Development of Acid Sulfate Soil Transformation Models to Manage Disturbed Freshwater Wetlands on Norfolk Island

Abstract

This paper describes models used to explain Acid Sulfate Soil (ASS) transformation processes on Norfolk Island wetlands. Prolonged drying (1970–2020) and a range of human disturbances (from cattle pugging to excavated drains) have led to lower groundwater tables and the formation of Sulfuric organic soils (pH < 4). It builds on a companion paper, which provides the methodological framework by establishing five descriptive soil-landscape models of 14 ASS wetlands affected by anthropogenic disturbances over three drying-wetting cycles (drying until 2020, wetting in 2021, and flooding in 2022). The study aims to enhance land management and improve communication about ASS by applying four simplified soil-landscape models: (1) A descriptive model: Describes processes leading to transformations in the properties of ASS during drying–wetting cycles. It is based on the descriptive models of a range of scenarios presented in the companion paper. (2) An explanatory model: Shows ASS transformation processes, including wetting, drying, and disturbances from excavation and cattle pugging, highlighting reversible and irreversible changes. (3) A predictive (4D) model: Illustrates ASS transformation across diverse environmental conditions, considering three drying–wetting cycles and five disturbance categories. (4) Two predictive evolutionary models: Depicts long-term ASS changes under different conditions, identifying factors that stabilise or accelerate soil changes over recent geological time. These models help non-specialists (such as land holders and community groups) recognise ASS types, monitor changes, and implement either nature-based solutions or remediation management options. They could also be applied to other islands in the south Pacific region.