Exotic Earthworms Decrease Cd, Hg, and Pb Pools in Upland Forest Soils of Vermont and New Hampshire USA

Area of Science:

• Environmental Science
• Soil Ecology
• Biogeochemistry

Background:

• Exotic earthworms are increasingly prevalent in northeastern USA forests.
• Their impact on soil pollutant metals, including cadmium (Cd), mercury (Hg), and lead (Pb), is understudied.

Purpose of the Study:

• To determine if the presence of exotic earthworms reduces strong-acid extractable concentrations and pools of Cd, Hg, and Pb in forest soils.
• To compare metal levels at sites with low earthworm abundance (LEA) versus high earthworm abundance (HEA).

Main Methods:

• Field study comparing LEA (≤10 g m⁻² earthworms) and HEA (>10 g m⁻² earthworms) sites across five watersheds in Vermont and New Hampshire.
• Analysis of Cd, Hg, and Pb concentrations and bulk inventories in different soil horizons.

Main Results:

• Organic horizons at HEA sites had lower concentrations of Cd, Hg, and Pb compared to LEA sites.
• Soil pools of Cd and Hg in the organic horizon and total soil were negatively correlated with earthworm biomass.
• Overall soil profile concentrations of Cd and Hg were reduced at HEA sites.

Conclusions:

• Exotic earthworms appear to decrease the accumulation of Cd, Hg, and Pb in forest soils.
• Potential mechanisms include enhanced metal mobilization via organic matter disruption or bioaccumulation by earthworms.