The Soil Physical and Chemical Properties of Restored and Natural Back-Barrier Salt Marsh on Isles Dernieres, Louisiana

Abstract

Isles Dernieres is a transgressive barrier island arc in southeast Louisiana associated with the Bayou Grand Caillou headland of the Lafourche delta complex, which was abandoned 600 to 800 years ago. During the past two decades Trinity and Whiskey Islands have been eroding at rates of >18 m/y, and East Island has been eroding at a rate of 11.8 m/y. The Isles Dernieres Barrier Island Stabilization Project, implemented in 1998, dredged material from various sites in the bay behind the barriers for dune and marsh restoration of East, Trinity, and Whiskey Islands. The 1998 restoration increased the overall height and width of the islands but marsh habitat has not developed on the restored material behind the barriers. This study characterizes the physical and chemical properties of soil from restored and natural back-barrier salt marsh on Isles Dernieres to determine the restoration timeframe in which restored marsh soils develop to conditions more similar to natural marsh soils. Additionally, the goal is to identify the soil properties in restored marsh that could be modified to enhance back-barrier marsh habitat.Laboratory analyses of 60 cores from four different vegetation density classes in restored marsh and nine cores from natural marshes included bulk density, soil moisture content, grain size, sorting, pH, conductivity, total carbon, and total nitrogen. Vegetation density in restored marshes had no significant effect on soil properties, with the exception of bulk density. Marsh type had a significant effect on all measured soil properties. Variations in the soil properties of restored and natural back-barrier salt marsh are primarily the result of differences in soil texture and elevation.