SALT MARSH SOIL DEVELOPMENT 



John L. Gallagher 



College of Marine Studies 

 University of Delaware 

 Lewes, Delaware 19958 



Salt marsh creation may be consid- 

 ered to be basically a problem of devel- 

 oping salt marsh soils from marine sedi- 

 ments. First, it must be decided what a 

 marsh soil is and how it develops. Sec- 

 ond, must be determined what character- 

 istics of the original sediment (i.e., 

 dredged material) are especially impor- 

 tant in enabling us to predict whether 

 it might be easily transformed into a 

 salt marsh soil. Third, the natural 

 system to select plants which may facil- 

 itate the desired changes in the sub- 

 strate must be examined. 



The concept of soil depends on the 

 viewpoint of the investigator. Since 

 our concern is in creating coastal eco- 

 systems and a major step is getting 

 vegetation to grow on the substrates, 

 our viewpoint is edaphical. Sediments 

 from which natural marshes develop are 

 tidally deposited resulting in rather 

 uniform grain size fractionation. Dredg- 

 ing is the usual method of deposition of 

 sediments for marshes created artifical- 

 ly on the coast. This technique leads 

 to complex and variable parent material, 

 making the establishment of proper con- 

 ditions for plant growth difficult. Re- 

 gardless of the method of deposition, 

 the objective is to duplicate the nat- 

 ural anatomy of soil which takes the 

 form of a profile changing with depth. 

 Numerous soil formation processes (Table 

 1) interact to develop the anatomy which 

 reflects both the parent material and 

 the environment. 



The original variable mixture of 

 minerals will have organic matter added 

 by plant, animal, and microbial activity 

 (humification). In some cases, dredged 

 material will already be rich in organic 

 material. The amount of air and water 

 in the soil will depend on sediment 

 grain size, elevation relative to the 

 tides, and soil structure. Depending on 

 the salinity of the tidal water and fre- 

 quency of inundation, salinization may 



be a major process in determining the 

 final nature of the soil. Structure is 

 often minimal in marsh soils because of 

 sodium saturation of the cation exchange 

 capacity. These puddled conditions re- 

 duce drainage, resulting in even more 

 poorly drained soils than occur at simi- 

 lar nonsaline sites. Anaerobiosis in 

 the waterlogged soils results in gleiza- 

 tion. 



Soils are classified by a method 

 similar to the classification of plants 

 and animals, (i.e., orders, suborders, 

 great groups, subgroups, families, and 

 series). From profile descriptions, the 

 taxonomic position of the soil may be 

 determined. Most marsh soils fall into 

 one of two orders. Those which are pri- 

 marily organic are Histosols. In the 

 coastal areas where sulfates from sea- 

 water are reduced to sulfides, the soils 

 are called Sulfihemists. The other order 

 of soils represented in the marsh are 

 the Entisols (recently formed mineral 

 soils). Within that group, the Sulfa- 

 quents are common salt marsh soils. The 

 description in Table 2 of the Capers 

 Series is typical of many marsh soils 

 along the southeast Atlantic coast of 

 the U.S. Table 3 contains a description 

 of a typical marsh soil from a sandy 

 Georgia marsh. There is no "0" horizon 

 of partially decayed organic matter in 

 many southern marshes. The combination 

 of tidal flushing and rapid litter turn- 

 over interacts to reduce organic matter 

 accumulation in the most hydrological ly 

 active marshes. 



An "0" horizon at the top is much 

 more common in the northern latitudes, 

 e.g., in Maine, and along the Pacific 

 Northwest coast. These organic layers 

 develop where decay is not as rapid as 

 it is in the south. There is a series 

 of other horizons, A, B, and C, which 

 are basically mineral horizons. "B" ho- 

 rizons are not frequently seen in salt 

 marsh soils. Usually in southern salt 



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