Water in the restored wetlands of the Glacial Ridge National Wildlife Refuge near Crookston, Minn., has extraordinarily high levels of toxic methylmercury, according to a new U.S. Geological Survey research report.
The 7,000-acre refuge, established in 2004, is made up of lands that once were wetlands, were drained for farming, and then were restored as wetlands.
Extensive sampling of the water was conducted in 2007-09. The highest levels of methylmercury – the type of mercury that is a health threat for fish and the people and animals that consume the fish – found in the refuge were among the highest such levels ever recorded in sites not contaminated by industrial discharges, according to the USGS report.
While the refuge does not have fish, the methylmercury is a potential threat for the ducks and geese that visit the refuge’s wetlands and a threat to downstream waters that drain the wetlands.
Researchers do not understand what has caused the high concentrations. But the report notes:
“The methylation research indicates that restoring wetlands may result in higher rates of mercury methylation and higher methylmercury concentrations than older, established wetlands where water levels are relatively stable.”
Read the USGS report. Read a Pioneer Press article about the research.