Forest floor decomposition, metal exchangeability, and metal bioaccumulation by exotic earthworms: Amynthas agrestis and Lumbricus rubellus.
Earthworms have the potential to reduce the retention of pollutant and plant essential metals in the forest floor (organic horizons) by decomposing organic matter and increasing exchangeability of metals. We conducted a laboratory experiment to investigate the effects of two exotic earthworms, Amynthas agrestis and Lumbricus rubellus, on forest floor decomposition, metal exchangeability, and metal bioaccumulation. Eighty-one pots containing homogenized forest floor material were incubated for 20, 40, or 80 days under three treatments: no earthworms, A. agrestis added, or L. rubellus added. For earthworm treatments, A. agrestis and L. rubellus were stocked at densities observed in previous field studies. Pots containing either A. agrestis or L. rubellus had lost more forest floor mass than the control plots after 40 and 80 days of incubation. Forest floor pots containing A. agrestis had significantly lower % C (16 ± 1.5 %) than control pots (21 ± 1.2 %) after 80 days. However, L. rubellus consumed more forest floor and C mass than A. agrestis, when evaluated on a per earthworm biomass basis. Exchangeable (0.1 M KCl + 0.01 M AcOH extractable) and stable (15 M HNO3+ 10 M HCl extractable) concentrations of Al, Ca, Cd, Cu, Mg, Mn, Pb, and Zn in forest floor material were measured. Stable concentrations and % exchangeable metals in forest floor material were similar among treatments. Although exchangeable metal concentrations varied significantly for most metals among treatments (except Mg and Zn), we conclude that earthworms did not increase or decrease the exchangeability of metals. However, earthworms bioaccumulated Cu, Cd, Zn, and Mg and had potentially hazardous tissue concentrations of Al and Pb. This was best illustrated by calculating bioaccumulation factors using exchangeable concentrations rather than total concentrations. Future research is needed to understand the effect of earthworms on metals in other soil types.
Environmental Studies Program, Dartmouth College, Hanover, NH, 03755, USA. justin.b.richardson@dartmouth.edu.
J B
JB
Richardson
Department of Plant and Soil Science, University of Vermont, Burlington, VT, 05405, USA.
J H
JH
Görres
Environmental Studies Program, Dartmouth College, Hanover, NH, 03755, USA.
A J
AJ
Friedland
D000818:Animals; D018533:Biomass; D065928:Forests; D008670:Metals / Q000737:chemistry* / Q000378:metabolism*; D009835:Oligochaeta / Q000737:chemistry* / Q000378:metabolism*; D012987:Soil / Q000737:chemistry*; D012989:Soil Pollutants / Q000032:analysis*
D008670:Metals; D012987:Soil; D012989:Soil Pollutants
Exchangeability; Forest floor mass; Heavy metals; Nonnative earthworms; Plant nutrients; Trace metal