Bronte Wells
The Mississippi River, the second-longest river in the United States, has been significantly polluted due to its extensive use for commercial purposes since the 19th century. Engineering projects aimed at improving navigability and preventing floods have severely degraded the river's ecosystem, leading to the introduction of various pollutants. These pollutants include industrial waste, agricultural runoff, chemical toxins, microplastics, and unregulated chemicals. The construction of levees and dams has altered natural flood patterns, creating hypoxic dead zones at the river's mouth and exacerbating the negative impacts on the surrounding ecosystems.
| Characteristics | Values |
|---|---|
| Cause of pollutants | Engineering projects aimed at enhancing navigability and preventing flooding, natural flood patterns, construction of levees and dams, industrial activities, agricultural runoff, waste disposal, chemical runoff from farms, toxic waste dumped by chemical plants, oil spillage, refuse dumping, debris from human structures, urban runoff, silt |
| Pollutants | Furan, trichlorobenzene, DDT, TCA, PCBs, heavy metals, phosphorus, nitrogen, microplastics, unregulated chemicals, fertilizers, oil, grease, sediment, road salt, lead, arsenic |
| Impact | Decline in water quality, disappearance of various species, creation of hypoxic areas or "dead zones", adverse impact on aquatic life and humans, loss of fishing, hunting and trapping grounds, damage to residential and commercial centers |
| Area affected | Gulf of Mexico, Louisiana, Texas coastlines, Lake Pepin, Minnesota, Mississippi River Basin, Minnesota, Mississippi River tributaries, Illinois River |
| Improving water quality | Implementation of the Clean Water Act, efforts by environmental groups and organizations sponsoring recreational use of the river, soil conservation techniques, vegetation protection of stream banks |
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What You'll Learn
Industrial activities, agricultural runoff, and waste disposal
Industrial Activities
Large-scale industrial farming has led to increased manure production, with some ending up as agricultural runoff. This runoff adds nutrients, such as nitrogen and phosphorus, to the water system, causing eutrophication. Eutrophication is a natural process, but human activities, especially industrial agriculture, have accelerated it. Corn (maize) is the number one crop in the United States, and farmers often over-fertilize to avoid lower yields and poor-quality produce. This excess fertilizer, along with animal waste, is carried into the Mississippi River by runoff or leaching, contributing to the eutrophication of the river.
Agricultural Runoff
Agricultural runoff is the leading cause of water pollution in the United States. It is a significant contributor to the impairment of U.S. waterways, including the Mississippi River. The nutrients from fertilizer and manure cause algal blooms, which block sunlight from penetrating the water's surface, inhibiting photosynthesis. When the algae die, they sink to the bottom, where bacterial decomposition consumes oxygen, leading to the death of marine life due to a lack of oxygen, known as hypoxia. This hypoxic zone, or "dead zone," is found in the Gulf of Mexico, along the Louisiana and Texas coastlines.
Waste Disposal
The Mississippi River also faces plastic pollution and trash problems. A recent study revealed the presence of over 11 million pounds of plastic pollution in the river and its surrounding areas. Trash from the river's drainage basin ends up in the river itself and eventually flows into the Gulf of Mexico and the ocean. Efforts to reduce plastic waste and increase recycling are ongoing, with city-specific projects and educational initiatives being implemented.
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Eutrophication and algal blooms
Eutrophication is a condition caused by nutrient enrichment, which leads to an abundance of algae. This algae blocks sunlight from penetrating the water's surface, inhibiting underwater plant growth. When the algae die, they are consumed by bacteria, which use up the oxygen in the water, leading to the death of marine life.
The Mississippi River has been severely affected by eutrophication, which has been exacerbated by engineering projects aimed at enhancing navigability and preventing flooding. The river's banks, once rich in biodiversity, have suffered from the introduction of pollutants from industrial activities, agricultural runoff, and waste disposal. These pollutants include furan, trichlorobenzene, DDT, trichloroethane, and polychlorinated biphenyls (PCBs). The high levees built along the river have also altered natural flood patterns, creating areas of hypoxia, or "dead zones," particularly at the river's mouth.
