two meters, and are bordered by cypress- 

 tupelo swamps and fresh marshes of the 

 Sagittaria f alcata , Phragmites communis , 

 and Typha types. The habitat covered 

 35,823 ha (88,485 acres) in the MDPR in 

 1978 (Table 5). 



Lac des Allemands, in the upper 

 Barataria basin, is described below as 

 representative of the entire region. 

 This lake is relatively large (62 km 2 

 or 23.930 mi 2 ) , slightly alkaline, 

 shallow (average depth 2.1 m or 7 ft), 

 turbid (average Secchi disc depth 0.41 m 

 or 1.34 ft) and eutrophic, or high in 

 plant nutrients and chlorophyll (Butler 

 1975). Water from the lake flows into 

 Lake Salvador via Bayou des Allemands. 



Freshwater lakes in the MDPR have 

 been affected by human changes and land 

 development. Nutrient loading is in- 

 creasing, most dramatically in the upper 

 freshwater regions of MDPR hydrologic 

 basins (Craig and Day 1977; Day et al. 

 1977; Kemp 1978). Frequent algal 

 blooms, aperiodic fish kills, and fish 

 population shifts favoring catfish, gar, 

 and shad are typical of such eutrophic 

 water bodies (Hopkinson and Day 1979). 



Nitrogen and phosphorus inflows to 

 Lac des Allemands exceed outflows by 1.9 

 and 1.8 times, respectively, indicating 

 that the lake is acting as a nutrient 

 sink. The bottom sediments are presuma- 

 bly taking up the nutrients, which is 

 presently preventing the eutrophication 

 of downstream water bodies. At some 

 point, however, lake sediments will 

 become saturated and will no longer 

 remove excess nutrients from lake water. 



The dominant lake primary producers 

 are blue-green algae (Cyanophytes) and 

 green algae (Chlorophyta) (Butler 1975), 

 with blue-greens the most abundant 

 (Lantz 1970). Turbid waters prevent 

 light penetration to the lake bottom and 

 limit benthic primary production. 



The lake ecosystem is heterotro- 

 phic, i.e., annual community respiration 

 exceeds community primary production. 

 Nevertheless, Lac des Allemands is very 

 productive throughout the year. Bayous 

 and rivers in the MDPR typically have 



lower primary production and respiration 

 than freshwater lakes because of reduced 

 sunlight caused by overhanging trees. 

 Lac des Allemands is most productive 

 between April and September, a period of 

 extensive blue-green algae blooms (Day 

 et al. 1977). 



Three groups are considered to be 

 the major components of the lake food 

 web: zooplankton, benthos, and fish. Of 

 the zooplankton, Cladocera and Rotifera 

 are the most abundant in Lac des Alle- 

 mands (Lantz 1970) . The zooplankton 

 feed on organic matter and phytoplank- 

 ton. Chironomidae (Dipteran insect 

 larvae) and Tubificidae (Oligochaeta) 

 are the dominant members of the benthic 

 macrofaunal community (Lantz 1970). The 

 fish population is composed of many spe- 

 cies, of which gizzard shad and channel 

 catfish make up most of the biomass. 

 Lac des Allemands supports a commercial 

 catfish industry that harvests 1.12 mil- 

 lion kilograms (2.47 million pounds) of 

 fish annually (Lantz 1970). 



Reptiles, including alligators 

 ( Alligator mississippiensis) and many 

 species of snakes, spend much time in 

 the fresh aquatic habitat. Amphibians, 

 wading birds, waterfowl and mammals are 

 also common consumers. 



FRESH SCRUB-SHRUB (10) 



The scrub-shrub (Cowardin et al. 

 1979) habitat is found in freshwater 

 areas that are not flooded enough to 

 support marsh (Figure 27). Broad-leaved 

 deciduous and evergreen shrubs present 

 here include willow, Cottonwood, and wax 

 myrtle (Wicker 1980). Altered marshes 

 invaded by baccharis, hackberry, button 

 bush, and palmetto are also included. 

 Thus, both natural scrub-shrub communi- 

 ties and reclaimed wetlands with pioneer 

 (invading) shrubs make up this habitat 

 type. 



The scrub-shrub habitat is small in 

 area, ranking 15th overall. It covered 

 13,188 ha (32,600 acres) in 1978 (0.4% 

 of the total MDPR) , an increase of more 

 than 6,000 ha (14,800 acres) since 1955 

 (Table 5). Although scrub-shrub is 



56 



