marsh soil, the transition is from an 

 "A" horizon, where the organic matter 

 degraded into small particles and to 

 humus, right into a "C" horizon, where 

 the material has not been affected very 

 much by processes of soil formation. In 

 some sections of the country, the Soil 

 Conservation Service is mapping salt 

 marshes by soil types which will help 

 characterize soils in local situations. 

 If descriptions of the various soils 

 that occur in your area are available, 

 this can serve as a reference source to 

 indicate how far along the process of 

 soil formation is in a marsh. More com- 

 plete discussions of soils in general 

 may be found in Buol et al. (1973) and 

 Brady (1974). Salt marsh soils are less 

 thoroughly understood than upland soils, 

 but a literature is developing (Cotnoir 

 1974; Coultas and Calhoun 1976; Gallag- 

 her et al., 1977; Coultas 1978). 



The problems associated with the 

 development of salt marsh soils from ma- 

 rine sediments are in one of five cate- 

 gories: stability, acidity, moisture, 

 salinity, and nutrients. These can be 

 considered separately, although it is 

 clear they interact and depend to some 

 degree on one another. Without stability 

 the other factors do not matter. Salin- 

 ity may reduce soil structure and de- 

 crease stability. Similarly, high mois- 

 ture conditions may decrease stability 

 by increasing the flow characteristics 

 of the soil. Of concern is the ability 

 of the material to be confined until 

 such time that roots of the marsh plants 

 can add to substrate stability. Through 

 the Dredged Material Research Program, 

 the U.S. Army Engineer Waterways Experi- 

 ment Station in Vicksburg, Mississippi, 

 has produced a large amount of litera- 

 ture about techniques for protecting 

 dredged material from erosion and meth- 

 ods for stabilizing it. 



A second problem is acidity. The 

 Dutch recognized this problem in their 

 acid meadow soils called Katterklei, re- 

 ferred to as "cat clays" in this coun- 

 try. The extreme acidity, which may be 

 as low as pH 2, arises as the conse- 

 quence of a series of reactions begin- 

 ning with the accumulation of sulfides 

 which are produced by the reduction of 

 sulfates from seawater. The resulting 

 iron polysul fides in the sediments cause 



no acidity problems until the sediments 

 are exposed to oxygenated conditions 

 where iron sulfate and sulfuric acid are 

 formed. The acid yield depends on the 

 ratio of iron to sulfur, as well as the 

 total amount present. This cat clay sit- 

 uation arises in marsh creation sites 

 where the sediment is placed high in the 

 intertidal zone with the objective of 

 producing a transitional zone marsh (the 

 high marsh area which grades into up- 

 land). Effects of low pH on the plants 

 may be direct or indirect through its 

 influence on soil ion balance. Tied 

 closely to the cat clay problem is that 

 of soil moisture since the degree of 

 waterlogging determines the oxygenation 

 of the soils. 



The soil moisture situation in- 

 volves both the degree of saturation and 

 the periodicity of various moisture re- 

 gimes. The lower elevation salt marsh 

 soils are usually near saturation much 

 of the time. The anaerobic conditions, 

 coupled with salinity, play a major role 

 in the zonation seen in marshes. Much 

 effort has been directed toward under- 

 standing the environmental factors in- 

 volved in controlling the distribution 

 of salt marsh plants over the last 75 

 yr. A brief discussion of zonation in 

 wetlands can be found in Gallagher 

 (1977). 



Soil salinity is influenced by five 

 factors. The first is the salinity of 

 the estuarine water flooding the marsh. 

 The second factor is elevation relative 

 to the intertidal zone. Evapotranspira- 

 tion from the marsh results in water 

 loss and accumulation of salt. Low in 

 the intertidal zone where flooding is 

 frequent and soil water circulation rel- 

 atively great, soil salinity is similar 

 to that of the estuarine water. At 

 higher elevations in the marsh where 

 water circulation is reduced, salinities 

 are increased. Near the marsh fringe, 

 salinities again drop as the relative 

 influence of rainfall to salt water in- 

 creases. The third factor in determining 

 the soil salinities is the environmental 

 complex; temperature, pan evaporation, 

 and rainfall all interact to influence 

 water balance in the marsh. A fourth 

 factor is soil texture. Coarser textured 

 soils are generally more responsive to 

 flushing by rainfall and tidal waters. 



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