The use of δ 13C signature of C-3 and C-4 plants in determining past depositional environments in rapidly accreting marshes of the Mississippi River deltaic plain, Louisiana, U.S.A.

Abstract

The stable carbon isotope compositions of vegetation and soils of marshes of Louisiana's Barataria Basin were determined. The δ 13C-values of organic soils taken from fresh, intermediate, brackish and salt marshes are similar to the δ 13C-value of its vegetation. The δ 13C of a sediment profile taken from a salt marsh in a rapidly subsiding distributary of the Lafourche delta, an older distributary of the Mississippi River, showed that the δ 13C signature of buried peats represents original organic sources (e.g., fresh marsh plant species). The δ 13C signature at depth representing a C-3 plant-dominated freshwater environment corresponded to reported depositional reconstruction using paleo-environmental techniques. Vertical accretion rates determined by 137Cs dating support historical and measured δ 13C-values in the profiles corresponding to earlier freshwater environments.