Pedogenesis and Hydromorphology of Soils in Mid-Atlantic Barrier Island Landscapes

Abstract

Barrier islands are an important and dynamic component of coastal ecosystems. While a number of studies have focused on the geomorphology, landform dynamics, vegetation patterns, and ecology of barrier islands, there has been relatively little attention paid to the soils, which are an important ecosystem component. The goal of this study was to improve our understanding of the processes and factors influencing soil development on Mid-Atlantic barrier islands. The study was conducted at Assateague Island National Seashore, a barrier island located on the eastern coast of Maryland and Virginia. Study sites ranged in relative surface stability (soil age) and topography, allowing for comparison of the influence of time and soil moisture on pedogenic processes. Soil development was limited because of the young age of the soils and weathering resistant parent material. Evidence of pedogenesis was reflected primarily in accumulations of organic matter and formation of A and O horizons. Carbon accumulation was controlled by the magnitude of carbon inputs (plant biomass), which increased with soil age and wetness, and by decomposition, which was regulated by soil saturation and anaerobiosis. On a global scale, average soil carbon stocks in these soils tend to be low, due to their young age and the environmental stresses faced by plants in these environments (which limits organic inputs). However, relatively high total carbon stocks were documented on the older, forested parts of the island. Soil wetness also affected the development of subsoil horizons. Weak Bw horizons, with brighter chromas and redder hues, were described in relatively well drained, oxidized soils due to slight accumulations of iron (hydro)oxides and organic matter. In poorly and very poorly drained soils iron was reduced, precluding the formation of Bw horizons. Reduced subsoil horizons had low chroma matrix colors. Despite meeting the requirements for hydric soils, many of the wet barrier island soils do not have morphologies typical of hydric soils. Nevertheless, the low chroma colors and organic accumulations at the surface (Oa horizon) proved to be a reliable indicator of soil wetness and became the basis for a proposed set of hydric soil field indicators for Mid-Atlantic barrier islands.