systems, alum treatment, and herbicide treatment are often necessary to prevent and manage HABs. Additionally, in areas where affected water bodies are used for drinking water, additional clean-up procedures are required, further increasing costs.

Human and Pet Health

Direct contact with water bodies affected by HABs can cause various health issues in humans and animals, including dermal rashes, respiratory problems, and gastrointestinal distress. The healthcare costs associated with treating these health issues can be substantial, particularly in coastal states where HABs are more prevalent.

Waste Processing

Preventing phosphorus runoff and reducing the occurrence of HABs involves processing livestock waste and recovering phosphorus. This requires specialized technology and infrastructure, incurring significant costs for waste management and treatment.

Overall, the economic costs of nutrient pollution are extensive and impact various sectors, including real estate, tourism, recreation, healthcare, and waste management. These costs highlight the urgency of addressing nutrient pollution and implementing effective mitigation strategies.

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