Effects of acid mine drainage and acidity on the activity of Choroterpes picteti (Ephemeroptera: Leptophlebiidae).

Survival and behavior of the mayfly Choroterpes picteti (Leptophlebiidae) exposed to acid mine drainage (AMD: pH 3.3-6.4) and a reservoir polluted with arsenic (pH 6.8) from Sao Domingos mine (Portugal) were studied in laboratory and in situ bioassays (48 h) with the Multispecies Freshwater Biomonitor, and compared with water from a reference river and acidified reference water (acid only). Metal body-burdens showed a negative pH dependency for Mn and As, a positive one for Pb, and for Zn, Cu, Co, and Cd a decrease at pH < 4.4. Generally, survival decreased with decreasing pH. The 48-h LC(50) (pH) for AMD and for acid only were similar (pH 4.8-4.9); however, the LT(20) (h) at pH 3.3 revealed AMD to be less toxic than acid only. C. picteti show diurnal rhythm with increased locomotor activity in the night. The circadian rhythm was weakened by acid exposure, but less so by AMD exposure. Compared to reference river water, ventilation was stimulated at pH < 6.0 in acid only and in reservoir water. Locomotion was stimulated at pH 5 in acid only and reservoir; however, it was reduced in all other treatments, when compared to reference river water. Under acid-only exposure, both locomotion and ventilation were significantly higher compared to AMD exposure at the corresponding pH values. The laboratory results were field validated.