Lake Ponchartrain

Lake Pontchartrain ( ) is an estuary located in southeastern Louisiana in the United States. It covers an area of with an average depth of . Some shipping channels are kept deeper through dredging. It is roughly oval in shape, about from west to east and from south to north.

In descending order of area, the lake is located in parts of six Louisiana parishes: St. Tammany, Orleans, Jefferson, St. John the Baptist, St. Charles, and Tangipahoa. The water boundaries were defined in 1979 (see list of parishes in Louisiana).

The lake is crossed by the Lake Pontchartrain Causeway, the longest continuous bridge over water in the world. A power line also crosses the lake. Its towers stand on caissons in Lake Pontchartrain, and its length can be used to visually demonstrate the curvature of the earth.

Toponymy

Lake Pontchartrain is named for , . He was the French Minister of the Marine, Chancellor, and Controller-General of Finances during the reign of France's "Sun King", Louis XIV, for whom the colony of was named.

The name itself comes from the place in France where 's is situated. It is thought that this name originates from it being where a bridge (french: pont) crossed the river on the ancient route from to ().

Lake Maurepas, directly west of Lake Pontchartrain, was named for the son of , , , who was also a French statesman.

Description

Lake Pontchartrain is an estuary connected to the Gulf of Mexico via the Rigolets strait (known locally as "the Rigolets") and Chef Menteur Pass into Lake Borgne, another large lagoon, and therefore experiences small tidal changes. It receives fresh water from the Tangipahoa, Tchefuncte, Tickfaw, Amite, and Bogue Falaya rivers, and from Bayou Lacombe and Bayou Chinchuba. It is one of the largest wetlands along the Gulf Coast of North America.Keddy, P.A., D. Campbell, T. McFalls, G. Shaffer, R. Moreau, C. Dranguet, and R. Heleniak. 2007. The wetlands of lakes Pontchartrain and Maurepas: past, present, and future. Environmental Reviews 15: 1- 35. It comprises more than 125,000 acres of wetland, including bottomland hardwoods and cypress swamps (although these have been severely degraded by past logging), along with a complex mixture of herbaceous wetlands including fresh, intermediate, and brackish marsh.

Salinity varies from negligible at the northern cusp west of Mandeville up to nearly half the salinity of seawater at its eastern bulge near Interstate 10. Lake Maurepas, a true freshwater lake, connects with Lake Pontchartrain on the west via Pass Manchac. The Industrial Canal connects the Mississippi River with the lake at New Orleans. Bonnet Carré Spillway diverts water from the Mississippi into the lake during times of river flooding.

History

The lake was formed 2,600 to 4,000 years ago as the evolving Mississippi River Delta formed its southern and eastern shorelines with alluvial deposits. One recorded Indigenous name for the lake is ('wide water'). In 1699, French explorer renamed it after .

Human habitation of the region began at least 3,500 years ago but increased rapidly with the arrival of Europeans about 300 years ago. The great American naturalist, William Bartram, explored the north shore during a trip west in 1777.Keddy, P.A., D. Campbell, T. McFalls, G. Shaffer, R. Moreau, C. Dranguet, and R. Heleniak. 2007. The wetlands of lakes Pontchartrain and Maurepas: past, present and future. Environmental Reviews 15: 1-35. In 1852 a railroad was constructed to link New Orleans to the north. Engines turned at Pass Manchac. However, the pilings were burned to the water line in the Civil War. The great cypress swamps of the area were heavily logged in the early 20th century; many have not regrown.Keddy, P.A. 2008. Water, Earth, Fire: Louisiana’s Natural Heritage. Xlibris, Philadelphia. 229 p.

Conservation and restoration

Owing to past exploitation, the ecosystems of the lake have been placed under stress. Marshes, for example, are turning to open water, and cypress swamps are being killed by saltwater intrusion. However, brown pelicans and bald eagles, once scarce, are now a common sight along the shores. A team of experts assembled by The Nature Conservancy assessed the situation in 2004. They identified seven target habitat types that were in particular need of conservation management: bottomland hardwood forest, cypress swamp, relict ridge woodland, fresh/intermediate marsh, brackish/salt marsh, lake open water, and littoral submersed aquatic vegetation. The bottomland hardwood forest and cypress swamp are suffering from a lack of freshwater input and sediment deposition owing to the levees upstream from the lake. In addition, bottomland hardwoods are being invaded by exotic species such as Chinese tallow, while freshwater marshes are being invaded by exotic species such as elephant's-ear. The team also identified four key animal species that could indicate the degree to which the system declines or improves. These were the rangia clam (representing lake bottom habitat), gulf sturgeon and paddlefish (representing fish communities), and the alligator snapping turtle (one of the largest freshwater turtles in the world, but in decline owing to over-harvesting).

The future of the lake depends, in part, on restoring annual spring floods to the wetlands of the lake basin, and controlling urban sprawl on the north shore. Selected species, like the paddlefish and alligator snapping turtle, would benefit from reduced harvesting. The lake could change considerably without such conservation planning. A few examples of future change might include more cypress swamps converting to anthropogenic marsh or open water, Chinese tallow displacing native forests, and, with a warming climate, mangrove trees replacing brackish marsh. Hence, the ecosystems of the lake now, and in the future, depend very much upon some basic decisions about human activities in the vicinity of the lake, and, even more so, human activity upstream along the Mississippi River.

The current population in the region is over 1.5 million. There have been many problems with the conservation management of the forests and wetlands. The United States Geological Survey is currently monitoring the environmental effects of shoreline erosion, loss of wetlands, pollution from urban areas and agriculture, saltwater intrusion from artificial waterways, dredging, basin subsidence and faulting, storms and sea level rise, and freshwater diversion from the Mississippi and other rivers. With proper management of this lake and its wetlands, there is great potential to enhance the productivity of wetlands, and to maintain biological diversity to support an ecotourism industry that will diversify the economy.

Northshore

The area north of Lake Pontchartrain is known as the North Shore, Northshore, or Northlake region. It includes the cities of Mandeville, Covington, Abita Springs, Madisonville, Pearl River, Lacombe, and Slidell in St. Tammany Parish; Ponchatoula, Hammond, Amite, and Kentwood in Tangipahoa Parish; and Bogalusa and Franklinton in Washington Parish.

These three Northshore parishes are the eastern Florida Parishes. The landscape here is mostly uplands that were once dominated by long leaf pine savannas and interrupted by occasional large rivers. The savannas were maintained by regular fires caused by lightning; they produced the distinctive fauna and flora of this region.

Lake Pontchartrain's south shore areas (dominated by New Orleans), instead of being designated by that name, are more likely to be referred to as either "East bank" or "West bank," depending upon their position with respect to the general north-south course of the Mississippi River. Lake Pontchartrain forms the northern boundary of the city of New Orleans, which is coterminous with Orleans Parish