tailed grackle (Quiscalus mexicanus ) and 

 the red-winged blackbird ( Agel aius 

 phoeni ceus ) are the most numerous of the 

 other marsh birds. The latter two 

 species, especially, are abundant during 

 the spring breeding season. They are 

 migratory and are absent during the 

 winter. Northern harriers are also seen 

 frequently in all marsh environments. 



Some of these species are endangered 

 or rare (Table 28). The beautiful brown 

 pelican, in particular, has been almost 

 lost from the delta (King et al . 1977). 

 It has been reintroduced from Florida and 

 is found in two nesting colonies on man- 

 groves on Queen Bess Island in Barataria 

 Bay and North Island just west of the 

 Chandeleur Island chain. 



Carbon Budget 



One v/ay of summarizing quantitatively 

 the productivity and trophic relations 

 discussed is with a C budget. Most C 

 budgets are primarily input-output budgets 

 that treat the ecosystem under study as a 

 black box so that internal details of the 

 trophic structure are ignored, and metabo- 

 lism of all consumers is lumped as commu- 

 nity respiration. In particular, higher 

 consumers contribute little to community 

 respiration and are usually ignored. Both 

 Day et al. (1973) and Costanza et al . 

 (1983) are exceptions to this generaliza- 

 tion; they calculated metabolic rates for 



Table 28. Birds of the Mississippi 

 Deltaic Plain on the Audubon Society "Blue 

 List," indicating that their populations 

 are declining (Mabie 1976). 



Brown Pel ican (Pelecanus occidental is ) 

 American White Pel ican (P. erythrorhynchos ) 

 Reddish Egret (Egretta rufescens ) 

 White- faced Ibis (PI egad is chihi ) 

 White Ibis (Eudocimus albusl 

 Black-crowned Night Heron (Nycticorax 



nycticorax ) 

 Red-shouldered Hawk (Buteo 1 ineatus ) 

 Northern Harrier (Circus cyaneus ) 

 Osprey (Pandion hal iaetusT 

 Bl ac k vul ture (Coragyps atratus ) 

 Loggerhead Shrike (Lanius ludovicianus ) 



Endangered species, 



a number of consumer groups. However, I 

 will consider the overall input-output 

 budget without this detail. Unfortunately, 

 several key flows in the budget are still 

 not quantified. As a result, any carbon 

 balance inust be considered tentative even 

 today. 



Day et al . (1973) published the first 

 budget for a delta salt marsh. It was 

 based almost entirely on aboveground 

 primary production, benthic commmunity 

 respiration, and calculated energy flow 

 through the abundant consumers. Loss to 

 deep sediments was assumed to come from 

 root production, and both were ignored in 

 the balance. These authors concluded that 

 50 percent of net production was exported 

 from the marsh. It has not been possible 

 to measure this organic export directly. 



Happ et al . (1977) calculated the 

 export of total organic carbon (TOC) from 

 the Barataria estuary to the nearshore 

 gulf from the gradient of decreasing TOC 

 across the passes and an estimate of the 

 turnover rate of bay water. They 

 estimated that the export of TOC was about 

 150 g/m^/yr. Since aquatic primary 

 production and community respiration in 

 the bay appear to be about equal (Allen 

 1975), this export from the estuary must 

 reflect marsh export. It amounted to 

 about one-half of the Day et al. estimate. 



Hopkinson et al . published additional 

 salt marsh respiration data in 1978. 

 Since then Smith et al . (1982) published 

 an incomplete carbon budget for the same 

 area which includes estimates of methane 

 evolution and new data on CO2 

 evolution. I have attempted to create a 

 new budget from all this information and 

 some direct carbon dioxide flux 

 measurements of photosynthesis that 

 include root production (Gosselink et al . 

 1977). The weakest links in all these 

 budgets are the paucity of root production 

 infonnation and our inability to measure 

 marsh export directly. 



Figure 51 shows measurements of CO2 

 flux through a S_. al terni flora stand at 

 different seasons. The cuvette used to 

 collect these data enclosed 0.07 m^ of 

 marsh, including sediment and aboveground 

 vegetation, so the data should represent 

 the whole community. Notice that nearly 



71 



