rates average about 1.4 cm/yr, while 

 accretion in inland marshes is lower, 

 about 0.75 cm/yr. Table 9 shows the 

 deposition rate of certain soil components 

 as given by Hatton (1981). Mineral 

 deposition, which is directly proportional 

 to bulk density, is much faster in salt 

 than in fresh marshes. Even though the 

 fresh marshes are much more organic than 

 the saline marshes, the rate of deposition 

 of organic carbon is no faster in these 

 marshes. It only appears to be because 

 the organic material deposited is not 

 "diluted" by as much mineral matter. 



Salt 



One component of the mineral sediment 

 is salt. Despite the earlier discussion 

 of discrete marsh vegetation zones, the 

 salt gradient is horizontally stratified. 

 Rather, sediment salinity decreases 

 gradually from the coast inland (Figure 

 33). There does not seem to be much of a 

 gradient from the edge of a stream into 

 the marsh interior. In many marshes 

 salinity actually increases 

 elevation increases, and the 

 infrequently flooded soils 

 because evaporation exceeds 

 in these delta marshes this 

 does not occur. In fact, impounded marshes 

 typically become less saline as surplus 

 rain gradually leaches out the sediment 

 sal ts. 



Table 8. Accretion rates (mm/yr) in 

 Louisiana delta marshes, based on the 

 1963 ^''Cs fallout peak (S=streamside, 

 I=inland; Hatton 1981). 



elsewhere, 

 inland as 

 salts in 

 accumulate 

 rain. But 



o 



I. 



V) 



3 



a. 



Vt 



o 



OJ 



o 



o 



.o 



S- 

 (0 



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o 



00 



c 

 c o 



* Number of cores represented. 



3. CM *:}■ 



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35 



