Mississippi River

 

Factfile

  • Length: 3,730 km

  • Sources: Lake Itasca

  • Key Tributaries: Arkansas, Illinois, Missouri, Ohio and Red rivers

  • Basin area: 2.981 million km^2

  • States within: USA (Missouri, Illinois, Tennessee, Kentucky, Arkansas, Mississippi & Louisiana)

  • Basin Population: 30 million

  • Discharge: 16,790 m³/s

 
Hernando de Soto Bridge over the Mississippi River, Memphis, Tennessee

Hernando de Soto Bridge over the Mississippi River, Memphis, Tennessee

Physical Geography

The Mississippi river is the second largest river in the U.S.A. at a length of 3,730 km, flowing from its source in Lake Itasca, Minnesota southwards through 7 states before the river terminates at its mouth in the Gulf of Mexico where the Mississippi delta is formed. As the catchment area for the Mississippi basin covers 2.981 million km² the physical setting of the basin varies greatly, as such below we will break this system down allowing for analysis of the entire fluvial system.

Formation/Geology

The Mississippi river system has been an integral part of the formation of the landscape seen across the U.S.A., with this fluvial system serving as one of the busiest commercial waterways across the globe as well as providing the region with some of North America’s most fertile agricultural land. The Mississippi itself has been a stable part of North America for over 100 million years, as outlined by geological evidence including the deposition of fluvial material over bed rocks of the Cretaceous period. The Mississippi river has multiple tributaries that contribute to the flow of the river across its 3,730 km course with the most notable being the Missouri river, the longest river in North America, which enters the Mississippi river north of St. Louis, Missouri. The combination of these to fluvial systems would in fact make this river system the longest in the world.

Geomorphology

The Mississippi river can be divided into four distinct sections: the upper-, middle-, lower-course and the Mississippi delta.

The upper course of the Mississippi runs from its source to the confluence with the Missouri river north of St. Louis. This section of the river is in fact the remnants of an ancient glacial fluvial system, River Warren, that connected the ancient glacial lakes of Minnesota to the Gulf of Mexico. The Upper Mississippi contains many geomorphological landmarks with the most notable in this section being the Mississippi gorge, formed from the recession of a waterfall back upstream that carved out the limestone bedrock of the region over a great period of time. However, much of the natural function of the Upper Mississippi has been hindered as a result of anthropogenic action, with a large portion of the upper-course being controlled using a system of 29 dams and locks to moderate the flow of water within this section of the river. These anthropogenic actions began in the 1930’s and were mostly completed in the 1940’s to improve transportation links using the Mississippi for industry, the series of locks and dams in this section also plays a pivotal role in regulating water levels and discharge downstream. 

The middle course of the Mississippi is much more understated with this stretch of river being 310 km in length from the confluence with the Missouri river, north of St. Louis, to the confluence of the Mississippi with the Ohio River at Cairo, Illinois. This section has been modified much less than the upper course by anthropogenic actions being allowed to meander across the landscape.

The lower course of the Mississippi spans a length of 1600 km from Cairo, Illinois to the Gulf of Mexico and is the most used section of the Mississippi river. The anthropogenic management of the lower course is also extremely noticeable across this section of the river with the interlinked dams and locks of the upper course being replaced with a series of leveés and dykes allowing for flood management and transportation along the river course. As a result of the interference by humans and the hard engineering strategies that were implemented to manage the lower course there has been a substantial loss of natural habitats in the region as well as a reduction in the natural sediment supply throughout the course of the river.

Once the Mississippi meets the Gulf of Mexico at New Orleans, Louisiana it forms the largest and one of the most identifiable geomorphological landforms that is found in this system, the Mississippi Delta. The Mississippi delta is a river-dominated deltaic system as is seen by the current shape of a birdfoot delta showing the dominance of the river in the region over the tides of the Gulf of mexico. This delta has been formed as a result of millions of years of sediment deposition from the Mississippi River, spanning an area of 77,700 km², while on the surface the delta covers 28,500 km², with the Mississippi once depositing 200 million tonnes of material annually to the Gulf allowing for the sheer scale of the current delta to be achieved. However, as a result of the previously mentioned anthropogenic interactions with the Mississippi and the many hard engineering strategies implemented in the region much less of this material now reaches the delta itself and is leading to the erosion of the delta reducing its area.

