Predicting Continental-Scale Soil Mercury Concentrations in Australia to Refine Global Frameworks

Area of Science:

• Environmental Science
• Geochemistry
• Ecology

Background:

• Global mercury (Hg) cycle research is heavily biased towards the Northern Hemisphere.
• Australia's unique environmental characteristics (arid regions, weathered soils, fire-adapted ecosystems) provide a novel context for Hg research.
• Existing data inadequately represent global Hg patterns due to regional biases.

Purpose of the Study:

• To conduct a continental-scale analysis of environmental predictors for soil Hg concentrations in Australia.
• To address the Northern Hemisphere bias in global mercury cycle understanding.
• To generate a high-resolution national Hg distribution map for Australia.

Main Methods:

• Analysis of 2,396 soil samples from 1,141 catchments covering 76% of Australia.
• Utilized boosted regression trees and random forest models to identify environmental predictors.
• Developed spatially explicit random forest models for national Hg mapping.

Main Results:

• Ferrosol index was the strongest predictor of soil Hg concentrations, especially in southeastern Australian temperate forests.
• Positive associations found with loss on ignition (soil organic matter), soil nitrogen, leaf area index, and nickel/lead concentrations.
• Negative associations observed with soil electrical conductivity and water availability.
• Hg concentrations in Australia are higher in ferrosols and nitrogen-rich soils compared to podosols and oxisols, differing from global patterns.

Conclusions:

• Ferrosols and specific soil properties are key drivers of mercury distribution in Australia.
• Findings underscore the need to incorporate regional data to improve global mercury cycle models.
• Highlights the limitations of extrapolating findings from limited geographical datasets.