Pedogenesis on the Sefton Coastal Dunes, NW England

Abstract

This work examines the use of pedo-properties to identify dune soil system responses to environmental change on the Sefton coast, based on the development of conceptual pedogenic models. Previous environmental change and shoreline dynamics are determined through O.S. maps and aerial photographs, while present day processes are investigated through a dune-toe photographic survey and seasonal monitoring by fixed point photography. Topsoil (0-5 cm) physico-chemical characteristics are presented in a series of baseline GIS maps, displaying spatial pedo-property variation across the dune landscape. Combined with vegetation data, topsoil analysis identifies 10 distinct pedo-environments. Physico-chemical characteristics of associated National Soil Resources Institute (NSRI) soil profile classifications and an exposed stratigraphic section are presented graphically in a proposed sequence of development. Topsoil and soil profile samples are analysed for soil pH, soil organic matter (SOM) content, particle size, geochemical composition and mineral magnetism. Significant differences (p <0.05) are apparent for the suite of topsoil characteristics collated, indicating discrete dune environments are influenced by specific soil properties. Distinct down-profile variations in soil characteristics are also apparent between dune environments, highlighting pedological dynamism. Multivariate Factor analysis groups bare sand and mobile dune communities into ‘frontal dunes’ and fixed dune community, pasture, scrub, deciduous woodland and coniferous plantations into ‘hind dunes’, separating these topsoil environments from heath and slack communities. Factor analysis also identifies linkages between pedo-characteristics within soil profile horizons, suggesting pedogenesis on the Sefton dunes initiates as raw sand, progressing to sand-pararendzinas through leaching of nutrients. Desalinization and decalcification processes lead to brown earth development, followed by increased acidicification, subsequently, resulting in micro-podzol formation. Groundwater gley soils are associated with dune slacks, where drainage is inhibited and anaerobic conditions prevail. Analysis of buried soils suggests such pedo-environment formations are cyclic, responding to phases of shoreline regression/transgression, dune activity and stabilization. Conceptual models are designed to graphically demonstrate pedogenesis under both erosion and deposition regimes on the Sefton coast. Regression equations and correlation coefficients between pedo-properties and distance from mean high water are used as a proxy for soil age, which represent lateral soil maturity from the unstable frontal dunes to the stable hind dunes inland. The models simulate formation and process of the full array of soil properties, accounting for geomorphological impacts and anthropogenic influences. This has great implications for dune managers by raising awareness of pedogenesis as an integral part of nature and associated habitats, which could be incorporated in future shoreline management plans (SMPs).