as a source of calcium carbonate (and 

 road building material) the shells are 

 obviously not being replaced as fast as 

 they are mined from the lake. Whereas 

 Rangia at one time dominated the lake 

 bottom, the most numerous macrobenthic 

 organisms in the lake bottom in 1980 

 were two species of small snails 

 (hydrobids)that seem to tolerate certain 

 kinds of toxins present in the lake 

 (Sikora et al. 1981). 



The community of meiobenthos 

 (animals smaller than 0.5 mm) in Lake 

 Pontchartrain also reflect a stressed 

 environment. These animals are rela- 

 tively few in number and species rich- 

 ness compared with similar oligohaline 

 estuaries (Sikora et al. 1981). 



The nekton community in Lake Pont- 

 chartrain appears to have changed since 

 1953, when it was studied by Suttkus et 

 al. (1954), although this change is 

 difficult to assess. Nekton are diffi- 

 cult to quantify in large water bodies 

 because of their motility, tendency to 

 school, and differential ability to 

 avoid trawls. Nevertheless, fishes that 

 feed in and/or live on the lake bottom, 

 such as flatfishes, have possibly de- 

 clined (B. Thompson, LSU Coastal Ecology 

 Laboratory, personal communication, 

 1982). The zooplankton community also 

 appears to have declined in average 

 density since 1953, and more individuals 

 of the dominant zooplankter (Acartia 

 tonsa) were found recently at the bottom 

 interface than in the water column 

 (Sikora and Sikora 1982). Nevertheless, 

 shrimp, blue crabs, oysters, catfish, 

 and other fishery species are still 

 harvested from the estuarine open water 

 habitat in the Pontchartrain basin. 



Mercury, PCB's, Chlordane, Para- 

 thion, Dieldrin, and Aldrin have been 

 found at levels far exceeding the EPA 

 water quality criteria at the north and 

 west shores of Lake Pontchartrain, and 

 have been associated with the major 

 freshwater inputs to the lake. Along 

 the south shore high PCB, 2,4-D and 

 2,4,5-T levels have been recorded in 

 lake water. Apparently Dieldrin, 

 Diazinon, DDT, 2,4-D, and 2,4,5-T have 

 been added to Lake Pontchartrain in 



significant amounts along with Missis- 

 sippi River water through the Bonnet 

 Carre Floodway (Sikora and Sikora 1982). 

 Knowledge of the fate of these toxins 

 within the lake is not available. A 

 major portion is presumed to be concen- 

 trated in bottom sediments and in living 

 organisms that feed on the bottom. This 

 includes the majority of all of the 

 species that use the lake (Stone 1980b). 

 Herbicides that enter the lake from its 

 drainage basin may partially account for 

 the low primary productivity mentioned 

 above . 



All of this evidence adds up to a 

 picture of an estuary that is deterior- 

 ating, and the prognosis does not look 

 good in light of the increasing devel- 

 opment pressure on the shorelines and 

 drainage basin of Lake Pontchartrain. 



Good water quality in Lake Pont- 

 chartrain, and in other examples of 

 estuarine open water habitat in the 

 MDPR, is closely related to the via- 

 bility of the few remaining marshes and 

 swamp forests that once completely sur- 

 rounded the lake. These wetlands have 

 been encroached on by the spread of New 

 Orleans and other urban centers, logged, 

 and cut off from the open water by flood 

 control levees. Only a small portion of 

 marsh and swamp remains connected to 

 Lake Pontchartrain. 



New Orleans 



The second major influence in the 

 Pontchartrain hydrologic unit is its 

 urban habitat, most of which is occupied 

 by the City of New Orleans. New Orleans 

 is more than a large urban habitat; 

 because of its strategic location and 

 position as an active port, its func- 

 tional importance transcends both basin 

 and regional levels of organization. 

 Lewis (1976) provides an excellent 

 description of the major forces that 

 have shaped New Orleans. 



New Orleans was founded in 1718 by 

 John Baptiste Le Moyne , Sieur de Bien- 

 ville, on the highest land on the 

 natural levee of the Mississippi River, 

 10 ft above sea level, and 30 leagues 

 from the Gulf of Mexico. Except for the 



102 



