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Environmental Status and Trends - Status and Trends of the Lake Pontchartrain Basin Contributors: Penland, Maygarden, Beall
The Lake Pontchartrain Area (LPA) lies in the central part of the Marginal Deltaic Basin geomorphic region and encompasses the entire Lake (Figure 1). The Tangipahoa and Liberty-Tchefuncte watersheds drain into this Area. The LPA has lower salinities in the western portion gradually increasing to the east. Near the mouth of the IHNC, where saline water introduced through the MRGO enters the Lake, salinities are generally high (Figure 5). The influence of this high-salinity water has been profound. At times stratification of saline and fresh water occurs, leading to hypoxia in this portion of the Lake (see Inner Harbor Navigation Canal: Velocity Profile and Water Quality). The hypoxia negatively affects the benthic organisms, including the Rangia clam (see Rangia Clams as an Indicator of Hypoxia in Lake Pontchartrain). The Lake is connected to Lake Borgne and the Gulf of Mexico through the Chef Menteur and Rigolets Passes, through which tidal exchange occurs and introduces more saline water into Lake Pontchartrain. The salinity in Lake Borgne is diluted, however, by fresh water draining from the Pearl River system (Bonnet Carré and Pearl River Salinity Impact Models).
Throughout the Twentieth Century, the draining and filling of wetlands to accommodate urbanization in the New Orleans and north shore areas negatively impacted the water quality of the Lake by introducing excessive nutrients and pollutants. Nutrient overloading, originating in river watersheds or drainage canals, sometimes leads to algal blooms in the Lake (see Nitrogen Loading into Lake Pontchartrain). The largest recorded bloom occurred after the opening of the Bonnet Carré Spillway in 1997 introduced large volumes of nutrient-rich Mississippi River water into the Lake.
Urbanization, armoring of the shoreline and other disturbances to the natural conditions of Lake Pontchartrain are believed to have contributed to the decline and change in distribution of SAV in the Lake (see Spillway, Hurricane, and Drought Effects on SAV (Grassbeds)).
Shell dredging, the process by which Rangia clam reefs were mined from the Lake bottom for use in road and levee construction, increased the turbidity of the Lake and altered the Lake bottom, perhaps permanently. The practice was prohibited in 1990, and its cessation has contributed to the greatly increased clarity of the Lake's water (see Recent Trends in Water Clarity and Clam Abundance).
In recent years, there have been improvements in water quality along the south shore of Lake Pontchartrain. In 1962, the LDHH issued an advisory discouraging swimming along the south shore of the Lake due to high levels of bacterial contamination. Repairs and changes in the sewerage systems in Jefferson and Orleans Parishes, including re-routing Jefferson Parish sewage discharge away from the Lake, have contributed greatly to this improvement. Safe swimming on the south shore is again possible when conditions are right, and the public is informed weekly about water quality conditions. There is still a potential for bacterial contamination to be a health threat, especially shortly after a rain event flushes the city's drainage canals (see Recreational Use Risk Assessment) and the resulting plumes of water enter the Lake (see Urban Stormwater Discharges on South Shore). Continued monitoring of these conditions will be essential, on both the south and north shores near the centers of population, especially at mouths of rivers and canals.
Fisheries in Lake Pontchartrain have historically been of cultural and economic importance to the area, and because Lake Pontchartrain is a large, shallow estuary it supports a rich estuarine assemblage of fish and shellfish. Blue catfish, red drum, spotted seatrout, blue crabs and brown and white shrimp are all commercially important species in the Lake. The anadromous Gulf sturgeon is a threatened species commonly found in Lake Pontchartrain. Tables 2, 3 and 4 summarize the status and trends statistics for a selection of animal populations in this area. The fisheries populations have remained generally steady, while the numbers of the threatened brown pelican have increased dramatically in recent years and are expected to continue to rise.
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