Geotechnical Characterization of a Saline Wetland with Implications Towards Quantifying Peat Collapse

Abstract:

To date, a lack of field data exists on the shear strength of salt marshes and collapsed interior ponds, limiting our understanding of how the marsh loses structural integrity as it converts from vegetated marsh to open water. In this study, we use cone penetrometer data collected along a chronosequence of marsh collapse in a Spartina alterniflora-dominated salt marsh in Louisiana, USA, along the Northern Gulf of Mexico. The objectives of the study were to (1) quantify how the sediment shear strength changes as a healthy vegetated salt marsh converts to open water; (2) quantify how soil shear strength varies over time in a ponded state; and (3) identify stratigraphic features of these ultra-soft wetland soils using cone penetrometer data, which can indicate wetland collapse. Sediment cores were taken simultaneously with cone penetrometer measurements to characterize changes in the shear strength and the structural integrity of the marsh soil. We observed correlations among the geotechnical data and changes in sediment layer thickness following marsh collapse, and discuss the implications of pore-space collapse in the soil column on the ability of coastal wetlands to keep pace with relative sea-level rise.