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Environmental Overview - Regional Description of the Lake Pontchartrain Basin Contributors: Penland, McCarty, Beall, Maygarden
Since the initial biological inventory (Suttkus et al., 1954), submersed aquatic vegetation (SAV) in Lake Pontchartrain has declined by more than 50% (Cho and Poirrier, 2000). A UNO study revealed a 50% decrease between 1973 and 1985 (Montz, 1978; Mayer, 1986) and a 17% decrease between 1985 and 1991 (Burns et al., 1993). From 1996 to 1998, no grass beds were found along the south shore (personal observations by UNO researchers). The loss appears to be caused by the high nutrient input from urban runoff and by the armoring of the shoreline.
|Figure 9: Vallisneria americana near Bayou Lacombe during low-water period. |
Hurricanes, such as Hurricane Andrew in 1992, and prolonged salinity fluctuations appear to influence the species composition and distribution of SAV in Lake Pontchartrain. Hurricane Georges in 1998 did not have a direct effect on SAV coverage in the Lake, but subsequent high salinity and low rainfall influenced the distribution of species and led to an increase of Ruppia maritima. Surveys conducted in spring and fall of 1999 showed a decrease in Vallisneria americana (Figure 9) and an increase in Ruppia maritima. Invasive or exotic species of SAV also have caused shifts in species composition around the Lake. For example, Myriophyllum spicatum has replaced dominant species at freshwater sources and areas like Lake St. Catherine, which receives freshwater flow from the Pearl River.
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