marsh. These changes decrease the suitability of the area as habitat 

 for species such as alligator that prefer wetter conditions. 



The increase in water depth in the borrow channel converts the 

 ditched area from a brackish marsh to a channel or canal. Within 

 the ditched area, phytoplankton may increase (Corliss and Trent, 

 1971) while marsh vegetation is eliminated. The net primary produc- 

 tion per unit area of the phytoplankton may increase. However, when 

 compared to the overall production of the original marsh, the net 

 primary production in the ditch is lower (Darnell, 1976). 



Increases or decreases in consumers are difficult to predict since 

 many of the organisms can use organic material from various marsh 

 sources. Bourn and Cottam (1950) and Adkins and Bowman (1976) have 

 shown increases and decreases in various species, though Trent 

 et al. (1972) noted a general decrease in consumer biomass when 

 comparing residential canals and tidal creeks. Shifts in relative 

 species abundance as well as changes in absolute numbers have been 

 noted by Dale (1975) for channelized streams, and by Lindall et al. 

 (1973) and Adkins and Bowman (1976) for canals. 



Consumers associated with phytoplankton might be expected to increase 

 relative to other consumers. Deeper areas furnished by the ditches 

 may be favorable habitat for alligator and wading birds depending 

 upon the food and cover provided. However the area! extent of this 

 aquatic habitat is smaller than the decrease in brackish marsh 

 resulting from levee and ditch construction. The productivity of 

 the ditched area does not compensate for the loss of marsh. 



The change in duration of standing water and increase in frequency 

 of emergence will allow better gaseous exchange between the atmos- 

 phere and the soil. This, plus the increase in soil salinity, will 

 give a competitive advantage to marshhay cordgrass over most of the 

 other marsh plants. The other major plant group, consisting of 

 rushes and sedges, is particularly significant as food for waterfowl 

 and furbearers. The decline in abundance of this plant group would 

 decrease the suitability of the area as habitat for these consumers. 

 Predators such as the red wolf that depend upon furbearers for food 

 might be adversely affected, though the increased cover from marsh- 

 hay cordgrass and the availability of other food items might 

 compensate. 



Both' major emergent plant groups provide cover and food materials 

 for the small mammals and insects that are prey for predators and 

 raptors as well as wading and shorebirds. Decreases in one plant 

 group are roughly requited by increases in the other group. There- 

 fore, the effects on most other consumers in the influenced area are 

 minor. 



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