10 20 30 40 50 60 70 



Percent Mineral (Ash Percent of Oven Dry Weight) 



BO 



90 



100 



Figure 2. Relationship of bulk density and mineral percentage. 



natural plant communities in Louisiana marshes. Freshwater marsh ranges from 0.0 to 6.66 ppt 

 salt; intermediate marsh from 0.39 to 9.80 ppt salt; brackish marsh from 0.42 to 28.08 ppt salt; 

 and saltwater marsh from 0.62 to 51.88 ppt salt. In addition to containing more soluble salts, the 

 soils have a population of exchangeable cations that reflect the ionic composition of seawater. 

 Seawater has an approximate cation composition of 3.4% calcium, 17.6% magnesium, 77.4% 

 sodium, and 1.6% potassium. The anion composition is approximately 0.4% bicarbonate, 9.2% 

 sulfate, and 90.2% chloride. Soils influenced by seawater soon equilibrate to have higher 

 proportions of exchangeable sodium and magnesium than surrounding upland soils or soils in 

 freshwater marshes. The salinity of the soil solution in the surface layer remains essentially in 

 equilibrium with that of tidewater. Salinity of soil water varies because of variations in rainfall, 

 storm tides, evaporation, and other features. Researchers have found a wide range in salt content 

 in the soils of the coastal marshlands of Louisiana (Lytle and Driscoll 1970; Lytle 1971; Brupbacher 

 et al. 1973). Soil salinity classes based on the electrical conductivity of the saturation extract are 

 given below. 



The loss of surface elevation after a soil with organic or fluid layers is artificially drained is 

 termed subsidence (Stephens and Speir 1969). Subsidence of organic soils after drainage is 

 attributed mainly to shrinkage due to desiccation, consolidation by loss of the buoyant force of 

 ground water and by loading compaction, and biochemical oxidation. Elevation loss due to the 



63 



