Mercury distribution in the biota of a Great Lakes estuary: Old Woman Creek, Ohio

A study of mercury contamination in a wetland ecosystem was undertaken to assess degree of contamination in various compartments of the food web, and determine the most important routes for mercury to enter fish species. Old Woman Creek is a freshwater estuary on the southern shore of Lake Erie and has been recognized as an important nursery area for fish. Although there is no point source of mercury to the wetland there is evidence of biomagnification of mercury in the food web. Mercury concentrations in water were not detectable (< 20 ng/L) by methods used in this study. The sediments had a mean concentration of 0.04 mu g total Hg/g wet weight. Zooplankton, benthos, and microphytes had less than 0.05 mu g total Hg/g wet weight, but mean concentrations in fish tissue ranged from 0.001 to 0.636 mu g total Hg/g wet weight. There was a positive correlation between mercury concentration and both length and weight in channel catfish Ictalurus punctatus and common carp Cyprinus carpio. In general channel catfish accumulated higher levels of mercury than common carp, suggesting that the pelagic food web may be more efficient in delivery of mercury (to channel catfish) than the benthic pathway (to common carp). The highest value for fish occurred in a bowfin Amia calva. Tissue from one great blue heron Ardea herodias had the highest concentration ai 1.62 mu g total Hg/g wet weight. In this system, as in others, top predators tended to accumulate the highest mercury levels and were therefore mast susceptible to mercury poisoning, even at sublethal levels.