SEDIMENTATION AND APPARENT SEA-LEVEL RISE AS FACTORS 

 AFFECTING LAND LOSS IN COASTAL LOUISIANA 



R.H. Baumann 

 R.D. DeLaune 



Center for Wetland Resources 



Louisiana State University 



Baton Rouge, LA 70803 



ABSTRACT 



RatHS of apparent sea-level rise and marsh aggradation were determined with the 

 aid of Cs dating, artificial marker horizons, and water level data for the lower 

 Barataria and Calcasieu estauries. These marshes are not vertically accreting at a rapid 

 enough rate to maintain their intertidal elevation and have been subjected to net 

 submergence since at least the mid-1950's. This has resulted in a conversion of marsh to 

 open water habitats. 



Rates of apparent sea-level rise at the two study areas were 1.2 and 1.3 cm/yr 

 from 1954 to present. Sedimentation rates through the same period were approximately 

 0.7 cm/yr over most of the area of investigation, though streamside marshes aggraded at 

 a rate of 1.35 cm/yr. The transformation of marsh to open water will be complete in a 

 few decades if present trends continue. A research strategy that will narrow 

 management alternatives is briefly outlined. 



INTRODUCTION 



The recognition of wetland loss as a problem in coastal Louisiana is widespread, the 

 consequences of wetland loss have been reasonably projected, and management agencies 

 and groups appear ready to commit resources towards resolution. Until the how and why 

 of wetland loss are understood, however, we will not know the most appropriate 

 mitigating procedures. The how and why are the processes of wetland loss. 



Wetland loss can be viewed as the inability of wetlands to maintain themselves. In 

 subsiding environments, such as coastal Louisiana, the continued existence of marsh is 

 partially dependent on its ability to maintain its elevation within the tidal range through 

 vertical accretion. This must be accomplished through some combinaton of peat 

 formation and mineral sediment accumulation. The two can be interrelated as the influx 

 of sediments also supplies nutrients for plant growth (DeLaune et al. 1979). Increased 

 plant growth results in more material available for peat formation and increases in stem 

 density result in an enhanced ability to further entrap and stabilize sediment (Gleason et 

 al. 1979). Thus, the process appears to have a synergistic effect and a reduction in 

 sediment supply can result in an exaggerated effect. 



