The Mississippi River Pollution: Causes And Concerns

The Mississippi River is one of the most polluted rivers in the world. The river carries an estimated 1.5 million metric tons of nitrogen pollution into the Gulf of Mexico each year, creating a dead zone in the Gulf each summer about the size of New Jersey. This pollution is caused by a variety of factors, including agricultural runoff, fertilizer use, sewage treatment plant discharges, and plastic waste. While efforts have been made to reduce pollution in the Mississippi River, it continues to be a significant environmental issue.

Nitrogen and phosphorus pollution

Nitrogen and phosphorus, specifically nitrate (NO3-), nitrite (NO2-), ammonium (NH4+), and orthophosphate (PO4-3), are chemical compounds essential for the growth of living organisms. However, when present in high concentrations, they can have toxic effects on both humans and the environment. Nitrogen and phosphorus pollution in the Mississippi River is primarily attributed to animal waste, fertilizer runoff, and sewage treatment plant discharges.

Fertilizer runoff is a significant concern, as farmers often over-fertilize their crops to maximize yield. This excess fertilizer is then washed into the river, increasing the concentration of nutrients. For example, the Mississippi River discharged approximately 900,000 metric tons of nitrate and 35,000 metric tons of orthophosphate into the Gulf of Mexico between April 1991 and April 1992. It is estimated that 75% of the nitrate in the river today is anthropogenic, with most of it originating from non-point agricultural sources.

To address nitrogen and phosphorus pollution, the MRC Nutrients Group closely monitors its causes and effects and advocates for protective numeric nutrient standards at the state level. The Clean Water Act (CWA) also plays a role in regulating both point source and non-point source pollution, although its effectiveness in addressing nitrogen and phosphorus pollution is limited due to the prevalence of unregulated agricultural sources.

Reducing nitrogen and phosphorus pollution in the Mississippi River Basin is crucial to protecting freshwater resources and mitigating the Dead Zone in the Gulf of Mexico. This can be achieved through a combination of regulatory measures, improved agricultural practices, and increased awareness of the impacts of nutrient pollution on the environment and human health.

Agricultural runoff

Nitrogen and phosphorus are the most common agricultural pollutants found in the public waters of the Mississippi River Basin. These chemicals act as fertilizers for harmful algae, leading to excessive algae blooms. The algae blooms block sunlight from penetrating the water's surface, inhibiting the process of photosynthesis. As the algae die, they sink to the bottom, where bacterial decomposition consumes large amounts of oxygen, leading to asphyxiation and the death of marine life. This phenomenon is known as eutrophication, resulting in the creation of "dead zones" devoid of aquatic life.

The dead zone in the Gulf of Mexico, fueled by nutrient runoff from the Mississippi River, has grown to the size of the state of New Jersey. It forms annually due to the combination of excess nutrients from agricultural runoff and the stratification of waters in the Gulf. The freshwater from the Mississippi River, carrying high levels of nutrients, flows into the Gulf and remains above the denser saltwater. This layering effect prevents the mixing of oxygen-rich surface water with oxygen-poor water below, resulting in extremely low oxygen levels in the deeper waters.

To address the issue of agricultural runoff, the Environmental Protection Agency (EPA) has requested that states along the Mississippi River develop Nutrient Reduction Strategies. These strategies aim to reduce nitrogen and phosphorus pollution in surface waters and include initiatives such as restoring wetlands, which act as natural filters for pollution. Additionally, the MRC Agriculture Group works to minimize the impact of fertilizer runoff and animal waste from farms, providing guidelines for fertilizer application and soil management to reduce nutrient loading in local waterways.

Non-point source pollution

Agricultural practices are a significant contributor to non-point source pollution in the Mississippi River. Fertilizer runoff from farms and fields located near the river results in nutrient loading, leading to eutrophication and hypoxia. Corn, for example, is a crop that requires substantial fertilization, and over-fertilization is common to ensure high yields and quality. This excess fertilizer washes into the river, causing an overload of nutrients.

Another source of non-point pollution is animal waste. The Mississippi River Basin has a high concentration of agriculture, and animal waste from farms contributes to the excessive nitrogen and phosphorus levels in the water. These nutrients can have toxic effects on plants, wildlife, and pets, and they also negatively impact human activities, such as swimming and beach recreation.

Sewage treatment plant discharges are also a concern. When sewage treatment is inadequate or improperly managed, it can release high levels of nitrogen and phosphorus into the river. These nutrients contribute to the dead zone in the Gulf of Mexico, where freshwater from the Mississippi meets the seawater. The layering of freshwater and saltwater, influenced by differences in density and temperature, prevents the mixing of oxygen-rich and oxygen-poor waters, leading to very low oxygen levels (hypoxia) that are detrimental to aquatic life.

To address non-point source pollution, economic incentives, design standards, and voluntary actions are employed. Economic incentives include grants, subsidies, and taxes aimed at encouraging better pollution control practices. Design standards involve technology specifications, such as Best Management Practices (BMPs), which promote the use of advanced technology to reduce pollution. Individuals are also encouraged to take voluntary actions, such as proper fertilizer and pesticide application, recycling grass clippings, and proper disposal of hazardous materials like motor oil and antifreeze.

Sedimentation

One significant consequence of sedimentation is the accumulation of silt in the backwaters, which destroys vital habitats for fish and other wildlife and buries spawning grounds. This leads to a decline in fish populations and disrupts the ecosystem's balance. Additionally, the silt itself can transport and carry pollutants like PCBs and heavy metals, further contaminating the water and endangering aquatic life.

Another impact of sedimentation is the high cost of dredging required to maintain the Mississippi River's 9-foot navigation channel. The accumulation of sand in the main channel contributes to the frequent need for dredging, which is economically and logistically challenging.

The Upper Mississippi River is particularly vulnerable to sedimentation due to two main reasons. Firstly, the river drains a vast land area, collecting sediment from a large geographical region. Secondly, the lock and dam system has altered the river's natural movement of sediment, disrupting its natural flow and exacerbating the sedimentation issue.

Poor waste management

The Mississippi River is one of the most polluted rivers in the world. The river's drainage basin covers parts of 31 US states and 2 Canadian provinces, and it is surrounded by a large human population. Poor waste management is a significant contributor to the pollution of the Mississippi River.

The river acts as a funnel for trash from the heart of the country to the Gulf of Mexico. Plastic waste is a significant issue, with plastic making up 75% of the total trash found in and around the river. This includes items such as plastic bottles, single-use plastic bags, personal protective equipment, clothing, shoes, and fishing gear. Cigarette filters, which are made of cellulose acetate, a type of plastic, are also a concern as they can take up to 10 years to decompose and can leach toxic chemicals into the water.

Agricultural runoff is another leading cause of pollution in the Mississippi River. Fertilizer runoff from adjacent farmland contributes to nutrient loading and eutrophication. Corn is a very sensitive crop, and farmers often over-fertilize to ensure high yields and good quality produce. This excess fertilizer can wash into the river, leading to high levels of nutrients such as phosphorus and nitrogen. These nutrients cause a biological dead zone, known as hypoxia, to form at the river mouth in the Gulf of Mexico. Hypoxia leads to a severe decrease in the amount of life in the affected area, including fish kills and harm to ecosystems.

Non-point source pollution is the biggest threat to rivers and is difficult to regulate effectively. The Clean Water Act (CWA) and economic incentives, such as grants and subsidies, aim to address non-point source pollution. Local and state governments are responsible for fulfilling non-point source regulations, and educational initiatives also play a role in reducing pollution.

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