Deposition and transport of trace metals in an acidified catchment of Central Ontario

Abstract

In Plastic Lake catchment, Ontario, Canada, there are two patterns of trace metal transport. One pattern (Pb, Cu) can be explained by the metals' affinity for dissolved organic carbon (DOC). The other pattern (Cd, Zn) can be explained by the metals' solubility in dilute acid and mineral soils. These two patterns are observed when following in sequence the aqueous metal concentrations (i) first in the precipitation and then through the catchment to (ii) a low DOC, acidified, upland soil water seep, (iii) a high DOC wetland outflow and (iv) Plastic Lake outflow. Despite the highest relative values of Pb and Cu in precipitation, they have their lowest median concentrations at the soil water seep, elevated concentrations at the wetland outflow and then lower concentrations at the lake outflow. The pattern is identical to that of DOC and organic Al. Clearly the high DOC at (iii) dominates transport through the catchment, while the low DOC at (ii) reduces transport from the upland soils. In contrast, the other metals (Cd, Zn) exhibit their highest median concentrations at the acidified soil water seep (ii) and reduced values further downstream. With this group, soil acidification rather than DOC appears to be the major factor enhancing metal transport.