Mapping soil corrosivity in an Australian arid environment and comparing corrosion rates of exclusion fence netting with different zinc coatings

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Exclusion fencing and feral-free nature reserves are a key component of many threatened species recovery strategies in Australia. Soil corrosion damage (rust) sustained on exclusion fence netting can create entry points for feral animal incursions into areas of high conservation value. The use of soil physicochemical data to produce corrosivity risk maps is an approach used by project managers to identify the type of corrosion control measures (e.g. use of galvanised zinc coatings) needed to sufficiently limit the deterioration of buried metal infrastructure. This approach is commonly used in subsoil environments (e.g., underground piping), but very few studies have investigated the corrosivity potential of surfaces soils. This paper used surface soil pH, salinity and texture data collected from 69 field sites to map soil corrosivity potential (i.e., fence corrosion risk) at the Arid Recovery nature reserve in South Australia. The majority (72%) of soils in the reserve were predicted to be moderately corrosive and only 16% were predicted to be highly/very highly corrosive. Standard zinc-aluminium fence netting samples buried at six field sites for 18 months were used to validate map predictions. Zinc corrosion on netting samples at field sites were highly variable, particularly at the highly saline (ECe ≥ 5 dS/m) sites. Maximum predicted zinc corrosion rates were within 1.3 μm/year of measured maximum rates at four of the six sites. The fence corrosion risk mapping method used was able to reliably predict areas of low to moderate fence corrosion, but further research is needed to refine its ability to identify high risk areas. An accelerated corrosion experiment (9-month incubation at 65% WHC and elevated ambient temperatures) was used to assess the relative performance of standard zinc-aluminium (124 g/m2 zinc coating), heavy zinc-aluminium (410 g/m2) and heavy galvanised (650 g/m2) fence netting in different soil environments present on the nature reserve. The standard zinc-aluminium wire coating provided sufficient corrosion-resistance for use in the weakly saline (ECe < 5 dS/m) soils (Rhodic Arenosols, Calcic Chromic Solonetz and Chromic Cambisols). However, the increased corrosion-resistance of the heavy zinc-aluminium is needed in the highly saline (ECe ≥ 5 dS/m) Chromic Luvisol. None of the tested fence products were suitable for use in the highly saline Cambic Calcisols. A more corrosive-resistant alternative such as stainless-steel would be more suited for this very highly corrosive environment. Further research is recommended to confirm the long-term (>5 year) suitability of these products in these different soil types.