| I tested the hypothesis that mercury bioaccumulation in crayfish inhabiting acid mine impacted streams increases with the severity of acidification. Nineteen stream 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) that are characteristic of acid mine drainage (AMD) in this region. Ten crayfish (Orconectes sanbornii) (carapace length 18+/-3 mm) were captured from each site. Composite samples of their tail tissue were analyzed for mercury using GC-ICP-MS. Composite sediment samples from six of the study sites were also analyzed for mercury content. We found that sediment MeHg concentrations at the six sites ranged from 0.03 - 0.479 ng/g, typical of background (uncontaminated) levels for lakes and streams in this region. Methyl mercury (MeHg) concentrations in crayfish tail tissue ranged between 26.7 ng/g to 122 ng/g, (below the United States Environmental Protection Agency's aquatic impairment threshold of 0.3 ig MeHg/g in fish tissue). Contrary to my hypothesis, total Hg and MeHg in crayfish tissue were negatively correlated with acid mine impact (r = -0.4790, p = 0.036; r = -0.04873, p = 0.0293, respectively), suggesting crayfish bioaccumulate Hg more slowly in acidified streams. This pattern is contrary to previously reported patterns of increased bioaccumulation rates in acidified lakes.;I expanded the study to investigate the reasons behind the observed unexpected trend in Hg bioaccumulation. I tested the hypotheses that the observed reduction in mercury bioaccumulation with increasing acid mine impact is due to the effects of AMD on factors including crayfish diet, crayfish trophic position and changes in macroinvertebrate community structure and prey availability. Crayfish trophic position decreased with increasing AMD impact and so did macroinvertebrate diversity and abundance thereby supporting the result of the initial study. The counterintuitive decrease in mercury bioaccumulation with increasing AMD impact may be due in part to a decrease in macroinvertebrate abundance with increasing acid mine impact at the study sites resulting in relatively reduced availability of animal prey items at highly impacted sites. Multiple regression analysis revealed that the interactions between environmental variables are significant in determining Hg bioaccumulation. |