Agricultural runoff, which includes chemical fertilizers and pesticides, is a major contributor to eutrophication in the Mississippi River. These chemicals increase the levels of nitrogen and phosphorus in the water, which cause an overgrowth of algae. This overgrowth of algae, known as an algal bloom, can impact water quality, recreation, businesses, and property values. Algal blooms can also produce toxins that are harmful to human health and aquatic life.
The Gulf of Mexico, into which the Mississippi River flows, is home to one of the largest dead zones in the world. This dead zone is caused by the combination of excess nutrients from agricultural runoff and seasonal stratification of Gulf waters. The nutrients create an ideal environment for algae to grow, and the stratification of the waters prevents the algae from being washed out, leading to a persistent algal bloom.
Efforts are being made to reduce the impact of eutrophication and algal blooms in the Mississippi River and the Gulf of Mexico. State and federal agencies are implementing plans to build large-scale river sediment diversions to capture sediment during spring flood pulses and redirect it to eroding coastal basins. These diversions will also increase freshwater and nutrient inputs, which may affect algal bloom formation. Environmental groups such as the Izaak Walton League and Greenpeace have also been advocating for the federal government to take measures to protect the Mississippi's ecosystems and reduce pollution.
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Microplastics and unregulated chemicals
The Mississippi River is a vital resource, supplying drinking water to 70 cities in the United States. However, it faces significant pollution challenges, particularly from microplastics and unregulated chemicals.
Microplastics
Microplastics have been detected in the Mississippi River, with studies finding these pollutants in fish species such as Gizzard Shad, Largemouth Bass, Bluegill, and Longear Sunfish. The occurrence of microplastics increases in the Lower Mississippi River, with fragments being the most common morphology and polypropylene the most prevalent polymer. The river's vast aquatic and terrestrial expanse suggests it may contain substantial microplastic levels, posing risks to the watershed's biodiversity.
Unregulated Chemicals
The Mississippi River has also been affected by unregulated chemicals, including "forever chemicals" like perfluorooctanesulfonic acid (PFOS). These persistent chemicals have been detected in the river at concentrations far exceeding interim federal drinking water guidelines. PFAS chemicals, which include PFOS, are widely used in consumer products such as non-stick cookware and water-repellent clothing. They have been found not only in the river but also in fish, shellfish, groundwater, and even rain. The detection of these unregulated chemicals has sparked calls for increased testing and stricter regulations to protect the environment and public health.
Agricultural runoff is a significant contributor to chemical pollution in the Mississippi River. As one of the most productive agricultural regions globally, the Mississippi River Basin experiences extensive chemical use, with over 100,000 metric tons of pesticides and 6,500,000 tons of commercial nitrogen fertilizers applied annually. This has led to the transport of pesticides and nitrates into the region's streams, aquifers, and atmosphere, ultimately impacting the Gulf of Mexico.
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Toxic disposal, oil spillage, and refuse dumping
The Mississippi River has been a site of numerous industrial accidents, one of which occurred between 1962 and 1963. This incident spilled 3.5 million gallons of soybean oil into downtown Mankato, with citizens draining 2.5 million gallons into nearby rivers, including the Mississippi. The oil covered the river from St. Paul to Lake Pepin, creating an ecological disaster that harmed bird, mammal, fish, and turtle populations.
The Mississippi River has also been impacted by industrial and municipal wastewater, with organic contaminants and synthetic-organic chemicals being released into the water. This has resulted in the detection of pollutants like polynuclear aromatic hydrocarbons (PNAs) and adsorbable organic halogen (AOX) in the river's sediments and water. PNAs, which originate from combustion processes, urban runoff, and industrial activities, have been identified as priority pollutants by the U.S. Environmental Protection Agency.
