Probabilistic relations between acid–base chemistry and fish assemblages in streams of the Western Adirondack mountains, New York, USA

Surface waters across much of New York’s Adirondack Mountains were acidified in the late 20th century but began to recover following the 1990 amendments to the Clean Air Act. Little data, however, are available to characterize biological impacts and predict recovery of fish assemblages in streams of the region. Quantitative fish and chemistry surveys were completed in 47 headwater streams during summer 2014–2016 to develop logistic (probabilistic) models that characterize the status of contemporary fish assemblages and predict how different nitrogen (N) and sulfur (S) deposition loads may affect future fish assemblages. Models for inorganic monomeric aluminum (Al_i) and richness ≥1 species and for acid neutralizing capacity (ANC) and total density >400 fish/0.1 ha, total biomass >1500 g/0.1 ha, brook trout (Salvelinus fontinalis) density >0 or >200 fish/0.1 ha, and brook trout biomass >1000 g/0.1 ha were suitable for evaluating community and population responses to changes in acid–base chemistry. Anticipated changes in national (US) secondary standards for atmospheric emissions of nitrogen oxides (NO_x) and sulfur oxides (SO_x) to achieve target N and S deposition loads will alter acid–base chemistry and the probabilities for observing various levels of fish metrics in streams across the region and elsewhere.