The distribution and contaminant burdens of adults of the burrowing mayfly, Hexagenia, in Lake Erie

Hexagenia populations, eradicated in the 1950s by anoxia, are recovering in the western basin of Lake Erie. Water from the Detroit River, which provides the largest contaminant loan into the lake, flows west-to-east through the center of the western basin. We hypothesized that body burdens of Hexagenia would reflect a gradient of decreasing contamination from west to east across the basin, and from the central axis toward shorelines. In summer 1994, we used light traps or mane use of lakeside dock lights to collect subimagos (females and males) and imagos (females)for 2 h pr sunset at three locations on the Detroit Rivet and at 22 locations throughout Lake Ei ie. Imagos were found throughout the western basin, but at only three locations in other areas of Lake Erie. Mayflies were analyzed for 59 organochlorine compounds including 42 congeners of PCBs by electron-capture detector gas chromatography. Results were analyzed using principal component analysis to reduce autocorrelations among contaminants. There was a I:I correspondence for PCB concentrations between subimago and imago stages, indicating no change in body burdens between moults. The highest contaminant burdens of adults at Monroe, Michigan (an Area of Concern) reflects local sources of contaminated sediments. There are high concentrations in mayfly body burdens at Middle Sister and East Sister islands and lower concentrations near both northern and southern shorelines of the basin. Hexagenia are confirmed as effective and efficient monitors of organochlorines.