Soil properties on sub-Antarctic Macquarie Island: Fundamental indicators of ecosystem function and potential change

Abstract

We examined the nature and properties of soils on Australian sub-Antarctic Macquarie Island to determine key environmental factors driving their distribution, development and change. We provide the first classification of these soils using Australian and international (WRB) systems while combining elemental, stable and radio-isotope analysis to interpret processes of soil formation and key controlling environmental factors. Soil organic carbon (SOC) and total nitrogen (TN) concentrations across the island were influenced largely by elevation and topographic position with coastal soils and wetter depressions containing more SOC and TN compared with drier and higher elevation locations. Soils on the high, exposed plateau of the island contained low SOC and TN concentrations by comparison. Results suggested that soils of the coastal zone are subject to ongoing aggradation with significant inputs of nutrient, particularly extractable P (Ext P), from oceanic and especially avifauna sources. Nutrient subsidy was concentrated on coastal margins and the more sheltered eastern side of the island, diminishing significantly with increasing elevation and distance from the coast. Soils of the central plateau contained very low Ext P concentrations throughout the profile and appear to be relic if not degrading. Further comprehensive soil mapping, classification and monitoring across Macquarie Island will elucidate the important role that soils serve for healthy ecosystem function in these sub-Antarctic environments and provide early warning indicators of significant environmental change.