Climate

Due to the size of the Mississippi river the climate characteristics vary greatly across the catchment area, ranging from the much colder subarctic setting of its source in Minnesota to the much warmer subtropical setting of Louisiana at the mouth of the river. As such during the winter months the acreage temperature ranges from -12°C in the upper course to 13°C at its mouth, while during the summer months the average temperature ranges from 21°C to 28°C in the upper course and at the river mouth respectively. The variation present in temperature is also present in other climate factors including precipitation with an average range of 130 mm in the upper section to 75 mm in the middle-course during winter and spring months, while in the summer and autumn precipitation events come as a result of sporadic weather fronts and thunderstorms. Overall, the Mississippi basin receives an average of 900 mm/year with this being divided into 77% rainfall and 23% snow. The lower-course of the river is also susceptible to major weather events most notably Hurricanes coming up from the Gulf of Mexico into the mississippi basin, this was seen during one of the USA’s worst hurricanes Katrina in 2005, which not only caused major infrastructural damage to transportation links, building and the levee system that was in place in New Orleans causing $125 billion in damages but also took the lives of 1,836 people many of whom lived within the lower Mississippi basin.

Ecosystems

As a result of anthropogenic actions and alterations made throughout the Mississippi basin there are very few natural areas left within the basin, greatly impacting the function of the Mississippi basin. As such biodiversity in the region has been limited with many invasive species being prevalent in aquatic, riparian, terrestrial environments. The Mississippi basin is home to many ecoregions and assemblages with the most notable being the Mississippi Alluvial Plain, an ecoregion that is found predominantly in Arkansas, Louisiana and Mississippi following the Mississippi River from the Midwest to the Gulf of Mexico and the Mississippi Lowland forests, which is one of the most heavily converted regions in the USA with little of the riparian forests remaining.

Ecological Setting

The Mississippi Basin is the largest drainage area in the USA with the basin historically providing the resources that helped form the USA into its current setting,  aiding commerce, tourism and the fishing industry within the United States. The basin itself is one of the largest and most complex floodplain river ecosystems in the Northern Hemisphere, with an ecosystem that includes the forests of Minnesota as well as the bayous of Louisiana. As such, there is a rich amount of both flora and fauna located in this region.

Flora

Along the Upper course of the river the riparian forests consist mostly of hardwood trees such as Silver Maple, River Birch, Bur Oak, Green Ash, Hackberry Cottonwood, Swamp White Oak. With many plants and bushes including nettles, Gray-headed Coneflower, Ostrich Fern and Cardinal flowers. The further distance downstream the more changes that occur to the types of trees that are found along the floodplain with an increase in the number of Cottonwood, Hackberry, Pecan, Elm and Willow trees. The upper course of the Mississippi is also home to a variety of Fens, bogs and wetlands within the upper reaches of the river with these regions also having unique flora with the presence of Tamaracks, a type of conifer, Labrador tea and Orchids. 

In the Southern reaches of the Mississippi river the ecology changes greatly to the upper region of the basin with the dominant presence of swamps meaning that the dominant tree species of the region are the Bald Cypress, Tupelo gum, Swamp blackgum, Swamp red maple and green ash. The swamp region of the basin is also home to plant species that include moss’, such as spanish moss, and orchid species that grow on the bark of the trees in the region and obtain most of their nutrients from the air rather than soil.

Further changes in flora are observed into the coastal marshland associated with the Mississippi basin, where the Mississippi meets the Gulf of Mexico, the more saline water leads to changes in the types of species that can flourish, such as grass species like Roseau cane. However, as a result of anthropogenic action, the erosion of the coastal marshes has increased at an alarming rate potentially leading to the loss of the species associated with this region.

