Natural Recovery of Contaminated Nearshore Sediments of the St. Lawrence River at Cornwall, ON

Session: Poster session

Katherine Moir, St. Lawrence River Institute of Environmental Sciences, [email protected]
MacKenzie E. Waller, St. Lawrence River Institute of Environmental Sciences, Cornwall, Ontario, [email protected]
Matthew Windle, St. Lawrence River Inst., [email protected]
Jeff Ridal, St. Lawrence River Institute, of Environmental Sciences, [email protected]

Abstract

Mercury (Hg) contamination of sediments has been an ongoing issue in the St. Lawrence River (Cornwall) Area of Concern, stemming from legacy industrial contamination at Cornwall. The Cornwall Sediment Strategy (CSS) was implemented in 2005 to address the high sedimentary concentrations of Hg and other contaminants, and prescribes a series of administrative controls combined with monitored natural recovery (MoNR) of the sediment. However, recent monitoring has identified clusters of high Hg concentrations in nearshore surface sediments, despite the CSS regulations. We collected three sediment cores from two contaminated nearshore areas along the Cornwall waterfront to assess temporal changes in Hg concentrations and to determine whether the sediment is acting as a sink for Hg, as proposed by the CSS. Though Hg concentrations declined toward the surface in all three cores, surface concentrations remain above provincial limits, and radioisotope dating of the cores suggests that sediments are likely being disturbed at two of the three sites. It remains unclear whether high surface Hg concentrations are a result of slow recovery of the sediment or on-going external sources of Hg. These findings illustrate potential limitations of MoNR in heterogeneous nearshore environments, and hold implications for policy development relating to contaminated nearshore sediments.

1. Keyword
sediments

2. Keyword
St. Lawrence River

3. Keyword
mercury

4. Additional Keyword
radiodating