The concentration of total Hg was compared among 45 wetlands in three regions of Ontario. Twenty-two of these wetlands were located in the Muskoka-Haliburton Highlands and Temagami - North Bay regions and included bogs, fens, and marshes. Twenty-three were riverine marshes along the St. Lawrence River, near Cornwall, a Great Lakes area of concern, where Hg has been released through industrial activity. Overall, significant but weak negative relationships were found between pH and alkalinity of the surface waters and total water Hg concentrations (r2 = 0.28-0.30, p < 0.001). A significant positive relationship was found between dissolved organic C and total water Hg (r2 = 0.30). On average, St. Lawrence wetlands had lower total water Hg when compared with the inland wetlands. While a strong positive relationship was found between sediment organic matter and total sediment Hg concentrations (p < 0.001), the relationship was significantly different between the St. Lawrence and inland wetlands. In general, the St. Lawrence wetlands, despite the proximity to point sources of Hg, actually had lower sediment Hg, likely because of the lower organic matter. However, the St. Lawrence wetlands had twice the amount of Hg per unit of organic matter; the consequences of this difference for methyl mercury production and bioaccumulation need to be addressed.
Assessing condition of macroinvertebrate communities and sediment toxicity in the St. Lawrence River at Massena Area-of-Concern
