Element mobility and partitioning along a soil acidity gradient in central Ontario forests, Canada

Area of Science:

• Environmental Science
• Soil Science
• Geochemistry

Background:

• Assessing metal mobility in forest soils is crucial for environmental risk evaluation.
• Soil-solution partitioning coefficients (K(d)) are key metrics, but data is limited for many elements.
• Forest soil metal mobility is influenced by factors like pH and vegetation type.

Purpose of the Study:

• To determine soil-solution partitioning coefficients (K(d)) for 17 mineral elements across diverse forest types.
• To investigate the relationship between soil pH and metal partitioning in forest soils.
• To assess the influence of forest type on elemental partitioning and vegetation response.

Main Methods:

• Collected A-horizon soil samples from 46 forested sites bordering the Precambrian Shield in Ontario.
• Measured soil pH(aq) and determined soil-solution partitioning coefficients (K(d)) for 17 mineral elements.
• Used empirical linear regression to model the relationship between Log K(d) and soil pH, and analyzed foliage for elemental concentrations.

Main Results:

• Log K(d) values for all 17 elements were predictable by soil pH (r(2) = 0.17-0.77), independent of forest type.
• Thirteen elements showed positive relationships between acid-extractable metal concentration and pH(aq).
• Specific elements (Al, Ba, Fe, Ga, K, Li, Rb, Tl, V, Ca) exhibited strong pH-dependent partitioning, while tree species varied in foliage elemental responses to soil pH.

Conclusions:

• Soil pH is a significant predictor of metal mobility (K(d)) in forest soils, crucial for environmental risk assessment.
• Elemental partitioning in mineral soil is largely independent of forest type, but vegetation responses to soil chemistry differ.
• Interpreting K(d) values requires considering both solid-solution phases and species-specific vegetation responses in elemental cycling.