Microbial Biomass Carbon (MBC)

AUS-AIF-CON-SMB General Moderate confidence

Benchmark Value

No specific value — see range

Range: 200 to 700 mg/kg

Optimal Range: 200 to 700

Direction: Higher is desirable ↑

Form: OptimalRange

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 9 benchmarks together — the OptimalRange form drives the primary score, while 8 guard(s) constrain the result.

Contributing Benchmarks

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

Evidence & Context

The reference value represents the peak functional state ('boom' phase) observed in recently inundated floodplain soils (0-10 cm depth) of a semi-arid Australian river system.

Metric Definition:

Microbial Biomass Carbon (MBC), representing the mass of carbon contained within the living component of soil organic matter—primarily bacteria and fungi.

Benchmark Definition:

Microbial Biomass Carbon (MBC) indicates the mass of carbon in living soil microbes, reflecting soil biological health in arid inland floodplains under conservation. This benchmark represents the dynamic healthy range during natural flood and drought cycles.

Justification:

Derived from direct field measurements in a semi-arid Australian floodplain representing the best available proxy for a healthy conservation landscape, supported by ecological principles and literature.

Sources (1)

Provisioning of bioavailable carbon between the wet and dry phases in a semi-arid floodplain

Provisioning of bioavailable carbon between the wet and dry phases in a semi-arid floodplain

View Source

Supporting Sources (13)

Additional references from the underlying research that informed this benchmark.

(PDF) Provisioning of bioavailable carbon between the wet and dry ...

Direct Evidence Journal

Lake Eyre Basin Synthesis Report - Queensland Environment Department, accessed July 19, 2025

View Source

ALLOCHTHONOUS CARBON LOADS AND POTENTIAL ... - La Trobe, accessed July 22, 2025,

Contextual Support Journal

Australian dryland soils are acidic and nutrient-depleted, and have unique microbial communities compared with other drylands | Request PDF - ResearchGate

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Aridity thresholds of soil microbial metabolic indices along a 3,200 ...

Contextual Support

Aridity thresholds of soil microbial metabolic indices along a 3,200 ...

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fertile clay soil: Topics by Science.gov, accessed July 22, 2025,

Contextual Support GreyLiterature

fertile clay soil: Topics by Science.gov

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final repport - Department of Primary Industries, Queensland, accessed July 22, 2025,

Contextual Support Journal

final repport - Department of Primary Industries, Queensland

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Interpreting Microbial Biomass Carbon | Fact Sheets | soilquality.org.au, accessed August 28, 2025,

Contextual Support GreyLiterature

Interpreting Microbial Biomass Carbon | Fact Sheets | soilquality.org.au

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Lake Eyre Basin Rivers Assessment Implementation Plan Project - ResearchGate, accessed July 22, 2025,

Contextual Support

Cycling of phosphorus in grazing systems - NSW Department of Primary Industries

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Lake Eyre Basin: its rivers and catchments. Strategic Plan. - DCCEEW, accessed July 21, 2025,

Contextual Support Journal

Lake Eyre Basin: its rivers and catchments. Strategic Plan. - DCCEEW

View Source

Protected Areas: Buffering nature against climate change - PreventionWeb.net, accessed July 21, 2025,

Contextual Support Journal

Protected Areas: Buffering nature against climate change - PreventionWeb.net, accessed July 22, 2025

View Source

Preview of Response of Soil Microbial Communities in Extreme Arid Deserts to Different Long-Term Management Methods - MDPI, accessed July 22, 2025,

Response of Soil Microbial Communities in Extreme Arid Deserts to Different Long-Term Management Methods - MDPI, accessed July 22, 2025,

Contextual Support Journal

Response of Soil Microbial Communities in Extreme Arid Deserts to Different Long-Term Management Methods - MDPI

View Source

Sources of organic carbon supporting the food web of an arid zone floodplain river | Request PDF - ResearchGate, accessed July 22, 2025,

Contextual Support Journal

Sources of organic carbon supporting the food web of an arid zone floodplain river | Request PDF - ResearchGate

View Source

Preview of The relevance of wetland conservation in arid regions: A re-examination of vanishing communities in the American Southwest | Request PDF - ResearchGate, accessed July 22, 2025,

The relevance of wetland conservation in arid regions: A re-examination of vanishing communities in the American Southwest | Request PDF - ResearchGate, accessed July 22, 2025,

Contextual Support Journal

The relevance of wetland conservation in arid regions: A re-examination of vanishing communities in the American Southwest | Request PDF - ResearchGate

View Source

Wetlands Strategy for South Australia - Department for Environment and Water, accessed July 22, 2025,

Contextual Support Journal

Wetlands Strategy for South Australia - Department for Environment and Water

View Source

Context

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

Lifecycle

Status Active
Version 1
Effective From 5 Jun 2026

Notes

Lower Critical Threshold: 200 mg/kg. No upper detrimental threshold — benefits plateau at natural saturation determined by resource availability. Reflects peak functional capacity during flood 'boom' phase.

Related Benchmarks

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