Agricultural runoff is another significant contributor to the pollution of the Mississippi River. Farms located in the Mississippi River Basin discharge agricultural waste into the water system, leading to eutrophication and the creation of "dead zones" in the Gulf of Mexico. These dead zones are characterized by high algal growth and low oxygen levels, resulting in the asphyxiation and death of marine life.
Urban runoff is also a leading cause of non-point source pollution in the Mississippi River. As cities expand, paved surfaces increase, preventing water absorption. Consequently, polluted water flows directly into the river, carrying various contaminants.
To address these issues, the United States has implemented pollution-control laws and improved sewage treatment plants, leading to positive changes in water quality. However, the complex nature of pollutant sources and the varying levels of success in different regions highlight the ongoing challenges in mitigating pollution in the Mississippi River.
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Navigation, dredging, construction, and wetland development
The Mississippi River is a vital waterway for the United States, facilitating the transportation of goods and commerce. However, the river faces significant challenges due to varying water levels, which impact navigation and require constant dredging to maintain its navigability. These issues have led to increased costs and complexities in managing the river.
Navigation
Navigation on the Mississippi River has deteriorated over the decades due to shifting water levels. Research by the federal government and Princeton University examined water levels from 1963 to 2020 and found that both low and high water levels impact different sections of the river. The Upper Mississippi is more affected by high water levels, while the Lower Mississippi struggles with low water levels. These conditions strand traffic, restrict shipping capacity, and impact commercial activities. Despite these challenges, cargo volumes have increased due to the adaptation of captains and crews to the changing conditions.
Dredging
Dredging is a critical activity to maintain the Mississippi River for commerce and navigation. The U.S. Army Corps of Engineers is responsible for dredging large quantities of sand to keep the channel open for barge and boat traffic. However, alternating extremes of heavy rainfall and drought make it challenging to predict and plan the dredging operations. Additionally, finding suitable locations to place the dredged sand, especially in the narrow upper reaches of the river, has become increasingly difficult due to continuous sediment flow. The dredging program incurs significant costs, with the Upper Mississippi dredging costing an average of $45.4 million annually between 2014 and 2023.
Construction
Construction activities along the Mississippi River, such as bridge replacements and new crossings, can impact river navigation and require careful planning. For example, the early demolition of the Blackhawk Bridge, which connects Iowa and Wisconsin, was necessary due to structural issues and safety concerns. The construction of a new span just 75 feet away has led to extended closures and disruptions, pushing back the completion date to 2027. During these projects, alternative river crossings and transportation options are explored to minimise the impact on commuters and businesses.
Wetland Development
The Mississippi River Delta and coastal Louisiana are facing significant land loss, with nearly 1,900 to 2,000 square miles of land disappearing since the 1930s. One of the primary causes of this collapse is the construction of huge levees to control river flooding and protect communities and infrastructure. However, these levees have cut off the supply of sediment-filled water to the delta, disrupting the cycle of wetland growth. The sediment is instead lost to the Gulf of Mexico, allowing saltwater to penetrate deep into the wetlands and destroy the freshwater ecosystem. The vast network of shipping channels and energy infrastructure development has further accelerated land loss and altered the natural hydrology of the region.
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Frequently asked questions
The Mississippi River is polluted with excess phosphorus and nitrogen, which produce a dead zone in the Gulf of Mexico, where oxygen is choked off for fish and plants.
Nutrient pollution is caused by agricultural runoff, which is the number one contributor to the impairment of U.S. waterways.
Other sources of pollution include industrial waste, chemical runoff from farms, oil spillage, and urban runoff.
Pollution has led to the creation of a hypoxic or dead zone at the mouth of the river, which extends into the Gulf of Mexico. This area is one of the largest dead zones in the world, where marine life cannot survive due to a lack of oxygen.
Public, private, and nonprofit partners are working to reduce pollution and enhance the river's ecology. Efforts to protect the Mississippi's ecosystems have been advocated by environmental groups and organizations sponsoring recreational use of the river. The Clean Water Act has also helped reduce pollution from industrial sources and improve water quality.