Fauna

As the Mississippi spans such a large area and over 10 states the fauna within the basin is extremely diverse with terrestrial species such as Deer, Red Squirrels, Beavers, muskrat, otters, racoons, foxes, rattlesnakes, bobcats, coyotes, Black bears

40% of North American water birds migrate along the Mississippi which is 326 individual species    Among these species are bald eagles (in Winter), song birds & pelicans (in spring) and tundra swans (in Autumn). Other avian species that call the mississippi basin home include hawks, turkey, peregrine falcons, great blue heron, egrets, geese, ducks, cormorants, and turkey vultures

Aquatic

Even with the intensive anthropogenic manipulation of the Mississippi river there are still over 260 fish species that reside within the Mississippi river, this is a quarter of all North American fish species. These species include pallid sturgeon, multiple mussel species, crappie, largemouth bass, striped bass, sunfish, walleye, catfish, white bass, and bluegill, carp, and ancient species such as the bowfin, sturgeon, paddlefish, and alligator gar. While other aquatic species such as Snapping turtles, found in the southern reaches of the Mississippi, have habitats in the river system. However there is a high level of threat to many of these species meaning that the number of species in the basin could potentially decrease leading to the loss of biodiversity across the basin.

  • snapping turtles

Human Geography

Pollution of the river

As the Mississippi is one of the main arterial rivers for industry in North America, there is a long history of anthropogenic actions and their effects on the river itself. Along its course there are numerous changes in land-use from Agricultural activity to industry and urban areas, as a result of this the number of sources of pollution for the Mississippi river is great. The leading cause of pollution for the Mississippi actually comes from agricultural activity throughout the basin, with the overuse of pesticides and fertilisers entering the fluvial system through surface runoff. This diffuse source of pollution can pose major threats to the environmental health on both a local scale, affecting the ecology and safe usage of the surface water, as well as on a basin wide scale as evident with the hypoxic zone in the Gulf of Mexico as a result of eutrophication. With the Hypoxic zone in the Gulf of Mexico being attributed to the Mississippi due to the abundance of nutrients that are delivered from the river. Regulations have been implemented across the United States such as the clean water act that was introduced in 1972 to improve the quality of all rivers across America by 1985, however, the aims of this act were not fully achieved as is evident by the current setting of the Mississippi. Other efforts such as the regulation of specific fertilisers and pesticide usage have been implemented, however, these are primarily on a state or local level meaning that change is not seen across the whole basin. As such, it would be imperative to use a basin wide approach in order to obtain positive changes to the current issues of agricultural pollution along the course of the Mississippi.

Climate Change

Anthropogenic climate change is a major issue for the mississippi basin with the increase in sea-level affecting the lower-course of the river as well as increases in temperature of sea surface temperatures being a major contributing factor in the increase in severity and the total number of hurricanes that could potentially impact the Mississippi basin. The increased potential for hurricanes in the region is a major issue for the basin with many areas, especially the lower socio-economic areas, still not recovering from hurricane Katrina with long lasting damage to the defences that were put in order to regulate the Mississippi itself. The increase in the frequency and severity of hurricanes in the region also leads to the potential for more destructive storm surges in the lower course of the river and its delta that could lead to further infrastructural damage in the region and a greater potential for the loss of life.

Anthropogenic modification of the river

The modification of the Mississippi River has been occurring since the introduction of the New Deal Franklin D. Roosevelt with modification occurring in both the upper course with the interconnected dams and locks to manage the flow of water in this section of the river. In the lower course, extending from Cairo, Illinois to New Orleans, a system of levees were built in order to prevent storm surges from hurricanes. As a result of this anthropogenic modification there have been severe damages to ecology within the course of the Mississippi leading to ecological deterioration throughout the course of the Mississippi and its delta. 

The levee system that was constructed in New Orleans failed during hurricane Katrina as a result of the poor maintenance leading to the flooding of 80% of New Orleans. A total of 50 levee failures occurred in the Greater New Orleans area leading to the deaths of 1,500 of the total 1,833 people being In New Orleans, many as a result of drowning, as well as leaving millions homeless. As a result of the poor governmental efforts to rebuild the region many areas have still yet to recover, showing the scars of Katrina, over 15 years later.