Physical Properties of Natural Organic Soils in Carolina Bays of the Southeastern United States

Abstract

Hydrologic models are useful tools for designing wetland restoration projects, but they are difficult to use for sites with natural organic soils because few soil property data are available for these soils. The objective of this study was to measure the physical properties of organic soils needed to calibrate hydrologic models of three natural Carolina Bay wetlands in the southeastern USA. Undisturbed soil cores were collected at each site for laboratory measurement of saturated hydraulic conductivity, soil water characteristic curves, bulk density, particle density, and total porosity. Field measurements of saturated hydraulic conductivity were also made. The Oi, Oe, and Oa horizons in the natural organic soils had similar bulk densities (0.16 g cm -3 ), total porosities (0.90 cm 3 cm -3 ), and particle densities (1.50 g cm -3 ). However, field-measured saturated hydraulic conductivities decreased as the level of decomposition increased, going from 45 to 7.1 to 1.5 cm h -1 for the Oi, Oe, and Oa horizons, respectively. Soil water characteristic data revealed an abundance of large pores (>0.3 mm) in the Oi horizons, which likely explains their high saturated hydraulic conductivity relative to the Oe and Oa horizons, which had fewer large pores. Using the data collected in this study, mathematical relationships were developed to predict the total porosity and the saturated hydraulic conductivity of these organic soils based on more easily obtainable data, such as bulk density and the organic horizon type.