found in fresh marshes (Table 11). Cal- 

 cium is tightly bound to organic material. 

 (However, on a volumetric basis neither Ca 

 nor organic content shows a wide range of 

 values, and as a result the statistical 

 association is not strong). Nitrogen 

 distribution is similarly affected. It is 

 relatively constant in organic material 

 (C:N = 16.5; Chabreck 1972), and most of 

 the N in the sediment is tied up in organ- 

 ic form. 



Sulfate distribution is interesting 

 because the major source is presumably 

 seawater, but the concentration in marsh 

 sediments is as much as four times that 

 expected from the sulfate:chloride ratio 

 in seawater. However, the biochemistry of 

 sulfur (S) in anaerobic soils is complex; 

 sulfates are reduced to insoluble sulfides 

 that can accumulate in the soil and later 

 be re-oxidized to sulfate. 



Summarizing, the distribution of 

 nutrient elements in the delta marsh zones 

 (Figure 34) is understandable in light of 

 the source of each and its soil chemistry. 

 The ions Na , K, and Mg, associated with 

 sea water, decrease from salt to fresh 

 marshes as salinity decreases. Phosphorus 

 also decreases, but for a different 

 reason; it is carried into the marsh with 

 sediment and sedimentation rates decrease 

 inland. Calcium increases inland since it 

 is derived mostly from upland runoff. 

 Nitrogen is fairly constant across the 

 marshes since it is closely associated 

 with organic matter. 



Vegetation 



I have discussed the physical and 

 chemical traits of the vegetation zones in 

 delta marshes in some detail. It is time 

 now to consider the vegetation itself. 

 Based on a classification from early 

 studies by Penfound and Hathaway (1938), 

 Chabreck surveyed and classified the 

 Louisiana marshes in 1968 and 1978. I 



S 2.5V 



.'Aa) 



2- 



z 

 o 



; 1-5 



c 

 ►- 

 z 

 111 

 u 



I ' 



o 



.5- 



im 



S B I F SB I F 

 Na MG 



S B I F 

 K 



S B I F 

 Ca 



SB I F 



P 



S B I F 

 N 



Figure 34. Concentrations of available 

 Na, Ca, K, Mg, P, and N in different marsh 

 zones (Rainey 1979) . 



Table 11. The ratio of the major cations to the chloride ion in 

 nomal seawater and in the saline, brackish, intermediate, and 

 fresh marshes of Louisiana (Rainey 1979). 



From Riley and Chester (1971), 



37 



