Biogeochemical Impacts of Anthropogenic Disturbance on Brook Trout (Salvelinus fontinalis) Distributions in the Southwestern Adirondacks

Energy generation in the Midwest has left a legacy of acid deposition across the East Coast and particularly in the Adirondack Mountains, NY. While modern emissions restrictions have resulted in improved air quality and decreased acid deposition over much of this region, persistent effects of acid deposition can still be found in Adirondack fish communities.  Efforts to clearly identify these effects have been hindered by the inability to clearly distinguish anthropogenic from naturally occurring acidity.  The base-cation surplus, a modified ANC calculation which includes strong organic acids, represents an unambiguous method for quantifying anthropogenic acid deposition, and the resultant leaching of toxic inorganic aluminum into surface waters.  Base-cation surplus values were calculated for lakes surveyed by  the Adirondack Lakes Survey Corporation and compared against Brook trout abundance and distribution measures.  Brook trout distributions were found to be extremely sensitive to base-cation surplus levels with clear thresholds evident.  Interestingly, these threshold values closely corresponded to the base-cation levels at which lethal concentrations of inorganic monomeric aluminum would be present.  These results suggest 1) modern acid deposition may still be exerting significant control over Adirondack fish communities and 2) the base-cation surplus represents a biologically-relevant measure of anthropogenic impacts on aquatic systems.