Sedimentation patterns in a gulf coast backbarrier marsh: Response to increasing submergence

The rate of vertical accretion was determined on two backbarrier marshes in the Mississippi River Plain, using ¹³⁷Cs dating techniques. An average accretion rate of 0-55 cm yr^?1 was found on Grande Terre, and 0.78 cm yr^?1 on Grand Isle. Analysis of mineral organic content of the marsh profile shows that the backbarrier marshes accrete through (1) accumulation of low density organic matter, and (2) episodic deposition of high density mineral sediment probably associated with major hurricanes or storm events. The rates of vertical accretion were two to three times less than the rate of submergence due primarily to rapid subsidence in the deltaic plain, and imply that these backbarrier marshes will progressively deteriorate.