fonii is present year round. Free ammoniuin 

 is the only forn of inorganic nitrogen 

 available to plants in these reduced 

 soils. In streamside marshes it is 

 naintained at a low level of 1 - 2 pg/ml 

 by plant uptake during the spring and 

 suiii'iier, building up in the fall when plant 

 growth tapers off. 



Epiphytic Algae 



Where emergent grasses and algae grow 

 together the grass is probably nearly 

 always the dominant producer. Certainly 



it develops the largest biomass, but this 

 is not a good criterion for comparison 

 because the turnover rate of algae is much 

 faster than that of grass. In a study in 

 which the carbon dioxide uptake of both of 

 these groups was measured simultaneously 

 (Gosselink et al. 1977), the algal 

 community was responsible for only 4-11 

 percent of the photosynthesis but 61 - 76 

 percent of the total respiration (Table 

 18). It has not been possible to separate 

 out from the plants the respiratory 

 associated with the active 

 - bacteria, fungi, protozoans, 

 invertebrates - found in this 



activi ty 

 consumers 

 and other 

 communi ty . 



Stowe (1972) found that only along 

 the edges of the marsh where adequate 

 light penetrated did photosynthesis exceed 

 respiration (Figure 50). He estimated 

 that net carbon (C) fixation amounted to 

 about 60 g C/m^ annually at the water's 

 edge, compared to -18 g C/m^ inland. The 

 inland community was consuming more 

 organic carbon than it produced. Nearly 

 all of the photosynthetic activity was 

 associated with organisms growing on the 

 base of S_. al terniflora culms rather than 

 on the sediment surface. 



Filamentous algal production was 

 dominated by the genera Enteromorpha and 

 Ectocarpus in the winter and Bostrichia 

 and Polysiphonia in the summer. The 

 diatom community was also abundant; the 

 cells clustered on the intertidal portion 

 of the culms, decreasing in concentration 

 upward into the drier environment (Figure 

 51). Although quantitatively the algal 

 community appears to be rather 

 insignificant, the cells are much higher 



Table 18. Percentage of marsh community 

 metabolism by Spartina al terniflora 

 (Gosselink et al . 1977), 



December March May 

 1975 1976 1976 



Figure 49. Seasonal changes in various 

 physical, chemical, and biotic factors in 

 a Barataria basin salt marsh. 



Gross photosynthes 89± 6 92±6 96+3 



Respiration 36±11 36±5 24±9 



Mean±standard deviation. 



54 



