Response of a New Zealand mayfly (Deleatidium spp.) to acid mine drainage: implications for mine remediation.

Investigating the toxicity of acid mine drainage (AMD) on benthic communities in receiving waters can be highly challenging because of the difficulty in unraveling the effects of acidity, dissolved metals, and precipitates. Furthermore, the survival of different species may vary depending on any natural adaptation they may have acquired to low pH, metals, or sedimentation. We investigated the effect of different pHs and AMD on the survival of a common New Zealand leptophlebiid mayfly (Deleatidium spp.) in 96-h laboratory trials. Our results indicate that the primary driver of toxicity in AMD was pH, although some mortality could be attributable to the presence of dissolved heavy metals at low pH (<or=3.6). Mayflies sourced from three naturally acidic streams (pH approximately 5.7-6.5) had a distinctly higher tolerance to AMD and low pH (3.5-4.0) compared to mayflies sourced from three circumneutral streams (pH approximately 7.0-7.4). This indicates that the chemistry of the natal stream strongly influences the sensitivity of mayflies to AMD, which, in turn, could have consequences for the successful remediation of a given AMD-impacted stream. Furthermore, the water chemistry of unimpacted streams that could be sources of potential recolonists might provide ecologically relevant water-quality targets for remediation of AMD-damaged streams. Understanding the variable tolerances of common lotic benthic taxa can provide ecologically relevant water-quality criteria for mine remediation.