Response of Stream Chemistry and Young-of-Year Brook Trout to Lime Applications in Acidified Tributaries to Honnedaga Lake

Despite decades of acid deposition, a brook trout population has survived in Honnedaga Lake in the Adirondack region of New York.  Open-lake trap net catches declined throughout the 1970s, when brook trout were considered extirpated from the lake but survived in some circum-neutral tributaries.  Clean Air Act amendments in 1990 mandated reductions in sulfate and nitrogen oxide emissions.  By 2000, brook trout had re-colonized the lake coincident with reductions in surface-water sulfate, nitrate, and inorganic aluminum.  Brook trout are currently absent or at low densities in acidified tributaries with associated toxic inorganic aluminum levels (>2 µmol/L).  The acidified nature of most (78%) tributaries to the lake is hypothesized to limit the distribution and abundance of young-of-year brook trout.  We are investigating the potential to accelerate the recovery of brook trout abundance through lime applications to tributaries.  Early results show comparable increases in pH and decreases in inorganic aluminum in two tributaries; while young-of-year brook trout density increased 3-to-10 fold in one tributary but was not different in the other tributary.  The differential response by young-of-year brook trout appears to be related to the amount of groundwater inputs and spawning activity specific to each tributary.