Development and urbanization in the New Orleans region over the past 300 years is projected to continue and places stress on the Lake Pontchartrain Basin environment.
Earliest human habitation began at least 3,500 years ago, but concentrated rapid growth in the area between Lake Pontchartrain and the Mississippi River began nearly 300 years ago with influx of European settlers, resulting in a population of over 1.5 million people. Today, the Basin faces many challenges, all of which are affected by the geologic character of this dynamic coastal region. The more significant of the environmental issues include erosion of Lake Pontchartrain shores, wetland losses, water and sediment pollution from urban outfalls and agricultural runoff, saltwater intrusion from navigation waterways, possible effects of past commercial shell dredging, impacts of basin subsidence and faulting, effects of storms and sea-level rise, and potential impacts on circulation patterns of future freshwater diversions from the Mississippi River. Continued losses of wetland and estuarine habitats, water and sediment pollution, and diminished fish and wildlife resources are some of the results if historical trends continue.
The U.S. Geological Survey (USGS) is uniquely qualified to conduct research needed to increase scientific knowledge of the Lake Pontchartrain Basin's character.
The long-term investigation extends previously completed and ongoing USGS geologic studies in the Mississippi River deltaic plain of southern Louisiana on topics such as barrier island erosion, regional-scale wetlands losses and deterioration, the long-term effects of marsh management, and water quality. Investigations of the Lake Pontchartrain Basin complement studies by several Federal and State agencies with which USGS scientists collaborate. An evaluation conducted in preparation for this study determined necessary baseline data, information, and geo-science studies required to better understand the character of the Basin and the geologic processes affecting the region. The evaluation suggested a well-defined set of geologic issues that could be addressed jointly with other organizations having expertise that complements geoscience expertise available in the USGS.
USGS scientists are increasing their knowledge of the geologic sedimentary framework within which processes are taking place.
Shorelines, wetlands, and the lakebed in the Lake Pontchartrain Basin have been in a state of dynamic flux since the Basin formed several thousand years ago.
Perceptions are widespread and common among the general public that Lake Pontchartrain Basin is both a source and a sink for contaminated sediments.
Scientific baseline data are being systematically collected to document Basin-wide sources and conditions of contamination. These data allow USGS scientists to differentiate natural background chemicals in the sediments from chemicals derived from human activity. Many known contaminants are associated with fine-grained sediments, such as mud and silt, particularly the organic-rich sediments comprising much of the lakebed. Muddy sediments are stabilized by sea grasses growing on parts of the lake floor, but muddy sediments in bare areas of the shallow Basin are frequently resuspended by waves, currents, and flooding. Resuspension may lead to redistribution of contaminants and generally increases turbidity. Recent flooding during May 1995 in the New Orleans area illustrates how contaminants can potentially enter the basin and be redistributed. This study provides systematic collection of lakebed sediment samples, analyses for sediment composition and geochemical characteristics, and inclusion in a computer database. In addition, instruments are deployed to monitor waves, currents, and turbidity. This information is extrapolated across the Basin using state-of-the-art high-resolution satellite imagery and 3-dimensional computer models of Basin circulation.
USGS researchers are determining wave energy distribution and circulation patterns at varying time scales.
Studies of these kinds are necessary to understand the transport and dispersal of turbid waters and sediments in the Lake Pontchartrain Basin. Circulation, controlled largely by inflow and outflow of fresh and tidal water and by atmospheric conditions, is the primary process for moving, dispersing, and concentrating fine-grained sediments and associated contaminants. Currently, little information is available on wave energy and movement of sediments and water masses in the Basin. Early physical and computer models have given preliminary results, but predictions of future conditions influenced by a variety of new engineered structures still have a high degree of uncertainty. Circulation models will be used to predict changes in distribution of turbid waters, rates of flushing in the Basin, and changes in salinity gradients resulting from engineering projects like the Bonnet Carre diversion.
USGS will distribute results of investigations and scientific analyses to a wide variety of user groups.
Interim and final results of field investigations and scientific analyses will be distributed to engineers, coastal zone managers and planners in Federal, State, and local government and universities, and to scientific colleagues and to the general public. A variety of information transfer methods, used successfully in other coastal studies, will be employed in this study. Communicating information and results to the citizens of Louisiana through educational materials is an important objective. Partnerships with local and environmental-interest groups will foster the kind of public education needed to insure the long-term sustainable use of Pontchartrain's resources.
U.S. Department of the Interior, U.S. Geological Survey
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