WATER QUALITY IMPACTS ON THE LAKE PONTCHARTRAIN ESTUARINE SYSTEM

This paper summarizes the present and potential water quality impacts on the Lake Pontchartrain Estuarine System. A 4-year study has been concluded using field surveys, numerical and physical models. The latter part of the study involved a severe drought, which significantly altered the salinity regime of the System. Field data show increasing salinity associated with low rainfall and high evapotranspiration. A major concern with salinities above 6 ppt is the survival of bald cypress in the Manchac Swamp at the western end of Lake Pontchartrain. Saltwater intrusion from the Gulf of Mexico via the IHNC has been documented. The saltwater intrusion takes the form of a stratified high salinity lens that covers up to 250 km2 of the lake bottom. This lens was found to be most persistent in the summer months when hypoxia was common. Intermittent salinity stratification occurred during the winter, but no hypoxia was been observed during this period. Several factors have been identified that contribute to the summer hypoxia: a) greater potential for saltwater intrusion due to the thermal expansion and alongshore currents in the Gulf of Mexico, b) higher Sediment Oxygen Demand due to higher bottom water temperatures, and c) predominately southerly winds which do not destabilize the stratification. The information of this study provides a baseline to help define the problems and to evaluate possible management alternatives such as the diversion of Mississippi River water into the Pontchartrain System.