Influences of Hurricanes, Floods, and Organic Production on River‐Delta Evolution

The modern Mississippi River Delta plain has been largely disconnected from the main distributary by a highly engineered system of levees and floodways. This vast and fragile landscape is experiencing land-loss and is increasingly susceptible to inundation. Intense debate exists in the scientific community as to whether direct fluvial or hurricane-driven re-suspension and sedimentation are the present dominant sources of mineral sediment to the wetland surfaces of the modern delta complex. The relative importance of these sources remains a matter of public discussion and scientific debate, and this lack of clarity strongly influences development of tools, strategies, and policies to conserve coastal Mississippi River Delta lands.

Research fueling this debate has been restricted both spatially and temporally thus far. Furthermore, the contribution of organic production is unknown at these scales. A comprehensive study of the Lafourche and Plaquemine-Balize Mississippi River Delta complexes at a temporal scale similar to that of natural deltaic cycles (10² - 10³years) is being completed to address the deficiencies in our current understanding. A suite of 38 5m vibracores and 33 co-located 1m piston cores are being analyzed at moderate- to high- resolution for bulk density, grain-size, organic matter, magnetic susceptibility, and X-ray fluorescence to create the recognition criteria necessary to distinguish sedimentary sources for this time period.

²¹⁰Pb and ¹³⁷Cs data show that despite rapid subsidence and sea-level rise, many studied wetlands are still able to maintain their elevations. Sedimentary accumulation rates in the subaerial components of the Lafourche complex would seem to indicate that following distributary abandonment/cutoff and the elimination of pre-levee and overbank flooding and crevasse sediments, resuspension by cold fronts and hurricanes has become the primary sediment source for affected wetlands.