The Role of Storms In the Dynamics of Deltaic Coastal Wetlands

Storm impacts are a natural feature of coastal wetland dynamics in Louisiana. Conceptual models of coastal landscape development during the Holocene, including the Penland model for barrier island development, include gradual wetland loss as a key component. Previously, a three-stage model for wetland loss was proposed based on a changing balance between organic and inorganic contributions to wetland soil development. Observations and measurements of coastal wetland response post-Katrina show how the mineral contributions to soil development influence vulnerability of interior marshes to disturbance by storms. These observations build on those from previous storms and have been used, together with studies from other researchers, to develop a revised conceptual model of coastal wetland sustainability incorporating marsh edge erosion, marsh surface sedimentation, and interior marsh loss.

Marsh edge erosion has been documented by Penland and co-workers as a significant contribution to overall land loss. The gradual expansion of coastal bays is critical to the development of barrier islands and also allows for positive feedbacks between increasing fetch length and wave erosion. The role that the size and location of open bays plays in storm surge dynamics has been the subject of study since Hurricane Katrina. In the conceptual model, increased surge and wave activity over the marsh disturbs the surface only if the soil is dominantly organic. Otherwise, there is a net contribution of mineral sediment, aiding vertical sustainability.