adequate for Louisiana's coastal marsFies because of either recognizability (color) or 

 density (sinkage) problems. White clay (Feldspar 26 1 -F) is one substance that is easily 

 recognizable from marsh sediments and is not subject to sinkage provided the organic 

 content of the marsh soil is less than 30% on a dry weight basis (Baumann 1980). In 

 Louisiana, this generally restricts its use to saline and brackish marshes. 



I "^7 

 The combination of the ' "^ Cs and artificial marker techniques provides more 



information than either technique alone can produce. The results of the two techniques 



can be compared, thereby providing an additional check on method reliability. The two 



techniques are compatible as some of the disadvantages of one technique are the 



advantages of the other. Artificial markers do not provide information on the past 



whereas Cs does. Artificial markers provide information on variability of 



sedimentation rates through time, whereas Cs is generally limited to providing 



average sedimentation rate information. Artificial markers can be sampled at any time 



interval desired, therefore one can obtain data on possible seasonal trends, the role of 



storms, etc. This frequency of sampling freedom allows one to examine processes of 



sedimentation more fully, but the disadvantage is that one must wait for sedimentation 



to occur. 



Sea-level rise was calculated by linear regression analysis of tide gauge data 

 available from the U.S. Army Corps of Engineers, New Orleans District. 



Land loss rates for the Barataria site were extracted from Adams et al. (1978) and 

 rates for the Calcasieu site were mapped and measured from available aerial photographs 

 using the methods described by Adams et al. (1978). 



RESULTS AND DISCUSSION 



Barataria Site 



1 37 



Cs analysis showed that marshes bordering water bodies such as lakes, bayous, 



and ponds were aggrading (vertically accreting) at a rate of 1.35 cm/yr whereas marshes 



more distant from water bodies were aggrading at a rate of 0.75 cm/yr (DeLaune et al. 



1978). These two types of marshes are commonly referred to as streamside and inland 



marshes, respectively. The difference in sedimentation rates are to be expected as 



streamside marshes are closer to the source of sediments. This situation is analogous to 



the levee and backswamp situation bordering many of the rivers and bayous of Louisiana 



except the scale of elevation and sedimentation rate differences are much less in the salt 



marshes. Density and organic carbon analysis of the core samples revealed that 



aggradation occurs by both plant detritus and mineral sediment accumulation (DeLaune 



et al. 1978). 



Aggradation of the salt marsh as measured by artificial marker horizons from 1975 

 to 1979 was 1.5 cm ± 0.4 and 0.9 cm ± 0.2 for streamside and inland marshes, 

 respectively (Baumann 1980). The slightly higher values resulting from the artificial 

 marker horizon method could be due to the different time interval of sampling (5 versus 

 25 years), less compaction due to the shorter time interval or other unidentified 

 reasons. Considering the natural variability in the environment, the difference in results 

 between the two methods is quite small. 



