Soil pH — Benchmark Detail - Nature Index

Benchmark Value

4.5 pH

Direction: Lower is desirable ↓

Form: MaximumOnly

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

Therefore, a lower critical threshold of pH < 4.5 (1:5 soil:water suspension) is proposed for Australian alpine and subalpine ecosystems.

Metric Definition:

Lower critical soil pH threshold below which ecological function and native alpine flora health are compromised due to metal toxicity and nutrient imbalances.

Benchmark Definition:

This benchmark marks the critical lower soil pH limit below which alpine ecosystems in Australia experience ecological harm due to toxicity and nutrient issues.

Justification:

Based on evidence of increased aluminium and manganese toxicity and nutrient deficiencies below this pH, impacting native flora and microbial processes.

Sources (1)

Preview of Pastures and acid soils - NSW Government

Pastures and acid soils - NSW Government Journal

What do you see and when? What could this indicate? What test can I do to confirm? - MLA

Supporting Sources (18)

Additional references from the underlying research that informed this benchmark.

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

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

Contextual Support Journal

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

Preview of An introduction to the soils of the Australian Alps

An introduction to the soils of the Australian Alps

Contextual Support Journal

Impacts of Road Disturbance on Soil Properties and on Exotic Plant ...

Preview of Application of the Soil Security Concept to Two Contrasting Soil Landscape Systems—Implications for Soil Capability and Sustainable Land Management - MDPI

Application of the Soil Security Concept to Two Contrasting Soil Landscape Systems—Implications for Soil Capability and Sustainable Land Management - MDPI

Contextual Support Journal

Arctic, Antarctic, and Alpine Research. (2005). Recovery of Alpine Vegetation from Grazing and Drought. 8

Preview of Australian Government / ALA. (2023). Conservation actions for Australian alpine and sub-alpine peatlands. 25

Australian Government / ALA. (2023). Conservation actions for Australian alpine and sub-alpine peatlands. 25

Contextual Support Journal

Australian Government / ALA. (2023). Conservation actions for Australian alpine and sub-alpine peatlands. 25

Preview of Australian Journal of Ecology. (2006). Vegetation of an alkaline pan - acidic peat mosaic in the Hardwood River Valley, Tasmania. 17

Australian Journal of Ecology. (2006). Vegetation of an alkaline pan - acidic peat mosaic in the Hardwood River Valley, Tasmania. 17

Contextual Support Government

Australian Journal of Ecology. (2006). Vegetation of an alkaline pan - acidic peat mosaic in the Hardwood River Valley, Tasmania. 17

Preview of Biogeosciences. (2025). Alkalinisation significantly disrupts peatland functioning. 16

Biogeosciences. (2025). Alkalinisation significantly disrupts peatland functioning. 16

Contextual Support Journal

Australian Alps National Parks. (2013). Soils of the Australian Alps (Fact Sheet). 9

Preview of Climate change impacts on our soils - AdaptNSW

Climate change impacts on our soils - AdaptNSW

Contextual Support Journal

Climate change impacts on our soils - AdaptNSW

Preview of Effects of simulated acidification on soil basic chemical properties (2024/2025)

Effects of simulated acidification on soil basic chemical properties (2024/2025)

Contextual Support Journal

NCBI / PMC. (2024/2025). Effect of simulated acidification on soil basic chemical properties. PMC11994667. 20

Preview of estuaries.dwer.wa.gov.au, accessed May 12, 2025

estuaries.dwer.wa.gov.au, accessed May 12, 2025

Contextual Support Journal

Turner, B. L., et al. (2014). Soil organic phosphorus speciation in Australian alpine and sub-alpine soils. Journal of Soils and Sediments.

Preview of Frontiers in Plant Science. (2013). Aluminum (Al) cation Al3+ is highly rhizotoxic and is a major stress factor to plants on acid soils. 5

Frontiers in Plant Science. (2013). Aluminum (Al) cation Al3+ is highly rhizotoxic and is a major stress factor to plants on acid soils. 5

Contextual Support Journal

Frontiers in Plant Science. (2013). Aluminum (Al) cation Al3+ is highly rhizotoxic and is a major stress factor to plants on acid soils. 5

Preview of Full article: Impacts of Road Disturbance on Soil Properties and on Exotic Plant Occurrence in Subalpine Areas of the Australian Alps - Taylor & Francis Online, accessed May 28, 2025

Full article: Impacts of Road Disturbance on Soil Properties and on Exotic Plant Occurrence in Subalpine Areas of the Australian Alps - Taylor & Francis Online, accessed May 28, 2025

Direct Evidence Journal

www.nrc.nsw.gov.au, accessed on May 27, 2025

Preview of Gully erosion assessment and control guide - Local Land Services, accessed on May 29, 2025,

Gully erosion assessment and control guide - Local Land Services, accessed on May 29, 2025,

Contextual Support Government

www.climatechange.environment.nsw.gov.au

Preview of NCBI / PMC. (2021). Ecosystem index score for the reference, treated and untreated zones in Alpine National Park. PMC8367960. 11

NCBI / PMC. (2021). Ecosystem index score for the reference, treated and untreated zones in Alpine National Park. PMC8367960. 11

Contextual Support GreyLiterature

NCBI / PMC. (2021). Ecosystem index score for the reference, treated and untreated zones in Alpine National Park. PMC8367960. 11

Preview of Scherrer, P., & Pickering, C. M. (2006). Rehabilitation of a Walking Track in Kosciuszko National Park. Arctic, Antarctic, and Alpine Research. 28

Scherrer, P., & Pickering, C. M. (2006). Rehabilitation of a Walking Track in Kosciuszko National Park. Arctic, Antarctic, and Alpine Research. 28

Contextual Support Journal

Freiburg University. (2012). Plant and soil P determine functional attributes of subalpine Australian plants. 13

Preview of Soil and Landscape Grid National Soil Attribute Maps - pH (Water) (3" resolution) - Release 1

Soil and Landscape Grid National Soil Attribute Maps - pH (Water) (3" resolution) - Release 1

Contextual Support Government

CSIRO. (2021). Soil and Landscape Grid National Soil Attribute Maps - pH - CaCl2. 26

Preview of Soil condition 2024 | NSW State of the Environment, accessed July 7, 2025,

Soil condition 2024 | NSW State of the Environment, accessed July 7, 2025,

Contextual Support Government

Soil pH | Environment, land and water - Queensland Government, accessed August 11, 2025,

Preview of theaustralianalpsnationalparks.org, accessed on May 29, 2025,

theaustralianalpsnationalparks.org, accessed on May 29, 2025,

Direct Evidence Journal

Soil Conservation in Alpine Catchments - The Kosciuszko Huts Association, accessed August 17, 2025,

Preview of Victorian Resources Online. Soils of Suggan Buggan/Buchan. 18

Victorian Resources Online. Soils of Suggan Buggan/Buchan. 18

Contextual Support Journal

Victorian Resources Online. Soils of Suggan Buggan/Buchan. 18

Context

Region Australia
Biome Alpine and Subalpine Complex
Land Use Conservation / Protected Natural Areas
Assessment Pristine Reference
Evidence Type DegradationThreshold

Lifecycle

Status Rejected
Version 1
Effective From 3 Jun 2026

Notes

Below pH 4.5, risks of metal toxicity and nutrient imbalances increase significantly, compromising ecosystem health. Pipeline correction 2026-06-03b: Rejected — erroneous BenchmarkForm (MaximumOnly+UpperGuard on lower-harm threshold). Correct MinimumOnly+LowerGuard equivalent already exists as benchmark ID 1399.

Related Benchmarks

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