Mercury in Ontario wetlands: Concentrations in water, sediments, and a common aquatic plant in relation to geochemical variables.

Abstract

The factors that regulate bioaccumulation of mercury in wetland systems and aquatic plants in particular have yet to be identified. Concentrations of total mercury were determined in water, sediments, and the yellow pond lily (Nuphar variegatum L.) for 22 wetlands from South-Central Ontario (Lat. 45$\sp\circ\ 11\sp\prime,$ Long. 78$\sp\circ\ 50\sp\prime$; Lat 46$\sp\circ\ 19\sp\prime$, Long. 80$\sp\circ\ 47\sp\prime)$ and for 23 wetlands from the St. Lawrence River (Lat. 45$\sp\circ\ 02\sp\prime,$ Long. 74$\sp\circ\ 44\sp\prime).$ The South-Central wetlands are remote from any industrial sources of mercury, whereas the wetlands from the St. Lawrence River come from an area where known Hg contamination exists. Positive correlations were found between the organic content of the sediments and the sediment Hg concentrations for both the South-Central and the St. Lawrence River wetlands. However, no relationships between water Hg and pH, alkalinity, and dissolved organic carbon (DOC) were found in either wetland group. The yellow pond lily is a common floating leaved aquatic plant which is the nutrient and energy source for a variety of wildlife. Thus, the importance of determining if the yellow pond lily accumulates toxic levels of mercury is evident. The results indicated that Nuphar variegatum does not accumulate mercury in relation to pH, alkalinity, DOC, or the organic content of the sediment, despite a wide range in these variables from the two wetland groups. Nuphar variegatum is an "excluder" or "non-indicator" of mercury. Remote South-Central wetlands had significantly higher concentrations of mercury in the sediments and the water compared to the St. Lawrence River wetlands. The South-Central wetlands also had significantly higher amounts of organic matter in the sediments and DOC in the water, both of which are known to bind mercury. (Abstract shortened by UMI.)