River Deltas
A river delta is a landform that forms when sediment-filled water from a river flows into an ocean, lake, reservoir, or another river. Delta is a Greek letter shaped like a triangle and the term describes the triangular shape of a river delta. River deltas form beneath tidally-influenced waters and occur when sediment accumulates over time at the bottom of a shore defined by a decrease in wave energy. This wave energy loss is due to the narrowing of a rivermouth, the presence of offshore bars, or the introduction of fresh water into the sea.
River deltas are divided into two types: tide-dominated deltas and wave-dominated deltas. Tide-dominated deltas occur in areas where there is a large tidal range and wave-dominated deltas occur in areas where there is a small tidal range. The type of delta a river forms depends on the balance between sediment supply, subsidence, and sea level rise.
Mississippi River Delta
The Mississippi River Delta is located in the southeastern United States, stretching from northern Louisiana to southern Mississippi. It is the fourth largest delta in the world and has been designated as a Ramsar Wetland of International Importance. The Mississippi River Delta is a tide-dominated delta, meaning it experiences high tidal energy and is characterized by large amounts of suspended sediment.
The Mississippi River carries approximately 4.3 gigatons of sediment each year, making it the ninth largest sediment transporter on Earth. The average sediment contribution of the Mississippi River Delta to the global sediment budget is 7.3 percent. However, this sediment is not only significantly decreasing due to a variety of human impacts, but it is also dynamically shifted across the delta.
Absolute Location of the Mississippi River Delta
The absolute location of the Mississippi River Delta can be located in United States coordinates between 29.7-33.3 degrees N, and 89.4-91.8 degrees W. The delta begins at the intersection of the Mississippi and Yazoo River and stretches over 6500 square miles of continental shelf. It is separated into three distinct sub-deltas: the Chandeleur Islands, Isle Grand Terre and Atchafalaya Basin Delta.
The Chandeleur Islands were formed in the late 19th century by the deposition of sediment from the Mississippi River. The islands extends out from the continental shelf, providing a buffer to the mainland from wind and wave energy and serve as important fish nurseries. The Islands are part of the Breton National Wildlife Refuge, a protected area under the National Wildlife Refuge System.
The Isle Grand Terre is located in the extreme southeast of Louisiana and is a flat-topped offshore platform. The delta has less wave energy due to its isolation from the mainland. It is characterized by numerous small domes with a muddy surface and supports a diverse selection of animal species.
The Atchafalaya Basin Delta is a region made up of a vast network of braided distributary channels. It is the most dynamic part of the Mississippi River Delta and is constantly adjusting to changes in land form and sediment supply. It’s an important part of the region’s wildlife as it provides a safe harbor for numerous species of fish, birds, and plants.
Environmental Impact of the Mississippi River Delta
The health of the Mississippi River Delta is in decline due to a combination of anthropogenic activities and natural processes. This decline is due to not only the reduced amount of sediment in the river and the delta, but also the increasing loss of coastal wetland and barrier islands. Wetlands provide important services, from improving water quality, to trapping sediment and providing habitats for fish, birds, and wildlife. Conservation of these wetlands and the delta are critical to maintaining the health of the environment.
Coastal land loss has been particularly impactful due to the unprecedented rate of sea level rise and subsidence of the deltaic plain. Subsidence occurs when the underlying sediment of the delta compacts, resulting in an increased rate of coastal erosion and inundation as the water rises. In addition, increased pressure of oil and gas extraction activities, as well as agricultural activities, pose a significant threat to the delta, leading to the loss of valuable wetlands and ecosystems.
Restoration Efforts in the Mississippi River Delta
In recent years, there have been various efforts in the Mississippi River Delta to restore and protect its fragile ecosystems. The Mississippi River Delta restoration program, led by the US Army Corps of Engineers and the Environmental Protection Agency, is a multi-faceted effort to protect and restore the wetland ecosystems of the delta. Projects include the construction of sediment diversions, the placement of sediment barriers, and the establishment of coastal restoration areas.
Sediment diversions are man-made structures that mimic the natural sheet flow of the river and allow for the reintroduction of sediment in the delta. These diversions help to rebuild marsh and provide a stable platform for wetland plants to establish. Sediment barriers are also used to restrict ocean and river water in the delta, which help to trap sediment in areas of erosion. Finally, the establishment of coastal restoration areas help to protect important wetlands and provide a buffer against further coastal erosion and inundation.
Maintenance of the Delta
In recent years, the maintenance of the Mississippi River Delta has become increasingly important to the health of the regional ecosystem. Government and private organizations have been working together to restore these important ecosystems and ensure they are protected for generations to come. Various methods of restoration, protection, and monitoring have been implemented to preserve the delta’s health and prevent further damage.
The maintenance of the delta is reliant on the availability of freshwater, sediment, and nutrients, as well as a diversified natural habitat. As climate change continues to impact the region, these elements become even more essential to the long-term health of the delta and the surrounding environment.
Conclusion
The Mississippi River Delta is an incredibly important region for both wildlife and human life. Its absolute location can be found in the southeastern United States between 29.7-33.3 degrees N and 89.4-91.8 degrees W. It has been designated as a Ramsar Wetland of International Importance and carries an average sediment contribution to the global sediment budget of 7.3 percent. There have been multiple restoration efforts to protect the fragile ecosystems of the delta, as well as various management and monitoring programs to ensure its long-term health. It is essential we continue to protect this important region and its inhabitants for generations to come.
