Soil pH — Benchmark Detail

Benchmark Value

4 pH

Direction: Higher is desirable ↑

Form: MinimumOnly

Scoring Curve

This curve shows how a field measurement for this indicator would score across all available benchmark forms in this context. The scoring engine uses 15 benchmarks together — the OptimalRange form drives the primary score, while 14 guard(s) constrain the result.

Contributing Benchmarks

OptimalRange Primary OptimalRange Guard MaximumOnly Guard MaximumOnly Guard OptimalRange Guard MinimumOnly Guard MaximumOnly Guard MinimumOnly Guard MaximumOnly Guard OptimalRange Guard Point Guard MinimumOnly Guard MaximumOnly Guard OptimalRange Guard MinimumOnly Guard

Evidence & Context

The Lower Critical Threshold is pH < 4.0.

Metric Definition:

Lower critical pH threshold indicating catastrophic ecosystem degradation due to Acid Sulfate Soil activation.

Benchmark Definition:

This benchmark marks the critical lower pH boundary below which ecosystem function collapses due to Acid Sulfate Soil oxidation in arid inland floodplains.

Justification:

Based on documented catastrophic acidification events in inland floodplain wetlands, notably Bottle Bend Lagoon.

Sources (2)

Ecological impacts of flood mitigation and drainage in coastal lowlands - AustLII

Ecological impacts of flood mitigation and drainage in coastal lowlands - AustLII, accessed July 21, 2025,

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Preview of National Guidance on Acid Sulfate Soils - Water Quality Australia

National Guidance on Acid Sulfate Soils - Water Quality Australia Journal

Managing soils - Department of Primary Industries and Regional Development, accessed July 17, 2025

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Supporting Sources (10)

Additional references from the underlying research that informed this benchmark.

(PDF) The pH of Australian soils: field results from a national survey - ResearchGate, accessed July 25, 2025,

Direct Evidence Journal

Caritat, P. de, & Cooper, M. (2011). The pH of Australian soils: Field results from a national survey. Soil Research, 49, 172-182.

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ASC - VERTOSOLS - Soil Science Australia

Contextual Support

What are the optimum nutrient targets for pastures? - Soil Health Knowledgebase

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AusEarthed. (n.d.). Soil Reading.

Contextual Support Journal

Victorian Resources Online | Resources | Support and resources ..., accessed July 21, 2025,

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Australian Soil Classification edition 3 - CALCAROSOLS

Contextual Support Government

Monitoring changes in soil salinity and sodicity to depth, at a ...

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Government of South Australia, Department for Environment and Water. (n.d.). Soil Health and Condition.

Contextual Support Government

Soil acidity - Department for Environment and Water

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Soil Constraints in an Arid Environment - Encyclopedia.pub

Contextual Support GreyLiterature

Soil Constraints in an Arid Environment - Encyclopedia.pub, accessed July 27, 2025

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Soil pH - SA | Fact Sheets | soilquality.org.au

Contextual Support Government

Soil Acidity - NSW | Fact Sheets | soilquality.org.au

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Victorian Resources Online | Resources | Support and resources ...

Contextual Support Government

Structural controls on the orientation of erosion gullies in mid-western New South Wales, Australia, accessed July 22, 2025

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Water and sediment quality in the Diamantina-Georgina River ..., accessed July 21, 2025,

Contextual Support Journal

Water and sediment quality in the Diamantina-Georgina River ..., accessed July 21, 2025,

View Source

Water and sediment quality in the Diamantina-Georgina River catchment, Lake Eyre Basin

Direct Evidence Journal

Water quality in the Georgina-Diamantina River catchment

View Source

Context

Region Australia
Biome Arid Inland Floodplains & Ephemeral River Systems
Land Use Conservation / Protected Natural Areas
Assessment Pristine Reference
Evidence Type DegradationThreshold

Lifecycle

Status Active
Version 1
Effective From 3 Jun 2026

Notes

Represents a rapid, catastrophic shift into a toxic biogeochemical state with lethal effects on aquatic life.

Related Benchmarks

Other benchmarks in the AUS-AIF-CON-SPH family.