Acidification of native brook trout streams in Virginia

A survey of 344 streams in the Appalachian Mountain region of Virginia that support reproducing populations of native brook trout (Salvelinus fontinalis) was conducted in the spring of 1987. The surveyed streams represent about 76% of the identified trout streams in the region. Relative to commonly applied sensitivity criteria, 93% of the streams are sensitive (alkalinity ≤ 200 μeq L−1), 49% of the streams are extremely sensitive (alkalinity ≤ 50 μeqL−1) and 10% of the streams are currently acidic (alkalinity ≤ 0.0 μeq L−1). Sulfate is the dominant anion in the streams, but all catchments associated with the streams are retaining significant amounts of atmospherically deposited sulfur (median retention=68%). Estimates of past and potential future acidification were obtained using a simple linear model relating changes in concentrations of base cations to changes in concentrations of sulfate. Sulfate concentration changes were determined as the difference between currently observed concentrations and estimated past and future steady state concentrations. Changes in concentrations of base cations were calculated, assuming base cation increase factors equal to 0.4 and 0.8 times the sulfate increase. The median historical alkalinity loss for the sampled population is estimated as 29 and 9 μeq L−1 for the two assumed factors, with 3 and 0% of the streams estimated to have had historical alkalinities < 0.0 μeq L−1. The median future alkalinity loss is estimated as 90 and 30 μeq L−1 for the two assumed factors, with 88 and 32% of the streams estimated to have future alkalinities < 0.0 μeq L−1.