SOILS OF LOUISIANA'S COASTAL MARSH 



Kenneth Murphy 



U.S. Department of Agriculture 



Soil Conservation Service 



Crowley, LA 70526 



ABSTRACT 



The vast and unique coastal area of Louisiana was formed through thousands of years of 

 geological change which included sea-level changes, subsidence, and sediment deposition. The 1.3 

 million ha area of coastal marsh is a very delicate ecosystem composed of two slightly different 

 areas: the Deltaic marsh of southeast Louisiana and the Chenier marsh located along the southwest 

 coastline of the State. 



All of Louisiana's coastal marsh soils have the common characteristics of wetness, flooding, low 

 elevation, and low relief. They vary widely in many other characteristics, however, that are 

 important to their use and management. Unfortunately, these characteristics are not evident from 

 surface features or vegetation and require soil borings and examination to determine their nature. 

 Soil surveys made by the Soil Conservation Service, U.S. Department of Agriculture, in cooperation 

 with the Louisiana Agricultural Experiment Station are based upon subsurface examinations and 

 can provide much vital information for land-use decisions on these fragile soils in the coastal marsh. 



INTRODUCTION 



The Louisiana Coastal Region encompasses an area of nearly 3.2 million ha. About one-half 

 of this is water, one-third is natural marsh, and the remainder is beaches, cheniers, spoil deposits, 

 and artificially drained marshes. Some 40% of the coastal marshes in the continental United States 

 are located along Louisiana's Gulf of Mexico coastline. 



The coastal region has been divided into two segments on the basis of origin and physiography. 

 The area east of Vermilion Bay and occupying two-thirds of the coastal region has been designated 

 as the Deltaic Plain. The Deltaic Plain is the site of the various delta systems. The area west of 

 Vermilion Bay has been named the Chenier Plain and was formed from river sediment swept 

 westward by long shore currents in the Gulf of Mexico (Coleman 1966). 



The coastal marshes are a product of the Mississippi River. During the Recent Epoch, seven 

 Mississippi River Delta systems have developed because of diversions in the river channel. The 

 large number of deltas has caused considerable variation in the physiography of the area. During 

 coastal development, prairie formation deposits of Pleistocene age were overlain with a wedge of 

 recent sediment primarily from the Mississippi River (Kniffen 1968). The developmental process 

 of the Chenier Plain was considerably different from that of the Deltaic Plain. Silt and clay 

 sediment from the Mississippi River was carried westward by currents in the Gulf of Mexico and 

 gradually accumulated as mud flats against the shoreline. The amount of material carried and the 

 duration of flow determined the extent of the buildup. The mud flats soon became occupied by 

 salt-tolerant vegetation and new marsh was thus created (Coleman 1966). 



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