WHAT IS THE AEOLIAN COMPONENT OF BACKBARRIER MARSH SEDIMENTATION?

A saltmarsh depends on compensatory rates of organic and inorganic sedimentation to maintain elevation with respect to relative sea-level rise. A better understanding of saltmarsh inorganic sediment sources, which are commonly modified by anthropogenic activities (watershed management, development, dredging, etc.), increases our ability to sustain marshes through better coastal management and to make future predictions of saltmarsh density and distribution more accurate through better model parameterization. Fringing backbarrier marshes, located away from river systems, receive inorganic sediment from the estuary, eroding shorelines, and the barrier island. The frequency of island overwash is commonly assumed to be the main factor regulating the flux of sand to backbarrier marshes. In comparison to overwash, aeolian transport of sand across a barrier has received little attention in saltmarsh research, but this process could be important for marsh accretion. The contribution of aeolian sand to backbarrier marshes is examined here with marsh cores and measurements of wind-blown sediment transport across transgressive and regressive parts of a barrier island. Backbarrier marshes fronted by a wide washover fan or a high-elevation dune ridge are supplied with aeolian sand that significantly contributed to vertical accretion, especially near the marsh edge. The percent volume of the marsh originating from aeolian sand, based on the upper 1 cm of marsh sediment, decreases by an order of magnitude only ~20 m from the marsh edge. Sandy beds at depth in the marsh are composed of aeolian sand and were sampled in every marsh core. Sand beds were likely emplaced over time after storms deposited a sandy washover fan near the marsh and/or reduced vegetation cover across the island. Sand beds preserved within backbarrier marsh deposits are commonly thought to have been emplaced rapidly during a past storm; however, post-storm aeolian transport should also be considered as an important mechanism for emplacing sand beds over a longer period of time within saltmarsh strata. The contribution of aeolian sand to backbarrier marsh accretion should only increase as sea level continues to rise causing many barrier islands to narrow and making shorter transport distances between the dune and marsh.