Cypress-tupelo swamp productivity 

 in the upper Barataria basin has been 

 shown to be strongly coupled to the hy- 

 drologic regime (Conner et al. 1981). 

 Swamps that experience regular periods 

 of inundation and drying show higher 

 productivity than those with very slug- 

 gish or stagnant water. Conner et al. 

 (1981) found that an impounded swamp 

 site showed significantly less net pro- 

 duction 890 g dry wt/m'/yr, than a near- 

 by naturally flooded site 1,166 g dry 

 wt/m^/yr. Even higher productivity was 

 found in an area where water level vari- 

 ation was artificially augmented by 

 pumping. This area was flooded from 

 late fall to early spring and drained 

 the rest of the year. While flooded, 

 water was pumped through to ensure high 

 oxygen levels. The net production for 

 this area was estimated to be 1,780 g 

 dry wt/m 2 /yr (Conner et al. 1981). 



Swamp floor organisms have been 

 separated into two separate communities: 

 Denthic detritus and floating communi- 

 ties (Sklar and Conner 1979). The 

 former consists of dead organic materi- 

 al, associated microorganisms, and bac- 

 teria, as well as larger organisms 

 feeding on detritus, including crawfish. 

 Floating herbivores are associated with 

 the duckweed and water hyacinths at the 

 water surface. These include amphipods, 

 oligochaetes, and lepidoptera. Bivalves, 

 snails, and isopods are some examples of 

 benthic herbivores. Primary consumers 

 are mostly predatory insects. Snakes, 

 turtles, alligators, birds, and mammals 

 are the top carnivores. 



FRESH AQUATIC BED (7) 



The fresh aquatic bed habitat 

 (Figure 24) consists of submerged aqua- 

 tic, floating, and floating-leaved vege- 

 tation in shallow fresh water bodies. 

 It covered only 6,278 ha (15,452 acres) 

 in 1978 (Table 5) . 



Most of the fresh aquatic bed habi- 

 tat consists of floating vegetation, 

 usually water hyacinth ( Eichornia cras- 

 sipes ) or duckweed ( Lemna sp . , Spirodela 

 polyrhiza ) , which form dense mats on 

 sheltered water (Wicker 1980). The 



distribution of these mats frequently 

 changes in relation to physical factors, 

 such as wind direction, flooding, and 

 currents, and to biotic factors, such as 

 shading, competition, grazing, and human 

 eradication (Penfound and Earle 1948). 

 Floating aquatic plants die and sink 

 below the water surface every winter 

 (Wicker 1980). Flotant freshwater 

 marshes are included with the fresh 

 marsh habitat rather than with the fresh 

 aquatic bed habitat. 



Submerged aquatic plants include 

 widgeongrass ( Ruppia maritima ) , wild 

 celery ( Vallisneria americana ) , several 

 pondweeds ( Potomogeton spp.), and water- 

 milfoil ( Myriophyllum spp.). Light 

 often limits the distribution of sub- 

 merged aquatic flora. The Secchi disc 

 depth (a measurement of light penetra- 

 tion) of many large fresh water bodies 

 in the MDPR does not exceed 50 cm (20 

 inches) (Hopkinson and Day 1979). Tur- 

 bidity is thus too high to allow enough 

 light to reach the bottom to sustain 

 plant growth in most regions of these 

 lakes, which reach about two meters in 

 depth. 



Little is known about the animal 

 communities associated with submerged 

 freshwater aquatic flora in the MDPR. 

 Where it occurs, ducks feed on it and 

 fish, crustaceans, and insect larvae 

 live in it. 



FRESH MARSH (8) 



The fresh marshes in the MDPR can 

 be divided into two types: flotant and 

 emergent. It is uncertain exactly how 

 much area is covered by each group. The 

 total area of fresh marshes in the MDPR 

 in 1978 was about 165,000 ha (407,000 

 acres) (Figure 25), compared to about 

 364,000 ha (899,000 acres) in 1955 

 (Table 5). In 1978 fresh marsh com- 

 prised only 4.79 % of the MDPR, while in 

 1955 it made up 10.57 %, a very signif- 

 icant decline. 



Flotant mat is composed of an area 

 of active root production covered by de- 

 composing litter, floating on the sur- 

 face of the water. The marsh plants 



51 



