Mercury Bioaccumulation in Crayfish in Acid Mine-Impaired Appalachian Streams

Abstract

We tested the hypothesis that mercury (Hg) bioaccumulation in crayfish inhabiting acid mine-impacted streams increases with the severity of acidification. Sixty-four sites in southeast Ohio were ranked for severity of acid mine impact using an index of six water chemistry parameters (Fe, Mn, Al, sulfate, acidity, and pH) characteristic of acid mine drainage. Macroinvertebrate communities along the acid mine drainage (AMD) gradient were sampled by kick and dip net, and the abundances of different functional feeding groups characterized to evaluate differences in dietary prey availability to crayfish inhabiting AMD-impaired streams. Mercury in crayfish (Orconectes sanbornii) was measured at 19 sites. Composite samples (N = 10) of tail tissue from these sites were analyzed for mercury, along with sediment from six sites. Sediment methyl mercury (MeHg) ranged from 0.03 to 0.479 ng/g, typical of background (uncontaminated by Hg or AMD) levels for lakes and streams in this region. MeHg concentrations in crayfish tail tissue ranged from 26.7 to 122 ng/g. Contrary to our hypothesis, total Hg and MeHg in crayfish tissue were negatively correlated with acid mine impairment (r = −0.479, p = 0.036; r = −0.049, p = 0.0293, respectively), suggesting that crayfish bioaccumulate Hg more slowly in acid mine-impaired streams. This pattern is opposite of trends for increased bioaccumulation rates in food webs of lakes acidified by atmospheric deposition. Total macroinvertebrate (prey) abundance at study sites declined with increasing AMD impact. The reduced Hg accumulation in acid mine-impacted waters may be related to a change in diet, greater reliance on detritus-based food items, and/or lower trophic status of crayfish in acidified streams.