Trace elements in peat bog porewaters: indicators of dissolution of atmospheric dusts and aerosols from anthropogenic and natural sources

Peat bogs are often used as archives of atmospheric deposition of trace elements (TEs). However, chemical analyses of TEs in peat provide little information about their ecological significance, subsequent to atmospheric deposition. There is potential for the most reactive dusts and aerosols to dissolve in acidic (pH 4), organic-rich, bog water, thereby releasing TEs. Here, we use TEs in bog waters as indicators of the chemical reactivity of atmospheric particles. Porewaters were sampled from bogs i) near open pit bitumen mines of northern Alberta (AB) known to have elevated rates of dust deposition, primarily in the form of coarse particles, and ii) in southern Ontario (ONT), known to have had elevated rates of Pb deposition since industrialization began, supplied mainly as fine aerosols. In the AB bog waters, the elements most often elevated in abundance, relative to the reference site (Utikuma), are Li and Fe, most likely due to proton-promoted and reductive dissolution of their mineral hosts, respectively. In the bog waters collected in ONT, Pb concentrations and enrichments (relative to Y), are far greater than the AB bogs, reflecting the profound differences in cumulative inputs of industrial Pb in the two regions combined with proton-promoted dissolution of Pb-bearing aerosols. Given the affinity of natural organic matter for Pb ions, surface complexation and ligand-promoted dissolution also may have played a role in Pb release. Regardless of the dissolution mechanisms involved, peatland waters provide new insight into the chemical reactivity of dusts and aerosols. These transformations may have broader significance for the chemical composition of peatland drainage waters, and the organic-rich receiving waters of the boreal zone.