Survival of Brook Trout in a Bog‐Derived Acidity Gradient

The acidity in Bear Meadows Bog water (pH 3.7 — 4.7) is not due to carbonic acid or to any other volatile acid. The approximate pK of the unknown bog water acid(s) is 6.0 — 6.5. Fish do not occur in Bear Meadows Bog or in Sinking Creek over a 4.8—km section below the bog where water pH is too low for their survival. The lowest pH in which brook trout and white suckers were caught in Sinking Creek was 4.25 at area 5 (5.25 km below the bog) after a period of unusually heavy rainfall. At a different time brook trout alone were caught at area 4, 5.2 km below the bog, when the pH was 4.75. The lowest recorded pH at this site was 4.0. Survival times of hatchery brook trout placed in boxes in Sinking Creek was directly related to pH. Individual differences in tolerance to low pH were quite marked.