Identification and soil characteristics of coastal terraces along the northern coast of the Gulf of Mexico.

Delineation of relict marine terraces along the Northwest Florida coast facilitated investigation of soil development within the Gulf of Mexico (GOM) coastal plain. Previous research in the region that defined coastal terraces primarily relied on topographic studies with little consensus on the number and extent of terraces. Research investigating soil development within the GOM coastal plain is also limited. Our study utilized GIS and a LiDAR-derived Digital Elevation Model (DEM) to apply a Surface Classification Model (SCM) for selection of terrace surfaces based on slope and surface roughness. Hypsographic analyses of the SCM output identified potential terrace surfaces but visual interpretation along transects across the surfaces was necessary to refine the bounding terrace elevations. Five terraces were defined. Soil properties known to exhibit time related trends were analyzed across the delineated terraces. At increasing elevations, and presumably increasing ages, soils exhibited a thickening of both the solum and Bt horizon, an increase in clay content, and a decrease in organic matter content. The lowest terrace had the greatest solum thickness due to the presence of thick Histic epipedons and thick Spodic horizons. Bt horizons were observed at increasingly greater depths, with the exception of the highest terrace, where it was at a shallower depth. This is likely due to advanced erosion associated with the older age of the terrace and the higher elevation and greater exposure of the surface. This study demonstrates that GIS and LiDAR-derived DEMs are valuable tools to systematically and semi-automatically map marine terraces on a regional scale.