Assessing benthic recovery in the Torch Lake AOC

Session: Connecting Management Needs and Science Information (2)

Anya Leach, MTU Civil and Environmental Dept., [email protected]
Cory McDonald, Michigan Tech. Univ., Dept. of Civil & Env. Eng., [email protected]

Abstract

Torch Lake, located in Michigan’s Upper Peninsula, was a site of copper ore processing from the 1850s through the 1960s. During this time, various mining by-products were deposited into the lake and along its shoreline, including mine tailings and chemical pollutants such as polychlorinated biphenyls (PCBs) and heavy metals (Cu, Hg). Torch Lake was established as an Area of Concern (AOC) site and remediation focused on ecological impacts. Presently, two Beneficial Use Impairments (BUI) remain for the lake, including degradation of benthos. It was anticipated that natural sediment deposition would cover and attenuate toxic sediments over time. A baseline survey of benthic macroinvertebrates was conducted in 1999/2000, but the benthic community status has not been recently assessed. In 2018, an updated survey was conducted to assess the progress of benthic recovery.  There is some evidence of recovery; organism density has increased in most of the lake. Organism densities and recovery rates are spatially variable and may be associated with rates of sediment deposition. This survey will assist future decisions regarding additional remediation actions and restoration criteria.